The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.
5
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2answers
161 views
Relativistic equivalent of a spring-force?
Usually what helps me understand a concept better in physics is to write a simulation of it. I've got to the point where I'm competent in the basics of special relativity, but, I can't figure out how ...
6
votes
1answer
224 views
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 ...
3
votes
1answer
43 views
Doppler redshift in special relativity
I came across this exercise in Elementary General Relativity by Alan MacDonald:
A source of light pulses moves with speed v directly away from an observer at rest in an inertial frame. Let $ \Delta ...
2
votes
1answer
66 views
Anti-symmetric 2 particle wave function
Suppose we want to construct a wave function for 2 free (relativistic) fermions. As we are dealing with fermions the total wave function has to be antisymmetric under interchange of the coordinates,
...
2
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1answer
51 views
Field Tensor and classical limits
I would be very grateful if someone would kindly explain this generalization of the Lorentz force law to the special relativity domain. Please bear with me.
Classically, the Lorentz force law is ...
2
votes
1answer
120 views
Retarded time Lienard Wiechert potential
In a potential which needs to be evaluated at the retarded time, is this the time which represents the actual time the "physics" occurred? So $t_{\text{ret}}=t-\frac{r}{c}$, not just because it may be ...
2
votes
1answer
72 views
Understanding bending light beam perpendicular to motion
I'm just reading a book about gravity. An example it gives is a spaceship accelerating. A beam of light travelling at right angles to the direction of movement of the spaceship enters it via a small ...
1
vote
1answer
104 views
The definition of Lorentz transformation
I know that the Lorentz transformation, when two frames $\mathcal{S}$ and $\mathcal{S}'$ are in standard configuration (the axes are all parallel to their counterparts in the other inertial frame) is ...
1
vote
1answer
221 views
Special relativity paradox and gravitation/acceleration equivalence
One of the features of the black hole complementarity is the following :
According to an external observer, the infinite time dilation at the horizon itself makes it appear as if it takes an ...
1
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1answer
195 views
Why can't this speed be measured?
Superman and Supergirl were playing catch. When Superman is moving with a speed of 0.800c relative to Supergirl, he threw a ball to Supergirl with a speed of 0.600c relative to him.
a. ...
0
votes
1answer
134 views
Why does weak equivalence principle say gravity is equivalent to acceleration?
I am told that the weak equivalent principle, that $m_i=m_g$ (inertial and gravitational masses are equivalent) is equivalent to the statement that in a small system you can't tell whether you are in ...
-1
votes
1answer
73 views
Speed astronauts measure moving at the speed of light
Lets suppose a spaceship travels with v = 0.9c relative to the Earth. The time inside the spaceship would pass slower than on Earth. Would the astronauts measure a different speed (that means, a ...
-6
votes
1answer
204 views
Speed of light is not fixed?
In my research, I found that the speed of light is not fixed. IS it true?
Namely, We know that light refracts when the medium it travels through changes. Actually, light travels in the same medium ...
7
votes
0answers
104 views
Status of experimental searches for tachyons?
Now that the dust has settled on the 2011 superluminal neutrino debacle at OPERA, I'm interested in understanding the current status of experimental searches for neutrinos. Although the OPERA claim ...
6
votes
0answers
80 views
Why do we identify symmetric 2nd rank tensors with spin-2 particles in string theory?
I am going through Tong's lecture notes on String Theory and came across the following irrep decomposition (Chap 2, p.43) of the bosonic string first excited states:
$$\text{traceless symmetric} ...
5
votes
0answers
195 views
What is the difference between the properties of Electron spin and Photon polarization/helicity?
What is the difference between a photon's polarization/helicity and an electrons spin half? I know that the photon is spin 1 but isn't its polarization analogous to spin half?
This question stems ...
4
votes
0answers
100 views
What's wrong with this QFT thought experiment?
In quantum field theory, the propagator $D(x-y)$ doesn't vanish for space-like separation. In Zee's book, he claims that this means a particle can leak out of the light-cone. Feynman also gives this ...
4
votes
0answers
87 views
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 ...
