The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.
6
votes
2answers
372 views
Charge conjugation in Dirac equation
According to Dirac equation we can write,
\begin{equation}
\left(i\gamma^\mu( \partial_\mu +ie A_\mu)- m \right)\psi(x,t) = 0
\end{equation}
We seek an equation where $e\rightarrow -e $ and which ...
2
votes
3answers
155 views
Why geometrically four acceleration is a curvature vector of a world line? And what is proper acceleration?
Why geometrically four acceleration is a curvature vector of a world line?
Geometrically, four-acceleration is a curvature vector of a world line.
Therefore, the magnitude of the ...
9
votes
2answers
693 views
Is the “How to break the speed of light” minute physics video wrong?
I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views.
In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
3
votes
1answer
89 views
Intervals as infinitesimals of same order (Landau & Lifshitz)
I don't understand the following statement in Landau & Lifshitz, Classical Theory of Fields, p.5:
$ds$ and $ds'$ are infinitesimals of same order. [...] It follows that $ds^2$ and $ds'^2$ must ...
0
votes
0answers
30 views
Relatively faster than light [duplicate]
Possible Duplicate:
Travelling faster than the speed of light
If one spaceship travels in one direction at 3/4 of the speed of light and another spaceship travels in the opposition ...
-1
votes
2answers
114 views
Can time dilation be explained by limitations on computing power?
Are there any ideas of explaining the time dilatation as limits in "computing power"? What I mean is basically that the greater is a concentrated mass, the harder is to "compute" what happens in such ...
1
vote
0answers
99 views
I need to understand the Lorentz transformation [closed]
Two observers A and B, in different initial system describe the same physical event with their particular, different space time coordinates . Let the coordinate of the event be $x^\mu$ for observer A ...
3
votes
2answers
196 views
Matrix operation in dirac matrices
If we define $\alpha_i$ and $\beta$ as Dirac matrices which satisfy all of the conditions of spin 1/2 particles , p defines the momentum of the particle, then how can we get the matrix form ?
...
9
votes
1answer
296 views
How is quantum mechanics compatible with the speed of light limit?
Consider a free electron in space. Let us suppose we measure its position to be at point A with a high degree of accuracy at time 0. If I recall my QM correctly, as time passes the wave function ...
3
votes
1answer
70 views
Empirical meaning of relativity in the context of QM
In special relativity an event E is mapped to coordinates (x,t) in one inertial frame, and to coordinates (x',t') in another, and SR provides the relation between (x,t) and (x',t').
What is the ...
10
votes
4answers
342 views
The definition of an inertial reference frame in Einstein's relativity
I'm reading Sean Carroll's book on general relativity, and I have a question about the definition of an inertial reference frame. In the first chapter that's dedicated to special relativity, the ...
1
vote
1answer
107 views
Photons and Relativity
Consider a Photon from Sun and travels with a velocity $c$. Now think we are that photon. For us, it looks like Sun is moving away from us with a velocity $c$. So, why don't we get attracted back ...
4
votes
2answers
197 views
What do massive photons have to do with superconductivity?
I keep reading that the idea of massive photons leads to an explanation of the Meissner effect but I fail to see how photons are involved with the repulsion of fields inside a superconductor.
How ...
0
votes
1answer
101 views
Scattering Amplitudes in Centre of Mass Frame
I'm reviewing page 59 of the QFT notes here and am a little confused by a reference frame argument. You can compute the second order probability amplitude term for nucleon-nucleon scattering to be
...
0
votes
1answer
195 views
Calculating the speed of an object moving relative to another moving Object (Frame of reference) [duplicate]
Possible Duplicate:
How to deduce the theorem of addition of velocities?
Let's say that you are in a rocket speeding at 90% the speed of light away from Earth. Now fire a bullet inside the ...
4
votes
2answers
290 views
Lorentz invariance of the integration measure
This is regards to the lorentz invariance of a classical scalar field theory. We assume that the action which is $S= \int d^4 x \mathcal{L}$, is invariant under a Lorentz transformation. How do you ...
2
votes
2answers
312 views
Why do many people say vector fields describe spin-1 particle but omit the spin-0 part?
