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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Why does time slow down when traveling at high speeds

One of the effects of traveling at high speeds is slowing down of clocks. I can understand gravity time dilation effect but not how would velocity affect clock speeds. How correct it is, if I say ...
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5answers
92 views

Confusion about Length Contraction (ex in Muon decay)

I am a bit confused about the implications of length contractions; For example, in the muon decay problem, we assume that the distance between the muon and the earth is contracted only in the frame ...
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48 views

Show that there exists a Lorentz transformation such that two events are happening at the same time? [on hold]

I'm havin problems with the following exercise in a theoretical physics course: Show that there always exists a Lorentz transformation such that the two events $P$ and $P^0$ in the figure are ...
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16 views

Is uncertainty in velocity via HUP reference frame dependent? [duplicate]

Simply put HUP involves position and momentum, further more consider a mass of 1kg. as momentum is mass X velocity = 1X velocity = velocity for calculation purposes. now for a stationary observer the ...
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42 views

Lorentz transformations on momentum space Weyl spinors

The Weyl spinor in momentum space can be given by the inverse Fourier transform: $$\psi_L(x) = \int \frac {d^4 p} {(2\pi)^4}\psi_L(p)e^{-ip\cdot x}, and we also have$$ $$\psi_L(x)=\int \frac ...
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32 views

Maxwell's Equations for Accelerated Conductors

I asked a question about accelerated conductors in a magnetic field but nobody unfortunately answered. That is: Ohm's Law for Accelerated Conductors Maybe, I could not state my question well. I ...
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2answers
46 views

If a photon is exists in 'timeless' state, how can objects around it move? [duplicate]

My understanding is that light does not experience time. In attempting to understand what the universe would be like from the perspective of a photon, the answer I get is that the universe would be ...
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2answers
79 views

Why scalar function of vector can only depend on norm of vector?

In Field Quantization by Greiner and Reinhardt as well as The Qunatum Theory of Fields by Weinberg, concerning the spectral function, the authors say a scalar function of the four-vector $p^\mu$ can ...
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1answer
117 views

Lever “paradox”?

Let's say we have a lever with two weights A and B with the same mass overlapping at the midpoint. Suppose they start to separate with each other at the speed of light simultaneously. From our point ...
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0answers
23 views

Extreme temperatures, relativity and kinetic theory

According to kinetic theory, average kinetic energy is proportional to temperature. Supposing $k_BT/2$ per particle, can we use relativity and kinetic theory to calculate, e.g., the temperature and ...
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0answers
46 views

2 questions on 4-velocity

Firstly 4-velocity is defined by $u^\mu=\frac{dx^\mu}{d\tau}$ let us consider the component $x_i$ of $x^\mu$ then this derivative can be written as: ...
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50 views

$E=mc^2$ what is unique about the speed of light? [duplicate]

What unique property of light, makes it the conversion factor between energy and mass? It has to be more than a coincidence that the speed of light, just happens to be the correct number number to ...
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47 views

$E=mc^2$ is incomplete? [duplicate]

So I was going through youtube and I found out these: http://www.youtube.com/watch?v=mkiCPMjpysc http://www.youtube.com/watch?v=NnMIhxWRGNw Can anyone here explain to me (with derivation if ...
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0answers
37 views

Is time dilation a mechanical slowdown only? [duplicate]

I've recently read about the time dilation occurs at very high speeds. But I'm really wondering if it is just a mechanical slowdown of the clock only? What if we use clocks that does not use moving ...
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1answer
27 views

Does spinning actually decrease the time experienced by the spinner?

In this xkcd, Megan spins around to attempt to take momentum away from the Earth to slow its spinning. I was wondering, if Megan spinned around, wouldn't this cause her relative velocity to the rest ...
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2answers
226 views

How to understand non-associative composition of velocities in STR?

In STR the composition of non parallel movements is in general non-associative. The formula is $\displaystyle\bar{u}\oplus\bar{v}= \frac{\bar{u}+\bar{v}_{\|}+\bar{v}_\bot/\gamma}{1+\bar u\cdot\bar ...
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1answer
61 views

Decoherence, collpse, and WHEN does the collapse occur?

