The universe was smaller and more dense in the past. Why we can see the oldest galaxies in the world when we look at the outskirts then?

Question

I just can’t wrap my mind around this. Can we see them anywhere? Why, if the universe was smaller? Or is there like one place in space where the aftermath big bang happened (I know there was no space at the time and big bang kinda went everywhere ofc) and we are pointing our telescopes at it?

Using human logic we should see the youngest galaxies (as their images in the past) far away and just won’t be able to spot the elders.

In: 25

Answer 1

Okay here’s a mind bender for you — the Big Bang did not happen at a point in space, it happened to space itself. Which is very confusing but let’s look at it another way:

*Every* line of sight looking away from the earth is looking back in time toward the Big Bang, no matter which direction you’re looking. It’s weird but it *has* to be true, because every photon also emerged from the Big Bang — so if we can see it, it came from the same place. If you traced any two rays of light that reach our eyes (or telescopes) backwards along their timeline, they will get closer together than they are now, because the universe was smaller. If the Big Bang itself actually happened at a singular point (this is a huge “if” by the way), then those two rays would *have* to converge at that point at the moment of the Big Bang, because there is nowhere else for them to *be.* But we could (theoretically) see that single point no matter which direction we looked, as long as we looked far enough back — it would be stretched out across the entire night sky, like the inside of a sphere surrounding our observable universe.

So from our perspective, the past smaller, denser universe is not in a specific region of space that we have to look toward. That earlier state of the universe *surrounds us* like a shell. No matter where we look, if we look far enough away, we see younger stars and galaxies that are clustered together more closely than the older stars and galaxies closer to us. The furthest away we can see, the first light emitted by the universe, is the Cosmic Microwave Background radiation, which shows a picture of a universe so dense that it basically looks like the inside of a star. The fluctuations in temperature are about one part in a thousand. At the time the CMB was emitted, the observable universe was only about 100 million light years across, but from our perspective the CMB appears to create a sphere around us that is ~80 *billion* light years across, due to the expansion of the universe since then.