We know a vector field is a $(\frac{1}{2},\frac{1}{2})$ representation of Lorentz group, which should describe both spin-1 and spin-0 particles. However many of the articles(mostly lecture notes) I've ...
8
votes
3answers
327 views
Why do Maxwell's equations contain each of a scalar, vector, pseudovector and pseudoscalar equation?
Maxwell's equations, in differential form, are
$$\vec\nabla\cdot\vec{E}=~\rho/\epsilon_0,$$
$$\vec\nabla\times\vec B~=~\mu_0\vec J+\epsilon_0\mu_0\partial\vec E/\partial t,$$
$$\vec\nabla\times\vec ...
1
vote
1answer
165 views
Lorentz Invariant Equation of Motion for Scalar Field
I'm trying to understand why you can't write down a first order equation of motion for a scalar field in special relativity.
Suppose $\phi(x)$ a scalar field, $v^{\mu}$ a 4-vector. According to my ...
1
vote
0answers
61 views
Does Bernoulli's principle hold in moving reference frames? [duplicate]
Possible Duplicate:
Bernoulli’s equation and reference frames
Sometimes in train, when setting behind opening window, I can feel strong gale blowing in. The closer to the window the ...
3
votes
2answers
95 views
Mass-Energy Equivalency
We call $E=mc^2$ the Mass-Energy Equivalency because it equates mass and energy together. But, by that same logic, shouldn't we call $E=\frac{1}{2}(mv^2)$, the equation of kinetic energy in Newtonian ...
10
votes
2answers
271 views
Limitations on how far one can travel in the universe
Someone once incorrectly told me that, given the speed of light is the speed limit of the universe, aliens would have to live for hundreds of years if they are to travel distances of hundreds of light ...
12
votes
2answers
278 views
What does a sphere moving close to the speed of light look like?
What shape does the viewer in a reference frame with $v=0$ perceive? I suppose that since the sphere moves in one direction only (oX only, not oY) its section would change into an ellipse, where the ...
7
votes
1answer
267 views
Classical vs. Quantum use of the spin 4-vector
I have a few basic questions about the Pauli-Lubanski spin 4-vector S.
I've used it in quantum mechanical calculations as an operator, that is to say each of the components of S is a matrix operator ...
1
vote
1answer
81 views
Proper times of two observers in a three-torus
Consider two observer in a tree-torus space of size $L$. Observer $A$ is at rest, while observer $B$ moves in the $x$-direction with constant velocity $v$. $A$ and $B$ began at the same event, and ...
5
votes
1answer
173 views
How much does a proton weigh when it is going around the LHC at CERN?
Considering that speed increases weight and the proton is going at almost the speed of light, I would like to know how much a speeding proton would weigh in the LHC.
0
votes
0answers
77 views
Sequence of events in special relativity [closed]
I am taking a general education course on special relativity, and get quite confused by problems asking about which event happens first according to different observers. Is there an effective way to ...
0
votes
2answers
72 views
Minimal voltage in linear accelerators to achieve relativity?
Could anyone tell me what is the minimal voltage between anode and cathode in a linear accelerators to achieve speeds where relativity starts to show?
Let me ask in a different way: "What is the ...
2
votes
2answers
147 views
Is there a way to formulate relativistic dynamics in a way that “hides” the finite speed of light?
I'm not referring to the dimensional choice that makes $c=1$; rather I'm imagining something more about replacing all references that apparently involve velocities with the appropriate $\gamma$ ...
1
vote
1answer
153 views
Connecting 4-velocity to equation for adding velocities
Is there a way to connect 4-velocity to equations for adding speeds? I know 4-velocity $U^\mu$ is derived like this:
\begin{equation}
\begin{split}
P^\mu &= m U^\mu \Longrightarrow
U^\mu = ...
0
votes
0answers
70 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 ...
2
votes
2answers
78 views
Terminology for opposite null lines
Is there a name for two null lines that lie on the opposite sides of the null cone? Each line can be obtained from the other by reflection in the axis of the null cone (the time-axis). In terms of ...
11
votes
8answers
985 views
The Four-Clock Special Relativity Conundrum
Two open-car trains approach each other at fixed velocities. Each has a radar to see how quickly the other train is approaching, but apart from that the trains have no a priori knowledge of each ...
