If I understand the big bang theory correctly our whole universe was in a hot dense state. And then suddenly, rapid expansion happened where everything expanded outwards presumably from the singularity. We know for a fact that the universe is expaning and has been expanding since it began. So, theoretically if we go backwards in time things were closer together. The more further back we go, the more closer together things were. We should eventually reach a point where everything was one, or where everything was none (depending on how you look at it). This point should be the center of the universe since everything expanded from it. But after doing a bit of research I have discovered that there is no center to the universe. Please explain to me how this is possible.
Thank you!
In: Physics
As you say the centre of the universe was where it started and expanded from. All points of the universe fit this description so everywhere is the centre or alternatively nowhere is.
You are correct your thought process but you run into the “trap” a lot of people run into. You imagine the big bang as a single point where everything started like a bomb. This isnt true, the big bang happend everywhere, everywhere was just much closer together and thus matter was also much denser but the universe still was infinite. This is confusing because most people think that something that is infinite cant become bigger but it can.
To explain that it is much easier to go one dimension down and explain it in 2D.
Think about a 2D area like the surface of a balloon.
If we blow up the balloon the surface expanses.
Is there any point on this surface that could be called the center?
No from each point all other points move away if we blow up the balloon more.
Same we see with telescopes looking into the deep space.
Picture a super-stretchy rubber sheet that goes on and on in all directions forever – an infinite rubber sheet. There’s no center to the sheet – it’s infinitely large. Now imagine there are tiny dots everywhere on the sheet as close together as is possible to place such dots, really squeezed together so that you really can’t tell where one dot ends and another dot begins (but they are separate dots nonetheless). And now image that the sheet is stretched evenly right and left and forward and backward, it just keeps getting stretched and stretched and stretched. As it’s getting stretched, it doesn’t get any larger (it was infinite to begin with), but the dots are all getting stretched further and further apart. So the sheet is expanding, and everything on it is getting further and further away from everything else on the sheet, but there is no center of expansion – it’s expanding everywhere all at once. Bump that up to three dimensions and picture an infinite (and infinitely stretchy) block with dots crammed in everywhere. Stretch that up and down, right and left and forward and back. All the dots move away from all the other dots, yet there is no center. The expansion looks the same no matter where you are in that block.
The big bang was not an explosion of stuff moving out into space, it was an explosion of space itself carrying the stuff with it. Galaxies and galaxy clusters are gravitationally bound to each other, but every galaxy cluster is moving away from every other cluster.
If you blow up a balloon, every point on the surface of the balloon is moving away from every other point. A two dimensional person on the surface of the balloon would not be able to point to the center of the expansion, they would only know that *everything* is expanding. This is only an analogy, we don’t know if there are other spatial dimensions that we can’t comprehend, but it works well for getting the idea across.
think of a spong un-squishing equally after being squished. there was no 1 singularity, which is the only wrong thing in your post. all parts of space just started expanding together.
Some scientists believe that the universe is finite, but still does not have any “edges”, because of its geometry. If you “freeze” the universe to stop it from expanding, and then keep going in one direction for a very very long period of time, sooner or later you will end up in the same place where you started.
Imagine you have a one-dimensional movement freedom within a two-dimensional object (circle on a piece of paper). If you keep moving along the circle, you will end up at some point where you started. Now, imagine a two-dimensional movement across a three-dimensional object (moving on a surface of a sphere). If you keep moving in any direction, as long as it’s being constant, you will again end up in the same direction. The same goes for the universe, but You need to think of one additional dimension to put into the equation.
Now, let’s get back to the example of moving on a sphere. Assume the sphere keeps getting bigger and bigger (simulating the universe expanding). Regardless of the place you start from, all points of the sphere’s surface keep getting further and further from each other, which makes it seem like the place You started from is the center of the sphere’s surface. However, if you pick another spot on that surface, the same will be true.
The same principle applies to the universe, but instead of it being a two-dimensional surface, it’s a three-dimensional space.
If someone is able to explain it better, please do. I keep trying to wrap my head around this concept and am constantly looking for other ways to approach this.
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There’s a few fundamental traps that are hard to intuitively grasp about the big bang as a “starting point”.
1 – the big bang is everything, everywhere. It didn’t “happen and then now we’re after that”, we are currently experiencing it, the expansion of space is still happening, and that’s our primary evidence for its occurrence. “the big bang” describes the entirety of the *present* existence of the universe, not an event that kicked it off.
2 – The big bang is the start of *space* existing as we know it. Not just matter. This can be hard to intuit because we think of it as “all the matter was closer together in empty space, then moved away from each other, occupying different space”, which is only kind of true. But the big bang describes *space itself* expanding, meaning the objects didn’t necessarily “move into other space” (there wasn’t space to move into), but in many cases could be thought of as the *space between objects growing*, while the objects didn’t really move. This one is really hard to explain, and even harder to understand because it’s just entirely unintuitive and runs contrary to our thinking about every day scale and the movement of objects.
3 – In many current models of understanding, “spacetime” is one thing, and includes space and time dimensions. This is how relativity is modeled, why things “experience time differently” in gravity wells or at high speeds etc etc. What this *means*, is that the big bang is the starting point for *time* as well as matter and space. Effectively, as you “travel back toward the big bang”, and the universe gets more dense… the time distance to the “beginning” also increases. Time is weird and hard to really grasp (and hard to model), but ultimately what this means is that getting to “time = 0” at the big bang would take infinite amounts of time. I find it helpful to think of it like a mathematical graphic asymptote, where reaching T=0 is impossible, and things get infinite and unintuitive the closer you get.
It’s not that things are expanding into previously empty space. The space itself is expanding. Where did the Big Bang occur? Literally everywhere.
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