The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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1answer
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What are the consequences of relativistic angular velocities?
If I take a rod of some radius $r$ and length $L$, and I spin this rod with angular velocity $\omega$. How would the geometry of the rod appear to an observer as one converges to $c$? What are the ...
3
votes
3answers
144 views
How does relativity explain gravity, without assuming gravity [duplicate]
I have seen the "objects pull down on space-time" explanations, but they assume a "pull down" force themselves. Could anyone explain the space-time explanation without assuming gravity in the first ...
0
votes
6answers
176 views
Inertial Frames of Reference - Inertial vs. Accelerated Frames
According to Robert Resnick's book "Introduction to Special Relativity", a line states the following as the definition of an inertial frame of reference: "We define an inertial system as a frame of ...
6
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5answers
174 views
In coordinate-free relativity, how do we define a vector?
Relativity can be developed without coordinates: Laurent 1994 (SR), Winitzski 2007 (GR).
I would normally define a vector by its transformation properties: it's something whose components change ...
2
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1answer
641 views
Question about Time Dilation
I just have a quick question about time dilation/proper time because my physics book makes it a little confusing. Let's say we have an observer on Earth, and then an observer on a space ship. The ...
0
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0answers
47 views
Homework Help Please? [closed]
An electron is accelerated from rest through a voltage drop of .13 MeV, and then travels at constant velocity.
a. How long does it take the electron, after it has reached its final velocity, to ...
3
votes
2answers
98 views
Superluminal particles with causality
What kind of CLASSICAL theories would allow to true (non-apparent) superluminal particles (beyond speed of light, BSOL) agreeing with causality to exist? I mean, are causal superluminal classical ...
6
votes
8answers
698 views
Reactionless Drives
According to the third law of motion, you van't have an mass move in a particular direction unless there is a proportional opposite mass/acceleration ratio in the opposite direction.
No-one has been ...
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votes
2answers
94 views
Repulsion does not exist; Gravity assist slingshot as a repulsive force [closed]
unification theory might say that there is only one force in universe that is called gravity(attraction).
So at atomic level for same charges that repel eachother(electrons etc.), if thought of as a ...
0
votes
1answer
123 views
Why can't we accelerate objects past the speed of light? [duplicate]
Is there any intuitive reasoning behind why there would be this universal speed limit? It just seems so arbitrary. I know that there must be things that are unknown, but what reasoning is there behind ...
1
vote
0answers
29 views
Mercury's Orbital Precession in Special Relativity
I am researching Mercury's orbital precession. I have considered most perturbations and general relativity. I am still not satisfied. I need your help.
I need a solution to Exercise 13, Chapter 6, in ...
13
votes
5answers
441 views
Why can't you escape a black hole?
I understand that the event horizon of a black hole forms at the radius from the singularity where the escape velocity is c. But it's also true that you don't have to go escape velocity to escape an ...
1
vote
1answer
36 views
What is the Lorentz tensor with a superscript and subscript index?
I have been reading about symmetries of systems' actions, e.g. the Polyakov action, and I have encountered Lorentz transformations of the form: $\Lambda^{\mu}_{\nu} X^{\nu}$. I am moderately familiar ...
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votes
6answers
2k views
Is time travel possible? Is it possible to go back in time?
I read somewhere that according to relativity, black holes and other space related stuff it is possible to jump into past.
Is it possible for anything to go back in time either continuously or by ...
9
votes
4answers
1k views
Is time travel possible? [duplicate]
Time travel -- often featured in movies, books, or facetiously in conversation. There are also theories treating time as simply another dimension, which to the layperson might imply forward and ...
3
votes
2answers
69 views
Mirror image at relativistic speeds
Imagine moving parallel to the surface of a very large flat mirror at relativistic speeds. What would be the effect of viewing yourself in the mirror? At non-relativistic speeds your image would be ...
1
vote
1answer
82 views
Could the shadow move with faster-than-light speed? [duplicate]
If I make a huge laser with a figure for shadow in front of the laser, and I shine it on to the moon, will I see the light from the laser AND the shadow moving the same speed? (I read somewhere the ...
