How big in light years is the universe?
I'm not sure what you mean by saying, "the universe." There is an observable universe, which we see, and the entire universe which the observable universe has yet to expand into.
The observable universe is 92 billion light years across whereas the entire universe may be infinite in size.
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I percieve your question to be 'What is the size of our universe?'
Rather than size of observable universe .
Size of universe is yet undefined , some say it is infinite while the others sughest that it must be finite but an extremely large value .
Perhaps, we know size of observable universe that's around 94 billion light years .
Space is expanding into itself , it seems just like if you zoom the graph at "desmos.com" .
know why i said rather typed "our universe"? that's because some astronomers suggested existence of more than one universe , isn't this stuff cool?
Dark energy is believed to be alien to our universe .
So, yet the question is pending , How big is
To answer that we need to know how old is our universe ,
If we know how much old it is we need to work out some calculations based on entropy and red shift, may be yielding some result ..
Actually this stuff isn't yet as simple as i told ,
"Any other challenge left?"
Yes, The worst part of astrophysics comes in when you see some equations with so many variables denoted by greek alphabet , no need to get dissapointed for now , i heard a quantum physict say that those equations are not really boring or dangerous , whatever! as they seem to be.
What about answer to question ?
I got no idea but just a mind to think about it!