Cosmologist claims Universe may not be expanding(nature.com)

58 pointsby xd13 anni fa61 comments

Cosmologist claims Universe may not be expanding

http://www.nature.com/news/cosmologist-claims-universe-may-not-be-expanding-1.13379

11 comments

The article contradicts itself...

The idea may be plausible, but it comes with a big problem: it can't be tested. Mass is what’s known as a dimensional quantity, and can be measured only relative to something else. For instance, every mass on Earth is ultimately determined relative to a kilogram standard that sits in a vault on the outskirts of Paris, at the International Bureau of Weights and Measures. If the mass of everything — including the official kilogramme — has been growing proportionally over time, there could be no way to find out.

The way to measure the increase in weight is actually described in the article itself: observe a shift in absorption/emission spectra.

Of course, such a shift may be infinitesimally small and undetectable over short timespans. However, this is precisely the sort of theory (like all the neutrino theories, for example) for which you set up a very long-term experiment.

The experiment is simple: measure the absorption spectrum of hydrogen in space with an extreme level of accuracy and a bajillion measurements (that's the scientific term). Record that for posterity. In 10 years (the equivalent of observing something 10 light-years away), repeat the measurement. Keep doing this until you either observe a shift or have made a measurement that based on observations of the real world (i.e. galaxies drifting away).

The experiment might take 100, 1000 or even 10'000 years, but eventually we'd have an answer!

UPDATE: Heh. isomorphic points out that this is actually not feasible given that it's impossible to make these measurements accurately without relying on mass being constant... So much for this. retracts

aufreak313 anni fa

Haven't read the paper, but another problem that occurred to me - if the mass of all particles is increasing over time, over whose time is it increasing. The rate of progress of time depends on the frame of reference, right?

isomorphic13 anni fa

How do we measure frequency (or time) precisely if the emission spectra are changing?

swombat13 anni fa

We'd need to calibrate against some kind of effect that is more heavily influenced by forces other than mass. You're right actually, that might be a lot more tricky than it seems on the surface. If we're left with the Weak and Strong forces to play with, that makes experimental design pretty difficult (and perhaps impossible).

Hmm...

ggchappell13 anni fa

If the two really are indistinguishable experimentally, then might we say that the expansion of space and the changes in mass are just two different ways of describing the same phenomena?

marcosdumay13 anni fa

It's very clear that there is a difference. What is not clear is if we can observe that difference in a human timeframe (thousands of years or less).

lcedp13 anni fa

> If the mass of everything — including the official kilogramme — has been growing proportionally over time, there could be no way to find out.

?! Actually the gravity would increase. Quadraticly, cause you mass would increase and Earth's as well.

aneth413 anni fa

I became extremely fascinated by null cosmology, which explains red shift as the result of light losing energy to [background] radiation as it travels. That [background] radiation becomes essential in the cosmological cycle involving the endless birth and death of galaxies via black holes.

While the theory seems to be collecting dust, I've not found anything to fully discredit it.

http://www.nullphysics.com/pages_cosmology.php

Update: I'm writing from my iPhone and haven't looked into this in a while. When I said radiation I was referring to low energy cosmic microwave background, which is easily scattered. Read the FAQ if you have questions. I do not claim to fully represent the theory in the above paragraph.

lisper13 anni fa

> light losing energy to radiation as it travels

> I've not found anything to fully discredit it

Well, for starters, there's the minor problem of light never having actually been observed to lose energy as it travels. If light loses energy to radiation as it travels, then this radiation should be detectable. Where is it?

Then there's the slightly less minor problem of having to rewrite all the known laws of physics from scratch, starting with electromagnetism and quantum mechanics. (I presume that you're not going to toss out conservation of energy because the whole point of the exercise it to account for the cosmological red shift, yes?)

But other than that, I can't think of anything that would discredit it either.

aneth413 anni fa

At the very least you should probably look at the theory before claiming to discredit it. The "radiation" is lower energy microwaves which are quickly scattered.

As for your other questions, these are addressed in the theory. How about reading that first.

lisper13 anni fa

> At the very least you should probably look at the theory before claiming to discredit it.

I didn't claim to discredit it. All I did was point out that there's no evidence for the theory, and that it would require rewriting most of the known laws of physics. Other than that I specifically said I saw no problem with it.

> The "radiation" is lower energy microwaves which are quickly scattered.

