If Looking Into Space is Like Looking Back in Time, Why is it the Same in Every Direction?

Question

After seeing the James Webb space picture, in which a tiny sliver of the sky the size of a piece of rice from our perspective here on Earth was examined and revealed contain, as expected, an abundance of galaxies and stars, I am wondering how this confirmation coincides with the Big Bang theory and the concept that Earth is in a non-privileged location in the Universe.

A common line NASA uses regarding the Webb telescope is that "looking into space is like looking back in time", which is true, for it take time for light from those distant objects to reach us. So, by examining far enough into a region of space, we are able to "wind back the clock" to see early galaxies now long dead and some of the earliest stars in the history of the Universe. What seems odd to me is that we see the same things at roughly the same distance from every direction in space.

If Earth was located in an unprivileged spot, anywhere but the center of the Universe, then some of the space around us should go "farther back" than others.

I understand that we are limited in the amount of light we are able to see. An apt comparison would be that we are in a sort of bubble isolated from the rest of the Universe and can only a uniform distance back in all directions. But this doesn't explain why each direction contains roughly the same timeline of events. We can see back a uniform distance, but the fact that this uniform distance seems to reveal the same information in all direction is confusing to me.

It won't do just to say the Universe had no "point" in which is started - the BB should be thought of as a sort of circle, the center of which all events spread uniformly from. We are just one event way off in a region of that circle necessarily closer to some part of the circumference than others, since our galaxy did not exist at the beginning of the Universe. So, we should be able to look one way and see nothing beyond galaxies roughly our own age and no early stars, and look the exact other way and see a much richer history, with more early stars and galaxies layered atop one another. But this is not the case - we see the same "density" of events from all directions. Unless, in some way, we are also seeing future events in some direction? Not sure how that would work.

Answer 1

If Earth was located in an unprivileged spot, anywhere but the center of the Universe, then some of the space around us should go "farther back" than others.

This is not the case, at least not if cosmologists have anywhere close to the correct concept of the universe. It is far better to view the big bang as an explosion of space rather than an explosion in space.

What this means is that regardless of location in space, all of space appears to be expanding centralized on that location. What we see from Earth is distant galaxies retreating from us, regardless of direction. What some alien species in a galaxy far far away sees is that all galaxies that are distant to them are retreating from them, regardless of direction.

Answer 2

Assuming, as you seem to do, that there is an edge of the universe, what if we were very far from the edge, so that the part we can observe (the observable universe) is a very small circle inside the big circle of the universe? Do you agree that in that case we would see the same amount of history in every direction?

This is a semplification, of course. The universe is not a circle, it doesn't have an edge. A better shape to imagine the universe is the surface of a ball. If the universe were an expanding ball and we and all the galaxies were on its surface. Then, wherever you stand on the ball, wherever you look, you see the same amount of history, in the same way that a person standing on the surface of Earth sees the same amount of land/sea in every direction.

Answer 3

The simplest model of the universe is that it is infinite in space. If that is true, then, any direction you look, you see all the way back in time to what is essentially the end of the big bang, redshifted down to the 3 degree background radiation. There is not "less to see" in one direction than another, because there is no distance in any direction where galaxies start to peter out. The limit in how far you can see is just how much time there has been for light to get here.

And somebody billions of light years away would have the same experience. No matter which direction they looked, they would see all the way back to the tail end of the big bang and no further.

I think it is conceivable that space is infinite, but only a finite bubble has matter. But, if that is true, the bubble would have to be much bigger than our observable universe. So, again, no reason to think we are at the center. The part of the universe with galaxies could be trillions of light years across. So our multi-billion-light-year bubble could be anywhere and you wouldn't notice any difference in the direction you looked, unless we were right near the "edge". But most scientists think the inifinite-galaxies model is theoretically better.

Another possibility is that the universe wraps back on itself on large enough scales. Once again, there would be no center in that case. It could be like the old computer game of Asteroids, where, if you went off one edge of the screen, you came back on the other. In that game, the screen has a center, but the playing area really doesn't.

Answer 4

Perhaps in the part we are detecting/viewing, the matter of scale means that in our viewing area the rate of change has been so small that we cannot detect any difference, and also statistically the variations in the matter are within the range of probability. To see a difference we probably need to see more than we will ever see. Remember there is considerable amount of universe outside our observable zone.

Answer 5

the BB should be thought of as a sort of circle, the center of which all events spread uniformly from.

Yes, correct. the Bang is at the center and space expands into future time:

We can't rotate our cam and look at the Bang since the rotation angle is a complex number. This is because the spatial distance to anything in the past is a negative number, according to the Einstein spacetime metric:

To get the absolute (Lorentz-invariant) distance between 2 events, you SUBTRACT the elapsed time between them.

The absolute distance is called an "interval." It's the unit of length in Lorentzian geometry, and it can be zero or negative.

You can see why the galaxies must get further apart:

What is the universe expanding into?

It's expanding into the future, which is just another direction. It expands into the future just by continuing to exist.

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You can validate this by noticing that the radius expands at c. This means that the circumference -- the universe -- expands at 2 pi times c. It is trivial to show that every year, the megaparsec's share of that 6.3 new light years of space is 71 km/s/Mpc. The generally-accepted value.