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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Derivation of $E=pc$ for a massless particle?

In classical mechanics, massless particles don't exist because for $m=0$, $p=0$. The relativistic relation between energy, mass and spatial momentum is: $E^2= (pc)^2 + (mc^2)^2$ . So it is said that ...
2
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1answer
65 views

How can parity be meaningful in an affine space?

I've recently begun a course in QFT (within a Physics Master's), and despite (admittedly limited) reading I can't get my head round the idea of parity. Here's what I think I understand: the Minkowski ...
5
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2answers
165 views

What is the correct relativistic distribution function?

General Statement and Questions I am trying to figure out the proper way to model a velocity/momentum distribution function that is correct in the relativistic limit. I would like to determine/know ...
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1answer
47 views

Range of a mediating particle

My book describes the derivation of the formula $R\approx\hbar/2mc$ by: $$(\Delta E)(\Delta t)\geq\hbar/2$$ The violation of energy conservation is $\Delta E=mc^2$ to create the particle’s mass. Also, ...
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4answers
125 views

Why light moves sideways?

Greatings! I'm trying to understand special relativity and have one question bugging me. In almost every book or video about the subject there is a thought experiment with moving light clock. I hope ...
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1answer
48 views

Special relativity, calculate velocity

Lets assume that a spaceship travels to a star 8 light-years away, in a time its crew considers to be 8 years. How do we calculate the speed of the ship? Is at as simple as saying: since the star is 8 ...
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1answer
35 views

Integral Represation of Four Current with proper time

I have a question about the four current in covariant representation. the four current is defined as $$ J^{\alpha} = \binom{c\rho}{\vec{j}} $$ and i'm having a point charge, ...
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2answers
75 views

How can magnetic fields pass through a grounded shield?

Suppose an electron outside a wire is moving with the same velocity as the electrons inside, then due to length contraction, there would be excess positive charges per unit area causing attraction of ...
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1answer
23 views

How to spatially rotate the frame of reference Faraday Tensor? Special Relativity and Galilei Transforms

Hey I'm currently just starting out doing special relativity and I stumbled upon following problem: If I have the faraday antisymmetric tensor $F^{\alpha \beta}$ and I perform a spatial rotation of ...
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2answers
70 views

What makes energy content of a body harder to accelerate it?

There was this video http://www.youtube.com/watch?v=Xo232kyTsO0 where the host explains the "Real meaning of $E=mc^2 $" by saying that even at the most microscopic level even the fundamental particles ...
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2answers
57 views

Will my mass increase in my perspective while approaching near the speed of light?

Suppose I start my journey by a spaceship accelerate the velocity to 0.7c from Earth. Now the question arises that- Will my mass increase gradually as I'm going to a speed of .7c in my perspective and ...
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2answers
43 views

How does this incorrect model of a wire give the correct result for B-field produced?

I see in Griffith's book Introduction to Electrodynamics, 4th edition, the following model (paraphrased). Consider a wire (infinitely-long) with positive linear charge-density $\lambda$ moving to ...
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0answers
27 views

Why does inter-electron distance in wire grow with acceleration?

When you have an electrically neutral wire, and apply a voltage across it, free electrons (provided by source) flow through the wire and thus an electric current is created. Assuming an ideal ...
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1answer
109 views

Space time diagrams and world lines

When you draw a space-time diagram and the associated world line for an object moving through space-time, the diagram will be dependent upon the reference frame you are observing from, right? Like for ...
3
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1answer
46 views

What if an object had enough speed that from another perspective it was enough to form a blackhole? [duplicate]

Suppose a baseball is traveling through a vaccum towards another object extremely fast. If it's travelling fast enough then shouldn't its kinetic energy give it enough mass that the observer thinks it ...
0
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1answer
71 views

Quantum Mechanics and Causality

Causality coupled with special relativity states that no particle can travel faster than light. Interpreting in terms of quantum mechanics, it means that dirac delta wave-function at x=a, can't ...
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1answer
104 views

An apparent contradiction to $m = m_0/\sqrt{1-v^2/c^2}$ [duplicate]

