All Questions
59
questions
9
votes
4
answers
659
views
Understanding expansion of the Universe as things flying apart
Say that we have a Universe uniformly filled just with matter (let's not bring dark energy into this). And say that we fill it with very light particles (so that the gravitational interaction between ...
2
votes
2
answers
109
views
How do we account for the 'one way' drag of moving space?
As I understand it, the rotating space outside a Kerr black hole drags radially falling particles into circular motion. Similarly the river model posits that the inward flow of space ensures particles ...
- 6,217
1
vote
1
answer
133
views
Does dark energy cause the creation of spacetime?
The universe is expanding, in theory because of 'dark energy'. Does this mean that this dark energy is causing an increase in the amount of spacetime? I.e., does dark energy cause the creation of ...
- 1,011
0
votes
1
answer
38
views
Does the dating of the formation of the world take into account the effect of space-time curvature? [duplicate]
For example, when we calculated that the age of the universe is about 13.8 billion years, did we take into account the difference between the flow of time back at the early universe, where mass was ...
- 1
1
vote
1
answer
100
views
Is the gravitational tidal force equivalent to expanding space?
If you fall towards a black hole, the particles in front and the back of you, in the direction of the center, are accelerating away from you. So, seen from a freely frame, can we say that space is ...
4
votes
3
answers
2k
views
Will a light come back within finite years?
In this answer Javier said
Imagine the universe was the inside of a ball. We're 3D now, so no one is hiding any dimensions. This ball has a border, except it's not really a border. You should think ...
- 405
4
votes
3
answers
759
views
Constant speed of light violates accelerating expansion of universe?
My question regards the following:
One of the most fundamental principles of Einstein's GR is that all free bodies move through spacetime with constant velocity $c=1$.
However, in 1998 Hubble showed ...
- 201
-2
votes
1
answer
123
views
Does general relativity prohibit spacetime expanding in a higher dimensional space?
Are there theoretical considerations that prohibit the 4-dimensional spacetime as described by general relativity to be situated in a higher dimensional spacetime? If not, could that explain why the ...
13
votes
2
answers
952
views
Does the expansion of spacetime add energy to matter? [duplicate]
If I understand correctly when the universe expands the matter in it is expanded as well but the "rest length" of the matter that gets stretched stays the same. So let's say I have a crystal ...
2
votes
1
answer
59
views
What is observed by Astronauts traveling from M at just under $c$, but proper distance increases at greater than $c$ due to spacetime expansion?
A rocket is traveling at a reasonable speed directly away from planet M at a large distance D. M is shaped like a coin and to the astronaut looking through a telescope directly out the back of the ...
- 143
2
votes
1
answer
221
views
Can we have positively curved space within negatively curved spacetime?
Thinking about the universe as a whole. One could imagine that the three spatial dimensions each have the same, say positive, curvature, making space spherical, while time is negatively curved, making ...
- 371
1
vote
2
answers
157
views
If spacetime is expanding, shouldn't lengths expand at an equal rate? [duplicate]
I frequently hear that galaxies are moving apart (in some instances, faster than the speed of light) because the fabric of spacetime is expanding. The common analogy is two people standing on the ...
1
vote
1
answer
337
views
Did the Big Bang cause an outward push of gravity?
There is a theory that the big bang’s blast caused an outward push, a kind of reverse gravity if you will, of our universe and everything within it.
My question is how could this have happened? If it ...
- 179
3
votes
1
answer
101
views
Motion vs space expansion
Let us consider two particles A and B in empty space, and let us assume that I am an observer attached to particle A. Also let us assume that, according to my measurements, I see that the distance ...
- 81
1
vote
1
answer
100
views
Explaining accelerating spacetime expansion?
I should begin by noting that I am NOT a physicist, I study differential geometry and so my physics background is extremely limited. That being said I was reading a textbook on general relativity and ...
