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

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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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190 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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148 views

Will a relativistic rocket be destroyed by incident photons?

I have read, that as a rocket approaches light speed, objects in front of it become blue shifted and also intensity of light increases. Does this mean that at some point any rocket will be destroyed, ...
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274 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 ...
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3answers
196 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 ...
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2answers
334 views

If I travel close to the speed of light and come back, why is everyone else dead, and not me? [duplicate]

Consider the following scenario: I get in a spaceship, and travel really close to the speed of light for a while, and then come back. A lot of time has passed on the Earth, but since I was traveling ...
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262 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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2answers
107 views

Light & Observer moving perpendicular to each other

Light is the yellow arrow. Observer is the black arrow. Observer is moving at a constant speed of v, w.r.t to a Galilean frame of reference. Now from the point of view of the observer (O), how ...
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4answers
546 views

Why acceleration is not relative in General Relativity?

I was thinking of it, If I say: "I'm moving at a velocity $v_1$ relative to a reference frame $M$ then the acceleration will be the derivative of $v_1$ relative to the reference frame $M$." In other ...
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66 views

The speed of light as it approaches a massive body

No matter how fast you go, you will aways perceive the speed of light as constant. Taking that as a fact, the special relativity theory was formulated. Now, for what I understand about general ...
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1answer
152 views

Question about gravity in 1 dimension

Consider 2 pointmasses in 1D space. More specific ; object $A$ with mass $m_a$ and object $B$ with mass $m_b$. $A$ and $B$ are a distance $d$ away from eachother. Let these pointmasses $A,B$ have no ...
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434 views

Relation between coordinates and frames of reference

I always get a little uneasy that all the theories I can think of (at least since Newton) are constructed in a way such that they would be true in heaven and on earth ... but we can never go ...
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438 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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88 views

Is a particular force different in different frames

Can a particular real force have different magnitude in different frames?
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1answer
313 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
111 views

How is relativistic N-body simulation possible without knowing the entire histories of each particle?

In n-body simulation you need to know the positions of the particles in order to calculate the force between them. The new velocity of each particle can then be calculated given a simulation timestep ...
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97 views

Why does Relativity effect the melting point of mercury?

I know there is a related question, that references the Dirac Equation, that relies on relativity, but I've just watched this video: http://www.youtube.com/watch?v=NtnsHtYYKf0 Which seems to say ...
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2answers
171 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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825 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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What prevents an orbiting object from getting a speed which is greater than $c$? [duplicate]

Consider an object orbiting around a point with radius $r$ and angular velocity $\omega$. Here its linear velocity is $v=\omega r$. If we choose a large enough $r$ and reasonable $\omega$, $v$ might ...
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4answers
457 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
529 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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1answer
440 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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5answers
405 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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2answers
307 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
177 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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936 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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855 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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89 views

Speed cannot be greater than speed of light. How about acceleration? Does it have limit?

We know that $c$ is the largest speed in the universe. How about the acceleration, does it has limit?
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2answers
124 views

Doesn't Warp theory violate causality?

I have heard many physicists (ex:- Michio Kaku) saying "Warp speed" from Star Trek doesn't violate any known physical laws. But doesn't it violate causality? Say, we make warp drive possible and ...
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1answer
204 views

Can we live forever by taking advantage of the time dilation effect?

I have been reading about Time dilation and twin paradox in Relativity. So,I thought that if It can be the difference of 10 yrs between the Girl in space and on Earth, then why can't anyone not age ...
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1answer
276 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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1answer
104 views

Lorentz transformation - need a little clarification

So the question states: A's and B's systems are related by the standard Lorentz transform. B simultaneously fires off two photons from transmitters distance D apart along the x' axis, and in the ...
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3answers
164 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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2answers
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Recovering 4-vector Lorentz transformation from spinor formalism

I'm trying to recover the 4-vector transformation laws using spinors. I have defined $$v^{\dot{a}b} = v^{\nu} \sigma_{\nu}^{\dot{a}b}$$ as usual, with $\sigma_0=1$. Now with the rules for dotted ...
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1answer
260 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
112 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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183 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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1answer
48 views

Circular motion and time dialation

Einsteins' time paradox was shown when two atomic clocks were synchronized and one was sent in a super sonic plane and the other kept at rest. When the two where then checked it was shown that yes ...
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2answers
282 views

Does a single electron moving at velocity $v$ have an associated magnetic field, ignoring intrinsic spin?

I have seen explanations of the magnetic field due to an electric current as being due to a Lorentz contraction of the moving electric charges. Would this explanation work for a single electron. There ...
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187 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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403 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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Current state of the existence of absolute space debate [closed]

Samir Okasha writes about the controversy concerning the existence of absolute space in Philosophy of Science: A Very Short Introduction (2002): One of the intriguing things about the ...
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How do we generalize limitations on the propagation speed of sinusoidal waves to limitations for transmitting any kind of information?

Our calculations on EM waves basically deal with harmonic waves and through such calculations and relations, we derive some relations and limitations for wave like phenomena. Of these relations are ...
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0answers
99 views

How to name different approaches to relativistic quantum theory

In the introductory chapter of the QFT book by Mark Srednicki the author notes that [p. 26] So now we have two different approaches to relativistic quantum theory [...] Which [one of those two] we ...
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1answer
351 views

Ephemeris calculations: Light time correction of the moon

I am currently trying to calculate apparent positions from raw JPL data. I've got it pretty much figured out, but there is one thing that's bugging me: Has the light time correction of the moon to be ...
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0answers
157 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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4answers
113 views

How should observers determine whether they can be described as being “defined on a Lorentzian manifold”?

Consider infinitely many distinguishable observers, no two of whom ever meet; and who generally "keep sight of each other", but not necessarily "each keeping sight of all others". How should they ...
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Did relativity make Newtonian mechanics obsolete?

Did Einstein completely prove Newton wrong? If so, why we apply Newtonian mechanics even today? Because Newton said that time is absolute and Einstein suggested it relative? So, if fundamentals are ...
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Can a scalar field model gravity? How accurate would be the results? Are there any difficulties with such a model?

Newtonian gravity can be described by the equation: $$ \nabla^2 \phi = 4 \pi \rho G $$ where $\rho$ is the mass density, $\phi$ is the gravitational potential, and G is the universal gravitational ...