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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Relative Lorentz factor for two shells

Shell 1 is travelling at a speed $v_1$ with Lorentz factor $\Gamma_1$, and shell 2 at speed $v_2$ with Lorentz factor $\Gamma_2$. Just before the two shells meet, the relative lorentz factor ...
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Does it make sense to say that objects moving at relativistic velocities appear in space-time cross-section?

Let object A move at relativistic velocity relative to a frame O. In 4D space-time (Minkowski diagram) the space view of O at any given moment of its own time is a space-like hypersurface (hyperplane, ...
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41 views

Distance and Time

I understand that if an object is 10 light years away then the light I am seeing from that object is actually from 10 years ago. If this is the case, which a few posts on this forum seem to concur, ...
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118 views

Twin Paradox Problem

In every book the solution of twin paradox is that one have to accelerate thus two observer does not trace parallel lorentz vectors thus can't be compared. Through GR we get the one who accelerate ...
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61 views

The chirality of (2+1)D Dirac equation

Are there any definitions about the chirality of (2+1)D Dirac equation? For the (3+1)D Dirac equation, the Dirac field can be written as the sum of left- and right-hand Weyl field. Can this be reduced ...
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Navigating to a distant star

Suppose I have a space ship that can travel at $0.9c$, and I'm going to a star located at 20 light years or so from the Sun. From a practical point of view, if I keep pointing the nose of my space ...
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What happens to the observed thermal energy of objects at relativistic speeds?

When an object is observed to move near the speed of light, what difference in thermal energy is observed? Does time dilation imply that it's colder?
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59 views

Will I sunburn faster when driving compared to being parked?

I'm not sure if the same logic applies to light and rain when comparing running/driving with a stagnant situation. See, e.g. Why does driving faster make my windshield catch more rain? Suppose I have ...
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58 views

time distortion

Observer A is standing on a planet, and observer B is on a ship. At t=0 B is 1 light year away from A. Also at t=0 B will accelerate its ship to a 0,999999999...$c$ instantaneously (yes, its a very ...
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51 views

Is the car/wall comparison valid for speeds close to $c$? [duplicate]

At school, people commonly think about momentum and conservation of energy using the example of a car collision. A common phrase is "Do not try to think of two objects moving, think of one moving at ...
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84 views

Will objects heat up and become hidden at relativistic speed?

Let us assume there is a mirror travelling at extremely relativistic speeds, perhaps few picometers away from speed of light, and let us assume we have a very thin detector which is very small perhaps ...
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122 views

Objects colliding at relativistic speeds combined energy?

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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60 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. Due to length contraction it appears as a vertical ellipsoid, when it ...
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63 views

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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1answer
41 views

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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102 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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87 views

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 [closed]

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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1answer
95 views

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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1answer
143 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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56 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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19 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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3answers
145 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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1answer
50 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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2answers
61 views

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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93 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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1answer
170 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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27 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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352 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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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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161 views

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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214 views

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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1answer
76 views

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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1answer
218 views

What does the ratio $\frac{x-ct}{x'-ct'}$ 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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143 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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“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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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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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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4answers
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Does a ticking watch have more mass? [duplicate]

In the video on YouTube, The Real Meaning of E=mc² | PBS| Space Time Studios, it claims that a ticking watch has more mass then a non ticking watch due to the intrinsic KE, PE and thermal energy of ...
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2answers
149 views

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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2answers
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Is momentum an invariant? [closed]

Is the value of momentum an invariant?, specificly for instance the momentum value $\mathbf p_{\text{lab}}[~\Lambda^0~]$ of a $\Lambda^0$ baryon (drifting from the (actual) interaction point of a ...
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36 views

Inelastic cross section derivation

I am trying to derive the inelastic cross section (the mass changes). I looked up the elastic derivation on Peskin's book (are there any alternatives?): $$d \sigma = \frac{1}{2 E_a 2 E_b \left| ...
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4answers
242 views

How is relativity related to anti-particles? [duplicate]

I have heard that a positron is like an electron moving backward through time. Can someone elucidate this statement for me. I would like to hear a deeper explanation of what we believe anti-matter to ...
3
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2answers
117 views

Where does the equation $p=\frac{1}{c}\sqrt{T^2 +2mTc^2}$ come from?

Where does the relativistic formula $$p~=~\frac{1}{c}\sqrt{T^2 +2mTc^2}$$ come from? What is the derivation from Einstein's formula? $T$ is the kinetic energy $m$ is the mass $p$ is the momentum.
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1answer
169 views

How many days it takes to travel to Cygnus? [duplicate]

BACKSTORY I read today newspaper and made discovery of planet Cygnus (in news paper of course :v) that human can live there! The distance is 1400 Lightyear. Assuming I travel with the world fastest ...
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40 views

Constancy of speed of light $c$ with perpendicular motion [duplicate]

Suppose light is travelling in a straight line parallel to $y$-axis takes time $t$ to reach from $y_1$ to $y_2$ in a reference frame $S$. Let there be another frame, $S'$, which is travelling parallel ...
0
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1answer
108 views

Does an object traveling near the speed of light create a gravitaional field? [duplicate]

Does a particle traveling near the speed of light create an observable/measureable gravitational field around it? I know most elementary particles travel near the speed of light and have no ...
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1answer
81 views

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 ...
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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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170 views

Klein-Gordon equation and wave velocity

It looks like solutions of the KG eqn travel faster than light, because if $$\omega^2 - k^2 = m^2$$ then $$\mid\ \omega\mid \ > \ \mid k\ \mid$$ and I thought the wave velocity was $\omega / k$. ...
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173 views

What's the max speed a man-made satellite can travel in space before its circuitry stopped working?

Assume it could withstand extreme temperatures in either direction. I'm mainly curious what would happen to its circuits as it approached the speed of light.