3
votes
0answers
58 views
Right-angle lever paradox in special relativity
I remember to have read somewhere an interesting special relativity "paradox" considering two perpendicular rods $A$ and $B$ of equal proper length $L$ fixed at point $O$.
In the "rest" frame equal ...
3
votes
0answers
140 views
Should the Jacobian be negative in $\mathrm{d}^4 x$?
In page 24 of Srednicki's QFT textbook, he says that $\mathrm{d}^4x$ is a Lorentz scalar. I understand that the determinant of a Lorentz matrix is always $\pm 1$. So in an improper Lorentz ...
3
votes
0answers
83 views
How would an observer perceive movement on a train that's travelling near the speed of light?
Person A is on Earth and a train (or whatever you want to imagine) travels past him at near the speed of light. How would person A perceive movement on the ship? If time is slowed on the ship from the ...
3
votes
0answers
43 views
Spectrum of a quantum relativistic “distance squared” operator
This question disusses the same concepts as that question (this time in quantum context). Consider a relativistic system in spacetime dimension $D$. Poincare symmetry yields the conserved charges $M$ ...
2
votes
0answers
27 views
minimal proper time curves bounded on acceleration
Assuming Minkowski spacetime, we know that the longest proper time curve joining two points is the rect joinining both events, While the shortest time-like curve is not a compact set (because there ...
2
votes
0answers
36 views
Is it possible to have uniform proper acceleration along a large object without breaking it?
I'm learning about accelerating reference frames (to eventually get grasp of general relativity too).
I've just read about the Rindler coordinates and this one caught my eye
Note that Rindler ...
2
votes
0answers
66 views
Solving the equation of relativistic motion
How does one solve the tensor differential equation for the relativistic motion of a partilcle of charge $e$ and mass $m$, with 4-momentum $p^a$ and electromagnetic field tensor $F_{ab}$ of a constant ...
2
votes
0answers
82 views
Fermi Walker vs. Fermi transport
A vector field $f^\mu$ is said to be Fermi-Walker transported along a curve $\gamma$ parametrized with $\tau$ if the following holds $$\frac{\mathrm{D}}{\mathrm{d}\tau}f^\mu = -(a^\mu v^\nu - a^\nu ...
2
votes
0answers
76 views
Car parking special-relavity puzzle
Hi I read the following puzzle from an old text book long time ago. However it doesn't provide the answer. So what is the solution?
Let's suppose a car is going to park to a garage and the garage is ...
2
votes
0answers
118 views
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 ...
2
votes
0answers
87 views
Does the passage of time effect a photons entanglement with another?
I recently read an article about "Delayed-choice entanglement swapping". Here is an excerpt from the article:
Delayed-choice entanglement swapping consists of the following steps.
(I use the ...
1
vote
0answers
34 views
Wick rotation and relativity
CMIIW, but as I understand it, Wick rotation replaces the Minkowski basis (t,x,y,z) with the Euclidean basis (it,x,y,z). Suppose that $t_2=t_1 cosh \beta+x_1 sinh \beta$ and $x_2=t_1 sinh \beta+x_1 ...
1
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0answers
22 views
Calculate the acceleration of the trailing muon bunch
Two separate suitably short but intense bunches of muons, "A" and "B", are both supposed to be constantly accelerating (in an otherwise sufficiently flat region) with constant proper acceleration ...
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0answers
153 views
Does Mansuripur's Paradox involve fictitious charges?
Mansuripur's Paradox involves a magnet moving at relativistic speeds in an external electric field.
Additional: thanks to Retarded Potential, who found the original paper.
If I understand correctly, ...
1
vote
0answers
164 views
Matrix manipulation for Dirac matrices
From the Dirac equation in gamma matrices, we know that $$\gamma^i=\begin{pmatrix}
0 & \sigma^i \\
-\sigma^i & 0
\end{pmatrix}$$ and $$\gamma^0=\begin{pmatrix}
I & 0 \\
0 & -I
...
