Is the popular understanding of C.M.B.R. too simplistic?

[marcus]

... There is no source for this as this is my own assertion. My reasoning is simple. The different teams endeavering to establish a "constant" kept coming up with results that did not match...

But back in the 1970s and 1980s they did not come up with different estimates of the Hubble constant because they were looking in different sectors of the sky. The different estimates were because there were differences of opinion about the best ways to estimate distance. They needed better technology to settle the issues about measuring distance.

Finally a figure of around 71 km/s per Mpc was arrived at in around 1998, using the Hubble Space Telescope. The 71 varies little based on direction you look. Only a slight doppler correction because of the solar system motion, which had nothing to do with the earlier differences.

So you have a problem, Peter. You have an idea which is, perhaps, a pet idea of yours, but which is baseless---no evidence for it whatsoever. Sometimes people experience this kind of thing as a permanent mental roadblock. A pet idea, if it is wrong and you cannot free yourself from it, can prevent you from further learning and from really communicating with others. So it could be a serious problem. Or maybe it won't be, depending on how you deal with it. I will wait and see.

 

[russ_watters]

Just been looking back over old questions; seems we've been here before. There is no source for this as this is my own assertion. My reasoning is simple. The different teams endeavering to establish a "constant" kept coming up with results that did not match. The expectation was that a single figure would be found, the fact that it wasn't led to discord. What it should have led to was acceptance of the fact that different angles of view produce different rates of recession. This can be easily illustrated in two dimensions by picturing a spoked bicycle wheel representing a slice through an expanding mass of matter that extends from the hub to the rim. If an observer should be situated at a distance 55% along one of the spokes it will be self evident that recession rates will vary according to his angle of view. The inward view will appear to be moving away from him as he moves away from them, the outward view will actually be moving away from him.

That's a very good logical proof of why evidence points to the universe having no center. That variation based on angle of view that you think should exist, doesn't.

 

[Tanelorn]

For those like myself who only follow Cosmology as a great interest rather than a profession, is there a simple chart by which we can more easily see which method, assumption and existing measurement is used to determine a measurement such as Hubble constant and other large scale measurements?

Sometimes it seems like measurement A is used to determine measurement B which is used to determine measurement C which is then used to determine measurement A, if you get my drift. I assume that no one is ever going to fall into doing something like this unless the situation is far more complex, but does this ever happen?

 

[marcus]

For those like myself who only follow Cosmology as a great interest rather than a profession, is there a simple chart by which we can more easily see which method, assumption and existing measurement is used to determine a measurement such as Hubble constant and other large scale measurements?

Sometimes it seems like measurement A is used to determine measurement B which is used to determine measurement C which is then used to determine measurement A, if you get my drift. I assume that no one is ever going to fall into doing something like this unless the situation is far more complex, but does this ever happen?

Interesting lecturer buy Terrence Tao THE COSMIC DISTANCE LADDER


a bit over one hour.

start with measuring small distances and ratchet up step by step to longer
use each rung to check the next method

You can find written stuff to go with the video lecture, or to read separately, if you google
"cosmic distance ladder" or "tao distance ladder"

 

[Peter Watkins]

This forum frequently uses the inflation theory to explain or answer various points raised. This would lead one to the conclusion that this theory is largely accepted. This in turn states that contributers believe that the universe was once small. It is now large. There is no possible way that it could have expanded in all directions without divergence. Therefore, an observer viewing from an equatorial site would see a different recession rate from an observer, viewing at the same angle, from the north or south pole, or indeed, anywhere in-between. This, surely, is irrefutable.
If you could explain how expansion could occur without divergence I would be most interested, I'm nothing if not open minded! But please, not the stretched rubber sheet nor the expanding balloon surface. We live neither in, nor on, such a universe.

 

[Tanelorn]

Marcus, thanks very much for the link and reply ;)

 

[marcus]

This forum frequently uses the inflation theory to explain or answer various points raised. This would lead one to the conclusion that this theory is largely accepted. This in turn states that contributers believe that the universe was once small. It is now large. There is no possible way that it could have expanded in all directions without divergence. Therefore, an observer viewing from an equatorial site would see a different recession rate from an observer, viewing at the same angle, from the north or south pole, or indeed, anywhere in-between. This, surely, is irrefutable.
If you could explain how expansion could occur without divergence I would be most interested, I'm nothing if not open minded! But please, not the stretched rubber sheet nor the expanding balloon surface. We live neither in, nor on, such a universe.

