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 (5)

1
vote
1answer
106 views

Do photons have no mass? [duplicate]

My Quantum Mechanics' teacher said today on the class that photons don't have mass. I was puzzled because I knew that photons have momentum. If a particle hasn't mass then its momentum sould be $0$ ...
2
votes
2answers
95 views

Where does the 3-velocity live?

Imagine a four-dimensional affine space $\mathcal{M}$ with the standard metric $\eta = \text{diag} (1,-1,-1,-1)$. Let $\mathcal{C}$ be a worldline of a point particle parametrized by an affine ...
-3
votes
1answer
108 views

Is This Educational Model of Relativity Right? [closed]

After watching and reading about Special Relativity I am still left with some questions unanswered. Can you please tell me if this educational model of relativity, simplified to level of a cartoon, ...
1
vote
1answer
66 views

Taking the classical limit $v\ll c$ in special relativity

I'm trying to understand some of my class notes. My professor reached 2 equations: $$m_0c^2 \frac{d\gamma}{dt}=\textbf{F} \cdot \textbf v\tag{1}$$ and $$m_0\frac{d\gamma \textbf v}{dt}=\textbf ...
0
votes
1answer
93 views

Can observers in different reference frames agree on the time an event took after the fact?

Ok, I don't think I did a good job of communicating this, so here's a better way to phrase the experiment. There is a spaceship traveling horizontally in the x-direction at near the speed of light ...
0
votes
1answer
49 views

Why are the topological dimensions of spatial\timelike\null infinities 0\0\2 respectively?

I have a question regarding spatial, timelike and null infinities in Minkowski spacetime. I shall start with an explanation of my intuitive understanding of these concepts, and then proceed to my ...
3
votes
1answer
318 views

In what sense is BMS a symmetry? (What is kept invariant?)

Recently I've started to read about BMS (Bondi-Metzner-Sachs), and I've encountered several statements such as the following (from [1]). [I]t turned out that the asymptotic symmetry group at null ...
1
vote
1answer
76 views

Work out components $F^{01}$ and $F^{ij}$ of the antisymmetric tensor $F^{\mu\nu}$ under the Lorentz Transform [closed]

Work out explicitly how the components $F^{0i}$ and $F^{ij}$ of the antysymmetric tensor $F^{\mu\nu}$ introduced in chapter I.6 transform under a Lorentz transformation This problem is from Zee, ...
0
votes
1answer
370 views

Did Einstein plagiarize Poincare? [closed]

http://www.bibliotecapleyades.net/esp_einstein.htm This site makes such claims including: Jules Henri Poincaré (1854 - 1912) was a great scientist who made a significant contribution to special ...
1
vote
0answers
48 views

What is the equation of a ellipsoid in motion and how to obtain its semi-axes? [closed]

The equation of an ellipsoid is given by $$\dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}+\dfrac{z^2}{p^2}=1$$ where $a,b,p$ are the length of the semi-axes. If $a=b=p=R$ then this ellipsoid is a sphere of radius ...
-1
votes
1answer
86 views

Warp Drive conundrum - Speculative science question [closed]

Let me begin by stating that this question about Warp Engines/Drives, which i understand is a speculative, also I am not a Professional scientist or someone with a degree in physics. The question will ...
5
votes
3answers
613 views

How to prove a symmetric tensor is indeed a tensor?

Our professor defined a rank $(k,l)$ tensor as something that transforms like a tensor as follows: $$T^{\mu_1' \mu_2'...\mu_k'}{}_{\nu_1'\nu_2'...\nu_l'} ~=~ ...
4
votes
4answers
252 views

Are photons inside the media massive? If yes, why there is no Meissner effect?

We all know in vacuum travels with speed $c$, hence its rest mass has to be 0. In the media the light speed $v<c$. Then the photon renormalized by the medium (call it "quasi-photon" if you like), ...
2
votes
1answer
106 views

De Broglie wavelength of a massive particle as v approaches c

We understand that from a relativistic version of De Broglie's wavelength-momentum relation that as velocity approaches 0 the wavelength trends to infinity and as velocity approaches the speed of ...
-2
votes
2answers
93 views

Electromagnetism and a simple doubt [duplicate]

Why don't electromagnetic waves need a medium to propagate? How does light get such a magnificent velocity?
-4
votes
2answers
73 views

Can light travel with a speed less than its speed at same time?

