The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.

learn more… | top users | synonyms (3)

-1
votes
2answers
80 views

Special relativity thought experiement

Say you see a spaceship moving relative to you. On this ship you see a timer. When a beam of light is emitted from one end of the ship the timer starts. When the light reaches the other end of the ...
4
votes
1answer
168 views

Spin of vector boson in higher dimension

A vector boson $V^{\mu}, \mu = 0,...,3$ has spin 1. To my understanding (correct me if I'm wrong) this is because it transforms as a 4-vector under Lorentz transformation $SO(1,3)$. So the $\mu = ...
0
votes
0answers
42 views

Is special theory of relativity compatible with quantum mechanics? [duplicate]

Is special theory of relativity compatible with quantum mechanics? If yes, which is a good starting book which deals with this ? "Bird is bird. Knife is knife. Death is death." So special theory of ...
2
votes
1answer
47 views

How would an observer distinguish between space and time in a “Lineland” universe?

Note: "Lineland" here is borrowed from the Flatland novella. If you were placed as an observer inside a "Lineland" universe, i.e. a Minkowski spacetime that has one space dimension and one time ...
1
vote
1answer
81 views

What is the relation between a basis transformation and an induced transformation $\psi(\Lambda^{-1} p)$ on the wave function? [closed]

I'm having trouble understanding why is $\psi(\Lambda^{-1}p')$ the correct wave function in the Lorentz transformed frame $p' = \Lambda p$. Suppose the state in frame $O$ is given by $$ ...
0
votes
0answers
26 views

Faster than light travel at half speed [duplicate]

Peter and Susan are facing each other in outer space. Both of them ignite their their incredibly powerful jet pack thrusters and accelerated away from each other to just over half the speed of light. ...
0
votes
3answers
73 views

Does light itself experience time dilation?

This seems weird for me. Every time I see light, I will think, "Hey, that light travels from the past far away from us!" Correct me if there is misconception.
-1
votes
3answers
88 views

Is it possible to not move?

Whenever we consider velocity, it is always from a frame of reference. This means that if I am travelling .5c, I'm travelling at a speed between the speed of light and my current frame of references' ...
0
votes
1answer
43 views

What are the differences between special and general relativity? [duplicate]

What are the differences between special relativity and general relativity? I am looking for a naive, non-mathematical explanation.
3
votes
3answers
108 views

How is it possible for the wavelength of light to change in a medium?

So my physics class has just finished a long unit on optics while at the same time I've been trying to teach myself relativity. I admit my understanding is probably rudimentary, but I figured all the ...
1
vote
1answer
71 views

Four-vectors and metric tensor

I think it's safe to say that if $x^\mu=(x^0,x^1,x^2,x^3)$, then $x_\mu=(x^0,-x^1,-x^2,-x^3)$. But I don't really understand why one follows from the other. Could someone explain? Also, I've been ...
0
votes
2answers
69 views

Relativity Paradox involving two charged particles

Suppose there are two charged particles separated by some distance $d$ both with an equal positive charge of $q$. The particles also have equal masses of $m$. $m$ and $q$ are chosen so the ...
-4
votes
2answers
135 views

$? = mc^{1.9}$ makes me crazy [closed]

If energy equals mass times the speed of light squared, what is mass times just under the speed of light? It's not energy,,,yet. Michio Kaku said in a physics video that the faster mass goes, the ...
2
votes
1answer
66 views

If tachyons existed, would we notice them?

In special relativity the space-time can be seen as a static four-dimensional picture that contains the entire past and the future of a flat universe. And the patterns in it are subject to several ...
1
vote
1answer
88 views

What is the role of the spacetime algebra?

For Minkowski space $M^4=\mathbb{R}^{1,3}$ the Clifford algebra $Cl_{1,3}$ (Dirac algebra) with $\{\gamma^\mu, \gamma^\nu \}=2 g^{\mu \nu}$ is sometimes called "spacetime algebra". What is its ...
2
votes
0answers
45 views

Finding Casimir operators for the Poincare group $ISO(1,2)$

I was asked to write the generators for translations and Lorentz-transforms in 1+2 dimensions and then to find the Casimir operators. For the generators I can take the same ones as in 1+3 case ...
0
votes
0answers
21 views

Measuring speed of an object relative to what? [duplicate]

I understand that everything in the universe is moving through spacetime and the spacetime vector is equal for all the objects. So if If something is moving at speed of light, the mass of it is zero ...
2
votes
1answer
278 views

What does v=c in the Lorentz transformation for time tell us?

