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Questions tagged [special-relativity]

The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.

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Special Relativity pothole paradox

Consider a man who is 1 metre in width and is running (at relativistic speeds) towards a pothole in the ground which is also 1 meter in width. In the reference frame of the man it appears as though ...
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Does Doppler effect happen instantly?

Assume that a far star sends light toward a receiver. If we move this antenna such that it accelerate first for a moment, and then it moves with constant speed, we can see that the frequency of the ...
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Would possibility of instant communication break physics?

I recently read a sci-fi book, where some (very few) people can communicate telepathically, which happens to be instantaneous. So, every spaceship has a crew member who telepathically communicates ...
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Shooting someone's past self using special relativity

Suppose A and B are a long distance apart initially. B takes off in a spacecraft in A's direction at a really high speed. Both were aged 0 when B took off. When B about to cross paths with A, A ...
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Time dilation and twin paradox - can this be explained in plain English? [duplicate]

If one twin goes with an extremely fast rocket to Alpha Centauri and back, time is going slower for him, so when he comes back, the twin that stayed on the Earth is older. But... if we look from the ...
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Clock on a pendulum

If a clock is swinging on a pendulum (assume it's on some massive object with gravity) what happens when that system is moving at relativistic speeds? To an inertial observer, on the back-swing (i.e. ...
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In Special Relativity, is it allowed to ask 'How much time has elapsed in a second inertial frame at a particular moment in the first inertial frame'?

Or is it a meaningless question? For example, A and his friend B are the same age initially. B travels relative to A at a very high speed. A keeps observing B from his frame. At one moment, A ...
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Gravitons and self-interaction

In the book quantum field theory and standard model by Schwartz, there is a problem 9.4 that says by considering lorentz invariency of compton scattering, you can prove that for spin 1 field there ...
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To prove: the integration measure is Lorentz invariant (Schwartz's problem 2.6b)

I am stuck on Schwartz's ("Quantum Field Theory and the Standard Model") problem 2.6b, and would be grateful for clarification. (I'm aware that this question has been asked and answered elsewhere (...
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Timelike, spacelike etc. for higher-order tensors

Vectors $V^\mu$ in relativity can be classified into those which are timelike, spacelike and null. A similar classification is available for tensors: A tensor $$T^{\mu_1\mu_2...\mu_p}_{\phantom{\mu_1\...
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Loss of simultaneity in special relativity

I was recently reading Introduction to Classical Mechanics by David Morin and while reading special relativity I came up with a paradox I am not able to resolve. It is basically related to the loss in ...
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Do SR account for one sixth or one third of the anomalous perihelion shift?

In answers to two other questions on this site: Mercury's Orbital Precession in Special Relativity and Do 2-body elliptic orbits precess in special relativity? it is stated that special ...
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Hypothetical effect of Solar System/Orion Spur traveling near speed of light

I was hoping that some genius could explain what we would observe in the universe around us in the following hypothetical scenario in which the earth itself were traveling at or near the speed of ...
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A query on group velocity of light in a vacuum of 30c

I have read that the speed of information propagation in a light packet is equal to the group velocity. But here I wonder if that is always correct. This article below that claims to have ...
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Why is the onboard trip shorter when riding on a relativistic rocket as compared to a Newtonian rocket? [duplicate]

In the top answer for this question on the Space Exploration StackExchange, it's calculated that a rocket traveling at constant 1g of acceleration over 100,000 light years would, under Newtonian ...
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167 views

Simulation of relativistic probe passing through an external solar system

I recently read about the Breakthrough Initiative to launch "StarShot", a nano-probe that is designed to travel to Alpha Centauri at $0.2c$. One of the challenges to be solved involves the precise ...
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D'Inverno Exercise: velocity between reference frames given angle of a rod

I'm trying an exercise from D'Inverno book "Introducing Einstein's Relativity" that says S and S' are in standard configuration with $v = \alpha c$ $(0 < \alpha < 1)$. If a rod at rest in S' ...
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Why has Einstein gotten the credits for “inventing” Special Relativiy, while Lorentz wrote down the Lorentz tranformations first? [on hold]

At the heart of Special Relativity lie the Lorentz transformations, invented by the Dutch physicist Hendrik Antoon Lorentz (the name of the transformation was given by Poincaré in 1905). He wrote them ...
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Help understanding the speed of light in media with refractive index < 1

I have read the standard explanations on this, but I still have trouble with convincing myself that information is not propagating at faster than the speed c in media of refractive index less then ...
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How fast can we get to Alpha Centauri?

Suppose in the near future we send an Antimatter rocket that is capable of constant $1g$ acceleration to our nearest star, Alpha Centauri, $4.3$ light years away and suppose we want the spacecraft to ...
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Checking index notation question [closed]

These seem correct, can I get another set of eyes on here pleae? Source: Self-study in Sean Carroll's Spacetime and Geometry textbook Let $$ X^{\mu\nu} = \left( \begin{array}{cccc} 2 & 0 & ...
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How does a particle move under a constant 4-force?

This question pertains specifically to the case of a constant pure 4-force in special relativity, of the form $\textbf{F} = (f_0, f_x, 0, 0)$, where $f_0 = \frac{γ}c \frac{dE}{dt}$. I understand how ...
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What is the definition of contravariant dual field tensor?

This is p.205 of Ta-pei cheng book. The dual field tensor is defined in $(10.52)$ in terms of the covariant tensor. Then I think the definition of contravariant dual field tensor is just reversing the ...
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Doubt about mathematical construction underlying physical systems

Consider the first and second videos of this playlist $[1]$. It seems the professor tried to discuss some heuristic approach between number theory abstract algebra and physics; Classical Physics is ...
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Special relativity application to a problem [on hold]

Disclosure: This is a homework problem You are on the earth when Einstein starts running away from earth at a speed of $\,0.1c$. When he is $3$ light years away from you (according to you), he ...
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What's incorrect about this reasoning regarding special relativity?