Peter at this and other cosmo forums in my experience we get a type of obstinate antiscience troll who just wants to argue (based on some popular misconceptions) and not learn. You need to take special care to distinguish yourself from that type of actor. I would suggest you stop arguing for a while and ask questions. Avoid setting up strawmen misconceptions, like the plague.

Your post is full of non-sequiturs.

I for one keep an open mind about inflation. There is no one version you can call the inflation theory and there are certain other professionally-researched cosmologies that do not require a special episode of inflation at the start of expansion.

But even without inflation (a special type of expansion) the mainstream cosmology does say that the observable part of the universe was once small.

However mainstream cosmology (with or without an episode of inflation) does not say that the universe was once small. In common models the universe has infinite volume today and had infinite volume at the start of expansion.

This in turn states that contributers believe that the universe was once small.
No that is wrong. Your reasoning is faulty. It could have been infinite at the start of expansion.

There is no possible way that it could have expanded in all directions without divergence.
I don't know what you are talking about. The model fits the available data astonishingly well and it predicts approximately uniform expansion in all directions, because of the very nearly uniform distribution of matter. Galaxies are peppered all over so close to even that its fair to estimate the expansion was for all practically purposes even. No preferred directions.

Therefore, an observer viewing from an equatorial site would see a different recession rate from an observer, viewing at the same angle, from the north or south pole, or indeed, anywhere in-between. This, surely, is irrefutable.
This sounds like nonsense. Looking at the cosmos as a whole it has no N or S pole or any equator. And our experience is that expansion is extremely close to uniform in all directions.
Only a tiny correction (typically one percent or less) is needed to account for the solar system's own motion relative to the average bulk of ancient matter. One percent is no big deal.

But please, not the stretched rubber sheet nor the expanding balloon surface. We live neither in, nor on, such a universe.
The expanding balloon surface is a 2D analogy to one of the more likely ways that 3D space could be. The expanding 3D hypersphere is one of the simplest ways to imagine the universe in the finite volume case. In the case that it was not infinite volume at the time of the big bang, but was, and is now, finite volume, then the most common model people use is the expanding 3D hypersphere.

Since the balloon surface is a straightforward lower dimensional analog of that, it is a useful tool for developing intuitive grasp.

You may be rejecting the 3D hypersphere model without knowing what you are rejecting. It sounds peculiar that you would declare flatly that "we live neither in, or on, such a universe."

It seems to me that the ability to entertain that possibility would be a reasonable prerequisite for participating in constructive discussion at a forum like this. So see if you can wrap your head around it.

One way to imagine would be to first focus on a flat circular disc and think of shrinking the border circle, the boundary, down to a point---as if by a kind of "drawstring". That gives a closed bag, or in other words a balloon surface.

Next you jack your imagination up by one more dimension and instead focus on a round ball with a spherical surface. Analogous to pulling the drawstring in the case of the disk, imagine you can shrink that spherical boundary down to a point. That gives a 3D hypersphere.

Other people may have better analogies and mental imagery to offer, that's what comes to mind for me as an imagination exercise. Anyway, please give it a try and stop saying
"we live neither in, or on, such a universe." Because we might well in fact. It can't be ruled out. At present we don't know whether the real world is the spatial infinite case or the spatial finite case. Both are possible given the data we have so far.

 

[marcus]

I do not understand what you mean by "[~ z = 1000]". Would a GRB at 13.2 billion light years not have happened at t ~ 500 million years and have a redshift z ~ 10?

To reply to Jorrie, I would google "wright calculator" and get
http://www.astro.ucla.edu/~wright/CosmoCalc.html
and look down in the lower right corner where there are some links, and a link to a LIGHT TRAVEL TIME to redshift calculator:
http://www.astro.ucla.edu/~wright/DlttCalc.html

So I woud click on the "light travel time" or LTT version of the wright calculator
and I would put in 13.2 billion years (a time, not really a good measure of distance because of expansion)
and click the "general" button to get it to calculate.

And it will say z = 10.253 which is about 10. Jorrie suggested it might be.

 

[russ_watters]

OP's question has been answered and the thread is no longer proceeding in a productive direction (Tanelorn, feel free to start a new thread if you want). Locked.