Expansion question

[Realitycheck]

If we are 45.6 bly from the CMB, then should we consider ourselves at the forefront of the expansion of the universe or should we consider there to be 13.7 - 5 = 8.7 by of expansion in front of us? (the 5 denoting the age of our solar system)

[Martin]

If we are 45.6 bly from the CMB, then should we consider ourselves at the forefront of the expansion of the universe or should we consider there to be 13.7 - 5 = 8.7 by of expansion in front of us? (the 5 denoting the age of our solar system)

 

thanks for asking a question, Agent.

 

you offer an EITHER OR choice and if i understand you, the correct answer is NEITHER

 

I'll try to explain. Every point is equal, there is complete democracy here. We are all somebody else's CMB material.

 

we are 45.6 Gly from the material which, long ago (before it condensed into galaxies and stars) shone the CMB light which we are now seeing.

 

now what is out there today? Presumably galaxies and stars like ours. If they have radiotelescopes able to detect CMB they can be pointing in our direction and picking up the light with OUR atoms shone back at the same time. So WE are the source material of the CMB, for them.

 

it is entirely reciprocal and all places and atoms in the universe are equally the source matter for the CMB.

And for every observer in the universe, the source of what he is now seeing is the same distance away----namely 45.6 Gly.

 

Does that make things clearer for you?

 

In other words, to answer your question, nobody is in the forefront of expansion in front of anybody else. There is no forefront.

All contemporaries are pretty much equal.

[Realitycheck]

That's kind of what I was afraid of. Because when the sun was born, as the universe continued growing outward, there were already galaxies drifting ahead of us at faster rates, skewed by other gravitational forces, and there probably is no way to tell where we are in the heap or where we were at when the sun was born.

 

However, what we should be able to do is this. Monitoring positions and movement of a number of stars, accounting for galaxy movement and galaxy spin and anything else that you can think of, we should be able to vaguely trace all movements back to the BB singularity and point to where it happened. It would take a lot of astronomical data and a powerful computer system, but it could be done.

[losfomot]

That's kind of what I was afraid of. Because when the sun was born, as the universe continued growing outward, there were already galaxies drifting ahead of us at faster rates, skewed by other gravitational forces, and there probably is no way to tell where we are in the heap or where we were at when the sun was born.

 

However, what we should be able to do is this. Monitoring positions and movement of a number of stars, accounting for galaxy movement and galaxy spin and anything else that you can think of, we should be able to vaguely trace all movements back to the BB singularity and point to where it happened. It would take a lot of astronomical data and a powerful computer system, but it could be done.

 

The problem with that is... you would find that WE are where the BB started... and anyone else, anywhere in the universe would calculate that THEY are where the BB started... and we would all be correct.

[Realitycheck]

I don't buy it. The universe is growing, has been growing for 13.7 by. We should be able to point to a region in space where we all came from, instead of saying that we are all there because we were all there.

[Martin]

I don't buy it. The universe is growing, has been growing for 13.7 by. We should be able to point to a region in space where we all came from, instead of saying that we are all there because we were all there.

 

You seem to be having a problem that is probably familiar to a lot of us.

I've seen a lot of people have it. sometimes the raisin bread dough analogy helps them.

 

I think it comes from thinking too verbally instead of mathematically (visually) but that is only a hunch.

 

In my experience this problem gets taken care of a few weeks into a first year General Astronomy course. At Cal there was a terrific lecturer who did a "Poets Astronomy" course for non-majors that was so well taught that astro majors would sit in on the lectures. I used to audit sometimes. I remember he used the analogy of a uniform dough for raisin bread with yeast in, so it is RISING.

It is an infinite lump of dough, extending infinitely in all directions, so it would make a very big loaf, but we arent going to bake it, we just observe it rising.

 

Each raisin (i.e. galaxy) thinks it is at the center of expansion because it sees all the other raisins going away from it.

 

But actually there is no center---all the raisins are getting farther and farther from each other UNIFORMLY.

 

and there is the balloon analogy. people always return to it.

 

Anyway, no, there is no point in our space that we could trace the expansion back to.

 

If we are not obsessively self-centered we can project our imagination to how it would look from some other galaxy and it looks just the same. they see us and everybody else spreading out from them.

 

there is no lop-sidedness or asymmetry in the expansion that could be used to deduce a preferred direction that it might be coming from.

 

and if the expansion HAD a center in our space, that would screw up the Friedmann equation. General Relativity would have broken and we would need a new theory of gravity.

Fortunately the data does not fit your idea, it fits the usual Friedmann equation model.

 

What you have is a VERBAL idea (an expansion must have a center) induced by the words that popularizers have used to convey the mathematical model. Verbalizing always misrepresents models to some extent and runs the risk of introducing confusion.

 

An extremely leftbrain or verbal person might (I suppose) be permanently unable to let go of the verbal misconception and get the correct picture. But I never saw a case of that. Everybody eventually gets it. Expansion needs no center. You will see it, just give yourself time.

 

Have you read the Scientific American article I gave links to? It is called Misconceptions about the Big Bang. It has good pictures in the sidebars and deals with a number of common misconceptions. Check it out. Great article!

[Realitycheck]

I think the problem is that most of my case is using logic where yours uses hard data, etc. I am not sure how to reconcile the two, because the rising bread dough fits in just fine with my logic and nothing has changed.

 

It says here that we have identified "200,000 extended optical sources, which are galaxies, star clusters, nebulae of all descriptions, or quasistellar objects. Even this number is dwarfed by the total number, running into the hundreds of millions or billions, that can be photographed with modern telescopes." Obvioiusly, we cannot see the galaxies on the other side of the universe because they are too far away. However, it seems like we should be able to triangulate the movement of many of these nonlocal galaxies back towards a focal point of the BB. We can triangulate the movement of stars and the Andromeda galaxy already, right?

[losfomot]

I think the problem is that most of my case is using logic where yours uses hard data, etc. I am not sure how to reconcile the two, because the rising bread dough fits in just fine with my logic and nothing has changed.

 

the 'infinitely large' rising raisin bread dough fits in just fine with your logic?

 

Pick a raisin... from that raisin's point of view, what center are all the other raisins moving away from?

[Edtharan]

I think the problem is that most of my case is using logic where yours uses hard data, etc. I am not sure how to reconcile the two, because the rising bread dough fits in just fine with my logic and nothing has changed.

Flawless logic, based on incorrect data will give you a wrong answer.

 

The aincent greeks used to think that they could answer any question about the nature of the world (Universe) simply by using logic and without resorting to actual observations. They invented what we call logic, and their logic was very good. But, to put it simply: They got a lot of things wrong .

 

Take arrows and tortises. By the time an arrow has move half the distance to the tortise, the tortise will have moved on a bit. Then the arrow covers half that distance left, and the tortise moves on a bit more. If you keep breaking the distance to the tortise in hlaf, then the tortise will have alwaysed moved on a bit more which menas that arrow can never hit the tortise .

 

But observation says otherwise. We have flawless logic, but observation disagrees. Actually, there is a branch of logic that can give us an answer that matches observation it is called Calculus.

 

So, the lesson here is, no matter how flawless you logic is, if it dissagrees with observation, then the logic is wrong and can usually be attributed to incorrect assumptions or application of the logic.

 

Oh, and sorry to hear about your shoulder injury. I also have a shoulder injury so I can sympathise with you about how disruptive they can be to your life. Mine was a pretty bad injury (I dislocated it in the worst way possible, the shoulder was under strain and the muscles were tightened) and I now have permenent damage (it partially dislocates - subluxes - several times a day dispite having 6 opperations on it).

 

I hope yours gets better soon.