The idea that decoherence stands behind the so-called collapse (reduction) of the wave-function doesn't seem satisfactory. Consider a quantum particle whose wave-function is of the form (1) ...
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7answers
236 views

“Reality” of length contraction in SR

I was in argument with someone who claims that length contraction is not "real" but only "apparent", that the measurement of a solid rod in its rest reference frame is the "real length" of the rod and ...
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1answer
51 views

Twin paradox…what happens to the ship?

The earth bound twin looks up and sees his travelling twin moving slower inside his spaceship because he is whizzing by at some percent speed of light. But what does the motion of the ship itself ...
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0answers
32 views

Books on special and general relativity? [duplicate]

I have idea about all the theories related to space and time and stuff. But I wanna dig deep into it and understand all the theories like special and general relativity to begin with for now. Can ...
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1answer
68 views

Einsteins idea about solving the ether problem [duplicate]

I'm struggling a bit with my Special Relativity course. Most exercises are quite trivial and can be done without much effort, but when you really start to think and analyse why and how certain things ...
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3answers
59 views

Center of mass of two $\gamma$ rays moving in opposite directions

Suppose there are two $\gamma$ rays with frequencies $\nu_1$ and $\nu_2$ moving in opposite directions according to a reference frame $S$. I want to find the velocity of the center of mass of this ...
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2answers
307 views

Are virtual particles limited by the speed of light? [duplicate]

I have recently been reading about Quantum Electrodynamics which I found very interesting, but even more confusing. I understand photons mediate the electromagnetic force and interactions between ...
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65 views

Define what Einstein says [closed]

I came across an equation $E^2=(m_0c^2)^2 + (pc)^2$ Could you please explain each term and how to use this equation? Also substituting the left side of the equation ie, $E = mc^2$ gives another ...
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1answer
46 views

Passage of time on a faster-than-light (FTL) vessel [closed]

Yes, this is already wild speculation. I'll retract this question if it isn't well received. As I understand, within an event horizon, spacetime gets rotated so that the singularity is in the future, ...
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56 views

Ohm's Law for Accelerated Conductors

My questions are about the Ohm's law for a moving conductor in a stationary magnetic field. As we know this law is stated based on following relation with respect to the fixed frame of reference ...
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2answers
2k views

What do physicists mean by “information”?

On the question why certain velocities (i.e. phase velocity) can be greater than the speed of light, people will say something like: since no matter or "information" is transferred, therefore the ...
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1answer
54 views

What would be observed by two observers traveling away from one another at 0.75c? (And why?) [closed]

What would be observed by two observers traveling away from one another at 0.75c, and why? Suppose that two observers O1 and O2 are at a point S. Then, they begin traveling away from one another at ...
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0answers
22 views

Recommendation for contra-variant and contra-variant vectors in the context of special relativity [duplicate]

I have just started studying covariant and contra-variant vectors in special relativity. I am finding difficulty understanding this topic. Can anyone recommend a book (with a detailed chapter) or ...
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98 views

Natario warp drive [closed]

There are two solutions to Einstein's equations that allow for warp drive. One is the Alcubierre warp drive and the other is the Natario warp drive. What is the difference? Is the Natario warp drive ...
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3answers
143 views

How to theoretically define a concrete operation to perform in order to measure the length of an object?

EDIT: Some answerers pointed out that the title of this question is in contrast with what is actually been asked in the body of the question, so I changed the title accordingly. The original title was ...
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4answers
108 views

How, in practice, could instantaneous signalling violate causality?

I know that instantaneous signalling can result in different observers not agreeing on the order of events, but how can that result in causality violation in practice? In other words, if one had two ...
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3answers
578 views

If we traveled at almost light speed with a mirror in hand [duplicate]

What would we see if we hold the mirror in front of us and behind us.
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92 views

Bound electrons don't move, right?

