All Questions
44
questions
-1
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1
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53
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If an area in 2D cannot be curved and finite is the same regarding the space of our pressumed 3D universe?
Is the sentence in the title right that our universe is infinite? And if so does it mean that stars are not evenly distributed along our universe but they all move from a populated centre to a fairly ...
- 2,255
0
votes
0
answers
73
views
Are there any ways to conceptualize the relationship between gravity and space-time other than curvatures?
This might sound like a random question, but it came to me while I was trying to conceptualize the size of the universe and started thinking of entire galaxies resembling grands of sand floating ...
-4
votes
1
answer
78
views
The background of the universe [closed]
Mass(-energy-momentum) curves space(-time).
However - what is space-time?
Is it (the background) necessarily flat(without something in it) ?
If there were an empty universe - is there still spacetime ...
- 63
2
votes
2
answers
414
views
What is the cardinality of intervals in space, and what is the cardinality of intervals in spacetime?
The interval $|(0, 1)| = |\mathbb{R}|$. I naively thought that one could treat intervals in space in kind, i.e., that the cardinality of any interval in space has the cardinality of the continuum. You'...
- 23
0
votes
0
answers
44
views
Effects of anisotropy and non-homogeneity in the universe's symmetries...?
I was reading Philip W Anderson's essay "More is Different" (https://www.tkm.kit.edu/downloads/TKM1_2011_more_is_different_PWA.pdf) and at some point he links the isotropy and homogeneity of ...
- 2,462
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
1
vote
3
answers
136
views
Is the solar system sitting in the centre of curved spacetime and if so, are we viewing the rest of the universe from inside that "bubble"?
I read an article about a huge bubble being discovered in which the solar system sits bang in the middle. It got me thinking about the curvature of spacetime. The bubble was created by several ...
3
votes
2
answers
1k
views
Space is flat but spacetime is curved?
In the picture below a triangle has been drawn on a spherical shaped object. The angles add up to 67+48+73=188 degrees. Since the surface of earth is also almost spherical therefore an experiment can ...
- 717
3
votes
2
answers
149
views
Does spacetime bending contradict the universe following euclidean geometry?
According to experiments the universe is believed to be flat, meaning that it would follow euclidean geometry. However, is that compatible with the fact that spacetime bends due to gravity? Does ...
- 31
0
votes
0
answers
41
views
In general relativity, could our curved spacetime be embedded in a higher dimension flat spacetime (5D+1) of the compatible metric? [duplicate]
I took General Relativity at university, years ago and have a question that has recently occurred to me. This might be a dumb one, so I apologise if the answer is a well known negative.
Mathematically,...
- 1,087
1
vote
1
answer
463
views
Einstein's Static Solution with $\Lambda =0$ to The Friedmann Equations?
Is it possible to show the universe is static (i.e., $a=a_*=\rm{const}$) without assuming $a=\rm{const}$ to begin with, and using a mix of $w=0$ and $w=-1$? Let $\Lambda=0$ in the Friedmann equations, ...
- 61
2
votes
1
answer
897
views
Static solution to the Friedmann equation [duplicate]
I want to find the static solution for the Friedmann equation:
$$ \bigg(\frac{\dot{a}}{a}\bigg)^2=H_0^2\bigg(\Omega_m\bigg(\frac{a_0}{a}\bigg)^3+\Omega_v+\Omega_k\bigg(\frac{a_0}{a}\bigg)^2\bigg) $$
...
- 135
1
vote
0
answers
51
views
Can a cosmological constant model inhomogeneities?
Consider the following zero-order approximation to the universe:
Spacetime is perfectly homogeneous, and
The cosmological constant is exactly zero.
This doesn't quite work. Neither assumption is ...
0
votes
1
answer
105
views
What does a universe with a boundary look like?
Physically, what would it look like if we lived in a universe with a boundary at finite distance?
- 423
4
votes
1
answer
415
views
On the topic of imaginary-time
I apologize for my crude line of questioning, as I'm not well-versed in physics at all but it fascinates me. I was researching the concept of "imaginary-time" and the shuttlecock model of ...
- 41