If the universe is infinite in size, you don’t really need to worry about this conundrum. The universe, being all there is infinitely big and has no edge, so there’s no outside to even talk about.
In 1929, the American astronomer Edwin Hubble discovered that galaxies are flying away from each other like pieces of cosmic shrapnel in the aftermath of a titanic explosion.
So, in the history of the universe, we haven’t received light from every single galaxy. The current width of the observable universe is about 90 billion light-years.
Cosmologists aren’t sure if the universe is infinitely big or just extremely large. To measure the universe, astronomers instead look at its curvature. The geometric curve on large scales of the universe tells us about its overall shape.
“The universe is flat like an [endless] sheet of paper,” says Mather. “According to this, you could continue infinitely far in any direction and the universe would be just the same, more or less.” You’d never come to an edge of this flat universe; you’d only find more and more galaxies.
One reason involves the “cosmological principle,” said Robert McNees, an associate professor of physics at Loyola University Chicago. The cosmological principle states that the distribution of matter in any part of the universe looks roughly the same as in any other part, regardless what direction you look in; in scientists’ terms, the universe is isotropic.
Current observations and measurements of the curvature of the universe indicate that it is almost perfectly flat. You might think this means the universe is infinite. But it’s not that simple. Even in the case of a flat universe, the cosmos doesn’t have to be infinitely big.
One analogy often used to describe this edgeless universe is the surface of a balloon. An ant on such a surface can walk in any direction and it would look like the surface was “unbounded”. So even though the surface of a balloon is a finite number of square units, there’s no edge to it, no boundary (since you can go forever in any one direction).
When you imagine the universe, you might think of a giant ball that’s filled with stars, galaxies and all sorts of interesting astrophysical objects. You may imagine how it looks from the outside, like an astronaut views the globe of the Earth from a serene orbit above.
Because space is expanding, it’s possible for the galaxies to appear as if they are moving faster than light, without violating relativity — which says that nothing can go faster than light in a vacuum.
It could very well be that our universe does indeed have an “outside.” But again, this doesn”t have to be the case. There’s nothing in mathematics that describes the universe that demands an outside.
The actual size of the observable universe is 46 billion light-years in any direction, even though the universe began only 13.8 billion years ago, Mack said. But that still sets a limit on the size of the universe humans can see, called the observable universe.
Anything outside of that radius of 46 billion light-years is not visible to Earthlings, and it never will be. That’s because the distances between objects in the universe keep getting bigger at a rate that’s faster than the light beams can get to Earth.