For the simpler cases as boost in the x-direction, the time dilation formula following the Lorentz transformation for time is $$\Delta t'=\gamma(\Delta t-v\frac{\Delta x}{c^2})$$Now, we observe that ...
0
votes
3answers
102 views

What “is” energy in sub-atomic particles?

This question may be simple or not, I don't know but I can't find the answer anywhere. The electromagnetic spectrum is the range of light particles in different wavelengths and is supposed to be ...
0
votes
0answers
41 views

If I am a light travel around Earth, what relativistic phenomenons do I have?

In school, or even in university, we are only taught Lorentz transformation in one direction. It is quite easy: $$\begin{align} t' &= \gamma \left( t - \frac{vx}{c^2} \right) \\ x' &= ...
0
votes
2answers
53 views

How would I relate $\Lambda=e^{-i\omega_{\mu\nu}J^{\mu\nu}/2}$ to the Lorentz boost matrix?

$\omega_{\mu\nu}$ contains infinitesimal parameters and $J^{\mu\nu}$ contains generators of boost and rotation. Any 4-vector transforms as $p^\mu=\Lambda^\mu_\nu p^\nu$. Starting from given ...
0
votes
1answer
29 views

Definition of a symbol $s_{NN}$ appearing in particle physics

What is the meaning of $s_{NN}$ in particle physics? See e.g. here http://www4.rcf.bnl.gov/brahms/WWW/thesis/karabowicz_phd_thesis.pdf page 18 in the pdf. What is its relation to energy? I ...
0
votes
1answer
62 views

What are the effects of increased mass on persons traveling at near light speed?

It's been a long time since I studied physics (and then only very superficially), so please bear with my gross naivete. This question's been running around in my head for about two weeks now, and I ...
2
votes
1answer
48 views

light falling on a completely reflecting friction less mirror

If you had a perfectly reflective mirror whose face was perpendicular to the ground and was kept on a friction less track on the ground, and you shined a flashlight on it, what would happen? Would ...
1
vote
0answers
35 views

How do I prove the Lorentz-invariance of the Dirac equation? [closed]

How do I prove the invariance of the Dirac equation under Lorentz transformation? $$ \left[ \gamma^{\mu}\left( i\hbar\partial_{\mu} - \frac{e}{c}A_{\mu}(x) \right)-mc \right]\psi(x) = 0$$
0
votes
2answers
58 views

Trying to understand relativistic action of a massive point particle

I got badly lost in derivation of relativistic formulas for energy and momentum. I stumbled upon relativistic action as follows (which should explain relativistic motion of a classical particle): $$ ...
1
vote
3answers
84 views

Spacelike to timelike four vectors

First at all, let me just say that I'm not a Physicist, I study mathematics. So, I have this question. If you have a spacelike four vector, is there any transformation that could change it to be a ...
0
votes
2answers
79 views

Causality and Simultaneity in special relativity

I am a little confused about the implications of special relativity on causality and simultaneity. Are the following two statements true? For two events A and B that are close enough in space and ...
0
votes
0answers
25 views

Time dilation: different clocks [duplicate]

The plane is flying with a speed u=300m/s. How much time Δt′ would have to pass for a passanger on that plane for time difference 1s to occur between the time Δt′ on the plane and the time Δt on the ...
0
votes
0answers
60 views

Why is my understanding of the second postulate of special relativity incorrect?

SR postulate 2 states that light propagates in free space at a defined velocity that is independent of the motion of the emitting source. Since velocity is a vector quantity, it is directional. In ...
2
votes
3answers
111 views

Does time pass slowly in water?

In water the speed of light is slower than it is in vacuum. By special relativity the speed of light is constant. Typically, for the basic explanation of special relativity a clock which has a mirror ...
1
vote
2answers
98 views

Which is proper time $(t_0)$ and improper time $(t')$?

A lighthouse has two blinking spotlights 0.4 meters apart. The spotlight on the right blinks 5 seconds after the one on the left. How much time elapses between the blinkings of the spotlights as ...
0
votes
1answer
91 views

Vector representations of Lorentz transformation in terms of $E$ and $p$

Hello everybody the things I understand are the transformation properties of a four vector given as $\tag{1} p^\mu = \Lambda^\mu_{\,\,\nu} p^\nu.$ and an arbitrarily boosted transformation is of the ...
-1
votes
1answer
52 views

Every Relativistic Field Satifies the Klein-Gordon Equation?

