# 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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Let 2 electrons A and B be moving parallel with constant velocity $c/10$ in (near) vacuum without a strong gravity field (where $c$ is speed-of-light). A and B create an electromagnetic field that is ...
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### Relativistic drift velocity of electrons in a superconductor?

Is there a formula for the effective speed of electron currents inside superconductors? The formula for normal conductors is: $$V = \frac{I}{nAq}$$ I wonder if there are any changes to this ...
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### Maxwell equations invariant under Lorentz transformation but not Galilean transformations

Why Maxwell equations are not invariant under Galilean transformations, but invariant under Lorentz transformations? What is the deep physical meaning behind it?
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### Information relationship to Special Relativity

How do we write mathematically that "information" cannot go faster than light? And along a similar line of thought, how do we relate "information" with special relativity. Lastly, what is the ...
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### Derivation of the Lorentz transformation

I have been reading Young's book called: University physics with modern physics and on page 1284 author states that we can derive Lorenz time transformation by eliminating two equations for Lorentz ...
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Both the General & Special Relativity discarded Newtonian mechanics of absoluteness. According to Einstein's view, Time, Mass, Length and Space are interdependent. So, Did Relativity discarded ...
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### Increased mass from signals traveling close to the speed of light

As you travel close to the speed of light, it is to my understanding you gain mass. Does this also apply when the brain sends electrical signals to the muscles? Do the signals (that are traveling at ...
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### 3 inertial frames compared in STR

Suppose an event is observed in 3 inertial frames K, K' and K''. The coordinates in K are $(x,t)$ in K' are $(x',t')$ in K'' are $(x'',t'')$. The K' and K'' coordinates are then Lorentz-transformed to ...
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### Is there a strong force analog to magnetic fields?

In special relativity, magnetism can be re-interpreted as an aspect of how electric charges interact when viewed from different inertial frames. Color charge is more complex than electric charge, but ...
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### Causality without light

Related to my prior question: Would a species insensitive to light have developed special relativity? Imagine a species insensate to light and other em radiation. They are very attuned to sound ...
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### Would it be possible to develop special relativity without knowing about light?

My understanding of special relativity is that it is fundamentally based on the constancy of the speed of electromagnetic radiation - that this speed is a physical law (or derivable from physical laws ...
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### Darwin term and Zitterbewegung

I've noticed that in the discussion of the fine structure of Hydrogen atom standard QM texts claim that the Darwin term, which corrects energy of $\ell=0$ (or $s$-) states only, is related to the ...
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### What happens when a photon hits a mirror?

When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
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### Time slowing down problem

When someone moves, time slows down for him. Let, a man standing still and another moving very very very fast, this happens for an hour (as measured by the standing man). Time has moved slower for the ...
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### Why did Einstein get credit for formulating the theory of special relativity?

See The Principle of Relativity here: The Principles of Mathematical Physics. This was written by Poincaré in 1904, a year before Einstein published his theory of relativity. It appears from this and ...
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### Could one transmit a signal with equally-tuned casimir plates across the quantum field?

It seems, one could exploit the Casimir effect to send messages across arbitrarily-large distances with carefully-tuned Casimir plates. Obviously, relativity would preclude FTL information transfer, ...
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### Lorentz Invariance of Maxwell Equations

I am curious to see a simple demonstration of how special relativity leads to Lorentz Invariance of the Maxwell Equations. Differential form will suffice.
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### Filming light in motion?

Regarding this video http://www.youtube.com/watch?v=Y_9vd4HWlVA, which claims to "film" light in its motion. Is it not an absolute nonsense? Even if photons could even be "seen" (meaning, returning ...
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### Is “Causality” the equivalent of a claim that the future is predictable based on the present and the past?

In classical (Newtonian) mechanics, every observer had the same past and the same future and if you had perfect knowledge about the current state of all particles in the universe, you could ...
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### What were the intention/conclusions for Michelson-Morley experiment?

Which of the following were the intentions of M&M? to disprove the existence of aether. to show that the aether has no effect on matter and energy and therefore is as good as non-existent. ...
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### relativistic spaceship, CMB radiation and thermodynamics

Scenario: a spaceship is travelling at a high fraction of $c$. The interstellar gas and CMB radiation has blueshifted significantly and we are facing a possible melting of the front radiation shield! ...
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### Is it possible to transfer classical bits of information faster than light speed?

Is there any known, verifiable way to transfer classical information faster than light, using quantum entanglement or other phenomenon? Does quantum teleportation, or other known phenomenon, allow ...
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### Is it best to look at light as a particle when trying to understand special relativity?

So my course about special relativity explains time dilation using a moving train, where one sends up (i.e. perpendicular to the direction of movement) a light pulse which gets reflected etc. (a ...
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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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### Two trains at the speed of light [closed]

Okay. Two trains travelling towards each other at the speed of light. So, from one train (let's call it train A), the other is moving towards it at the speed of light. The other train shines a torch. ...
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### Galileo's dictum and how light cannot violate it

Okay. So I've been told that the speed of light is constant and cannot violate Galileo's dictum, but even if it weren't constant (in a vacuum), how would it violate it anyway? Say you are on a train ...
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### Special Relativity: What differential equation describes an accelerated object from a non-inertial reference frame?

