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Gravity, Acceleration, Time Dilation and the Equivalence Principle

Three clocks are started at exactly the same time on Earth. The first and second clocks are taken into the vacuum of space. The first clock accelerates until it reaches 100,000m/s, then stays at this ...
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1answer
46 views

Graviton detector thought experiment

I was recently thinking of a thought experiment: Assumptions Graviton detectors can exist The equivalence principle will hold in the final theory of quantum gravity We can accelerate the graviton ...
3
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0answers
47 views

What is the inertial mass of a black hole?

Or the inertial mass of any spherically symmetric object, can I calculated by measuring very accurately the spacetime distortion this object produces in its surroundings? With 'inertial mass' I mean ...
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4answers
221 views

Can there be acceleration without velocity?

If I was in a spaceship continually accelerating at $9.81m/s^2 =1g$ in a straight line, I would reach near light speed within a year. On Earth, we are in a gravitational field of $1g$, which ...
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2answers
51 views

Time dilation and freefall (follow up and simplification) [closed]

A person is four miles up in the atmosphere, and freefalls towards earth. Another person is standing on earth, watching them come down. During this period of freefall, which person experiences more ...
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1answer
46 views

Acceleration in Space

Lets assume a body with a certain mass is in a region of space that has zero $g$ (or pretty close to zero $g$). Would acceleration in a straight line produce $g$-forces? Would that mass acquire ...
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0answers
30 views

Dark Matter and Equivalence Principle

Dark Matter effects show up in galaxies. Why isn't it considered as a violation of equivalence principle instead of assuming all these extra non-interacting particles as gravitational mass and ...
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1answer
120 views

F=ma is true in an accelerating coordinate system [closed]

There are plenty of similar topics about the physical or intuitive meaning of the equivalence principle or statement such as ''laws of physics are true in every frame of reference''. Usually answers ...
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0answers
54 views

Is the equivalence principle Machian?

There is a lot of discussion on the subject of Mach's principle, and whether it has any place in the theory of relativity. But it seems to me that one could argue that Mach's principle is at the heart ...
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1answer
41 views

Is a force acting on a freely falling body? [duplicate]

Albert Einstein in his equivalence principle stated that a freely falling body does not experience force, but if I let a ball free fall its velocity increases periodically (it accelerates). How is ...
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0answers
41 views

Bending of light in a gravitational field & the principle of equivalence

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 ...
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0answers
21 views

Does any ordinary object emit radiation due to Unruh effect and equivalence principle? [duplicate]

I am just wondering is there Hawking radiation for any object (that has mass) due to its gravity. Base on the Unruh effect and equivalence principle, any object should emit Black-body radiation or ...
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2answers
69 views

How does general relativity explain the impact force after radial inward fall toward Earth?

I understand that, in the context of the Schwarzschild spacetime (General Relativity), a radially inward falling observer follows a time-like geodesic with zero four-acceleration. There are no forces ...
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1answer
62 views

Einstein equivalence principle cannot entirely predict gravitational time dilation

The Einstein equivalence principle can be used to derive the gravitational redshift of photons, but it does so in an unusual way. The derivation is as follows. Consider an source of photons on the ...
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0answers
24 views

Energy-Mass Equivalence applied to governing equations

To start off with this is an extremely general (vague) questions, and as such I expect vague answers. I've recently been studying the Navier-Stokes equations which govern fluid motion. These ...
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1answer
57 views

Accelerated reference frame in Minkowski space vs pure gravitational field

I just finished reading Einstein's "Relativity: The special and the General Theory", and if I understand Einstein correctly, he says that an accelerated reference frame in Minkowski space (i.e., empty ...
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1answer
27 views

EM wave generation from different frames of reference

Take 2 observers and a charged particle, Observer S is stationary to the particle and sees the electric field and no magnetic field as he is stationary to the particle. Observer A decides to ...
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1answer
163 views

Why must inertial mass and gravitational mass be equal, not just proportional?

I'm certain I'm just under a grave misapprehension. I really just don't understand how one can conclude that inertial mass is equal to gravitational mass. It seems to me that we've simply scaled our ...
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2answers
123 views

Falling with same acceleration and meaning of gravity

My question is what does falling with same acceleration has to do with what Einstein concluded concerning the gravity in terms of the curvature?
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0answers
41 views

Is there any such thing as gravity? [duplicate]

So I was seeing this documentary and ended up knowing that there is no such thing as gravity. It said that we are not being pulled by Earth but being pushed by the space time curvature acc. to general ...
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2answers
61 views

Principle of equivalence

Einstein's principle of equivalence states that one can not distinguish between a freely falling nonrotating system in a gravitational field and a uniformly moving system in the absence of a ...
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2answers
65 views

Black Hole horizons and the Equivalence Principle?

In the reference frame of a freefalling observer, does crossing the event horizon not cause a contradiction between two classical principles that supposedly apply at the event horizon: the equivalence ...
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1answer
47 views

What does gravitational mass mean if (weak) equivalence principle invalid? [closed]

As equivalence principle states Mass and weight are locally in identical ratio for all bodies. --Newton This implies that the gravitational mass does only depends on its inertial mass. Suppose ...
0
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1answer
29 views

The equivalence principle and experiments concerning it?

Imagine that we are in a rocket accelerating with some magnitude $a_1 = dx^2/d^2t$, also imagine that we have a stationary rocket ship in close proximity to ours, stationary relative to our reference ...
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3answers
93 views

Einstein's principle of equivalence; Standing on earth vs sitting in accelerated car

When I am seated in a car that is accelerating in a particular direction I could, for example, throw a ball and it would appear to be flying the opposite way. With the windows covered etc. An ...
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8answers
10k views

Why does a free-falling body experience no force despite accelerating?

Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum. From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational ...
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1answer
130 views

Curvature of spacetime and the equivalence principle

Assuming the Einstein equivalence principle, formulated as following: The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the ...
1
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1answer
476 views

Graviton and principle of equivalence

Is it possible that in a theory of gravitons, i.e., a quantum field theory of gravitation, general relativity's principle of the equivalence of gravitational mass and inertial mass, no longer holds?
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6answers
5k views

Does a person inside a falling bus fall to the front of it?

So I was watching Final Destination 5 and something caught my attention. There's a part where a bridge collapses and everything falls apart, so there's this bus that has a person inside (unaware of ...
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3answers
247 views

I think I am misunderstanding Einstein's equivalence principle and his elevator

I'm having difficulties understanding why a gravitational acceleration can be guaranteed to be locally equivalent to an accelerating frame. Doesn't it matter on how the force is being applied? If the ...
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3answers
223 views

Gravitational potential in GR

Why in GR does the $g_{\mu\nu}$ describe potential?
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2answers
142 views

Why acceleration cannot vanish everywhere?

In attempt to introduce gr concepts When there are gravitational accelerations present, as for example in the gravitational field of the earth, the space cannot be the flat Minkowski space. Indeed, ...
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4answers
350 views

Taking selfies while falling, would you be able to notice a horizon before hitting a singularity?

I am generally interested in the role of "pings"(0a) between participants (a.k.a. "signal roundtrips"(0b), as familiar for instance from Synge's "five point curvature detector") in the determination ...
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2answers
344 views

Why do we feel resistance to gravity rather than the acceleration of gravity?

What's the reason it behaves differently from all other forces? What I mean is, if you're in orbit you're accelerating toward the earth at almost 9.8m/s^2, but you feel nothing. If you are riding a ...
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1answer
131 views

Equivalence principle for test fields

My question is very simple. We all know that, for a test particle(classical) in a gravitational field, the motion is only determined by the geodesic lines(let's forget about the initial conditions for ...
2
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1answer
131 views

Clarification with Einstein's explanation of inertial mass and gravitational mass from his book

In the book "Evolution of Physics" - Albert Einstein and Leopold Infeld, the following explanation is given for two types of masses: A body at rest gives way before the action of an external ...
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2answers
63 views

Free fall for a longer time

When I'm in free fall, I'm weightlessness for only about 1-2 seconds. Is there any way I can feel weightlessness for a longer period of time?
0
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1answer
46 views

Conservation of Energy in Blue Shift

Imagine light coming down and hitting a neutron star. It light is blue-shifted. I know that energy/mass is conserved and that the energy to blue-shift it comes from the gravitational field, but how is ...
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2answers
396 views

Can gyroscope work in zero gravity?

Most ships have two or more gyroscopes to balance on water, man made satellites uses gyroscope for orientation as they fall around earth. All these applications seems to be associated with gravity, ...
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5answers
2k views

In circular motion, with a constant distance, why does the mass of the orbitting object have no effect on its revolution at all?

Using Newton's universal equation and some circular motion equation, the orbiting object's mass cancels out. But can someone please explain why this is without using pure algebra?
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3answers
255 views

Is the lay explanation of the equivalence principle wrong?

The common explanation/trope for the equivalence principle always has something to do with you being inside an elevator or spaceship, and your supposed inability to differentiate, say, gravity from a ...
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1answer
154 views

Relativity of simultaneity in Galileo's Leaning Tower of Pisa experiment

Galileo's conclusion can be roughly summed up as: objects of different masses, when dropped from the same height, descend in the same time interval, independent on their masses (neglecting friction). ...
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2answers
255 views

Is there an accepted axiomatic approach to general relativity?

I am reading Steven Weinberg's book Gravitation and Cosmology. He makes a big deal out of the equivalence principle and showed a bunch of deductions you can make based on it. This surprised me since ...
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1answer
260 views

Inertial and Non-inertial frames of reference

I'm really beginner in physics and I recently started to study the concept of frames of reference, inertial and non-inertial ones. In the end, I thought I had understood it: frames of reference ...
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1answer
85 views

Confusion about Weinberg's discussion of equivalence principle. Help understanding formula

I am reading Steven Weinberg's book Gravitation and Cosmology. On pages 67-68, he begins his discussion of the Principle of Equivalence of Gravitation and Indertia by saying the following: The ...
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2answers
263 views

What am I missing in this thought experiment about a black hole?

I've got a problem setting up a general relativity (GR) thought experiment. Thanks for your help! I'm the observer, in a lab that is falling through the event horizon of a black hole, observing a ...
1
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1answer
92 views

How much of General relativity follows from the invariance of $c$ and an escape velocity?

Just supposing Einstein hadn't come up with his idea of the equivalence principle, leaving him blind for a while. Would he still have been able to come up with General Relativity just using the ...
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4answers
861 views

Is it correct to say that falling object are standing still?

As I was browsing youtube I came across the BBC video "Brian Cox visits the world's biggest vacuum chamber - Human Universe: Episode 4 Preview - BBC Two" He drops a bowling ball and a feather in a ...
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0answers
61 views

Is there a theory that physically explains the origin equivalence principle / explains gravity via acceleration?

I've been thinking about how gravity could arise from a 4th dimensional spinning cylinder with space-time that has pliability like rubber (which I think is a generally accepted analogy). The ...
0
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1answer
60 views

If a place a spring in a box and drop the box, what happens?

Suppose I a holding a box in my hands, and inside the box a spring with some mass attached hangs from the cieling of the box. Initial the system is at equilibrium, then I let go of the box and it ...