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

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Is the rate of light emissions actually the frequency of the light?

I am confusing with the concept of frequency in the context of Doppler effect studying SR. The Schutz says, if the source emits pulses more frequently, then the observer would see the lights not only ...
3
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1answer
94 views

Can $E=mc^2$ be derived from the Minkowski spacetime metric? $s^2=x^2+y^2+z^2-(ct)^2$?

Can $E=mc^2$ be derived from the Minkowski spacetime metric? $s^2=x^2+y^2+z^2-(ct)^2$? If so, how? Can the equivalence of mass and energy be derived from the Minkowski spacetime metric? Has someone ...
4
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1answer
66 views

What is the Lorentz group representation for a general spin?

Setup, as I understand things so far: One way to think about where the spin of a quantum field comes from is that it is a consequence of the ways that different types of fields transform under ...
0
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0answers
63 views

What is the equation of state for a relativistic fluid/gas? [closed]

say we have a relativistic fluid/gas. now let us write: $e$ - energy density in the fluid's rest frame. $P$ - pressure in the fluid's rest frame. $n$ - number density in the fluid's rest frame. ...
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1answer
24 views

Synchronization of clocks

I have read the book "Introduction to special relativity " by Robert Resnick In the book I have found that "If the distance between the clocks is L, one observer will see the other clock lag his by ...
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1answer
65 views

Plane Wave Solutions of the Dirac Equation

I'm trying to understand the plane wave solutions of the Dirac Equation. But I'm still a newbie on indices notation and contravariant and covariant objects. What I don't understand is how to get: ...
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2answers
119 views

Meaning and logic of Einstein's train thought experiment

This seems to be a recurrent topic but I wasn't able to find any satisfactory discussion about this tought experiment. I will quote the original story from Einstein's and put my doubts inside: Up ...
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1answer
61 views

Force, Mass, Motion? $E = mc^2$

Does any object needs force to move? If 'yes', does the matter needs mass to form a force? These questions arises from me because $E = mc^2$ and $F = ma$ does not relate and one does not agrees with ...
3
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1answer
53 views

Radiative equilibrium of a relativistic black body

A black body in empty space in the CMB rest frame should (discounting starlight) come to an equilibrium temperature of around 2.7 K. However, if the body is moving relative to the CMB frame, one side ...
0
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1answer
81 views

Why is the speed of light being invariant and finite in all inertial reference frames?

I understand the basics of Lorentz transformation and Riemann Geometry but I still cannot understand why the speed of light is the same in all inertial references. Has anyone ever researched about ...
30
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2answers
3k views

Were Michelson-Morley results a surprise?

How unexpected were the Michelson-Morley experiment results? Did physicists have theoretical reasons to predict that the speed of light would result to be invariant?
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2answers
56 views

How time and speed of light are related? [closed]

I want to know how speed and light and time are related? How will motion with highspeed effect time? I am not a physics student. I want an answer which is free of mathematical relations. I want an ...
1
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1answer
50 views

Behaviour of Dirac Bilinears

Dirac bilinears transform in the Lorentz indices as, $\bar{\psi}\psi$ scalar $\bar{\psi}\gamma^\mu\psi$ vector $\bar{\psi}\sigma^{\mu\nu}\psi$ 2nd rank (antisymmetric) tensor ...
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1answer
22 views

How to express in terms of spacetime intervals the average speed of one participant having moved between two suitable others

Given a flat region of spacetime as set $\mathcal S$ of events together with values of spacetime intervals (up to a common non-zero constant) for each pair of events, $s^2 : \mathcal S \times \mathcal ...
1
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1answer
16 views

How to express in terms of spacetime intervals whether two participants in a flat region were at rest to each other

Given a flat region of spacetime as set $\mathcal S$ of events together with values of spacetime intervals (up to a common non-zero constant) for each pair of events, $s^2 : \mathcal S \times \mathcal ...
-1
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1answer
67 views

Dot product in index notation [closed]

This is a question about a small exercise I am trying to do in order to check if I am correct. Such type of quantities can appear in propagators in QFT. Since I am not an index expert I need some ...
0
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1answer
67 views

Relativistic acceleration of a rocket?

