The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.
7
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7answers
933 views
Rotate a long bar in space and get close to (or even beyond) the speed of light $c$
Imagine a bar
spinning like a helicopter propeller,
At $\omega$ rad/s because the extremes of the bar goes at speed
$$V = \omega * r$$
then we can reach near $c$ (speed of light)
applying some ...
-4
votes
3answers
190 views
There must be free positive charges, moving oppositely to electrons for the wire with current to stay neutral
All popular expositions (e.g. these ones) of relativistic electromagnetism claim univocally that electrons in motion become more dense due to the speed. They teach that Lorentz contraction of charges ...
10
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2answers
315 views
Does relativistic mass have weight?
If an object was sliding on an infinitely long friction-less floor on Earth with relativistic speeds (ignoring air resistance), would it exert more vertical weight force on the floor than when it's at ...
0
votes
2answers
69 views
Limit on velocity in Minkowski Spacetime geometry
Let A be a rocket moving with velocity v.
Then the slope of its worldline in a spacetime diagram is given by c/v.
Since it is a slope, c/v = tan(theta) for some theta > 45 and theta < 90.
Does ...
4
votes
1answer
108 views
How to understand the emergent special relativity in the superfluid?
The superfluid vacuum theory was proposed to understand some features of the vacuum (aether) from the emergence point of view. Although made up of non-relativistic atoms, the low-energy excitations of ...
1
vote
0answers
51 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 ...
7
votes
3answers
129 views
Do velocity and acceleration time dilation factors add?
For a spinning space station such as in 2001, A Space Odyssey, what would be the time slowing in the perimeter of the spinning space station with respect to the center axis of the station?
The ...
2
votes
4answers
273 views
Relativistic origin of magnetic field
There is an explanation in the Wikipedia. Unfortunately the article is quite verbose and doesn't clearly explain why both positive and negative charges vary density even if only one is moving.
It is ...
7
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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 ...
4
votes
2answers
178 views
What is the Andromeda Paradox?
I have been studying causality (specifically why there is no such thing as a simultaneous instant of time across all observers) recently and I keep hearing references to the Andromeda paradox. Can ...
3
votes
2answers
369 views
Lorentz transformations in Dirac equation
Let's denote a spinor $\xi$. If $(\theta ,\phi)$ are the parameters of a rotation and pure Lorentz transformation, then how $\xi$ could be written as
$$\xi ~\rightarrow~ \exp\left(\ i ...
4
votes
3answers
97 views
Bound State of Only Massless Particles? Follows a Time-Like Trajectory?
Is there any way in which a bound state could consist only of massless particles? If yes, would this "atom" of massless particles travel on a light-like trajectory, or would the interaction energy ...
3
votes
3answers
105 views
Reaching the speed of light via quantum mechanical uncertainty?
Suppose you accelerate a body to very near the speed of light $c$ where $v = c - \epsilon$. Although this would take an enormous energy, is it possible the last arbitrarily small velocity needed -- ...
0
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1answer
137 views
An accelerating and shrinking train in special relativity
Suppose when a train is at rest, it has a length of $L$. Let the position of the back of the train at any time be $A$, and let the position of the front of the train at any time be $B$.
Now assume ...
0
votes
1answer
79 views
Einstein’s Thought Experiment of a Stationary Box and a Photon
1) First of all, let us consider a particle of light, also known as a photon. One of the interesting properties of photons is that they have momentum and yet have no mass. This was established in ...
3
votes
2answers
96 views
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 ...
8
votes
3answers
95 views
How do we measure the range of distant objects despite relativistic effects?
When we observe astronomical objects like distant galaxies there are several complicating factors for estimating the distance:
Relativistic speed result in length contraction
Relativistic speed ...
1
vote
1answer
94 views
The status / acceptance of block time?
What is the current status or acceptance of block time as it relates to Einstein's theory of relativity? Has quantum mechanics ruled it out or is it still the favored view of the world? Perhaps there ...
9
votes
2answers
172 views
Relativity of Simultaneity
Relativity of Simultaneity seems to be about OBSERVING two events simultaneously (please correct me if I am wrong).
However, as long as the two events are separated by a distance (any distance) then ...
2
votes
1answer
117 views
What is Relativistic Navier-Stokes Equation Through Einstein Notation?
Navier-Stokes equation is non-relativistic, what is relativistic Navier-Stokes equation through Einstein notation?
1
vote
2answers
142 views
Doppler shift of radio signals to an accelerating observer
Suppose a man leaves from Earth to a star which is 1000 light years away. He accelerates to a velocity such that the entire trip lasts a year, from the reference frame of the rocket.
Now lets pretend ...
3
votes
1answer
63 views
Relativistic Computation?
Is it possible to employ relativity to develop computational technology?
Here is a really basic example:
Build a Computer and Feed it the Problem (say the problem is projected to take 10 years to ...
4
votes
1answer
53 views
Live feed from a Rocket traveling near the speed of light?
Okay, odd question popped up in my physics class today. If a rocket ship is traveling at .99c for 1 year, and is streaming a video at 30 frames/sec to earth, how would the earth feed be affected? ...
0
votes
1answer
45 views
if i want action to be positive number then it require that $\tau_i$ be bigger than $\tau_f$, isn't it true? [closed]
the action is the length of the geodesic
$S=-E_o\int_i^f d\tau$
we get an action that is minimised for the correct path.
if i want action to be positive number then it require that $\tau_i$ be ...
1
vote
3answers
177 views
Integration by parts to derive relativistic kinetic energy
I have come across a weird integration during derivation of relativistic kinetic energy. Our professor states that i can get RHS out of LHS using integration by parts:
$$
\int\limits_0^x \! ...
