I have not read any "scientific facts" that convince me that the red shifts we see from galaxies are caused by the expansion of space and not simply from the galaxies moving away from earth. If you have a strong argument I would like to hear it?

I think one of the main arguments is that if all the distant galaxies we observe to be receding, were receding through space, we would find our position to be the centre of the universe, in violation of the cosmological principle.

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

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There is no such thing as "absolute space", relativity only recognizes spacetime as having invariant (frame-dependent) properties. You can partition it into space and time pretty much any way you like by choosing a system of observers in bizarre interconnected reference frames. So there is no more absolute truth in "space is expanding" than there is in "the galaxies move through space", both of those statements attribute to space properties that it simply does not have.

So why do so many people say "space is expanding"? Because what they really mean is that the cosmological principle offers to us a particularly convenient coordinatization of spacetime, wherein space is chosen to be "attached to the average motion of the galaxies", and time is chosen to be the proper age of the universe for objects following the locally average motion. These are called "comoving coordinates", and when that arbitrary but convenient choice is made, then you find that your coordinatization of space looks like the coordinatization of something that is expanding. On the other hand, there is no globally convenient coordinate system in which the galaxies are moving through space-- as pointed out above, you can only get that if you treat the Earth as being in a special place. It isn't wrong, but it is unnecessarily complicated mathematically, and it is pedagogically awkward in how it treats our own egocentric location. I think such forced coordinates would also not be "good" coordinates relativistically speaking, they would not preserve the form of the laws of physics-- a very big inconvenience indeed.

Why would the billions upon billions of galaxies throughout the universe all be moving away from the infinitesimal speck of a planet we call Earth?

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Choosing to argue the movement away from Earth (not even the Sun) leads to the question:
*- Do you consider earth or perhaps a location on it the center of the universe?
If so then there won't be any point to trying to convince you using reasoning or science.

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Distant supernovae. Expanding space, rather than recession through static space, increases the radius of the sphere on whose surface the light from the supernova is spread, more rapidly than the 4*pi*R^2 of Euclidean space. This is observed in type Ia supernovae - correcting for this is a much larger effect than the more subtle evidence for an accelerating expansion. (That is, if you don't correct for it, the SN luminosities aren't even approximately constant at various redshifts). My notes aren't here at the moment - IIRC, this factor alone amounts to a decrease by a factor (1+z) in an object's flux, and Type Ia SN are the best standard objects now available. The same issue would of course apply to galaxies, but they have such a wide range of properties that their change sin stellar mix with age would utterly swamp this effect by itself.

I think you are assuming the "static space" is Minkowskian, are you not? If you relax that assumption, I suspect you can account for the 1+z effect well enough-- but you still end up with a horribly awkward parametrization of the situation. The point is, I don't think you can actually make physical distinctions between what is "happening to space" and what is "happening to matter", it simply isn't meaningful in an absolute way as one might wish. But you can certainly tell the difference between an elegant picture and a vastly more convoluted one that is very arbitrary, jury-rigged, and treats the Earth in a special way simply because we are here. (I suspect you are right that CosmosGP is imagining Euclidean space, so relaxing that would already defeat what he was hoping to get away with imagining. I just don't like to make physical claims that cannot actually be supported empirically, like what is happening to space.)

Put a sheet over your head like a ghost.

Lift up your arms.

There, see, space has expanded.

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If you have an alternative proposal, why don't you prove that, instead of expecting everyone else to do the work? The way you wrote the words scientific facts in speech marks, seems to indicate that you consider them otherwise.
If you have a strong argument I would like to hear it

In a way, red shift is caused by all the galaxies moving away from us... relatively speaking. The spectrum shift toward the red would not be apparent otherwise. What you seem to not realise, is that we are moving away from them as well.

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You know, Ral, everytime I get to feeling like I'm just a source of static here, clogging up bandwidth with the forum version of white noise, and getting in the way of the real good works being done here by scientists, you come along and make me feel better.

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Yes, if you used static deSitter coordinates, your space is no longer flat, but curved. The metric factor is (1 - k*r^2), where k is c^2*Lamdba/3, IIRC. Just like Schwarzschild that factor appears in both the time and radial part of the metric (which is the characteristic of static spherically symmetric spacetimes, IIRC).

Being merely a different coordinatization of the same space-time, it will give exactly the same observerable predictions.

IIRC, deSitter (lambda only) is a good approximation out to a certain z, which I forget, but I think it's a couple or three billion light years. After that, you'd have to use the full LCDM space-time for full accuracy, which, while not as simple, certainly would admit something very similiar to static deSitter.

-Richard

Is there any difference between a distance-dependent acceleration on the galaxies from the perspective of one frame, and the viewpoint of the intervening space expanding?

