# Does the expanding Universe have a knowable center?

1. Mar 21, 2014

### gymjim

Since the speed of light is a constant, no matter what location from which a search of the universe is made, matter would appear to be accelerating in the expansion in the same way to the observer. It is understood that about 14 billion years ago the expansion started. From any vantage point, the universe would appear to have started the 14 billion years ago, and the size of the universe would appear to be the same. If the universe is appears expanding in the same way from any point in the universe, the center of the universe than is unknowable.

2. Mar 21, 2014

### dauto

It is unknowable and most likely doesn't exist. Not everything has a center and the Universe probably doesn't.

3. Mar 21, 2014

### ChrisVer

probably you cannot define a center, because there was never such a thing as a "center"...

4. Mar 21, 2014

### Staff: Mentor

The latter part is true, but it's not because the speed of light is constant; it's because the universe happens to be expanding in that particular way. It's perfectly possible to come up with other valid solutions to the Einstein Field Equations with different expansion properties, and the speed of light will still be constant in all those solutions.

True. (More precisely, it's true for "comoving" observers, observers who see the universe as homogeneous and isotropic. We here on Earth are not exactly "comoving" observers, but we're close enough to it for most purposes. But, for example, someone flying by Earth at nearly the speed of light would see the universe as highly non-isotropic, and would *not* assign the same age or size to the universe as we do.)

No; the "center of the universe" is a meaningless concept, not unknowable.

5. Mar 21, 2014

### bcrowell

Staff Emeritus
We have a FAQ on this: https://www.physicsforums.com/showthread.php?t=506991 [Broken]

Last edited by a moderator: May 6, 2017
6. Mar 21, 2014

### PAllen

There is a center of the universe per Sydney Coleman's "egocentric coordinate systems". Each sufficiently egocentric researcher defines themselves as the center of the universe.