2
votes
1answer
57 views
Difference between vector and pseudo-scalar
In physics, a pseudo-scalar is a quantity that behaves like a scalar, except that it changes sign under a parity inversion such as improper rotations while a true scalar does not.
Can someone show me ...
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votes
0answers
36 views
effect of gravity on chemical reaction rates [closed]
a chemical reaction is done on earth in very vacuum and that chemical reaction is also done in space so that gravity higgs field not affect that reaction.
Which reaction will be fast wrt gravity and ...
0
votes
1answer
63 views
Spacetime and Timelike Intervals
The difference between a “timelike” spacetime interval and a “spacelike” spacetime interval can be understood in the following way: If the spacetime interval between two events is timelike, there ...
6
votes
1answer
79 views
Is there a relativity-compatible thermodynamics?
I am just wondering that laws in thermodynamics are not Lorentz invariant, it only involves the $T^{00}$ component. Tolman gave a formalism in his book. For example, the first law is replaced by the ...
-1
votes
0answers
18 views
Finding Velocity for Equal Received Wavelength from Two Moving Objects Emitting Light [closed]
In the diagram below, Spaceship 1 and Spaceship 2 are traveling towards earth from
opposite directions. Both spaceships have headlights which emit light, which, when measured in
the reference ...
0
votes
2answers
46 views
Relativity Problem with Three Reference Frames
I'm having trouble with the understanding on this last problem from my homework set.
Two cars playing demolition derby are moving towards each other with constant velocity,
as measured by ...
0
votes
2answers
51 views
Relativity Problem Given Rest Length and Proper Time
A relativistic train with a rest length of 500.0 m takes 780 ns to pass a stationary observer
standing on the train platform, as measured by the stationary observer.
(a) What is the speed ...
3
votes
3answers
136 views
Having trouble seeing the similarity between these two energy-momentum tensors
Leonard Suskind gives the following formulation of the energy-momentum tensor in his Stanford lectures on GR (#10, I believe):
$$T_{\mu \nu}=\partial_{\mu}\phi \partial_{\nu}\phi-\frac{1}{2}g_{\mu ...
1
vote
0answers
82 views
Weyl's axisymmetric static solution
I'm currently doing a course on general relativity, and I'm struggling with the following exercise - I would greatly appreciate the help anyone might offer. It is as follows:
Weyl's solution to the ...
0
votes
0answers
41 views
Ricci tensor question
Suppose the Ricci tensor $R_{a}^{\;\;b}$, considered as a linear map on $T_{m}M$ at an even $m$, has only real eigenvalues. What are the five possible Jordan forms of $R_{a}^{\;\;b}$? Show that the ...
1
vote
0answers
56 views
Newman-Penrose tetrad question
I have a question/exercise relevant to students of mathematical relativity:
Let $\left \{ l^{a},n^{a},m^{a},\bar{m}^{a} \right \}$ be a Newman-Penrose tetrad, where only the direction of $l^{a}$ is ...
0
votes
2answers
95 views
What is the mass of a photon moving at the speed of light? [duplicate]
What is the mass of a photon moving at the speed of light?
And if it does not have mass, how is it affected by gravity?
Also why does Einstein's general relativity support that a gravitational wave ...
0
votes
0answers
41 views
What is an example of a situation where Quantum Mechanics and Relativity do not work together? [duplicate]
I've learned special relativity in school last semester, and this semester we began learning about Quantum Mechanics, and my teacher told us that there was a Relativistic Schrodinger equation.
I was ...
1
vote
1answer
163 views
Degrees of freedom in the infinite momentum frame
Lenny Susskind explains in this video at about 40min, as an extended object (for example a relativistic string) is boosted to the infinite momentum frame (sometimes called light cone frame), it has no ...
6
votes
7answers
1k views
How does Newtonian gravitation conflict with special relativity?
In the Wikipedia article Classical Field Theory (Gravitation), it says
After Newtonian gravitation was found to be inconsistent with special relativity, . . .
I don't see how Newtonian ...
1
vote
2answers
83 views
“as measured in a local Lorentz frame”?
I've seen the phrase "as measured in a local Lorentz frame" tagged on the end of so many sentences.
What does it mean precisely?
To give an explanation with an example, consider the context of ...
