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

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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}} \eta_{\...
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2answers
125 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 ...
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2answers
83 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
143 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 ...
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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 ...
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24 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 ...
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427 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 ...
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1answer
90 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 ...
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134 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 ...
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234 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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57 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, $P_a$ ...
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4answers
95 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
94 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
86 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
183 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 (...
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1answer
203 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 ...
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3answers
181 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 ...
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3answers
102 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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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 ...
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1answer
77 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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1answer
141 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
123 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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27 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 ...
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53 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 ...
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3answers
136 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 ...
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2answers
225 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 ...
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1answer
104 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 ...
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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
109 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
119 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 second?...
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2answers
90 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 ...
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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 ...
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1answer
72 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, ...
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81 views

Relativistic Effects of Radioactive Decay in Carbon Dating

Theoretically if in early years the earth was moving at an astronomically different pace (whether in orbit or rotation, whatever sounds better) wouldn't that alter the science of carbon dating? As I ...
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105 views

Black Holes and Einstein Field Equations

I recently watched a video where Michio Kaku argues that there must be something fundamentally wrong with the theory of General Relativity because it gives time t=0 as a solution at the centre of a ...
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1answer
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Do matter that falls in a black hole go to the future and the end of the universe?

Black holes are black because everything that enters don't exists anymore. When you pass the event horizon, the time stops for you, all the future of the universe has passed for you and the universe ...
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2answers
154 views

The Twin Paradox using reference frame following the ship

The Twin Paradox is undoubtedly one of the most discussed things in special relativity and have a tendency to confuse most of us. Classically, it's resolved by either stick to one of the three ...
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1answer
101 views

Einsteins thought experiment on travelling with a light wave

This might be better suited to the science.history.SE; but I thought I would try here first. Einstein reportedly considered a thought experiment where one considers travelling alongside a light wave; ...
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2answers
208 views

Does deceleration (or negative acceleration) feel like acceleration?

This may seem like a dumb question, but I'm having a hard time trying to intuit the answer. The question is in relation to Einstein's famous thought experiment which says that it is impossible for a ...
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2answers
181 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 ...
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90 views

Help with relativity simultaneity paradox

To begin I will explain briefly a classic thought experiment used to demonstrate simultaneity; There is a 100m long train rushing towards a 100m tunnel at a fraction of the speed of light, from an ...
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42 views

Ligth clock with spaceships side-by-side

In the reference frame of an observer, two spaceships travel in a straight direction (e.g. x axis) at a very high velocity and side-by-side; the distance between them is always d (km) = c (km/s) x 0.1 ...
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2answers
136 views

If there is no definite speed in the universe, only relative speeds, how does energy increase when velocity approaches the speed of light?

Is the concept of energy increasing as it approaches the speed of light based on the fact that this is only true relative to the observer? Lets say, there's a scenario where a person in a rocket ...
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1answer
100 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 reference?...
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2answers
152 views

How do we know the speed of light is constant and spacetime dilates rather than vice versa?

Some conspiracy nut was telling me that Einstein was BS and there's a giant conspiracy that he's wrong but scientists would loose all their jobs if they admitted it. Of course this is all baloney, ...
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2answers
558 views

Relativistic Energy

The question stated: By what percentage does your rest mass increase when you climb 30m to the top of a ten-story building? New to the concept of relativistic energy, I was a bit confused with ...
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4answers
290 views

Using Lorentz transformations

The question states that two particles in a high-energy accelerator experiment approach each other head-on with a relative speed of $0.890 \, c$. Both particles travel at the same speed on a straight ...
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37 views

Clarification of Type D space-time

I've asked this question on MathOverflow but received no feedback, so I thought I'd try better luck here. I've read the following formulation of the Goldberg-Sachs theorem in Chandrasekhar's ...
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3answers
111 views

Does the accelerated rate of expansion of the Universe have any effect on the speed of light in vacuum?

So I was just wondering about this as I finished reading about Michelson-Morley's experiment which disproved the ether theory. My question is since the Universe is constantly expanding and that too ...
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50 views

Model of spherical wave fronts in relativity

In relativity, the 3-surface formed by light rays emanating from an event as they evolve in time has the shape of a hypercone wich is flat. I have difficulties seeing how can a spherical wave front, ...