Scattered by what? The behavior of light is well understood. It doesn't just scatter randomly, whether or not it's "lower energy microwaves" (whatever that could possibly mean). And why would the fact that the microwaves are scattered matter? Microwaves would still be detectable even if they are "scattered". Look at the sky: that blue color you see is visible light scattered by the atoms in earth's atmosphere. Why would scattered microwaves be any less detectable than scattered visible light?

(Feel free to treat those as rhetorical questions, by the way.)

> As for your other questions, these are addressed in the theory. How about reading that first.

Life is too short to spend time doing a detailed debunking of every crackpot idea that comes along.

[deleted]13 anni fa

danbruc13 anni fa

[...] light losing energy to radiation [...]

Light is radiation. So we are are talking about radiating radiation...

Florin_Andrei13 anni fa

> red shift as the result of light losing energy to radiation as it travels

Yet another incarnation of the old so-called "tired light" idea. Just google it. Or start here:

http://en.wikipedia.org/wiki/Tired_light

You run very quickly into all sorts of problems once you assume light gets "tired" as it travels.

> While the theory seems to be collecting dust, I've not found anything to fully discredit it.

Start here:

http://hep.ucsb.edu/people/bmonreal/Null_Physics_Review.html

> I've not found anything

Odd, since a simple google search for "null physics" returns several strong rebuttals on literally the first page. Maybe you haven't actually looked?

EDIT: Oh boy, this "null physics" thing shows all the signs of crackpot "science". The author working on it "for decades". Studies physics, but becomes "disenchanted" and switches to engineering. Is a "visiting scientist" at a "university" nobody has heard about. His theory is not published in journals because journals "help the establishment". Compares himself with Ben Franklin, Bill Gates, and Faraday. The only thing he's published is this book; no articles, no nothing. On and on and on. There are literally hundreds of woo peddlers out there like this guy, and all of them are made in the exact same image.

http://www.ourundiscovereduniverse.com/pages_author.php

That page lit up the pseudo-science detector, firing up another alarm at each and every sentence. The only thing amazing about this guy is how well he fits the stereotype. It's surreal.

Brilliant quote from a link I posted above:

Much crackpot literature gives the impression of an old grudge being played out: "I learned quantum mechanics from some book that made me feel dumb; thinking up Quantum Aethro-Gyromechanics on my own made me feel smart." The sad thing is, this illustrates a sort of can-do spirit that's admirable in fields other than science. Stubbornly defying a swimming coach ("You'll never be an Olympian, kid") or editor ("Your manuscript 'Harry Potter and the Philosopher's Stone' does not meet our needs at this time") or venture capitalist ("Forget it, Mr. Fred Smith, there is no market for nationwide express delivery"), turns out to actually work sometimes; the people who pull this off are praised as heros. But science isn't like that. Whereas coaches, editors, and entrepreneurs have to rely on (fallible, human) gut instinct for many of their evaluations, science relies on explicit, rigorous go/no-go tests. I think that the dissonance between the value of stick-to-it-iveness in entrepreneurship, versus the value of mathematical rigor in science, is the root cause of a lot of physics crackpottery.

lukifer13 anni fa

Honest question: how you do you prevent your pseudo-science detector from succumbing to confirmation bias? I'm willing to wager that if you gathered up every single so-called crackpot on the planet and looked at their ideas in 50 years, there's at least a single person that will have turned out to be right.

Love the quote, by the way.

aneth413 anni fa

I agree it seems like pseudoscience.

Actually I did look for information to discredit the theory about a year ago. There appears to be more out there now. At that time I did lose interest after reading about problems with tired light.

Regardless, it's an interesting theory from a philosophical perspective, even if it has major problems.

[deleted]13 anni fa

aneth413 anni fa

That UCSB review is extremely amusing as is the other one linked.

Thank you for those.

http://hep.ucsb.edu/people/bmonreal/Null_Physics_Review.html

http://homepages.ihug.co.nz/~fiski/ouu_review.html

kghose13 anni fa

I found this a rather good explanation (well written article). My favorite para is in the closer:

"Others say that Wetterich’s interpretation could help to keep cosmologists from becoming entrenched in one way of thinking."

I like this attitude. Science is about playing with hypotheses and trying out new ideas. The most important thing for me is for my viewpoint to be zipped around and turned on its head - just for fun. I think it makes the mind more nimble.

Also, could a physicsy person elaborate a bit more on why we can't test increasing mass? Is it in the same class as 'we can't actually measure the increasing distance in the cosmic expansion, because locally, nothing is expanding'?

