Expanding Universe and the Red Shift

[PixyMisa]

The Big Bang Theory is vindicated by the Expanding Universe Theory, which in turn is vindicated by the Red Shift Theory.

No, but let's press on.

The Red Shift Theory was formulated to explain why immensely distance stars appear red in colour.

NO!!!!!!!!!!!!!

Distant stars DO NOT APPEAR RED IN COLOUR.

This is why all your alternatives are completely wrong.

 

[Genesius]

I think that's a perfectly valid thing to say. At least, our galaxy is at the center and every other galaxy is moving away from us. Of course, every galaxy could consider itself the center and they all would be right.

Each observer in a different galaxy would appear to be at the center from their own point of view, so your statement is more or less correct.

But that's not the point that Mel was making. Mel is saying that it's simpler *not* to think of the other galaxies as moving away from us, but instead it's simpler to think of them all as standing still, but the space between them is expanding. And that's valid.

No, it's not. The movement of those galaxies causes real physical differences which we can measure. For example, type 1a supernovas (or, for the pedantic, supernovae) are used as a standard candle. Their total time of explosion and peak luminosity are almost identical. However, in a distant galaxy the speed of recession causes relativistic effects to be observed. In distant type 1as, we can observe time dilation effects causing the explosion to take twice as long as expected. This shows that the galaxy in which the supernova is located is actually moving away from us at a high percentage of c. Of course, relativity causing strange effects, an observer in that galaxy looking at ours would see the same dilation effects happening here.

(Anybody got an aspirin? Talking about relativity always gives me a headache.)

 

[Wire]

None of described alternatives also explain widely observed distortions like Kaiser and Finger-of-God effects in redshift catalogues of galaxies.

 

[Nancarrow]

Is this just a matter of what words we use to describe the situation, or are the two situations really different somehow?

Suppose I and some nearby object are "really moving" away from each other at 1 m/s. Now suppose that we aren't "really moving", but that "the space between us is expanding" in such a way that the distance between us is increasing at 1 m/s. Do I notice anything different? If so, what?

I think there is a real difference, but it's been three years since I took a GR course and I can't say I really understood it much at the time, anyway here goes...

In all theories of mechanics, whether Newtonian or Einsteinian, special or general relativity, we have to have a mathematical description of motion. We do that by labelling the points of space with coordinates. Now that immediately introduces a difference between the mathematical descriptions of the two cases you've described. In the first, the coordinates of the nearby object (as measured by you) are changing, whereas in the second case they are not. Now here's a bit: in the second case, even though the coordinates are not changing, the distance from you is. This sounds bizarre at first. The thing to realise is, the distance between two points is generally NOT simply the difference in their coordinate. (Let's assume we have just motion along one coordinate axis, say the 'x' one)

This point is actually obvious for, say, spherical polar coordinates on the Earth's surface. If you move one degree of longitude to the left, you can't necessarily say you've moved a metre to the left. It depends what latitude you're at. You could have moved 110km if you were at the equator, but only a few inches if you're near the North Pole.

In general the distance between two points is given by the 'metric', a function of the change in coordinates, and of the coordinates themselves. In abstract geometry this metric can be any godforsaken pathology, but it takes a particular form in general relativity.

So basically, in the first case the object is moving through space, and you can take the metric to be that for simple Euclidean space with a Cartesian set of axes. In the second case, the object is not moving through space, but the metric itself is changing over time.

So that's the MATHEMATICAL difference between the two situations. As for what the PHYSICAL difference is (ie the answer to your question!), I'd have to say... er... no idea, sorry! I'll keep thinking about it.

 

[ynot]

No, but let's press on.



NO!!!!!!!!!!!!!

Distant stars DO NOT APPEAR RED IN COLOUR.

This is why all your alternatives are completely wrong.
[/size][/font]

OK . . . Thanks for that . . . sorry

Ok . . . I have another idea! . . . Perhaps my face is turning red because I’m running way so fast that the Doppler effect . . . . Nah, that wouldn‘t work either.

Thinks . . . Note to self . . .
(1) Make sure knowledge of basic facts is correct before trying to reinvent them.
(2) Don’t annoy the nice people on this forum to test uneducated, half-baked ideas (that’s what Google is for).
(3) Resist the urge to crawl back under the big rock.
(4) Read, examine, explore, ask questions and listen.

 

[Melendwyr]

So it is your contention that our solar system is at the center of the Universe and everything else is moving away from us?

