The theory of relativity in words of four letters or less(muppetlabs.com)
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The theory of relativity in words of four letters or less
http://www.muppetlabs.com/~breadbox/txt/al.html
26 comments
Exactly my thought reading that. That question, "Can you find out? Hell no," is relativity in a nutshell. If you really grasp what that means, the whole deal from simultaneity to time dilation to curved spacetime all falls out more or less intuitively. (Of course it was harder to work out the first time :P)
Most people implicitly believe that there must be some privileged reference frame, if not mine necessarily than at least one very close to mine, and for good reason. (I'd go so far as to say that most people believe explicitly that there is a privileged reference frame, and that it is an intelligent agent called God, but leave that alone for now.) Even if they do get past this statement with a, "Uh, okay, I guess so..." they probably have not actually adjusted their entire world view to account for that powerful fact, and if they seem to understand what you have told them it is likely that they have simply memorized the right answer.
Not that there's anything wrong with trying.
Most people implicitly believe that there must be some privileged reference frame, if not mine necessarily than at least one very close to mine, and for good reason. (I'd go so far as to say that most people believe explicitly that there is a privileged reference frame, and that it is an intelligent agent called God, but leave that alone for now.) Even if they do get past this statement with a, "Uh, okay, I guess so..." they probably have not actually adjusted their entire world view to account for that powerful fact, and if they seem to understand what you have told them it is likely that they have simply memorized the right answer.
Not that there's anything wrong with trying.
> I'd go so far as to say that most people believe explicitly that there is a privileged reference frame, and that it is an intelligent agent called God
????? Why do you assume God is a physical being inside the universe? (Do people really think that?) God created the universe - God is outside it. Like God is the computer and the universe is the program.
God isn't at rest/not at rest. The concept doesn't even apply.
????? Why do you assume God is a physical being inside the universe? (Do people really think that?) God created the universe - God is outside it. Like God is the computer and the universe is the program.
God isn't at rest/not at rest. The concept doesn't even apply.
In the United States it is the majority opinion (vocally, anyway) that God is a real thing with both interest and power to intervene in both historical and day-to-day events.
As to why? A lifetime of indoctrination and social pressure. The same reason anyone believes anything, I suppose.
As to why? A lifetime of indoctrination and social pressure. The same reason anyone believes anything, I suppose.
Really? The majority opinion is that God is a physical being that lives inside the universe?
I know there are some religions that believe that, but they are hardly the majority.
The concept of "reference frame" doesn't even exist for a non-physical being.
I know there are some religions that believe that, but they are hardly the majority.
The concept of "reference frame" doesn't even exist for a non-physical being.
I can't rigorously defend something I don't think is true, but I stand behind my previous statement as it is.
Your previous statement might be true - and also has nothing to do with a "universal reference frame".
A god that intervenes has nothing to do with whether or not the God is physical.
I suspect you are reading things into what people believe without actually understanding what they believe. i.e. that it's actually you that believes God has a reference frame, not that the majority of people in the US do.
A god that intervenes has nothing to do with whether or not the God is physical.
I suspect you are reading things into what people believe without actually understanding what they believe. i.e. that it's actually you that believes God has a reference frame, not that the majority of people in the US do.
Well, I'm not that interested in the theology of an interventionist God because it's not a very exciting fairy tale to me. But as I understand it God is omnipresent and omnipotent and either those things mean a physical presence that is everywhere at once or they mean nothing at all. That is precisely the thing proscribed by relativity.
I'm sure one could define God down into some kind of good-vibes field that could logically exist in our universe, and that's all good with me. But it's not what most Americans profess to believe. In any event, discard it if it offends you; it's completely irrelevant to the topic, which is super-cool physics.
I'm sure one could define God down into some kind of good-vibes field that could logically exist in our universe, and that's all good with me. But it's not what most Americans profess to believe. In any event, discard it if it offends you; it's completely irrelevant to the topic, which is super-cool physics.
> mean a physical presence that is everywhere at once
Everywhere at once means "no privileged reference frame". (Kind of like how light, from the point of view of light itself is everywhere at once, and light also has a the special privileged reference frame of no reference frame at all.)
You were the one who claimed the most people believe in a privileged reference frame based on God. Not me. Now you are backpedaling from that claim - which is fine, because not only do most people not believe that, it doesn't even make any sense.
And I agree that this should conclude the religious digression of the main topic. Not that there is a whole lot more to talk about, unless you want to talk about (argue with?) my comment above on light.
Everywhere at once means "no privileged reference frame". (Kind of like how light, from the point of view of light itself is everywhere at once, and light also has a the special privileged reference frame of no reference frame at all.)
You were the one who claimed the most people believe in a privileged reference frame based on God. Not me. Now you are backpedaling from that claim - which is fine, because not only do most people not believe that, it doesn't even make any sense.
And I agree that this should conclude the religious digression of the main topic. Not that there is a whole lot more to talk about, unless you want to talk about (argue with?) my comment above on light.
> Everywhere at once means "no privileged reference frame".
Probably you'll never read this now, but... Nope. Everywhere at once literally means a privileged reference frame. "Over there, now" is a concept with no logical meaning in our physical universe. Being in two places at once isn't physically impossible, it's just nothing.
And that imposes very serious constraints on God. If I am on the Earth and I pray for my husband on Mars, God on Mars can not hear my prayer until it is too late. You really think that's a statement most Americans agree with?
You're also off about light. Light is not "everywhere at once from its own perspective" as you seem to think. The fact that light cannot be everywhere at once is the same fact that dictates that light cannot have a point of view, that light experiences no time and has no perspective. (Mind you, if this is the comparison you would like to draw to God, I will happily assent.) Study up and be a bit more careful with your science, and you'll be able to throw much meatier punches theologically.
Probably you'll never read this now, but... Nope. Everywhere at once literally means a privileged reference frame. "Over there, now" is a concept with no logical meaning in our physical universe. Being in two places at once isn't physically impossible, it's just nothing.
