A clock that can detect tiny shifts in the flow of time itself(npr.org)
npr.org
A clock that can detect tiny shifts in the flow of time itself
http://www.npr.org/2014/11/03/361069820/new-clock-may-end-time-as-we-know-it
153 comments
But how about a person in the center of the Atlantic listening to a metronome broadcast from Death Valley and one from Mt. Everest, tick-tick-ticktick-ticktick-tick-a-tick-tick-a-tick :-)
He's really bored.
And death valleys ticks slower. He's at sea level, which is higher than Death Valley.
And death valleys ticks slower. He's at sea level, which is higher than Death Valley.
I always wondered what happens to quantum entanglement when time dilation is involved. For example if one of the particles falls into a black hole, can we get info out?
As I understand it, you can't actually use this to transmit information. If you entangle two particles, and then send one away, and attempt to measure the appropriate property (I think it's spin), hurray: you know that the other particle's spin is the opposite.
But that's not communication. It's like slicing a coin down the middle without looking at it, hiding each half in a box, and giving one of the boxes to someone going to the moon. A week later, you both open your box, and you know exactly which side of the coin the other person has - but that's not communication.
(Someone smarter than me, please correct whatever mistakes I've made, and explain this in a better way.)
But that's not communication. It's like slicing a coin down the middle without looking at it, hiding each half in a box, and giving one of the boxes to someone going to the moon. A week later, you both open your box, and you know exactly which side of the coin the other person has - but that's not communication.
(Someone smarter than me, please correct whatever mistakes I've made, and explain this in a better way.)
Wouldn't changing the spin be the way to communicate? Is spin not a changeable property?
Nope, the spin isn't changeable and you cannot communicate via entaglement. If the spin was changeable however we'd have a long distance bit (0 or 1).
Wikipedia says that spin can be changed:
http://en.wikipedia.org/wiki/Spin_(physics)
"Although the direction of its spin can be changed, an elementary particle cannot be made to spin faster or slower."
http://en.wikipedia.org/wiki/Spin_(physics)
"Although the direction of its spin can be changed, an elementary particle cannot be made to spin faster or slower."
Spin can be changed, but then you disentangle the two particles. So still no transmission of information.
Isn't disentanglement a form of transmission of information? I.e. if suddenly my particle disentangles, I can assume it's been manipulated? (which is a binary state of tangled/untangles (0,1))
And how can you tell if the particles are no longer entangled without observing both? It's not like there's some outward, observable property of the particle that says "I am entangled". It's simply a statistical correlation between the states of the two particles.
Interesting. Excuse my ignorance(which is certainly present), just trying to learn.
Can you expand on the last part about statistical correlation?
Can you expand on the last part about statistical correlation?
So, the statistical correlation between states of particles is literally the fundamental thing that defines quantum entanglement.
Suppose you and I both get a coin and we flip them. You then turn over your hand and reveal heads. If the two coins are "entangled", there is now a greater than 50% probability that my coin will be tails, which would not be the case if the coins weren't entangled.
Quantum entanglement works essentially the same way. "Flipping the coin" is equivalent to observing some state of the particle, like spin. In both cases, entanglement is evidenced by the correlation between the states, nothing more.
Now, imagine we had entangled coins and we were in separate rooms. We flip our coins and you observe yours, noting a heads. In my room, I can't know what you did or didn't observe. So when I observe my coin and see tails, I don't realize it's a consequence of your observation. From each of our individual perspectives the coin flip looks perfectly random. This is why information transfer isn't possible through quantum entanglement.
Suppose you and I both get a coin and we flip them. You then turn over your hand and reveal heads. If the two coins are "entangled", there is now a greater than 50% probability that my coin will be tails, which would not be the case if the coins weren't entangled.
Quantum entanglement works essentially the same way. "Flipping the coin" is equivalent to observing some state of the particle, like spin. In both cases, entanglement is evidenced by the correlation between the states, nothing more.
Now, imagine we had entangled coins and we were in separate rooms. We flip our coins and you observe yours, noting a heads. In my room, I can't know what you did or didn't observe. So when I observe my coin and see tails, I don't realize it's a consequence of your observation. From each of our individual perspectives the coin flip looks perfectly random. This is why information transfer isn't possible through quantum entanglement.
I now see the relation to the slit experiment.
Very interesting, thanks a lot to everyone who responded!
Very interesting, thanks a lot to everyone who responded!
The correlation is that you know from your reading what the other person will detect. For example, if you detect a spin up particle, they will detect spin down. But you don't know when they have, or if they have, done the detection.
You would know when you have two particles entangled at the moment of entanglement. You could know you have a half of a pair of entangled particles when the other half is sent away. But you could never know when the pair has become disentangled.
That's the common explanation, but its apparently wrong. There is not a fixed state of each 'quarter' in each 'box'. They are truly not determined until one is resolved; then the other is resolved simultaneously. Still, not communication.
Or by many worlds: the quarter is both ways in the box. When you each open your boxes, you yourself are pulled into the doubling. Now there are two pairs of you-and-them. In one pair, you hold heads and they hold tails. In the other pair, you hold tails and they hold heads.
Thinking about this makes it clear how communication is impossible. You will always get both answers - for different values of "you".
Thinking about this makes it clear how communication is impossible. You will always get both answers - for different values of "you".
> then the other is resolved simultaneously.
Relativity of course makes a hash of that.
Still it's as close as you'll get with a classical analogy, and if you only have access to a fixed basis is entirely correct. Expanding beyond the classical explanation is only truly necessary when you start measuring in different bases.
Relativity of course makes a hash of that.
Still it's as close as you'll get with a classical analogy, and if you only have access to a fixed basis is entirely correct. Expanding beyond the classical explanation is only truly necessary when you start measuring in different bases.
> There is not a fixed state of each 'quarter' in each 'box'. They are truly not determined until one is resolved;
Isn't that unknowable? And aren't both situations (fixed vs undetermined) effectively the same from an observer's point of view?
Isn't that unknowable? And aren't both situations (fixed vs undetermined) effectively the same from an observer's point of view?
No. What you are calling 'fixed' is a local hidden variable - an internal state that has yet to be measured but is already determined. This state of affairs is ruled out by Bell's Theorem - https://en.wikipedia.org/wiki/Bell%27s_theorem
That's only true if you take the Copenhagen interpretation. There are other interpretations (like 'consistent histories' for example). See: http://en.wikipedia.org/wiki/Copenhagen_interpretation#Alter...
Other interpretations of quantum mechanics do not generally violate Bell's Theorem, since it appears to be confirmed by experiment. There are other interpretations which choose to abandon locality rather than hidden variables, such as the De Broglie-Bohm pilot wave interpretation. But consistent histories doesn't even do that. It's actually pretty similar to the Copenhagen interpretation.
I didn't say anything about violating Bell's theorem. Yes pilot wave theory is a better alternative that doesn't require spooky action at a distance but consistent histories doesn't require wavefunction collapse (which is a huge source of spookiness as well).
Isn't it possible for the astronaut to also know whether the other person has opened their box? If yes, then this is where the analogy breaks down. However I'm probably remembering incorrectly. I just thought there was some property like "It's possible to detect whether the other person has made an observation yet."
I'm probably mistaken, because if this were possible, then you could use it as a 1-bit communication. "If you detect that I've opened my box, then blow up the moon. Otherwise, do nothing."
Time to re-study quantum mechanics... It's strange how easy it is to forget almost everything just by not thinking about it for two years. MIT OCW had some pretty great online courses on the subject.
I'm probably mistaken, because if this were possible, then you could use it as a 1-bit communication. "If you detect that I've opened my box, then blow up the moon. Otherwise, do nothing."
Time to re-study quantum mechanics... It's strange how easy it is to forget almost everything just by not thinking about it for two years. MIT OCW had some pretty great online courses on the subject.
> Isn't it possible for the astronaut to also know whether the other person has opened their box? If yes, then this is where the analogy breaks down.
The answer is no, and so the analogy doesn't break down. You can't observe the other person except by speed-of-light information transfer.
The answer is no, and so the analogy doesn't break down. You can't observe the other person except by speed-of-light information transfer.
I asked a similar question on physics stack exchange a few years ago, but I haven't seen a definitive answer.
http://physics.stackexchange.com/questions/8708/can-observat...
If you ran two two-slit experiments on entangled particle pairs, shouldn't you be able to detect if your counterpart was observing theirs?
If you ran two two-slit experiments on entangled particle pairs, shouldn't you be able to detect if your counterpart was observing theirs?
> Isn't it possible for the astronaut to also know whether the other person has opened their box?
How would you know without observing the particle yourself? In which case, how do you know if it collapsed because of your observation or the other person's?
Not an expert by any means, but from what I'm told you can't use it to transmit information, so that's how I think of it.
How would you know without observing the particle yourself? In which case, how do you know if it collapsed because of your observation or the other person's?
Not an expert by any means, but from what I'm told you can't use it to transmit information, so that's how I think of it.
http://en.wikipedia.org/wiki/No-communication_theorem
Has a nice analogy, that being two radio listeners do know what each other are hearing which is cool, but can't communicate anything between them.
I would have to think about the effect of creating a one time pad.
Has a nice analogy, that being two radio listeners do know what each other are hearing which is cool, but can't communicate anything between them.
I would have to think about the effect of creating a one time pad.
I've heard of that analogy before Brian Greene uses two boxes with a pair of gloves one box with the left glove and the other box the right glove.
It's kind of like when you go to a doctor and have tests done for a disease if the results are bad, positive, they call you and if the results are negative no call.
At some point a lab tech checks the sample and if it's negative for the disease they know at that moment but you know by the lack of information at some point in time; i.e. no phone call or letter.
The negative results are more like the quantum communication due to the lack of interaction than the positive results. Mine may not be not the best analogy.
It's kind of like when you go to a doctor and have tests done for a disease if the results are bad, positive, they call you and if the results are negative no call.
At some point a lab tech checks the sample and if it's negative for the disease they know at that moment but you know by the lack of information at some point in time; i.e. no phone call or letter.