I know that the velocity of light with respect to anything is constant ($c$) . What, then, is velocity of light with respect to light?
1
vote
1answer
105 views

Heisenbergs Uncertainty Principle in different intertial frames

Say there is a single particle in a box. If we switch to a different inertial frame (without the box) travelling close to the speed of light we see the box get smaller. At a high enough speed the ...
0
votes
1answer
57 views

How is $\dfrac{A^2}{8\pi}$ is the energy per unit volume of light?

In his 1905 paper, under the section: 8. Transformation of the Energy of Light Rays. Theory of the Pressure of Radiation Exerted on Perfect Reflectors, Einstein states: Since $\dfrac{A^2}{8\pi}$ ...
0
votes
1answer
63 views

What do we mean by saying that one clock had been “running slower” than another clock; or that two clocks had been “running equally”?

Several posts on this site, especially on the topic of relativity, refer to comparisons between clocks in terms of their "running"; one having "run faster" than the other, one having "run slower" than ...
4
votes
3answers
417 views

Explanation of Supplee's paradox

I was reading about Supplee's paradox, which is about whether a relativistic projectile, subject to uniform gravitational acceleration, would float or sink underwater. However the solution of the ...
1
vote
1answer
117 views

Time Dilation When In Orbit

Imagine a space ship orbiting the sun at near relativistic speeds, when compared to Earth (say from the reference frame of the sun) there would be x amount of time dilation. This would mean people on ...
0
votes
1answer
126 views

Is the amplitude proportional to frequency in electromagnetic waves?

In Einstein's 1905 paper, under the section: § 7. Theory of Doppler’s Principle and of Aberration Einstein derived the relativistic Doppler effect: $$f'=f\dfrac{1-\cos\phi \cdot ...
5
votes
1answer
131 views

Is there any way to measure the one-way speed of light?

Is there any way (practical or theoretical) to measure the one-way speed of light? The two methods that come to mind are: Stellar aberration, and Using adiabatic clocks: synchronize clocks, then ...
2
votes
1answer
75 views

Why $x=-ct$ line in a spacetime diagram?

I can understand why the $x=ct$ line is needed as follows: If $c \Delta t \geq \Delta x$ then the event can be causally related to your current position, so the event could not appear in reverse ...
8
votes
3answers
222 views

Alongside a light ray (in another medium)

It is a said fact that the speed of light is insurmountable. But can the validity of this fact be questioned in another medium? If I pass a beam of light in, say water (here the light speed is ...
0
votes
1answer
96 views

Is the relativistic mass of a photon non-zero?

A photon has rest $m=0$, but it is never at rest, so it has no rest mass, then the relativistic mass is according to me non-zero because: $E = \text{work}=m \times \text{acceleration} \times ...
2
votes
1answer
108 views

Can a baseball travel through the Sun?

A baseball moving sufficiently close to the speed of light could theoretically spend less than a nanosecond inside of the Sun in the balls frame. If a baseball were traveling close enough to the speed ...
1
vote
0answers
42 views

Lorentz transformation in “On the Electrodynamics of Moving Bodies”? [duplicate]

I must be certainly wrong, but there is something I don't understand when reading the paper on "On the Electrodynamics of Moving Bodies" from Albert Einstein. All the sources I found give the same ...
3
votes
1answer
223 views

Why does a function $\psi(v)$ appear when a Lorentz transformation is applied on Maxwell's equations?

In his 1905 paper, Einstein applies Lorentz transformation on Maxwell's equations, and relates the electric force $(X,Y,Z)$ and magnetic force $(L,M,N)$ in an inertial frame $K$ with spectime ...
3
votes
1answer
165 views

What is the intuitive meaning of $Q^2$?

In particle physics, $-Q^2$ is defined by the four momentum transfer squared: $$Q^2 = -(p_i - p_f)^2 = (\vec{p}_i-\vec{p}_f)^2-(E_i-E_f)^2$$ For elastic scattering, the meaning of $Q^2$ is clear - it ...
0
votes
0answers
38 views

Twin Paradox in a closed universe: who is younger when they meet? [duplicate]

Assuming that our universe is like a great balloon-- if you travel far and long enough, you will eventually come back to the original position. Now, a pair of twins are "travelling around the ...
4
votes
5answers
586 views

Twins Paradox - Does ageing depend on motion?

I am trying to understand the Twins Paradox (relativity) and its implications. Can we infer from the Twins Paradox that the ageing process (cell decay or other biological processes) depends on ...
0
votes
2answers
215 views

Why does the Lorentz transformation have to be a linear transformation? [duplicate]

In my textbook, they say the following statements before doing a proof for the Lorentz transformation: We know that the Galilean transformation $x' = x - vt$ is incorrect, but what is the ...
2
votes
8answers
581 views

Why is there a universal speed limit?

