The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.
4
votes
3answers
158 views
Setting up a local-coordinate system in space-time using only a single clock and light beams
I have a question to ask about the operationalist view of space-time. I am a mathematician who happens to be interested in physics, so if anyone thinks that my question is a silly or vague one, please ...
1
vote
1answer
85 views
Why does 'proper length' exist as a notion?
$$\text{proper time}= \tau= \sqrt{dt^2-d\mathbf{s}^2}$$
$$\text{proper length}= L= \sqrt{-dt^2+d\mathbf{s}^2}$$
What tangible benefit is brought about by calling $i \tau$ 'proper length' (applying ...
2
votes
3answers
119 views
Correct expression for D'Alembert operator in $c=1$ units
In QFT texts with $c=1$ units (most of them), D'Alembert operator is written as:
$$\Box ={\partial^2 \over \partial t^2} - \nabla^2$$
For pedagogical purposes, however, some texts don't set $c=1$, ...
1
vote
1answer
93 views
Does special relativity unify the two phenomena at the base of Faraday's flux law (was Feynman wrong in this case)?
Consider Faraday's flux law for the EMF generated in a conductor loop:
$$ \varepsilon = - \frac{d \phi}{dt},$$
where $\varepsilon$ is the EMF, and $\phi$ is the magnetic flux through the loop.
...
0
votes
3answers
206 views
Relativistic basic question - four vector, Lorentz matrix
I have heard relativistics only very compressed during my student time. Now I looked up the definitions again and a question comes into my mind:
A contravariant vector is transformed like this: ...
2
votes
1answer
103 views
Is there a stationary frame of reference?
My understanding of relativity is at the beginner level, so please bear with me to help a beginner to understand. Something which I don't understand is consider if you travel close to the speed of ...
4
votes
2answers
109 views
Where might hertz per dioptre actually be useful?
I once came across the strange, artificial unit "hertz per dioptre", which is dimensionally equivalent to "metres per second". Could this unit, by some stretch of the imagination, be used in some ...
0
votes
0answers
27 views
Run with speed of light with a mirror in hand [duplicate]
Possible Duplicate:
Reflection At Speed of Light
Imagine you are able to run with the speed of light holding a mirror in your hand.
Now will you be able to see yourself in the mirror?
0
votes
0answers
83 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 ...
2
votes
2answers
52 views
Is it part of special relativity that mass possessing energy is more dense?
I was reading http://www.edge.org/3rd_culture/hillis/hillis_p2.html and it says that a charged battery weighs more than a dead one or a rotating object weighs more than a stationary one (i.e. mass ...
0
votes
2answers
59 views
Why does isotropy principle require existence of inertial transformation when axes are reversed?
Assuming one spatial and one termporal dimension, let's assume an intertial transformation $A(v)$ as follows:
$$
\begin{pmatrix}
t' \\
x' \\
\end{pmatrix} = A(v)
\begin{pmatrix}
t \\
x \\
...
1
vote
1answer
67 views
particle accelerator in space
I'm attempting to learn special relativity and i'm having trouble calculating velocity and momentum for each part of the system after interactions.
I wanted to know how fast a linear accelerator and ...
4
votes
5answers
493 views
Why isn't the symmetric twin paradox a paradox?
Two twin sisters synchronize their watches and simultaneously (from the earth frame) depart earth in different directions. Following a predetermined flight plan, each sister accelerates identically to ...
2
votes
1answer
83 views
Graviton and photons interaction
If one believes in the theory of gravitons then by viewing a black hole you see gravitons affect photons. This in turn leads to the conclusion that force carrier's mass equivalences allow them to be ...
5
votes
3answers
89 views
Analyticity and Causality in Relativity
A few weeks ago at a conference a speaker I was listening to made a comment to the effect that a function (let's say scalar) cannot be analytic because otherwise it would violate causality. He didn't ...
1
vote
1answer
297 views
Special Relativity: Transforming Maxwell's equations
I'm working through Einstein's original 1905 paper*, and I'm having trouble with the section on the transformation of Maxwell's equations from rest to moving frame.
