# Tagged Questions

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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### Finding an explicit expression for inverse of Lorentz transformation ${\Lambda^\mu}_{\nu}$

I'm studying in a module titled "Symmetries and Action Principles in Physics." I'm having a small trouble with the notation, I think, of special relativity. We have in the text In fact we may ...
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### What do observers in relative motion agree on?

What are the measurements on which two observer in relative motion will agree? Other than the speed of light.
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### Is there a relation between time dilation and (relativistic) mass increase?

I noticed that what once called relativistic mass increase and now is called energy increase is ruled by the same formula the Lorenz factor of time dilation? The formula is too particular to suggest ...
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### Help with relativistic notation (Derivative of Lagrangian)

I am trying to learn QFT, but I haven't taken a course in general relativity so the relativistic notation stuff is taking me a bit to get used to. I do not understand how to do the following. For a ...
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### Spin state after boost

I am working through Weinberg's QFT book, and in problem 1 in chapter 2 I ran into copious amounts of algebra, so I am trying to "cheat" a little by using some assumptions, but am unsure of their ...
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### Oh-my-god particle: How can it get through Milky way in 10 seconds?

My question is concerning wikipedia article on Oh-my-God particle, to be precise, this paragraph: This particle had so much kinetic energy it was travelling at 99.99999999999999999999951% the ...
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### Translation Transformation on the Invariant Interval (Spacetime) [closed]

So we know that the invariant interval in a two-dimensional spacetime in special relativity is given by $$s = -c^2t^2 + x^2 = -c^{'2}t^{'2} + x^{'2}$$ So this scalar should hold true in all frames....
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### Could the Heisenberg uncertainty principle be derived from the speed of light limit? [closed]

Background: As I was thinking about an alternative approach to the question: "why is there a finite speed of light, and why its magnitude corresponds to c?" –ultimately, I was trying to understand ...
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### how long will take for an astronal travel in near lightspeed in his point of view

I always had a question about relativity. Suppose an astronaut in orbit Saturn just must reach earth fast as possible. Your ship can travel at any speed between 0 and the speed of light. the distance ...
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### Regarding relativity of simultaneity

I recently started studying Special Relativity an my book discusses the following: Say I have synchronized two separated clocks in a reference frame S, if then an observer in another reference frame ...
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### How do I form the four-momentum quantum operator?

I am trying to form the four-momentum quantum operator. These are the steps I have taken so far: The 3-momentum operator is given by $\hat{p}_{i} = -i\partial_{i}$. This is covariant because it is ...
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### Understanding the formula in an exercise

I'm stuck for quite some time now on this issue. I have the following question. Spaceship with velocity of $0.5c$ passes above two points $A$ and $B$ the distance between $A$ and $B$ respect to the ...
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### Special Relativity and Composition Law for Velocities with respect to an observer watching two objects moving away from a central point

So I understand that special relativity is all about the frame of reference and there is a lot to do with time dilation and how space-time is warped at velocities near $c$. So my question is what ...
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### Why does length contraction seem to conflict with invariance of intervals?

Suppose we have two simultaneous events, $A$ and $B$, separated by a distance $L$ (the simultaneity is in frame of reference $S$). Now suppose we have a second frame of reference $S'$ moving with ...
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### Can the constancy of the speed of light in vacuum be derived from a deeper theory?

Einstein's second postulate of special relativity is: The speed of light in vacuum takes the same value ($c$) for any observer in an inertial frame of reference. I know there is a lot of ...
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### Particle here at a given time, in another galaxy a second later… Really?

I read "The Quantum Universe (Cox & Forshaw)" that a particle can be measured at a given position at a given time, and in another galaxy one second later. The probability of such event may be ...
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### Hidden character in EPR paradox [duplicate]

I am a beginner in Quantum Mechanics so i am pretty new to the EPR paradox although i have heard about it a long time ago but finally studying in detail. And came across a doubt: Why the hidden ...
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### Minimum gravity required to suck light? [closed]

I was studying about gravitational forces of black holes when I came to a thought of what is the minimum gravity required to capture light in vacuum?BY capturing I mean the inability of light to ...
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### Is acceleration relative in relativity?

Suppose a box A is moving relative to a Box B, then by time dilation equation if I take 1 sec passed for an observer in A then for an observer in B will be little longer. Now if I suppose that the box ...
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### Is light send from the top of a ship to deck different when the ship is moving or not?

If you drop a ball from the top downwards to the deck it will follow a rather straigth line because the ball gets also a force horizontaly because the ship is moving. That is the cause in history why ...
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### Does antimatter travel faster than light

I have read in the answers here that an electron traveling backwards in time would behave as a positron. I also read in another there that antimatter is matter traveling backwards in time As far as I ...
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### Direction of the lightbeam in SRT thought experiments [duplicate]

Extending on the question about the time dilation on Wikipedia, namely this diagram in the accepted answer: Image credit: John D. Norton The thing that I don't understand is, why does the light ...
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### Rapid (ac/de)celeration in relativity does what to inertial clocks?

EDIT (to clarify my question): I think some of the answers here are accounting for light travel time and telling me what I'd actually see on Earth's clock, so I've edited my first paragraph to ...
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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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### 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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### 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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### 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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### 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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### 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 ...