And that imposes very serious constraints on God. If I am on the Earth and I pray for my husband on Mars, God on Mars can not hear my prayer until it is too late. You really think that's a statement most Americans agree with?
You're also off about light. Light is not "everywhere at once from its own perspective" as you seem to think. The fact that light cannot be everywhere at once is the same fact that dictates that light cannot have a point of view, that light experiences no time and has no perspective. (Mind you, if this is the comparison you would like to draw to God, I will happily assent.) Study up and be a bit more careful with your science, and you'll be able to throw much meatier punches theologically.
????? Why do you assume »God created the universe - God is outside it.« (Do people really think that?)
Because you can not create something and be inside it (i.e. be made of it) at the same time.
My point is more that believing God created the universe is not really an obvious thing to believe. Why not just believe that the nobody created the universe and it has been around forever? Or that the universe emerged out of »nothing«?
No? That can not possibly be true? How could something be around forever? And how could something so complex and beautiful as the universe with all the fancy stuff inside emerge out of »nothing«? No way.
But wait, it is no problem for God to be around forever? It is no problem to have an entity, powerful enough to create a whole universe, without explaining where it came from? Or should we just introduce a super-god that created God? Unfortunately this just shifts the problem to the next level and we are again back at square one.
Besides that you can obviously build a house and enter through the front door after you finished it.
No? That can not possibly be true? How could something be around forever? And how could something so complex and beautiful as the universe with all the fancy stuff inside emerge out of »nothing«? No way.
But wait, it is no problem for God to be around forever? It is no problem to have an entity, powerful enough to create a whole universe, without explaining where it came from? Or should we just introduce a super-god that created God? Unfortunately this just shifts the problem to the next level and we are again back at square one.
Besides that you can obviously build a house and enter through the front door after you finished it.
Wait. When did this morph into an argument of the existence of God? I thought we were talking about God being some sort of preferred relativistic reference frame.
> Besides that you can obviously build a house and enter through the front door after you finished it.
You did not enter the material house - you entered the empty space that was already there, which the material of the house surrounds. If you want to use the analogy you must actually change your physical body to be made of wood and nails.
> Besides that you can obviously build a house and enter through the front door after you finished it.
You did not enter the material house - you entered the empty space that was already there, which the material of the house surrounds. If you want to use the analogy you must actually change your physical body to be made of wood and nails.
> Wait. When did this morph into an argument of the existence of God?
You sort of brought it up yourself when you said "God created the universe." like it's a fact, didn't you? Maybe you could explain what that's supposed to mean here?
You sort of brought it up yourself when you said "God created the universe." like it's a fact, didn't you? Maybe you could explain what that's supposed to mean here?
Discussing God as a reference frame seems to naturally evoke the question if he exists. And I am definitely more comfortable discussing whether God exists or not than if he may be a (preferred) (inertial) reference frame; probably one of the strangest things I have ever thought about.
Yes, the analogy with building a house is not really strong but on the other hand the whole question if God - if he exists - exists inside or outside the universe (read spacetime) is difficult to say the least. What is outside of space? What is outside of time? Out of what is God made? And how does this affect his possibility to interact with the universe? Is he even able to interact?
Now that I got your point with being something and building the same thing, self-organizing systems come to mind - that's probably as close as you can get to being something and building the same thing. This does not address where the matter for the system come from so it is more self-shaping than self-building but ad hoc that's the best I can think of.
Yes, the analogy with building a house is not really strong but on the other hand the whole question if God - if he exists - exists inside or outside the universe (read spacetime) is difficult to say the least. What is outside of space? What is outside of time? Out of what is God made? And how does this affect his possibility to interact with the universe? Is he even able to interact?
Now that I got your point with being something and building the same thing, self-organizing systems come to mind - that's probably as close as you can get to being something and building the same thing. This does not address where the matter for the system come from so it is more self-shaping than self-building but ad hoc that's the best I can think of.
Of course God can do so, he's God. He can do anything!1!
Most people do not think it through that way. They probably don't think God is a physical being, and they probably don't have a very specific idea about his location, but they definitely think he is viewing the universe, wherever he is.
Most people do not think it through that way.
I suspect that not thinking it through that way is a precondition for truly believing in God for most people. That is to say, most people who start out believing in God and who attempt to think this through would give up their belief in God on the way - or, instinctively realizing that and being made uncomfortable by the thought, they would automatically shy away from the whole logic of it.
After all, explaining the world is not really what belief in God seems to be about. It seems to be more about some kind of warm fuzzy feeling that people get from it.
I suspect that not thinking it through that way is a precondition for truly believing in God for most people. That is to say, most people who start out believing in God and who attempt to think this through would give up their belief in God on the way - or, instinctively realizing that and being made uncomfortable by the thought, they would automatically shy away from the whole logic of it.
After all, explaining the world is not really what belief in God seems to be about. It seems to be more about some kind of warm fuzzy feeling that people get from it.
> That question, "Can you find out? Hell no," is relativity in a nutshell. If you really grasp what that means, the whole deal from simultaneity to time dilation to curved spacetime all falls out more or less intuitively. (Of course it was harder to work out the first time :P)
You cannot deduce relativity from the knowledge that you can't find out whether you're moving. In Newtonian physics you can't find out whether you're moving either. The essential ingredient is that the speed of light is the same in all reference frames. Furthermore curved spacetime is by no means trivial; that's general relativity. It took Einstein himself 10 additional years before he got from special to general relativity, and more still to really develop it.
You cannot deduce relativity from the knowledge that you can't find out whether you're moving. In Newtonian physics you can't find out whether you're moving either. The essential ingredient is that the speed of light is the same in all reference frames. Furthermore curved spacetime is by no means trivial; that's general relativity. It took Einstein himself 10 additional years before he got from special to general relativity, and more still to really develop it.