According to the Big Bang explanation, every place in the universe would see everything else in the universe rushing away from it (allowing for individual motion of little bits, of course). Hubble's Constant is considered to hold no matter where the observations are made. Therefore, our solar system is as much at the center of the Universe as anywhere else, and everything else is always "moving away from" everything else, everywhere.

 

[eri]

What a fun discussion! Sorry I missed most of it. To add my 2 cents:

On the subject of the Cosmic Sunset, you were right about that - kinda. Check out the interstellar reddening effect (http://www.astro.queensu.ca/~hanes/p014/Notes/Topic_063.html#reddening) described here. Basically, starlight can be scattered off of interstellar dust clouds, and more blue photons are scattered then red photons. But astronomers have known that for a long time, and we've come up with ways to correct for it. Never fear!

For my part, I'm glad to see that you're here asking questions, ynot. Far too many people come up with objections to accepted theory and decide that science must be wrong without looking into it any further. Kudos for asking questions!

 

[Genesius]

None of described alternatives also explain widely observed distortions like Kaiser and Finger-of-God effects in redshift catalogues of galaxies.

What'choo talkin' 'bout, Wire?

 

[CurtC]

But that's not the point that Mel was making. Mel is saying that it's simpler *not* to think of the other galaxies as moving away from us, but instead it's simpler to think of them all as standing still, but the space between them is expanding. And that's valid.

No, it's not. The movement of those galaxies causes real physical differences which we can measure.

The folks who wrote a feature article at Scientific American seem to agree with me:

The expansion of our universe is much like the inflation of a balloon. The distances to remote galaxies are increasing. Astronomers casually say that distant galaxies are "receding" or "moving away" from us, but the galaxies are not traveling through space away from us. They are not fragments of a big bang bomb. Instead the space between the galaxies and us is expanding. Individual galaxies move around at random within clusters, but the clusters of galaxies are essentially at rest. The term "at rest" can be defined rigorously. The microwave background radiation fills the universe and defines a universal reference frame, analogous to the rubber of the balloon, with respect to which motion can be measured.

 

[Genesius]

The folks who wrote a feature article at Scientific American seem to agree with me:

The folks at UCLA call it a draw. From http://www.astro.ucla.edu/~wright/cosmology_faq.html#TD :

Are galaxies really moving away from us or is space just expanding?

This depends on how you measure things, or your choice of coordinates. In one view, the spatial positions of galaxies are changing, and this causes the redshift. In another view, the galaxies are at fixed coordinates, but the distance between fixed points increases with time, and this causes the redshift. General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views. Part 3 of the tutorial shows space-time diagrams for the Universe drawn in both ways.

 

[Melendwyr]

Well then, you'll just have to use your brains instead of relying on copy-and-pasted excerpts from sufficiently intimidating sources.

Y'know, be a skeptic.

 

[PixyMisa]

Well then, you'll just have to use your brains instead of relying on copy-and-pasted excerpts from sufficiently intimidating sources.

Y'know, be a skeptic.

Being a skeptic does not mean "arguing endlessly over a point of terminology that makes no actual difference":

General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views.

That's what we've been saying all along. The maths works out the same regardless.

 

[Melendwyr]

Being a skeptic does not mean "arguing endlessly over a point of terminology that makes no actual difference":

Arguing over a point of terminology that does make a difference is another matter.

That's what we've been saying all along. The maths works out the same regardless.

But let's not forget the complexity of the other perspective.

 

[Genesius]

Well then, you'll just have to use your brains instead of relying on copy-and-pasted excerpts from sufficiently intimidating sources.

Y'know, be a skeptic.

I do use my brains. I'm smart enough to realize that I'm not an expert in this subject and to use the research materials at hand to collect information. Unlike you, who has a conclusion already decided and cherry-picks the data to fit.

Read back through the thread. You've had SpaceFluffer, with his PhD in astrophysics, tell you you're wrong. What credentials do you have that any of us should believe your interpretation over his? C'mon Mel, impress us with tales of your academic triumphs, or admit you're just blowing smoke.

 

[Melendwyr]

I do use my brains. I'm smart enough to realize that I'm not an expert in this subject and to use the research materials at hand to collect information. Unlike you, who has a conclusion already decided and cherry-picks the data to fit.

And you have determine that my conclusion was decided before I looked at the data... how, exactly?

It seems to me that you had decided that's what I'd done, and are now selectively referencing the available data to support your conclusion.