Thanks

Le_SDT13 anni fa

I am not sure to understand your question, it has been said in the article that if everything's mass was increasing proportionally we could not test it since we have to compare two things to see an increase. But I am no physicist I don't know if there would be another way actually to test mass increase without comparing two objects.

hga13 anni fa

What about a test over time?

I'd guess the time scale required is a bit long....

Le_SDT13 anni fa

I know what you mean. But an object of 1Kg today would still be 1Kg in 1000 years since everything gained mass (that includes what you are using to calculate the mass)... but like I said in my first response I am in no way the best person to give an answer to this question (still I lost karma :P). It is just a subject I find interesting!

marcosdumay13 anni fa

> But an object of 1Kg today would still be 1Kg in 1000 years since everything gained mass

Yes, but a 1m rule will get longer if everything gained mass, won't it? (I mean, the meter will get shorter, and the atoms should get bigger, even after compensating for the change on meter. Is there something I'm missing?)

Zikes13 anni fa

Mass is relative, measured by a standard object of arbitrary mass to which we've given a value. What we consider a "kilogram" is determined by one specific object sitting in a vault somewhere, and if that object were to be halved or doubled without us realizing it, then the official value of the kilogram would be similarly halved or doubled.

Since we determine the mass of things by comparing them against that object, if everything in the universe changes mass in precisely the same way at precisely the same rate then we would have no way of knowing. All we can do is compare them with each other, and relative to each other the masses would remain the same.

roc13 anni fa

What about astronomical objects that are distorted by gravitational lensing? Even if the mass of everything is increasing, couldn't we still note any otherwise-anomalous universal change in the presentation of many such systems?

dllthomas13 anni fa

This seems to make assumptions about a relationship between mass and gravity that may or may not hold as "mass changes" in this way, but it's certainly something to look at.

onezeno13 anni fa

I didn't understand this part of the article. We can measure the mass difference because, according to the theory, that is what we are measuring when we see a redshift. Should we not be able to measure the redshift in a laboratory, given equipment of high sensitivity and a large enough time delta for the change to register?

Edit: Looks like Le_SDT beat me to it :)

Zikes13 anni fa

I would imagine so, that part confused me as well. It's possible that the level sensitivity required is just too extreme, and would be subject to too much local interference.

There's one such test [1] that I find interesting that suffers from similar problems. It tries to detect gravitational waves traveling through the universe by pointing a laser at a mirror at the end of a 4km tunnel and measuring any changes in the total distance.

[1] http://en.wikipedia.org/wiki/LIGO

ollysb13 anni fa

Could you give an example of something that can be measured absolutely?

chimeracoder13 anni fa

I'm not sure if this is the answer you're looking for, but degrees/radians are considered dimensionless in that they're defined by the ratio of two lengths.

There's no way for the value of 1 radian to magically 'double' without causing π radians to magically amount to a full circle, which would seriously warp Euclidean geometry as we know it.

contingencies13 anni fa

If time is relative, and mass is relative, and space is relative ... then what's the point of science?

glogla13 anni fa

This remind me of the "gravity is entropy because everything is holographic" hypothesis made by physicist whose name I can't remember, when he had his passport stolen and had to wait in Paris for a week before they make him a new one :)

Steuard13 anni fa

The research here is based on the interesting premise that "the masses of electrons and protons were smaller" in the early universe, leading to different emission spectra that we have thus far interpreted as an expanding universe. I have not read the original research article in detail, but it is my impression that all masses would have to scale at the same rate in order to avoid changes in fundamental physical behaviors. (This seems consistent with the article's premise that the effect comes from some sort of field redefinition in the Lagrangian.)

As a particle physicist, I see this as highly unlikely. The first big obstacle that I see for such a theory to overcome is that electrons and protons get their mass from entirely different sources. As far as we know, electrons are fundamental particles: their mass is a fundamental parameter of the theory (presumably encoded as the electron coupling to the Higgs boson). But although protons are composed of three fundamental particles (two up quarks and a down quark), the quarks' fundamental masses are only a tiny fraction of the total proton mass. Instead, the vast majority of a proton's mass results from complicated non-linear QCD (strong nuclear force) self-interactions that draw on both the fundamental masses and things like the QCD interaction strength. We've had some success at simulating those QCD interactions in recent years, but there's no known way of just reading off the proton mass from a fundamental equation.

So for the idea behind this proposal to work, it seems to me that both the fundamental particle masses and these complicated QCD effective masses would have to scale completely in parallel. I'm not at all clear on whether a field redefinition (as proposed here) would work that way. Maybe it would be more natural than it seems, but that's my first big concern with the proposal.

gizmo68613 anni fa

Neat idea. If/when the paper gets published I hope I stumble upon it.

