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

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3
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1answer
107 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
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1answer
86 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
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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) ?
0
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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 atoms....
1
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3answers
111 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
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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
51 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.
1
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2answers
119 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
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0answers
50 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 ...
3
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1answer
41 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 ...
2
votes
3answers
81 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 ...
0
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1answer
46 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 haven'...
0
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1answer
54 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
1
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2answers
131 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: $$ ds^2=-(1-\omega^2r^2)dt^2+2r^2\...
1
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1answer
44 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 ...
0
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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 ...
-3
votes
2answers
100 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 ...
1
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1answer
36 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 ...
1
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0answers
31 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 $V_x=x^2+3y$ ...
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 ...
1
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3answers
70 views

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

Could someone please explain me intuitively how $ds^2$ represents distance in relativistic physics?
42
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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 ...
2
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3answers
141 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 ...
0
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2answers
45 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 ...
1
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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
128 views

Is there anything we are aware of that can't be slowed by time dilation?

While thinking about the ambitions of this post: Can radioactivity be slowed through time dilation? I was asking myself, is there even anything that is dependent on time and can't be slowed through ...
0
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1answer
44 views

Light's speed constancy

Trying to understand the special relativity I faced a problem,and have a question, well, with the speed of light being constant in every frame, the operation s=d/t (s for the speed of light d: ...
3
votes
4answers
186 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?
20
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5answers
3k views

Can someone conceptually explain time dilation?

Can someone intuitively explain how physically time dilation happens? Please don't explain about the invariant speed of light and the mathematical background, I am familiar with that. I just can't ...
1
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0answers
27 views

If mass increases as velocity increases, does gravity increase as well? [duplicate]

The way I understand it, velocity and mass are tied together with relativity. As I increase in velocity, I increase my mass until my mass is so great that it would take more energy than the entire ...
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1answer
65 views

What is the benefit of the relativistic effects (time dilation and length contraction)? [closed]

Can an observer ever experience the relativistic effects, or he just can observe them. For an observer these effects happens only on other objects that he observe, but can he realize if he is ...
0
votes
3answers
89 views

Tensor manipulation and showing equality

Im taking GR for the first time and it is definitely throwing me for a loop. The question I am working on is this: Prove that if a contravariant tensor $A^{uv}$ is symmetric, then it remains ...
0
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3answers
90 views

Universe expansion and general relativity [closed]

If the universe is expanding faster and faster, won't we reach a moment where the general relativity will make the mass so big, that the universe will have to decrease its acceleration?
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1answer
67 views

Where would you go to get feedback, advice and assistance for a new theory of physics? [closed]

I know that crackpots are constantly running down physicists to pitch them on a "new theory" that solves everything. This has understandably led to extreme skepticism for anyone not affiliated with a ...
0
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1answer
38 views

Three time dimensions and one spatial dimension degeneracy

Is there a sort of degeneracy in the space-time metric for our universe? What I mean is that it seems you would observe all the same properties of our universe if you simply placed a minus sign in ...
-1
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4answers
72 views

Are there any known non-zero mass objects travelling at almost $c$ observed in the universe so far?

Have we ever observed a body or particle with non zero mass traveling at almost $c$? I'm asking this because according to relativity as an object approaches light speed it's mass approaches infinity, ...
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0answers
46 views

Are objects like $a^{\mu \nu} a_{\mu \nu} b^{\mu \nu}$ consistent with Einstein summation?

I'm familiar with Einstein' summation notation and I understand objects like $a^{\mu \nu} a_{\mu \nu}$ just fine. But I'm wondering why I've never come across objects like this: $a^{\mu \nu} a_{\mu \...
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0answers
29 views

Classical Quantum or Relativistic? [closed]

An ensemble contains free electrons at 10^3 electrons per m^3 at 10^7 K. What can this ensemble be treated as: a Classical Quantum or Relativistic gas or in some overlapping domain?
1
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1answer
85 views

Michelson Morley experiment - why is there an interference pattern in the first place?

In descriptions of the experiment, the two arms of the interferometer have the same length. There's an interference pattern which was expected to be shifted when the system was rotated 90 degrees. But ...
1
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0answers
41 views

What is a Geodetic?

What is a geodetic? First I thought it was a typo (hehehe..). To me, the term "geodetic" is used to describe a curve that belongs to a congruence of geodesics...but, I also think I'm wrong. ...
0
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1answer
55 views

When travelling in the direction of light, what is my relative velocity?

If suppose I am traveling in the same direction as that of light, the relative velocity I am traveling with is speed of light + my speed in the direction of light. Is this correct? Does this have ...
1
vote
1answer
52 views

Is light relative? [duplicate]

I was wondering, if two cars (A and B) are going at different velocities let's say A=90km/h, B=80km/h then if we add the two speeds we get 170km/h meaning they are relative to each other. But if one ...
1
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0answers
35 views

Relativity Mapmaking in spacetime [closed]

The problem as stated: I do not know how I am supposed to map this. The instructions don't make sense to me and the textbook is really un-helpful. This is the map that I have to draw this on. I ...
0
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0answers
36 views

Does a photon arrive at the time it was emitted [duplicate]

I was thinking about the implications of time dilation and wondering if it has an effect on photons. Obviously a photon doesn't age. But is there any other effects on a photon traveling massive ...
0
votes
1answer
196 views

When will Einstein's theories become laws? [closed]

Einstein theories , specifically relativity, have been fascinating us for around 100 years yet with all the real and actual evidence of its validity we still consider it a "theory"..... How much more ...
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0answers
24 views

Topic on relativistic celestial mechanics [closed]

I have to do a small 10-15 minutes presentation about celestial mechanics, and I am searching for a topic. As a mathematician my background in physics is not very extensive, but I have some notions ...
0
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2answers
187 views

Does relativity violate uncertainty principle?

Let us say I sit on an electron. According to me the electron is at rest. Also, I will know the position of the electron accurately as I can take the electron as the origin. So, I know both position ...
2
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3answers
163 views

Is gravity Lorentz-invariant?

If I go whizzing past the Sun in my spaceship at 0.8c, I will see that the Sun looks like it has been squished. That is, it will be Lorentz-contracted along the direction of my motion (by a factor of ...
0
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1answer
49 views

Is the matrix representation of the Lorentz transform the same for all 4-vectors?

If I have a four vector of the form: $$ \left( \begin{array}{ccc} T\\ \vec{X}\end{array} \right) $$ where $T$ is the analogous time component (i.e. energy, angular frequency, scalar potential, charge ...