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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Electromagnetic tensor in cylindrical coordinates from scratch

I want to calculate the electromagnetic tensor components in cylindrical coordinates. Suppose I did not know that those components are given in Cartesian coordinates by $$(F^{\mu \nu})= ...
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1answer
95 views

Clock on constantly accelerating object approaches Gudermannian limit?

If an object is moving away from X with a constant acceleration of a, its velocity at time t (relative to X and accounting for relativity) is given by: ...
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2answers
81 views

Einstein's train-platform thought experiment — what if we're not talking about light

I'm trying to understand the famous train-platform thought experiment ( http://www.bartleby.com/173/9.html ). I understand part of the Theory of Relativity is that the speed of light is the same ...
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1answer
93 views

Does light still slow down in the direction of motion?

This is quite a naive question however I hope to learn from this - I had always learnt a light clock in a space ship is placed like so : That said as the light moves the light will seem to slow ...
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1answer
156 views

Time dilation confusion? [duplicate]

If I understand the theory correctly, time dilation causes a moving clock to tick slower than a stationary clock. If clock A is moving relative to clock B, then clock A ticks slower. However, ...
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2answers
168 views

Griffiths' argument that Newton's third law is invalid in special relativity [duplicate]

I believe that Newton's third law is valid in special relativity. But I read an argument in Griffiths' textbook Introduction to Electrodynamics (3rd edition), where he argued on page 517, that ...
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4answers
64 views

Time dilation and Lorentz transformation

I have trouble understanding the Lorentz transformation to proof the dilation of time. If I use: $$dt ^{'} = \frac{dt}{\sqrt{(1-(v^2/c^2))}}$$ Understanding that $S^{'}$ is the moving frame of ...
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1answer
85 views

Signal travels with speed greater than light breaks causality

Signal can't travel at speed greater than light speed in vacuum which is a assumption of special relativity. But if a signal travels at speed greater than $c$ then it will violate causality. I tried ...
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0answers
41 views

Measuring distance in a spaceship moving with 0.5c [closed]

If there are a spaceship moving at a speed of 0.5c that sent a photon when an asteroid was exactly $3\times 10^8$ m away, will the distance between the spaceship and the asteroid when the photon hits ...
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1answer
32 views

Particle lifetime doesn't depend upon longitudinal momentum

I am writing a report on an analysis of the $B_{s}$ meson from CDF data, and as part of the lifetime analysis, I have noted down that: $$\tau = \frac{l_{xy} m_{B_{s}}}{p_{T}}$$ Where $l_{xy}$ is the ...
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3answers
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Can radioactivity be slowed through time dilation?

Can radioactivity be slowed using the effect of time dilation? If you put cesium, tritium or uranium in a cyclotron at relativisitic speeds, do their half lives become longer in our frame? Could ...
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1answer
65 views

Gravitational waves induce changes in the $h_{00}$ (time) component of the metric?

I'm rather stumped by a subtle point regarding metric perturbations of GW. I'm well aware the GW are able to produce changes in the flat space metric, They are transverse and have planes of ...
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3answers
86 views

Time in spaceships near the speed of light

I know that the time on a moving object moves slowly compared to a stationery one, but if someone on a spaceship that moves at V=0.5c and a person is driving it. Will he notice that the clock on his ...
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101 views

General Relativity as a Special Relativistic Field Theory

In this question, I want to consider only the classical case. I have seen the statement that general relativity can be considered as a spin-2 field living on a Minkowski background. In that case, you ...
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1answer
45 views

Representing 1+1 Minkowski space as a surface in 3D Euclidean space

In 1+1 Minkowski space the distance between two points is given by$$ (x_1 -x_2)^2 -(t_1 - t_2)^2.$$ This is different from the Euclidean distance. But is it possible to come up with a 2D surface ...
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1answer
53 views

Exercise prob. in Lorentz invariance [closed]

