The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.

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6answers
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Wouldn't backwards time travel break the law of conservation of mass? [closed]

We know from the law of conservation of mass that the amount of mass in the universe is constant. Suppose there were a way for a person to travel backwards in time. Let's call this mass $m_t$ for some ...
15
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8answers
4k views

Is time travel possible? Is it possible to go back in time?

I read somewhere that according to relativity, black holes and other space related stuff it is possible to jump into past. Is it possible for anything to go back in time either continuously or by ...
0
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1answer
77 views

How to prove that “all unaccelerated frames behave likely for all isolated bodies”? [closed]

Say in an unaccelerated frame "S" a "isolated body A" moves with constancy of velocity , can we predict mathematically that any other such body B will move with same velocity in that frame.... My ...
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1answer
40 views

Relative speed of Geostationary satellite with respect to earth?

I was wondering whether relative speed of geostationary satellite with respect to earth is zero or not.Since angular velocity of satellite about earth is same as angular speed of earth about its own ...
2
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1answer
58 views

How far can a sub-light-speed particle travel? And how fast will it arrive? [duplicate]

If we send a photon away from earth, it would eventually reach a comoving distance of about 16.5 billion light years (the universe's event horizon). I'm interested in how far (in comoving distance) ...
2
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1answer
54 views

Is there a gravitational radiation reaction force?

As you may know, the linearized relativity theory (or gravitoelectromagnetism), obeys equations analogous to Maxwell's equations in electrodynamics. These equations in ED result in the troubling ...
0
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0answers
29 views

Age difference between hands and feet due to relativity?

According to relativity time passes faster the faster something moves, and gravity slows time. My head is moving faster than my feet (assuming I'm not at one of the poles). My head is further away ...
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2answers
107 views

Most stationary object in the universe

There is an object in the universe for which the Sun appears to be more stationary as it travels through the universe than a star on some other system. There is probably another object for which both ...
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4answers
72 views

Relativity: stationary vs moving

In the book The Elegant Universe, Greene describes a situation in which there are two space travelers, George and Gracie, moving in relationship towards each other at a constant velocity with no other ...
2
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1answer
60 views

A rope between Earth and Moon - Length and Speed of Light [duplicate]

An earlier question was asked on what would happen if a rope was attached between Moon and Earth, but the question was more about the impacts in terms of geology. We keep the same experiment setup : ...
1
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0answers
39 views

Biological concept behind time dilation [duplicate]

What is the exact mechanism which makes aging process slow for persons travelling at higher velocity relatively. How does our body cells responds to gravity and undergo aging?
1
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2answers
97 views

Time in general relativity

A physical quantity is introduced by its operational definition. In general relativity we use a differential manifold to describe the 4-dimensional space-time and, to identify a point in it, we use a ...
1
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1answer
40 views

Does an observer measure magnetic field when moving inside a static E field?

Imagine a static electric field shaped as a sinusoid created by an array of electrodes on an infinite line. Does an observer flying parallel inside this e-field measure an h-field ?
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1answer
103 views

Boundary conditions of fields from the stationary action principle

First principle of stationary action Consider a real Klein-Gordon scalar field $\phi$ living in a $D$ dimensional flat spacetime. The field is considered off shell (the on shell condition is defined ...
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0answers
30 views
0
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1answer
59 views

Spacelike interval and length contraction

I am having a serious trouble finding an agreement between the two facts in Special Relativity: (1) given two events $A$ and $B$ in spacetime separeted by a spacelike interval $s$, the distance in ...
1
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0answers
26 views

Simple special relativity problem [closed]

A body at rest in a frame of reference $S$ disintegrates into two pieces moving in opposite directions. The masses of each fragment are $3.0 \ kg$ and $4.0 \ kg$ and their velocities $0.8 \ c$ ...
1
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4answers
94 views

What if a light clock travels perpendicular to mirrors that make up the clock?

