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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Subluminal speed when going in a circle around someone

Some time ago I thought about such situation: There are two people in the room. Both have synchronized watches on their wirsts. Then the person A starts running around person B with the speed of ...
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How do I transform onto a relativistic rotating frame of reference?

In classical mechanics, the usual formula to translate the evolution of a quantity as seen from an inertial frame of reference to a rotational frame is: $$\frac{d \textbf{A} }{dt} \vert_{Inertial} = ...
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What is “special” and what is “general” in Relativity?

Initially I thought in special relativity the velocity was constant, whereas general relativity allowed treatment of accelerated frames as well. But now I have heard that SR is only valid locally?
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Entanglement and simultaneity

According to the special theory of relativity, distant simultaneity depends on the observer's reference frame. And, according to the quantum theory, in the case of two entangled particles, a measure ...
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1answer
52 views

If I kept getting closer and closer to the speed of light, what would be the gravitational effects appearing like to an observer? [duplicate]

Now, with special relativity applied to the scenario of me getting closer and closer to light speed, my mass would increase with respect to the observer, and also my length would contract in the ...
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39 views

Mass of photon, is it possible? [duplicate]

$P=E/C$ In relativistic mechanics a Photon is defined as. $P=hf/C$ Replacing "P" $ mc=hf/C$ $M=h/CT$ What does it mean, did they have mass?
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34 views

Synchrotron radiation and special relativity

My questions below are for all those who assume the point-like electron of special relativity, that strange entity with no inner structure (!), but with intrinsic (?) rest energy, magnetic moment and ...
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1answer
137 views

Is imaginary time a fifth dimension? [duplicate]

I've read that by introducing the concept of imaginary time, the dimension of time can be treated like a spatial dimension mathematically. Assuming, without imaginary time, one considers the universe ...
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1answer
72 views

Turning off point for 1g acceleration

Let's say I am on a ship accelerating with 1g. I want to keep the engine running for half a year ( to an observer from my point of origin ) but due to time dilation it would have to be sooner than ...
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74 views

Twin paradox, different starting locations

Let's say I have a twin who is at rest relative to myself and ten light years away from me, we are both in rocket ships. We have agreed that I will send a laser pulse and that when he receives it we ...
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1answer
96 views

Do paradoxes exist due to velocity addition?

Do paradoxes exist due to velocity addition ? .. In the above diagram, we have a very lengthy 259,627.885 km long space station. Rocket "A" is parked at the left end of the space station. Let us ...
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25 views

Lorentz transformation of scalar field [closed]

How can I show that $$\phi(x^{\mu}) - \frac{1}{2}\lambda^{\sigma \rho}L_{[\sigma \rho]}\phi(x^{\mu}) = \phi(x^{\mu} + \lambda^{\mu \nu}x_{\nu}) \,\,\, ? $$ Here, $\lambda^{\rho \sigma}$ are the ...
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Why isn't length contraction permanent even though time dilation is?

It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that ...
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What does Weinberg–Witten theorem want to express?

Weinberg-Witten theorem states that massless particles (either composite or elementary) with spin $j > 1/2$ cannot carry a Lorentz-covariant current, while massless particles with spin $j > 1$ ...
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3answers
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In special relativity, do explanations involving clocks require that the clocks are ticking and that $c$ is fixed?

Are the explanations involving clocks only valid if the clocks are ticking when light hits? Is it true that these thought experiments experiment could only be valid due to the invariance of $c$?
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Can asymmetrical Lorentz forces account for Relativistic affects near the speed of light?

The underlying thought here is that at low relativistic speeds all objects are subjected to emf radiation from all directions. This is basically the sum of all the radiation (light, infra-red, ...
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1answer
57 views

Prove the relation between relative velocity ,momentum and energy

In Chapter 8 of F.Mandl's book Quantum field theory, during the derivation of the differential cross section, the following relation is used: $$E_1E_2v_{rel}=\sqrt{(p_1p_2)^2-m_1^2m_2^2} \,\, ,$$ ...
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Is it correct that there is time dilation and time contraction in the same reference frame?

I have played a bit with spacetime diagrams and Lorentz transformation and can see time dilation, length contraction and the relativity of "at the same time". Classical: ...
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Why does the group velocity of 2D plasmon diverge at small wave number?

Now plasma represents collective wave-like motions of charged particles. In 3D, their frequency is well known to be almost a constant, $\omega^{3D}_p \approx \sqrt{4\pi n e^2/m}$, with $n$=charge ...
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44 views

Lorentz transformations of spinors in $SL(2,\mathbb{C})$

I was wondering what the matrix representations of all the coordinate rotations and Lorentz boosts of the $SL(2,\mathbb{C})$ were along with a general method of solving for them. I've been able to do ...
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0answers
21 views

Real representations of chiral fields

Why we can´t have real representations of chiral fields, i.e. why does a multiplet of chiral field (Weyl spinors) under a real representaiton of a Lie Group transforms as a "vector". It is easy to see ...
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1answer
104 views

Schroedinger Equation and Special Relativity

From what I understand, the Schroedinger equation describes how the wave function of a quantum system evolves in space over a given time (I am referring to a relativistic version of the Schroedinger ...
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1answer
70 views

Relativistic Kill Vehicle

What would happen if a significantly supra-molecular object (say ranking from grams to low kilotons) would be accelerated to relativistic speeds (>.10 c) such that its worldline would intersect with a ...
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132 views

Why should we believe in clock hypothesis? [on hold]

It is often assumed in special relativity that the rate of a clock in a non inertial frame does not depend on the proper acceleration of the observer. The point is, Rindler's observer shows us that ...
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58 views

How are these types of time dilation related?

