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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48 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 ...
0
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2answers
100 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
73 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 ...
3
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0answers
77 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
54 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
30 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 ...
4
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1answer
124 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 polynomial ...
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1answer
38 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
81 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
134 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 ...
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2answers
155 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
146 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 ...
4
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2answers
223 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
41 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
451 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
110 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
42 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
118 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 ...
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2answers
230 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
66 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
81 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
152 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 ...
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1answer
82 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
79 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
29 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 ...
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1answer
129 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 ...
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1answer
431 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
75 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 space....
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4answers
324 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 ...
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0answers
93 views

Can a pair of members of a “rotating system” be characterized by one value of displacement magnitude?

There seems to be a claim (cmp. Goldstein, "Classical Mechanics", eq. (4-126); or also perceptable here) that values of "velocity", and of "speed", of some participant, say $P$, can not only be ...
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0answers
29 views

Reaching the speed of light [duplicate]

This is a very elementary question, and I'm sure there's a simple answer. However, I must ask... So I had this random thought... Imagine you had a bullet that would fire an additional bullet. Just ...
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1answer
52 views

If the distance between two objects is increasing with increasing rate, can we determine which object is under influence of force?

Suppose two bodies, A and B, are together in free space. One of them, let’s say- A, accelerates away, then retards, stops, accelerates back and stops again when it reaches B. Although we can see the ...
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1answer
24 views

Lifting an analogy of a pond to question signals at natural or artificial boundaries in space-time [closed]

I conjured up an idea to lift an analogy into the language of QFT and GR. I thought up the universe as a pond with a liquid. If we imagine a liquid poured into some pond (sort of bang and inflation ...
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3answers
164 views

Does the force between two point charges change when inertial reference frame changes?

The two point charges are as below: Then the Coulomb force between them is: $$F_1=\frac{q^2}{4\pi\epsilon_0 r^2}$$ When the inertial reference frame moves left at $v$(or the point charges move ...
4
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1answer
265 views

What is problematic about the Moving magnet and conductor problem?

The problem is posed as follows: There is a conductor and a magnet in relative motion. This motion induces emf in the conductor. The value of the induced emf is independent of whether it's the ...
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1answer
55 views

Gravity and velocity increase and time effects problem

First I must specify I am a math major and not currently taking any classes on physics and this is a casual interest/hobby of mine. Therefore I apologize in advance if my questions seem naive. An ...
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1answer
113 views

Tomorrowland movie and tachyons? [duplicate]

Would be possible if tachyonic existed to send info to the past or see the future? since the tachyons according to special relativity could travel to the past? i have searched in wikipedia and the ...
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4answers
99 views

Relativity and “light years”

As I understand relativity, time is relative to your velocity, meaning your watch moves slower relative to those who are stationary (relatively) when moving at great speeds. So if that's true then ...
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0answers
26 views

Is static gauge quantization of the particle equivalent to covariant quantization?

In the covariant quantization one is able to get directly (from the constraint $p^\mu_\mu+m^2=0$) the Klein-Gordon equation. But if one uses the parametrization $\tau=X^0$ then the Schrodinger ...
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1answer
137 views

Constant Jerk Relativistic Rocket [duplicate]

A quick google search will give many helpful pages and calculators regarding constant acceleration relativistic rockets, but my question is somewhat different. What if jerk is the parameter to be ...
4
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3answers
195 views

Why cannot a perfect clock exist?

I have a question about the reason Feynman gives for why a perfect clock - a clock that remains in sync while in motion with a stationary clock, cannot exist. It is clear why the "light clock" (...
1
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3answers
88 views

Prove that the spacetime interval is not invariant under Galilean transformations [closed]

The spacetime interval $(\Delta s)^2 = (\Delta x)^2 + (\Delta y)^2 + (\Delta z)^2 - c^2(\Delta t)^2$ is invariant under the Lorentz transformation and this isn't the case for the Galilean ...
5
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2answers
163 views

Is the double slit experiment valid in all inertial frames?

In a double slit experiment done with particles having mass (say electrons), the results are inferred as being caused by probability waves. The wavelength of these waves is dependent upon the velocity ...
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1answer
89 views

How can light cross $c$ in the given hypothetical experiment? Where I am wrong? [closed]

There is a concave mirror, which has somehow maintained the speed $\frac{c}{2}$ toward west ( for instance) , and there is a light wave or you can say a ray of light is moving in N-E direction. So we ...
1
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1answer
83 views

Boosting massless particles

How does one calculate the boost matrix to go from a photon of (standard) four-momentum $k^\mu = (k,0,0,k)$ to $p^\mu = (p,0,0,p)$? (in terms of $|p|/|k|$) Weinberg in his Quantum Field Theory Vol.1 ...
2
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1answer
200 views

What is a Lagrangian of a photon? [duplicate]

In sense of classical mechanics+special relativity what is lagrangian of a photon? Lagrangian of a relativistic massive particle is as follows: $$ L_{massive}= -mc\sqrt{c^2-v^2} $$ So is it a zero?
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1answer
205 views

Does the rest mass energy include the potential energy of the particle?

The potential energy (as far as I have studied - that is, mainly classical physics) depends on the reference level, since its absolute value cannot be calculated. It can therefore be negative as well. ...
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1answer
74 views

Does constant acceleration (from starship crew pov) to relativistic speeds look newtonian?

The last 25 years I thought that time dilation, mass increase and length contraction is "scaled" that way that on the first glance the crew of an accelerating starship could think everything is ...
1
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2answers
128 views

Why is the speed of light a limit? and why is it just $3×10^8\,\text{m/s}$? [duplicate]

Why does light travel with speed $3×10^8\,\text{m/s}$? and why not more?
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1answer
112 views

Relativistic approach of a car and a train to a crossing: seeming contradiction

Suppose a car is approaching a railroad crossing at a high relativistic speed, while on the tracks, a square rail car is also approaching the crossing at the same speed. (The road and the railroad ...