How we do prove that $\langle p\vert q\rangle$ is an invariant by a boost along $z$ axis knowing that: $$\langle p\vert q\rangle=(2\pi)^3\cdot2\cdot E\cdot\delta(p-q)$$ where $\delta(x)$ is the Dirac ...
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36 views

Relativistic Particles [closed]

The question: An electron is moving at $0.6c$ in the lab frame. For an observer moving at $0.8c$ in the same direction as the electron's motion, what is the electron's kinetic energy (in MeV)? ...
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2answers
69 views

A definition for relativistic energy without quantum mechanics

What are the minimal postulates to define energy in special relativity? Let us assume that momentum has not been defined yet (it can be defined from the energy in fact). I expect we are looking for ...
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140 views

Relativistic electrodynamics between two point charges moving in perpendicular directions [closed]

Let there be two point charges, positive or negative, having velocities in directions perpendicular to each other. I need to evaluate the total interactive force on those (Lorentz force). I do it by ...
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1answer
57 views

How to use Special Relativity in simple numericals? [closed]

So I was recently thinking about what an electron's velocity would be after it was accelerated through a potential difference of 1 V. Doing simple calculations like just dividing its energy (which ...
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1answer
148 views

Feynman Lectures on Physics, Michelson Morley question about angle of light

My question is similar, if not identical, to this one, but I don't find the answer satisfying, given the context of experiment. First, here is an outline my understanding of the motivation behind the ...
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2answers
58 views

Why is the SR behavior of mass and a clock different? [closed]

A frame contains a mass and a clock, an an adjacent frame contains an identical mass and clock. One frame travels and returns. The special relativity equations for mass and time are identical in ...
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76 views

Why did Einstein allow unphysical objects in his 1906 paper on $E=mc^2$?

In the first part of this paper, Einstein considers a "rigid cylinder", "massless cavity", as well as a "massless carrier mechanism" that is used to transport the massless cavity. These hypothetical ...
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53 views

Transformation of coordinates in relativity

I'm doing some self studying through a textbook. Here I will post the question exactly, and show what I have done to solve the problem. I'm completely convinced there is an error in the text, and I ...
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0answers
68 views

Light at the Speed of Light [duplicate]

Since light particles travel at the speed of light, we know it's possible for something to travel at that speed. However, since all things are relative, and if time does stop at the speed of light, ...
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1answer
76 views

Special relativity - Nokton theory [closed]

Is this theory described in this link Nokton theory respects special relativity conditions.
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1answer
54 views

Effects of FTL travel on time [closed]

The twin paradox explains, using relativity theory, what happens to a person travelling close to the speed of light. When he returns to Earth, he finds his twin brother much older because the ...
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2answers
117 views

Why invariance holds for the electromagnetic waves but not for the mechanical waves?

Why the electromagnetic wave equation provides a wave with constant speed in all reference frames, but the mechanical elastic wave equation (from linear elasticity) does not? The electromagnetic wave ...
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1answer
74 views

Trouble in understanding spacetime

I have a problem in understanding spacetime. What i understood from the conversion of time to distance is that the interval between any two events is always the same for any observer. But how is that ...
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4answers
211 views

Explanation for a much simpler version of the twin paradox?

I have seen the classical twin paradox before. It uses a twin stationary on Earth and the other traveling away and back. I have seen many contradictory solutions for it, some use general relativity, ...
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1answer
50 views

Confusion with Thomas precession

Suppose an inertial frame $S^\prime$ is moving with a relative velocity $\textbf{v}=v\hat{n}$ w.r.t another intertial frame S with their axes parallel and $\hat{n}$ is an arbitrary direction. In that ...
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4answers
158 views

How is it that we can send signals faster than the speed of light?

I came across this while reading The Feynmann Lectures on Physics (Vol.1,Ch.7)- According to Newton, the gravitational effect is instantaneous, that is, if we were to move a mass, we would at once ...
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1answer
41 views

Twin paradox on hypertorus [duplicate]

I will not describe the twin paradox again. But let's suppose we have two twins, one stationary and the other moving with uniform velocity $c/2$ for instance. And let's suppose that they live in a ...
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4answers
138 views

Does sound waves pick up the speed of its source?

