The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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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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2answers
226 views
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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5answers
442 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 ...
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2answers
170 views
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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1answer
333 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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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 ...
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1answer
95 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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9answers
676 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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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
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 ...
6
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4answers
589 views
Help Me Gain an Intuitive Understanding of Lorentz Contraction
I'm having a hard time getting an intuitive understanding of Lorentz Contraction. I understand what it is by definition but I don't 'get it.' I'm not a physicist, just an amateur, so sorry if this ...
6
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3answers
294 views
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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3answers
293 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 ...
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2answers
663 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
539 views
Cross-section in relativistic limit: Fermi's golden rule still valid?
In order to calculate the cross-section of an interaction process the following formula is often used for first approximations:
$$
\sigma = \frac {2\pi} {\hbar\,v_i} \left| ...
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2answers
265 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
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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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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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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1answer
370 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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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
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 ...
0
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0answers
103 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
643 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
326 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
196 views
Why absoluteness of time implies galilean transformations?
In Landau course, vol.1 Mechanics, one finds the statement: "...the absoluteness of time necessarily implies that the ordinary law of composition of velocities is applicable to all phenomena."
I ...
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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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1answer
325 views
Decomposing geodetic/de Sitter effect into Thomas precession and spatial curvature
According to Rindler the geodetic effect can be considered as consisting of Thomas precession combined with the effect of moving through curved space.
Wolfgang Rindler (2006) Relativity: special, ...
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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 ...
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6answers
802 views
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 ...
5
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4answers
784 views
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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5answers
503 views
Time Dilation - How does it know which Frame of Reference to age slower?
Okay, I'm asking a question similar to this one here: Time Dilation - what happens when you bring the observers back together?. Specifically, I am curious about a specific angle on the second part of ...
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4answers
597 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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3answers
517 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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3answers
329 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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0answers
235 views
How to formulate Lorentz invariance without the temporal dimension? [closed]
The role of "time" in fundamental physics has changed a lot in recent decades. Some physcists believe time is an emergent property rather than a most fundamental parameter of nature laws.
However, ...
10
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4answers
987 views
Newton's Bucket
This thought experiment is originally due to Sir Isaac Newton. We have a sphere of water floating freely in an opaque box in intergalactic space, held together by surface tension and not rotating with ...
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3answers
566 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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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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4answers
389 views
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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6answers
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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 ...