I sort of meant "given experimental observations it all seems quite intuitive", not "you can derive it all a priori". No offense intended to the hard work of Einstein and others :)
What I was trying to express by "inky void, not even a star" was that the void didn't even include anything resembling an aether. "You are the only body in that void" is meant to include non-material bodies. All this passage is trying to establish is that in order to distinguish constant motion from absolute stillness, there has to be something else to measure against. Whether or not our universe contains something that can serve as an absolute frame of reference is not the point -- yet.
So yes, it really is meant to be talking about a self-evident fact (once you think about it).
But you're right; I'm not a physics teacher. I'm willing to concede that I underestimated the potential stickiness of this point, and/or that I failed to overcome my handicap in expressing this point.
So yes, it really is meant to be talking about a self-evident fact (once you think about it).
But you're right; I'm not a physics teacher. I'm willing to concede that I underestimated the potential stickiness of this point, and/or that I failed to overcome my handicap in expressing this point.
It's only obvious because that's what you were taught. Aristotle thought that a moving body would come to a halt by itself, unless you keep pushing it. He thought that this was a law of physics. This didn't require any aether or other substance. It was almost 2000 years later that Galilei came with the idea bodies set in motion will remain in motion, and that the fact that they usually stop was solely the result of friction. But even then it is not clear that there isn't some other method by which you can find out your absolute velocity. It was only in 1887 that the Michelson-Morley experiment showed that you can't do that with light! So this is not a triviality that can be deduced by logical reasoning, it's an experimental result of physics.
This makes you wonder which falsehoods we currently take for granted, that later generations can't even fathom anymore.
This makes you wonder which falsehoods we currently take for granted, that later generations can't even fathom anymore.
I find myself disagreeing still. I would say that the idea that you can't measure your own motion without something else to measure against, is obvious to the casual person. (Whether that "something" is a physical object, the background radiation, the luminiferous aether, or whatever.) The possibility that it might not be true is actually far less intuitive, since it would require there to be some intrinstic frame of reference that is impossible to leave behind, even in a thought experiment.
I think using the word "obvious" is very misplaced here. Obvious would suggest that fully understanding the statement is something the casual person would arrive at given no help or extraneous thought into the statement. This is simply not true given what we know about the average intelligence of humans.
So you're saying that what laymen mean when they intuitively understand that you can't measure your own motion is something else than what is meant by a physicist in the context of relativity. In particular a physicist means that you can't do that even when you have access to light, or those other things. A layman understands that you can't measure whether you're moving without access to those things, but he does not understand that it's still impossible with access to those things. In that case you cannot appeal to layman intuition on the former to conclude the latter, which is exactly what's necessary for an understanding of relativity.
Also, even with this interpretation it's questionable. In Aristotle's mind you can determine whether you're moving or not, even if you are completely alone in the universe. You take an object that you have with you (e.g. your t-shirt), throw it in a random direction with a specified velocity relative to you. According to Aristotle both you and the watch will decelerate. But since the deceleration is relative to the absolute reference frame in which you will eventually come to a halt, you can deduce whether you're moving from the relative deceleration between you and your watch (although interestingly if the deceleration has a special form, then you cannot determine whether you are moving, but that is again a non trivial fact that is not obvious to a layman). To Aristotle, and the people after him until Galilei, the idea of a special reference frame was perfectly intuitively obvious! (though, of course, incorrect)
Also, even with this interpretation it's questionable. In Aristotle's mind you can determine whether you're moving or not, even if you are completely alone in the universe. You take an object that you have with you (e.g. your t-shirt), throw it in a random direction with a specified velocity relative to you. According to Aristotle both you and the watch will decelerate. But since the deceleration is relative to the absolute reference frame in which you will eventually come to a halt, you can deduce whether you're moving from the relative deceleration between you and your watch (although interestingly if the deceleration has a special form, then you cannot determine whether you are moving, but that is again a non trivial fact that is not obvious to a layman). To Aristotle, and the people after him until Galilei, the idea of a special reference frame was perfectly intuitively obvious! (though, of course, incorrect)
This whole thread of discussion seems irrelevant to me. The article is obviously not intended to provide a rigorous treatment of relativity. It is not meant to derive relativity from first principles. It is not even meant to be accessible to people who don't have prior knowledge of relativity. It is meant to be funny, and it succeeds at that.
You can measure acceleration without needing a special frame. More significantly, you can measure rotational motion without something to measure against.
See that Feynman quote I linked in my original post; he discusses exactly this point.
See that Feynman quote I linked in my original post; he discusses exactly this point.
Which is exactly why that passage confined itself to talking about constant motion.
But the argument you used would seem to apply to both of those thing. That's what makes it flawed -- you claim it is obvious, when in fact this line of argument is very subtle and often misleads laymen. (Notice that in this very thread there seem to be people who think you couldn't detect acceleration.)
This still happens in cartoon/TV/movie physics: the engines of a space ship cut out, and the space ship coasts to a halt (even when the space drive is obviously Newtonian, and not magic).
This got me thinking. If you are floating along in a void, and float past a virtual particle - you can legitimately say you are moving (of course you could instead say the virtual particle is moving).
Assume now the virtual particle winks out of existence. Have you suddenly stopped moving? Were you wrong/incorrect somehow to have chosen the particle as the rest frame? Has conservation of (your) momentum just been violated?
Assume now the virtual particle winks out of existence. Have you suddenly stopped moving? Were you wrong/incorrect somehow to have chosen the particle as the rest frame? Has conservation of (your) momentum just been violated?
Not only is the point not-self-evident, the analogy is fundamentally flawed. You may not have an absolute speed but you can accelerate. If you really want a reference frame to compare to, you can use the one you started in before leaving.
Edit: sorry, changed wording while being replied to
Edit: sorry, changed wording while being replied to
> If you really want a reference frame to compare to, you can use the one you started in before leaving.
Nah, the analogy is fine there -- you "wake up" in a new reference frame, and weren't able to make any measurements to compare it to your old one. Whether you can measure your motion against the old reference frame starting from this situation is actually the question!
Nah, the analogy is fine there -- you "wake up" in a new reference frame, and weren't able to make any measurements to compare it to your old one. Whether you can measure your motion against the old reference frame starting from this situation is actually the question!
