Can someone explain this (about the size/age of the universe)?

Question

From Wikipedia:

"The most precise estimate of the universe's age is 13.7±0.2 billion years old..."

and,

"...space itself appears to have expanded. This expansion accounts for how Earth-bound scientists can observe the light from a galaxy 40 billion light years away, even if that light has traveled for only 13.7 billion years; the very space between them has expanded. This expansion is consistent with the observation that the light from distant galaxies has been redshifted; the photons emitted have been stretched to longer wavelengths and lower frequency during their journey."

I always thought light was red-shifted because the source was moving away from us. If space itself is expanding, causing light waves to expand, then wouldn't our observational tool also expand, negating any observable difference? How do they know that space is expanding, rather than the object moving away? This is the first time I've seen this, can anyone clarify?

If the doppler-effect explanation is the right one, then how can the observable universe be 90 billion ly across and only 14 billion ly old?

Answer 1

We observe redshifted light because of the source's motion away from us, the curvature of the universe, and the universe's expansion during the photon's trip.

Yes, space itself is expanding, that's the whole point of the Big Bang. The BB was NOT an explosion that happened somewhere in space, creating an expanding sphere of "stuff" within space. That is not, and never has been, a theory of cosmology. The universe is filled with galaxies everywhere, and there is no void place into which the galaxies are streaming, and no expanding sphere of "stuff." The universe is filled with galaxies everywhere, but the space is expanding between them. The galaxies aren't really moving through space either; we observe them receding because the space between us and them is expanding.

This expansion is not going to affect you or your measuring equipment. The rate of expansion is the Hubble constant, 71 kilometers per second per Megaparsec. If you work that out, that's 4 parts in 10^17 per second. Not very much. Your measuring equipment doesn't even notice that. If you were to put your hands on the spectroscope and ever so gently pull on either side, that force would be billions of times greater than the stress on the spectroscope due to the universal expansion. But on universal scales, 4 parts in 10^17 generates a heck of a lot of new space every second. For instance, every second, ten kilometers or so are inserted between here and the Andromeda galaxy due to the expansion.

The difference between the universe being 13.7 billion years old and the most distant galaxies being 40 billion light years away is an effect of General Relativity. In GR, you can't really measure times or distances accurately outside of your local reference frame. The farther you try to measure, the less meaningful "distance" itself becomes. out at cosmological distances, there are many ways to measure distance, each of them valid, and each of them will yield different results because of the curvature of spacetime. The distant galaxies are 13.7 Gly away, as measured by light travel time, but in coordinate distance (which is what a Relativist means when he says "distance"), they are 40 Gly away. You would measure the coordinate distance to distant galaxy Z by first measuring the distance to nearby galaxy A (by any method you like; since it is nearby they all agree). Then add the distance from A to B (again, a short distance all methods agree on), then the distance from B to C, etc, until you get to Z. Again, this effect is due to curvature of the spacetime.

Answer 2

In an expanding universe, the red-shift for light is related to that expansion. For example, suppose that the universe has expanded by a factor of 2 since the light left its source. Then the red-shift factor will also be 2. It is technically incorrect to describe the red-shift from expansion as being due to the doppler effect, although for close galaxies, it is a good approximation.

So, no, the expansion of the detecting instruments is not relevant.

Answer 3

This is a very interesting question, Santa, and I don't think anyone has the absolute right answer. The way I see it is that the universe, as we know it, consists of time, space, matter, energy and the forces holding it together. There are maybe other things but we still don't know them. Now, I think it makes sense to say that the universe can't exist if you remove one of the items. Can space exist without time, or can matter exist without the strong atomic force? I think not.
Long before Hubble's discovery, Einstein was once asked if the universe was expanding or contracting. Einstein answered that he didn't know but one thing was certain: It wasn't stationary. Nothing is.
I think that time is the observable effect of the universe expansion. Space, time and everything else that is part of the universe, expands. It is hard to understand; as hard as to make a drawing of it. When we look at the sky, we see things in four dimensions: space and time. Anywhere you look, you look at the past. The popular vision of the Big Bang as an explosion in three dimensions is wrong. We simply have to admit that, as far as we can observe today, the expansion of time, space, matter, energy and forces, is the only explanation ... so far.

Answer 4

well yes there is a red shift from the light source moving away from us. however, dont think of it as space expanding, think more of space between objects expanding. and to clarify, the source of light is moving away from us and therefore by definition, expanding.
i think the problem is that you are confused about "the photons emitted have been stretched to longer wavelengths and lower frequency during their journey." but this isnt such a great way to think about it. you were right in the first place. the doppler effect is the same with sound. its just like when an ambulance drives by and the pitch changes.

Answer 5

what objects are 40 billion light years away? that seems contradictory. ~IF~ the universe is 13.7 billion years old and we know that it's expanding at a pace that is slower than the speed of light, how then could space have expanded to 40 billion light years in 13.7 billion years at sub-light speed?

Answer 6

yeah ofcourse the universe is expanding its for cent % sure,if an object is moving away it means that the place in which it is there is also expanding,no body knows that is our universe having any boundaries or not,the universe is colder this shows that its expanding!!!!!!!!
bye..........

Answer 7

that sound about right