The paper proceeds as follows:
...
3
votes
1answer
269 views
The Particle-Antiparticle Problem in Relation to Special Relativity
Prelude:
Let’s consider a pair of events $A(t_1,x_1)$ and $B(t_2,x_2)$,having a spacelike separation wrt an inertial frame denoted by K.In the frame K’ moving along the positive x-x’ direction with a ...
2
votes
2answers
348 views
A Paradox in Special Relativity
Two inertial frames K and k’ are considered. They are in relative uniform motion along the x-x’ direction with relative speed =v.
In the frame K’ we have a cuboidal piece of dielectric [at rest wrt ...
0
votes
1answer
105 views
What is the maximum time dilation between two objects, if one is standing still and the other is moving at $c$?
What is the maximum ratio in the rate of change in time in reference to object $A$ which is standing still and object $B$ which is moving at the speed of light?
2
votes
1answer
81 views
Relativity exposition from the “naïve” viewpoint
A naïve observational viewpoint doesn't automatically try to correct for signal delays. In other words, the time co-ordinate is retarded.
For example:
In popular expositions of relativity you'll ...
1
vote
2answers
192 views
Why lagrangian is negative number?
In the special relativistic action for a massive point particle,
$$\int_{t_i}^{t_f}\mathcal {L}dt,$$
why is the Lagrangian
$$\mathcal {L}=-E_o\gamma^{-1}$$
a negative number?
0
votes
1answer
39 views
reltivistic action is negative or positive number? [duplicate]
Possible Duplicate:
Why lagrangian is negative number?
In the special relativistic action for a massive point particle,
$$\int_{t_i}^{t_f}\mathcal {L}dt,$$
where the Lagrangian
$$\mathcal ...
0
votes
0answers
38 views
How to calculate the scatterng angle of a particle collision [closed]
z0 decays to electron + positron pair as below. The momentum of z0 is 150 Gev/c and its mass is 90 Gev. Find the scattering angle of the electron
1
vote
1answer
90 views
what is use of relativistic action?
this is relativistic action:
$$S=\int_C \mathcal {L}dt$$
where the $\mathcal{L}$ is $-m_oc^2\gamma^{-1}$
what is use of relativistic action!?
3
votes
3answers
175 views
Proof for $p=\gamma_Pmu$
As I'm reading about Relativistic Momentum, my book states the following:
$$p=m \frac{\Delta x}{\Delta t}=m\frac{\Delta x}{\sqrt{(1-u^2/c^2)}\Delta t}=\frac{mu}{\sqrt{1-u^2/c^2}}=\gamma_Pmu$$
...
0
votes
1answer
97 views
Confusion about time shift in special relativity
I have never really found a way to comfortably comprehend the idea of time shift even though I know its not the hard part of relativity theory. In that light, can someone point out what is wrong or ...
5
votes
1answer
225 views
What is the speed of time
When we measure the speed of a moving element we do it with the help of a reference frame. Now if we need to measure the speed of time, is it possible? Is time really has speed?
Thanks in advance.
3
votes
1answer
51 views
Single electron non-perturbing detector
I am designing an experiment where I need to trigger the release of an electron by a radioactive source (Sr-90).
The easy way to do it is to use a thin scintillator right after the source collimator. ...
3
votes
1answer
383 views
How does a particle of light reach the max speed of light? [duplicate]
Possible Duplicate:
How can a photon have no mass and still travel at the speed of light?
First of all I am not a professional physicist. I was curious as to how a particle of light can ...
16
votes
7answers
10k views
How can a photon have no mass and still travel at the speed of light?
I've read a number of the helpful Q&As on photons that mention the mass/mass-less issue. Do I understand correctly that the idea of mass-less (a rest mass of 0) may be just a convention to make ...
0
votes
1answer
33 views
Speed of light and lorentzian factors [duplicate]
Possible Duplicate:
How can a photon have no mass and still travel at the speed of light?
