It’s hard for me to comprehend the idea that space never ends. Is there really no boundary to space? How do scientists know this?
In: Planetary Science
The universe is expanding, which we know because objects are uniformly moving away from Earth and much faster than we’d expect given everything else we know about them and how they are moving relative to us. It’s better to think about this less as a wave of “something” flowing into “nothing” but rather as a big web of “something” where the distances between each thing are getting bigger. The farther away something is, the greater this inflation of empty space. This is one sense in which we could never reach the “boundary” to space.
The other sense is that once something is sufficiently far away from Earth, the expansion of the universe is such that we can never reach it, even if we travelled directly towards it at the speed of light. Conversely, only part of the universe is close enough to Earth that light from it has ever reached us. We call this the “observable universe,” and for many purposes, you can think of it as the bounded region of space that you have in mind. While it’s incredibly unlikely that a human will ever reach the distant reaches of the observable universe, it’s technically possible, and light generated on Earth (or, more realistically, by our sun) is making that journey now. However, it’s currently considered impossible (absent truly weird stuff like wormholes) to leave the observable universe.
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