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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What is the intuitive meaning of $Q^2$?

In particle physics, $-Q^2$ is defined by the four momentum transfer squared: $$Q^2 = -(p_i - p_f)^2 = (\vec{p}_i-\vec{p}_f)^2-(E_i-E_f)^2$$ For elastic scattering, the meaning of $Q^2$ is clear - it ...
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Twin Paradox in a closed universe: who is younger when they meet? [duplicate]

Assuming that our universe is like a great balloon-- if you travel far and long enough, you will eventually come back to the original position. Now, a pair of twins are "travelling around the ...
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10 views

Lorentz invariance of proper acceleration in 1+1D

I want to show that proper acceleration ($\alpha$) is Lorentz invariant. I started trying to show that in a reference frame $S'$ moving at speed $V$ relative to $S$ we get $\alpha' = \alpha$, where ...
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2answers
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Why does the Lorentz transformation have to be a linear transformation?

In my textbook, they say the following statements before doing a proof for the Lorentz transformation: We know that the Galilean transformation $x' = x - vt$ is incorrect, but what is the ...
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3answers
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Twins Paradox - Does ageing depend on motion?

I am trying to understand the Twins Paradox (relativity) and its implications. Can we infer from the Twins Paradox that the ageing process (cell decay or other biological processes) depends on ...
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Could gravitational source provide a fixed reference frame for the speed of light measurements?

I have wondered if a gravitational source could provide the fixed reference frame for the measurements of c? There is, at least one, experiment which could prove my hypothesis wrong, I mean an object ...
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4answers
91 views

Why is there a universal speed limit?

I am looking for an answer that does not rely on Special or General Relativity -and without recourse to the fact that the speed of light is frame invariant. Is there another way of showing this ...
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2answers
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The action of a relativistic point particle, the meaning of its parametrization invariance and possible potential terms

i am currently toying around with the behaviour of a classical relativistic point particle a bit. For a free one we get the action \begin{align} S =\int_\tau - m\sqrt{- \dot X_\mu \dot X^\mu}. ...
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The effect of relativistic near misses

Alice and Bob are both floating in free, empty space. Alice does not like Bob very much. Thus one day, believing that there is no such thing as overkill, Alice takes her programmable hyper-energetic ...
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1answer
34 views

Does motion with constant proper acceleration, in a flat region, necessarily mean straight hyperbolic motion?

Is motion of a participant with constant proper acceleration, in a flat region, necessarily straight, hyperbolic motion (with respect to members of any inertial system, in that region)? Or is for ...
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4-vectors in special relativity and spacetime interval

In one of my vector mechanics lectures, the lecturer said the the space time interval was the dot product of the four position vector. But then he proceeded to show it was this: $s^2$ = $\Delta r^2$ - ...
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Confusion I have regarding Einstein's 1905 derivation of LT

In his 1905 paper, Einstein derives the Lorentz transformation using the two postulates of SR;constancy of $c$ for all inertial frames and the Invariance of the laws of physics for all inertial ...
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3answers
51 views

Regarding synchronization of clocks in special relativity

I am trying to read of synchronization of two clocks in same inertial frame in special relativity. Suppose we have two synchronized clocks in an inertial frame placed at positions $x_1$ and $x_2$ in ...
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1answer
54 views

Best twin paradox trajectory for constant acceleration rocket?

Let's say I have a rocket that can provide constant (proper) acceleration (let's say of 1 gee) for an infinte amount of time. Let's say I want to use this rocket as a means of "suspended animation," ...
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2answers
547 views

Exact definition of momentarily comoving reference frame (MCRF)

Consider a particle $P$ in the framework of special relativity with position $r(t)=(ct,x(t),y(t),z(t))$ respect to an inertial reference frame $\Sigma=(ct,x,y,z;O)$. I need to know if the following ...
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Why is this 4x4 tensor a 16-dimensional representation of SO(3,1)?

In his QFT book "A Modern Introduction to Quantum Field Theory" (http://www.nucleares.unam.mx/~alberto/apuntes/maggiore.pdf, pages 20-21), Michele Maggiore describes the tensor product of the ...
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Does space expansion change value when traveling near the speed of light?

To draw an analogy, we receive roughly the same amount of cosmic background radiation from all directions. However if we were to travel near the speed of light relative to the reference frame where ...
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1answer
50 views

How does work function transform in Einstein's special theory of relativity?

A photon with energy greater than the work function hits the metal, and an electron is knocked off. Now, suppose we were in an inertial frame moving with a velocity $v$ with respect to the metal such ...
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2answers
66 views

How is Einstein's arbitrary additive constant $C$ constant during the emission of light?

This is a follow up on this question. In his paper under the title:Does the inertia of a body depend upon its energy-content, Einstein considers two inertial frames $(x,y,z)$ and $(\xi,\eta,\zeta)$ ...
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Is potential energy frame dependent in special relativity?

In newtonian mechanics, As far as I'm aware, only kinetic energy is dependent on frames of reference, since kinetic energy is a function of velocity(squared) and velocity is dependent on frames of ...
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Higgs Boson mathematical elimination process [closed]

I heard that if the Higgs Boson could be mathematically eliminated, it would be easily accelerate the particles up to the speed of light. If so, how can the Higgs Boson be removed out from the ...
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1answer
30 views

What is disadvantageous about measuring time events using light signals sent from events?