Oh, that's not what I meant. I meant use the reference frame from when you first woke up. But I'll make a more detailed scenario:
* Wake up in the void. Label your current reference frame R0.
* Notice that there is no real way to label 'speed' vs. void.
* We can however measure angular speed via tension on body parts, it seems to be 0.
* Accelerate somehow
* * for some magical reason it's forbidden to have more than one object, so I thought up a couple minimally-magic ways to do it that I am pretty sure don't cause physics problems by themselves.
* * * You could throw something then immediately pretend the thing you threw doesn't exist, forbidding it as a reference frame.
* * * You could make a punching motion and use magic to cause your arm to disappear.
* * * You could swing all your limbs away from your body and use magic to reverse the direction of one of them.
* Now you are in reference frame R1 because you accelerated.
* Hooray you accelerated without any other objects to compare to. If you insist on comparing to a reference frame, use R0.
* Wake up in the void. Label your current reference frame R0.
* Notice that there is no real way to label 'speed' vs. void.
* We can however measure angular speed via tension on body parts, it seems to be 0.
* Accelerate somehow
* * for some magical reason it's forbidden to have more than one object, so I thought up a couple minimally-magic ways to do it that I am pretty sure don't cause physics problems by themselves.
* * * You could throw something then immediately pretend the thing you threw doesn't exist, forbidding it as a reference frame.
* * * You could make a punching motion and use magic to cause your arm to disappear.
* * * You could swing all your limbs away from your body and use magic to reverse the direction of one of them.
* Now you are in reference frame R1 because you accelerated.
* Hooray you accelerated without any other objects to compare to. If you insist on comparing to a reference frame, use R0.
>* * * You could swing all your limbs away from your body and use magic to reverse the direction of one of them.
No you can't, this leads to the twin paradox. Assume you could use magic to simply reverse the direction of an object. Take two clocks, and have one travel away from you at relativistic speeds, then turn around and come back. Because of time dilation, when the clock returns, it will have observed less time pass then you, because it was moving at relativistic speeds. However, from the clocks perspective, you were moving at relativistic speeds, so you will have observed less time pass. The resolution to this paradox involves the fact that the clock was accelerated in order to turn around.
An interesting side point is that in the hypothetical void, you actually have no way of knowing weather or not you are accelerating. For example, the space station is currently in free fall towards the earth, but from within the station you cannot detect this fact. Similarly, if you are in a plane that is descending at the rate of gravity, you will appear to be in zero-g. The mathematics behinds this is considerably more difficult than special relativity.
No you can't, this leads to the twin paradox. Assume you could use magic to simply reverse the direction of an object. Take two clocks, and have one travel away from you at relativistic speeds, then turn around and come back. Because of time dilation, when the clock returns, it will have observed less time pass then you, because it was moving at relativistic speeds. However, from the clocks perspective, you were moving at relativistic speeds, so you will have observed less time pass. The resolution to this paradox involves the fact that the clock was accelerated in order to turn around.
An interesting side point is that in the hypothetical void, you actually have no way of knowing weather or not you are accelerating. For example, the space station is currently in free fall towards the earth, but from within the station you cannot detect this fact. Similarly, if you are in a plane that is descending at the rate of gravity, you will appear to be in zero-g. The mathematics behinds this is considerably more difficult than special relativity.
You're talking about accelerating. The original passage was just talking about simple constant motion. The point being that you can't distinguish constant motion from remaining perfectly still without something else to measure against. That's really all I was trying to say. Obviously I failed!
For what it's worth I think you did a good job overall, but flaws are pretty much inevitable when your word choice is so restricted.
The point the original author is implicitly trying to make is that you can't compare to your original frame, where you went to sleep.
This is the part I'm objecting to:
To move, you have to move to or away from ... well, from what? You'd have to say that you don't even get to use a word like "move" when you are the only body in that void.
You can move. You can have a delta v. You don't have an absolute position or velocity, but you don't need those to move.
I don't see any comparison to the pre-sleep state, this is a statement about the void, and it overreaches.
To move, you have to move to or away from ... well, from what? You'd have to say that you don't even get to use a word like "move" when you are the only body in that void.
You can move. You can have a delta v. You don't have an absolute position or velocity, but you don't need those to move.
I don't see any comparison to the pre-sleep state, this is a statement about the void, and it overreaches.
This is a metaphor breakdown because you pushed it too hard, rather than a real problem with the idea. In the ideal case you are a floating point, and you haven't got discrete parts of yourself to fling away, but of course that's an abstract step too far away for the target audience of this piece.
Reflections on Relativity [1] in fact does build up to a generalize concept of relativity (not just Einsteinian relativity) starting with points in an unknown space (building up to a concept of distance, rather than assuming such a thing), but it's a mathematical treatment of the problem rather than an intuitive one. And certainly not in words of one syllable.
[1]: http://mathpages.com/rr/rrtoc.htm , the part I'm referencing starts right off at 1.1.
Reflections on Relativity [1] in fact does build up to a generalize concept of relativity (not just Einsteinian relativity) starting with points in an unknown space (building up to a concept of distance, rather than assuming such a thing), but it's a mathematical treatment of the problem rather than an intuitive one. And certainly not in words of one syllable.
[1]: http://mathpages.com/rr/rrtoc.htm , the part I'm referencing starts right off at 1.1.
I think I haven't made it clear enough what my objection is. In my opinion it is the article that pushed the analogy too far. It works great to show that you can't tell what is moving. But when the analogy tries to claim that you can't move, well, it's pretty much begging the question. Of course a floating point can't move, and it says nothing about physics. That's why I assumed some mechanism for trying to cause motion: you can't see if you failed if you didn't try.
I guess I wasn't clear (no sarcasm). My point is based on the idea objecting that an analogy doesn't stand up to being pushed "too far" isn't a useful one; analogies always break down when pushed too far. If they didn't, they wouldn't be analogies, they'd be explanations. Analogies are dangerous ways of thinking, but again, this is generally targeted at people for who that is all they have available.
