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trying to understand the universe


boo

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im not a scientist, but i came here because there is a question bugging me.

here goes...

the universe is approx 13.8 billion years old, it has been expanding since its beginnings, so it was much smaller at one time than it is now.

  and we can see galaxys which are over 13 billion light years away, therefore what we see when we look at them is how they looked when the universe was very young and therefore a lot smaller than it is now. .

but here are my questions  if the further out we look,  we are looking at a smaller and smaller universe, then why don't these galaxies appear bigger and bigger the farther away they are?  or why dont they appear closer than they really are since the universe was very small back then?

 

i can partly answer my own question but im not sure if im right.

im assuming these galaxies are not 13 billion light years away from us now,  but in fact ,they were 13 billion light years from us 13 billion years ago, (what a coincidence!)   but now, they are probably much further away, long past the cosmic horizon,   we are basically looking at a snapshot of something that is no longer there.   am i right i saying all this?  but that still doesnt explain why they dont look bigger than the closer galaxies since their universe was much smaller.  (then again maybe they do look bigger than they should look LOL.).

id appreciate some feedback on this. 

thanks :-)

 

Edited by boo
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The reason the galaxies appear smaller is the sheer distance to those galaxies. The universe being smaller in the past doesn't change that. As you correctly noted the universe is expanding. However we are part of the universe.

 So we do not directly see the universe shrinking in a certain direction but can only infer the universe must be smaller in the past by reverse extrapolation of the expansion. This is because we are included in the expansion.

You are correct that we see the past so see where the galaxies were once located.

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  • 2 weeks later...

We usually start with what we observe. Foreign galaxies were seen before the expansion of the universe was discovered. So there was no expectation on how large a faraway galaxy would look because we were already seeing some of them. Through looking further back in time and studying the universe at all of its distances scientists can further refine their theories about the size and age and rate of expansion. That the light of those furthest galaxies has traveled through expanding space for 13 billion years raises many questions, but you can say that the light has reached us and through comparing what we observe of it to the light of other galaxies we can learn more of those nuances such as how large the universe was at any given time.

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On 8/21/2019 at 10:21 AM, boo said:

im assuming these galaxies are not 13 billion light years away from us now,  but in fact ,they were 13 billion light years from us 13 billion years ago, (what a coincidence!)   but now, they are probably much further away, long past the cosmic horizon

Not quite.

Those galaxies would have been something like 5 billion light years away when they emitted that light. Because of expansion, it took 13 billion years for the light to reach us (rather like walking the wrong way up an escalator).

Now, they would be over 40 billion light years away. But not beyond the cosmic horizon, because if they were we wouldn't be able to see them.

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