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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2answers
132 views

General “relativity” without special relativity

I was wondering if there could be a way of using the principle of equivalence and develop a theory of warped space-time without using special relativity, ie, without assuming any maximum possible ...
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Sampling Maxwell-Jüttner distribution for non-unity mass and speed of light

I am trying to sample Maxwell-Jüttner distribution using the Sobol method as described in Zenitani Loading relativistic Maxwell distributions in particle simulations (2015). Equation (2) in the paper ...
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Applying a General Lorentz Boost to Multi-Partite Quantum State in Dirac Notation

I would like to apply a General Lorentz Boost to some Multi-partite Quantum State. I have read several papers (like this) on the theory of boosting quantum states, but I have a hard time applying ...
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Why all theories are Lorentz invariant?

Ok, in studying of Maxwell equations we have violation of Galilean relativity. This implies necessity of other transformations which make Maxwell equations covariant (invariant in form) under this ...
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1answer
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Building the Lagrangian of electromagnetism from the Lorentz invariant?

The definition of the relativistic Action is $$ S=\int_a^b ds $$ The Lorentz invariant of electromagnetism is $$ s^2=\frac{1}{c^2}||\mathbf{E}||^2-||\mathbf{B}||^2-2i\frac{1}{c}(\mathbf{B}\cdot \...
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Clock postulate validity

As far as I understood, the generalized clock postulate says that there is no difference between the measurements of a non-inertial observer (NIO) and those of his co-moving inertial observer (CMIO) ...
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1answer
124 views

Images traveling faster than light

Please help me understand my mistake(s) in this reasoning. I will write as if I knew exactly what I'm talking about for the sake of clarity, but I of course don't. Consider observer A and its ...
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Thought experiment and possible contradiction between electromagnetism and special relativity (Part I)

I have designed a simple and qualitative thought experiment through which I believe that I have encountered an inconsistency in the relativistic electromagnetism. A point charge $+q$, with respect to ...
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86 views

Einstein's train experiment-Do waves from lightning flashes meet after the same number of cycles for all observers? [closed]

In Einstein's thought experiment about moving and stationary observers and two lightning flashes, let's say that we replace the lightning flashes with a pulses of mono-chromatic light, with both ...
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63 views

Why do electrons have rest energy?

E=mc² so inserting the value of m and c we get 0.511 MeV for electron but then what does this energy account for coz according to me electrons are not made up of any particles so this doesn't account ...
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32 views

Proof of skewsymmetry of electromagntic function in Minkowski spacetime

I have been studying special relativity from the Gregory Naber's book: "The geometry of Minkowski spacetime" and I found a very strange proof. In Section 2.1, just before of equation 2.1.2. the book ...
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1answer
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Special Relativity Frame Ambiguity [duplicate]

If I have some predefined coordinate system — “my rest frame,” then I pick an “inertial frame” moving at some velocity with respect to my “rest frame.” Special relativity states that in the rest frame,...
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The imaginary time [duplicate]

Some people work with the interpretation that the time basis vector has magnitude sqrt(-1) to justify the negative sign in a -+++ Minkowski metric signature. I came across a Youtube comment that ...
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2answers
105 views

Why physics should be the same in all inertial frame? [closed]

One of the postulates of special relativity is that physics should be the same in all inertial frame. Suppose we have two observers $A$ and $B$ suppose that $A$ is accelerated. Now suppose that we ...
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Transverse Relativistic Doppler effect in Non-inertial reference frame

If I have a Non-inertial reference frame in Earth (rotating camera or just my rotating head with eyes) and I am watching the Moon. If my Non-inertial reference frame in Earth rotating with the speed ...
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56 views

Work on two charges in mutually retarded field

Consider two particles with charges $q$ and $Q$ and with an initial distance of $3L$. Now I move each charge a distance $L$ closer to the other, such that the final distance is $L$. The initial and ...
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1answer
41 views

