The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.

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relation between speed and temperature in relativistic gas

What is the correct formulation of the relation between the speed and temperature in the relativistic kinetic gas? I have found one mentioned in problem 3.24 of the third edition of Pathria's ...
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1answer
22 views

relativistic temperatures energy assumptions

why is the assumption $k_bT>>mc^2$ made for relativistic temperatures, where did the kT come from and how is it related to mc^2?
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0answers
14 views

Pair production in different reference frames

I understand that energy of photons is defined by their wavelength/frequency. This frequency (and so energy) will be different for different observers: observer moving towards the photon will see ...
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1answer
43 views

The elevator and the bolt [on hold]

I had this question, I don't seem to get what I am doing wrong so here it goes:An elevator car whose floor to ceiling distance is equal to $2.7 m $ starts ascending with a constant acceleration of ...
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0answers
31 views

Difference in time for clock in attic vs clock in cellar [on hold]

This question is regarding relativity: Two clocks are stationed in a house, one in the cellar and one it the attic. Which one of the following statements is true? A : The clocks tick at the ...
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0answers
13 views

What is the difference in subjective time experienced by an orbiting and stationary observer? [on hold]

Two observers start in rockets 1000kms above Earth's north pole. Observer 1 remains stationary relative to Earth, burning fuel to hover in place. Observer 2 is in a circular polar orbit. Both ...
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2answers
80 views

What the live streaming of a time traveler will look like?

Consider a hypothetical situation: In which a time traveler travels in a spaceplane at close to speed of light circling the earth and I get a live telecast of inside of that plane to my television. ...
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0answers
31 views

Electron in a Magnetic Field: Force parallel to velocity?

According to the four-force given in this question, Force is parallel to velocity. But the Lorentz Force is perpendicular to velocity in a constant magnetic field. Is this a contradiction? [a ...
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3answers
164 views

Is it possible to express various nonlinear motions as straight lines in transformed spacetime?

I am trying to understand simple examples of space-time curvature. Assume for the moment that $c$ is infinite (classical curvature due to Newton's laws). Also, I will only consider 1+1-dimensional ...
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5answers
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What is time dilation really?

Please will someone explain what time dilation really is and how it occurs. There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for ...
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0answers
19 views

Time Dilation for a photon [duplicate]

Does a photon experience any time. Since a photon is massless and hence travels at (c) then it should suffer infinite time dilation, and hence shouldn't experience no time?
3
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3answers
160 views

Relative velocity of light beams

Assume two light beams moving in the same direction i want to use the relativistic velocity transformation equation to find the relative velocity with each other, Note : i let $C$=1 ...
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0answers
25 views

In the GPS system, does the satellite clock see the earthbound clock moving slower, due to relativity?

In the GPS system, does the satellite clock see the earthbound clock moving slower, due to relativity? Suppose that a GPS satellite was moving at .9c. Would it see the earthbound clock running ...
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1answer
50 views

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 ...
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2answers
114 views

(Hyper)Surface of Simultaneity

How can I determine the surfaces of simultaneity if I know the metric? In particular, what are the surfaces of simultaneity for rotating disk with Langevin metric: $$ ...
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0answers
19 views

Is absorption probality modulated by interferance instanteneous or retarded effect?

Let say the absorption probability at some atom 1 location is modulated by photo ionized electron wave (ionized from 1) that scatters by neighboring atom 2 and returns to the 1. (Around the absorption ...
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1answer
112 views

What would we see if a camera orbiting close to light speed beamed down images of us on earth?

If a camera was sent up in a satellite, put in orbit at close to light speed, and instructed to beam down images to earth, what would we see if we watched its video feed? (Ignoring the fact that ...
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2answers
64 views

Do Einstein's postulates of relativity emerge from the Minkowski spacetime metric?

Does the constancy of the speed of light for all observers naturally emerge from the Minkowski spacetime metric? Do Einstein's two postulates of relativity emerge from the Minkowski spacetime metric? ...
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0answers
17 views

Why the angular distribution of the X-rays from Roentgen tube is not along the decelaration of electrons? [duplicate]

As I understand the X-ray generation from Roentgen tube, is a result from the bremsstralung (and also characteristic lines): from decelerating electrons in the presence of the potential of heavy ...
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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 ...
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1answer
83 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 ...
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0answers
10 views

How is specific output chosen in circular synchrotrons to radiate X-rays?