Gravity, acceleration, and space-time curveature are supposed to be equivalent under general relativity. Hence, the distance-dependent acceleration of the galaxies in a specific frame can be related to a space-time curveature and expansion, right?

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What would "convince" you? Certainly, the redshifts could be caused by galaxies moving through space, rather than by the expansion of space itself. However, that implies two necessary consequences: (1) we are at the center of the universe and (2) special relativity is false. The former is physically possible, but philosophically unpleasant, while the latter is scientifically unacceptable.

The "scientific fact" you are looking for is the theory of special relativity, which has a great deal of experimental verification to back it up (i.e., What is the experimental basis of Special Relativity?). Special relativity does not allow any object to travel through space at a speed greater than that of light. So use a classical, non relativistic Doppler shift, and let the redshift z be simply the change in wavelength over the rest wavelength, and you readily see that any z greater than 1 implies a recession velocity greater than c, the speed of light, which is the speed of an electromagnetic wave through space, and is constant in classical electromagnetism, without resorting to relativity theory.

Since a recession velocity greater than c violates the laws of physics (i.e., special relativity) the classical explanation cannot be correct. There must be another theory to allow for the appearance of recession velocities greater than c, without violating special relativity. General Relativity does the job, and is also known to be consistent with observation (i.e., Will, 2006).

So, the published fact that convinces everyone else is the assumption that the redshift is a simple non-relativistic Doppler shift violates the laws of physics, and therefore must be false.

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I don't think it necessarily says we are at the center of the universe.

Take an infinite field of arbitrarily positioned particles and give then v = H*d velocity from the "origin". Now move your coordinate system to track any of the particles, and you'll find that the same relation holds v = H*d, where d is the distance from wherever you are tracking. Of course you'd have to add in reletavistic effects as v->c, but I'm pretty sure it doesn't break the coordinate invariance.

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He didn't do it because it would have required posting to ATM instead of Q&A. A fine distinction, perhaps, but my guess is he is OK here simply because he does not advance a specific ATM position, but simply says he is "not convinced" by the mainstream arguments.

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Sounds good to me. What else would you have him do? I think he did it right.

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In your rush to call everyone "entrenched" or closed-minded or "limited" you fail to note that the "limit" here has a very natural boundary: that point at which the evidence stops. - JayUtah

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Space itself is expanding.

Space is a relative concept. With nothing to be in between, there is no space. Therefore, as the galaxies move apart, space increases between them.


It expands. What more proof do you want than that?



And Earth is the center of the universe, because it appears that way. Haven't you people read your Aristotle? Sheesh.

If it's as you claim, then we're at the precise center of the universe and origen of the big bang, as they're all moving away from us.

Given the literally billions and trillions of stars/planets in the visible galaxies, the statistical liklihood of that is ridiculously beyond the possible.

It's far, far, far (repeat about a billion times) more likely that space itself is expanding. This would make it appear that stars are moving away from use regardless of where we were located in the universe.

My explanation isn't "proof," just reasoning. I believe others here are more qualified to offer proof.

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If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

It doesn't though. An expansion scenario from a perfectly newtonian or SR perspective doesn't provide any special reference frame. See my post above. (Of course, they don't explain the source of the acceleration either, but the frame independence is consitent, at least).

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Thank you for transforming my vague claims into concrete mathematical descriptions.

Right, and that motivates a certain language to picture what is happening. The issue is whether one "can" do it that way or if one "must".

I think there is still a lot of confusion on this thread. Let me give you a concrete example to explain why the concept of "distance" and the concept of "coordinatization" of spacetime are related, such that one cannot make uniquely correct statements about "what space is doing". There is nothing at all physically wrong with adopting a length standard that changes with time. We could have, starting in the year 2000, redefined a "meter" as a meter times 2000 divided by the current year. All equations of physics would change in unnecessarily complicated ways, and the distances to all galaxies would be rapidly increasing with time, as enumerated in that unit of distance. We have chosen a coordinatization of spacetime (not a very clever one, of course). It is obvious in that case that the "expansion of space" is an artifact of our distance convention. It is less obvious in the actual distance convention that we have chosen-- but it is the same. Relativity tells us what is "real" and what is just an artifact of coordinatization-- yet we ignore that lesson because, basically, we just don't like to think relativistically. So we constantly revert to a more absolute form of thinking, in violation of the very principles that empowered us to create that picture in the first place. Now, there is nothing wrong with imagining that "space is expanding", it is a very useful picture indeed. But we must not go around telling people it really is, unless we plan to distinguish empirically that from all models that don't have space expanding. Do we claim that what is "really happening" is whatever is least cumbersome to our intellect?

Hmm. As I venture near the edge of the precipice of my understanding here - does "observed wavelengths of electromagnetic radiation emitted at known wavelengths" constitute a physically useful measure in this sense?

