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

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6answers
167 views

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 ...
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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?
0
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1answer
110 views

If time is like space, why entropy always increases with time? [duplicate]

If time is like space, why entropy always increases with time I should not be able to distinguish whether I am going forwards or backwards in time. As entropy always increase with time. I can ...
1
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1answer
54 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
119 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
32 views

Topics required before studying Tensor Calculus [closed]

Which topics do I need to know before going through tensor calculus?
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1answer
63 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 $0.8 \ c$ ...
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4answers
116 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 ...
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0answers
23 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 ...
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0answers
76 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
72 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 ...
1
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1answer
49 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 ...
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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. ...
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1answer
55 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
70 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
77 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
49 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
104 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
82 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 ...
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1answer
123 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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1answer
38 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 ...
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
415 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
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1answer
87 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 ...
9
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1answer
129 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
209 views

Relativistic time dilation on Mars compared to Earth?

What is the time dilation in Mars, compared to earth? Can we accurately calculate it? What information is needed to do these calculations?
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2answers
55 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
86 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 ...
2
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2answers
85 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 ...
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2answers
74 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 ...
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2answers
179 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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1answer
159 views

Time dilation triplet paradox

Here is the twin paradox with a twist. Scenario 1: An observer (A) leaves from the equator of the earth and travels with an acceleration of $9.8\,\mathrm{m/s^2}$ in a north direction ( i.e. in the ...
0
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3answers
174 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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3answers
97 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 ...
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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
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1answer
66 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$, ...
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0answers
111 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 ...
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1answer
117 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 ...
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0answers
26 views

Index Placement for Spinors in Relativity

This may ultimately be a silly question, but a pedantic mind like mine gets tied into knots over differing notation. (Disclaimer: I'm a mathematician.) Let $\mathbb{W}$ be a complex two-dimensional ...
1
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1answer
43 views

Metric Tensor and Strain Rate Tensor- Comparison of Units

Is there any way the metric tensor can have a dimension in general relativity? I ask because there is an equation where the strain rate tensor of continuum mechanics is expressed as a difference of ...
0
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3answers
135 views

can a spaceship decelerate relativistically? [closed]

Say I have a spaceship, and on board is a laboratory set to accomplish some sort of experiment, simulation, or computation which might take upwards of a few hundred years or more to complete. Instead ...
2
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2answers
220 views

Can all of physics be described by simple math? [closed]

Recently I was browsing through A Dynamical Theory of electromagnetic field by Maxwell and wondered because the paper did not seem to include any vector calculus or any vectors. I thought of the ...
0
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1answer
92 views

Acceleration of objects with speeds comparable to $c$. Can we find acceleration of the frame by treating $v$ in $1/\sqrt{1-v^2/c^2}$ as variable?

We know that the $v-t$ graph for constant acceleration is a straight line. But when the speed becomes comparable to $c$, the speed of light, relativistic effects come into play. Suppose if a rocket on ...
0
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1answer
53 views

Why Space Element of Four Momentum Vector is 3 Momentum Vector?

For example, if we look at the relation between space element of 4-velocity and 3-velocity; and space element of 4-force and 3-force $V = v\cdot\gamma(v)$ $F = f\cdot\gamma(v)$ But ...
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1answer
108 views

Is This Educational Model of Relativity Right? [closed]

After watching and reading about Special Relativity I am still left with some questions unanswered. Can you please tell me if this educational model of relativity, simplified to level of a cartoon, ...
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3answers
115 views

At what rate would I travel back in time at $2c$? [closed]

I was thinking about Einstein's equations and the solutions using imaginary mass and imaginary time. How fast would I have to travel over $c$ to be traveling back in time at minus one meter per ...
-2
votes
2answers
87 views

How to literally slow time [closed]

Let's say there is this car in a bubble of some sort. I want to slow time for that car in the bubble, let's say, by half so if the car is going 40 mph, outside of the bubble, people see it as going 80 ...
0
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0answers
75 views

Two synchronised clocks accelerated perpendicular to Earth's gravitational field [duplicate]

If I have two synchronized (at the station while waiting for me) clocks on a train, one at front and the other one at back, and I start to accelerate the train perpendicular to Earth's gravitational ...
2
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1answer
63 views

Do objects' velocities slow down going into black holes? Would they appear to?

I always hear that time slows down as you enter a black hole, and when I hear this, I always mentally imagine all of a person's motions, including their net velocity relative to the black hole, ...