Types of Galaxies in Our Universe

Jun 1, 2020
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Nice link. It states, "Probably some 2 trillion galaxies existed in the early universe,..."

There has been two different lines of evidence that support this figure, though it's an approximation.

The most distant galaxies are from billions of years ago and they are smaller, on average, than what we see closer to us.

If we assume 100 billion stars for an average for all those 2 trillion, the total no. of stars is very roughly 2 x 10^23. As the huge telescopes come along and that number grows by 3x, then we would have an Avogadro number of 6e23! [A good way to remember it.]

It's possible that the no. of exoplanets may match that number. It's an incredible thought.
 
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Jun 1, 2020
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Since we can never observe the whole extent of the Universe, surely we cannot estimate its overall density, and any figures can only be guesses?

Cat :)
Right! If you knew the numerator you could calculate the density, if you knew the denominator. *wink* [This is that dumb, "If we had some bread, we could make a ham sandwich, if we had some ham."}
 
Somewhere we are not talking the same language;

"Since we can never observe the whole extent of the Universe,"

Even without expansion, the Universe is so large that light from the most distant parts can never reach us. Even if one does not accept this, then it becomes true when taking expansion into account.

" . . . . . . surely we cannot estimate its overall density,"

If we cannot observe the whole extent of the Universe, we have no reason whatsoever to assume that the density of the unobservable part is the same as the observable part - especially when the unobservable part can be any billions of times larger than the observable, and of totally unguessable compoosition.

Ergo " and any figures can only be guesses? " aka assumptions.
I stand by this, and cannot accept post #6. I am rather surprised that you call my post "dumb", unless this has a different meaning this side of The Pond.

Cat :)
 
Jun 1, 2020
987
692
1,260
Somewhere we are not talking the same language;

"Since we can never observe the whole extent of the Universe,"

Even without expansion, the Universe is so large that light from the most distant parts can never reach us. Even if one does not accept this, then it becomes true when taking expansion into account.

" . . . . . . surely we cannot estimate its overall density,"

If we cannot observe the whole extent of the Universe, we have no reason whatsoever to assume that the density of the unobservable part is the same as the observable part - especially when the unobservable part can be any billions of times larger than the observable, and of totally unguessable compoosition.

Ergo " and any figures can only be guesses? " aka assumptions.
Agreed, which is why the ”Universe” has previously only been the observable universe; if regions beyond can never be addressed, why bother addressing them in any specific fashion that would imply we can (e.g. density).

I stand by this, and cannot accept post #6. I am rather surprised that you call my post "dumb", unless this has a different meaning this side of The Pond.
You may have read it too fast. The word “joke” was implied in, “This is analogous to that dumb joke about the ham sandwich...”. If that’s a pond separation thing then it would be interesting to learn why. I will go with “my brevity is oft witless”. :)
 

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