All our observations about the Universe is based on Earth based observations and satellites that are near Earth, or somewhere in Solar System. But there could be some large scale astronomical phenomena which is not observable in ordinary dimensions just like strong and weak forces are not observable in macroscopic distances. And some force or something like that could make this Universe to be very large and expanding as we observe, but which may not be actual truth.
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The light that we can see indicates that physics works the same everywhere in the observable universe. It strongly suggests that we do in fact see galaxies that are billions of light years away, and that physics works the same way there as it does here.
There are some weird things that only seem to happen on very large scales. Dark matter, for instance, has no noticeable effect inside star systems, but it starts having an effect on galactic scales, and we can see that by measuring how stars are moving inside galaxies. Dark energy, an even more mysterious force that pushes things apart, does not dominate gravity until you get to extragalactic scales (tens of millions of light years).
Furthermore, if inflationary theory is correct, there may be other parts of the Universe, vastly removed from our location, where space underwent phase transitions differently and resulted in different forces and physical constants. We can never reach these places due to the speed of light limit, but if they exist, they would represent a very bizarre effect on a scale much bigger than anything we've measured so far.
There are some weird things that only seem to happen on very large scales. Dark matter, for instance, has no noticeable effect inside star systems, but it starts having an effect on galactic scales, and we can see that by measuring how stars are moving inside galaxies. Dark energy, an even more mysterious force that pushes things apart, does not dominate gravity until you get to extragalactic scales (tens of millions of light years).
Furthermore, if inflationary theory is correct, there may be other parts of the Universe, vastly removed from our location, where space underwent phase transitions differently and resulted in different forces and physical constants. We can never reach these places due to the speed of light limit, but if they exist, they would represent a very bizarre effect on a scale much bigger than anything we've measured so far.
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Well, given observation is done using the electromagnetic spectrum which has a speed limit, we can't observe anything beyond the distance that light has had a chance to travel in the time its had to travel, so from this perspective, we can't know.
But we may be able infer from observations from the limits of our experiments which may allow for observation beyond that ... for example, the microwave background radiation which stem from the remnants of the big bang could indicate some area in which, say for theoretical argument, a region where where another universe has come in contact with our universe in which case we could deduce something further, like the size of our universe.
But we may be able infer from observations from the limits of our experiments which may allow for observation beyond that ... for example, the microwave background radiation which stem from the remnants of the big bang could indicate some area in which, say for theoretical argument, a region where where another universe has come in contact with our universe in which case we could deduce something further, like the size of our universe.