Moving clocks observed with different observers

If a clock is moving near to speed of light with constant velocity it'll slow down, but if I were to observe from the clock will the observer on Earth slow down?
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33 views

Red shift of radio signals

If a radio signal is red-shifted does it still last the same amount of time? Knowing the signal wavelength is now longer but still is traveling at the speed of light one would assume the radio message ...
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2answers
70 views

Effect of finite speed of light on timings of events

In relativity when an observer records an event some distance away from him, the timing of the event he measures would be different from what he would measure if he was close to the event as light ...
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1answer
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The spinor metric, basic spinor calculations and spinor indices

I'm currently reading the textbook "Finite Quantum Electrodynamics" by Günter Scharf, but I find myself stuck already on page 24. Background Scharf introduces the index-raising symbol (spinor metric)...
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2answers
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What is the mass of photon? [duplicate]

I'm sorry if this question is asked before, but I searched through the site and none satisfied me. In most of the books I've come across, they just write "rest mass of photon is zero." But never talk ...
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4answers
145 views

Einstein's train, considering the thunder

From Einstein's "easy" explanation https://www.bartleby.com/173/9.html (Yes, I have reviewed 8 other answers to similar questions. Please bear with me.) M is on the platform, T (aka M') is on the ...
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Relativistic constant acceleration in the framework of general relativity

Regarding the constant acceleration of a spacecraft towards relativistic velocities, the general equations are found at the following link: Baez However, if the distance covered is in excess of 1 ...
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2answers
60 views

Relativistic Doppler Effect between rotating bodies

The Wikipedia article "Relativistic Doppler effect - One object in circular motion around the other" confused me. There they say that when the light source orbits the observer, the observation of ...
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1answer
180 views

$z$ component of angular momentum under Lorentz transformation for massless particle

This question is related to this Helicity states. Suppose we have $k=[\omega,0,0,\omega]$. In Weinberg's book The Quantum Theory of Fields: Volume I he defines the state $|k,\sigma\rangle$ as an ...
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Which frame to consider for time dilation? [duplicate]

Clearly for constant motion we cannot define absolute rest or motion. So ,when dealing with time dilation problems for example twin paradox , how do we define which frame is in motion? If we ...
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Basic Special Relativity Question [closed]

I am trying to understand the implications of c being relative to the frame of reference. Is the following analysis correct? N is on a slow train moving 3 m/s and M on the platform next to N both ...
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Helicity states

On page 71 of Weinberg's book The Quantum Theory of Fields: Volume I, he defines the operators $$A=J_2+K_1$$and $$B=-J_1+K_2$$ where ${\mathbf{J }}=(J_1,J_2,J_3)$ are the rotation generators and ${\...
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1answer
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Sagnac Effect and clocks synchronization

I read this from "The Sagnac effect and its interpretation by Paul Langevin", in cylindrical coordinates $$ ds^2=c^2t^2-dr^2-r^2d\theta^2 $$ ...This transformation means that the observer O (...
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1answer
62 views

Helicity under rotation

Suppose that the state $|p,\sigma\rangle$ (for a massless particle) has 3 momentum ${\bf p}=p_3$ (that is the momentum is in the $z$ direction) and that $J_3|p,\sigma\rangle=\sigma|p,\sigma\rangle$ ...
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1answer
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Why I think the Michelson-Morley experiment was originally flawed, and would have failed either way [closed]

I was recently reading about how physicists were heavily relying on the existence of Luminiferous Aether for their physics to work. I read about how the Michelson-Morley experiment attempted to prove ...
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4answers
164 views

Elapsed time between two events is greater for moving observer

Lorentz's equations show the elapsed time between two events in moving frame is greater than rest frame. But moving observer's clock ticks slower. Isn't that an inconsistency? Consider two observers, ...
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1answer
64 views

Using Lorentz transformations with variable velocity

A particle is moving in a system of reference $S$. In its proper system of reference, say $S'$, the particle is still and it is described by the event $(c\tau,0,0,0)$. In the inertial frame $S$, the ...
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1answer
80 views