Accelerating charged particles are supposed to emit radiation. In sychrotrons does the particles emit always during the circular motion or only at specific location (undulator) ?
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3answers
99 views

Precedence and quantum entanglement: The Alain Aspect experiment in spacetime

Recall that the spin components of a spin-entangled pair do not exist until one of the pair undergoes quantum observation, at which time both of the pair immediately obtain quantum random opposing ...
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0answers
40 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
45 views

“Einstein showed that everything is relative.”? [closed]

Is this statement accurate? I've been sitting on this for a bit and cannot come to terms with my thoughts, so I need insight on this statement, from both a Physics and/or Philosophical perspective.
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2answers
610 views

Introduction to relativity books [duplicate]

Possible Duplicate: Getting started general relativity I am an engineer who loves to read science fiction books especially when there's more science than fiction but usually I see that I ...
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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 ...
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1answer
159 views

Time dilation triplet paradox

Here is the twin paradox with a twist. Scenario 1: An observer (A) leaves from the equator of the earth and travels with an acceleration of $9.8\,\mathrm{m/s^2}$ in a north direction ( i.e. in the ...
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0answers
44 views

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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1answer
39 views

Femtosecond photography

My question regards comments made around the 9:23 minute mark in Ramesh Raskar's TED talk, "Imaging at a trillion frames per second". At this point in the talk, an image shows "light ripples" that ...
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3answers
79 views

Is it possible to travel near light speed and not notice relativity?

Suppose I have no idea about relativity and find an ancient spaceship that takes me to Proxima Centauri in just 1 year more than it takes light to make the trip (so some observer might say it took ...
3
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7answers
855 views

Is there a universal rest frame of reference?

I am still struggling with C being a constant and what that implies. So can an experiment be done to find the resting state for the universe? Take a device with an observer and a light source and two ...
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1answer
42 views

Relativistic Electrodynamics [closed]

What are the applications of relativistic electrodynamics I've been learning about it in a theoretical physics module however I don't understand what implications or uses it has in real life and ...
33
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6answers
4k views

What is the proper way to explain the twin paradox?

The paradox in the twin paradox is that the situation appears symmetrical so each twin should think the other has aged less, which is of course impossible. There are a thousand explanations out there ...
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1answer
45 views

3 points in space, relative motion, and the speed of light

I'm new to thinking about relativity, as well as phenomena related to the speed of light, time dilation, length contraction, simultaneity, etc. I am pondering a paradox. Assumptions: Motion is ...
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0answers
23 views

Relativistic mass increment [duplicate]

Is the mass increment with an increase absolute velocity of a body, a direct consequence of energy to mass conversion
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1answer
42 views

Could the rest mass be somehow considered as a very exotic kind of kinetic energy?

In its rest frame a free system of invariant mass $m$ has energy $E=mc^{2}$. That frame is moving in spacetime with a four-velocity whose magnitude is $c$. Inside my brain something asks: Would ...
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0answers
40 views

complete layman trying to understand time relativity [duplicate]

I am trying to understand intuitively why time slows down as speed increases. I have watched many pseudo-documentaries explaining the concept, but I cannot get at the core of the explanation. The ...
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2answers
96 views

Rational for the Principle of Relativity [closed]

When Galileo postulated his principle of relativity, it seems like quite a logical assumption. After all, velocities combine cleanly, and everyday observation seems to show that the laws of physics on ...
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2answers
685 views

How will the Twin Paradox become, for Time Dilation, if no acceleration was ever involved?

I think one catch in Twin Paradox was about the big acceleration that can turn back the traveling twin from light speed outward bound, to become light speed inward bound. What if there is strictly no ...
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1answer
29 views

Transmit / receive frequency differences from ground to satellites due to relativity

Clocks on GPS satellites run faster than on the surface due to relativity and must be periodically corrected to compensate (i.e. we definitely observe the difference on the ground). So, if I were ...
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0answers
30 views

Relativity Coordinate transformation of Vector [closed]

I'm taking a first course in General Relativity but I've been struggling with coordinate system transformation. For example, if I have a Vector defined in Cartesian (x,y) coordinates as $V_x=x^2+3y$ ...
3
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4answers
168 views

What is a metric? [closed]

I was taking a basic course in general relativity. They introduced a concept of a metric which I wasn't able to understand can somebody explain it to me why do we need a metric in curved spaces?
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3answers
66 views

What is the $ds^2$ notation in relativistic physics?

Could someone please explain me intuitively how $ds^2$ represents distance in relativistic physics?
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3answers
135 views

Newton's gravity vs Einstein's gravity

Hello so if i were to simplify the difference between gravity as seen from Newton and gravity as seen from Einstein, could i say that Einstein's gravity is just adding the fact that gravity does not ...
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1answer
77 views

How much real and how much relative is our universe?

Apologies in advance if my question appears more philosophical than practical. It is indeed philosophy, but a philosophy relating to our scientific understanding of the universe as a whole. Special ...
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2answers
40 views

When e/m varies with velocity, charge is variable

It is found that the e/m ratio of an electron varies with velocity. Current physics assumes that it is mass that is variable with speed. Is there any fundamental reason why it cannot be assumed that ...
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2answers
184 views

Can photons travel through space independent of time?

I read an article about advanced photons and they stated that photons traveled back in time to hit an electron. Can photons really travel back in time and if so, how?
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0answers
38 views

Do relativistic frames imply different realities? [duplicate]

From Einstein's principle of relativity space-time and mass are relative to the frame from which they are being observed. Now would that mean a ball moving at the speed of light wrt to earth would ...
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4answers
5k views

Does velocity or acceleration cause time dilation?

What causes time dilation? Acceleration or velocity? I've seen multiple comments on this forum that assert velocity is the cause, but that doesn't seem right to me. You can't have velocity without ...