The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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relativity and aberration of light
I am dealing with math and physics only at amateur level and I am writing regarding my question on relativistic aberration of light. Reading "Realtivity and Common Sense" by Hermann Bondi and some ...
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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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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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3answers
699 views
How to calculate time dilation in approaching speed of light
If a spaceship travels close to the speed of light (say, at 0.9c), how do I calculate the time as the spaceship pilot experience it? I thought the formula was
$$t = \frac{t_0}{\sqrt{1-v^2/c^2}}$$
...
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4answers
315 views
Reducing General Relativity to Special Relativity in limiting case
I understand that general relativity is applicable to gravitational fields and special relativity is applicable to case when there is no gravity. But is there a derivation on how to reduce General ...
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2answers
419 views
Nature of spacetime 4-vector and tangent space?
An entry level confusion about spacetime. I understand that a 4-vector describes a point or event in spacetime. But I've also read (Bertschinger, 1999) that re spacetime "we are discussing tangent ...
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3answers
1k views
Difference between timelike and spacelike vectors
Other than one having a positive invariant scalar product and the other a negative one, what are the actual physical differences between these vectors?
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1answer
327 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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2answers
180 views
How do I adjust the kinematic equations to avoid reaching speeds faster than light?
I like some 'science' in my 'science fiction', so I started crunching out the kinematic equations for some of the scenarios my characters are getting involved in, and ran smack dab into an issue. ...
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2answers
162 views
Using Einstein's Relativity: Who is younger?
Suppose we have a person A and a person B.
Person B travels very close to speed of light and never returns. He's constant in speed. Then, we can say two things:
B is younger than A.
A is younger ...
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2answers
665 views
Galilean invariance proof
I'm studying for a physics test, but I think I don't really understand Galilean invariance. In my textbook there is an example in which they proof that if you consider 2 frames S and S' in standard ...
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1answer
647 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 ...
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1answer
212 views
Thought experiment about acceleration
Case 1: two people wake up in spaceships accelerating at 1g. They can measure or observe anything inside the room but not outside. They couldn't determine if they were on a spaceship or on earth. ...
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3answers
148 views
When a high speed neutrino just misses an old neutron star, why isn't it trapped?
Suppose a neutrino is seen travelling so fast that its Lorentz gamma factor is 100,000. It races past an old, no longer active neutron star, narrowly missing it. As far as the neutrino is concerned, ...
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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
69 views
reletivistic mass as seen by different observers
Imagine there are two observers $A$ and $B$ and a particle $P$.
$A$ and $B$ are at about the same point, $P$ is some distance away.
From $A$'s point of view, $P$ has velocity $V$ and $B$ has ...
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2answers
336 views
Mass in terms of energy
Given the relationships between mass and energy in relativity, and given that particles with mass can be created given energy over the threshold energy, and vice-versa, can we say that mass is simply ...
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2answers
151 views
Finding wave-fuctions of a Dirac particle for given 4-momentum and spin 4-vector
I've been reading through various materials on relativistic quantum mechanics, but I find the lack of simple examples disturbing.
I'm acquainted with the general form the solutions to the Dirac ...
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0answers
117 views
How do I extend the Lorentz transformation metric to dimensions>4?
How do I extend the general Lorentz transformation matrix (not just a boost along an axis, but in directions where the dx1/dt, dx2/dt, dx3/dt, components are all not zero. For eg. as on the Wikipedia ...
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9answers
677 views
understanding time: Is time simply the rate change?
Is time simply the rate of change?
If this is the case and time was created during the big bang would it be the case that the closer you get to the start of the big bang the "slower" things change ...
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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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2answers
136 views
What will happen if we use a speed greater than light speed and find a body'motion and energy relative to it?
In Einstein's papers, he used light speed as a reference speed. What if we use a greater finite speed and do the same calculations. Won't this greater speed then be the limit.
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1answer
50 views
Derivation of superluminality in astronomy
Can somebody provide derivation of the relativistic explanation of (apparent) superluminality in astronomy? The derivation on wikipedia seems to be a bit confusing.
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1answer
138 views
Does a light cone look the same from all reference frames?
If there were a light cone centered at some point $P$, and you were to look at that light cone from different reference frames, would it change its shape? I know that points inside and outside the ...
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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 ...
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4answers
263 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
136 views
Is time the property of an object?
I don't know if the title makes much sense, but hopefully it will become clear with the text.
Temperature is not a property of a point in the three dimensions, but actually of the object occupying ...
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2answers
266 views
Where does the minus sign appear from in the metric tensor?
Trying to understand Schutz's AFCIGR, where does the minus sign appear from in the metric tensor?
I understand that this expresses the invariance of the spacetime interval. Schutz says (I think) ...
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2answers
85 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 ...
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1answer
254 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 ...
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2answers
79 views
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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1answer
134 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
140 views
Finding the correct units for the energy-momentum tensor?
I'm trying to understand the energy-momentum tensor $T^{\mu\nu}$ but I'm confused about the units. My textbook says the components of $T^{\mu\nu}$ are $\mathrm{Jm^{-3}}$. Four-momentum is is given ...
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1answer
39 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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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
129 views
What is the mass of individual components in a gravitationally bound system?
When material of rest mass M falls from infinity onto a black hole accretion disk, it gets heated and then emits so much light that the energy radiated away can measure up to about 30% or so of M c^2. ...
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3answers
257 views
How to take into account the reference frames with the revolution and rotation of the Earth in OPERA's superluminal neutrinos?
Since the Earth is moving around the Sun, which is moving around Milky Way, etc... What reference frame is used for the complete motion of the begin/end points (which are non-inertial right?)?
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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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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
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 ...
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1answer
194 views
What is the speed for an object that travel close to the speed of light?
I have some questions regarding Einsteins theory of Relativity that should be fairly easy to answer. Lets say we make an experiment where we have a rocket (with an astronaut inside) that travels very ...
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1answer
58 views
Does relativity apply to something experiencing Centripetal forces?
If I tie a rope to a clock and spin it over my head, would it lose synchronization with a clock sitting at my feet?
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1answer
260 views
Pulsar gravitational binding energy?
A Newtonian homogeneous density sphere has gravitational binding energy in Joules $U = -(3/5)(GM^2)/r$, G=Newton's constant, M=gravitational mass, r=radius, mks. The fraction of binding energy to ...
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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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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
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 ...
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2answers
408 views
Careers in physics that are related to quantum mechanics or relativity?
Personally I learned Physics in high-school and found it very interesting, I read up a lot about physics in my free time.
Personally I am also a programmer which I think is also good when it comes to ...
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0answers
131 views
heliocentricity and the theory of relativity [duplicate]
Possible Duplicate:
Why do we say that the earth moves around the sun?
I should preface by stating that I'm not a physicist and my knowledge of the theory of relativity is limited to what ...
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3answers
982 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 ...