The analogy is useful, I agree there. The problem is that the article first uses the analogy for something it fits, then uses the analogy again for something it doesn't fit. The conclusions drawn from the second use are invalid. I don't object to the analogy, I object to that second use.
I had the same objection as the op actually - if you wake up at "rest" with just yourself and a bed, and accelerated away from the bed, you can in fact know whether "you are moving" or "the bed is moving". It is because one of the two have only been in 1 reference frame, while the other has been in 2.
Basically the same issue as the twin "paradox". I can appreciate the assumption of a constant velocity on wake though, as a way to simplify the story.
Basically the same issue as the twin "paradox". I can appreciate the assumption of a constant velocity on wake though, as a way to simplify the story.
I don't think you can accelerate in an empty universe - no speed, no speed difference.
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Without a reference frame, what experiment can you perform that would tell you that you're accelerating?
I guess the GP understood special relativity, but not general ;)
Well, to be really pedant, if you were spinning around yourself, you'd feel an acceleration.
Well, to be really pedant, if you were spinning around yourself, you'd feel an acceleration.
There will be 'gravity' -a force- in the opposite direction you are accelerating in. You should know the feeling, it happens when you accelerate in a car, or when a plane lifts off.
If it's really you floating around, you will be able to feel it. (I reckon you could even guess at the amount by comparing it to the acceleration of 9.81 m/s^2 that you're used to.)
>There will be 'gravity' -a force- in the opposite direction you are accelerating in.
Wouldn't there be a force in the direction you are accelerating in?
Anyway, when you accelerate a car, you are not feeling acceleration, you are feeling the force of the car on you. Imagine being inside of a box that is in free fall. What experiment could you run to determine if you were accelerating?
Wouldn't there be a force in the direction you are accelerating in?
Anyway, when you accelerate a car, you are not feeling acceleration, you are feeling the force of the car on you. Imagine being inside of a box that is in free fall. What experiment could you run to determine if you were accelerating?
>Wouldn't there be a force in the direction you are accelerating in?
Well, yes, that would be the standard way to look at it. Sorry for being confusing.
>Anyway, when you accelerate a car, you are not feeling acceleration, you are feeling the force of the car on you.
According to [Force = Mass * Acceleration] you can take them as equal (apart from the constant factor of your mass). In the freefalling box that is accelerating (and thus no longer in free fall) you'd also feel a force. No need for experiments if you have your normal senses. You'll be pressed against one side of the box. (And if the acceleration is 9.81 m/s^2 you couldn't distinguish it from a box on earth.)
That is actually the basic premise of general relativity - the equality of 'inertial mass' that resists against acceleration and 'gravitational mass' that happens because of, well, gravity. It's like the idea of constant speed of light for special relativity.
edit: Unless you're talking about gravity, which accelerates all parts of the setup equally, thus no force results.. but that would need something else in the experiment, either a great amount of matter or energy. But then you'd have a reference frame right there. (Mathematically. As for an experiment.. hm. Check for perturbances from space-time distortions that result from rotating gravity sources, maybe.. most gravity sources in this universe are rotating. There's an experiment done that checked that for Earth.[1])
[1] https://en.wikipedia.org/wiki/Gravity_Probe_B
Well, yes, that would be the standard way to look at it. Sorry for being confusing.
>Anyway, when you accelerate a car, you are not feeling acceleration, you are feeling the force of the car on you.
According to [Force = Mass * Acceleration] you can take them as equal (apart from the constant factor of your mass). In the freefalling box that is accelerating (and thus no longer in free fall) you'd also feel a force. No need for experiments if you have your normal senses. You'll be pressed against one side of the box. (And if the acceleration is 9.81 m/s^2 you couldn't distinguish it from a box on earth.)
That is actually the basic premise of general relativity - the equality of 'inertial mass' that resists against acceleration and 'gravitational mass' that happens because of, well, gravity. It's like the idea of constant speed of light for special relativity.
edit: Unless you're talking about gravity, which accelerates all parts of the setup equally, thus no force results.. but that would need something else in the experiment, either a great amount of matter or energy. But then you'd have a reference frame right there. (Mathematically. As for an experiment.. hm. Check for perturbances from space-time distortions that result from rotating gravity sources, maybe.. most gravity sources in this universe are rotating. There's an experiment done that checked that for Earth.[1])
[1] https://en.wikipedia.org/wiki/Gravity_Probe_B
drop something? If it accelerates away from you, you are accelerating (or held stationary in a gravity field, but AFIAK, those are the same things).
That wouldn't work.
If you dropped something it would simply stay right next to you, even if you were accelerating - both of you are accelerating at exactly the same rate.
If you dropped something it would simply stay right next to you, even if you were accelerating - both of you are accelerating at exactly the same rate.
Why? What's making it accelerate? I wasn't trying to talk about some kind of universal/aether acceleration. I meant you and only you should accelerate.
And how do you accelerate - do you have a rocket attached to your feet?
It doesn't really matter. But there should be some mechanism. A rocket attached to your feet works quite well if you ignore the exhaust for purposes of reference.
If you want a useful thought experiment about physics then you need to give reasonable physics tools. Otherwise you get something like "Pretend you are an inanimate green blob. You can't climb a hill, can you? Therefore climbing a hill is an illusion."
If you want a useful thought experiment about physics then you need to give reasonable physics tools. Otherwise you get something like "Pretend you are an inanimate green blob. You can't climb a hill, can you? Therefore climbing a hill is an illusion."
If you have a rocket on your feet why do you need to drop something to figure out if you are accelerating? You can feel the pressure on your feet.
The only type of acceleration that is undetectable is gravity - and gravity will effect the dropped object exactly as much as you.
The only type of acceleration that is undetectable is gravity - and gravity will effect the dropped object exactly as much as you.
Great! You just simplified the experiment!
Dropping something was only one idea, but feeling pressure is much simpler.
