I mean if I drop a rock into a lake, its makes circles and the outermost circles are the oldest. Or if I blow something up, the furthest debris is the oldest.
In: Physics
The Big Bang IS the whole universe. Can’t have a center of something that is everything all at once at the same time.
Despite the name, the Big Bang wasn’t an explosion: it was the start of a cooling-off process. It began at a point, but that point wasn’t the center of the universe: at that moment, the point was the *whole* universe. Space has been expanding ever since, but every point in the universe now was a part of that point back then, and still bears some of the residual energy from having *been* at that point. That’s why we can’t find a center: as far back as we can look, every point looks basically the same.
You’ve seen plenty of anecdotes — here is the one I use. Imagine a bag of popcorn in the microwave. the moment before the kernels start popping is before the big bang, and the popped kernels are post big bang.
Lots of wrong or incomplete answers here, understandably, because this is a complicated question. It’s easy to get caught up in the difficult physics but this question is reducible to a problem of geometry. When presented right, you can all but ignore the physics.
This is an open question with three possibilities and one of them must be true, including the possibility of a universe with a well defined center.
Scenario 1: The universe is infinite in size and has no boundary. In geometry you must have a boundary to have a center. Imagine that I ask you to find the center of a circle but tell you that the radius is infinite. Without a boundary no concept of a center can exist. There is currently no compelling evidence to say that the universe is *not* infinite in size. The limit of the observable universe may prevent ever falsifying scenario 1.
Scenario 2: The geometry of the universe is non-Euclidean. An analogy here would be if I asked you to find the center of the surface of the earth. While you can find the center of the earth, no concept of the center of the surface of the earth exists. People give hand-wavy explanations of this analogy with “higher dimensional” nonsense. If the universe is non-Euclidean then it follows the rules of non-Euclidean geometry. If the universe has a boundary but the geometry of the universe is not “flat,” then similar to the surface of the earth analogy it would make no sense to talk of a center of the universe. Again the limit of the observable universe rears it’s head. If the universe is finite and bounded but sufficiently large, even a closed or open universe would appear flat as far as the very limits of observation can tell. This scenario may also never be falsified.
Scenario 3: The geometry of universe is flat and the universe has a boundary. In this scenario there is a center. That’s an inevitable consequence of geometry. Yet again the size of the universe poses a problem. In this scenario, in order to know that there is a boundary and center, you need to be able to observe part of the boundary or at least effects of the boundary. Imagine being inside of a beach ball but being able to see only 1cm away. If you are near the edge of the beach ball you can deduce that you are in a boundary and determine exactly where the center is. If you are not near the edge you have no way of knowing if there is a boundary and thus no way of knowing that there must be a center. From all possible places you could be in that beach ball, most positions will not allow you to answer this question. If this scenario is true, it appears that we are not in a position to be able to observe part of the boundary and thus calculate where the center is.
The ultimate answer is unsatisfying. There may or may not be a center of the universe and even if there is (or isn’t!) we may not ever have any way to know.
There is. It’s earth. At least as long as you’re on it. So I’m reality the sun is circling the earth from our pow
The responses you got so far are spot on and explain the subtle details of an expansion of the universe without a center with many examples.
I would like to add an explanation that is visual and has helped me to really understand what is going on:
[https://www.vttoth.com/CMS/physics-notes/359-why-cosmic-expansion-has-no-center](https://www.vttoth.com/CMS/physics-notes/359-why-cosmic-expansion-has-no-center)
Here you just have to align a picture with its “expanded” version and see for yourself that, whatever you do, it will seem like the expansion is moving outward of the center that you choose.
Imagine that the entire universe and everything in it existed in a single point. Consider that, even though infinitely small in dimension, there is still the capability for space to exist within. We didn’t know for sure what space was like back then but for the sake of my explanation, assume that the entire universe was 1000 astronomical units from one end to another. In this hypothetical situation, if a big bang did occur, the length of each astronomical unit itself would literally begin to expand. Not like if all of humanity arbitrarily decided that a meter would now be considered to be the length of a mile, I mean that every bit of space would essentially extend in all directions, literally growing.
I like to think that the universe was and will always remain infinite in dimension. That, in a sense, the universe was always the same size, but rather than 1000 astronomical units, its infinite astronomical units. So considering that, if every point in an infinite space is growing, how could there be a center of infinity? There is none.
Because the big bang was not an explosion of matter into an empty space. The name is pretty misleading.
The big bang was space itself expanding.
And that’s really damn hard to wrap our brains around. Human brains evolved to work here in Middle World where a kilometer is a long distance, a centimeter is a short distance, a second is a short time and a year is a long time. We don’t deal well with stuff that’s murch removed from that.
But space and time were all there in the beginning, just squeezed really darn tight.
Space expands everywhere, so anywhere you stand you see infinity stretching out, and space expanding out around you. We feel that we’re at the center of the universe because EVERYTHING is at the center of the universe. Or because center is a null concept when we’re talking about universes, take your pick.
Dropping a rock in a pond does create ripples moving outwards, but this is more like dropping the whole pond. At once. Perfectly flat.
There is no centre to the ripples because the whole pond arrived at once. So instead we get the little bits of wishy washy movement left over, but there’s structured order to it beyond “this was caused by dropping a giant sheet of water all at once”.
Me: Does a bubble have a center?
Kid: Yeah, the very middle. The inside.
Me: That’s correct. Do you think the surface of the bubble has a center?
Kid: I don’t understand.
Me: Can you take a pen, and draw a dot on the surface that is the center of that bubble?
Kid: No, that’s silly.
Me: You’re right. The idea is silly. But what if we shrink the bubble?
Kid: It gets smaller.
Me: What if we shank it down to the center of the entire bubble?
Kid: Then there’s no bubble. There’s no more surface.
Me: That’s true. But from another perspective, every single point on the surface of the bubble is now at the center.
Kid: But there is no surface.
Me: You’re right. There is nothing there. The big bang is like that. From an infinitely tiny point, the entire surface of the bubble appeared.
Looking at the universe, every single point. Every up and down, left and right, and side to side. If we went backwards in time, all of it would squish and squish until it all landed on the center. *Everywhere* was at the center, and *everywhere* spread out and away from the center.
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