1
vote
1answer
131 views
Why is energy-momentum 4-vector so much easier to explore/observe than spacetime 4-vector
I have read that spacetime 4-vector is quite difficult to observe/explore and that energy-momentum 4-vector is much more appropriate for CERN etc.
Why is that? Could anyone give me a brief ...
2
votes
2answers
196 views
Two photons of different frequencies collide to create electron and positron
A photon of frequency f, and another of frequency f' (take f' as given) collide to create an electron-positron pair. The frequency f is such that when the collision is head on, there is exactly enough ...
4
votes
1answer
110 views
Temporal part of Quantum Wavefunction
I was hoping that someone could give me the more fundamental reason that we take as the temporal part of a quantum wavefunction the function $e^{-i\omega t}$ and not $e^{+i\omega t}$? Clearly ...
5
votes
2answers
377 views
What's the difference between space and time?
I'm having a hard time understanding how changing space means changing time. In books I've read people are saying "space and time" or "space-time" but never explain what the difference is between the ...
4
votes
2answers
211 views
Does General Relativity encompass Special Relativity?
Can all of the predictions made in Special Relativity (SR) also be made in General Relativity (GR)?
1
vote
1answer
152 views
4-momentum and an $y$ component of momentum
I have 2 coordinate systems which move along $x,x'$ axis.
I have derived a Lorentz transformation for an $x$ component of momentum, which is one part of an 4-momentum vector $p_\mu$. This is my ...
-2
votes
1answer
279 views
How to express $ds$?(when we know expression for $ds^{2}$) [closed]
We know that $$ds^2 = g_{\mu\nu}dx^{\mu}dx^{\nu},$$
Can you say how to calculate $ds$?
1
vote
1answer
105 views
Accelerating expansion of universe - entire universe a non-inertial frame of reference?
If the expansion of the universe is accelerating, doesn't that mean that the entire universe is a non-inertial frame of reference? And if so, what implications does this have (if any)?
1
vote
0answers
40 views
Adittional ways of writing down the gamma in relation to speen direction
I have managed to proove below that equation $\gamma(v')=\gamma \gamma(v)\left(1-v_x \, u\!/\!c^2\right)$ holds if whole speed $v$ is in the direction of axis $x,x'$. So $v$ equals $v_x$ and therefore ...
0
votes
1answer
72 views
Lorentz Transformations and Aberration
Why does the azimuthal angle, $\phi$, remain unchanged between reference frames in special relativity?
Edit: Here is a link from "Radiative Processes in Astrophysics": ...
0
votes
0answers
42 views
Help identifying an expression for the action
I found the following expression for the action of a (free, I think) relativistic particle in my notes but I can't remember from what it came from:
$$ S = \int_{0}^{N} \left [ ...
0
votes
2answers
116 views
Acceleration and relativity
Usually in physics books this equation used $a=\frac {dv}{dt}$ to calculate the relativistic acceleration.
It is true that speed $v=\beta c$ don't have relativistic (Lorentz) factor, But time have a ...
0
votes
2answers
222 views
If acceleration causes relative time dilation does the eventual deceleration reverse it?
If acceleration causes relative time dilation does the eventual deceleration reverse it?
For example: traveling to Alpha Centauri
Based on me reading this site: ...
1
vote
2answers
127 views
deriving a Lorentz transfomation for velocity vector components
If $S'$ and $S$ are two different inertial reference frames and $S$ moves along the $x$ axis of $S$ in a standard configuration, then the Lorentz transformation will be:
$$x'=\gamma(v)[x-\beta ct]$$
...
2
votes
2answers
513 views
Why does an object with higher speed gain more (relativistic) mass?
Today, in my high school physics class, we had an introductory class on electromagnetism. My teacher explained at some point that an object with a very high speed (he said it started to get somewhat ...
1
vote
3answers
136 views
Special Relativity [closed]
Could someone explain to me how special relativity works?
I know there are thousands of sources and databases of knowledge out there, but I find it difficult to understand, even after reading up on ...
2
votes
1answer
132 views
Vector transformation in special relativity
Please note that I am very new on this website so have some difficulties in writings as required here but trying really hard to learn quickly. La-Tex is the main problem but please understand me that ...