I googled the speed of sound and found that it only depends on the medium (just like the speed of light but with different parameters). I can't see how it doesn't pick up the speed of its source! I ...
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2answers
79 views

Boldly taken postulates

Einstein's Special theory of relativity was a landmark in physics, which totally changed our viewpoint of observing physical phenomena. While proposing his new theory, Einstein assumed two simple but ...
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Twin paradox with horns [closed]

I am trying to figure out if my conception of time dilation is correct. In order to avoid the acceleration-deceleration complexity in the traditional twin paradox statement, I came up with my own ...
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1answer
55 views

Geometrically deriving Lorentz transformation from Minkowski diagram

How can we derive Lorentz transformation from a Minkowski diagram (like below image) by using only geometry theorems such as sines theorem and Pythagoras theorem?
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64 views

Are there (interesting) Poincare-invariant QFTs with non-invariant Lagrangian densities?

In all QFTs I know, the Lagrangian density is completely invariant under the Poincare group, $$ \mathcal L \to \mathcal L. $$ On the other hand, the action would be invariant even if the Lagrangian ...
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1answer
98 views

Working with indices of tensors in special relativity

I'm trying to understand tensor notation and working with indices in special relativity. I use a book for this purpose in which $\eta_{\mu\nu}=\eta^{\mu\nu}$ is used for the metric tensor and a vector ...
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1answer
79 views

Can the value of $c$ be calculated from Relativity? [duplicate]

I have three related questions about what theories or equations can calculate and what is an input parameter/constant to the theories. This question is not about parameter units (as another similar ...
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1answer
68 views

Theory of relativity paradox? [duplicate]

I have seen the classical twin paradox before. It uses a twin stationary on Earth and the other traveling away and back. I have seen many contradictory solutions for it, some use general relativity, ...
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0answers
27 views

Special Relativity - Observing events multiple times [duplicate]

At t = -1, you observe an event to your left. At t = 0, you accelerate to 0.5c (to your right). Might you then observe that same event (to your left) again? For example, say you observe an event x = ...
2
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1answer
77 views

Special relativity and uniform circular motion

Suppose we have two observers A and B. A is in some inertial frame. B is undergoing uniform circular motion with some speed $v$ as observed by A. They each have a clock. My concern is with what A ...
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2answers
140 views

Speed bigger than light? [duplicate]

We know, according relativity theory, no information or matter can travel with velocity bigger than light. However, consider the following situation: a completely empty water hose is hypothetically ...
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2answers
186 views

Relativity gedanken experiment

Lets consider the following thought experiment: A spaceship is in circular orbit around Earth traveling at 99% of $c$ (the orbital distance is chosen in such a way that inside the ship there are no ...
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1answer
25 views

Rest mass of a moving particle that decys into two phtons

A particle of rest mass M is moving along the positive x direction. It decays into two photons having energies 1 GeV and 0.82 GeV, and these go in different directions making angles of 45 and 60 ...
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1answer
54 views

What does it mean to say that something is “relativistic for an electron”?

I want to understand a concept better. I did a homework problem where I solved it all the way, then checked my answer with a solution set. My answer was different, so I followed the solution set from ...
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0answers
26 views

Linkal causality in special relativity

I have a slight variation of the barn / ladder paradox, where there is a ladder too long to fit into a barn at rest, but when moving at a sufficient speed, it is length contracted with regards to the ...
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2answers
68 views

Exercise 18b in Schutz's First course in GR

The question is as follows: Show that a timelike vector and a non-zero null vector cannot be orthogonal. So we have a timelike vector $\vec{A}$, s.t $\vec{A}^2<0$; and a non-zero null vector, ...
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1answer
60 views

Heisenberg Uncertainty Relation and Relativity

It's well known that in QM the position and momentum of a particle cannot be known simultaneously. It's also well known that in special relativity the idea of simultaneity loses its meaning. Would it ...