I'm trying to solve a physics brain-teaser and getting nowhere fast. My knowledge of special relativity is very basic. In the problem a rocket is flying linearly at relativistic speeds (say ...
2
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2answers
63 views

How does SUSY avoid to create non-Lorentz interactions?

A three-legs fermion interaction or boson absorbing a fermion are things we do not see in QFT because the corresponding terms in the Lagrangian are not Lorentz invariant. But in susy, naively, such ...
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0answers
35 views

Gradient of $ct'$ axis in spacetime diagrams

This is either an unimportant piece of information or it's meant to be obvious, but I can't find anywhere what the gradient of the $ct'$ axis in a spacetime diagram should be. I know that the $ct'=1$ ...
6
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3answers
145 views

What's the problem with light traveling at speed higher than $c$?

I'm trying to understand how Einstein concluded that time is relative based on thought experiments such as a torch attached to the end of a rocket. Based on answers to questions like this one, this ...
0
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4answers
115 views

Tensor calculus in special relativity

We say that any function $f(t,x,y,z)$ is a tensor of rank {0 0} because it takes no vectors or one-forms in order to give a real number. But couldn't we have just written the same function as ...
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1answer
27 views

Multiple Objects at Constant Speed

Imagine 1 million objects travelling in space, at a constant speed, along an imaginary line. They don't deviate from that line for the sake of this argument. Now, object 1 has a velocity of $v_{1}=1$ ...
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Can the energy released from a black hole be calculated at the time of birth?

this might be a stupid question but when a black hole is formed it releases a lot of energy our satellites just catch the gamma rays and X rays released by the black hole. can we estimate the amount ...
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24 views

What's the consensus on the block universe? Is time frozen? [duplicate]

What's the consensus view on the block universe? Is time frozen? Do the past and future exist? Was Einstein right when he said, “People like us, who believe in physics, know that the distinction ...
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1answer
48 views

How does time dilation occur due to velocity and gravity [duplicate]

I am trying to understand and clarify the way time dilation occurs due to general and special relativity and for which reason. In the case where an object is approaching a planet in free-fall how does ...
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1answer
66 views

Different definitions of the parity transformation for the Dirac spinors

There are two definitions of the parity transformation acting on the Dirac spinors: $\Psi_P = \eta \gamma^0 \Psi$ with $\eta = i$ ($P^2=-1$ as in Srednicki) and $\eta=1$ ($P^2=+1$ as in Peskin & ...
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156 views

How can we prove charge invariance under Lorentz Transformation?

We have gravitational force between two massive particles and we have electromagnetic force between two charged particles. When special relativity suggests that mass is not an invariant quantity why ...
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3answers
63 views

Mass and frequency of photons [duplicate]

Light is affected by gravity which means light has got mass. Quantum theory tells us that light consists of discrete quanta of energy, which we call photons. These photons have a rest mass of zero (as ...
5
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0answers
118 views

Can special relativity be derived from the invariance of the interval?

As far as I know, the classical approach to special relativity is to take Einstein's postulates as the starting point of the logical sequence, then to derive the Lorentz transformations from them, and ...
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3answers
147 views

Why did Einstein took speed of light unit or constant in his equation of relativity?

We can find that no object can have speed more than light from Einstein's equation of relativity because if anything have speed more than light then we get -ve value within square root. But why did ...
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2answers
56 views

Planes of Simultaneity on Minkowski diagrams

As seen from a "stationary" reference frame, Why do lines of simultaneity for fast-moving observers run parallel to distance axis instead of perpendicular to the time axis. Obviously, in a regular t ...
0
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2answers
368 views

How to achieve speeds faster than light? [duplicate]

So, I heard that all speed is relative. And that nothing can travel faster than light. Then I guess it is OK for a spaceship to leave Earth at 0.6c constant speed. And what if an other spaceship were ...
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27 views

Helicity of massive particle at high enengy

We know that massless spin-1 particle like photon only has two helicity state (-1,1), what about the helicity of massive spin-1 particle (W boson) at very high energy? Does it have helicity 0 state ...
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30 views

How do I make a slowly rotating neutron star using fortran code?