Using theoretical framework of the special relativity, we can show that the quantity that we classically regard as energy does have a property of inertia. And particularly, if the total energy of a ...
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1answer
82 views

Deriving proper time invariance from first principles

I'm trying to learn special relativity right now, and for various reasons I'd like to start by getting the invariance of proper time, rather than starting with the Lorentz transformations - if you can ...
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0answers
44 views

Confusion in Special Relativity: Rotating frame of reference

Suppose we are observing a rotating frame from an inertial frame, free from gravity, and try to measure the circumference of a circle drawn in the rotating frame. Since our measuring rod would be ...
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2answers
47 views

Why is it that when I do some substitution, I get $p=1$ for a photon? [closed]

I know that this is wrong, but where did i make a mistake? I just use a few equations and substitutions and I get that the momentum of a photon is one. Here is my math: $p=h/λ$ $p=hf/c$ (substituted ...
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2answers
79 views

What is the meaning of the square of the four-velocity?

The square (or dotproduct) of the four-velocity u is -1 or 1 (depending on the metric convention and with c=1, I think (in flat spacetime)). What does this physically mean? It sounds like "my speed" ...
2
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1answer
46 views

Why a motionless proton doesn't feel any force in a magnetic field according to special relativity?

In this ( https://www.youtube.com/watch?v=1TKSfAkWWN0 ) specific video uploaded by Veritasium on YOUTUBE , we come to know about how special relativity makes magnets work. We observe that when a ...
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0answers
61 views

Michelson–Morley experiment's aether; Why is the time gained from travelling downwind less than that lost travelling upwind?

From the Wikipedia article on the Michelson–Morley experiment, explaining one of the concepts behind the landmark experiment: "If the Earth is traveling through an aether medium, a beam reflecting ...
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1answer
40 views

Extra mass due to near light like speeds [duplicate]

Why does mass seem to increase as you near the speed of light?
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1answer
26 views

Do you really need to be moving to feel B-field from wire?

If the explanation for the B-field due to a current in a wire that I've heard (length contraction by moving electrons in conductor) is true, would you really need to be moving to feel the "B-field" of ...
3
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1answer
89 views

Representation of the Lorentz group

Is there any representation of the Lorentz group where $$U^{-1} f(x) U = f(\lambda^{-1}x)$$ other than the (0,0) representation? If not then is it possible for a field (with a well defined ...
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0answers
44 views

What is the distance covered? [closed]

Observer A boards a ship. This ship will instantaneously accelerate to a speed close to $c$ (like $($c$-1mm)/s$. The observer will count 1 second while traveling at cruise speed and then ...
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1answer
37 views

What is the dilation relation of the distance to a moving point (in special relativity)? [closed]

A frame $F_b$ is being translated with a speed $v$ according to another frame $F_a$. A point $A$ is attached to $F_a$. $B$ is attached to $F_b$. $D_a$ is the distance $AB$ viewed from $Fa$ and $D_b$ ...
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1answer
47 views

Gravity vs. Velocity time-dilation [duplicate]

Is there any difference in effects from time dilation of that due to gravity vs. that due to velocity?
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1answer
81 views

Time dilation: linear or exponential or other?

As you near the speed of light, time slows for you relative to the world around you. So you would be traveling at more than one hour per hour. Is the rate of time slowing for you linear or exponential ...
3
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2answers
140 views

What happens in circuits where the propagation time of the electric field is significant?

Kirchhoff's current law assumes "that whenever current flows into one end of a conductor it immediately flows out the other end". I want to understand what happens when we cannot make this ...
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1answer
83 views

proper time interval

We have two frames s and s' , s' moves with a constant velocity 'v' with respect to s in positive x direction, a particle B is thrown downwards from s' , and it collides with a particle A , the point ...
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2answers
177 views

Why is $d^4p$ “obviously” Lorentz invariant?

Is there a mathematical and a physical reason? I believe it follows from the jacobian of the Lorentz transformation. But, if that is so, I don't see why it would be "obvious" unless you can do such ...
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1answer
36 views

Are the edges of a galaxy moving inwards?