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0answers
40 views
Adittional ways of writing down the gamma in relation to speen direction
I have managed to proove below that equation $\gamma(v')=\gamma \gamma(v)\left(1-v_x \, u\!/\!c^2\right)$ holds if whole speed $v$ is in the direction of axis $x,x'$. So $v$ equals $v_x$ and therefore ...
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0answers
203 views
Could someone 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, ...
1
vote
0answers
245 views
How equivalent are heat energy and work energy in connection with a spinning flywheel?
Let's say we have two identical spinning flywheels, that have arbitrary geometry, and are made of copper.
Now we apply some heat energy at the center point of flywheel A, causing it to slow down a ...
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0answers
42 views
How does special relativity affect this photon/mirror experiment?
Here is a simple experiment showing how amplitudes add and cancel in a simple photon-mirror experiment.
In the comments, someone pointed out
What confuses me about the actual verification of ...
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0answers
66 views
Relativistic canonical transformation
What is relativistic canonical transformation? I need every piece of information about it.
Does anyone know a reference or an article about relativistic canonical transformation?
For example, in ...
0
votes
0answers
43 views
Relativistic solution for Zeno's stadium paradox?
The stadium Zeno paradox (not the same paradox from the Quantum-Zeno-Effect, but the same Zeno) gives a paradox about time, when two runners move toward a standing person from different directions. ...
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0answers
65 views
Relativistic interaction: gamma + proton = delta
We have a proton at rest, and there's an incident photon that is absorbed by the proton producing the excited state "delta".
Photon energy: $\hbar \omega$,
Proton rest Energy: $m_p c^2$,
Delta rest ...
0
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0answers
105 views
About the theory of relativity
Why is speed of light constant in every non inertial frame of reference? Is there any theoretical explanation behind this postulate Since we cannot completely depend upon the experimental results?
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0answers
86 views
Alternate derivation of kinetic mass increase in special relativity, from Maudlin
I've recently come across a derivation, which I've not seen before, of mass increase in special relativity. It seems to make sense, but I get tripped-up on an intermediate step, and I can't seem to ...
0
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0answers
32 views
time oscillation
Can there be a situation, where the time dilation is oscillating, in the sense that one observer notes that the time for the other frame is moving faster then slower, etc...? Can this oscillation be ...
0
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0answers
73 views
Proper time and 4-velocity
I am trying to derive 4-velocity, but i get stucked when i try to derive equation for proper time. I end up confused as i get $\scriptsize\textrm{d}\tau = \frac{\textrm{d}t}{\gamma(v)}$ instead of ...
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0answers
43 views
Help identifying an expression for the action
I found the following expression for the action of a (free, I think) relativistic particle in my notes but I can't remember from what it came from:
$$ S = \int_{0}^{N} \left [ ...
0
votes
0answers
199 views
Is there an easy derivation of relativistic velocities addition and relativistic doppler shift?
Is there an easy derivation of relativistic velocities addition and relativistic doppler shift?
I'm looking for some easy derivation of the above. Like this ...
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votes
0answers
18 views
Is there a way to compute or explain if a decay prefers decaying into mainly mass or mainly energy?
Is there a way to compute or explain if a decay prefers decaying into mainly mass or mainly energy ?
I know quarks prefer to decay into the most massfull quarks : ...
0
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0answers
143 views
Newton Gravitational constant $G$, Plank constant $\hbar$ , Speed of Light $c$ : The Dream Team of moderators?
The 3 great constants of Nature are well known :
The Speed of light $c$ (special relativity)
The Plank constant $\hbar$ (quantum mechanics)
The Newton ...
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0answers
166 views
Lorentz transformations of the polarization vector
Let $\bf{n}'$ be a unit vector in the direction of a wavevector in the plasma rest frame and $\bf{B'}$ be a unit vector along the magnetic
field in the plasma rest frame. The electric field of a ...
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0answers
153 views
Comparing Lagrangian in Special Relativity vs General Relativity for a weak gravitational field
This is a sequel to this question.
Who knows a difference between the Lagrangian in SR and GR for a weak gravitational field in non-relativistic case? What is the reason of this difference?
