Ask Gugel Anything About the Big Bang

[Bill Haywood]

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the Big Bang did not start from a tiny point.

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So expansion was not propelled by anything like an explosion? It's all inflation of space? How about now -- are galaxies "moving" away from each other with velocity, or is it that more space is being created between us? And how in the hell do we tell the difference?

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the observable universe extends about 47 billion light years in each direction, due to the metric expansion of space. This is basic cosmology.

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That's mighty obscure information to get all condescending about. The division of Korea was created in 1945 when junior US and Soviet officers picked a line on a map to define their occupation zones. This is basic history, didnja know?.

Nerd slugfest.

[Ohgod]

I agree it is slightly subtle - on the other hand, it IS basic information for someone setting themselves up as any kind of 'authority' on matters cosmological

[Bill Haywood]

Okay, new question about whether there is a center point to the universe. I understand the idea that space itself expands. The universe itself may be endless, but what about the matter originating in the BB? None if it is more than 14 billion or 47 billion apart. Or I guess that would be actually 94 BLY apart, if it's 47 in each direction. So within the infinite, shapeless universe, isn't there an expanding globe of stuff -- our observable universe -- that has a center point? If the universe is 94 billion LY wide, can't 47 BLY in from the frontier be considered a center point? And where in the sky would it be?


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I agree it is slightly subtle - on the other hand, it IS basic information for someone setting themselves up as any kind of 'authority' on matters cosmological

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He understands that. The critics are just pouncing on something ambiguous, inadequately explained prose. It would be much more adult to say "Don't you mean 47 BLY?" rather than "gotcha, you wrong, wrong, wrong, bow before my superior intellect for all the world to see."

[Ohgod]

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Okay, new question about whether there is a center point to the universe. I understand the idea that space itself expands. The universe itself may be endless, but what about the matter originating in the BB? None if it is more than 14 billion or 47 billion apart.

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I dont't think this is 'knowable' - nothing more than 47 BLY from us can have emitted light that has reached us, so it cannot affect us or be observed by us in any way. Thus, we are at the centre of our own obsevable universe. Similarly, another galaxy that we can see is at the centre of its own observable universe, which overlaps ours but is not identical to it. So there is nothing particularly special about the 'centre of the observable universe'.

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Or I guess that would be actually 94 BLY apart, if it's 47 in each direction. So within the infinite, shapeless universe, isn't there an expanding globe of stuff -- our observable universe -- that has a center point? If the universe is 94 billion LY wide, can't 47 BLY in from the frontier be considered a center point? And where in the sky would it be?

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Here. But that's not really surprising, and would also be true anywhere else.

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I agree it is slightly subtle - on the other hand, it IS basic information for someone setting themselves up as any kind of 'authority' on matters cosmological

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He understands that. The critics are just pouncing on something ambiguous, inadequately explained prose. It would be much more adult to say "Don't you mean 47 BLY?" rather than "gotcha, you wrong, wrong, wrong, bow before my superior intellect for all the world to see."

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On the other hand, it's not a minor matter. It is an easy slip to make, but it could also indicate that the OP has some fundamental misconceptions. Further discussion should help to indicate which. Similarly, if I have made any mistakes (since I am definitely not a specialist in the field), I welcome corrections.

[Arp220]

[ QUOTE ]
Okay, new question about whether there is a center point to the universe. I understand the idea that space itself expands. The universe itself may be endless, but what about the matter originating in the BB? None if it is more than 14 billion or 47 billion apart. Or I guess that would be actually 94 BLY apart, if it's 47 in each direction. So within the infinite, shapeless universe, isn't there an expanding globe of stuff -- our observable universe -- that has a center point? If the universe is 94 billion LY wide, can't 47 BLY in from the frontier be considered a center point? And where in the sky would it be?


[ QUOTE ]
I agree it is slightly subtle - on the other hand, it IS basic information for someone setting themselves up as any kind of 'authority' on matters cosmological

[/ QUOTE ]

He understands that. The critics are just pouncing on something ambiguous, inadequately explained prose. It would be much more adult to say "Don't you mean 47 BLY?" rather than "gotcha, you wrong, wrong, wrong, bow before my superior intellect for all the world to see."