One thing that I don't get with the hypothesis is how it deals with conservation of energy. Its well understood that mass is a form of energy, so if atoms were to simply grow in mass, then that would either require some other energy source, or violate conservation of energy. Obviously, this is a huge an obvious problem that should preclude this hypothesis from serious consideration. The fact that this does not do so suggests to me that this issue is somehow resolved within the theory.

JonnieCache13 anni fa

Consider yourself stumbled. The paper is here: http://arxiv.org/abs/1303.6878/

rprospero13 anni fa

Well, it doesn't have any more of a conservation of energy issue than the current theory already does. Loosely speaking, cosmology currently states that the acceleration of the galaxies away from each other comes from dark energy. However, if we don't use that dark energy for pushing the galaxies around, we should have enough left over to increase the rest mass of every particle in the universe. Neither theory has a good explanation as to what this dark energy is, but both theories have it.

omegant13 anni fa

Is it possible to difereciate between a expanding universe due to the big bang?, or an expanding universe due to this part of universe coming out of a more compressed stream (like coming out of a 3d venturi tube). I don't know if that makes sense. And if red shifted light is not red due to the expansion, but due to some kind interaction with dark matter?. I suppose this questions are dumb, and surely they have been discarded and replyied lotsof times, but never found that info. Does any body know a place were this kind of thinks are explained?

cpleppert13 anni fa

I would say not really! The real problem isn't the effect can't be replicated it is that replacing cosmological expansion with something else requires the something else to exactly mimic all the other things we can observe about the universe.

Dark matter is a great example. Due to gravitational lensing this can mimic directly the redshift we can observe. But then you have to explain how all this dark matter is distributed(not to mention created) in a way that doesn't mimic cosmic expansion in one part of the sky but everywhere at once.

I found the teaching company course on cosmology(from what I saw of it) to be absolutely fantastic as a general introduction: http://www.thegreatcourses.com/tgc/courses/course_detail.asp...

omegant13 anni fa

Thank you very interesting, I´ll check it. Some times I get the feeling that somehow in cosmology there is some kind of advanced modern day epicycle squeme that is giving correct predictions but is not really what is out there. I just love to follow the advances in cosmology.

cpleppert13 anni fa

I'm not sure I understand how this effect actually works. Cosmological redshift isn't due to galaxies moving away from us but the expansion of the universe occurring underneath light as it travels in an expanding universe. So replacing velocity with mass increases doesn't actually work as far as I can tell because the mechanisms aren't equivalent. You actually need some physical mechanism that produces this mass increase over time that happens to be exactly the same as that observed by cosmological redshift.

cma13 anni fa

Are you sure about that? There is blueshift and redshift as you move towards or away from light sources.

While the speed of light doesn't ever change no matter your reference frame, the frequency/wavelength indeed does.

cpleppert13 anni fa

I'm not sure we disagree. Cosmological redshift doesn't rule out additional changes in observed frequency that compound due to the ones we observe by the expansion of the universe. Hubble originally explained his observed redshifts in other galaxies entirely due to the doppler effect but changed his mind when he observed a correlation between the distance of a receding galaxy and its redshift. If the doppler effect could explain cosmological redshift then galaxies would seem to have to 'know' how far they were from the observer!

If you go back and see the original 46 galaxies that hubble plotted by comparing observed redshift to the distance hubble had observed you can see considerable 'scatter' in the observations. This scatter is due to the Doppler effect.

The velocity distance relationship in hubble's law isn't due to the doppler effect but a model that relates recessional velocity to the general expansion of the universe.

xanderstrike13 anni fa

I don't like how similar the words "Cosmology" and "Cosmetology" are.

I was very confused upon first reading the title of this article.

kenj041813 anni fa

My cosmetologist told me I was gaining mass too. She recommended a diet though - not further research.

drzaiusapelord13 anni fa

Ah yes, I've also been to the "Girl, your ass is gettin big" symposium.

mtdewcmu13 anni fa

It's interesting that you clicked on it anyway.

vital13 anni fa

Say, you are deep inside a huge forest with your eyes closed all the time. Then, you blink once. Can you from the information received via that blink deduce if the forest is expanding or shrinking? Did it have a big bang or a small one? Just asking... On the other hand given the situation one needs to be extremely delusional and detached from any sense of reality to consider any bang fantasy seriously.

fargolime13 anni fa

A much simpler explanation that adds no new assumptions and shows that space itself need not be expanding to explain what we observe is at http://finbot.wordpress.com/2008/03/06/expanding-space-obvia.... It also solves the flatness problem, a major problem in cosmology.

cpleppert13 anni fa

That doesn't make sense at all. The whole point of cosmological expansion is to explain relations between redshift and distance. That is what was suggested to Hubble back in the 1920's when he plotted this relationship. If you don't hypothesize any global relationship between these two values then every galaxy just happens to have a larger velocity depending on distance. The link doesn't explain why this would happen.

