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

learn more… | top users | synonyms

2
votes
1answer
89 views

Does Heat Cause Time Dilation?

Since heat is defined as the movement of molecules, and because of relativity time slows for faster moving objects, would a hot object be in a slower time frame then a cooler object, because the hot ...
-1
votes
0answers
26 views

Frame dragging VS Mach's principle: rotating body in an empty universe

What I understand about Mach's principle VS modern physics: According to classical physics, there are ways to distinguish weather a body is rotating or not. For example if it is rotating, the ...
4
votes
4answers
3k views

Space-like and time-like: where do the names come from?

Space-like separated events are events that, in a well-chosen reference frame, can take place at the same time but never happen at the same location. On the other hand for time-like events, one can ...
0
votes
1answer
38 views

The relativity of all motion [on hold]

From a basic text on special and general relativity, I've gleaned that accelerated motion provided Einstein a headache initially because it seemed like his principle of relativity- that all motion ...
-12
votes
1answer
108 views

After proving that the photon remains stationary in the fourth dimension, must we conclude that the fourth dimension is moving at c? [on hold]

Firstoff, in his general relativity Einstein showed that dimensions could bend, curve, and move. This is an experimentally proven fact. Dimensions can, and do, move. In an earlier post we ...
-2
votes
1answer
88 views

According to Einstein & Brian Greene, does the photon remain stationary in the fourth dimension? [duplicate]

According to Einstein and Brian Greene, does it logically follow that the photon remains stationary in the fourth dimension? In An Elegant Universe, Brian Greene writes: “Einstein found that ...
2
votes
3answers
106 views

Would a particle the size of a neutron, if it had enough mass, collapse into a blackhole?

For example, a neutron is a particle that occupies a certain volume. If you pack enough mass into that volume, it would collapse into a black hole (I assume there is not enough mass now). At least if ...
1
vote
1answer
122 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 ...
1
vote
2answers
125 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: $$ ...
1
vote
2answers
68 views

Trouble understanding spacetime and invariant interval

First, how is the invariant interval useful? How can it help us understand things around us in the universe? Second, I know that they changed time into space or better say SPACETIME in order to ...
-1
votes
1answer
25 views

Is the time for light to go a certain distance the same amount of time sped up through relativity?

If you were to stand on the tower of my Lemmon and had an atomic clock that was exactly synchronized with one at tucson, (6734 feet difference) for 24 hours, it was shown to be roughly a 20 nano ...
0
votes
2answers
50 views

How to show invariance using the Maxwell tensor?

I want to show the invariance of $E^2-c^2B^2$ under the Lorentz transformations. The obvious way to do this is to show that $$E^2-c^2B^2=E'^2-c^2B'^2,$$ where $E'$ and $B'$ are the Lorentz ...
4
votes
1answer
78 views

Are all diffusion-like processes described as wave-like in relativity-compatible formulations?

Citing from Wikipedia's article on relativistic heat conduction: For most of the last century, it was recognized that Fourier equation (and its more general Fick's law of diffusion) is in ...
0
votes
2answers
66 views

In relativity, perpendicular motion does not show contraction… Isn't the whole concept lost?

I read in HC Verma's Concept of Physics that a body moving in direction perpendicular to length, doesn't show Length Contraction. And Length Contraction, they said, is to maintain the velocity of ...
0
votes
1answer
131 views

Can a black hole move at speed of light?

Black hole comes in all sizes ranging from microscopic black hole on a quantum scale to supermassive black hole that resides in the center of probably every galaxy. Photon have no rest mass hence they ...
7
votes
3answers
28k views

How is light affected by gravity?

Light is clearly affected by gravity, just think about a black hole, but light supposedly has no mass and gravity only affects objects with mass. On the other hand, if light does have mass then ...
1
vote
1answer
56 views

Finding a physics-made-simple book… A longshot

Years ago I had a book that explained at a high level a college physics 1 course. It touched in gas, light, gravity and relativity. It was about 250 pages, it didn't use very much math and the ...
3
votes
2answers
83 views

Plane wave shift in a differential operator

Does anyone can help me to prove the following equation \begin{equation} e^{-i\vec{k}\cdot\vec{x}}f(\partial_{\mu})e^{i\vec{k}\cdot\vec{x}} = f(\partial_{\mu}+ik_{\mu}) \end{equation} Where ...
18
votes
4answers
2k views

Does a box containing photons have more inertia than an empty box?

A box containing photons gravitates more strongly than an empty box, and thus the equivalence principle dictates that a box containing photons has more inertia than an empty box. The inescapable ...
1
vote
1answer
68 views

Why can an object not reach the speed of light by falling in a gravitational field with constant acceleration?

I recently learned in school that the gravitational potential energy of an object is equal to $mgh$. I also learned that the kinetic energy of an object is $\frac12 mv^2$. If an object falls in a ...
1
vote
1answer
203 views

Time Dilation Question

I know physicists don't often like to hear about "photon's frame of reference", so I apologize in advance :) If the time dilation at the speed on light is infinite, it should mean that if Bob is ...
1
vote
1answer
197 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 ...
8
votes
3answers
652 views

Speed of gravitational waves vs speed of light

I own an educational YouTube channel on physics and astronomy. I am currently working on a gravitational waves video extension to my "How Fast Is It" video book on relativity theory. I have a question ...
0
votes
0answers
21 views

Can deformations of time-space continuum violates law of momentum conservation?

Based on Einstein’s theory of relativity a mass as property of physical objects creates deformation of time-space continuum. Therefore the light path bends in gravitational fields of massive objects. ...
3
votes
1answer
24 views

Orbital Velocity & LLR

As I understand it, light that is emitted from a source is not imparted with the motion of the source and so always follows a "straight line". If this is correct, I am having a difficult time ...
32
votes
4answers
5k views

If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?

I'm a big fan of the podcast Astronomy Cast and a while back I was listening to a Q&A episode they did. A listener sent in a question that I found fascinating and have been wondering about ever ...
-1
votes
2answers
56 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 ...
2
votes
3answers
102 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. ...
1
vote
1answer
134 views

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 ...
1
vote
1answer
26 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?
0
votes
0answers
20 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 ...
0
votes
1answer
45 views

The elevator and the bolt [closed]

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 ...
0
votes
0answers
33 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 ...
2
votes
3answers
165 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 ...
40
votes
5answers
5k views

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 ...
1
vote
0answers
20 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
votes
3answers
167 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 ...
-1
votes
0answers
30 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 ...
0
votes
0answers
21 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 ...
-2
votes
2answers
71 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? ...
0
votes
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 ...
3
votes
1answer
103 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 ...
0
votes
1answer
85 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 ...
0
votes
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) ?
1
vote
3answers
107 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 ...
0
votes
0answers
42 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 ...
-4
votes
1answer
49 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.
4
votes
2answers
617 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 ...
1
vote
2answers
110 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 ...
0
votes
0answers
46 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 ...