I make a slowly rotating neutron star code but I am little bit confuse, when I solved the coupled differential equation using runga-kutta 4th order method. These coupled differential equations as ...
0
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0answers
70 views

Derive Galilean transformation. (The meaning of the relativity)

In the book The meaning of the relativity Einstein says that in classic mechanics two postulates are previously supposed: 1.- The time is absolute. 2.- The longitude is absolute. And this implies ...
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1answer
73 views

Does there exist finite dimensional irreducible rep. of Poincare group where translations act nontrivially?

I read several textbooks of QFT and find that there are two ways to classify the particles or fields. The first one is to study the irreducible representation of Lorentz group (or exactly the ...
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3answers
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Confusion on relativistic electromagnetism of two charge particles

When I was introduced to the relativistic nature of electromagnetism, the following scenario is introduced: Two protons are fired such that they travel at the same velocity in parallel directions ...
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0answers
10 views

How can I do a nested lightcone integral?

I want to do an integral of the form $I(x-y)=\int d^{D+1}z_1...d^{D+1}z_n f(x-z_1)...f(z_n-y)$ where $x,z_1,...z_n,y$ are all (D+1) vectors and $f$ depends only on the proper times between them. ...
6
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1answer
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Signification of “finite but unbounded universe”?

I recently read Einstein's book about relativity and he says that his theory predicts the shape of the universe. It would be finite but unbounded. But how is this possible? What's the difference ...
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0answers
17 views

Compressed length of a moving body [closed]

This question is on behalf of someone else without access to a computer so any further clarification or responses may be delayed. The question comes in the form of photos of the original questions as ...
0
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1answer
38 views

Speed of light in vacuum in special relativity

In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why?
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39 views

Thought experiment on special relativity

If we were travelling in a spaceship, accelerating (arbitrary value) from a velocity 0, and we assumed that times and distances outside of the spaceship remained the same as that of ours, would we be ...
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1answer
54 views

Can information be sent faster than speed of light [duplicate]

I just had this idea one day and I decided upon a thought experiment to verify it. Imagine 2 people A & B sitting on two sides of a pipe which is stretched to a length of 3x10^8 m. The pipe is ...
0
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1answer
56 views

Are Coulomb's Law and Lorentz force always true for all phenomenon in physics?

I saw two equation about charge: Coulomb's law $$\mathbf F=k \frac{q_1q_2}{ r_{12}^{2} }\, \mathbf{\hat r} $$ and magnetic Force $$ \mathbf F=q \, \mathbf v\times \mathbf B$$ My question ...
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1answer
52 views

Stacked motors thought experiment

first of all, I'm not a mathematician, just curious about something that came up to my mind and maybe you can help me out. Scenario: I have a motor that spins let's say at 20K revolutions per ...
1
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2answers
105 views

Where do I begin in order to study relativity? [duplicate]

I am in high school now and I want to get the basic idea of what relativity. Can anyone suggest me a book or website for it? I am also curious about the mathematics behind it. Is it possible for me to ...
4
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0answers
41 views

Why is there a minus in the Gauge Field Lagrangian kinetic term? [duplicate]

For vector Gauge fields we usually write the kinetic term: $$ \mathcal{L} ~=~ - \frac{1}{4} F_{\mu \nu} F^{\mu \nu}$$ while for matter fields e.g. for a real scalar: $$ \mathcal{L} ~=~ \frac{1}{2} ...
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What is wrong with this derivation of the lorentz factor

in attempting to derive the lorentz contraction, I assumed that light speed is measured the same from all inertial reference frames. The situation set up is object A is standing still, whilst object B ...
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2answers
201 views

Is there a limit to how hot an object can get?

If heat is the measure of how fast the atoms are moving in an object, than isn't there a limit to how hot that object can get as nothing can go as faster than the speed of light. So because the atoms ...
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25 views

Value of $E_x$ through an $X-\textrm{boost}$

Suppose I'm standing at the (0,0,0) point of a coordinate system and I see an electric field where $E_x=f(t,x,y,z)=\sin(x\cdot y\cdot z\cdot t)$ and at time $t_0=0$ I start moving on the x-axis at ...