All Questions
Tagged with gravity general-relativity
486
questions
132
votes
15
answers
35k
views
How can anything ever fall into a black hole as seen from an outside observer?
The event horizon of a black hole is where gravity is such that not even light can escape. This is also the point I understand that according to Einstein time dilation will be infinite for a far-away-...
- 1,717
492
votes
21
answers
54k
views
How does gravity escape a black hole?
My understanding is that light can not escape from within a black hole (within the event horizon). I've also heard that information cannot propagate faster than the speed of light. I assume that the ...
- 5,039
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
48
votes
3
answers
8k
views
What is the weight equation through general relativity?
The gravitational force on your body, called your weight, pushes you down onto the floor.
$$W=mg$$
So, what is the weight equation through general relativity?
user17093
21
votes
5
answers
6k
views
How does "curved space" explain gravitational attraction? [duplicate]
They say that gravity is technically not a real force and that it's caused by objects traveling a straight path through curved space, and that space becomes curved by mass, giving the illusion of a ...
- 2,172
34
votes
6
answers
10k
views
Is gravitational time dilation different from other forms of time dilation?
Is gravitational time dilation caused by gravity, or is it an effect of the inertial force caused by gravity?
Is gravitational time dilation fundamentally different from time dilation due to ...
- 663
60
votes
4
answers
31k
views
Does a photon exert a gravitational pull?
I know a photon has zero rest mass, but it does have plenty of energy. Since energy and mass are equivalent does this mean that a photon (or more practically, a light beam) exerts a gravitational pull ...
- 2,808
21
votes
6
answers
4k
views
Better explanation of the common general relativity illustration (stretched sheet of fabric)
I've seen many science popularisation documentaries and read few books (obviously not being scientist myself). I am able to process and understand basic ideas behind most of these. However for general ...
- 313
16
votes
9
answers
5k
views
How can gravity affect light?
I understand that a black hole bends the fabric of space time to a point that no object can escape.
I understand that light travels in a straight line along spacetime unless distorted by gravity. If ...
56
votes
3
answers
13k
views
Why can't I do this to get infinite energy?
I know that I cannot do this because of conservation of energy, so I am looking for an answer as to why this will not work.
So by my understanding of Einstein's whole famous $E=mc^2$ thing it is ...
- 871
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
42
votes
5
answers
7k
views
Why is a black hole black?
In general relativity (ignoring Hawking radiation), why is a black hole black? Why nothing, not even light, can escape from inside a black hole? To make the question simpler, say, why is a ...
31
votes
4
answers
11k
views
Speed of light in a gravitational field?
How do I solve the speed of light in gravitational field?
Should I just add gravitational acceleration in speed of light?
$$c'=c_0+g(r)t~?$$
- 936
34
votes
4
answers
8k
views
How can we recover the Newtonian gravitational potential from the metric of general relativity?
The Newtonian description of gravity can be formulated in terms of a potential function $\phi$ whose partial derivatives give the acceleration:
$$\frac{d^2\vec{x}}{dt^2}=\vec{g}=-\vec{\nabla}\phi(x)=\...
- 1,406
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