1
vote
4answers
184 views
What is the exact mechanism by which time dilates?
What is the exact mechanism by which time dilates for a fast moving object?
Can the time dilation be explained by any theory other than relativity?
0
votes
3answers
118 views
Stuff can't go at the speed of light - in relation to what? [duplicate]
We all know that stuff can't go faster than the speed of light - it's length becomes negative and all kinds of weird stuff happens.
However, this is in relation to what? If two objects, each moving ...
3
votes
1answer
58 views
Rate of spontaneous tachyon emission
It's not possible for an electron to emit or absorb a photon without the presence of a third particle such as an atomic nucleus; without the third particle, it's impossible for such a process to ...
2
votes
2answers
104 views
Faraday tensor, antisymmetric rank two
$F^{\mu \mathcal{V}}$ is defined in
http://www.lecture-notes.co.uk/susskind/special-relativity/lecture-7/relativistic-lorentz-force/
How to show that $F^{\mu \mathcal{V}}$$F_{\mu \mathcal{V}}$, is ...
6
votes
3answers
337 views
Can something travel faster than light if it has always been travelling faster than light?
I know there are zillions of questions about faster than light travel, but please hear me out. According to special relativity, it is impossible to accelerate something to the speed of light. However, ...
1
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1answer
81 views
Faraday tensor, antisymmetric electromagnetic tensor
I want to write $F^{\mu \nu}F_{\mu \nu}$ in terms of $F_{\mu \nu}F^{\mu \nu}$. How to do it?
3
votes
3answers
143 views
Having trouble seeing the similarity between these two energy-momentum tensors
Leonard Suskind gives the following formulation of the energy-momentum tensor in his Stanford lectures on GR (#10, I believe):
$$T_{\mu \nu}=\partial_{\mu}\phi \partial_{\nu}\phi-\frac{1}{2}g_{\mu ...
7
votes
1answer
120 views
Cancelling special & general relativistic effects
We know that for a GPS we need to make a correction for both general and special relativity: general relativity predicts that clocks go slower in a higher gravitational field (the clock aboard a GPS ...
0
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1answer
29 views
If there's a light ray and it's turned to a new location by a certain angle
Imagine that there's a light ray, with source at point A, and it's directed towards point B (which is very far from point A) and it continues for a huge distance.
How will an observer at point B ...
1
vote
2answers
186 views
Relativistic Doppler effect derivation
This is about a step in a derivation of the expression for the relativistic Doppler effect.
Consider a source receding from an observer at a velocity $v$ along the line joining the two. Light is ...
1
vote
2answers
124 views
Does an accelerating spaceship move backwards due to length contraction?
Let's assume I have a spaceship in front of me let's say at 1000000km distance. Now let's assume I have also a stationary wall just behind the spaceship at 999999km. Initially the spaceship's speed is ...
2
votes
1answer
105 views
Proton-proton collisions
I have a question about proton-proton collisions at the LHC. Firstly, the 4-momentum $p^\mu=(E/c,\vec{p})$ can be represented as $p^\mu =(m_T \cosh \Psi, p_T \cos \phi , p_T \sin \phi, m_T c \sinh ...
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. ...
5
votes
3answers
413 views
Does entanglement not immediately contradict the theory of special relativity?
Does entanglement not immediately contradict the theory of special relativity? Why are people still so convinced nothing can travel faster than light when we are perfectly aware of something that ...
1
vote
1answer
71 views
$\frac{dt}{d\tau}=\gamma$ in special relativity
I hope this is not too silly a question: We often see
$$\frac{dt}{d\tau}=\gamma=\frac{1}{\sqrt{1-v^2}},$$ taking $c=1$.
Problem:
I don't understand why...
In the Minkowski metric, using the ...
14
votes
4answers
2k views
How is the classical twin paradox resolved?
I read a lot about the classical twin paradox recently. What confuses me is that some authors claim that it can be resolved within SRT, others say that you need GRT. Now, what is true (and why)?
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votes
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 ...
4
votes
1answer
63 views
Relativity of simultaneity - An example
I am trying to understand the relativity of simultaneity in different frames, and I am trying to work out an example.
Suppose along the x-axis there are two points 2000m apart. Event A happens at t=0 ...
14
votes
10answers
7k views
Does the Pauli exclusion principle instantaneously affect distant electrons?
According to Brian Cox in his A night with the Stars lecture$^1$, the Pauli exclusion principle means that no electron in the universe can have the same energy state as any other electron in the ...
4
votes
2answers
116 views
Can dark matter be relativistic dust?
As far as I know the mass of an observed object increases as it approaches the speed of light.
Is it possible that the excess mass called "dark matter" is due to relativistic dust?
Surely, stars ...
-1
votes
2answers
128 views
Do objects have energy because of their charge?
My gut feeling tells me things should have energy because of their charge, like they have energy because of their mass.
Is this possible? Has it been shown? If not then what is missing to make such ...
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votes
3answers
167 views
Is there absolute proof that an object cannot exceed the speed of light?
Have any known experiments ruled out travelling faster than the speed of light?
Or is this just a widely accepted theory?
1
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3answers
157 views
What truly is mass, and is there a direct way to measure it?
We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we ...
1
vote
2answers
73 views
Can acceleration feel like constant gravity for indefinitely long?
So here's the setup: I'm in a spaceship, without windows as always, and the ship is accelerating upwards at a constant rate of $1\,\text{g}$. So inside the spaceship it feels like I'm being pulled ...
1
vote
1answer
92 views
The Klein–Gordon equation
As we know that the Schrödinger equation presents basis of Quantum Mechanics and analogy with Newton second law in Classical Mechanics, I thought that relativistic interpretation of Schrödinger ...