The negative results are more like the quantum communication due to the lack of interaction than the positive results. Mine may not be not the best analogy.
Probably nothing more than usual. The local operations you can do to entangled particles are all commutative w.r.t. the operations applied by the other side. So whether they happened at the same time or before or after or slower or faster than the other side doesn't affect the local outcome
(That should also make it clear why you can't use entanglement to communicate instantaneously: the other side must get the same results whether they measure before or after you've sent your message. So if entanglement allowed communication instead of just esoteric types of coordination, you could use it to send messages backwards in time.)
(That should also make it clear why you can't use entanglement to communicate instantaneously: the other side must get the same results whether they measure before or after you've sent your message. So if entanglement allowed communication instead of just esoteric types of coordination, you could use it to send messages backwards in time.)
Quantum entanglement cannot communicate information, regardless of any other factors. See http://en.wikipedia.org/wiki/No-communication_theorem
Also may depend on what kind of watch you wear, like quarts watches are sensitive to magnetic field.
Sadly no. That would be a convenient and nifty way to vary frequency for ham radio applications if it were the case. Even just a couple dozen PPM in a magnetic field would be sufficient for transmit receive switching but it just doesn't work. Also if that were the case mounting a crystal nearby a power transformer or fan would generate massive noise in the output signal unless magnetically shielded, which also doesn't happen.
I would imagine magnetizing a mechanical watch would really mess things up, so at a "just under really messed up" threshold it would probably have the claimed effect.
You may be thinking of YIG garnet oscillators which are very dependent on magnetic field but they haven't been common tech in maybe 30 years. Even used on ebay they cost more than modern new microwave VCOs which is annoying. I have a box of old YIG osc in my basement which I actually used for ham radio experiments before modern solid state VCOs took over.
I would imagine magnetizing a mechanical watch would really mess things up, so at a "just under really messed up" threshold it would probably have the claimed effect.
You may be thinking of YIG garnet oscillators which are very dependent on magnetic field but they haven't been common tech in maybe 30 years. Even used on ebay they cost more than modern new microwave VCOs which is annoying. I have a box of old YIG osc in my basement which I actually used for ham radio experiments before modern solid state VCOs took over.
Yeah, they're not sensitive to magnetic fields. But they do drift with temperature. Which leads to fancy semi-improv solutions, like placing the quartz in a small case, together with a heating element and a temperature sensor, to keep that sucker incubated at constant temp. A lot of HAMs used to do this back in the day - or maybe they still do, I dunno.
Also, placing a small variable capacitor in series with the quartz is an easy way to tune it, if it's too fast. I actually have a wall clock that looks nifty but is too fast, and I'm gonna tune it by trial and error, inserting small caps in series with the crystal.
Also, placing a small variable capacitor in series with the quartz is an easy way to tune it, if it's too fast. I actually have a wall clock that looks nifty but is too fast, and I'm gonna tune it by trial and error, inserting small caps in series with the crystal.
The heating setup is still used today. In fact, you can get integrated components called OCXOs (Oven Controlled Crystal Oscillator) that do the whole job in one small package with precision over time on the order of 1ppb. Cheaper, and less precise, are TCXOs (Temperature Compensated Crystal Oscillators) where a crystal is paired with a circuit that has an opposite dependency on temperature so that the errors tend to cancel each other out.
> Yeah, they're not sensitive to magnetic fields. But they do drift with temperature
Also, gravity: https://www.youtube.com/watch?v=zILwgQhjC_Q
Also, gravity: https://www.youtube.com/watch?v=zILwgQhjC_Q
Degauss? You can speed up some clocks with degauss. So isn' it sensitive to magnetic field?
Relativistic time effects are changes in the rate of time itself, not changes in the mechanism of a clock. If there was a magnetic field effect, that's a different, additional thing.
Yeah clock, not time.
"At this level, maintaining absolute time scale on earth is in fact turning into nightmare," Ye says. This clock they've built doesn't just look chaotic. It is turning our sense of time into chaos.
This seems a bit sensationalist. The new clocks will be more accurate than any we have now, for existing applications. Those who develop new applications that actually use the increased precision will just need to be more careful about which frames of reference they use. Those who built GPS already solved some version of these problems.
This seems a bit sensationalist. The new clocks will be more accurate than any we have now, for existing applications. Those who develop new applications that actually use the increased precision will just need to be more careful about which frames of reference they use. Those who built GPS already solved some version of these problems.
If you can't synchronize the clock with any other clock in the world, timekeeping gets a bit meaningless.
But you can predict and account for relativity; We already have good protocols for dealing with expected drift. NTP already takes into account that your PC is not keeping time as accurately as the upstream servers, and keeps a driftfile that guesses at the time differential needed. The NTP daemon silently adjusts the time every second to deal with this.
If two clocks are at different heights, they can compute the differential in their rates and agree on a time unit. Sure, it might be 1 quadrillion ticks in on one clock and 1 quadrillion and 1 ticks on the other, but it's still a 'second' so long as both sides see it as simultaneous.
If two clocks are at different heights, they can compute the differential in their rates and agree on a time unit. Sure, it might be 1 quadrillion ticks in on one clock and 1 quadrillion and 1 ticks on the other, but it's still a 'second' so long as both sides see it as simultaneous.
That doesn't help if one clock is drifting because it's being moved by tectonic activity, or being vibrated slightly by gravitational waves.
If you have a protocol and enough fancy clocks, you don't have to know what's causing the perturbations or how big they are. At some level, there isn't actually a "real" time at all (partially, for the reasons you state). Rather, there is a time that we can agree upon. If some precise operation requires better time coordination than we can obtain via a particular configuration of these fancy new clocks, then we just need a different configuration, probably with more of them.
It's not a perturbation in the timekeeping of a single clock. This clock keeps incredibly reliable time. The fact is that time passes differently for each location in space. If you put another clock at a different altitude, they would keep different time, and they would both be correct.
Let me put it this way: if we had really fast trains (or just imagine some other schedule that must be coordinated over some distance), then it would matter that time passes differently for each location. However, we could still deal with that, with an appropriate time communication protocol and enough fancy clocks (probably spaced out along the train track).
Even if you could measure altitude to centimeter precision, the clock speed would depend on gravity, not altitude, and the Earth is too lumpy (in terms of density) for that centimeter to tell you much when comparing two different locations. I also think (speculate) that with this degree of sensitivity, we will be able to measure some gravitational fluctuation due to the currents of molten iron swirling inside the Earth.
With all this uncertainty, all you could do, after getting two clocks to approximately the same altitude, would be to say that clock A is currently running a factor of X faster than clock B. What you wouldn't know is how much of the delta was due to altitude, how much due to unequal density underneath, and other such factors, compared to how much was due to the internal differences in the clocks themselves that you were trying to factor out by using multiple clocks.
With all this uncertainty, all you could do, after getting two clocks to approximately the same altitude, would be to say that clock A is currently running a factor of X faster than clock B. What you wouldn't know is how much of the delta was due to altitude, how much due to unequal density underneath, and other such factors, compared to how much was due to the internal differences in the clocks themselves that you were trying to factor out by using multiple clocks.
> we will be able to measure some gravitational fluctuation due to the currents of molten iron swirling inside the Earth.
As a geologist, I really wish that were possible, but what you're describing is just far too small of an effect to be detectable from the surface. Gravitational acceleration follows an inverse square law. Any signal from flow in the outer core is completely swamped by the far larger (at the surface) changes from things like local hydrological conditions, ongoing human activity, etc.
On the bright side, though, we can already measure changes in the acceleration of gravity incredibly precisely without directly using relativistic effects. Even from orbit, things like regional flooding and changes in the mass of ice sheets can be detected purely from changes in acceleration of gravity. Have a look at some of the work that came out of the GRACE mission (also see the ESA's GOCE satellite): http://www.jpl.nasa.gov/news/news.php?release=2004-224
As a geologist, I really wish that were possible, but what you're describing is just far too small of an effect to be detectable from the surface. Gravitational acceleration follows an inverse square law. Any signal from flow in the outer core is completely swamped by the far larger (at the surface) changes from things like local hydrological conditions, ongoing human activity, etc.
On the bright side, though, we can already measure changes in the acceleration of gravity incredibly precisely without directly using relativistic effects. Even from orbit, things like regional flooding and changes in the mass of ice sheets can be detected purely from changes in acceleration of gravity. Have a look at some of the work that came out of the GRACE mission (also see the ESA's GOCE satellite): http://www.jpl.nasa.gov/news/news.php?release=2004-224
That is crazy. Like, I always knew that was technically possible, but we quickly shot the thought experiment down as silly in high school/college. I mean, feeling the changes in gravity to monitor the surface of a planet? That's patently absurd.
I'm having a lot of fun being wrong today!
EDIT: Aaaand that's from 2004. Which means I really wasn't paying attention while in college. Considering my roommate went to JPL to work on a sister project, I feel a bit of shame just learning about it now.
I'm having a lot of fun being wrong today!
EDIT: Aaaand that's from 2004. Which means I really wasn't paying attention while in college. Considering my roommate went to JPL to work on a sister project, I feel a bit of shame just learning about it now.
I think there is a huge difference between having a measurement of time be affected by gravity and detecting that such an effect influenced your measurement. After all that implies an even better standard to compare against and that's the whole problem here.
So even if this difference is undetectable for geological purposes it could very well screw up really accurate time measurements. It all depends on whether or not those effects compound or cancel out, in the case of gravity they will likely only compound.
So even if this difference is undetectable for geological purposes it could very well screw up really accurate time measurements. It all depends on whether or not those effects compound or cancel out, in the case of gravity they will likely only compound.
If we designed houses around planck lengths as the unit of measurement, we'd get nothing done.
It's not that timekeeping gets meaningless- it just means that there is a threshold where the variability of unsynchronized clocks disrupts certain highly precise problems.
It's not that timekeeping gets meaningless- it just means that there is a threshold where the variability of unsynchronized clocks disrupts certain highly precise problems.