1
vote
1answer
85 views
How much time has passed for Voyager I since it left the Earth, 34 years ago?
34 years have passed since Voyager I took off and it's just crossing the solar system, being approximately at 16.4 light-hours away. How much time have passed for itself, though?
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votes
0answers
37 views
Need help with relativistic dynamics
I understand the concept, but I'm having a hard time applying the consequences of conservation (energy/momentum). For example:
A proton with kinetic energy 437 MeV hits a proton at rest elastically ...
0
votes
0answers
16 views
Period of Transmission of signals in different frames
A radar transmitter (T) is fixed to a system $S_{2}$ which is moving to the right with speed v relative to system $S_{1}$. A timer in $S_{2}$, having a period $\tau_{0}$ (measured in $S_{2}$) causes ...
1
vote
1answer
74 views
Could light travel more slowly than the “universal speed limit”? Could this imply quantization of spacetime?
One description of relativistic effects that I've heard/read goes something like this:
Everything moves through spacetime at a constant speed. An object's direction of travel through spacetime can ...
3
votes
1answer
172 views
Is a preferred reference frame of the universe the old aether?
About two years ago I posted a question about a symmetrical twin paradox: Here.
Recently a new answer was posted and an intense discussion ensued: Here.
One of the points discussed concerns a ...
-1
votes
1answer
98 views
How do photons experience time? [duplicate]
I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below.
1)So I want to know how time is perceived from the point of view of the photon?
2)Since ...
0
votes
1answer
93 views
Deriving infinitesimal time dilation for arbitrary motion from Lorentz transformations
I'm trying to derive the infinitesimal time dilation relation $dt = \gamma d\tau$, where $\tau$ is the proper time, $t$ the coordinate time, and $\gamma = (1-v(t)^2/c^2)^{-1/2}$ the time dependent ...
0
votes
3answers
102 views
Black hole accretion of dark energy
Dark energy physically can be interpreted as either a fluid with positive mass but pressure the negative of its density (pressure has units of energy/volume, and energy is mass), or a property of ...
6
votes
2answers
145 views
Do the energy levels of electron orbitals change relativistically?
When an electron emits a photon from changing energy levels, the frequency of the photon depends on the difference between the energy levels.
But if someone is moving with respect to the atom, the ...
12
votes
2answers
122 views
Cascade in relativistic turbulence
The Kolmogorov theory of turbulence indicates an energy cascade in turbulence. Is there a corresponding version of relativistic fluid?
3
votes
3answers
308 views
Why do clocks measure arc-length?
Apologies in advance for the long question.
My understanding is that in GR, massive observers move along timelike curves $x^\mu(\lambda)$, and if an observer moves from point $x^\mu(\lambda_a)$ to ...
1
vote
1answer
253 views
Time travel to future [duplicate]
Possible Duplicate:
Is time travel possible?
Is time travel possible? According to my friend, it is possible to go to the future but not the past.
In Physics, particles move faster than ...
0
votes
0answers
52 views
A Mathematician Who Wants to Learn Particle Physics [duplicate]
Possible Duplicate:
Book recommendations
I'm a grad student in pure math, wrapping up a thesis in Lie theory. After years of talking to mathematicians and physicists, I've decided that it's ...
0
votes
2answers
191 views
Photons in a gravitational field
I have been really staring for a while in a MP-Beiser book and I totally disagree with a statement he does there. On a page 85 he states that photons act as they have a mass $m$. He derives this by ...
8
votes
4answers
559 views
Does the future already exist? If so, which one?
In the NOVA Fabric of the Cosmos program, Brian Greene explains a theory in which there is no "now", or more specifically, now is relative. He describes an alien riding a bicycle on a far off planet ...
6
votes
3answers
292 views
Getting back out of an Alcubierre warp bubble
Does the theory on paper provide a way for hypothetical travelers to get back out of the bubble that has gotten them close to their distant destination by compressing all the space in front of them ...
1
vote
1answer
109 views
How to relate photon's higher frequency to time dilation?
The usual explanation for photon's higher frequency in lower altitudes (higher gravity), when the photon is going downward towards a massive body, is that gravitational potential energy is converted ...
