I’ve always accepted the Big Bang as plausible, but recently I read that when astronomers study stars deeper and deeper in space, they do not find stars “crunched” more and more together…as one would expect when looking back at the evidence of an explosion. Is this true? And, if so, how do astronomers explain this paradox?
You might start off by providing a cite
A) The Big Bang wasn’t an “explosion”, it was an inflation of space containing the energy from the singularity that condensed into the forms of matter and energy that we see today
B) When astronomers look at the objects fartherest away–those from which light has spent the longest time travelling–they see objects with behavior and composition consistent with the early universe as predicted by the theory
C) When astronomers look “deeply” into space, i.e. at the Cosmic Microwave Background, they see a highly isotropic distribution of radiation consistent with early inflation just after the universe became transparent
D) What paradox, exactly?
Stranger
One of the big misconceptions that people have about the Big Bang is that they think of all of the matter in the universe squished down into a single point, that then explodes into an already existing but empty 3-D space.
That is incorrect.
Space itself is expanding. If you were to magically stick a flag at some point in space, and it would stay there and never move, and then you could magically stick another flag some distance away from that, and again that second flag also never moves, the two flags will move apart from each other, even though they aren’t moving. What is happening is that space itself is spreading out.
Every piece of space is moving away from every other piece of space. If you rewind that, then every piece of space gets closer to every other piece of space until it all collapses down into a single point. Play it forward from that point, and it’s kinda like an explosion of both space and matter, a really big bang.
People like to use the balloon analogy, but that often ends up confusing people, because a balloon is a 3-D sphere. But imagine that you only have two dimensions, like a piece of paper. If you draw two dots on that piece of paper, then you can imagine traveling from one dot to another. Simple. But the universe isn’t like that piece of paper scaled up to have 3 dimensions. Instead, it’s like the surface of a balloon. Now this balloon only exists in two dimensions, so you can draw two dots on its surface, and you can imagine traveling from one dot to another, but you don’t ever go up off of the surface of the balloon, because we’re only talking about 2 dimensions here, like your piece of paper. Now you inflate the balloon, and those two dots you drew are farther apart, but they didn’t move. They are still on the same points on the surface of the balloon.
That is what the universe is like, only it has 3 dimensions instead of 2.
There was no explosion at any point in space. If you draw dots all over your balloon, as you shrink the balloon smaller and smaller, all of the dots start touching, and soon they are all smooshed together into one big dot. Now as you go forward in time, you inflate the balloon, and all of these dots spread out farther and farther apart. Which dot on the balloon is the one where the expansion started from? There isn’t any one dot. The expansion started with all of the dots together, so pick any dot, and every other dot moved away from it. Pick any other dot, and it’s the same thing. All of the dots moved away from each other. There is no central dot on the surface of the balloon.
All of your dots are roughly uniformly placed around the surface of the balloon, and as we look into space, matter is roughly uniformly distributed through the universe. It’s not perfectly smooth like the surface of a balloon is. Instead it is kinda lumpy and clumpy, but then we’re talking about individual chunks of stuff that stick to each other through gravity, and not inflating latex. Even though it is a bit lumpy and clumpy, it is still mostly evenly distributed. There’s no crunching, and at this point no one expects to find crunching.
The expansions of space itself is conceptually a bit difficult to wrap your head around, but once you get it, you’ll understand why the Big Bang wasn’t really an explosion in the conventional sense. It’s just that an explosion is kinda the closest thing that describes it.
Probably worth adding:
When astronomers look back into deep space with telescopes, they can only see so far - and within the limits of the instruments we currently have, that doesn’t get us anywhere near far enough back in time to see the universe in a state before galaxies had already formed. However when they do look back that far, what they see is a universe that isn’t the same as ours, and as Stranger On A Train points out - it is consistent with what we would expect it to look like at that time, assuming things started at the big bang.
As we get better and better instruments, we can see further back, the most important new instrument on the agenda is the James Webb Telescope. This is the notional successor to the Hubble Space Telescope as the world’s pre-eminent telescope, and its ability to see dimmer things, and further into the infra-red, means it will see further back in time than anything we have so far. No-one expects it to be able to see back to pre-galaxy time, but it will see more early galaxies, and these galaxies are expected to have significantly different properties to more modern ones. For instance early galaxies have not had enough time to have stars go though multiple generations, and so the relative abundance of the elements is significantly different. These sorts of results are so far all consistent with our understanding of the big-bang theory.
But one thing we can see that is very very old is the cosmic background radiation. That is because it is everywhere in the universe in equal amounts. No matter where you are, it is there. Looking at it is an after-image of the state of the universe at a very early time - before much of anything had started to assemble. Again, what we see is consistent with what we expect to see given our current understanding of the big-bang physics.
While we’re at it, the distances between stars are incomprehensibly larger than the stars themselves. You would need a truly absurd amount of contraction before stars would be “crushed together”. And while we were at that level of compression at some point very early in the Universe’s history, that was a time long before any stars had formed.