1. ### I Equivalence principle: an electric charge and a coil

The near-range magnetic field ##\vec{B}## of a point charge ##q## at distance ##\vec{r}##, moving at a non-relativistic velocity ##\vec{v}##, is given by $$\vec{B}=\frac{q}{4\pi\epsilon_0c^2}\frac{\vec{v}\times\hat{r}}{r^2}.$$ Faraday's law of induction for the induced EMF ##V_c## in a coil...
2. ### I Falling EM system contradicts the equivalence principle?

The following is an improved version of my previous post https://www.physicsforums.com/threads/falling-electric-dipole-contradicts-the-equivalence-principle.964594/ Consider the following system comprising a particle on the left with charge ##+q## that is a large distance ##d## away from two...
3. ### I Gravitational time dilation using an accelerating light-clock

I've been trying to understand gravitational time dilation by considering a light-clock of length ##l## undergoing an equivalent acceleration ##a## from rest along the direction of the bouncing light pulse. I find that the time ##t## that the light pulse takes to travel to the forward receding...
4. ### I The Equivalence Principle -- Is this a way to distinguish between a gravitational field and an accelerated rocket?

If we are in a cabine in a gravitational field and inside, we have a racket and a ball. We put strings in each side of the racket and we connect the racket to the ceiling of the cabine. This strings only allows us to keep the weight of the racket. Then, we drop a ball to the racket. We do this...
5. ### I Falling electric dipole contradicts the equivalence principle?

Consider an electric dipole consisting of charges ##q## and ##-q##, both of mass ##m##, separated by a distance ##d##. If the dipole is given an acceleration ##a## perpendicular to its moment the total electric force on it, due to each charge acting on the other, is given approximately by...
6. ### I Equivalence principle

Einstein's equivalence principle states that: The sets of inertial frames in the real world that correspond to (portions of) the ideal set of inertial frames discussed in special relativity consist of freely falling local frames. In other words,can we say that since all the local frames are in...
7. ### A Why doesn't an electron sitting on the Earth radiate?

I have some puzzles when I combine the Equivalence principle and Unruh's effect. Equivalence principle says that acceleration is equivalent to a uniformly gravitational field, or locally equivalent to gravitational field. Then the electron sitting on earth should have Unruh's effect, i.e...
8. ### I Time dilation vs the Equivalence principle

Some time ago there was a similar thread https://www.physicsforums.com/threads/clock-hypothesis-gravity-time-dilation-and-equivalence-principle.929838/ but what I want to discuss is similar but not the same and I would like to specify my question in such way, that it hopefully wont go sideways...
9. ### I Inertial & non-inertial frames & the principle of equivalence

One particular form of the equivalence principle states that The laws of physics for freely falling particles in a gravitational field are locally indistinguishable from those in a uniformly accelerating frame in Minkowski spacetime My question is, does one arrive at this conclusion from a...
10. ### I Questions about the general principle of relativity

One of the founding principles in GR is the principle of general relativity, which loosely states that all coordinate frames (inertial and non-inertial) are equivalent in the sense that the laws of physics are invariant. My question is, does the justification for this come from Einstein's...
11. ### I How does energy source curvature?

TL;DR Why does the Einstein equivalence principle imply that all forms of (non-gravitational) energy source curvature? Now, as understand it, the Einstein equivalence principle (EEP) implies (or at least suggests) that gravity is the manifestation of spacetime curvature, the reason being that...
12. ### I Understanding the Einstein equivalence principle

The Einstein equivalence principle (EEP) states that “The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its position in spacetime.” I’m trying to make sure I’ve understood this correctly. I’m I correct to...
13. B

### I Clock hypothesis, gravity time dilation and Equivalence Principle

1. The Clock Hypothesis states that the rate of a clock does not depend on its acceleration but only on its instantaneous velocity. This has been experimentally verified at very high accelerations. 2. A clock in a gravitational field experiences time dilation and runs slower that one not in a...
14. T

### I Really parabolic light ray in an accelerated elevator?

In an elevator "vertically" accelerated at g in outer space, the equivalence principle says a "horizontal" light ray in the elevator looks like a parabola. I completely understand that the light ray is curved but don't understand why the deflected light ray is an exactly parabola. Almost all...
15. ### B Does a moving bar magnet create charges?

