The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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Points in Spacetime
Assume there are two points in spacetime $a=(t,x,y,z)$ and $a'=(t',x',y',z')$. Let's say that the first one is in the origin of spacetime i.e. $a=(0,0,0,0)$. The point $a'$ has two possibilities
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3answers
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Violation of Newton's 3rd law
I'm just expressing my guess.
Let two particles A and B experiences forces $F_1$ and -$F_2$ between them and let guess also there are two observer, one is stationary and other is moving with ...
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0answers
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1D Kinematics - Relative Motion involving non-inertial frames of reference
I recently came across a question involving non-inertial frames of reference. I didn't quite understand the way it had been solved due to some conceptual confusion regarding certain deductions made to ...
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3answers
150 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 ...
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5answers
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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 ...
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48 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 ...
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2answers
100 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 ...
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0answers
32 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 ...
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2answers
96 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 ...
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1answer
38 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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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 ...
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1answer
125 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 ...
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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 ...
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1answer
59 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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1answer
66 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 ...
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1answer
80 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 ...
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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 ...
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0answers
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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 ...
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2answers
52 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 ...
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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 ...
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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 ...
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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 ...
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0answers
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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 ...
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2answers
98 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 ...
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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 ...
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2answers
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“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 ...
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1answer
86 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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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 ...
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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 ...
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6answers
180 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 ...
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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 ...
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1answer
104 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 ...
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1answer
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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 ...
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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 ...
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3answers
310 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 ...
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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 ...
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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 ...
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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 ...
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4answers
562 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 ...
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1answer
180 views
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 ...
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6answers
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Why are distant galaxies not actually tiny bits of matter?
Distant galaxies are said to be moving away from the Milky Way (and us) at speeds approaching the speed of light. Since Special Relativity tells us that any object moving away from us at a velocity of ...
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1answer
58 views
Are branes in 4D-spacetime moving, or are they static?
Given that a worldline, worldsheet, worldvolume, are representation in a 4D-spacetime of a point particle, a string or a brane, respectively, I was wondering if those objects necessarily have to be ...
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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 ...
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1answer
192 views
Which kinds of Physics laws do and don't comply with the principle of relativity?
In Physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference.
However, according to this and ...
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2answers
199 views
Am I faster than my shadow?
I guess that everything that happens to me (or I do), happens before my shadow "records" the information. Is that right? Is it the same for any observer?
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2answers
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Cascade in relativistic turbulence
The Kolmogorov theory of turbulence indicates an energy cascade in turbulence. Is there a corresponding version of relativistic fluid?
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2answers
179 views
Blue-shifting as opposed to violet-shifting
A recent XKCD comic implies that the sky is blue as opposed to violet due to human physiology, and that animals more sensitive to shorter wavelengths will perceive the Earth's sky as the shortest ...
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1answer
133 views
Why is energy-momentum 4-vector so much easier to explore/observe than spacetime 4-vector
I have read that spacetime 4-vector is quite difficult to observe/explore and that energy-momentum 4-vector is much more appropriate for CERN etc.
Why is that? Could anyone give me a brief ...
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2answers
163 views
Relativistic Hamiltonian Formulations [duplicate]
Possible Duplicate:
Hamiltonian mechanics and special relativity?
The Hamiltonian formulation is beautifully symmetric. It's a shame that the explicit time derivatives in Hamilton's ...
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4answers
170 views
Is there a default notation for 4-vectors while handwriting?
In printed paper 3-vectors can be denoted bold italic while 4-vectors can be denote just bold.
While handwriting 3-vectors are denoted by arrows above letters.
Is there a similar way to denote ...