Dropping something was only one idea, but feeling pressure is much simpler.
Yes, but when you drop something, you're creating a reference frame, aren't you?
Ah, you're misunderstanding the term reference frame as it's being used here. A reference frame is like a coordinate system for velocity; it's not something physical.
No. When you drop something nothing whatsoever happens.
And as shardling said, a reference frame isn't a physical thing that is created and destroyed - it's simply the zero point for your system of measurement - but the measurement would work just fine if you started with any number, zero is just convenient.
And as shardling said, a reference frame isn't a physical thing that is created and destroyed - it's simply the zero point for your system of measurement - but the measurement would work just fine if you started with any number, zero is just convenient.
I understand a frame of reference doesn't have to be physical. However, if you're in an apparently empty and dark universe, and you're interested in knowing whether you're accelerating or not, postulating a frame of reference is not going to be of much help.
I may have missed the point of dropping an object, though. I thought the idea was to create a physical point we could anchor the coordinate system to, and in that way be able to measure acceleration.
I may have missed the point of dropping an object, though. I thought the idea was to create a physical point we could anchor the coordinate system to, and in that way be able to measure acceleration.
Dropping an object that won't get accelerated is one way to measure acceleration, but not the only way. If you are the actor causing the acceleration on yourself, as I originally intended, then presumably you already know / measure-by-doing how much you have accelerated, and you can use dead reckoning to watch the earlier reference frame fly by.
If the force is external and doesn't apply pressure then you have to drop an object.
If the force affects the entire universe the same way then that's aether and can't be measured / doesn't exist. But that was not the kind of force I was using to disprove "you can't move".
If the force is external and doesn't apply pressure then you have to drop an object.
If the force affects the entire universe the same way then that's aether and can't be measured / doesn't exist. But that was not the kind of force I was using to disprove "you can't move".
> If the force is external and doesn't apply pressure then you have to drop an object.
What kind of force is external and doesn't apply pressure, and also doesn't affect the dropped object? There is no such force, and therefor no such test.
What kind of force is external and doesn't apply pressure, and also doesn't affect the dropped object? There is no such force, and therefor no such test.
> However, if you're in an apparently empty and dark universe, and you're interested in knowing whether you're accelerating or not
You can't. There is absolutely no test that can tell you this.
You can't "drop" anything - whatever force is accelerating you also accelerates the object, so letting go of it tells you nothing.
You can't. There is absolutely no test that can tell you this.
You can't "drop" anything - whatever force is accelerating you also accelerates the object, so letting go of it tells you nothing.
I use the void concept to explain my absurdity. I usually fall back on explaining the thought process that follows awakening in a void. The loss of identity, speech, motion, etc. Now, I wish I had taken a physics class.
What if there were two bodies instead of one and they were 1 light year apart. What would motion be like then?
I don't understand. What would the alternative be? If the answer to "can you find out" is "yes", then how?
The alternative is that there's some fundamental reference frame. The obvious example is the theory of the aether I alluded to: light would propagate in different speeds in different reference frames.
More generally, you can't know that the laws of physics are the same in all reference frames until you actually do the experiments. If you think otherwise, you underestimate nature's ability to confound human intuition! A good example is is parity, which you'd think would be a good symmetry of nature, but is actually violated by some interactions: http://en.wikipedia.org/wiki/Parity_violation#Parity_violati...
More generally, you can't know that the laws of physics are the same in all reference frames until you actually do the experiments. If you think otherwise, you underestimate nature's ability to confound human intuition! A good example is is parity, which you'd think would be a good symmetry of nature, but is actually violated by some interactions: http://en.wikipedia.org/wiki/Parity_violation#Parity_violati...
Interesting read and I like the concept, but I think the 4-letter rule added an arbitrary constraint that didn't necessarily make it easier to read or understand.
If the idea was "explain relativity simply" then it could have been done better -- word complexity (ie "reading level") is a better measure than outright word length.
If the idea was simply to see if it could be done with 4-letter words, well, mission accomplished :)
If the idea was "explain relativity simply" then it could have been done better -- word complexity (ie "reading level") is a better measure than outright word length.
If the idea was simply to see if it could be done with 4-letter words, well, mission accomplished :)
It was in fact the latter.
(I was inspired in part by Douglas Hofstadter, who did something similar on a smaller scale in "Le Ton Beau de Marot".)
(I was inspired in part by Douglas Hofstadter, who did something similar on a smaller scale in "Le Ton Beau de Marot".)
Sounds very similar to Guy Steel's "Growing a Language" talk. His constraint was to not use any word greater than one syllable unless it is defined by either one-syllable words, or other words that had been previously defined.
That really is a great talk! It's on Youtube too: http://www.youtube.com/watch?v=_ahvzDzKdB0
Wow. I was sure this was inspired by George Boolos' great "Godel's Second Incompleteness Theorem Explained in Words of One Syllable".
http://www2.kenyon.edu/Depts/Math/Milnikel/boolos-godel.pdf
I wonder if Hofstadter was inspired by Boolos?
http://www2.kenyon.edu/Depts/Math/Milnikel/boolos-godel.pdf
I wonder if Hofstadter was inspired by Boolos?
Actually, Hofstadter states that he was inspired by a magazine contest.
I think it would be easier to read without all these colloquial bits "like, you know, heck, get over it". Anyway it's impressive effort.
The Up-Goer Five Text Editor is a pretty great resource with similar constraints: "Can you describe a topic using only the thousand most common English words?"
The results in their Hall of Fame are fascinating. It's inspired by the xkcd linked elsewhere in this thread.
http://splasho.com/upgoer5/halloffame.php
The results in their Hall of Fame are fascinating. It's inspired by the xkcd linked elsewhere in this thread.
http://splasho.com/upgoer5/halloffame.php
I found that four letters added some ambiguity and some uneeded complexity. Maybe 5 or even 6 letters?
Still, this is a great intro to relativity and it was a fun read. Also a cool literary feat.
Still, this is a great intro to relativity and it was a fun read. Also a cool literary feat.