I am looking for an answer that does not rely on Special or General Relativity -and without recourse to the fact that the speed of light is frame invariant. Is there another way of showing this ...
6
votes
1answer
208 views

The effect of relativistic near misses

Alice and Bob are both floating in free, empty space. Alice does not like Bob very much. Thus one day, believing that there is no such thing as overkill, Alice takes her programmable hyper-energetic ...
14
votes
1answer
1k views

Confusion I have regarding Einstein's 1905 derivation of LT

In his 1905 paper, Einstein derives the Lorentz transformation using the two postulates of SR;constancy of $c$ for all inertial frames and the Invariance of the laws of physics for all inertial ...
2
votes
2answers
168 views

The action of a relativistic point particle, the meaning of its parametrization invariance and possible potential terms

i am currently toying around with the behaviour of a classical relativistic point particle a bit. For a free one we get the action \begin{align} S =\int_\tau - m\sqrt{- \dot X_\mu \dot X^\mu}. ...
4
votes
3answers
214 views

4-vectors in special relativity and spacetime interval

In one of my vector mechanics lectures, the lecturer said the the space time interval was the dot product of the four position vector. But then he proceeded to show it was this: $s^2$ = $\Delta r^2$ - ...
0
votes
1answer
45 views

Does motion with constant proper acceleration, in a flat region, necessarily mean straight hyperbolic motion?

Is motion of a participant with constant proper acceleration, in a flat region, necessarily straight, hyperbolic motion (with respect to members of any inertial system, in that region)? Or is for ...
0
votes
3answers
76 views

Regarding synchronization of clocks in special relativity

I am trying to read of synchronization of two clocks in same inertial frame in special relativity. Suppose we have two synchronized clocks in an inertial frame placed at positions $x_1$ and $x_2$ in ...
0
votes
1answer
76 views

Best twin paradox trajectory for constant acceleration rocket?

Let's say I have a rocket that can provide constant (proper) acceleration (let's say of 1 gee) for an infinte amount of time. Let's say I want to use this rocket as a means of "suspended animation," ...
2
votes
1answer
72 views

Why is the Mixed Faraday Tensor a matrix in the algebra so(1,3)?

The mixed Faraday tensor $F^\mu{}_\nu$ explicitly in natural units is: ...
1
vote
2answers
149 views

Doubts regarding Einstein's 1905 derivation of mass-energy equivalence

This is a follow up on this question. In his [paper][2] under the title:Does the inertia of a body depend upon its energy-content, Einstein drives the famous $E=mc^2$ equation. His argument can be ...
2
votes
0answers
51 views

Does space expansion change value when traveling near the speed of light?

To draw an analogy, we receive roughly the same amount of cosmic background radiation from all directions. However if we were to travel near the speed of light relative to the reference frame where ...
1
vote
2answers
138 views

Is potential energy frame dependent in special relativity?

In newtonian mechanics, As far as I'm aware, only kinetic energy is dependent on frames of reference, since kinetic energy is a function of velocity(squared) and velocity is dependent on frames of ...
2
votes
1answer
48 views

tensor products in special realitivity

Use the definition of a tensor as a linear function on vectors and 1-forms. For a one (2,1) tensor T, use a single vector as argument e.g. T(V) which converts it to a (1,1) tensor. However, if you ...
0
votes
1answer
39 views

What is disadvantageous about measuring time events using light signals sent from events?

In his paper: On the electrodynamics of moving bodies, under the section entitled I. KINEMATICAL PART: § 1. Definition of Simultaneity, Einstein discusses time and gives it an operational definition. ...
0
votes
1answer
72 views

Do relativistic electrons have more charge?

Gauss's law tells us that the total electric flux out of a closed surface is equal to the charge enclosed divided by the permittivity. When a charged particle is moving close to the speed of light ...
1
vote
0answers
41 views

Are relativistic spacecraft slowed down by oncoming gamma ray photons?

I recently read that a proton having an energy of ten billion GeV can travel across our galaxy in about 5 minutes from the frame of the proton. From the Earths frame we would see it take roughly ...
2
votes
1answer
49 views

Derivation of relativistic mean free path

I am working through a short derivation found in Abramowicz 1991 regarding the mean free path of a photon. We have a fluid moving in a particular direction with velocity $v$ and in an inertial rest ...