How are these two phenomena related (if at all): 1. Gravitation slowing down time 2. High speed slowing down time
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54 views

Relativity and light speed communication

Say Alice could instantly encode another human being, Bob, into photons. Say Alice then beams those photons to a receiver on another planet, Vogon, one light year away. Charlie is controlling the ...
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Length contraction in cyclic space

Consider a flat universe with at least one finite cyclic spatial dimension: travel x meters in one direction, and you will end up back where you started. For an object that is of small size relative ...
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Energy of resultant photons from meson decay

I am a little unsure how to answer the following question, Find the energies of two photons emitted in opposite directions along the pion's original line of motion if the pion has a r.m.e of 500MEV ...
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Occlusion of light with very fast objects

Take this graphic: On the left there is a light emitter, which can fire light on command, towards the right. There are also two receptors, A and B, both $1$ light second away from the emitter. ...
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1answer
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Rotating Observers in Special Relativity: Coriolis-like effect?

Do any noninertial "forces" [terms in the metric] (like Coriolis in Newtonian mechanics) appear to a rotating observer (reference frame) in special relativity? Is the resulting spacetime after ...
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2answers
81 views

Will heating up an object increase its mass? [duplicate]

According to the $E=mc^2$ equation, will an object whose thermal energy (temperature) rises also weigh more? And by the same token, will the mass of an object decrease as its temperature approaches ...
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2answers
83 views

Collisions in special relativity

I am wanting to teach some basic trigonometry to school age kids using relativity and would like help to check my reasoning. First, is my problem formulation correct with respect to special ...
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50 views

Electromagnetic mass of a continuous charge distribution [closed]

I am trying to understand if it is possible to have a consistent solution to Maxwell's equations and Lorentz force equation simultaneously with no other forces present. The Lorentz force density is ...
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2answers
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Why does the equivalence principle not violate special relativity?

If the equivalence principle asserts that there is no way to determine whether our reference frame is accelerating or is being acted upon by gravity (i.e. the laws of physics are the same in both ...
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41 views

Decompose a massive four vector in to two massless ones

I'm trying to decompose a massive four-vector, $p_1$ with $p_1^2=m^2\neq0$, in to two massless ones, $k_i$ with $k_i^2=0$. But I'm having trouble find basis vectors $k_i$ such that I can always ...
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51 views

Length contraction, front middle or back

I still don't have a solid understanding of Length contraction. Imagine we have a ruler of length $L$ that starts at rest upon a ground with markings on it, then accelerates until nearly the speed of ...
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1answer
42 views

What is the definition of density in a relativistic context?

In this question, there seems to be a clear presence of ambiguity, which raises the question: what is density in relativity? First of all, the question asks for the relativistic mass, "the apparent ...
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1answer
42 views

Textbook for relativity: modern version of Bondi's Relativity and Common Sense?

I am looking for a textbook on relativity for school children. A background in simple vector based mechanics could be assumed. Primarily it needs to be readable at high school English reading level ...
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1answer
49 views

Magnetic force and frames of reference

I'm having a hard time trying to understand the next situation: Suppose that I have a magnet that creates a quite uniform magnetic filed $\vec B$. In the vicinity of this magnet there is a particle ...
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1answer
272 views

What happens in the twin paradox if the ship doesn't return?

What happens if the twin in the spaceship doesn't return? Would he still be younger than his other twin? Is the symmetry broken simply by accelerating out of earth? If it is still symmetrical when ...
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3answers
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Why is light different than sound in terms of the assumptions we make regarding causality?

I am having trouble understanding, from a conceptual point of view, why it would be impossible to travel faster than the speed of light. I have read one explanation given in the form of an example ...
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1answer
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Einstein's space-time theory [closed]

I'm a high school student who never studied any relativity before, but I'm just wondering what was THE question that Einstein asked himself before going into this field. I knew he has done lots of ...
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1answer
44 views

The Relativity of Simultaneity and its Impact on “Seeing” Events

Will the rocket really see the supernova L first for sure? The position of the rocket is not specific. We just know that it is at the left of the galaxy. We know that R will explode first in the ...
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2answers
212 views

Length Contraction Confusion

i'm having a bit of trouble wrapping my head around special relativity, so i'd like to explain what I think is going on, to see whether or not I have understood. The question i'm thinking about is ...
2
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1answer
49 views

Does Special Relativity require a “ruler postulate” analogous to the “clock postulate”?

It's fairly well known that the clock postulate is needed in Special Relativity when dealing with accelerated clocks, so does something analogous exist when dealing with accelerated spatial ...
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2answers
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Consistent answers in special relativity [closed]

I was doing a question about if a train fits in a tunnel. From the train frame it does not and from the tunnel frame it does. Then the question asked are these two answers consistent? What does this ...
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1answer
61 views

Can matter be annihilated to form kinetic energy

I don't know much about conversion of energy and all, but I had a simple question: Can the energy released by converting matter into energy be used to set other particles in motion (increase their ...
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2answers
55 views

Question from Griffiths (EM): Synchronized clocks

There's this vague conceptual question from the textbook Introduction to Electrodynamics by David Griffiths Problem 12.5 Synchronized clocks are stationed at regular intervals, a million km apart, ...
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0answers
37 views

Spin of an operator in supersymmetric theories

How exactly is the spin of an operator in the context of a supersymmetric theory defined? For example, in page 25 of [1], $\mathcal{N} = 2$ supersymmetry is defined to have operators $J, G^{+}, G^{-}, ...
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48 views

Scalar products in the spinor helicity formalism

In A. Zee's book Quantum Field Theory in a Nutshell (2nd edition), Chapter N.2, page 486, the momentum $p$ is written as a $2\times 2$ matrix: $$ p_{\alpha\dot{\alpha}} = p_{\mu} ...