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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How do two observers see the same photon?

Here's what I'm trying to solve. Suppose we have two observers (call them A and B). Both are inertial. Their frames of reference are represented on the following space-time diagram (the black axes ...
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What kind of tensor is $\psi^\dagger\psi$?

I'm trying to find how does this quantity $$\psi^\dagger\psi$$ transforms under a Lorentz transformation. Where $\psi$ is a Dirac spinor. What I've tried so far: It is known that a Dirac spinor ...
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Discovering vector potential from moving field analysis

First I would like to remind Lorentz transformation of length and time as a matrix: $$ \begin{pmatrix} ct'\\ x'\\ y'\\ z' \end{pmatrix} = \begin{pmatrix} \gamma & - \frac{v}{c} \gamma & 0 &...
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Why is Maxwell's equations correct and not Newton's laws of motion?

In many books, while introducing Special relativity it is shown that Maxwell's equations are not consistent with Galilean transformations.So either Galilean transformations(and consequently Newton's ...
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Transformation law for 3-velocity

I am kind of stuck with a problem mentioned in my current reading about special relativity. Given the Lorentz transformation $$x^{\bar{i}} = L^i{}_k \, x^k \quad ,$$ one has to find the transformation ...
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Terrell-Penrose effect and surface reflectance

All explanations of Terrell-Penrose effect seem imply that the effect makes some of the back-facing walls of a passing-by object visible. You can see some examples of those in many different ...
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Does dark matter follow all principles of regular physics?

Is dark matter bound by all the laws of regular physics? i.e. laws of thermodynamics, speed of light, length contraction, mass-energy relation. What about Newton's laws of motion (since all of Newton'...
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What would I measure if I place a relativistic particle on a weighing scale?

The concept of relativistic mass is considered outdated and when people refer to mass now, it's the invariant or rest mass. If I understand the idea correctly, back in the day people tried to rewrite ...
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Is the postulate of Euclidean space needed to derive the Lorentz-transformations?

There are many alternative derivations of the Lorentz-transformations (LT) out there, which try to not use Einstein's 2nd postulate of the constancy of speed of light. Most of the derivations I've ...
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Magnetism through Relativity

If relativity tells that from a moving charge's frame (observing current carrying wire) protons contract in length and its charge density increases making the charge experience a electrostatic force. ...
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Components of light's velocity [duplicate]

Imagine a train moving in the +x direction with a velocity of v ( close to the speed of light). And suddenly someone flashed a light in the in the +z direction( speed = c ). Now, For a stationary ...
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How to explain path of light in different reference frame?

There is a standard diagram for deriving time dilation in special relativity. So say there's a ship in deep space with observer O' in inertial reference frame S' moving to the right with respect to an ...
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What's wrong with this “proof” that QFT violates causality?

In An Introduction to Quantum Field Theory, by Peskin and Schroeder, when discussing the quantized real Klein-Gordon field ($\phi=\phi^\dagger$), they show the commutator $[\phi(x),\phi(y)]$ vanishes ...
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Confusion on clock synchronization

I am reading through Polonyi's Classical Field Theory notes. It begins with a discussion of special relativity, and near the bottom of page 3, it introduces a procedure for synchronizing clocks. I've ...
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Why don't distant stars red/blue shift dramatically when we walk in different directions (due to the Rietdijk–Putnam argument)?

https://en.wikipedia.org/wiki/Rietdijk%E2%80%93Putnam_argument two people walking past each other in the street could have very different present moments. If one of the people were walking towards ...
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The exact nature of the spacetime interval

The book I will reference here is (specifically page XXXV of) The Geometry of Physics by Frankel. I asked this question a long time ago when I was a complete newcomer to general relativity. There was ...
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In what way observables are a representation of the symmetry group?

I was studying a course about Lie groups, Lie algebras and their representations (and classifications) when I encountered this statement : When a physical system admits symmetry, the observable form ...
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The Explosive Force of the Braking Alcubierre Drive - What would this look like? [closed]

The Alcubierre Drive and faster than light travel more generally may be locked away in the realm of fiction forever. That might be depressing to some people but I think their impossibility is really ...
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Relativity and the observation of distant objects [closed]

If two identical telescopes orbiting earth take a picture of a far away galaxy, would relativistic effects lead them to significantly different observations? If so, how?
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Is the number density of photons frame dependent?

In a relativistic context, the energy of a "single" photon, thought of as a massless particle with an on-shell condition $p^2=0$ or $E^2=\vec{p}^2$, depends on the frame. In other words, ...
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Why use two spacetime indices to label Lorentz generators?

I've seen (e.g. in Srednicki) the following notation for the connection between a Lorentz transformation $\Lambda$ and the Lorentz generators $M^{\mu\nu}$: \begin{equation} {\Lambda^\mu}_\nu = {\left(...
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1answer
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Why don’t objects approaching the speed of light form a black hole? [duplicate]

Although I’m rather new to physics and this site, I wanted to ask a question because it’s been sitting on my mind recently and I can’t figure it out... Forgive me if I’m missing something but here ...
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Explanation of an equation in special relativity

$$ {\partial (0.5 (\partial_{\mu} A^{\mu})^2) \over \partial(\partial_{\mu} A_{\nu})} = {(\partial_{\rho} A^{\rho}) g^{\mu \nu} } $$ Can somebody explain why this is true?
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Trying to use calculus to derive Lorentz transformations [closed]

Assumptions: Homogeneity of spacetime, Principle of relativity (if frame $A$ moves at speed $v$ wrt $B$, then $B$ must move at speed $-v$ wrt $A$). Also, differentiability of the curve traced by the $(...
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How was Quantum Mechanics and Special Relativity Combined in QED?

