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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Problem conserving 4-momentum at CoM frame in an inelastic collision [closed]

I am confused about the case where mass is not conserved in a collision (not due to relativistic factors). The center of momentum (CoM) frame is not the same before and after the collision. Let's ...
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61 views

Are photons just electric waves in an electron's frame of reference?

They say that electrons emit photons when they jump to a lower orbit. But the way electrons should see it, there's no any emission, really. There's just rapid change in electric field due to a rapid ...
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2answers
92 views

Energy in the Relativistic COM Frame

I have been taught that in Classical Mechanics, the total energy of a system of two particles in the Centre of Mass Frame is given by $$ E_\mathrm{total} = \frac{1}{2}MV^2 + \frac{1}{2}\mu v_r^2 $$ ...
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2answers
458 views

Why is the speed of light limited to (only) 299.792.458 m/s? [closed]

The speed of light (in a vacuum) is limited to 299.792.458 m/s. This sounds very fast, and it is on a global scale. But if you look at the Universe on a larger scale than it sounds quite slow, For ...
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1answer
156 views

Einstein on a train paradox: what's the resolution?

Okay, so Einstein is on a train looking at a mirror. The train is moving at $c - 1 \frac ms$. Einstein is facing in the direction of motion. All along the side of the train are stationary clocks. ...
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33 views

The effects of special relativity when accounting for two reference frames

If reference frame A is travelling past reference frame B could one argue that it is in fact B that is motionless as their motion is relative to each other? If this is the case then how does one ...
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1answer
58 views

Could light be limiting towards a more fundamental speed limit? [closed]

Could it be possible (as in strictly speaking, no evidence going against this) that light could be limiting towards a more fundamental speed, and that light truly does slow down when a mass goes a ...
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9answers
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If an event happens 10 light years away and we observe it here, did it actually happen 10 years ago?

I'm sorry if this question has been answered a squillion times; I need someone with smarts to explain it to me. If an event happens at a distance of 10 light years away, and we observe it here, at a ...
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91 views

Special Relativity: Time Dilation

I am having difficulty solving the following problem: How fast must a rocket travel relative to the earth so that time in the rocket "slows down" to half its rate as measured by earth-based ...
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335 views

Is the assumption that space-time has to be a continuum just a matter of mathematical taste?

Is the assumption that space-time has to be a continuum just a matter of mathematical taste? Isn't there any physical significance associated with it?
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154 views

Energy for acceleration towards speed of light is relative?

This seems a very simple question - and I guess it will turn out to be so. It's a given that accelerating particles with mass towards the speed of light takes more and more energy (ultimately an an ...
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2answers
95 views

How to construct generators and Lie Algebra for Lorentz group?

I'm trying to figure out Lorentz group in 2+1. First of all, I'd like to think the special orthgonal group as a combination of rotation and boost in space. Then I construct it as below. First rotation ...
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109 views

Event times in different reference frames in the context of Special Relativity

I'm having a bit of difficulty puzzling out the correct way to move between frames in the context of a basic Special Relativity problem. The problem basically states that two bodies ($A$ and $B$) ...
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1answer
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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2answers
291 views

Intervals as infinitesimals of same order (Landau & Lifshitz)

I don't understand the following statement in Landau & Lifshitz, Classical Theory of Fields, p.5: $ds$ and $ds'$ are infinitesimals of same order. [...] It follows that $ds^2$ and $ds'^2$ must ...
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2answers
109 views

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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23 views

Would it be ok to say that not all light travels at the same speed when you consider its own perspective? [duplicate]

The reason I am asking is because higher energy would cause greater gravitational time dilation. Therefore I would expect, from the perspective of a radio wave, a gamma ray having more energy would ...
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1answer
108 views

Definition of probablity current in dirac space not including spatial dimension?

I'm currently reviewing (basic) relativistic quantum mechanics and stumbled upon the probability current in "dirac space", defined as $j^μ = (j^0,\vec j)^\mathrm T$ with $j^0 = c\,ρ = c\,ψ^+ψ$ and ...
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44 views

Lorentz Symmetry

Quick question about Lorentz symmetry. From the wiki page the feature of nature that says experimental results are independent of the orientation or the boost velocity of the laboratory through ...
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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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40 views

Is Lorentz Transformation about the difference of coordinates or coordinates of itself?

I have seen different authorities talking about different interpretation of Lorentz transformation. In his book 'Introduction to Classical Mechanics', David Morin states We always talk about eh ...
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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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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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121 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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4answers
79 views

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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82 views

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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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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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
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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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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2answers
538 views

twin paradox question

I'm trying to wrap my mind around the twin paradox, but I can't figure out this one problem from my textbook. It uses the relativistic Doppler effect to demonstrate how the paradox works. The first ...
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1answer
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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81 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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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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2answers
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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2answers
115 views

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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1answer
144 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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2answers
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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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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
476 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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2answers
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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
51 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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3answers
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
425 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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0answers
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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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. ...