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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Colliding objects - Combine energy can surpass $c$? [duplicate]

LHC is currently capable of accelerating a batch of atoms faster than $0.5 \, c$. What if we made a second LHC that intersects the original at, lets say the atlas chamber, but that runs in the ...
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19 views

Length Contraction Understanding Problem

Suppose a ball moving with 0.9c in the x-axis on a frame S' with axes parallel to frame S on which an observer sees the ball. Sue to length contraction it appears as a vertical ellipsoid, when it ...
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106 views

What experience tells us that gravitational acceleration cannot vanish everywhere?

In attempt to describe the consequences of the Equivalence Principle: When there are gravitational accelerations present, as for example in the gravitational field of the earth, the space cannot be ...
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Would Michelson-Morkey experiment measure wind in non-vacuum?

If we derive the speed of light from the Maxwell equations we will find it's a function of the permittivity and permeability of the medium. Now let's play with the thought that we are living in a ...
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30 views

Increase of an electron's (relativistic) mass

Considering the equivalence of mass and energy, is we want to increase the (relativistic) mass of an electron 1000 times, should we give it 5*10^5 * 1000 = 5*10^8 eV of Kinetic energy => 1001 electron ...
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What can change a photon's frequency?

I found this question: Is it possible to apply force to a light particle? As it states, gravity can change the frequency of light by changing its momentum. My question regards other phenomena that ...
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Doppler-shift of AC-electricity

A tram is powered by overhead wire, the wire has alternating voltage of 1000 V RMS, the frequency of the alternating voltage is 50 Hz. The rails are the other wire. The tram is moving at speed 100 ...
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1answer
66 views

How are photons effected by gravity? [duplicate]

If we use E²=m²c⁴+p²c², and we know mass of photon is zero, and they have momentum but why aren't they affected by gravity.
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175 views

Finding the total energy in centre of mass frame

I'm working through a problem in a special relativity textbook (Woodhouse) and I'm having some difficulty. I have to show that if I have a particle of rest mass $M$, total energy $E$ colliding with a ...
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60 views

Representations of Lorentz group in interacting QFT

In QFT, we obtain a representation of the Lorentz group by defining a set of unitary operators whose action on (spinless) free particle states is given by \begin{equation} U(\Lambda) |k \rangle = ...
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Time taken by a point in the light to cross the length of an object moving with a high velocity wrt to an observer at rest

I am new to the field of special theory of relativity and while understanding its concepts the following question popped into my mind... Suppose there is an object O moving with a very high velocity, ...
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Sum according to a function - composition of velocities

An observation more than a question. Take any function $f$ (additional hypotheses may follow) and evaluate it on any two points $x_1, x_2\in\mathcal{D}_f$. Define then the sum of these two points as ...
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61 views

Asymmetry of relativistically treated EM force between atoms

There are two neutral atoms set separated at a long distance $R$ and let's consider them phenomenologically through Bohr model. Let's also assume that the nuclei (charged $+q$) of the atoms are fixed ...
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What's the name for the relativistic paradox with the train/car travelling over a gap?

There is a relativistic paradox I was introduced by a friend in Ithaca (Courtenay Footman). It involves a vehicle travelling over a ravine relativistically, so it's in the general family of ladder ...
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32 views

Proof of relativistic kinetic energy [on hold]

In the picture there is a proof of what the difference in kinetic energy is for a particle under a force $\vec{F}$ in relativistic mechanics. The derivation is given in terms of seven steps. 1)The ...
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Relativistic Doppler effect derivation

This is about a step in a derivation of the expression for the relativistic Doppler effect. Consider a source receding from an observer at a velocity $v$ along the line joining the two. Light is ...
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23 views

Does light accelerate when it meets a surface? [duplicate]

Does light accelerate when it meets a surface like mirror, we know that light changes path when it meets a surface like mirror.If light changes path,even if travelling at c,this means light has ...
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17 views

Why does time stand still for light? [duplicate]

The source for this is the book "Einstein for Dummies", page 330, chapter 10.
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87 views

How to decide which is the proper time?

I want to deduce Length Contraction using Time Dilation(which has already been deduced), but I encountered a problem that I feel tough. I first assume two observers, $A$ and $B$ are in two frames ...
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2answers
623 views

Why does weak equivalence principle say gravity is equivalent to acceleration?

I am told that the weak equivalent principle, that $m_i=m_g$ (inertial and gravitational masses are equivalent) is equivalent to the statement that in a small system you can't tell whether you are in ...
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1answer
106 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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Does light ever experiences acceleration? [duplicate]

Till now I have learned that light has fastest speed. But I have also noticed that wherever it travels it only experiences retardation. So I wanted to know if light ever felt acceleration naturally in ...
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1answer
25 views

Light photon direction in movement

I recently watched a couple science videos on YouTube and left me with a doubt. If a spaceship goes to a really fast speed in the (horizontal) $x$-direction, what would happen if it shoots a light ...
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Why two bodies won't attract each other? [on hold]

Two bodies cannot attract each other as a body contains mass and mass is a constituent of atoms and molecules,held by electrical force.The electrical force is too weak to attract other objects. And ...
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3answers
86 views

Why is this method valid in special relativity

Here is the question Two clocks are positioned at the ends of train of proper length $L$. They are synchronised in the train frame. The train travels past you at speed $v$. It turns out that if ...
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348 views