I find the fuzzing of proper names gets annoying, and it would be better if the rule were relaxed for proper names.
Personally, I found the abbreviated names made the piece even more hilariously irreverent than it already was. "Izzy" for Isaac Newton? Makes him sound like an 1980's heavy metal star or something.
Also, a quick google serach indicates that "Ike" is a more common nickname than "Izzy". (And that if Newton had any nicknames in his time, none seem to have survived.)
About the cool literary feat: I'm wondering if there are languages other than English in which it'd be possible to write something like this. I speak Spanish and French and I'm sure it's impossible in both -- they just don't have enough short words.
Probably Chinese and Japanese since Chinese characters have such high information density, but non-Western languages might defeat the purpose of the experiment.
This is phenomenal, does anyone have sources of more physics concepts explained simply?
Scott Aaronson's Quantum Physics is one: http://www.scottaaronson.com/democritus/lec9.html
Scott Aaronson's Quantum Physics is one: http://www.scottaaronson.com/democritus/lec9.html
Obligatory xkcd: http://xkcd.com/1133/
I want to point out that xkcd's criteria for usable words is a lot better than "four letters or less". There are some really obscure, yet very dense words out there.
I know I'm dumb, but can someone explain this part?
"Dana sees each rock at the same time, but Bert sees one rock and then sees the next rock."
How would anyone's movement, or lack of it, affect their perception of whether the rocks landed at the same time or not?
"Dana sees each rock at the same time, but Bert sees one rock and then sees the next rock."
How would anyone's movement, or lack of it, affect their perception of whether the rocks landed at the same time or not?
The rays that come from each rock move only so fast. They take time to get from the rock to Dana or Bert. And it is only by when those rays get to Dana or Bert that they can say if they were at the same time, or one and then the next.
Now. Bert is on the bus. It goes, let us say, from west to east on the road. Bert is half way from the west rock to the east rock when each rock hits land -- but he is on the move, and when the rays from the east rock hit his eyes he has gone some way east. The rays from the west rock have not yet got to him. Then, just a tad more time, and the rays from the west rock get to Bert's eyes.
But Dana does not move. She sits by the road. The rays from the west rock and the east rock hit her at the same time: each rock is, say, a yard from her, one west and one east.
So Dana sits and does not move; she sees the rays from each rock at the same time. Bert is on the bus, and goes from west to east; he sees the rays from the east rock and then the rays from the west rock.
And all that is fine. They both know that Dana does not move and Bert does. So they will say that each rock hit at the same time, for Dana (who did not move) saw them hit at the same time.
But (and this is the bit that may fry your mind) we can just as well say that Bert does not move and Dana does move! And then we will have to say that the east rock hit and then the west rock! How can that be?
We must say, even if you find it odd, that "did the east rock hit, then the west? or the west, then the east? or both at once?" just goes one way for Dana and not that way for Bert. Just like "is this rock to the east or to the west?" may not go the same way for both, if they are not at the same site.
(You are not dumb. This is hard. It took Al to work it out!)
Now. Bert is on the bus. It goes, let us say, from west to east on the road. Bert is half way from the west rock to the east rock when each rock hits land -- but he is on the move, and when the rays from the east rock hit his eyes he has gone some way east. The rays from the west rock have not yet got to him. Then, just a tad more time, and the rays from the west rock get to Bert's eyes.
But Dana does not move. She sits by the road. The rays from the west rock and the east rock hit her at the same time: each rock is, say, a yard from her, one west and one east.
So Dana sits and does not move; she sees the rays from each rock at the same time. Bert is on the bus, and goes from west to east; he sees the rays from the east rock and then the rays from the west rock.
And all that is fine. They both know that Dana does not move and Bert does. So they will say that each rock hit at the same time, for Dana (who did not move) saw them hit at the same time.
But (and this is the bit that may fry your mind) we can just as well say that Bert does not move and Dana does move! And then we will have to say that the east rock hit and then the west rock! How can that be?
We must say, even if you find it odd, that "did the east rock hit, then the west? or the west, then the east? or both at once?" just goes one way for Dana and not that way for Bert. Just like "is this rock to the east or to the west?" may not go the same way for both, if they are not at the same site.
(You are not dumb. This is hard. It took Al to work it out!)
[deleted]
Yes, you have the idea. You put down just a word or two, no more. But then you add to it, and then some more, and then the next you know, you have a page full of such text. It can be hard to stop once you get into it!
[deleted]
You're not dumb. It's a subtle point, otherwise special relativity wouldn't have been necessary to invent. (You may find it worthwhile to read a more normal article on special relativity -- it's much easier to understand than general relativity.)
The two rocks land just as Bert and Dana are closest to each other. The two rocks are equally distant from that point. But as the light propagates towards them, Bert continues to move towards the light from the impact ahead of him, and away from the impact behind him. Thus he will see the light from the former impact before the latter.
(The traditional thought experiment is described in terms of trains and lightning, instead of buses and moon rocks. If you do a web search for that plus "special relativity", you should find plenty of descriptions that are closer to the original.)
The two rocks land just as Bert and Dana are closest to each other. The two rocks are equally distant from that point. But as the light propagates towards them, Bert continues to move towards the light from the impact ahead of him, and away from the impact behind him. Thus he will see the light from the former impact before the latter.
(The traditional thought experiment is described in terms of trains and lightning, instead of buses and moon rocks. If you do a web search for that plus "special relativity", you should find plenty of descriptions that are closer to the original.)
Thanks to the both of you for taking the time to answer! Makes a lot more sense!
I feel relatively smarter now
I feel relatively smarter now
Now who can describe the theory of relativity in only four words?
Similar to this: http://www.wired.com/wired/archive/14.11/sixwords.html
Similar to this: http://www.wired.com/wired/archive/14.11/sixwords.html
Everything's relative except c.
Best I could do.
Best I could do.