I was looking for someone to make a comment like this. I also felt that it simply meant that the last few digits were less meaningful for applications such as sync, but it definitely doesn't mean that that's the case for all the digits.
You can still synchronize them, it's just that "synchronize" takes on a more complicated meaning. Both sides can use their clock, and the known positions of the two clocks over time, to predict the time that the other clock should be reading. The time deltas are no longer the same on both sides, but you can still transform between the two in order to compare them and detect errors occurring.
More pragmatically, we'll probably agree on a standard centralized time (i.e. International Atomic Time) and everyone will translate between their own locally perturbed time and the standardized time when synchronizing.
More pragmatically, we'll probably agree on a standard centralized time (i.e. International Atomic Time) and everyone will translate between their own locally perturbed time and the standardized time when synchronizing.
It's not like the issue they're dealing with doesn't exist with literally every clock in the world - it's just that we didn't have a clock that was sensitive enough to notice before.
In a sense, this is not a property of the clocks, but rather just the way nature is. We can't keep these clocks in sync at various places around the world, because the thing they measure is not in sync at various places around the world. But, we've known that for about one hundred years - what's the big deal?
nullc is right, this is a bad article.
In a sense, this is not a property of the clocks, but rather just the way nature is. We can't keep these clocks in sync at various places around the world, because the thing they measure is not in sync at various places around the world. But, we've known that for about one hundred years - what's the big deal?
nullc is right, this is a bad article.
That's only for measuring the time since 0 BC. If you're trying to measure the duration of a very precise experiment to a very precise degree, this kind of clock can be very useful.
If you can't synchronize the clock with any other clock in the world, the increased precision of this kind of clock gets a bit meaningless (or at least has only a very local usefulness).
Crappy article.
Sure, the more precise your oscillator is the more you need to worry about other effects. Basic cesium beam clocks are precise enough the altitude based corrections for relativity are required to achieve full accuracy. Each km of altitude is about 10ns/day of slew, ... I can measure this myself with equipment I have at home (I have an unusual home).
So sure, when you start making optical clocks with accuracy in the 1e-18 land then external effects may well be much harder to correct for, e.g. tides have an effect at the 1e-17 level ... but such a device could still keep time better than prior techniques. The "They just may not be able to tell us the time" is rubbish hyperbole that just serves to confuse readers who don't already know the subject well.
Sure, the more precise your oscillator is the more you need to worry about other effects. Basic cesium beam clocks are precise enough the altitude based corrections for relativity are required to achieve full accuracy. Each km of altitude is about 10ns/day of slew, ... I can measure this myself with equipment I have at home (I have an unusual home).
So sure, when you start making optical clocks with accuracy in the 1e-18 land then external effects may well be much harder to correct for, e.g. tides have an effect at the 1e-17 level ... but such a device could still keep time better than prior techniques. The "They just may not be able to tell us the time" is rubbish hyperbole that just serves to confuse readers who don't already know the subject well.
This is the worst kind of comment and what is wrong with Hacker News.
No one cares about your intellectual superiority, or the fact this might be a special interest for you. This article wasn't written for you, you already know and understand its content. There is literally nothing you could have got from it.
I on the other hand enjoyed the article. This isn't a field I'm familiar, so in general my knowledge was increased. That some concepts are misrepresented and dumbed down is obvious, but this is far out weighed by the general knowledge that was imparted.
Writing is all about picking an audience and conveying it effectively to the audience. It's fine to point out inaccuracy or build on the finer points, but don't be aggressive about it and don't insult the article because it offended your superior intellect.
No one cares about your intellectual superiority, or the fact this might be a special interest for you. This article wasn't written for you, you already know and understand its content. There is literally nothing you could have got from it.
I on the other hand enjoyed the article. This isn't a field I'm familiar, so in general my knowledge was increased. That some concepts are misrepresented and dumbed down is obvious, but this is far out weighed by the general knowledge that was imparted.
Writing is all about picking an audience and conveying it effectively to the audience. It's fine to point out inaccuracy or build on the finer points, but don't be aggressive about it and don't insult the article because it offended your superior intellect.
This is the worst kind of comment and what is wrong with Hacker News.
This article is poor scientific journalism. "New clock may end time as we know it." Seriously? How is that remotely true? There is nothing in this article that justifies that headline. If anything, this new clock affirms our understanding of the nature of time, pointing out the minute changes that we expect to see but have not had instruments sensitive enough to measure until now.
But that desire to pin down the elusive ticking of the clock may soon be the undoing of time as we know it: The next generation of clocks will not tell time in a way that most people understand.
Undoing of time as we know it? Will the existence of this clock somehow magically make all other clocks in the world turn incomprehensible? No, the truth is that most of society won't even be aware of this "undoing of time as we know it."
And on the subject of telling time in a way most people don't understand, that is already true of the cesium clocks they mention. We already have to deal with relativistic drift, of which most people are ignorant.
But this new clock has run into a big problem: This thing we call time doesn't tick at the same rate everywhere in the universe. Or even on our planet.
This line makes it out like we didn't know about relativity. Also, I hardly think more precision is a problem. If anything it gives us power to do things we never have done before. Technologies like GPS wouldn't work without the current generation of clocks. I'm excited about the new possibilities that an even more precise clock will open. It's not a problem.
They just may not be able to tell us the time.
What?!! This is incredibly misleading. The new clock will be just as able to tell time as all of the clocks we've had up until this point.
I could go on, but nullc is right, this article is crap. It is dripping with sensationalism.
This article is poor scientific journalism. "New clock may end time as we know it." Seriously? How is that remotely true? There is nothing in this article that justifies that headline. If anything, this new clock affirms our understanding of the nature of time, pointing out the minute changes that we expect to see but have not had instruments sensitive enough to measure until now.
But that desire to pin down the elusive ticking of the clock may soon be the undoing of time as we know it: The next generation of clocks will not tell time in a way that most people understand.
Undoing of time as we know it? Will the existence of this clock somehow magically make all other clocks in the world turn incomprehensible? No, the truth is that most of society won't even be aware of this "undoing of time as we know it."
And on the subject of telling time in a way most people don't understand, that is already true of the cesium clocks they mention. We already have to deal with relativistic drift, of which most people are ignorant.
But this new clock has run into a big problem: This thing we call time doesn't tick at the same rate everywhere in the universe. Or even on our planet.
This line makes it out like we didn't know about relativity. Also, I hardly think more precision is a problem. If anything it gives us power to do things we never have done before. Technologies like GPS wouldn't work without the current generation of clocks. I'm excited about the new possibilities that an even more precise clock will open. It's not a problem.
They just may not be able to tell us the time.
What?!! This is incredibly misleading. The new clock will be just as able to tell time as all of the clocks we've had up until this point.
I could go on, but nullc is right, this article is crap. It is dripping with sensationalism.
> We already have to deal with relativistic drift
You already mention GPS later in your comment, so it isn't that necessary, but I want to emphasize anyway: we are not only "dealing with", we are "making use of" it. Things we use every day would be impossible, if we wouldn't have precise enough clock to measure all that stuff already.
You already mention GPS later in your comment, so it isn't that necessary, but I want to emphasize anyway: we are not only "dealing with", we are "making use of" it. Things we use every day would be impossible, if we wouldn't have precise enough clock to measure all that stuff already.
And have since the 70s( http://support.radioshack.com/support_tutorials/gps/gps_tmli... ). Pretty wild.
The fact you don't like his comment doesn't make it "worst kind of comment". Nothing was essentially wrong about what he said. Maybe kinda harsh, I don't know and don't really care: it's plain stupid to favor fanciness of speaking to correctness of facts delivered.
In turn, there were wrong, imprecise and misleading statements in that article, which does make it bad to some degree. It's not the worst of it's kind, but still pretty bad. Actually I would consider it harmful, to write something that is easy to pick up for uneducated people, that gives them impression that they understand it while giving them wrong impression about the subject, that is, being misleading. I'm not sure I could appreciate that even if it was impossible to write easy-to-understand useful quasi-scientific articles/books, but as I've seen them I must conclude it's not impossible, so that makes people writing misleading stuff with attractive headlines even more guilty.
Your comment in it's turn contains nothing, but claiming somebodies comment is "worst" based only on that being not populistic enough. I would say it makes your comment "the worst kind of comment and what is wrong with Hacker News".
In turn, there were wrong, imprecise and misleading statements in that article, which does make it bad to some degree. It's not the worst of it's kind, but still pretty bad. Actually I would consider it harmful, to write something that is easy to pick up for uneducated people, that gives them impression that they understand it while giving them wrong impression about the subject, that is, being misleading. I'm not sure I could appreciate that even if it was impossible to write easy-to-understand useful quasi-scientific articles/books, but as I've seen them I must conclude it's not impossible, so that makes people writing misleading stuff with attractive headlines even more guilty.
Your comment in it's turn contains nothing, but claiming somebodies comment is "worst" based only on that being not populistic enough. I would say it makes your comment "the worst kind of comment and what is wrong with Hacker News".
I'm glad you enjoyed it, but in my opinion the article was misleading. Not just simplified.
I didn't go on and on in detail about systemic and random effects, linking to NIST tech reports on all the corrections they have to do on primary standards (http://tf.boulder.nist.gov/general/pdf/1846.pdf?origin=publi... on the redshift error at NISTs boulder facilities; and http://tf.boulder.nist.gov/general/pdf/2704.pdf on the sources of error in the F2 primary reference, see section 3.2 on relativistic effects), or pointing out people's amateur time keeping experiments where they demonstrate relativistic influence on decades old hardware ( http://leapsecond.com/ptti2006/tvb-project-great-ptti-ppt.pd... (this presentation is long and a ton of fun)), etc. or all the other bits of trash I could have pulled out to demonstrate knowing something here... because that wasn't my goal, the only point I was trying to make is that the article was likely to make many readers _less_ knowledgeable about the subject.
(But I will give those links now, because this argument is boring and time is neat!)
