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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When calc. time elapsed for an inertial reference frame during travel between two points, are length contraction and time dilation taken into account? [closed]

When calculating the amount of time elapsed for an inertial reference frame over the course of its travel at constant velocity between two points, are the effects of both length contraction and time ...
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107 views

Objects travelling relatively to each other faster than light?

When we say that something is travelling a certain speed, it's really travelling that speed relative to the Earth. When saying the speed of anything, it is, for the most part, relative to something ...
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A twin-like paradox, with no acceleration and no 3rd reference point. What would happen?

The following is a variation on the twin paradox, with no acceleration and no 3rd reference point (i.e. described purely in terms of relative motion). Imagine two observers initially located right ...
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Does Inertial time dilation demonstrate that Time is not a dimension? [duplicate]

If time is a dimension and 'now' simply an expression of your position with respect to that dimension, the progress of any object along that dimension should remain in step with all other objects. By ...
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How is the Lorentz group related to spin? [closed]

I've been reading about the agebra of the Lorentz group. It is given by, $$G\equiv SO(1,3) ~\cong~ SU(2)\times SU^*(2)$$ Now, representations of this group $G$ as labelled by $(j,j')$ where $j$ is ...
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Ether (LET) vs electromagnetic field in the double slit experiment

According to this answer, Lorentz Ether Theory (LET) is experimentally indistinguishable from SRT, because the Ether is immobile and practically redundant. However, on quantum scales, photons are ...
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Is this a fundamentally relativistic phenomenon?

This question was inspired by some silliness in other threads but is independent of that silliness. Say that a train car sitting on a track is accelerated uniformly along its length if each point on ...
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Does the existence of “gravitational waves” (assuming they exist) imply that time exists as a 4th dimension in the universe? [closed]

I'm new to thinking about special and general relativity and I have no formal training as a physicist. However, I've been doing a bit of thinking about spacetime recently. I was wondering if "...
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Can the passage of time be measured in the absence of motion? [duplicate]

All of the ways I have heard of to measure the passage of time involve measuring some sort of motion (e.g. vibrations of a cesium atom, movement of the hands on a clock, etc.). Can the passage of ...
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Would forcing a photon to travel under $c$ even after it leaves a medium break Relativity? [duplicate]

So, I stumbled onto this article which really blew my mind (http://www.bbc.com/news/uk-scotland-glasgow-west-30944584). To sum it up, these researchers set up some kind of material that slowed a ...
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57 views

Relativity of simultaneity: two light sources

A. Suppose a moving train. The train has two wheels(front and back) and each wheel is connected to light source inside the train. The light source is triggered(light is emitted) when train passes ...
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Lorentz contraction explanation correct? [closed]

I was having a heated SE chat debate with someone re relativity. One of us believes the explanation above is correct, while the other believes it is not. Who is correct, and, if the explanation is ...
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In relativistic electrodynamics , why doesn't the Lorentz force not change its formulation ? And only the electric and magnetic fields transform ?

My question is that when we want to find the Lorentz force acted on a particle moving in an electric and magnetic field , the equation is invariant in any two inertial relativistic frames. Why is that ...
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1answer
35 views

Lorentz Invariants and Time dilation/Distance contraction?

If distances contract in direction of motion and time dilates at high speeds, why are the rest mass $m_0$ and proper time $t_0$ called "invariant" under Lorentz transformations. Since depending on ...
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1answer
62 views

Does travelling towards something at relativistic speed cause it to appear to speed up?

If one were to travel towards a giant TV floating in space, at a fraction of the speed of light, would a video playing on the TV appear to play faster? I'm guessing the answer is no. From what I ...
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2answers
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Is the speed limit as light speed just based on what we see? [duplicate]

I know, the title makes no sense, generally. Let me explain. I am just asking a question for which I found an answer nowhere (not even here). i think similar questions has been asked before and, no ...
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Mass has the same value in all inertial reference frames?

Is mass the same in all inertial frames? If it is, why is that? If not, can you also explain?
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A train on a track--relativity paradox

While answering a question over on Worldbuilding.SE I found myself looking at a situation that I can't figure out: You have a train track of length L that makes a very large circle. You have a train ...
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2answers
131 views

(Hyper)Surface of Simultaneity

How can I determine the surfaces of simultaneity if I know the metric? In particular, what are the surfaces of simultaneity for rotating disk with Langevin metric: $$ ds^2=-(1-\omega^2r^2)dt^2+2r^2\...
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1answer
86 views

Michelson Morley experiment? [closed]

Its not that I question the conclusions reached concerning the Michelson–Morley experiment, however I would like to know how the following issue was addressed please? If I could pass bob through a ...
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1answer
32 views

Force required to produce a specific motion on a particle [closed]

This exercise comes from the Exercises for the Feynman Lectures, Chapter 15. The full question: 15-6 A particle of rest mass $m_0$ is caused to move along a line such that its position is: ...
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Using light clocks, can one derive the length contraction formula without the 'bouncing' of the photon?

In the following link, the equation for time dilation is derived by allowing the photon to just go from the lower mirror to the top, without reflecting back to the bottom: https://sciencebasedlife....
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Why is the spatial term for contravariant 4-gradient negative, whereas for other 4-vectors it is the covariant part that is negative spatially?

The contravariant 4-displacement is: $${x}^{\alpha} = (ct,\mathbf{r})$$ And the contravariant 4-gradient is: $${\partial}^{\alpha} = (\frac{1}{c}\frac{\partial}{\partial{t}},-\nabla)$$ From what I ...
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1answer
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Error in deriving relativity velocity addition formula [closed]

$D$ is traveling at .995c with respect to $C$ who is traveling at .995c with respect to $B$ all in the same direction. We want to compute $D$'s velocity as observed from $B$. Note that the Lorentz ...
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How is it possible to change the direction of a spin by boosting?

