All Questions
Tagged with cosmology space-expansion
1,604
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194
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Why does space expansion not expand matter?
I have looked at other questions on this site (e.g. "why does space expansion affect matter") but can't find the answer I am looking for.
So here is my question: One often hears talk of space ...
- 2,055
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Why isn't an infinite, flat, nonexpanding universe filled with a uniform matter distribution a solution to Einstein's equation?
In Newtonian gravity, an infinite volume filled with a uniform distribution of mass would be in perfect equilibrium. At every point, the gravitational forces contributed by masses in one direction ...
- 2,170
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votes
5
answers
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Can space expand with unlimited speed?
According to this article on the European Space Agency web site just after the Big Bang and before inflation the currently observable universe was the size of a coin. One millionth of a second later ...
- 783
65
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Why is the observable universe so big?
The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
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33
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9
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Is space really expanding?
In a book called "Einstein, Relativity and Absolute Simultaneity" there was this sentence by Smith:
There is no observational evidence for a space expansion hypothesis. What is observed are ...
user311398
31
votes
6
answers
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If spacetime itself is expanding, how could we ever tell?
If space is the measured distance between 2 objects, then saying the space expanded is nonsensical unless we have a measuring stick outside of the space fabric to measure the expansion. 2 objects ...
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31
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1
answer
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Why haven't we seen the big bang?
The Andromeda galaxy is 2,538,000 light years away, so if we view Andromeda from a telescope, we see Andromeda how it was 2,538,000 years ago. Now the diameter of the visible universe is 92 billion ...
- 1,925
29
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2
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Why is the Cosmic Microwave Background evidence of a hotter, denser early universe?
In his book Gravitation and Cosmology, Steven Weinberg says that the Cosmic Microwave Background (CMB) makes it "difficult to doubt that the universe has evolved from a hotter, denser early stage&...
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28
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4
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How did the universe shift from "dark matter dominated" to "dark energy dominated"?
In order to get dark energy to dominate, wouldn't you first need another form of energy to push the expansion until dark energy could dominate? Otherwise I don't understand how the universe could ...
- 1,137
27
votes
2
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What is the theoretical limit for farthest we can see back in time and distance?
13.2 billion years ago the universe was rather small, having started only half a billion years ago. Today, with the help of Hubble Space Telescope, we are able to capture the light of galaxies emitted ...
- 371
26
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9
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How can the universe expand if there is gravitation?
We live in an expanding universe - so I'm told. But how can that be possible? Everything imaginable is attracted by a bigger thing. So, why can't gravitation stop the expansion of the universe? I know ...
- 487
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7
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Why did the universe not collapse to a black hole shortly after the big bang?
Wasn't the density of the universe at the moment after the Big Bang so great as to create a black hole? If the answer is that the universe/space-time can expand anyway what does it imply about what ...
- 517
25
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2
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How does the Hubble parameter change with the age of the universe?
How does the Hubble parameter change with the age of the universe?
This question was posted recently, and I had almost finished writing an answer when the question was deleted. Since it's a shame to ...
- 358k
24
votes
7
answers
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Given that matter cannot escape a black hole, how did the big bang produce the universe we see today?
Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past.
If the matter contained within our ...
Daniel X Moore
24
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3
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Photons in expanding space: how is energy conserved? [duplicate]
If a photon (wave package) redshifts (stretches) travelling in our expanding universe, is its energy reduced?
If so, where does that energy go?
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