Perhaps you have enough background that you were not thrown off by the seeming claim that improved accuracy somehow makes these experimental references _less useful_, and you already know that relativistic effects aren't unique to optical lattice clocks and already must be compensated for, but I am sure that this is not universally the case.
What I get from the article isn't nothing... Potentially I get community around me which is less informed than they started and all that entails. Perhaps that's compensated for the fun they had reading about an interesting subject? or the additional learning they do after? I don't know, but I think the article could have been just as enjoyable without the bogus mystique that makes it misleading.
But if pointing out an article was, in my opinion, potentially misleading makes me everything that is wrong about Hacker News, I'll wear that proudly.
I, for one, think it's more likely the case that crappy shock headlines like "end time as we know it", constructed drama, and false freshness are a bigger drag on HN (and wider society) than any of my posts are likely to be... but to each his own.
I didn't go on and on in detail about systemic and random effects, linking to NIST tech reports on all the corrections they have to do on primary standards (http://tf.boulder.nist.gov/general/pdf/1846.pdf?origin=publi... on the redshift error at NISTs boulder facilities; and http://tf.boulder.nist.gov/general/pdf/2704.pdf on the sources of error in the F2 primary reference, see section 3.2 on relativistic effects), or pointing out people's amateur time keeping experiments where they demonstrate relativistic influence on decades old hardware ( http://leapsecond.com/ptti2006/tvb-project-great-ptti-ppt.pd... (this presentation is long and a ton of fun)), etc. or all the other bits of trash I could have pulled out to demonstrate knowing something here... because that wasn't my goal, the only point I was trying to make is that the article was likely to make many readers _less_ knowledgeable about the subject.
(But I will give those links now, because this argument is boring and time is neat!)
Perhaps you have enough background that you were not thrown off by the seeming claim that improved accuracy somehow makes these experimental references _less useful_, and you already know that relativistic effects aren't unique to optical lattice clocks and already must be compensated for, but I am sure that this is not universally the case.
What I get from the article isn't nothing... Potentially I get community around me which is less informed than they started and all that entails. Perhaps that's compensated for the fun they had reading about an interesting subject? or the additional learning they do after? I don't know, but I think the article could have been just as enjoyable without the bogus mystique that makes it misleading.
But if pointing out an article was, in my opinion, potentially misleading makes me everything that is wrong about Hacker News, I'll wear that proudly.
I, for one, think it's more likely the case that crappy shock headlines like "end time as we know it", constructed drama, and false freshness are a bigger drag on HN (and wider society) than any of my posts are likely to be... but to each his own.
For what it's worth, the new thing I got from the article is the unexpected idea that one could usefully measure non-time phenomena with a really precise clock, such as gravity or altitude. Definitely more thought inspiring than many other articles, in spite of the way it was written.
You didn't really respond to his No one cares about your intellectual superiority, or the fact this might be a special interest for you part of his comment.
Your tone and delivery is a bit offputting.
And the thing that I didn't see you comment on that I found particularly fascinating was that the increased resolution of these clocks is such that you can discern differences in relativistic effect between floor and wall. That changes how I think of time.
(My favorite headline that I read sometime around 1965 is "Dating Events in the Vicinity of a Leap Second.)
Your tone and delivery is a bit offputting.
And the thing that I didn't see you comment on that I found particularly fascinating was that the increased resolution of these clocks is such that you can discern differences in relativistic effect between floor and wall. That changes how I think of time.
(My favorite headline that I read sometime around 1965 is "Dating Events in the Vicinity of a Leap Second.)
OK. Dunno what to say there. I thought the article was misleading because it was intentionally sensationalized, not due to some lack of intellectual capability or because it wasn't addressed at an audience with a background in the subject. I'm sure that I know less about the subject than everyone interviewed in in the article. If anything, I think knowledge makes it better, since you're not likely to be mislead by it.
Wrt relativistic effect, the first NIST paper I cited shows that they needed altitude uncertainty less than 1m to avoid redshift from dominating the clock's error. The second shows that for the improved F2 reference redshift is one of the largest sources of uncertainty (and the corrected part is orders of magnitude larger than the other listed systemic errors). It's really cool, I agree. I'm happy to have people share in enjoying that, but sad about whatever causes the press to always have to present things as new and categorically different than what came before.
There are a number of really cool things they didn't mention: For example, these optical lattice clocks that they're talking about are solid state-- involving mostly only lasers and vacuum cells. Unlike cesium based atomic clocks, they may have reasonable prospects of being mass produced inexpensively in the future, and efforts to do this are being funded by DARPA (useful for many military applications, like jamming systems and anti-jamming, navigation, and various sensing applications). So unlike the state of the art atomic references these things may someday show up in very inexpensive equipment, and allow for some fun science experiments, improvements to reliable distributed systems, long baseline amateur radio astronomy, etc.
Or, Tom Van Baak measuring gravitational redshift with a minivan and some old HP cesium beam clocks. okay, not "floor to wall", but if you haven't read his presentation on it, you should, it's a load of fun and IMO, more accessible in that it's not talking about technology that exists in a rats nest of cables on an optical table in a single lab, but just old junk you can find surplus. :)
Wrt relativistic effect, the first NIST paper I cited shows that they needed altitude uncertainty less than 1m to avoid redshift from dominating the clock's error. The second shows that for the improved F2 reference redshift is one of the largest sources of uncertainty (and the corrected part is orders of magnitude larger than the other listed systemic errors). It's really cool, I agree. I'm happy to have people share in enjoying that, but sad about whatever causes the press to always have to present things as new and categorically different than what came before.
There are a number of really cool things they didn't mention: For example, these optical lattice clocks that they're talking about are solid state-- involving mostly only lasers and vacuum cells. Unlike cesium based atomic clocks, they may have reasonable prospects of being mass produced inexpensively in the future, and efforts to do this are being funded by DARPA (useful for many military applications, like jamming systems and anti-jamming, navigation, and various sensing applications). So unlike the state of the art atomic references these things may someday show up in very inexpensive equipment, and allow for some fun science experiments, improvements to reliable distributed systems, long baseline amateur radio astronomy, etc.
Or, Tom Van Baak measuring gravitational redshift with a minivan and some old HP cesium beam clocks. okay, not "floor to wall", but if you haven't read his presentation on it, you should, it's a load of fun and IMO, more accessible in that it's not talking about technology that exists in a rats nest of cables on an optical table in a single lab, but just old junk you can find surplus. :)
> This is the worst kind of comment and what is wrong with Hacker News.
> No one cares about your intellectual superiority, or the fact this might be a special interest for you.
Comments like this may often offer a fair bit of factually correct information and interesting insights. Opposing views, strong opinions, critical thinking—all this seemed more like a “feature” of HN rather than a “bug” to me.
(Sorry, I may have accidentally downvoted you; this was not intended.)
> No one cares about your intellectual superiority, or the fact this might be a special interest for you.
Comments like this may often offer a fair bit of factually correct information and interesting insights. Opposing views, strong opinions, critical thinking—all this seemed more like a “feature” of HN rather than a “bug” to me.
(Sorry, I may have accidentally downvoted you; this was not intended.)
I though the article was cute, but I wouldn't go so far as to say it was crappy. The essence of the article was on point.
You can't just report the time anymore, once special and general relativity become important, you have to report space-time. Sure, other effects are going to become important as well, but the essence of the article: time is not absolute, and this has practical difficulties for clock-makers, was well communicated.
You already can't do that, though. This isn't some new problem experienced only by this clock, though it's more sensitive to it.
The GPS satellites already had to correct for the passage of time being different for them relative to the surface of the planet. Decades ago.
The GPS satellites already had to correct for the passage of time being different for them relative to the surface of the planet. Decades ago.
The comment where the man makes a comparison to measuring electric current but tries to make it seem like we understand time better than electric current annoyed me. As if we have a greater fundamental understanding of what an electric charge "is" vs. time.
I love this page on that subject:
http://amasci.com/elect/charge1.html
It's not exactly 100% current (pun intended) but it makes the point nicely.
http://amasci.com/elect/charge1.html
It's not exactly 100% current (pun intended) but it makes the point nicely.
A "world in which your watch starts to tick faster, because you're working on the floor above me." and "your 3:30 happens earlier than mine, and we miss our appointment," seems ridiculous but it's not a totally foreign idea. For example, if your apartment is above the 150th floor of Burj Khalifa (the tallest building on earth), you must wait an additional 3 minutes to break the fast during the month of Ramadan, while if you live between the 80th floor and the 150th floor you only need to wait an additional 2 minutes. This mismatch in time happens for a different reason, but the result is the same and people seem to manage alright. Saying that this new clock might "End Time As We Know It" is pretty sensationalist.
The Ramadan fast ends at sunset. The sunset ends later for people at higher elevation because you can see over the horizon a little bit more. Not because of the time dilation of gravity.
Right, which is why I said that "This mismatch in time happens for a different reason."
Actually software developers have long been aware that different clocks can run at different speeds and tryto compare apples to apples.
Does anyone remember the name of that article that describes various clock synchronization techniques? I think it went something like "more than you ever wanted to know about computer time" and was based on an earlier similar title about another subject.
Does anyone remember the name of that article that describes various clock synchronization techniques? I think it went something like "more than you ever wanted to know about computer time" and was based on an earlier similar title about another subject.
Perhaps "what every programmer should know about time" and "what every programmer should know about memory" ?
Yep! THANK YOU
[deleted]
Both special and general relativity effects are well known to affect clocks. This is a major headache for GPS satellites, which have atomic clocks that gain about 38 microseconds a day vs earth-based clocks from the combination of speed and gravity difference.
38us/day slip is huge. That's 6 miles of GPS positional error. So GPS was designed with an correction and adjustment scheme to deal with this. So it's been a practical problem for decades.
38us/day slip is huge. That's 6 miles of GPS positional error. So GPS was designed with an correction and adjustment scheme to deal with this. So it's been a practical problem for decades.
As far as I know there is no headache, and although the theory is non intuitive, it just works as expected. The physics behind it can get complicated at the fundamental level, but computing a time dilation for an orbit is hardly rocket science. You don't even have to compute it, you can actually measure it right?
