…according to light.
The speed of light is the universal speed limit. This is because as you approach the speed of light, your local time slows down. Reach the speed of light and your local time stops. Your time can’t get any slower than stopped, so you can’t go any faster than the speed of light.
This means that from the point of view of light, getting from point A to point B is instantaneous. This is because since your time is stopped, everything takes 0 seconds to complete.
Example: You are a particle of light (photon) that just got emitted from the sun. Then you collide with the earth. Because your time is stopped (you’re light remember?), it took 0 seconds to get from the sun to the earth from your point of view. However, from the earth and the sun’s point of view, it took you 8 minutes because to them you are not ‘instant’, you travel at the speed of light. So basically the faster you go, the more time contracts. Since time and space are anchored to each other, all space contacts as well. So, as a photon traveling at the speed of light, the whole universe looks to be contracted to one infinitely small point.
My point is, from the point of view of light, the big bang hasn’t happened yet.
Also, another question that has plagued scientists is how the universe was at such a low level of entropy before the big bang. If the universe was 0 dimensional, then EVERYTHING existed at the point 1,1,1,1 since only 1 position of every dimension is possible in a 0 dimensional universe. Everything existing at one place at one time is the lowest entropy can every get.
So 3 (space) + 1 (time) dimensions are actually a property of things with mass, not a property of the universe.