So I understand that a charged particle moving relative to me has a magnetic field, and does not have one if its stationary relative to me... So is it true that a magnet moving relative to me has a charge? Say I took a bar magnet and threw it away from me way out in space, would it acquire a...
16. ### B Bending of light in a gravitational field

I have a few conceptual issues following a standard thought experiment to argue why light bends in a gravitational field and I'm hoping I can clear them up here. Consider an observer in a lift in free-fall in a uniform gravitational field and an observer at rest in the uniform gravitational...
17. ### I How can the Equivalence Principle hold when we consider tidal forces?

Tidal Forces: "It arises because the gravitational force exerted by one body on another is not constant across it". which implicitly implies that the acceleration is not constant on that body. Equivalence Principle: "weightlessness sensation occurs when one free falls in gravity" - which...
18. ### I How do we register/transfer information?

I have in mind thought experiment where physicist is in elevator falling towards the Earth. Question would be if he is not allowed to look outside, how would he detect the presence of the planet? Let's not take in consideration tidal forces and assume he is taking local measurements during small...
19. ### The World’s Largest Vacuum Chamber Settles an Old Question

Recently I came across an excellent video that brings to life an age-old physics teaching theme... The world’s largest vacuum chamber is NASA’s Space Power Facility in Ohio, pictured below. They remove around 30 tons of air from the chamber in order to test equipment during in-space conditions...
20. ### I Historical question: Indications for the need of GR

Hi. There were theoretical (find transformations under which Maxwell's equations remain invariant) and experimental (speed of light is constant, Michelson-Morley) indications that made the development of SR inevitable. But what about GR? Was there a "need" for this theory or was Einstein just...
21. ### I Galilean equivalence for extended objects

The Galilean equivalence principle (or weak equivalence principle) is the statement of the universality of free-fall under gravity. For example, according to Wikipedia, it can be stated as follows My question regards the limitation of the principle to point masses. Does universality of...
22. ### I Would there be an event horizon for a telescope?

Assume we drill a hole through the earth - through the center towards the other side. Then we use a telescope, point it through the hole and observe stars on the other side of the earth. The telescope experiences a constant acceleration from earths gravitation. Accelerated movements have an...
23. ### B Einstein’s equivalence principle for a collapsed star

The Equivalence Principle says depicting gravity as a field associated with matter is equivalent to picturing it as twisting of space. Is there a space-twisting equivalent of a collapsed star as a shell of condensed matter with interior of intense gravitational field energy (found in the field...
24. ### EM Wave creation in different frames of reference

OK, I'm sure I'm just not thinking about this the right way, so please point out my simple mistake. Imagine a charged particle and 2 observers. Observer S is stationary relative to the charged particle, so sees no magnetic field from it. Observer A moves back and forth in front of the...
25. ### I Principle of Equivalence

Equivalence principle says that gravitational forces are equivalent physically to inertial forces. Can someone explain what is meant by that and how was it concluded?
26. ### A Better Equivalence Principle

I am new to relativity, so bare with me. I do not want to argue against it; however, one must admit it is a rather awesomely unwieldy theory. In my self education on the subject, I am bothered by the Equivalence Principle, mainly this: An elevator accelerating through space is no different from...
27. ### Couldn't you unify gravity & the cosmological constant?

...through inertial mass, namely to explain away the sameness of inertial and gravitational mass? If you assume that only inertial mass is a "real" effect, then gravity would simply become a fictious force arising from inertial mass holding matter back from expanding alongside spacetime during...