Time contraction

This is my first time posting on this site. I am a computer programmer that stumbled across a physics text book and have a question on special relativity. So firstly, I understand that there is no ...
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33 views

The derivation of the irreducible representations of the Lorentz group

I took the way of classification of Lorentz group representations from Sexl, Urbantke, Relativity, groups and particles (Germ. ed. 1975). But I don't understand it as I outline in the following: In ...
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How would we experience sound if light velocity was (much) smaller? [on hold]

Imaging the velocity of light was just 110% or so of sound's. How would we experience sounds? How would a guitar sound, for instance? My best guess so far is that, as guitar's strings moved more ...
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127 views

Plane curve transform to moving inertial system coordinates

As a non-phycisist I hope my question makes sense and is understandable. It deals with special relativity. I suppose there is a e.g. plane curve ( e.g. a circle ) given in the x-y plane of of an ...
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3answers
157 views

Isn't the aether existent?

Before you say I'm wrong consider this, Einstein is supposedly the first person to get completely get rid of the various aether models that were proposed. But didn't Einstein actually prove them right ...
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24 views

Traveling near the speed of light? [duplicate]

Suppose we can travel on a spacecraft near the speed of light, how long it would take for the person on the spacecraft to travel one light year, not to a person observing him/her from Earth, if there ...
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Why isn't there a limit for a Euclidean rotation, as for a Minkowski rotation?

From invariance of the Minkowski scalar product, we get the Lorentz transformations. In addition, we get a constant $c$ preventing space-like and time-like intervals being rotated into one another. ...
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“If the astronaut found that light slowed down relative to his motion, he would have detected the very ether wind that Michelson failed to detect”?

The following extract is from Relativity Simply Explained by Martin Gardner (Amazon link): Consider an astronaut in a spaceship that is racing alongside a light beam. The ship is traveling with ...
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Understanding the difference between co- and contra-variant vectors

I am looking at the 4-vector treatment of special relativity, but I have had no formal training in Tensor algebra and thus am having difficulty understanding some of the concepts which appear. One ...
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Travelling near the speed of light, will radar give me sufficient warning of approaching debris?

If I’m travelling in space near the speed of light, I would like to use radar to give me advance warning of approaching hazards. However, will I have enough time to be able to react? From a ...
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Why don't two observers' clocks measure the same time between the same events?

Person A in reference frame A watches person B travel from Star 1 to Star 2 (a distance of d). Of course, from person B's reference frame, he is at rest and is watching Star 2 traveling to him. ...
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Will two clocks moving in opposite directions measure the same time as one at rest?

A rocket passes the earth and synchronises its clock with the earth. Years later, a rocket passes it going to the earth and synchronises its clock with the first rocket. When it reached the earth, ...
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Is the speed of light in vacuum always the same value?

The escape velocity of different planets and stars vary. If they vary, the velocities of bodies escaping from the respective stars or planets should also vary. Like, if I want a ball to reach 10 ...
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2answers
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I am confused about the idea that the speed of light is independent of the speed of the source of light

Imagine that a mast of a sailboat is 186,000 miles long, and the sailboat is moving to the right at a constant 10 miles per second. If you drop a ball from the top of the mast, the ball will land ...
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Do chemical bonds have mass?

When an exothermic reaction occurs, the energy in the chemical bonds of the reactants is partially transferred to the chemical bonds of the products. The remaining energy is released as heat. For ...
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What does the ratio (x-ct)/(x'-ct') signify?

$(x,t)$ being coordinates of any event in an inertial frame $A$ and $(x',t')$ being the coordinates of the same event in another frame moving with uniform velocity $v$ along the same direction in ...
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The returning light beam that is perpendicular to Earth’s motion

How did Michelson and Morley compensate for the fact that the returning light beam that is perpendicular to Earth’s motion would not arrive at the same point that it left the half-silvered mirror? ...
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44 views

A question about the physics involved in tracking satellites such as those used in the GPS system [duplicate]

I know that besides the effects of Newton's theory of Gravitation on the satellite's motion, one has to take account of the retardation of the satellite's clocks when compared to earth-fixed clocks. ...
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2answers
47 views

Is causality a necessary and sufficient condition for special relativity?

Is there a way to "build" special relativity by using causality as one of the axioms? Or is it just a consequence of a fact that the speed of light is same in all reference frames?
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Dilemma in race between muon and light

I have a dilemma concerning my understanding of Special Relativity. Maybe I am understanding or calculating something wrong and would hear so. The problem is based on muons created in the upper ...
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3answers
477 views

Are length contractions limited by Planck length?

While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. But we can not (even theoretically) consider length ...
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507 views

Is Kinetic Energy stored as (rest) mass?

I know that if some object acquires potential energy, it also gains (rest) mass - is it the same for kinetic energy?
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66 views

A pendulum clock vs. an atomic clock

A pendulum clock ticks slower on top of a mountain and ticks faster at ground level, but an atomic clock ticks faster on top of a mountain and ticks slower at ground level. Gravity affects pendulum ...
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Twin paradox modified for a periodic universe [closed]

I had received a homework problem by my professor. Please consider part (b) of the problem. Can part (b) be solved only using special relativity? And how can you solve this? I think that Alice will ...
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Relativistic flashlight and mirror

Say Alice is on on one end of a train moving at c/2 and there is a mirror at the other end. If she turns on a flashlight aimed at the mirror, from her perspective it takes the same time for the light ...