I've never been satisfied with the explanation that electrons have a “speed” and move close to the speed of light, thus incurring relativistic effects that make gold pretty and mercury wet. I learned ...
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4answers
103 views

Twin paradox where the twins start at different locations

Suppose we have this scenario with twins A and B: 1) Instead of the twins starting at the same location, let's say the twins start out some distance apart, in the same reference frame. 2) The ...
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1answer
64 views

Applying Lorentz Transformations and Time Dilation

My question is based on a popular question, usually posed in introductory courses on the special theory of relativity. Two rockets are on a collision course. Rocket 1 is traveling at the speed ...
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2answers
210 views

Interferometers and Earth's motion relative to the Aether

Why was the Michelson and not the Fabry-Perot interferometer used to detect the motion of Earth relative to the Aether? Maybe the Fabry-Perot was used but we all know that the most famous experiment ...
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4answers
66 views

Question about dot product of four vectors?

I am looking back over some old notes and see that I have written $\bar{p}=\left(\overset{E}{\vec p}\right)$ and $\bar{x}=\left(\overset{t}{\vec x}\right)$ (using Plank units) And then $\bar{p} ...
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2answers
110 views

Does rotation increase mass?

If an object is rotated on its axis near the speed of light would its mass increase? Normally if the object was moving (in relationship to the Earth for example) I would agree that its mass would ...
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3answers
64 views

Is it really possible to create some mass only from equivalent energy? [duplicate]

From Special theory of relativity we know that $E=m_0 c^2$, which says about mass energy equivalency. But my question : **Is there any real experiment where some mass is created purely from energy? ...
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26 views

$2\to3$ Phase space Integration

I have a $2\to3$ process ($P=p_1+p_2 \to p_3+p_4+p_5$) where all particles in the initial state and one of the particles in the final state ($p_3$) are massless. The other two ($p_4$ and $p_5$) have ...
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2answers
55 views

How to identify a “measuring rod”, and how to compare separated “measuring rods” with each other?

The notion of "measuring rod" has appeared in PSE here and there, and outside PSE as well. As far as I understand (and as perhaps all who refer to this notion do agree on), important constituents of ...
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6answers
2k views

Measuring speed of the moving train, if I'm inside it

So I am inside a coach in a train that is fully sealed (with no windows and a locked door). I have a torch, photo & time sensor and a scale with me. So, I place the sensor at one of the walls and ...
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2answers
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If the vacuum is not “emptiness” why the speed of the electromagnetic wave is independent of the frame of reference?

If the vacuum were "emptiness" it were easy to accept that there is no "preferred frame of coordinates" and the light velocity is the same in any inertial frame of coordinates. But the vacuum is an ...
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2answers
51 views

Is it possible to propagate a relativistic system of particles in time using Verlet?

The Verlet algorithm and its derivations are very popular methods to integrate Newton's equations of motion in time and obtain a trajectory for a system with $N$ particles. I work with classical ...
3
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3answers
66 views

Circumference of a circle in a co-rotating frame of reference

According to Einstein it should be greater than $2 \pi R$ for a co-rotating observer, i.e. $L' = \gamma L$ where $L = 2 \pi R$ in a non-rotating frame and $\gamma$ is the usual Lorentz factor, which ...
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4answers
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How does the Lorentz transformation $\Lambda^{\mu}{}_{\nu}$ transform?

For example the Four-velocity transforms as $$U^{a'}=\Lambda^{a'}{}_{\nu}U^{\nu},$$ the Faradaytensor as $$F^{a'b'}=\Lambda_{\,\,\mu}^{a'}\Lambda_{\,\,\nu}^{b'}F^{\mu\nu}$$ or in Matrixnotation: ...
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2answers
91 views

Does space between objects contract?

I had a question, let us assume a coordinate system where there is 2 objects moving at relativistic speeds (at same velocity) for the observer therefore the observer will observe the length ...
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2answers
70 views

Does a Michelson-Morley experiment uphold mass-energy equivalence and special relativity?

If there is an experiment that best supports $E=mc^2$, is it the Michelson-Morley experiment?
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2answers
69 views

A simple quantum mechanics question [closed]

Here is the problem: Find the energy of neutron, electron and electromagnetic waves of wavelength 0.1nm. English is my second language, so I am kind of confused about the meaning of problem ...