Read back through the thread. You've had SpaceFluffer, with his PhD in astrophysics, tell you you're wrong.

SpaceFluffer, at best, is not skilled at communicating and understanding communication in a written medium. His conclusions about what other people are arguing are of little consequence.

The reference frame that permits us to view those distant objects as moving makes some very peculiar assumptions (the existence of a spherical horizon boundary, for one) to make things work. Just as it's technically possible (but pointless) to view the Earth as the center around which the rest of the universe rotates, it's technically possible (but pointless) to view those distant objects as moving.

Hubble's Constant demands that objects at a certain distance be receeding at the speed of light. That isn't possible if the objects are actually moving, not without some fancy mathematical footwork that changes the assumptions about the nature of space those things are moving through. It's perfectly possible if space is expanding.

 

[ynot]

What a fun discussion! Sorry I missed most of it. To add my 2 cents:

On the subject of the Cosmic Sunset, you were right about that - kinda. Check out the interstellar reddening effect (http://www.astro.queensu.ca/~hanes/p014/Notes/Topic_063.html#reddening) described here. Basically, starlight can be scattered off of interstellar dust clouds, and more blue photons are scattered then red photons. But astronomers have known that for a long time, and we've come up with ways to correct for it. Never fear!

For my part, I'm glad to see that you're here asking questions, ynot. Far too many people come up with objections to accepted theory and decide that science must be wrong without looking into it any further. Kudos for asking questions!

Thanks

 

[69dodge]

The reference frame that permits us to view those distant objects as moving makes some very peculiar assumptions (the existence of a spherical horizon boundary, for one) to make things work.

What's a spherical horizon boundary?

Just as it's technically possible (but pointless) to view the Earth as the center around which the rest of the universe rotates, it's technically possible (but pointless) to view those distant objects as moving.

Certainly, one coordinate system might be more convenient than another for purposes of calculation, but the idea that actually they're all equally valid seems to me to be a pretty important point; it's what underlies the whole theory of relativity.

Hubble's Constant demands that objects at a certain distance be receeding at the speed of light. That isn't possible if the objects are actually moving, not without some fancy mathematical footwork that changes the assumptions about the nature of space those things are moving through. It's perfectly possible if space is expanding.

What assumptions about the nature of space does it change? And what are they changed to?

I guess the idea that space can expand is a pretty big change from the usual conception of space, too.

 

[Melendwyr]

What's a spherical horizon boundary?

Kinda like a black hole, only turned inside-out.

Certainly, one coordinate system might be more convenient than another for purposes of calculation, but the idea that actually they're all equally valid seems to me to be a pretty important point; it's what underlies the whole theory of relativity.

But there's a reason we regard heliocentrism as the model of the solar system, even though geocentrism is equally valid.

I guess the idea that space can expand is a pretty big change from the usual conception of space, too.

Yep.

 

[Complexity]

SpaceFluffer, at best, is not skilled at communicating and understanding communication in a written medium. His conclusions about what other people are arguing are of little consequence.

SpaceFluffer - My responding to this jerk in no way suggests that his criticism of you is sound.

Melendwyr - You have one hell of a lot of nerve criticizing anyone, you jerk. I've enjoyed and understood SpaceFluffer's communications, believe that he has been tracking discussions well, and I have a lot of respect for him and the field of science he has chosen to study.

You, on the other hand, are quite full of yourself without cause. Occasionally, you make some sense, but increasingly you are behaving like a fool. Shut up and learn something.

 

[SpaceFluffer]

Apologies for the derail...

I've been avoiding this thread, but I saw my name mentioned a few times and thought I should comment (note to self: be less vain).

Firstly in the interest of full disclosure I should point out that I don't currently have a Ph.D., but will be defending my thesis in a few weeks. I am an active researcher in the field, however, and on a world-leading experiment no less, so I feel that my words should carry some weight. The evidence and mass consensus of the scientific community, of course, carries almost infinitely more weight.

I'm glad to hear that at least one poster feels that I make myself relatively clear. Of course, most of us here are not writers and I'm aware that my posts are not always as clear as they could be. In general, when a poster appears not to understand my point, I assume that it was my explanation that was lacking, not their understanding. Obviously this is not always the case.

The way I see it, we're all hear to learn and/or to share our knowledge. I sincerely hope that ynot has learned a thing or two in this thread and has had his/her interest in the subject amplified, not dampened.