[/ QUOTE ]

Ok:

The 'comoving radial distance' is about 47 billion light years. Now, from this we can infer that there exist (say) two galaxies that are 94Glyr apart, but those two galaxies cannot see each other. We can see both of them though.

This alludes to this 'center of the universe' stuff. Its often stated that the universe has no center, but this is not exactly true. For all practical purposes, *we* are at the center of the universe, because we see everything expanding away from us in all directions. Now, its also true that, if we were to go live in another galaxy far far away, we would also see everything expanding away from us. In other words, wherever we are, we are at the center of the universe!

This sounds a touch egotistical, but in fact what its saying is that we are at the center of the *observable* universe. Which makes much more sense.

As to whether the universe has an absolute center - well, its rather a moot question, because, unless we work out a way to look beyond the particle horizon, its almost impossible to answer. We have no observed evidence for an absolute 'center', therefore we can say there is no center. Of course, if evidence comes along to contradict this then things will change.

There is however an observable absolute 'rest-frame' for the universe. If we look at the cosmic microwave background, we see that it is marginally hotter in one direction. This is called the 'dipole anisotropy', and is caused by our movement relative to the CMB.

As for Gugel - I applaud his efforts, but the fact remains that he said something demonstrably incorrect. It wasnt in the least bit ambiguous.

[Bill Haywood]

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we are at the center of the *observable* universe.

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Okay, keep helping me through this conceptual block I'm having.

Posit an observer way out there, say 200 BLY from our universe neighborhood. And let's ignore the complication that it takes awhile for our light to reach the observer.

The observer looks, and sees odd happenings over there -- an expanding bunch of hot specks.

From a god's eye point of view, isn't our observable universe an expanding globe? What am I missing?

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As for Gugel - I applaud his efforts, but the fact remains that he said something demonstrably incorrect. It wasnt in the least bit ambiguous.

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Okay fine, but his critics shouldn't be diccks about correcting him.

[Arp220]

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we are at the center of the *observable* universe.

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Okay, keep helping me through this conceptual block I'm having.

Posit an observer way out there, say 200 BLY from our universe neighborhood. And let's ignore the complication that it takes awhile for our light to reach the observer.

The observer looks, and sees odd happenings over there -- an expanding bunch of hot specks.

From a god's eye point of view, isn't our observable universe an expanding globe? What am I missing?


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Youre not necessarily missing anything [img]/images/graemlins/wink.gif[/img]

We, unfortunately, do not have a 'gods eye' point of view. If we did we might see many things.

Heres an example:

One way to visualize the expansion of the universe is to take a balloon, paint lots of tiny specks on the balloon, and then gradually blow it up. If you, as 'god', look at the balloon, you see all the points expanding away from each other. You see a 3 dimensional object (the balloon) expanding into a 3 dimensional space (the room youre in).

Ok, now lets change our point of view. The surface of the balloon, with all the galaxies on it, is effectively a two dimensional object (lets ignore the thickness of the balloon for now) that is 'curved' in a three dimensional space. So, now imagine you are a TWO dimensional resident of one of those little dots on the balloons surface. You look at all the other dots, expanding away from you in all directions. From your point of view, you are at the center of the observable universe, but you cannot identify an 'absolute' point from which everything is expanding away. Because, if you went and lived in another dot, you'd see everything expanding away from that dot.

Many people see this example and conclude that the expansion is simple - we are three dimensional, but the universe is expanding 'into' a fourth spatial dimension. This is however not accurate. If this was the case we would see some very clear indicators from particle physics, but we do not.

So, the ultimate answer to your question is that nobody really understands the fundamentals behind the expansion of the universe. We see that it is expanding. We see that it is not expanding into a bigger volume. We have evidence that the expansion is not due to a simple increase in the number of spatial dimensions.

So we're still trying to find out what exactly is going on.

[2OuterJitsu]

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Many people see this example and conclude that the expansion is simple - we are three dimensional, but the universe is expanding 'into' a fourth spatial dimension. This is however not accurate. If this was the case we would see some very clear indicators from particle physics, but we do not.

...We have evidence that the expansion is not due to a simple increase in the number of spatial dimensions.


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Could you expand on the quoted? I keep hearing/reading this, but never much more. Explain the both the indicators that would suggest expansion into another spatial dimension, and the evidence that the universe isn’t expanding into another spatial dimension.