2
votes
4answers
145 views

Can we think of gravity as space itself moving?

So if you move through space with a constant acceleration you experience longer time dilation than when you're at rest, but you also experience the same time dilation when you're under the effect of ...
-1
votes
0answers
37 views

Is gravity just relative rotational velocity?

Einsteins law of relativity states that velocity is relative. so when object $A$ passes object $B$ at $v$ kph, object $B$ also passes object $A$ at $v$ kph. Maybe gravity is the universes way of ...
0
votes
0answers
30 views

Mario Livio's book on symmetry and the relationship between gravity and acceleration

In his book: The Equation That Couldn't be Solved Mario Livio explains the equivalence principle in laymen's terms. I took the statement on page 209: The force of gravity and the force resulting from ...
0
votes
0answers
29 views

What are the technical differences between the various equivalence principles?

I understand the differences between the various equivalence principles at the level of words, but I'm not sure how they follow from various equations. If I'm given a theory of gravity with metric ...
1
vote
3answers
171 views

What makes matter travel along geodesics?

The relativistic explanation of gravity is geometric, the motion of a body in a field of space-time distortion can be described as being at rest and travelling along a geodesic of that field, but why ...
2
votes
2answers
141 views

How does the Einstein Equivalence Principle imply a spacetime with a metric (and a connection)?

I have at hand the book by Clifford Will, "Theory and Experiments in Gravitational Physics", and the following Living Reviews in Relativity article. He quotes the Einstein Equivalence Principle (EEP) ...
5
votes
2answers
193 views

Did people realize that gravity accelerated things before Einstein's elevator thought experiment?

I'm reading about the (very near) equivalence of gravitational mass and inertial mass in my undergrad GR course, and the text (Lambourne) describes this equivalence as the inspiration for Einstein's ...
0
votes
1answer
170 views

Is the result of (every) research on acceleration equivalent to gravity?

Is the result of an experiment on acceleration equivalent to another experiment in a gravitational field? If I have an experimental conclusion from research under uniform acceleration, can the ...
1
vote
2answers
129 views

Can acceleration feel like constant gravity for indefinitely long?

So here's the setup: I'm in a spaceship, without windows as always, and the ship is accelerating upwards at a constant rate of $1\,\text{g}$. So inside the spaceship it feels like I'm being pulled ...
3
votes
6answers
1k views

Surely space-time Curvature does not explain gravity, it just describe its effects?

In special relativity co-moving objects see the other's 4-velocity as being only temporal. When they move relative to each other they see the other's 4-velocity has rotated so that it points less in ...
3
votes
3answers
221 views

Does the equivalence principle mean that the Earth is expanding?

Popular books suggest that for an observer in the Einstein lift the following situations are equivalent: 1, the lift hangs motionless (relative to the Earth) on a cable in the gravitational field of ...
3
votes
3answers
1k views

How did Einstein derive general relativity?

How did Einstein derive general relativity (GR)? Did he use: the equivalence principle? The principle of least action? Anything else? Note, I'm not looking for a full mathematical derivation of GR! ...
1
vote
1answer
510 views

Curvature of spacetime in only required to explain tidal forces?

I'm a bit confused about the equivalence principle in GR. I'm quoting from Wikipedia: An observer in an accelerated reference frame must introduce what physicists call fictitious forces to ...
0
votes
2answers
2k views

Jumping in an elevator?

I've always been under the impression that jumping in an elevator wouldn't help at all, especially after reading a snippet of physics where Einstein said that free fall was identical to zero gravity. ...
1
vote
4answers
297 views

Freefall in/out of an enclosed environment

I've just been learning about Einstein, relativity, and the equivalence principle in Physics. I'm fascinated with the idea of being inside a free-falling enclosed environment (such as, e.g., rocket, ...
2
votes
2answers
151 views

Inertial Mass of a scalar field

Does it make sense to talk of the inertial mass of a scalar field? By the equivalence principle, it must be equal to its gravitational mass. We know that the scalar field contributes towards the ...
-4
votes
4answers
2k views

What is the difference between gravitation and magnetism?

If you compress a large mass, on the order of a star or the Earth, into a very small space, you get a black hole. Even for very large masses, it is possible in principle for it to occupy a very small ...
0
votes
1answer
195 views

Is relativistic motion equivalent to fluctuating gravitational fields?

The theory of relativity makes very precise predictions about how an object's motion through space-time affects the passage of time for both the object and observers in other frames of reference. I ...
9
votes
4answers
850 views

Is there a fundamental reason why gravitational mass is the same as inertial mass?

The principle of equivalence - that, locally, you can't distinguish between a uniform gravitational field and a noninertial frame accelerating in the sense opposite to the gravitational field - is ...
2
votes
2answers
791 views

What is the effect of temperature on electrostatic-gravitational balance?

We have two identical massive metal spheres at the same temperature at rest in free space. Both have an identical charge and the Coulomb force [plus the black-body radiation pressure if the ...
7
votes
8answers
533 views

Gravity theories with the equivalence principle but different from GR

Einstein's general relativity assumes the equivalence of acceleration and gravitation. Is there a general class of gravity theories that have this property but disagree with general relativity? Will ...
1
vote
9answers
2k views

How does this thought experiment not rule out black holes?

How does the following brief thought experiment fail to show that general relativity (GR) has a major problem in regards to black holes? The full thought experiment is in my blog post. The post ...