Do you know about any specific painful effect that was revealed only after general relativity was tried to be applied to GPS satellites in particular?
Do you know about any specific painful effect that was revealed only after general relativity was tried to be applied to GPS satellites in particular?
Time as "we" know it can only be coming to an end if by "we" mean those who are completely ignorant of early 20th century discoveries in physics, and who haven't even been exposed to enough science fiction (let alone nonfiction) to know about phenomena like the twin paradox. But for time as they know it to be coming to an end, there has to be some expectation that they will suddenly be enlightened. The existence of this new clock will certainly not the catalyst of that enlightenment.
We have already had clocks for decades whose perturbation by relativistic effects matters. Every GPS receiver (commonly found in now inexpensive technology in use by millions of consumers) makes relativistic corrections to the time base received from satellite signals, without which the positioning would be hopelessly inaccurate.
Why would this clock "end time as we know it", when millions of users of GPS navigation still have a naive view of time.
We have already had clocks for decades whose perturbation by relativistic effects matters. Every GPS receiver (commonly found in now inexpensive technology in use by millions of consumers) makes relativistic corrections to the time base received from satellite signals, without which the positioning would be hopelessly inaccurate.
Why would this clock "end time as we know it", when millions of users of GPS navigation still have a naive view of time.
A nitpick that doesn't detract from your main point: the relativistic corrections for GPS are applied on the satellites with a slight change in how fast their clocks run, so that they appear to run at the correct rate when seen from the ground. The receivers don't have to know about it.
I thought the reason time flows differently on top of Mount Everest is because the top of the mountain travels faster through space-time than the base (because of the rotation of the earth), not because of gravity...
Probably not. You're looking at a height difference of about 9 km [1], at a radius of 6380 km from earth's core [0] versus about an equatorial 6371 km. Rotational velocity at the equator is about 1040 mph [5], while Everest is looking at about 6380 km / 6371 km * 1040 mph = 1041.5 mph, assuming we moved Everest to the equator and kept everything else the same. One or two mph is really small compared to c, so much so WA just sorta says gamma = 1 [4].
And so is a mere 0.15% increase in height. But compare the gravitational acceleration at these two heights:
[2] Everest = 9.76322 m/s^2
[3] Sea Level = 9.831 m/s^2
Sea level is 0.69% stronger. That's somewhat more significant, and given that gravitational energy follows the inverse-square law, it makes some sense that it would amplify differences more than the linear effects of speed.
[0] https://www.google.com/search?q=radius+of+earth
[1] https://www.google.com/search?q=height+of+everest
[2] http://www.wolframalpha.com/input/?i=gravitational+accelerat...
[3] http://www.wolframalpha.com/input/?i=gravitational+accelerat...
[4] http://www.wolframalpha.com/input/?i=lorentz+factor+at+1.5+m...
[5] http://www.wolframalpha.com/input/?i=rotational+velocity+of+...
EDIT: forgot the reference to rotational velocity (and spelling). Note that the point is scale here. Gravity is n^2 versus velocity's n. It'll have a stronger effect in most cases (and any where speed overcomes, well, we call them relativistic speeds, and they'll often be some appreciable fraction of c, like 1% or more).
DOUBLE EDIT: 'AnimalMuppet makes a good point that the entire estimate for Everest's rotational velocity is flat out wrong. So I've changed my premise to match my initial incredibly incorrect assumption.
If I were to attempt to be correct about the problem, we'd see that Everest is cos(27.9881 degrees [10]) = 0.8837 [11] as fast as the equator, which sorta blasts out any height changes by long shot. (Note I'm assuming the earth to be a perfect, frictionless sphere here, and definitely not a oblate spheroid.)
[10] https://www.google.com/search?q=latitude+of+everest
[11] https://www.google.com/search?q=cos(27.9+degrees)
And so is a mere 0.15% increase in height. But compare the gravitational acceleration at these two heights:
[2] Everest = 9.76322 m/s^2
[3] Sea Level = 9.831 m/s^2
Sea level is 0.69% stronger. That's somewhat more significant, and given that gravitational energy follows the inverse-square law, it makes some sense that it would amplify differences more than the linear effects of speed.
[0] https://www.google.com/search?q=radius+of+earth
[1] https://www.google.com/search?q=height+of+everest
[2] http://www.wolframalpha.com/input/?i=gravitational+accelerat...
[3] http://www.wolframalpha.com/input/?i=gravitational+accelerat...
[4] http://www.wolframalpha.com/input/?i=lorentz+factor+at+1.5+m...
[5] http://www.wolframalpha.com/input/?i=rotational+velocity+of+...
EDIT: forgot the reference to rotational velocity (and spelling). Note that the point is scale here. Gravity is n^2 versus velocity's n. It'll have a stronger effect in most cases (and any where speed overcomes, well, we call them relativistic speeds, and they'll often be some appreciable fraction of c, like 1% or more).
DOUBLE EDIT: 'AnimalMuppet makes a good point that the entire estimate for Everest's rotational velocity is flat out wrong. So I've changed my premise to match my initial incredibly incorrect assumption.
If I were to attempt to be correct about the problem, we'd see that Everest is cos(27.9881 degrees [10]) = 0.8837 [11] as fast as the equator, which sorta blasts out any height changes by long shot. (Note I'm assuming the earth to be a perfect, frictionless sphere here, and definitely not a oblate spheroid.)
[10] https://www.google.com/search?q=latitude+of+everest
[11] https://www.google.com/search?q=cos(27.9+degrees)
You're forgetting that Everest isn't on the equator. Distance from the center of the earth doesn't matter; distance from the axis of rotation matters. So you need to multiply Everest's (height + radius) by the cosine of its latitude.
You're entirely correct, and I'm going to modify my answer to a convenient lie (in the true style of a physicist).
The point stands, but now I'm interested in what kind of cones we could make where relative heights and latitudes yield identical velocities. Prolly as useful a question as most XKCD What If? notes :)
The point stands, but now I'm interested in what kind of cones we could make where relative heights and latitudes yield identical velocities. Prolly as useful a question as most XKCD What If? notes :)
It's gravity. The mountaintop doesn't travel faster through space-time. There's no such thing as absolute speed, there's only the velocity compared to something else.
Special relativity covers time dilation due to relative velocity, general relativity covers time dilation due to gravity.
Special relativity covers time dilation due to relative velocity, general relativity covers time dilation due to gravity.
Even in relative terms, the top of Mt. Everest is traveling faster than objects at sea level, no?
Wikipedia says: "Time dilation is caused by differences in either gravity or relative velocity. Both factors are at play in the case of ISS astronauts (and are actually opposing one another)."
Why wouldn't the same apply to the top of Mt Everest. Sure, unlike the ISS, Everest is actually attached to the Earth, but still it is traveling a longer distance than the oceans over the same period, and therefore would be moving faster in relative terms AFAICS.
Wikipedia says: "Time dilation is caused by differences in either gravity or relative velocity. Both factors are at play in the case of ISS astronauts (and are actually opposing one another)."
Why wouldn't the same apply to the top of Mt Everest. Sure, unlike the ISS, Everest is actually attached to the Earth, but still it is traveling a longer distance than the oceans over the same period, and therefore would be moving faster in relative terms AFAICS.
Is the top of Mt. Everest traveling faster? The distance between here and there is a constant, no? From my frame of reference it's not moving at all.
your scenario to the extreme: a spacecraft is traveling at 0.5c in an circular path around earth at 1/pi light days of distance. From your (non inertial) frame of reference it's not moving at all. Yet the spacecraft is experiencing time dilation of about 15%.
Mt. Everest is higher. Because of the Earth's rotation, every point on earth traces 360 degrees every day. However the radius of these arcs depends on elevation. Ergo the top of Mt. Everest travels farther every day due to rotation that any other place on earth. That is the same as saying it is moving faster.
EDIT: I guess compared to a rotating reference frame this isn't true? Clearly this isn't my area of expertise.
EDIT: I guess compared to a rotating reference frame this isn't true? Clearly this isn't my area of expertise.
Not that I disagree with your point in any way, but I thought you might like to know - the top of Everest is not the furthest point from the centre of the earth. It is the highest point above sea level, but given the slightly ellipsoid nature of the planet, the spot with the largest radius value is actually in South America - http://en.m.wikipedia.org/wiki/Chimborazo
I think a way to rephrase the question is to ask, is the light coming from the top of mt. everest red shifted or blue shifted or neither? (I'm not certain of the answer, either. Physics was a long time ago.)
It depends on the location of the observer. (coming towards you = blue, moving away from you = red)
[deleted]
You're correct, and my napkin guess is that it's going about 1.5mph faster than sea level. But the ISS is going a whopping 16100 mph faster than sea level [0].
Popping that into MS Mathematics using the Lorentz equation, we see that gamma now is 0.2 billionths above unity. Which is super small, but definitely detectable. In contrast, 1.5mph doesn't yield anything - I'm guessing (1.5/670616629)^2 is nearing the floating point epsilon (I guess MS Math is using floats?) [1].
[0] http://www.wolframalpha.com/input/?i=orbital+velocity+of+ISS
[1] http://en.wikipedia.org/wiki/Machine_epsilon
EDIT: Right, as noted elsewhere, this assumes Everest is at the equator. Which Wikipedia tells me is not a great approximation for where Nepal is. So assume that Nepal ended up in the wrong place for a little while, and the arguement holds. Otherwise, we've got a bit more calculating to do.
Popping that into MS Mathematics using the Lorentz equation, we see that gamma now is 0.2 billionths above unity. Which is super small, but definitely detectable. In contrast, 1.5mph doesn't yield anything - I'm guessing (1.5/670616629)^2 is nearing the floating point epsilon (I guess MS Math is using floats?) [1].
