All Questions
480
questions
161
votes
6
answers
55k
views
Why would spacetime curvature cause gravity?
It is fine to say that for an object flying past a massive object, the spacetime is curved by the massive object, and so the object flying past follows the curved path of the geodesic, so it "appears" ...
- 1,926
82
votes
13
answers
8k
views
Turbulent spacetime from Einstein equation?
It is well known that the fluid equations (Euler equation, Navier-Stokes, ...), being non-linear, may have highly turbulent solutions. Of course, these solutions are non-analytical. The laminar flow ...
- 7,592
81
votes
17
answers
59k
views
How exactly does curved space-time describe the force of gravity?
I understand that people explain (in layman's terms at least) that the presence of mass "warps" space-time geometry, and this causes gravity. I have also of course heard the analogy of a blanket or ...
- 913
77
votes
6
answers
22k
views
Does gravity CAUSE the bending of spacetime, or IS gravity the bending of spacetime?
In reading these discussions I often see these two different definitions assumed. Yet they are very different. Which is correct: Does gravity CAUSE the bending of spacetime, or IS gravity the ...
- 4,783
70
votes
2
answers
9k
views
Is spacetime flat inside a spherical shell?
In a perfectly symmetrical spherical hollow shell, there is a null net gravitational force according to Newton, since in his theory the force is exactly inversely proportional to the square of the ...
- 2,163
55
votes
4
answers
3k
views
GR and my journey to the centre of the Earth
[General Relativity] basically says that the reason you are sticking to the floor right now is that the shortest distance between today and tomorrow is through the center of the Earth.
I love ...
- 643
48
votes
9
answers
29k
views
Why is the gravitational force always attractive?
Why is the gravitational force always attractive? Is there another way to explain this without the curvature of space time?
PS: If the simple answer to this question is that mass makes space-time ...
- 1,772
47
votes
15
answers
8k
views
Why does the speed of an object affect its path if gravity is warped spacetime?
I think I understand the idea of thinking about gravity not as a force pulling an object towards another object but instead a warping of space so that an object moving in a straight line ends up ...
- 579
45
votes
3
answers
7k
views
If spacetime is curved, how would anyone know? If anyone could tell, would that really be spacetime curving?
I never had a problem accepting that spacetime is curved as a result of matter, until I learned the LIGO experiments showed that evidently the curvature of spacetime can be measured. This, to me, is ...
- 1,663
36
votes
8
answers
6k
views
Does the curvature of spacetime theory assume gravity?
Whenever I read about the curvature of spacetime as an explanation for gravity, I see pictures of a sheet (spacetime) with various masses indenting the sheet to form "gravity wells." Objects ...
- 6,044
28
votes
3
answers
4k
views
Does theoretical physics suggest that gravity is the exchange of gravitons or deformation/bending of spacetime?
Throughout my life, I have always been taught that gravity is a simple force, however now I struggle to see that being strictly true.
Hence I wanted to ask what modern theoretical physics suggests ...
- 507
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
23
votes
6
answers
3k
views
Can we interpret the Einstein field equations to mean that stress-energy *is* the curvature of spacetime?
What do I mean?
There are two kind of equalities, or two ways to interpret an equality.
Take for example the ideal gas law $$PV = Nk_BT$$
We all know what this equation means: when you calculate both ...
- 5,220
23
votes
4
answers
909
views
Do we feel a gravitational pull towards where a mass will be in the future?
As an extreme example, suppose a black hole (BH) were moving with respect to us. Would we not only feel a gravitational pull to where the BH is directly located now but also where it was in the past ...
- 1,348
22
votes
5
answers
28k
views
Stephen Hawking says universe can create itself from nothing, but how exactly?
Stephen Hawking says in his latest book The Grand Design that,
Because there is a law such as gravity, the universe can and will create itself from nothing.
Is it not circular logic? I mean, how ...
- 329