All Questions
53
questions
-1
votes
1
answer
52
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Question on spatiotemporal dimensionality about the contradictions of time being a dimension
We can axiomatically see that all spatial dimensions have a fundamental rule where they can either move back or forwards infinitely. However, the temporal dimension started when the universe began and ...
0
votes
0
answers
32
views
Still having trouble understanding gravitational lensing [duplicate]
The normal diagram used to explain gravitational lensing shows a two-dimensional plane that is deflected by a heavy weight. This is a two dimensional description that requires an extra dimension to ...
- 319
9
votes
3
answers
6k
views
Why is Spacetime described as flat even though we live in 3 dimensions of space?
I’ve always heard and seen diagrams that show spacetime as being “flat” or in 2 dimensions with curvature. How does this correspond to the 3 spacial dimensions that we perceive to exist in?
- 135
1
vote
1
answer
148
views
In relativity, is the fourth spacetime dimension spatial or nonspatial?
In "An Introduction to Modern Astrophysics" Carroll and Ostlie describe the curvature of space by mass as:
curving in a fourth spatial dimension perpendicular to the usual three of "...
- 13
0
votes
2
answers
137
views
How do we make an observation of a 4D spacetime trajectory if we, observers, have only access to a 3D world?
So far, I know that a trajectory in general relativity is a 4-vector, and a force-free particle follows a geodesic which is in 4D as well. My question is: how do we make an observation of such a ...
- 959
0
votes
1
answer
33
views
If a car ahead of me suddenly speeds up close to the speed of light, what would I and the car observe each of us? [closed]
Suppose I and the car is beside each other and the car went a little ahead of me, then instantly speeds up close to the speed of light. Will I observe the car is going too slow or stuck at one place ...
- 21
1
vote
1
answer
315
views
The dimensions of the universe and the scale factor
How to get the universe’s volume from the universe’s scale factor? Taking into account that the scale factor is dimensionless and the volume has dimensions of $cm^3$ or $m^3$ ?
In this paper for ...
- 395
0
votes
1
answer
91
views
How could time move "slower" for some observer-A moving "faster" than another observer-B when velocity is relative? [closed]
I've never understood how time dilation due to speed works. Take the most well-known example of an astronaut orbiting around the earth at insane speed for a while and then returning to earth having ...
- 101
0
votes
1
answer
106
views
How do you use the Riemann tensor to show curvature in time?
I know that the Riemann tensor shows curvature in space. However, in the case of general relativity, where space AND time is curved, how would one use the Riemann tensor to show curvature in a ...
- 33
1
vote
1
answer
150
views
Is there a way to view Einstein's spacetime "from outside" to intuitively understand it?
Is there a way, in Einstein's relativity (special and general) to view spacetime from a point of view that sits "outside" of it, to intuitively understand it?
We humans can only see 3 ...
- 107
11
votes
2
answers
1k
views
Features of General Relativity applicable only to 3+1 dimensions?
While studying general relativity, I noticed that much of the theory could easily be generalized from a $(3,1)$-dimensional spacetime to an $(n,1)$-dimensional spacetime without any changes. So, is ...
- 1,588
-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 ...
4
votes
3
answers
371
views
What is the physical meaning and origin of the gravitational constant $G$?
Is $G$ just a value to fix the units in the equation? Something like a proportionality constant or a coupling constant?:
$$F=\frac{G m_{1} m_{2}}{r^{2}}$$
Does it have any physical meaning or physical ...
- 4,170
1
vote
0
answers
40
views
What is the lower bound on the dimension of the LOCAL imbedding of a General relativistic Lorentzian manifold in a pseudo-Euclidean spacetime?
What is the lower bound on the dimension of the LOCAL imbedding of a General relativistic Lorentzian manifold in a pseudo-Euclidean spacetime?
Imbedding is Isometric embedding to me.
What about these ...
- 1,268
25
votes
10
answers
7k
views
Why do physicists say that spacetime is not bending "into" or "out" of a fourth dimension?
I understand that there is no need for a fourth-dimensional space to bend into, but why do physicists seem to be against the idea? Is this simply because there is no proof of a fourth dimension, or is ...
- 510