I'm guessing you're all familiar with the classic intuitive way of explaining time dilation: with a light clock traveling at velocity v directed at a parallel direction to the mirrors that make up the ...
0
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0answers
22 views

Textbooks to teach myself physics [duplicate]

I'm currently studying mathematics in Switzerland and only have a couple hours of General Physics a week. I would like to teach myself physics at a more advanced level but I don't know what textbooks ...
0
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0answers
73 views

Why is special relativity still in use, if general relativity is more broad?

I always thought special relativity is only there because it is the building block for "The General theory of Relativity", until recently I encountered a text from my course book given below. A ...
0
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0answers
63 views

Graduate level orbital mechanics book

I recently finished an undergraduate course in classical mechanics and really enjoyed the subject, particularly the sections regarding the mechanics of orbits. I am considering pursuing a graduate ...
22
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5answers
3k views

How does “warp drive” not violate Special Relativity causality constraints?

I'm talking about this nonsense: http://www.washingtonpost.com/news/post-nation/wp/2014/06/11/this-is-the-amazing-design-for-nasas-star-trek-style-space-ship-the-ixs-enterprise/ Now, I'm aware that ...
1
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1answer
43 views

Transformation of energy of a photon

I'm new to the forum so excuse me if I'm doing anything in a wrong format. My question is this: A photon fired from a spaceship at rest has energy $E$, if the spaceship starts moving with speed ...
0
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0answers
27 views

4-velocity in an accelerated frame

I am trying to check some calculations of the displacement tensor from a paper that has been given to me by my advisor. And it seems I am stuck on the form of the 4-velocity in an accelerated frame. ...
-2
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1answer
48 views

is relativity an illusion , a measuring error? [closed]

In the proof of relativity through lorenz transformation it looks like the relativity is essentially a mis of accuracy to measure the time and lengths. Am I true?
3
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0answers
61 views

Michelson–Morley experiment's aether; Why is the time gained from travelling downwind less than that lost travelling upwind?

From the Wikipedia article on the Michelson–Morley experiment, explaining one of the concepts behind the landmark experiment: "If the Earth is traveling through an aether medium, a beam reflecting ...
0
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1answer
69 views

Are fully raised/lowered versions of Kronecker delta tensors?

I am confused. I have two textbooks contradicting each other, at least, it seems to me so. The first one – "Field theory" by Landau & Lifshitz says that by lowering or raising one index of ...
0
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0answers
43 views

Explicit calculation using metric tensor

I'm trying to calculate the following quantity: $$S_{\bar{\alpha} \bar{\beta}} \equiv \left( \Lambda^{-1} \right)^\alpha_{ \ \bar{\alpha}} \left( \Lambda^{-1} \right)^\beta_{ \ \bar{\beta}} ...
1
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2answers
73 views

Do things move towards each other in space?

I watched a video once explaining space-time curvature, and it said that one of the things that made Einstein think of it is because objects in free fall move radially inward, so two objects falling ...
0
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2answers
76 views

How does a flash of light appear to a high speed observer

Imagine two dark chambers separated by a light-proof partition each with a 30m high ceiling. Chamber A has a letter A painted in white on its black ceiling, chamber B has the letter B also in white on ...
-1
votes
1answer
82 views

proper time interval

We have two frames s and s' , s' moves with a constant velocity 'v' with respect to s in positive x direction, a particle B is thrown downwards from s' , and it collides with a particle A , the point ...
0
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3answers
153 views

Are there any well-known large body objects moving at a significant fraction of the speed of light relative to earth?

Introduction I've been reading a book called PsychoPhysics, part of the "Illuminati God Series" by Mike Hockney (a pseudonym). Without getting into too much detail, they basically believe that the ...
0
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1answer
35 views

Why does the light beam moves diagonally?

In almost all articles that explains Relativity or Time dilation. They start by saying the the Light is absolute and isn't affected by the inertial frames of reference yet when they start to explain ...
9
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1answer
109 views

How are the turbulent spectra determined in relativistic turbulence?