In Weinberg QFT section 2.5.5, he defines the states of momentum $p$ by $$\Psi_{p,\sigma}=U\bigl(L(p)\bigr)\Psi_{k,\sigma}$$ up to some irrelevant normalisation, and $L(p)$ is the Lorentz ...
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What is the meaning of $\mathrm{d}^4k$ in this integral?

From Gerardus 't Hooft's Nobel Lecture, December 8, 1999, he states the following equation (2.1): $$ \int \mathrm{d}^4k \frac{\operatorname{Pol}(k_{\mu})}{(k^2+m^2)\bigl((k+q)^2+m^2\bigr)} = \infty ...
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54 views

Twin Paradox From Neutral observers perspective

Suppose two planets A & B, with B moving away from A at velocity v. A spaceship departs from A in the direction of B at velocity v (putting it in the same inertial frame as B), and remains that ...
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60 views

Active transformation and passive transformation of a scalar field

For the Lorentz transformation $x \to x'=\Lambda x$, the active transformation is $\phi(x) \to \phi'(x)=\phi(\Lambda^{-1}x)$ and the passive transformation is $\phi(x) \to \phi'(x)=\phi(\Lambda x)$. ...
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Rational for the Principle of Relativity [closed]

When Galileo postulated his principle of relativity, it seems like quite a logical assumption. After all, velocities combine cleanly, and everyday observation seems to show that the laws of physics on ...
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51 views

Relativistic oscillator vs. non relativistic oscillator

Consider a particle of mass $m$ that is constrained to move under the potential $U=k|x|$. In the case where the particle's motion is non-relativistic, the Lagrangian for the motion is $L=T-V=\frac{m}{...
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Is there a maximum energy for a relativistic particle?

So I was told today that the Standard Model breaks down at really, really high energies. The lecturer mentioned particles such as electrons hypothetically having energies equivalent to that of entire ...
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A couple of questions on mass increase

I found these experimental data on mass increase. Data of the Bertozzi experiment show close agreement with special relativity. Kinetic energy of five electron runs: 0.5, 1, 1.5, 4.5, 15 MeV ...
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Is there an underlying physical reason why the Coriolis force is similar to the magnetic component of the Lorentz force?

I couldn't help but notice that the expression for the magnetic component of the Lorentz force, $$\mathbf F = q\,\mathbf v \times \mathbf B\,,$$ is very similar in its mathematical form to the ...
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1answer
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Motion in space

Does a space shuttle travelling in space experience any resistance to its motion? If a body in space is applied constant force, does it attain speed of light after sufficient time?
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Twin Paradox Variation using 2 rockets [duplicate]

Instead of a twin on earth and a twin on a rocket, what would happen if they were both on separate rockets facing opposite directions. One fires off at 0.7c and the the other fires off at 0.2c. Then ...
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How the state of elementary particles change under lorentz transformation?

Let us take three observers namely Alice, Bob and Charlie. Bob is stationary with respect to Alice, but his axes are rotated from her's.We can get Bob's coordinate axes by rotating Alice's through 60 ...
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1answer
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How to derive the components $\Lambda^i_j$ of a Lorentz-transformation given a boost $\vec{v}$?

I am stuck in deriving a specific formula concerning Lorentz-boosts. In my Classical Mechanics skript there is a chapter dealing with special relativity. In this chapter the Lorentz transformations ...
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Understanding what a tranformation on a Ray and Hilbert space

I've been referring to Chapter 2 of Introduction to Quantum Field Theory by Weinberg where he talks about symmetries and how they go about. Now, there are two points that he mentions. A ray, which by ...
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36 views

Relativity of simultaneity: light source inside and outside

(Orange are light sources and red are observers) There is a train, which is moving right. In each side, there is a light source, which emits light when the train passes certain point on a track. And ...
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1answer
59 views

What would happen if light was converted into matter as it is propogating?

If light is a form of energy and can be converted into matter then does light slow down since no mass full object can reach the speed of light
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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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2answers
85 views

Does invariant mass depends of temperature? [duplicate]

From special relativity theorie we know that $E = mc^2$. When a system acquires energy, mass becomes greater. That is clear for kinetic energy, because we have a formula that gives m as a function of ...
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Time Dilation diagram on wikipedia

The wikipedia article on Time Dilation (http://en.wikipedia.org/wiki/Time_dilation) has an explanation involving the following two diagrams: I have some problems with these diagrams. In the second ...
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How time dilation happens by velocity?

i got many explanation and proving that relative velocity causes time dilation. Einstein's moving light experiment proves it. but that is a clock works with light detector. as detecting the light gets ...
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1answer
60 views

Why is there a cap on the speed at which we can attain? [duplicate]

Also, If you are traveling 1 mph under the speed of light on a train and throw a baseball in front of you at 20mph what would a viewer outside the train see?
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How does light change directions? [duplicate]

To the best of my knowledge, light will always travel at the speed of light. How then does it get reflected and change directions? Wouldn't it have to decelerate, come to a stop, and then accelerate ...
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A few positrons collide with a solid body at rest; what can happen?

Suppose we have a macroscopic solid object. Now we have a beam of Positrons that is injected into this solid Body at vacuum. What can happen? There will take place a pair Annihilation of electrons ...
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1answer
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Canonical field momentum in quantum field theory

In the context of the second quantization and the use of fields in the canonical quantization, the canonical momentum of the field is defined as the derivative of the field by the time coordinate. But ...
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2answers
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Speed of light and infinite energy [duplicate]

While browsing some physics websites, I saw that to make an object reach the speed of light, it requires infinite energy and talked about its relation with Einstein's famous equation $E=mc²$. However, ...