I'm a little concerned about some of the other stated problems that the 'theory' tries to solve. For instance,

>>They believe that sufficiently large objects stretch or break apart, and proffer explanations as to why smaller objects, like galaxies, don’t do likewise.

Spacetime isn't an object! I think gravity is a great explanation why galaxies don't break apart..

fargolime13 anni fa

> The link doesn't explain why this would happen.

Physics doesn't answer why on anything. Hubble's observations still apply. He didn't try to explain why the observational data is what it is.

> Spacetime isn't an object!

Where was the opposite claimed? I don't see it.

> I think gravity is a great explanation why galaxies don't break apart..

That's fine, but you still have a flatness problem that also needs an explanation. If you don't need your explanation (by obviating the expanding space paradigm) the flatness problem vanishes.

cpleppert13 anni fa

You can edit my response and change the 'why' to 'how.' Doesn't matter. The author still posits no mechanism for why the distribution that Hubble observed holds for every galaxy in the sky nor does he ever address this point at all. He doesn't say it isn't relevant or can be explained in a simpler way he just ignores the evidence.

So given a proposed explanation that explains observed phenomena the author claims nothing at all except that it would be consistent (if you get rid of the observed phenomena) to not have the theory. That is a nonsensical argument that begs the question.

I.e. if gravity didn't exist apples would still be red Q.E.D. gravity is unnecessary

> Where was the opposite claimed? I don't see it.

He wants to say that because galaxies don't break apart but the universe does somehow there is an arbitrary limit on the size of objects that 'break apart.'(Do you think some other object other than the universe if being referred to here? What is breaking apart that is larger than galaxies and would remotely make sense here?)

This is rather strange because gravity(and the atomic forces) are far stronger than cosmological expansion so his 'point' doesn't make sense.

fargolime13 anni fa

> The author still posits no mechanism for why the distribution that Hubble observed holds for every galaxy in the sky nor does he ever address this point at all.

Hubble found that the galaxies are moving apart from one another in the simplest possible way they could do that. (If they weren't moving apart from one another they'd be moving toward one another, or some mixture.) No further explanation is needed unless one thinks that movement violates some other tenet of physics, like the cosmological principle or Einstein's speed of light limit; in that case you need an additional explanation like the expanding space paradigm so you can save the other tenet(s).

Also note that the expanding space paradigm just shifts the why / how question to some other chapter of physics. What is the mechanism that expands space itself? Nobody has that answer.

> He wants to say that because galaxies don't break apart...

Not he/she, not the author. What you quoted was about what cosmologists generally accept today. Cosmologists generally accept that there is some limit on the size of objects that break apart due to space itself expanding. Below that limit, gravity and the atomic forces keep the object from breaking apart, they believe.

phaemon13 anni fa

That page doesn't actually explain why the galaxies appear to be moving away from each other.

fargolime13 anni fa

Physics doesn't answer why on anything. For example, why does gravity hold me to my chair? Nobody knows. Physics explains only how gravity affects things.

phaemon13 anni fa

Of course it does. Gravity holds you to that chair because the mass of the earth is attracting the mass of you. This tells us that if you were sat on a chair on the moon, the hold on you would be less. Theory with prediction, see?

That's what that page doesn't answer: Why do the galaxies appear to be moving away from us?

fargolime13 anni fa

> Gravity holds you to that chair...

You've explained how the effects of gravity can be predicted, not why gravity holds me to the chair. What is the mechanism that causes the gravity that holds me to the chair? Is it undiscovered gravitons, or what? Likewise you wish to know the mechanism that causes the galaxies to move away from one another.

We already know that objects have freedom of movement in space. So why the galaxies appear to be moving away from us can be simply because they are moving away from us. There doesn't need to be a deeper explanation. If you would like to explain the observation using the expanding space paradigm then tell me why space itself is expanding, without saying "it just is". Tell me the mechanism by which it expands. Otherwise you've answered one why question by making an assumption that is left wanting for its own explanation as to why. You've traded one problem for another.

phaemon13 anni fa

So what? You can ask "why" all the way down, but the effect of you sitting on a chair still has an explanation.