Yeah, I was comparing with Euclidean pictures. Allan Sandage had some discourses on the distinction between the world picture and the world map in relativistic cosmology that are relevant here.

I'm not sure what you are asking, we are all agreed that the redshifts must be correctly reproduced by any useful model. There are models that reproduce redshifts and intensities of supernovae that are equivalent to the expanding space picture. Those models are generally much more mathematically and philosophically cumbersome, so we all just use the comoving-frame picture with a standard distance coordinatization, and in that elegant picture, space is expanding. It is the difference between what works and what works elegantly-- but claims of reality require more than elegance, to be scientifically supportable. I would say that at the very heart of relativity is the ability to identify equivalence classes of models that stem from the same observable reality, yet this is precisely the lesson that gets ignored in popular cosmology literature. But I understand the tradeoff-- maybe teaching relativity is not the goal, instead we wish to convey a picture that people can use.
I suspect the OP was as well, so your answer was certainly germaine.I would be curious to hear his take on that.

Alex Trebek would know.

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"Coordinatization"? Applying coordinates to? Only a native speaker of Deutsch could like that word. How about settling for a special sense of "coordinating"?

However, thank you and Richard for your comments, enlightening as usual. Good job!

Regards, John M.

Sorry I took so long to post.

O.K. I will do the hard work ! Here are the "Facts" as I see them:

1.The cosmic microwave background defines a "center". The Milky Way galaxy is approximately at that specific center. (this is a huge and unbelievable coincidence). The CMB is approx. 14 Billion light years away from Earth in all ( and I do mean All) directions. (Another huge coincidence).

2. Quantized red shifts have never been scientificaly proven false in 25 years. Now consider that quantized "galactocentric" red shifts are even more accurate and distinct. This means that quantized spherical shells of galaxies exist around our milky way galaxy. This has been proven for 20 years for millions of light years distance from our galaxy. I have never heard of a legitimate argument against these spherical shells around our galaxy. (these shells would not even be detectible unless we were within 100,000 to 1 million light years from the center of these shells.) This huge coincidence cannot be explained.

3. Forget the cosmological principle (this is a belief, a faith, an opinion).
Please open your mind and visualize what we see through a telescope and what we see in the light spectrum of distant galaxies. Facts of science should be visible and still working in our existing universe.

4. For expanding space to be a legitimate theory; space and matter must travel faster than the speeed of light after it reaches the Hubble radius (distance). This is impossible! Please Give me a legitimate rebuttle?

Well, there's your problem! No, it doesn't. It defines the limits of how far we can see, nothing more.

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That is simply not true. Whereever did you get this notion? You can find the contrary argument in about a thousand places, probably a hundred threads on this forum alone. You will never find a reliable argument that the CMB indicates we are at any kind of center.
What they have never been is taken seriously. I don't know the current status of debunking on them, you might check the ATM section of this forum, or google the idea.
It's pure nonsense that this has been proven. It is either known to be false, or remains a curious anomaly at the edge of what can be explained, like the Pioneer anomaly-- I don't know which. But the fact that it's been around for so long and has yet to inspire a credible cosmological model should tell you something.
Well now you have-- the data is overinterpreted. The geometry of the "cosmic web" of galaxies is well known, and it seems likely that misinterpretation of how that weblike structure can appear to produce steps in the data are the likely cause of the erroneous interpretation of quantization. I can't say more, other than the fact that few working astronomers take the claims seriously.
Incorrect, it is a hypothesis, and a very useful one indeed. Look up "scientific method".Again, this is covered in dozens of threads on here, and thousands of other places. Distances in general relativity can increase faster than c without any violation of the theory. That's just a fact.

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2. Quantized red shifts have never been scientificaly proven false in 25 years.

It's not that they've been proven false per se, but rather the value has continued to shrink as more data has become available. The reason is that early survey data was very "line of sight" and limited in its breadth, and since the large scale structure of the universe is very 'filament" in its structure, the data presented galaxies at specific redshifts. Surveys like the 2Df Redshift Survey and SDSS (eg, Hawkins 2002), which have considerably broader survey ranges, have shrunk Tiffts original value of around of 72.46km/s down to 2.68km/s.

Quote:
4. For expanding space to be a legitimate theory; space and matter must travel faster than the speeed of light after it reaches the Hubble radius (distance). This is impossible! Please Give me a legitimate rebuttle?

The "faster than light" restriction is a product of special relativity, which restricts motion through space to c. The expansion of space itself is another thing altogether and is described by general relativity. Objects receeding from us > c due to cosmolocgical expansion are still restricted to the laws of special relativity locally.

I hate to say it, but this sounds like a classic example of "a little knowledge is a dangerous thing" and the fact that you have stated "space and matter" only reinforces this. You need to learn a bit more about your subject matter before making such incorrect assumptions.