All Questions
21
questions
1
vote
0
answers
52
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Expansion of the Universe inside mattar [duplicate]
When talking about the expansion of the universe we usually refer to the Friedman equations so we assume homogeneous and isotropic solution to Einstein field equation which is true on cosmological ...
- 1,734
-3
votes
2
answers
267
views
Does anyone really know how dark energy/matter works?
If dark energy has no physical interaction with normal matter but it does interact with dark matter, wouldn't that cause an interaction with normal matter through its interaction with dark matter and ...
- 1
2
votes
2
answers
464
views
Why do matter and radiation densities scale differently in expanding universe, when all matter is energy and all energy is matter? [duplicate]
I sometimes see the first Friedmann equation expressed with different terms for the density of "matter" and the density of "radiation". It is said that with an increase in scale ...
- 213
0
votes
1
answer
41
views
How the universe is expanding? [duplicate]
If universe is expanding with the velocity of light then why the distance between earth and sun is constant? Also why the distance from one Galaxy to another remains constant? And so on...
-1
votes
1
answer
87
views
Does the expansion of the Universe cause internal stresses in solids (and other substances with similar internal resistance forces)? [duplicate]
Is my understanding correct?
Weren't it for the internal resistance forces between particles in a solid object, the expansion of the Universe would continuously increase the distances between all of ...
- 245
3
votes
3
answers
204
views
Expansion of space or contracting of matter? [duplicate]
Can the expansion of the Universe effect be explained by contraction of the overall matter instead? That is, all material objects are in fact contracting, due to what the universal space seems (and ...
- 31
2
votes
0
answers
46
views
Is every object in the universe really expanding? Even small scale objects like humans? [duplicate]
So I was asked a question by someone that "if everything in the universe is expanding, then the lens we use to look at stellar objects is expanding as well, meaning we shouldn't be able to tell the ...
- 121
5
votes
3
answers
237
views
Cosmological Inflation: If Photon expands, why not other matter?
I keep repeatedly reading in many Stack Exchange and Quora questions that space of universe expands but particles (matter) don't, see e.g. this Phys.SE post. The reason given is that particles are ...
- 149
0
votes
1
answer
613
views
As space expands does the density of matter remain same or increase? [duplicate]
I learned that space is always expanding. Even between sun and earth, it's just gravity is stronger.
Imagine space as graph paper and there is a square object that fills it.
Space expands, 1x1 cell ...
- 2,645
4
votes
2
answers
492
views
Intuition for why matter dominated expansion is faster than radiation domination?
In a matter dominated universe $a_{\rm mat.}(t)\sim t^{2/3}$, while in a radiation dominated universe, $a(t)_{\rm rad.}\sim t^{1/2}$. Therefore, a matter dominated universe is expanding more quickly, ...
- 3,492
0
votes
0
answers
55
views
Space expansion and conservation of energy [duplicate]
The phrase of 'expansion of universe' , as we are led to believe, is mostly referring to an expansion in space. But is space expanding in the sense that the space between two particles is increasing ...
- 126
1
vote
1
answer
756
views
How does mass affect the expansion of space?
I'm a layman and I'm curious to understand how mass affects the expansion of space and whether the expansion of space is uniform everywhere in the universe.
From looking at redshifts it seems we have ...
- 11
1
vote
1
answer
66
views
Would "gravity" and the "law of gravity" have a meaning in a universe without matter?
I was discussing the fact that if there was no matter in the universe, just vacuum and radiation, can we say that anything called gravity wouldn't exist?
In that universe, the Friedman equations ...
- 93
0
votes
1
answer
464
views
Solving the Friedmann Equation for a specific universe
Suppose instead of the cosmological constant there is a quantum field with equation state parameter $w = -1/2$. Assume also it is a flat universe with only this quantum field ($Q$) and with non ...
- 21
12
votes
2
answers
2k
views
What is the physics definition of space?
When astronomers, physicists say that space is expanding, does the definition of space include matter, energy and the particles within?
Or is space an empty 'stage' in which all of the above exist?
...
- 11.7k