[0] http://www.wolframalpha.com/input/?i=orbital+velocity+of+ISS
[1] http://en.wikipedia.org/wiki/Machine_epsilon
EDIT: Right, as noted elsewhere, this assumes Everest is at the equator. Which Wikipedia tells me is not a great approximation for where Nepal is. So assume that Nepal ended up in the wrong place for a little while, and the arguement holds. Otherwise, we've got a bit more calculating to do.
Thanks for the info!
What's the right answer if someone makes this counterargument: in the inertial reference frame of the Earth the Earth is not rotating, so neither the sea nor Mt. Everest are moving at all, so there is no relative velocity difference and no time dilation from velocity difference.
Btw, I'm not sure about the phrase "I'm guessing (1.5/670616629)^2 is nearing the floating point epsilon" (unlike physics, I do have a fair amount of expertise in floating point formats). The way you put it suggests that the "machine epsilon" represents the smallest increments that floating point can represent, and therefore suggests that (1.5/670616629)^2 represented as float will underflow to zero or be so inaccurate as to be meaningless (sorry if I'm misreading you).
I find the definition of "machine epsilon" given on that page somewhat confusing. I think it's more intuitive to think of floating point error in terms of percentages. That page says the "machine epsilon" for float is ~1e-7; an equivalent and IMO more intuitive way to say it is that float is accurate to ~0.00001%.
The range of float goes far smaller than 1e-7; FLT_MIN is ~1e-38, and that's not even considering subnormal numbers. So float can very easily represent the results of (1.5/670616629)^2 ≈ 5e-18, and like any other representable float this is accurate to no worse than ~0.00001%, which is pretty decent.
What's the right answer if someone makes this counterargument: in the inertial reference frame of the Earth the Earth is not rotating, so neither the sea nor Mt. Everest are moving at all, so there is no relative velocity difference and no time dilation from velocity difference.
Btw, I'm not sure about the phrase "I'm guessing (1.5/670616629)^2 is nearing the floating point epsilon" (unlike physics, I do have a fair amount of expertise in floating point formats). The way you put it suggests that the "machine epsilon" represents the smallest increments that floating point can represent, and therefore suggests that (1.5/670616629)^2 represented as float will underflow to zero or be so inaccurate as to be meaningless (sorry if I'm misreading you).
I find the definition of "machine epsilon" given on that page somewhat confusing. I think it's more intuitive to think of floating point error in terms of percentages. That page says the "machine epsilon" for float is ~1e-7; an equivalent and IMO more intuitive way to say it is that float is accurate to ~0.00001%.
The range of float goes far smaller than 1e-7; FLT_MIN is ~1e-38, and that's not even considering subnormal numbers. So float can very easily represent the results of (1.5/670616629)^2 ≈ 5e-18, and like any other representable float this is accurate to no worse than ~0.00001%, which is pretty decent.
On the topic of the floating point mechanics, I'll readily defer to you. I'll be honest: I was grasping for an explanation of why the result was simply a solitary "1", and there's likely a much smarter explanation (like "After a number of decimal places, nobody gives a damn." - false, but useful typically).
As for the counterargument: I don't think that works. And that's taking into account the harrowing liberties I'm willing to assume for the sake of a physics argument. In the inertial reference frame of the Earth, the Earth is rotating - as in, there's rotational inertia in that frame. This has measureable effects on stuff, from time dilation from velocity (very small) to time dilation from gravity warping spacetime (noticeably larger, but still small).
Put another way, here's a thought experiment. The mantel of the planet is molten rock, and can be treated as a viscous fluid. If the planet were spinning, the fluid would bulge out at the latitudes where the planet is spinning fastest (centrifugal force stuff). Otherwise the planet would be a sphere. This is directly measurable, and - in fact - the planet's a sphere. Mostly. It bulges out a bit at the equator [0].
So if you're careful, you'll note it's never fair to say you're in a non-rotating inertial frame on earth. But in practice it almost never matters. Unless you're doing something crazy like measuring femtillionths of a second with one of the most sensitive devices we can build - then we start being a bit wrong. Or you're just trying to be accurate with your GPS satellites (which are way higher and faster than a mountain top).
I rant a bit about this, as this sort of counterargument comes up a lot. I think it's due to the completely unreasonable mismatch of scales people are used to. Feynman ranted a bit on it about QM, and we're running into it here with relativity [1]. Here we're trying to talk about something reasonably, and the levels of precision are completely unreasonable: we're talking about a couple mile's difference over the span of thousands of miles to have an effect on the order of a few (bi|tri)llionths of a second; how do you keep such a scale in mind? It's like the silly analogies of hitting a baseball in NYC and nailing a bumble bee in San Fransico for precision. By the same token, we're hurtling through space, whipping around the sun and being wobbled so hard by the moon the ocean sloshes over our beachfronts. And that seems perfectly normal, even though it directly implies enormous forces at work.
/rant (and sorry for that - I find this sort of thing facinating)
TL;DR: I think that counterargument is simply wrong. But completely understandably so.
[0] http://image.gsfc.nasa.gov/poetry/ask/a11818.html
[1] http://bouman.chem.georgetown.edu/general/feynman.html
As for the counterargument: I don't think that works. And that's taking into account the harrowing liberties I'm willing to assume for the sake of a physics argument. In the inertial reference frame of the Earth, the Earth is rotating - as in, there's rotational inertia in that frame. This has measureable effects on stuff, from time dilation from velocity (very small) to time dilation from gravity warping spacetime (noticeably larger, but still small).
Put another way, here's a thought experiment. The mantel of the planet is molten rock, and can be treated as a viscous fluid. If the planet were spinning, the fluid would bulge out at the latitudes where the planet is spinning fastest (centrifugal force stuff). Otherwise the planet would be a sphere. This is directly measurable, and - in fact - the planet's a sphere. Mostly. It bulges out a bit at the equator [0].
So if you're careful, you'll note it's never fair to say you're in a non-rotating inertial frame on earth. But in practice it almost never matters. Unless you're doing something crazy like measuring femtillionths of a second with one of the most sensitive devices we can build - then we start being a bit wrong. Or you're just trying to be accurate with your GPS satellites (which are way higher and faster than a mountain top).
I rant a bit about this, as this sort of counterargument comes up a lot. I think it's due to the completely unreasonable mismatch of scales people are used to. Feynman ranted a bit on it about QM, and we're running into it here with relativity [1]. Here we're trying to talk about something reasonably, and the levels of precision are completely unreasonable: we're talking about a couple mile's difference over the span of thousands of miles to have an effect on the order of a few (bi|tri)llionths of a second; how do you keep such a scale in mind? It's like the silly analogies of hitting a baseball in NYC and nailing a bumble bee in San Fransico for precision. By the same token, we're hurtling through space, whipping around the sun and being wobbled so hard by the moon the ocean sloshes over our beachfronts. And that seems perfectly normal, even though it directly implies enormous forces at work.
/rant (and sorry for that - I find this sort of thing facinating)
TL;DR: I think that counterargument is simply wrong. But completely understandably so.
[0] http://image.gsfc.nasa.gov/poetry/ask/a11818.html
[1] http://bouman.chem.georgetown.edu/general/feynman.html
Your counter argument is correct, in my opinion.
There is no absolute velocity, but there is absolute acceleration. And the mountaintop is accelerating more because it's in circular motion with a larger radius.
However, the effect of gravity is much more significant (if it weren't, the mountaintop would be flying out into space due to centripetal force).
However, the effect of gravity is much more significant (if it weren't, the mountaintop would be flying out into space due to centripetal force).
But if I'm standing on the Earth's surface, it's not accelerating relative to me. It's always at the same distance and direction.
Since acceleration is change in velocity, it's impossible to have absolute acceleration without absolute velocity. You can only say that it's accelerating compared to X.
Since acceleration is change in velocity, it's impossible to have absolute acceleration without absolute velocity. You can only say that it's accelerating compared to X.
It actually is accelerating relative to you, in exactly the same way that a kid on the outside of a spinny-go-round is accelerating harder than a kid on the inside. Of course, there's not a huge difference, as a couple km is spare change to the radius of the planet, but it's there.
There's definitely a constant vector difference between you and Everest's peak, and that's likely what you're thinking of. But Everest itself is under a greater strain to maintain that vector compared to you. And that's actually a measurable difference (where measurable is on scales of stupefying precision not normally used in everyday life).
And as another noted, it really should maintain that relative vector - if it didn't, the earth wouldn't be in steady-state and you'd have a changing position vector between you and it, and that'd imply one of you was moving... hopefully it's you.
(Let's ignore all the techtonic complications, as that really ruins the simplicity of the argument :)
EDIT: As noted elsewhere in the thread, Everest isn't on the equator, and - if I may be bold enough to presume - you likely aren't either. So it's not clear if you or Everest is on the outside of the spinny-go-round in the analogy.
For the purposes of wondering if velocity or gravitational effects on spacetime are the dominant factors, this has no effect. If you're actually interested in the effective relative centrifugal forces between you and Everest, then it's damn near everything.
There's definitely a constant vector difference between you and Everest's peak, and that's likely what you're thinking of. But Everest itself is under a greater strain to maintain that vector compared to you. And that's actually a measurable difference (where measurable is on scales of stupefying precision not normally used in everyday life).
And as another noted, it really should maintain that relative vector - if it didn't, the earth wouldn't be in steady-state and you'd have a changing position vector between you and it, and that'd imply one of you was moving... hopefully it's you.
(Let's ignore all the techtonic complications, as that really ruins the simplicity of the argument :)
EDIT: As noted elsewhere in the thread, Everest isn't on the equator, and - if I may be bold enough to presume - you likely aren't either. So it's not clear if you or Everest is on the outside of the spinny-go-round in the analogy.
For the purposes of wondering if velocity or gravitational effects on spacetime are the dominant factors, this has no effect. If you're actually interested in the effective relative centrifugal forces between you and Everest, then it's damn near everything.
> Special relativity covers time dilation due to relative velocity, general relativity covers time dilation due to gravity.
It's actually due to acceleration, whether from gravity or from motion. And, given earth's rotation, points on the surface accelerate (except for the poles).