Space is expanding, but as I understand it, galaxies are not since gravity keeps them together. If you think of space becoming bigger, your galaxies just become further apart. But taking the size of ...
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2answers
395 views

Is there any theorem that suggests that QM+SR has to be an operator theory?

UPDATE To make my question more precise, I'll define what I mean by an operator theory: An operator theory is a theory in which the dynamical objects are operators, i.e., the equations of motion ...
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1answer
99 views

Can energy be weighed?

The binding energy of nucleus is calculated as- Mass defect = (Total mass of nucleons-Mass of the nucleus) And after that $E=mc^2$ is used for calculating the binding energy. Hot water is heavier ...
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0answers
62 views

Finding the final velocity of an accelerated proton using its kinetic energy? [closed]

So. I'm trying to find the final velocity of a proton that is being accelerated by a particle accelerator, just before it collides with a particle. All I have is its kinetic energy just before ...
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0answers
35 views

Speed of Light with trains [duplicate]

Suppose that there is a train (train1) going at 100 km/h. The train is infinitely long. Suppose that there is an other train inside train1 (train2), which has a speed of 100 km/h also. So for a ...
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1answer
64 views

Feynman lectures on physics: The Michelson-Morley experiment

I have a problem understanding something. I'm reading FLP and here I don't understand why when the system is travelling, the light doen't make the same angle in the mirror C... if B and C are moving ...
2
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2answers
94 views

Relativistic explanation of attraction between two parallel currents

This has been answered a lot of times, and I have been reading about it on many websites, including PSE, but I still don't get it. So please don't mark it as a duplicate unless it really is one. Two ...
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1answer
39 views

How does a laser beam change angle from frame to frame in special relativity?

I am at Point A, and I have a laser pointer. I point it at a mirror, one mile west of me, at point B. The beam travels to the mirror and comes back to make a nice round dot on my shirt at point C. In ...
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2answers
63 views

Complex conjugation of Weyl Spinors

Let $\chi$ be a left-handed Weyl spinor transforming as $$\delta\chi=\frac{1}{2}\omega_{\mu\nu}\sigma^{\mu\nu}\chi.$$ In my lecture notes it is explicitly stated that complex conjugation interchanges ...
3
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1answer
104 views

How can a photon “stop”? What does its world line look like? [duplicate]

Einstein famously made a thought experiment: what would he see if he sat on a beam of light? His answer was -- it's impossible. Owing to him being a body with mass, he can never ever reach light speed ...
3
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1answer
79 views

Is each succeeding dimension time? [closed]

I have been researching but I have found nothing on this topic (at least after basic google searching and some deeper searching on this site), I'm not sure if this is a common sense thing or it is ...
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1answer
75 views

Emitting flash of light at relativistic speed

Let's say we have two observers, one stationary and the other moving at relativistic speeds. The observers agree to emit a flash of light when their clock reads 10 seconds. I think it should be ...
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0answers
28 views

Why is the speed of light constant in all inertial frames? [duplicate]

I know this is a physical principle and cannot be derived at from other physical laws. But how can it be arrived at? What observations or what train of thoughts leads to this conclusion? e.g. the ...
0
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1answer
94 views

Did the mass of the electrons went infinite in the experiment done by William Bertozzi in the 1960s?

it is impossible to accelerate a particle to a speed greater than c, no matter how much kinetic energy we give it In an experiment published in 1964, electrons were accelerated to a large voltage ...
6
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1answer
406 views

Can we actually have null curves in Minkowski space?

I know that this sounds really stupid but, when I think of the Minkowski space I cannot imagine a null curve, only null lines. For me, the only possible way to have one is to change the basis of the ...
4
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0answers
71 views

General theorems on tachyon propagation?

I was reading the quite nice answer of QMechanic on the topic of compact support tachyon fields not propagating faster than light, but this case is a rather simple one, free scalar field in flat ...
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4answers
195 views

Why can't anything travel faster than light?

It is a well known fact, that nothing can travel faster than light. I have discussed that fun fact numerous times with my 8 year old son. One day he asked "why?", and I realized that I didn't know the ...