In his paper: On the electrodynamics of moving bodies, under the section entitled I. KINEMATICAL PART: § 1. Definition of Simultaneity, Einstein discusses time and gives it an operational definition. ...
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tensor products in special realitivity

Use the definition of a tensor as a linear function on vectors and 1-forms. For a one (2,1) tensor T, use a single vector as argument e.g. T(V) which converts it to a (1,1) tensor. However, if you ...
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The Twin Paradox using reference frame following the ship

The Twin Paradox is undoubtedly one of the most discussed things in special relativity and have a tendency to confuse most of us. Classically, it's resolved by either stick to one of the three ...
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Relativistic velocity in Special Theory of Relativity [closed]

Prove that, 0.5 m*v^2 , where m = M / (1- (v^2 / c^2))^0.5 ["M" is original mass, and "m" is mass with velocity] doesn't equal to the the Kinetic Energy of a particle moving at relativistic velocity. ...
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What is the difference between induced and motional emf?

At least from their names, it seems motional emf is induced, so what's the difference?
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Do relativistic electrons have more charge?

Gauss's law tells us that the total electric flux out of a closed surface is equal to the charge enclosed divided by the permittivity. When a charged particle is moving close to the speed of light ...
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Are relativistic spacecraft slowed down by oncoming gamma ray photons?

I recently read that a proton having an energy of ten billion GeV can travel across our galaxy in about 5 minutes from the frame of the proton. From the Earths frame we would see it take roughly ...
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That 10km/day error predicted if GPS satellite clocks not corrected for relativity

Some authorities have stated publicly and without explanation that if the theories of Special and General Relativity were not taken into account in the design of the GPS (by building the satellite ...
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2answers
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Quantum entanglement and special relativity PARADOX [closed]

Imagine two entangled atomic clocks. After we entangle them, we measure the time: it does has to be the same , right ? Now lets suppose that we entangle them , but don't measure them, then we plant ...
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1answer
31 views

Derivation of relativistic mean free path

I am working through a short derivation found in Abramowicz 1991 regarding the mean free path of a photon. We have a fluid moving in a particular direction with velocity $v$ and in an inertial rest ...
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understanding twin paradox [closed]

Is it really possible to observe such a phenomena in real life? I am confused. I have studied time dilation in relation to pion decay but am not sure if it will be true for us human being to observe ...
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Definitions: 'locality' vs 'causality'

I'm having trouble unambiguously interpreting many answers here due to the fact that the terms locality and causality are sometimes used interchangeably, while other times seem to mean very different ...
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Time relativity

Lets say that I am on a spaceship moving with the speed of 0,90c and I am looking on my friend who stayed back on earth. My friend is looking on me. From my perspective, my friend is moving 7 times ...
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1answer
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Is heavier object falls slower according to special theory of relativity?

I'm newbie in physics, but have some idea want to know whether it is correct! I saw some information about special theorey of relativity. It just like says "when objects go faster it becomes more ...
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A vertical variation of modern versions of Michelson-Morley

For almost a year now, I have been in the uncomfortable position of having an idea. However, there is one nice thing about this idea. It makes a concrete, exact and relatively easy to test physical ...
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2answers
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Why magnetic field lines and force are not orthogonal with magnets?

The below explanation why magnetism exists is superb in this video. The explanation about magnets is also great in this video. A magnet has atoms with unpaired electrons forming mini magnets. The ...
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Gauge transformation and Special relativity

While explaining gauge theories, a book makes a comment that the U(1) transformation definition, $ U= e^{i q \lambda(x)}$ is analogous to a special relativity transformation in freely falling ...
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4answers
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Is this a Lorentz-scalar? How do I tell?

I'm struggling to identify whether a scalar is a Lorentz-scalar. E.g: $$\partial_i A^i \quad i \in {1,2,3}.$$ How do I determine if this is a Lorentz-scalar or not? If got the same problem with ...
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1answer
134 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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Humans on earth seen from traveling space ship

If I would stand on a space ship traveling with a speed of 0,99c I would be moving 7 times slower from Earth's perspective. But if I would look back on Earth I would see everything moving 7 times ...
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Is there a standard of rest in the universe? [duplicate]

If you measure the cosmic background radiation you will find that in any direction it is roughly the same. However, if you were to travel near the speed of light relative to the Earth in a particular ...
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2answers
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Shape and even connectedness of accelerating components in SR is frame dependent?

In some inertial frame consider a disk of radius 1 lightyear at rest. Then along the edge of the disk there are some people in spacesuits at rest hovering right above the disk (which has negligible ...
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Why does the Lorentz transformation in special relativity have to be like this?

Basically I think Albert Einstein (A.E.) was trying to find a transformation that: Always transform a constant-velocity movement into a constant-velocity movement. Always transform a ...
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2answers
239 views

Why did Compton use X-rays in his experiment?

Why did Compton use X-rays in his famous experiment? Can it be done using other types of electromagnetic waves?
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Symmetrical twin paradox without changing direction

If I understood well, in the special relativity 1- A stationary observer sees other moving observer's clock works more slowly than the stationary clock. 2- Motion is relative, the moving observer ...
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Reflection At Speed of Light

I have looked online to no avail. There is two competing answers and I am curious to know which one is right. Someone asked me this question. If you are traveling at the speed of light can you see ...
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463 views

Euclidean geometry in non-inertial frame

Refer, "The classical theory of Fields" by Landau lifshitz (Chap 3). Consider a disk of radius R, then circumference is $2 \pi R$. Now, make this disk rotate at velocity of the order of c(speed of ...
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Explain the notion of light/electromagnetic waves/photons to a non-physicist

A non-physicist asked me about special relativity. My explanations naturally were based on gedankenexperiments involving light. This forced the question: "What is light? It is particles, isn't? Or is ...