But, as I pointed out elsewhere in this discussion, it's distance from the axis that determines acceleration from rotation, not distance from the center of the earth. (Distance from the center does determine gravity, though).
It's actually due to acceleration, whether from gravity or from motion. And, given earth's rotation, points on the surface accelerate (except for the poles).
But, as I pointed out elsewhere in this discussion, it's distance from the axis that determines acceleration from rotation, not distance from the center of the earth. (Distance from the center does determine gravity, though).
[deleted]
The bit about why humanity collectively seeks to measure time so accurately -- perhaps, because, in fact we don't really understand it at all -- is an interesting and salient morsel for us technologists to chew on. What do we do when we don't understand something? Measure it!
If you enjoy the article, you'd enjoy these guys:
http://www.leapsecond.com/time-nuts.htm
I hang out more with the volt nuts. (how bout that LTZ1000A voltage ref, eh? got three in my basement, because two aren't very useful LOL). I do not remember who begat who but there is probably commentary in the archives of both, if you go back far enough.
http://www.leapsecond.com/time-nuts.htm
I hang out more with the volt nuts. (how bout that LTZ1000A voltage ref, eh? got three in my basement, because two aren't very useful LOL). I do not remember who begat who but there is probably commentary in the archives of both, if you go back far enough.
'But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, "and you will start to see that difference." '
How do they do these differences? Surely they would need a second, equally accurate clock to compare it with?
How do they do these differences? Surely they would need a second, equally accurate clock to compare it with?
If it's repeatable, you can just raise and lower the clock a few times and see the difference. If the clock didn't keep good time, you'd just get a bunch of noise. But if it's good enough, you should see similar drift each time.
"My own personal opinion is that time is a human construct"
What is this supposed to mean?
We can measure time with non-human instruments and time is at the core of physics. How can it be a human construct?
Sure, hours, minutes, days, etc. are human constructs based on movements of the earth, but time itself?
What is this supposed to mean?
We can measure time with non-human instruments and time is at the core of physics. How can it be a human construct?
Sure, hours, minutes, days, etc. are human constructs based on movements of the earth, but time itself?
Time only defines the state of the extremely complex system known as universe. It's an idea to make things more simple for us humans, not a physics phenomena. Stop all the particles and waves in the universe and time has no meaning. At least that's how I understand what he meant by this.
I think his point is that time is so inherently relative to the location / inertia of the observer that it is in practice a human construct.
The physicists definition of time is "What clocks measure". It sounds like he was just saying the party line.
Seems to me they haven't built a clock: they've built a tricorder.
Put an array of these in a box. Then computationally map the changes in gravity from each clock. Bingo presto, you've just created a 3-D model of the mass in the local area.
Put an array of these in a box. Then computationally map the changes in gravity from each clock. Bingo presto, you've just created a 3-D model of the mass in the local area.
I build precision gravity sensors for a living. We tried doing something similar and demonstrated a proof of principle. It works, but gravity is often unkind to the experimentalist, chiefly through the combined facts that many mass configurations can yield the same signal and that the inverse-square law requires close proximity for good resolution. Almost any other sensor system you could dream up is more efficient. For three-dimensional arbitrary mass distributions, the inverse problem is extremely hard. For 2-D imaging or simply localizing a mass, things are easier.
If there's any application for pure gravitational sensing that can resolve the position of a higher-density mass to a few centimeters over distances of perhaps a meter or that can make simple statements about a meter-scale mass distribution, please drop me an email. We've tabled the project because we don't know of a single use for it, academic or commercial. Device cost would be in the low hundreds of thousands of dollars and require careful operation. We've thought hard about this, but haven't ever found an application for which some other sensor wouldn't be far more appropriate. X-rays, neutrons, resistivity, clever weighing, optical techniques, microwaves, touch probes, three-year-olds, lemurs, optical imaging, you name it, it's probably cheaper, better, and faster.
If there's any application for pure gravitational sensing that can resolve the position of a higher-density mass to a few centimeters over distances of perhaps a meter or that can make simple statements about a meter-scale mass distribution, please drop me an email. We've tabled the project because we don't know of a single use for it, academic or commercial. Device cost would be in the low hundreds of thousands of dollars and require careful operation. We've thought hard about this, but haven't ever found an application for which some other sensor wouldn't be far more appropriate. X-rays, neutrons, resistivity, clever weighing, optical techniques, microwaves, touch probes, three-year-olds, lemurs, optical imaging, you name it, it's probably cheaper, better, and faster.
If you can improve on current gravimeters, it should be marketable. Potential fields surveys are still a big business with a lot of customers. (As an exploration geologist in the oil industry, I use gravimetry on a daily basis.)
Generally speaking, though, accuracy of the sensor is rarely the limiting factor in gravity surveys.
For land-surveys, it's precisely knowing your elevation, correcting for the "unwanted" mass distribution around you, etc. For mobile surveys, it's correcting for the acceleration of whatever vessel the instrument is on. Any ideas you might have for improving the state of the art for the mobile case would probably be _very_ marketable.
On a separate note, though, the inverse problem, while fundementally very non-unique, is still solvable for many practical problems (e.g. we know the range of density of the materials involved and we can make a reasonable starting guess for the distribution of mass). Regardless, you're usually interested in distinguishing between a few scenarios that can be easily forward-modeled.
Generally speaking, though, accuracy of the sensor is rarely the limiting factor in gravity surveys.
For land-surveys, it's precisely knowing your elevation, correcting for the "unwanted" mass distribution around you, etc. For mobile surveys, it's correcting for the acceleration of whatever vessel the instrument is on. Any ideas you might have for improving the state of the art for the mobile case would probably be _very_ marketable.
On a separate note, though, the inverse problem, while fundementally very non-unique, is still solvable for many practical problems (e.g. we know the range of density of the materials involved and we can make a reasonable starting guess for the distribution of mass). Regardless, you're usually interested in distinguishing between a few scenarios that can be easily forward-modeled.
Our instruments ( http://www.npl.washington.edu/eotwash/ ) are really good at measuring near-field gravity gradients; we don't build gravimeters at all. We are adapting our gradiometers to make them more field-usable (which might have considerable use in prospecting), but that's not a huge science priority at present. Every few years, we look hard at whether or not we can make a superior mobile gradiometer. If we could, you'd probably know :). We have one new design that might fit into a borehole; if it works well-enough, we may chase commercialization.
A lot of the imaging market appears to come from security/defense applications, either in portal-monitoring or for IED detection. There are defense contractors working on both. The former is easily spoofed (put your uranium pit in a styrofoam sphere in a truck full of grain, done), and the latter is hard to do at speed in a rugged environment.
I've spent a lot of time trying to figure out how to do gravitational imaging on the sub-meter scale, and while it does work, it's hard to get sufficient image resolution to be useful for anything other than a party trick.
If our other science weren't more interesting, I'd be doing it for fun alone. Burning 3-6 months on the project to assess feasibility was as far as I wanted to go without a clear exit strategy.
A lot of the imaging market appears to come from security/defense applications, either in portal-monitoring or for IED detection. There are defense contractors working on both. The former is easily spoofed (put your uranium pit in a styrofoam sphere in a truck full of grain, done), and the latter is hard to do at speed in a rugged environment.
I've spent a lot of time trying to figure out how to do gravitational imaging on the sub-meter scale, and while it does work, it's hard to get sufficient image resolution to be useful for anything other than a party trick.
If our other science weren't more interesting, I'd be doing it for fun alone. Burning 3-6 months on the project to assess feasibility was as far as I wanted to go without a clear exit strategy.
I'm just a random internet commenter (and don't we know everything!), so take what I say with a grain of salt.
I wonder, however, if the problems you are describing are things that would work themselves out over time as the equipment improves? The precision of these clocks sound like they're many orders of magnitude better than the old gravity sensors. I think. Perhaps all we'er waiting on is some kind of crazy technological magic over the next 50 years that would involve miniaturization, improved accuracy, and an array of a million or so. (All of which I just made up)
I wonder, however, if the problems you are describing are things that would work themselves out over time as the equipment improves? The precision of these clocks sound like they're many orders of magnitude better than the old gravity sensors. I think. Perhaps all we'er waiting on is some kind of crazy technological magic over the next 50 years that would involve miniaturization, improved accuracy, and an array of a million or so. (All of which I just made up)
If the clocks get good-enough, then yes, They'll keep getting better.
To do it with a pair of clocks, there's a long way to go, as they measure differences in depth in a gravitational potential. If you change your distance from Earth's center by a meter, your gravitational potential will change by 9.8 m^2/s^2. If somebody heavy (100 kg) and spherical (I'm a physicist) stands a meter away from you, your potential will change by 7 x 10^-9 m^2/s^2. In short, the clocks need to get ten million (they can see a 1 cm height change) times better to sense a nearby person. Clever trickery with an ensemble of clocks will make that easier, but not by 10^7.
Not impossible, just hard. The fact that the time/frequency teams have encountered gravity, in particular through the gravitational potential, has just made their lives quite a bit harder. They now need to know a lot about the relative locations of other clocks and the mass distribution within the earth to make substantial strides forward. It's an incredible feat to have gotten to where they are, and a major challenge for the future.
To do it with a pair of clocks, there's a long way to go, as they measure differences in depth in a gravitational potential. If you change your distance from Earth's center by a meter, your gravitational potential will change by 9.8 m^2/s^2. If somebody heavy (100 kg) and spherical (I'm a physicist) stands a meter away from you, your potential will change by 7 x 10^-9 m^2/s^2. In short, the clocks need to get ten million (they can see a 1 cm height change) times better to sense a nearby person. Clever trickery with an ensemble of clocks will make that easier, but not by 10^7.
Not impossible, just hard. The fact that the time/frequency teams have encountered gravity, in particular through the gravitational potential, has just made their lives quite a bit harder. They now need to know a lot about the relative locations of other clocks and the mass distribution within the earth to make substantial strides forward. It's an incredible feat to have gotten to where they are, and a major challenge for the future.
For what it's worth, just directly measuring changes in gravitational acceleration is much easier and much more sensitive to changes in mass distribution.
