# 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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### Are gravitational time dilation and the time dilation in special relativity independent?

There are two kinds of time dilation: One because the other clock moves fast relative to me (special relativity). Another one because the other clock is in a stronger gravitational field (general ...
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### Is Young's Modulus a Lorentz Scalar?

If a spring is at rest and lies along $X$ axis in a frame $O$ with a spring constant $k_{0}$ then its spring constant in a frame $O'$ which is moving with a speed $v$ at an angle $\theta$ with the $X$ ...
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### Is it possible to determine maximum frequency of a disc using a relative circumference?

On Wikipedia there is an article that shows how to calculate the relativistic effects on a rigid spinning disc, I am referencing the formula under the "Ehrenfest's argument" section in the link. The ...
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### Speed of Dark experiment, does it *really* travel faster than light? [duplicate]

I have seen many folks doing this Moon shadow experiment concluding that shadow from point A on the Moon can travel to point B on the Moon faster than light. What I fail to understand here (and I am ...
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### Can't reach speed of light, but relative to who?

Imagine a stationary person (with respect to a spaceship) floating in space and looks at a clock on the spaceship going 0.5c and sees it's clock ticking slower than his own, and concludes that it is ...
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### Were the Michelson-Morley results a surprise?

How unexpected were the Michelson-Morley experiment results? Did physicists have theoretical reasons to predict that the speed of light would result to be invariant?
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### Spacetime and quantum mechanics

In special relativity, the particle has a fixed world line in spacetime. So its whole trajectory is determined. But how can we represent the world line of the particle in spacetime when we take ...
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### A photon lives life as a flat-lander? [duplicate]

Think length contraction... I was thinking about going close to the speed of light the other day, and I was thinking about the idea that, if you went close to the speed of light, time would slow down ...
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### Relativity paradox with mirrors and light pulses

Consider two very short light pulses emitted from the centre (C) of two mirrors A and B (as shown in the diagram). From the point of view of the lab frame, the apparatus is all moving to the left at ...
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### Is there any way to justify or derive the form of the Lorentz force from relativity theory?

Lorentz force is in this form: $$\vec{F}=q[\vec{E}+\vec{u}\times\vec{B}]$$ As we know, it is Lorentz-invariant. Is there any way to justify or derive its form from relativity theory?
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### Poincare Group (Wald, Chapter 4 Page 59)

In Wald's text on general relativity, he mentions that in special relativity, many different global inertial coordinate systems are possible and can be put into one-to-one correspondence with elements ...
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### What is the inconsistency between Maxwell's electrodynamics and newtonian mechanics?

As far as I understand, when a modification of a theory is made it is because some observation required this modifcation. Quantum Mechanics is a nice example of that: observations of microscopic ...
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### Relativistic mass of electron in a potential [closed]

An electron is accelerated through a 6 MV potential difference. what is the mass of the electron at the end of the path?
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### Help understanding Bell's spaceship paradox

The problem statement of Bell's Spaceship paradox is this: Two spaceships float in space and are at rest relative to each other. They are connected by a string. The string is strong, but it ...
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### Reference for Reichenbach synchronisation and non-standard special relativity

My professor introduced in the last lesson a new method for clock synchronisation, which he called "Reichenbach synchronisation". In this new method, two clock A and B synchronise themself with the ...
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### Parallel axes between inertial frames in Special Relativity

In "CLASSICAL ELECTRODYNAMICS" by J.D.Jackson, 3rd Edition , $\S$ 11.3, the author gives in equation (11.19) a generalization of Lorentz transformation as follows : If the axes in K and K' remain ...
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### What spacelike, timelike and lightlike really mean?

Suppose we have two events $(x_1,y_1,z_1,t_1)$ and $(x_2,y_2,z_2,t_2)$, then we can define $$\Delta s^2 = -(c\Delta t)^2 + \Delta x^2 + \Delta y^2 + \Delta z^2$$ which is called the spacetime ...
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### According to the theory of relativity, (relativistic) mass of an electron changes when it moves at very high speed; how and why? [duplicate]

It is given that $$\mathbf m' = \frac{m}{\sqrt{1-\frac{v^2}{c^2}}}$$ How does (relativistic) mass change here?
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### How do photons experience time? [duplicate]

I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below. 1)So I want to know how time is perceived from the point of view of the photon? 2)Since ...
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### How does a photon experience space and time?

To an an external observer it appears that time has stopped for photon. But this relation is reflexive, so for an observer travelling with the photon it appears the universe has stopped everywhere. ...
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### Does photon experience time? [duplicate]

According to the special theory of relativity, for all observers the speed of light is c. Any observer travelling at the speed of light c does not experience time. Hence even protons shouldn't ...
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### Are we traveling through time at the speed of light? [duplicate]

In the image below the y axis represents time and x represent velocity. Point D represents velocity c, point E represents 1 second per stationary observers second. What this chart is showing is as you ...
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### Calculating speed in four dimensions [closed]

If you are moving at $c$ in 3D space and $c$ in time axis too, What would be your total speed? Edit: Since question has been voted to be closed, I shall make an Edit. In 4D world all objects move ...
Lorentz contraction and time dilatation can be deduced without Lorentz transformation. Can you deduce also the theorem of addition of velocities $$w~=~\dfrac{u+v}{1+uv/c^2}$$ without Lorentz ...