I made a word cloud of this
I removed "and", "you", "the", "that", "a", and "to" as those were just a bit TOO big.
http://i.imgur.com/77V6OvQ.png
I removed "and", "you", "the", "that", "a", and "to" as those were just a bit TOO big.
http://i.imgur.com/77V6OvQ.png
Any one of us can work out x by x plus y by y plus z by z less c by t by t where x and y and z and t are each part of how to get from one "here and now" to a 2nd "here and now". I can try to tell you what c is or we can just say that it is one (i.e. c by t by t is just t by t). And the math that we do will work out the same if I work it out from what I see or if you work it out from what you see, even if I do not move at the same rate as you.
Reminds me of the story behind "The Cat in the Hat."
"In May 1954, Life magazine published a report on illiteracy among school children, which concluded that children were not learning to read because their books were boring. Accordingly, William Ellsworth Spaulding, the director of the education division at Houghton Mifflin who later became its Chairman, compiled a list of 348 words he felt were important for first-graders to recognize and asked Geisel to cut the list to 250 words and write a book using only those words. [33] Spaulding challenged Geisel to "bring back a book children can't put down." [34] Nine months later, Geisel, using 236 of the words given to him, completed The Cat in the Hat. It retained the drawing style, verse rhythms, and all the imaginative power of Geisel's earlier works, but because of its simplified vocabulary, it could be read by beginning readers."
From: http://en.m.wikipedia.org/wiki/Dr._Seuss
"In May 1954, Life magazine published a report on illiteracy among school children, which concluded that children were not learning to read because their books were boring. Accordingly, William Ellsworth Spaulding, the director of the education division at Houghton Mifflin who later became its Chairman, compiled a list of 348 words he felt were important for first-graders to recognize and asked Geisel to cut the list to 250 words and write a book using only those words. [33] Spaulding challenged Geisel to "bring back a book children can't put down." [34] Nine months later, Geisel, using 236 of the words given to him, completed The Cat in the Hat. It retained the drawing style, verse rhythms, and all the imaginative power of Geisel's earlier works, but because of its simplified vocabulary, it could be read by beginning readers."
From: http://en.m.wikipedia.org/wiki/Dr._Seuss
I've stumbled upon Brian's website before and have enjoyed many a writeup, including this one.
I recall particularly enjoying `A Monovocalic Sonnet on Dante's "Inferno"` (http://www.muppetlabs.com/~breadbox/txt/infirni.html) - the essence/joy being in the Notes section: http://www.muppetlabs.com/~breadbox/txt/infirni-notes.html - it's so random and intense - a true hacker spirit I say :)
I recall particularly enjoying `A Monovocalic Sonnet on Dante's "Inferno"` (http://www.muppetlabs.com/~breadbox/txt/infirni.html) - the essence/joy being in the Notes section: http://www.muppetlabs.com/~breadbox/txt/infirni-notes.html - it's so random and intense - a true hacker spirit I say :)
This reminds me of 'Gödel's Second Incompleteness Theorem Explained in Words of One Syllable'
https://news.ycombinator.com/item?id=4197284
https://news.ycombinator.com/item?id=4197284
There's an amusing though mean-spirited article of Paul Samuelson's purporting to debunk the use of the Kelly Criterion - [url]www-stat.wharton.upenn.edu/~steele/Courses/434F2005/Context/Kelly%20Resources/Samuelson1979.pdf[/url] (pdf). All the words are one syllable. I find the title rather poetic - "Why we should not make mean log of wealth big though years to act are long".
"Make things as simple as possible, but not any simpler" - Einstein. His own book from Dover is an excellent way to get started.
I wonder if something like this might be useful if added to Wikipedia's Simple English version of the Theory of Relativity page? That page seems a bit underdone right now.
https://simple.wikipedia.org/wiki/Theory_of_relativity
https://simple.wikipedia.org/wiki/Theory_of_relativity
There are many interesting pages on this site. The brainfk and Intercal resources are a fun read, also the tiny executables. The Tile World downloads are a bit out-of-date though.
Looking at the page full of short words, the whole text just looks very weird, strange and sometimes just distracting.
I never knew that I looked over the page so much as I was reading.
I'd prefer "The theory of relativity explained to four years old".. the "four letters or less", although funny, makes it harder to grasp IMHO.
I found the article hard to read because of the word length. It created a strange, artificial rhythm to the text that drove me to distraction.
As an explanation it's only mediocre, but it was a lovely poetic read. It felt on the verge of lyrical the entire time.
[deleted]
Am I being pedantic? That really should be four letters or fewer.
Yes to both.
Maybe he means "The theory of relativity in words of four letters or less [than the theory of relativity]" -- i.e., it is an _incomplete_ explanation -- which some of the people on this page seem to agree with.
Seriously, I thought this was extremely clever, and the short, clipped style reminds me of Hemingway or Mamet.
You don't always use "fewer" when talking about discrete units. For example, you say "less than 5 minutes ago". The same goes for measurements of length (less than 3 meters). I think "less" works here because letters is a measurement of length.
Why?
This article is exactly what I needed, I've been trying to understand the unification of Gravity, Inertia and Centrifugal force for years now, couldn't fathom it, now I can.
The best I can describe it is: "Matter is like water through a drain", I wrote a post with my consolation of how the three can be seen as one:
http://sentientmachine.blogspot.com/2013/05/matter-is-like-w...
The best I can describe it is: "Matter is like water through a drain", I wrote a post with my consolation of how the three can be seen as one:
http://sentientmachine.blogspot.com/2013/05/matter-is-like-w...
This is not as self-evident as the author believes.
1. Having taught a great many college level physics students, they have trouble grasping this.
2. More importantly, there's a reason people pursued the theory of the aether for so long -- you have to actually do the fucking experiments to show that there's no absolute reference frame you could be said to be moving in. Thinking that you can deduce physical facts about the universe a priori is the opposite of science.
e: Suddenly remembered a Feynman bit from Lectures where he talks about exactly the attitude of treating this is somehow obvious: http://www.sciencechatforum.com/viewtopic.php?f=10&t=207...