eli5-how do we know for sure how big space is? and how do we know we are right about everything we know in space?
In: Planetary Science
We don’t know how big space is.
We have been able to accurately measure the speed of light. And we can also accurately measure the shift of light over large distances. This gives us tools to work with when judging objects that are far away.
What we do see when we look out into space is there is a boundary called the ‘observable universe’. This boundary is where objects further than it are so far away that their light cannot possibly reach us, either because there hasn’t been enough time since the big bang or the universe is expanding too quickly for the light to get to us. Past this boundary we cant see anything, so we have no idea how much bigger space is.
We are never sure that we are “right” when we look at things in space. Everything is observational and quite often we make new discoveries. An example of this is that there exists a thing called dark matter that we literally know nothing about.
However based on what we do know, we are able to make predictions, and if those predictions come true, then generally we consider that we must know what we are talking about. An example of this is that the planet Neptune was predicted before it was actually observed.
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