I am looking for a set of differential equations (to be solved numerically for an educational program) that would describe the position and apparent time of an accelerated clock relative to a ...
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### A relative time dilation paradox.

Let us assume that there are two astronauts A and B who are floating in space. A sees B passing by and vice versa. A sends signals to B every minute. According to A since B is moving his clock will be ...
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### relativistic acceleration equation

A Starship is going to accelerate from 0 to some final four-velocity, but it cannot accelerate faster than $g_M$, otherwise it will crush the astronauts. what is the appropiate equation to constraint ...
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### Could the Heisenberg Uncertainty Principle turn out to be false?

While investigating the EPR Paradox, it seems like only two options are given, when there could be a third that is not mentioned - Heisenberg's Uncertainty Principle being given up. The setup is this ...
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### Expression for the (relativistic) mass of the photon [closed]

I started learning a bit ahead from an old physics book, and they were discussing the photoelectric effect and after that Planck's hypotheses and energy quantas. The book said that the mass of a ...
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### Special Relativity Second Postulate

That the speed of light is constant for all inertial frames is the second postulate of special relativity but this does not means that nothing can travel faster than light. so is it possible the ...
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### Does the (relativistic) mass change? Why?

I learned recently that when an object moves with a velocity comparable to the velocity of light the (relativistic) mass changes. How does this alteration take place?
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### Using Lorentz Invariance of Charge To Calculate Current Density

I'm attempting a problem from Zwiebach: A First Course in String Theory and am completely stuck. Could anyone give me a hint? The problem is as follows. Consider $S$, $S'$ two Lorentz frames with ...
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### Why are objects at rest in motion through spacetime at the speed of light?

I read that an object at rest has such a stupendous amount of energy, $E=mc^2$ because it's effectively in motion through space-time at the speed of light and it's traveling through the time dimension ...
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### Does the speed of light vary in noninertial frames?

The speed of light is the same in all inertial frames. Does it change from a non-inertial frame to another? Can it be zero? If it is not constant in non-inertial frames, is it still bounded from ...
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### First Postulate of Special Relativity: What does it mean?

Wikipedia has this quote: Special principle of relativity: If a system of coordinates K is chosen so that, in relation to it, physical laws hold good in their simplest form, the same laws hold ...
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### Relativity - time dilation

I'm learning about relativity and I'm having some issues with it and the twin paradox. I found many questions and answers on this subject but they did not answer my specific problem. In my thought ...
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### Time dilation - why the observers see each other the slow one but then one of them is older or younger?

I'm in trouble with time dilation: Suppose that there's two people on the Earth (A,B), they are twins and each other has a clock. (So they are at the same reference frame). B travels in a spaceship ...
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### Does the potential energy related to a particle determines its rest mass?

Would it be possible to determine the rest mass of a particle by computing the potential energy related to the presence (existence) of the particle, if this potential energy could be determined ...
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### Inner product of four-vectors in special relativity

Reference) "Feynman lectures on Physics Vol.3 , p.7-4 ." With four vectors $x_{\mu} = (t,x,y,z)\ , \ p_{\mu} = (E,p_{x},p_{y},p_{z})$ the inner product of these two four vectors is scalar invariant ...
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### Having trouble seeing the similarity between these two energy-momentum tensors

Leonard Suskind gives the following formulation of the energy-momentum tensor in his Stanford lectures on GR (#10, I believe): T_{\mu \nu}=\partial_{\mu}\phi \partial_{\nu}\phi-\frac{1}{2}g_{\mu ...
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### How do I extend the Lorentz transformation metric to dimensions>4?

How do I extend the general Lorentz transformation matrix (not just a boost along an axis, but in directions where the dx1/dt, dx2/dt, dx3/dt, components are all not zero. For eg. as on the Wikipedia ...
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### What should I call an n>4 dimensional Minkowski metric?

I am manipulating an $nxn$ metric where $n$ is often $> 4$, depending on the model. The $00$ component is always tau*constant, as in the Minkowski metric, but the signs on all components might be ...
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### quantum curvature

If a state can be a superposition of energy states, and mass equals energy (special relativity), and mass curves space-time (general relativity), then could we say that space-time around a quantum ...
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### Hamiltonian mechanics and special relativity?

Is there a relativistic version of Hamiltonian mechanics? If so, how is it formulated (what are the main equations and the form of Hamiltonian)? Is it a common framework, if not then why? It would be ...
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### What is the proper time used in relativistic non-equilibrium statistical physics?

In the literature one often finds covariant relativistic generalizations of classical non equilibrium statistical equations (Boltzmann, Vlasov, Landau, Fokker-Planck, etc...) but I wonder what is the ...
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### maximum distance between accelerating objects started at different times [closed]

Let there be two objects that have zero relative velocity with respect to each other in an inertial frame. If they both undergo identical accelerations, but one starts the acceleration at t = T1 and ...
In general relativity 4-volume element $\mathrm{d}^4 x = \mathrm{d} x^0\mathrm{d} x^1 \mathrm{d} x^2\mathrm{d} x^3$ is clearly a pseudoscalar (or scalar density) of weight 1 since it transforms as ...