I want to know why the galaxies are moving away from each other, because it appears that they should actually be attracted to each other by gravity. You've actually got two problems now: "why are the galaxies moving apart?" and "why isn't gravity working the way we thought it worked?" How is that simpler?

EDIT: I forgot; third problem: "why is the sky dark at night?"

fargolime13 anni fa

> You can ask "why" all the way down, but the effect of you sitting on a chair still has an explanation.

Trading one problem for another doesn't really solve anything. You take issue with the blog post for not answering your question but neither does current cosmology answer your question, except by raising another question. So the blog post doesn't have the disadvantage over current cosmology that you suggested.

> "why isn't gravity working the way we thought it worked?

Objects can move away from one another other even as they are attracted to one another by gravity. Are you thinking of how the galaxies are thought to be accelerating away from one another (dark energy)?

> "why are the galaxies moving apart?"

Physics doesn't need to answer that. Why isn't our Moon larger than it is? It's enough for physics that it's possible in principle for the galaxies to be moving apart from one another.

If something we observe is thought to be impossible in principle, then physics should change to address that. So maybe you're thinking of accelerating cosmic expansion here (dark energy).

> "why is the sky dark at night?"

That's Olber's Paradox. It's already explained by the redshift. The faster a galaxy moves away from us the more redshifted it is. At some degree of redshift our eyes receive only 1 photon per century on average, or less. So that spot in the sky is dark.

phaemon13 anni fa

> Trading one problem for another doesn't really solve anything.

Yes it does. You might as well say, "No-one knows why I'm stuck to this chair and invoking a complicated 'gravity' theory just trades one problem for another". It clearly does have an advantage though: it answers not just that specific point on chairs, but why rocks fall and how planets orbit and allows you to work out how these things would behave in different environments. A "it just is" theory does none of these things. A "we don't know, but we'll try and find out" theory is much better.

> Objects can move away from one another other even as they are attracted to one another by gravity.

No they can't, unless some external force is applied at some point. You don't just levitate out of your chair at random intervals for no reason. What was the external force applied to the galaxies?

Let's leave the other stuff. If we aren't agreed on the simple things, there's no real point discussing anything more complex.

fargolime13 anni fa

> A "it just is" theory does none of these things.

Sure. But the physics to predict the behavior for galaxies or other objects moving away from one another is already covered by a theory of gravity. When the blog post removes the expanding space paradigm as superfluous, nothing worse results.

> What was the external force applied to the galaxies?

Now that question makes more sense to me. Because once they're moving there's no mystery. The galaxies are currently attracted to one another by gravity, we can assume, even as they move away from one another.

I don't know what caused the galaxies to start moving away from one another. Let's suppose observations instead showed them to be moving toward one another. Would you then ask what started them doing that? Since they'd be moving in some fashion regardless, the only mystery I see is that they are mostly all moving away from one another.

Let's suppose the expanding space idea solves the mystery. Well it's not a very good solution because it immediately raises another question: what causes space itself to expand? It also leads to the flatness problem, a major problem of physics. If it's superfluous and its removal solves the flatness problem, physics would be advanced by removing it, even if that mystery remains.

phaemon13 anni fa

> Let's suppose observations instead showed them to be moving toward one another. Would you then ask what started them doing that?

No, because if I mentally rewind that tape back, I see things far apart now being pulled together. I know gravity pulls things together. Therefore it's reasonable to assume it's gravity pulling them together. I assume galaxies in the past were further apart and are now getting closer.

In the current scenario: I mentally rewind the galaxies moving apart, I see them being together and then moving apart. I don't have anything to explain this. Why did they move apart when they should have been pulled even closer together?

fargolime13 anni fa

I see your point. But I wouldn't accept that space itself must expand to move them apart in the current scenario, since that leads to the flatness problem and also creates a new problem as to what causes space itself to expand. It would be cleaner to reject the expanding space idea, letting the flatness problem vanish, and then assume that some other unknown physical phenomenon moved the galaxies apart. The expanding space idea also leads to the horizon problem and the dark energy mystery, the blog shows.

Tcepsa13 anni fa

It seems to me that this should be able to be tested by checking whether the gravitational force between two objects of a given mass increases over time. If it does, then their mass has increased. If it doesn't, then their mass has not. (Of course, if the gravitational constant is correspondingly decreasing then this idea goes out the window.)