We've been able to measure gravitational acceleration very precisely for over a century now.
An 80-year-old LaCoste & Romberg gravimeter will do the job quite nicely, though it's slow to use and you need to know the elevation you're taking the measurement at very precisely. (Interestingly, the ones made before ~1950 are more precise than the ones made in the 60's to 90's. It's basically a very well made and well calibrated spring. When they switched to mass-producing them, the quality fell.)
Now you have a second problem, though... Regardless of whether you've measured things through gravitation acceleration or time dilation, going from the measured effect back to an actual mass distribution is a non-unique inverse problem. There are an infinite number of equally correct solutions (and a larger infinite number of incorrect ones). You can make a pretty good guess at what the mass distribution by applying reasonable a-priori constraints, but there's no single unique way to get the mass distribution from the gravitational effect of the mass.
We've been able to measure gravitational acceleration very precisely for over a century now.
An 80-year-old LaCoste & Romberg gravimeter will do the job quite nicely, though it's slow to use and you need to know the elevation you're taking the measurement at very precisely. (Interestingly, the ones made before ~1950 are more precise than the ones made in the 60's to 90's. It's basically a very well made and well calibrated spring. When they switched to mass-producing them, the quality fell.)
Now you have a second problem, though... Regardless of whether you've measured things through gravitation acceleration or time dilation, going from the measured effect back to an actual mass distribution is a non-unique inverse problem. There are an infinite number of equally correct solutions (and a larger infinite number of incorrect ones). You can make a pretty good guess at what the mass distribution by applying reasonable a-priori constraints, but there's no single unique way to get the mass distribution from the gravitational effect of the mass.
it would take some time to develop "gravitationally stealth" F-22 :)
Can't wait to invade a country to secure America's source of cavorite.
If one part of this clock is accurate to 10^-16 but noise/error contributed by some other aspect of it is larger than that, then it is misleading to claim these clocks have an accuracy of 10^-16.
This is the same type of stuff they are dealing with in the gravitational wave experiments like LIGO and VIRGO. They have amazing sensitivity but it is still lost in the noise. They don't claim to be able to make measurements to accuracy which is lower than the noise levels. And I don't see why these clock people should either.
This is the same type of stuff they are dealing with in the gravitational wave experiments like LIGO and VIRGO. They have amazing sensitivity but it is still lost in the noise. They don't claim to be able to make measurements to accuracy which is lower than the noise levels. And I don't see why these clock people should either.
I may be wrong but this sounds like a confusion of accuracy vs. precision (http://en.wikipedia.org/wiki/Accuracy_and_precision)
edit: By which I mean that this clock could be precise to 10^-16 but be off by 10^-14 due to a mis-calibration.
edit: By which I mean that this clock could be precise to 10^-16 but be off by 10^-14 due to a mis-calibration.
All that this means is it's high time we abandoned our datetime's in favour of spacetime's.
(edit: formatting is hard)
from spacetime import spacetime, spacetimedelta
then_and_there = spacetime.here_and_now() + spacetimedelta(years=1, x=5, y=3, z=-2)
(edit: formatting is hard)
Hey I've been pondering this article for a little while now and my friends and I have come up with a question.
Say we have two people, Bob and Jane. Bob and Jane blink at similar rates when they are standing next to one another. Both Bob and Jane have the accurate watches described in this article.
Bob then takes a trip to space traveling near the speed of light. Right when he takes off a laser initiates both stopwatches (one on bob's wrist and one on jane's). At some time (...), from an equidistant point to both Bob and Jane a light originates and then stops both Bob's and Jane's wrist watches. Btw, both Bob and Jane have been blinking the whole time their watches have been running.
The questions:
Upon stopping the watches:
1. Do Bob and Jane see a different amount of time passed on their stopwatches? (most of us are not in contention about this one)
2. Have Bob and Jane blinked the same number of times?
Say we have two people, Bob and Jane. Bob and Jane blink at similar rates when they are standing next to one another. Both Bob and Jane have the accurate watches described in this article.
Bob then takes a trip to space traveling near the speed of light. Right when he takes off a laser initiates both stopwatches (one on bob's wrist and one on jane's). At some time (...), from an equidistant point to both Bob and Jane a light originates and then stops both Bob's and Jane's wrist watches. Btw, both Bob and Jane have been blinking the whole time their watches have been running.
The questions:
Upon stopping the watches:
1. Do Bob and Jane see a different amount of time passed on their stopwatches? (most of us are not in contention about this one)
2. Have Bob and Jane blinked the same number of times?
I'm a little sad this article doesn't make the connection to acceleration. The idea that sitting at different points of a gravity well is exactly equivalent to different points along an acceleration curve (from the perspective of time) is a delightful one and I wish it had been mentioned.
> It's one of the most accurate clocks on the planet: an atomic clock that uses oscillations in the element cesium to count out 0.0000000000000001 second at a time
For comparison, Planck time = 5.39106×10^-44 sec
We're pretty far from measuring time precisely.
For comparison, Planck time = 5.39106×10^-44 sec
We're pretty far from measuring time precisely.
Atomic clocks are cool.. if one wanted to transmit a sporting event in the era before time base correctors, one had to bring a video sync generator timed by an atomic clock from the TV station to the event. This gets you the same frame rate as the TV station (phase still needs to be adjusted to account for speed of light delay). With all the signals in sync you can switch to a commercial without messing up everyone's TV.
Time base correctors are also cool: the first generation ones were rack sized and used core-memory. I think they were an enabling technology for on-location news.
You can buy your own: rubidium standards sell for less than $300 on ebay.
Time base correctors are also cool: the first generation ones were rack sized and used core-memory. I think they were an enabling technology for on-location news.
You can buy your own: rubidium standards sell for less than $300 on ebay.
I don't understand what's so confusing about time.
"but what time really is, is a question that I can't answer for you."
O'Brian almost correctly answers that right off the bat:
"My own personal opinion is that time is a human construct"
Time is a measurement, nothing more. It's not magic, it's not difficult to understand, it's not separate from reality.
It'd be like calculating how long it takes you to walk around your coffee table, and then being confused by what it means or what that measurement consists of.
"but what time really is, is a question that I can't answer for you."
O'Brian almost correctly answers that right off the bat:
"My own personal opinion is that time is a human construct"
Time is a measurement, nothing more. It's not magic, it's not difficult to understand, it's not separate from reality.
It'd be like calculating how long it takes you to walk around your coffee table, and then being confused by what it means or what that measurement consists of.
http://en.m.wikipedia.org/wiki/International_Atomic_Time
The time we use it based on an average of many clocks.
The fact that time passes at different rates at different locations is already account for.
The fact that time passes at different rates at different locations is already account for.
Could we (easily) build a clock that accurately measures space time intervals? If you place two of them next to each other and synchronize them, you should be able to separate them and they should still be synchronized whenever you bring them back together no matter what happened in between.
It amazes me that our master clocks can be so accurate and yet our devices, which ostensibly get their time from the master clocks through networks, can be so off.
My Android phone is very frequently 30 seconds or more off from my friends' iOS phones. I don't even...
My Android phone is very frequently 30 seconds or more off from my friends' iOS phones. I don't even...
Well, it's off by 30 seconds now. But eventually....
> This new clock can keep perfect time for 5 billion years.
In theory.
In practice, I'll bet it stops keeping time before I do.
Check out the Long Now's 10,000 year clock project. http://longnow.org/clock/
In theory.
In practice, I'll bet it stops keeping time before I do.
Check out the Long Now's 10,000 year clock project. http://longnow.org/clock/
> Time itself is flowing more quickly on the wall than on the floor
Velocity is a function of distance and time. How can time have a velocity? Couldn't you also say the distances in the clock stretched or shrunk by the lorentz factor?
Velocity is a function of distance and time. How can time have a velocity? Couldn't you also say the distances in the clock stretched or shrunk by the lorentz factor?
Armchair astrophysicist here: any way that these clocks could be used to detect evidence of gravitational waves? Seems like it would be a good use case for increasingly sensitive clocks.
I'm glad to hear an actual scientist in this field also think what I've thought for a long time, which is that time is a human invention. I can't really explain it, but I've always felt like the universe doesn't really have a concept of time, that everything is just right now, hence why I don't believe in time travel either. Time is just a way for us to say 'something was' or 'will be', but in reality what was isn't anymore, it's not that it's in the past, but that the object was changed into what it now is.
This may make sense to a physical scientist, but biological phenomena do have a concept of time, because many biological molecules have an evolutionary history. It's not only that something was, but also that something is that embodies the trace of what was.
A network of clocks in space might be used to detect gravitational waves from black holes and exploding stars.
We need to fund this!
We need to fund this!
> "But it can tick for billions of years without loosing a second."
Is it loosing or losing? Are both correct?
Is it loosing or losing? Are both correct?
It's losing. For some reason, I see the "loosing" misspelling more often now than a few years ago. It seems to be a sort of orthographical meme that's spreading.
My brain always stumbles on the loose-lose pair. I don't usually substitute them for each other, but I always have to think about which one to write. I believe it is because of the odd spelling and pronunciation of the pair. The extra o does not change the vowel sound, instead it changes the sound made by the s (and neither sound like "close"). Typically, the hard and soft s sound depends on the one or two s's [1]: desert and dessert.
Or it could just be the auto-correct (now in desktop apps as well, not just mobile).
[1] I hate 's for plurals, but how else would you write "esses".
Or it could just be the auto-correct (now in desktop apps as well, not just mobile).
[1] I hate 's for plurals, but how else would you write "esses".
Right now, on the top of Mount Everest, time is passing just a little bit faster than it is in Death Valley. That's because speed at which time passes depends on the strength of gravity. Einstein himself discovered this dependence as part of his theory of relativity, and it is a very real effect.
"Just to be clear, the clock in Death Valley appears to run slowly from the point of view of the eagle-eyed observer standing on top of Everest.
To a person in Death Valley, the clock appears to tick at precisely the rate it would appear to tick if both person and clock were on top of Everest."