In a non-relativistic compressible fluid, the turbulent energy spectra are well-understood and appear to follow the Kolmogorov hypothesis. It would also appear that relativistic turbulence also ...
0
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1answer
23 views

In a system of two charges, if one charge disappears, does the force on other charge vanish instantaneouly?

It is commonly asked that if the sun dissappears, will earth shoot off in a tangent instantaneously or after some time. We know from the theory of relativity that the gravity waves travel at the speed ...
6
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1answer
405 views

Can we actually have null curves in Minkowski space?

I know that this sounds really stupid but, when I think of the Minkowski space I cannot imagine a null curve, only null lines. For me, the only possible way to have one is to change the basis of the ...
2
votes
1answer
80 views

Does the magnetic force depend on the reference frame?

Force due to a moving charge = qvB Immagine a charge moving with some velocity on earth and I calculate the force due to its magnetic field with Earth as reference frame for me. An astronaut in space ...
2
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2answers
73 views

Would Magnetic field be Zero if measured while moving along with charges?

According to Einstein's relativistic interpretation magnetic field caused by charges moving inside a wire is caused only by the relative speed between charges and the observer. So, if electrons are ...
0
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2answers
51 views

Time dilation and reference frame in an orbiting context [closed]

I have looked for other answers, but most confused me more than clarified and did not provide specific calculations. So I am still struggling with this simple question. Consider two persons, $P_a$ ...
0
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4answers
76 views

Relativity and “light years”

As I understand relativity, time is relative to your velocity, meaning your watch moves slower relative to those who are stationary (relatively) when moving at great speeds. So if that's true then ...
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2answers
61 views

Big Bang: Initial velocity of all matter in four dimensions? [closed]

Consider this hypothesis: Two objects A and B, are able to maintain their spatial distance. Object A is near a neutron star, and thus it clock is running at a different speed than object B, and both ...
0
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2answers
178 views

Is the intuition of “absolute simultaneity” necessarily wrong?

I read about Einstein’s theories of relativity with all the interesting stuff like time dilation, mass increase and whatnot. And also about the relativity or conventionality of simultaneity. The ...
0
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2answers
161 views

Special Relativity and Gravity

As Einstein was seeking a relativistic theory of gravity, he thought that special relativity should be upgraded to general relativity thus promoting the Minkowski space to curved pseudo-Riemannian ...
0
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2answers
156 views

Why does gravity affect time?

So Special Relativity states that for all non-accelerating objects of matter the laws of physics are the same. I'm confused on why this law of physic applies to objects in acceleration and gravity ...
0
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3answers
79 views

Equal and opposite reaction at light speed

My knowledge of physics is very limited. And this question is only really to help me put to rest a question i have had for some time. I would like the answer to be a simple one as i am not really in ...
0
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0answers
17 views

Michelson-Morley expression for relative phase

I am trying to find the relative phase when ether is propagating vertically versus when ether is propagating horizontally. The question is written below When the light (of wavelength) is split at the ...
0
votes
1answer
60 views

Why does photon have to travel in sideways to hit the light clock?

From this article, Let’s say Alice is holding a light clock, and Bob is watching her run by, while holding it, with speed V. Alice is standing still (according to Alice), and the time,$ \tau$, ...
0
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0answers
87 views

Can a black hole move at speed of light?

Black hole comes in all sizes ranging from microscopic black hole on a quantum scale to supermassive black hole that resides in the center of probably every galaxy. Photon have no rest mass hence they ...
1
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1answer
88 views

How relativity affects projectile motion?

If, for example, I'm in a train traveling on earth at $.99c$, and I drop a ball from a $1~\text{m}$ height inside that train how long would it take to hit the ground from the ball's frame of ...
-2
votes
1answer
104 views

Do Quantum Mechanics At The Macro Scale Disprove General Relativity or Prove Something New?

We all know about the discrepancy between relativity and quantum physics at the scale relative to particles. Wouldn't the fact that recent experiments show quantum effects at the macro-scale in some ...