Four-velocity of an accelerating particle

In the rest frame of a particle, the acceleration four-vector is $$ \mathbf{a} = (0, g) $$ (see https://users.physics.ox.ac.uk/~smithb/website/coursenotes/rel_A.pdf , Eq.3.51). By definition $$ \...
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Difference between position of indexes in tensor notation (SR) [duplicate]

I am learning SR, and don't understand the difference between the following notations of a Lorentz transformation $\Lambda$ $$\Lambda_{\mu\nu} , \Lambda_{\mu}\ ^\nu , \Lambda^{\mu\nu}$$ I know that ...
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1answer
198 views

Why can't we measure the one-way speed of light?

I believe the problem is because we need to synchronize clocks. But ok let's assume we can't do that. Can't we just use some external reference - Eg The Sun & Solar Noon? For example given the ...
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1answer
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Can a person from different universe which has its “own different laws of nature”, can go into our past in our Universe? [closed]

Suppose There is a Universe, which has different laws of nature than ours galaxy and they have much greater speed of light than $3* 10^8 $ m/s ,so some person from their universe visits our universe ...
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3answers
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Doesn't the speed of light limit imply the same electron can be annihilated twice?

If I understand correctly, there is a small probability the same electron to be found anywhere in the universe. Suppose that an anti-electron collides with an electron, annihilating it and producing ...
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1answer
62 views

A More Inspired Derivation for Time Dilation

I've always believed the classic derivation you see for time dilation in a intro physics course, however I also have always had the uncomfortable feeling that some things were getting brushed under ...
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3answers
102 views

What is the point of sub and superscripts in metric tensor

I am new to QFT and have to catch up with some things that I did not learn from my SR courses. I am learning about the tensor notation, in particular the metric tensor, $$g_{\nu\mu}=g_{\mu\nu}=\begin{...
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1answer
58 views

Condition for Lorentz transformation

Today I had my first class of a QFT course, and there were some things that apparently I am supposed to know, but I don't. One of them is regarding Lorentz transformations. My teacher stated that: $\...
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Relative velocity between 2 frames of reference [duplicate]

In special relativity formulas for changing coordinates x,t into x',t' are based on the relative velocity of the 2 frames. What is the base for assuming that if v is the velocity of frame O' relative ...
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Gamma traceless

I read this Under what conditions is a vector-spinor gamma trace free. And also read many papers about higher spin, but no one explains why irreducible spinor is gamma traceless spinor? Can anyone ...
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Are laws of Physics same in frames having zero relative acceleration?

If two frames have the same acceleration, then they'll be moving with a uniform speed with respect to each other. Are laws of Physics the same in these two frames?
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1answer
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Is there any known experimental violation of Einstein's $E=mc^2$?

Note that I am not talking about $E_0= m_0c^2$ but $E=mc^2$, where m is the relativistic mass. I know that one holds for stationary particles, moving particles, even light, I read that it even holds ...
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What will happen first: the rod's front end will hit the back wall of the cave or the left end of the rod will enter the cave? [duplicate]

A rod flies into a cave at the speed of 0,8c relative to the cave. In the reference frame of a stationary observer, the cave is 30 meters deep. According to the observer, who "sits" on the rod, the ...
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Grasping (Inertial) Frames of Reference [duplicate]

I am new to studying Special Relativity and have some trouble truly understanding what the phrase (Frame of Reference) tries to imply. So I understand that an inertial frame of reference, for example,...
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0answers
62 views

Why does FTL not leave behind a motion blur? [closed]

I once thought anything traveling faster than light would leave behind a motion blur that on one end recedes at the speed of light and at the other increases at the velocity of the object. If an ...
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6answers
9k views

If clocks themselves are based on light signals, wouldn't we expect the measured speed of light to always be the same constant?

I'm trying to work out if there is an alternative starting point for the second postulate of special relativity. My main observation is that all "clocks" are, internally, based on light signals. So ...