Say two spaceships start at the same point and from the vantage point of your inertial reference frame $S$, Spaceship A travels at $.75c$ and Spaceship B travels at $.25c$, travelling in the same ...
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Why is there a controversy on whether mass increases with speed?

Some people say that mass increases with speed, some people say that the mass of an object is independent of its speed. I understand how some (though not many) things in physics are a matter of ...
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88 views

Relativistic mass effect

Does relativistic mass phenomena only appear while accelerating or even when the object is travelling at constant velocity (say 90% speed of light)?
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Proper time for a relativistic particle in quantum mechanics?

It is an often cited fact that a muon falling through the atmosphere at great speed has a decay time longer than the one we would observe in the same particle at rest due to relativistic effects, and ...
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Another apparent time dilation paradox in special relativity that questions the symmetricness of time dilation

Let's have the classical setup of a stationary observer A and moving observer B moving in the direction of A starting from somewhere far-away. Let's assume the world is three dimensional and, WLOG, B ...
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2answers
78 views

Being $E \neq 0$ and $B \neq 0$ in one frame, is it possible to find $E = 0$ or/and $B = 0$ in another?

Consider a cylindrical symmetrical infinite wire with radius $R$. The wire has constant charge density $\rho$ and current density $\vec j$ (pointing to the right). This is measured from the stationary ...
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What's the relation between the Lorenztz group and spin of particles?

I know that particles are defined in terms of irreducible representations of the Poincaré group, and that the state of a massive particle is defined by its mass and spin, which are the eigenvalues of ...
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Does the derivation of the Lorentz transformation depend on space having at least two spatial dimensions?

Eisberg's 'Fundamentals of Modern Physics' derives the space contraction formula from a mirror experiment in which A reflects a light beam in a direction perpendicular to the motion of B, both ...
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Do $\rho$ and $\vec j$ change in a moving frame?

Consider a cylindrical symmetrical infinite wire with radius $R$. The wire has constant charge density $\rho$ and current density $\vec j$ (pointing to the right). This is measured from the stationary ...
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2answers
190 views

Lorentz contraction (or not) of an accelerated electron bunch

It's a well-known fact from special relativity that moving objects are subject to a length contraction: an object with a proper length $L_0$ moving at a high velocity $v$ will appear to a stationary ...
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Use of angular diameter to determine distance in special relativity

Summary: at relativistic speeds, if you compute a planet's relative distance using angular diameter (roughly proportional to 1/angular diameter), will that computed distance increase or decrease ...
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How does special relativity affect releative velocites? [closed]

For example, I am moving away from earth at a speed of $0.9c$ and I shine a light back to earth using my flashlight. If I am away 2 light years from the earth, will my light reach earth after 20 years ...
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A question on twin paradox [duplicate]

Let there be two children Allen and George . now Alan boards a train and the train moves at a speed comparable to light. now because George is on the station for George being at rest Allen is moving ...
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What is the proper way to explain the twin paradox?

The paradox in the twin paradox is that the situation appears symmetrical so each twin should think the other has aged less, which is of course impossible. There are a thousand explanations out there ...
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On the time dilation and Quantum Superposition [duplicate]

The time dilation says time will pass different for moving observers. But if the twins are in an experiment who have same metabolic rate... or in easy meaning changes occur at a same rate in both ...
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68 views

The Meaning of $u=c\sin\theta$ Equation in Special Relativity [on hold]

In the Introductory Special Relativity book, by W G V Rosser, page 19, the author is formulating the relativistic kinetic energy equation. In his derivation, he writes the following equation: $$u=c\...
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2answers
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Warping Space Time By Focusing on Getting Smaller Rather Than More Energy?

So all energy/mater warps space-time, right? However, whenever we talk about the human manipulation of space-time it is a far-off goal requiring nothing short of tremendous amounts of energy and ...
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7answers
15k views

Reflection At Speed of Light

I have looked online to no avail. There is two competing answers and I am curious to know which one is right. Someone asked me this question. If you are traveling at the speed of light can you see ...
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3answers
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Special Relativity - Clock Synchronization

In Special Relativity - Is their a definition of "synchronizing" clocks which are moving relative to each other? I suspect such a definition makes no sense - as moving clocks belong to separate ...
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60 views

The facts of travelling at the speed of light [duplicate]

I’m travelling at the speed of light. If I hold a mirror in front of me could I see my face?
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59 views

Effects of Relativistic/Inertial Mass

What would happen to a ball of ice in a remote region of space if spun in a circle accelerating toward the speed of light? As the ball of ice approaches the speed of light, does it melt/sublimate as ...
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Concerning the increase in mass as velocity increases [duplicate]

This increase in mass is relativistic. Let an object approach the velocity of light, as it does we as observers notice that its moving very slowly, and it's mass is increasing significantly. What ...
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180 views

SR: constant acceleration wordline simultaneity

A worldline $W$ with constant acceleration $a$ is given parametrically by $$t=\frac{c}{a} \sinh(\frac{a \tau}{c}), \quad x=\frac{c^2}{a} \cosh(\frac{a \tau}{c}).$$ Let $E=(0,0,0,0)$. I showed that for ...
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Electromagnetic Lorentz invariant apparent violation

We know that the scalar product $$\vec{E}\cdot \vec{B}$$ is a relativistic invariant in any inertial frame of reference. This made me pose the following question: Suppose we have a charged filament ...
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447 views

How can zero point energy vacuum be Lorentz invariant?

What distribution of electromagnetic radiation is Lorentz invariant? How can radiation look the same regardless of inertial frame? According to Marshall and Boyer a cubic distribution like $ \rho(\...