If I built a personal spaceship, launched myself into space and pressed a magic button which would bring me to absolute zero motion relative to the center point of the universe, what would I see? Would the Earth, Moon, Sun and, for that matter, the Solar System go wildly spinning away? Would the stars of the Milky Way rotate as it moved away from me on its journey out from the center (Big Bang)?
As best as we can tell, there is no center of the universe, and there’s no such thing as absolute zero motion relative to something which doesn’t exist.
Could one assume that the site of big bang is the center?
'Fraid not. The big bang didn’t happen at any particular point in space, since space itself did not exist prior to the big bang.
When the universe began, space was created and spread as the matter and energy it contained was also created and spread. There is no point in space where that happened.
Here’s my favorite metaphor for this: Think of a balloon that is filling up with air. If the surface of the balloon was thought of as space (just the surface, mind you), hypothetical two-dimensional astronomers, using telescopes that view the light which also stays in the surface, would see all the objects in their universe expanding away from them. They might hypothesize a time when the balloon had not yet been filled with air. But the center of the balloon is not a place in their universe! It doesn’t lie on the surface. So you can have a finite, expanding universe without having edges or a center.
But, back to your OP, you could choose to be stationary relative to anything you wanted. If that point of reference was moving relative to the Solar System, they would now appear to move relative to you.
Thanks for the balloon analogy. That makes better sense. I’ve always viewed the universe as an expanding spherical shaped place made up of galaxies racing outward from a center point.
So from any single point (coordinate) in the universe, all other points (coordinates) appear to be expanding away from it as if one were to draw graph lines on the expanding balloon, right?
Although every point can be considered the center of the universe, it’s still possible to measure whether we’re moving with respect to the big bang. If we were to get in a spaceship and head out in a particular direction at a significant speed (like 0.1c), the thermal noise would be blue-shifted (warmer) in front of us and red-shifted (even colder) behind us. So sitting still is when the background radiation is the same temperature* all around.
Right now, our galaxy is heading towards the Great Attractor at something like a million mph.
- All bodies radiate energy based on their temperature. It’s common with very low levels of radio energy to state it in terms of how warm something would need to be to radiate that amount. The background radiation left over from the big bang is equal to what something gives off when it’s at a temp of about 4 K, or -269 C.
That would be one interpretation!
This is cool. The OP reminds me of Zeno’s arrow paradox. Stop the Universe. What property of Duck Hook, or any other thing, will allow everything to continue when you restart it?
From Saltire:
While the balloon metaphor helped me to comprehend expansion, it does little to explain the universe as a 3 dimensional area.
If I assume the universe to be finite, could I not also assume that, if traveling in a straight line at a speed (for argument’s sake) faster than all other objects in the universe, there must be point on the “edge of expansion” where I would not see stars and galaxies in every direction? Otherwise, I would (like the old Asteroids video game) fly off the screen and back on the other side, eventually returning to my starting point.
There is no “edge of expansion”. What is expanding is all of space. To understand the balloon analogy you must think of yourself as 2D. The surface of the balloon is the whole universe. The center of expansion is “outside” the universe. (I put outside in quotes because we can’t assume there is anything outside.) To extend to 3D you have to imagine a 4D sphere with the 3D universe being the hyper-surface. If you went far enough you would return back to your starting point. (That is, if you ignore the fact that such a trip would take longer than the age of the universe even if you travelled at the speed of light.) The topology of Asteroids, BTW is that of a torus not a sphere.