I've read that every relativistic scalar field (and in some sense, any field) satisfies the Klein-Gordon equation. Is the reasoning for this just based on the quantum mechanical substitution of $E\to ...
8
votes
4answers
211 views

Do the integral forms of Maxwell's Equations have limited applicability because of retardation?

In the usual bookwork treatment, it is easy to show that the differential and integral forms of Maxwell's equations are equivalent using Gauss's and Stokes's theorems. I have always thought that ...
-1
votes
1answer
49 views

Electric field, special relativity, and charged particle

Given a uniform electric field in the $z$ direction and an observer moving at constant $v$ in the $y$ direction, how you would describe the motion of a charged particle that start at rest in the ...
3
votes
0answers
27 views

Fermi's understanding of the Doppler effect

I am now reading the classic paper by Dicke, The Effect of Collisions upon the Doppler Width of Spectral Lines At the very beginning of the paper, Dicke said ''Quantum mechanically, the Doppler ...
3
votes
3answers
269 views

Relativistic beamed photon propulsion

I am analysing the flight profiles possible with a lightsail powered by a photon beam, up into the relativistic regime. In an inertial frame, the sail acceleration is $A$. The onboard acceleration ...
0
votes
1answer
57 views

Why is the Poincaré group non-abelian?

Based on what I've learned, I gather the Poincaré group is the group of isometries of Minkowski spacetime and it is a non-abelian Lie group. Why is it non-abelian? Or perhaps rather, does the fact ...
0
votes
2answers
82 views

Calculating length contraction at speed $c$ (not near it)

Is the Lorentz transform applicable to speeds that are lower than light only?Because I'm trying to calculate length contraction of objects moving at speed $c$ (not near it) and it turns always 0. Is ...
1
vote
2answers
103 views

Beat Frequency for Police Radar with Special Relativity

"A radar speed trap operates on a frequency $v_o = 109 Hz$. What is the beat frequency between the transmitted signal and one received after reflection from a car moving at v = 30 m/s toward the ...
8
votes
7answers
359 views

What does the statement “the laws of physics are invariant” mean?

In the first paragraph of Wikipedia's article on special relativity, it states one of the assumptions of special relativity is the laws of physics are invariant (i.e., identical) in all inertial ...
3
votes
2answers
117 views

Explain the notion of light/electromagnetic waves/photons to a non-physicist

A non-physicist asked me about special relativity. My explanations naturally were based on gedankenexperiments involving light. This forced the question: "What is light? It is particles, isn't? Or is ...
1
vote
2answers
130 views

How does light actually behave?

Senario: I am walking 5 meters/second and have a laser pointer that I shoot a burst of light from perpendicular to to the path I am walking on. Would the light travel perpendicular to the path from ...
1
vote
3answers
73 views

Twin paradox - a further variant

I am still troubled by the "twin" paradox (thanks to those who have answered my previous question and suggested some reading which I will follow up). I have however thought of a variation on the ...
2
votes
2answers
174 views

Why do things slow down when you move faster, rather than speed up?

I've been trying to get to grips with SpaceTime. As I understand it, we move at a set rate through spacetime. Any increase in our rate of travel through space results in a decrease in our rate of ...
5
votes
2answers
108 views

What does memorylessness mean as a postulate of special relativity?

I was reading the wiki page on special relativity postulates. And wiki says, The two-postulate basis for special relativity is the one historically used by Einstein, and it remains the starting ...
0
votes
0answers
38 views

Forward and Behind Frames of Reference

It's my understanding that light travels at the same speed in all inertial frames of reference. Suppose there's a small train car 5 feet long (at our rest point of view) traveling at a constant speed ...
-2
votes
1answer
66 views

Can photons “stop time”?

If traveling past the speed of light causes time to reverse than does traveling in time make time "stop"? If not then how do photons/mass-less particles experience time, if at all.
2
votes
2answers
60 views

Basic Relativistic Question - length measurement

A while ago we did an easy, introductory exercise on length measurement. Back then it seemed pretty straightforward but now when I look at it I have trouble understanding the assumption which led to ...