If light travels at the speed of light, and anything with rest mass will experience relativistic ...
0
votes
3answers
129 views
where the proper time is invariant why $d\tau$ is not zero?
where the proper time is invariant why change (differential) in proper time $d\tau$ is not zero?
$\Delta \tau=\tau_f-\tau_i$
as i know.
$d(invariant)=0$
note to comment:
action
$S=-m_oc^2\int_C d\tau$
...
0
votes
1answer
77 views
Can the zeroth-component of a 4-velocity be negative?
Is it allowed to have the zeroth-component of a four-velocity be negative? I presume the answer is yes, but I just want to make sure. Many thanks.
This is referring to $V^0$ for a curved space ...
0
votes
0answers
31 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 ...
1
vote
1answer
171 views
Does the increase of (relativistic) mass, while flying near speed of light, has any impact on astronauts? [duplicate]
Possible Duplicate:
Would travelling at relativistic speeds have any impact on human biology?
I am asking myself this question for a few day. What is the answer on: Does the increase of ...
3
votes
0answers
137 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 ...
1
vote
2answers
306 views
Faster Than Light Communication Using Gravity?
Suppose two parties $A$ and $B$, some distance apart and at rest relative to each other both had control of one massive local object each.
If party $A$ lifted their local object upward relative to ...
3
votes
4answers
346 views
Does $p=mc$ hold for photons?
Known that $E=hf$, $p=hf/c=h/\lambda$, then if $p=mc$, where $m$ is the (relativistic) mass, then $E=mc^2$ follows directly as an algebraic fact. Is this the case?
7
votes
4answers
508 views
Does the “Andromeda Paradox” (Rietdijk–Putnam-Penrose) imply a completely deterministic universe?
Wikipedia article: http://en.wikipedia.org/wiki/Rietdijk–Putnam_argument
Abstract of 1966 Rietdijk paper:
A proof is given that there does not exist an event, that is not already in the past for ...
5
votes
2answers
308 views
Does quantum mechanics allow faster than light (FTL) travel?
Let's suppose I initially have a particle with a nice and narrow wave function[1] (I will leave these unnormed):
$$e^{-\frac{x^2}{a}}$$
where $a$ is some small number (to make it narrow). Let's also ...
11
votes
8answers
988 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 ...
20
votes
12answers
2k views
Is it possible for information to be transmitted faster than light by using a rigid pole?
Is it possible for information (like 1 and 0s) to be transmitted faster than light?
For instance, take a rigid pole of several AU in length. Now say you have a person on each end, and one of them ...
1
vote
2answers
99 views
What is 'past null infinity'?
For example, in the sentence "there is no incoming radiation at past null infinity".
3
votes
1answer
175 views
Can the overall sign of the Minkowski metric be changed?
If we take the Minkowski metric, $\eta_{\mu\nu}=(1,-1,-1,-1)$, instead of the usual $(-1,1,1,1)$, does this change the form of the Lorentz Transform? I think the standard Lorentz Transform looks like: ...
3
votes
1answer
238 views
How is the speed of light constant in all directions for all observers?
Please imagine the following thought-experiment:
Order of Events:
Pulse - A single pulse of light is emitted from the light towards the mirror
Reflect - The pulse hits the mirror and is ...
2
votes
2answers
198 views
D'Alembert operator and special relativity
We are currently covering special relativity in the theoretical physics lectures where we defined:
$$
\mathrm ds^2 := \mathrm dt^2 - \mathrm dx^2 - \mathrm dy^2 - \mathrm dz^2
$$
In Road to Reality, ...
9
votes
2answers
705 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 ...
-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 ...
0
votes
1answer
135 views
Does photon possesses no time to cover any arbitrary distance?
Photon travel 8 minutes (with speed $c$) from the sun to reach the earth. Any particle (or space-ship) with velocity $0.99 c$ covers the same distance (93 millions km) within less than 2 minutes ...
-1
votes
3answers
166 views
Does the Lorentz transformation not apply to light?
Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with ...
