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

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The Lorentz Transformations in the Micro-World

Two particles[or micro-observers] A and B are in relative uniform motion wrt each other in the x-x’ direction. The “observer” A decides to deduce[or interpret] the Lorentz Transformations wrt to B. ...
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287 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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236 views

Are objects in a gravitational well shortened?

Bob is in a gravitational potential well, he moves a long vertical stick up and down a distance of 1 meters. Alice observes the upper end of the stick, at upper location. There is the phenomenon of ...
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Why has the ether been disregarded as a valid medium through which light can propagate? [duplicate]

Possible Duplicate: Ether theory acceptance Although the Einstein's theory of relativity seemed to make the concept of an ether obsolete, did it necessarily invalidate it? Are there any ...
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190 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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frames of reference [duplicate]

Possible Duplicate: Help Me Gain an Intuitive Understanding of Lorentz Contraction Frames k and k' are inertial frames. Frame k' is moving at a velocity of magnitude v relative to frame k ...
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452 views

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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4answers
484 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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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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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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Paradox?: What is the form of radiation experienced by a harmonically accelerated observer?

Theory predicts that uniform acceleration leads to experiencing thermal radiation (so called Fulling Davies Unruh radiation), associated with the appearance of an event horizon. For non uniform but ...
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Relativity and predictability

My old theoretical physics professor used to say that (already) (special?) relativity shows that "the future is not predictable". Any ideas how this should be interpreted?
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536 views

Time traveling and Time dilation within a multiplayer videogame [closed]

First thing first, I'm looking to implement this within a multiplayer videogame as a "special" skill or powerup, but, I'm willing to build it upon a physics based explanation/theory. The question may ...
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274 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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142 views

Showing that a given matrix provides the desired Lorentz transformation

I am working on problem 5.12 in Halzen and Martin’s Quarks and Leptons. We are asked to show that the matrix $$ S = 1 - \frac{i}{4} \sigma_{\mu \nu} \varepsilon^{\mu \nu} $$ represents the ...
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204 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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How are accelerated reference frames non-symmetrical?

As in, if I'm accelerating away from the Earth, then does the Earth also appear to be accelerating away from me at the same rate? Or is there something to "break" this type of symmetry? My question ...
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2answers
967 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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750 views

Special Relativistic Time Dilation — A computer in a very fast centrifuge

Ok, I've stumbled onto what I think is a bit of a paradox. First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on ...
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383 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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561 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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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
2k 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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446 views

Length contraction in rotating frame?

If an observer were to rotate around a point at near light speeds, what sort of length contraction would he observe the universe undergo?
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172 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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105 views

Can space-like fields not commute and still forbid faster-than-light signalling? [duplicate]

Possible Duplicate: Is microcausality necessary for no-signaling? If we try to measure two non-commuting observables, only the earlier measurement would be valid. The later measurement ...
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1answer
471 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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Quaternions and 4-vectors

I recently realised that quaternions could be used to write intervals or norms of vectors in special relativity: $(t,ix,jy,kz)^2 = t^2 + (ix)^2 + (jy)^2 + (kz)^2 = t^2 - x^2 - y^2 - z^2$ Is it ...
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Why are four-vectors needed in the Dirac equation, when there are 4 linearly independent 2D matrices?

I was taught that for the Dirac-equation to "work", you need matrices of the following form: $Tr(\alpha^i) = 0$. Eigenvalues +1 or -1 2 previous points together: equal number of negative and ...
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729 views

Is there a relativistic (quantum) thermodynamics?

Does a relativistic version of quantum thermodynamics exist? I.e. in a non-inertial frame of reference, can I, an external observer, calculate quantities like magnetisation within the non-inertial ...
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403 views

Time Dilation - what happens when you bring the observers back together?

I'm having trouble getting my head around the time dilation paradox. Observer A and B are at the same "depth" in a gravity well. Observer B then descends into the well. A will observe B's time as ...
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660 views

Special Relativistic approximation to GR

Some time ago I was talking to a professor in college about some of the fundamental aspects and origin of General Relativity. I was surprised to learn, in fact, that a pretty good approximation to GR ...
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325 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 ...