I watched a presentation where special relativity was mentioned as being essential to understand electromagnetism, as in the case of current flowing in a cable, a charge moving next to the cable, due ...
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How do I interpret uncertainty in velocity greater than the speed of light?

I just studied Heisenberg's uncertainty principle in school and I came up with an interesting problem. Assume an electron which is moving very slowly and we observe it with a distance uncertainty of ...
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Does the classical relativity supports elastic particles going faster than $c$? [closed]

If we work in an experiment similar to that of Michelson-Morley and we assume that light is made up of small elastic particles, and we make light beams reflect multiple times from moving mirrors, ...
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How can classical relativity explain the Michelson–Morley experiment?

If we suppose that light is made of small elastic particles, does the classical Galilean relativity explain the Michelson-Morley experiment? I would greatly appreciate any point of view.
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Relativity without constancy of light speed

Using homogeneity of space, isotropy of space and the principle of relativity (without the constancy of light speed), one can derive: $$x' = \frac{x-vt}{\sqrt{1+\kappa v^2}}$$ $$t' = \frac{t+\kappa vx}...
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Demonstration of Electromagnetic Tensor antisymmetry

I've already made a post about this topic here, but I realized that I didn't understand the explanation on that post. in Chapter 7 of Rindler's book on relativity, in section about electromagnetic ...
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Is special relativity falsified by the Aharonov Bohm effect?

The Lorenz gauge is the only Lorentz invariant electrodynamic gauge. If the vector potential has physical meaning, as in the Aharonov–Bohm effect, then the gauge condition can not be arbitrarily ...
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How does the period of an oscillating mass-spring system comply with the relativistic time dilation as viewed by a moving observer?

Consider a simple mass-spring system. The spring is attached to the ceiling in the lab frame of reference and a block of mass $m'$ is suspended from the spring. The mass starts to oscillate with ...
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Inertial mass and gravitational mass [closed]

I would like to ask about gravitational mass. I know inertial mass is changing by motion (speed) according to $m=\frac{m_o}{(1-v^2/c^2)^{1/2}}$ And also that is inertial mass which sits in $E=mc^2$. ...
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Special relativity basic concept [closed]

When someone travels really fast, do things seem to slow down around him or do things go faster around him?
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Does matter exits in quantum realm? [closed]

I have been taught that matter exists but with double split experiment I was shocked to know that the matter doesn't even exits, it's the state we are which we feel as matter but in real scenario we (...
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What do I need to build special relativity?

If I postulate the principle of relativity and the constancy of the speed of light for every inertial observer can I then prove all SR? Or do I need some other postulate? For example: do I need to ...
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Why is the photon clock equivalent to all clocks?

I can understand why, if the speed of light is invariant, a photon clock would tick slower. I find this explanation very useful in terms of introducing the idea of time dilation (also because it ...
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Lorentz spinor in Lorentz $\rm Spin(3,1)$ signature and the real structure?

In this paper: J. Wang, X. Wen and E. Witten, "A new ${\rm SU}(2)$ anomaly", J. Math. Phys. 60 (2019) 052301, arXiv:1810.00844, it says the following in p.2, It says for $3+1$ dimensional ...
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Is mass actually relativistic? [duplicate]

Is mass physically relativistic in any way? I have seen many places online--such as derivations of relativistic momentum--where entities have a relativistic mass (where relativistic mass=rest mass* ...
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Which postulates did Einstein really use in his 1905 derivation of the Lorentz transformations? [closed]

Einstein explicitly states in "Zur Elektrodynamik bewegter Körper" that the only two postulates he requires for his derivation of the Lorentz transformations are 1) the principle of ...
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What would be the increase of gravity if we create a new world slightly bigger than the earth? [closed]

I need to know what would happen if I increased the earth's size by a small percentage to make a fictional world similar to earth. So my thought process is this: My thinking started with increasing ...
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Light catching up with a uniformly accelerating object

Is there a formula for how long it takes light to catch up with a constantly accelerating object given initial distance?
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Neglected effects of special relativity for the case of a fall into a black hole?

It has been said that falling into a black hole and crossing the event horizon would appear as "nothing out the ordinary" for the in-faller (especially for a super-massive BH, but lack of ...
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How relative is speed?

A short question, because the math got me confused. If in my inertial reference frame, I see a dude going away from me at a speed $v$. Then, from his frame of reference (which is also inertial) he ...
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Einstein: 'SR is a theory of invariants, not relativity' — source? [migrated]

It is occasionally remarked that Einstein was unhappy that SR became referred to as a ‘theory of relativity’, when in his eyes it was, much more importantly, a theory of invariants (Invariantentheorie)...
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In relativity, why does spacetime diagram have position on $x$-axis and time on $y$-axis?

In regular Newtonian physics, we use $ x(t) - t$ graph to under position of a particle but why is it that in special relativity that we switch up the axis notation? I was seeing the lecture by Leonard ...
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For Einstein's equation $E= mc^2$ is it energy that increases or mass as the velocity increases? [duplicate]

I will be surprised if no one asked this before and I would be happy if it is answered already although I haven't located it just yet! From Einstein's original paper "Does The Inertia of a Body ...
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Time dilation in Einstein's train

Wikipedia states that a clock that is moving relative to [observer] will be measured to tick slower than a clock that is at rest in their frame of reference and they explain it using two pictures: ...
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Can different observers observe different realities?

The question is extention of thought experiment proposed by Einstein of light pulses in a train cart called Einstein's train. Assume that light pulses are emitted from the end of cart, instead from ...
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Question about the circumstances of apparent causality violation due to objects with negative ADM mass

In The Generalized Second Law implies a Quantum Singularity Theorem, Aron C. Wall asserts that an object with a negative ADM mass would produce a "Shapiro advance" rather than the ...

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