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

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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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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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56 views

Is the charge of a current carrying wire real or hypothetical?

Realist753 Theory Relativistic Electrodynamics assert that a current carrying wire being neutral in a laboratory frame of reference appears electrostatically charged to an observer in relative ...
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2k 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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75 views

Minkowski metric and definition of coordinate differentials?

This is probably a really silly confusion I have about the definition of “coordinate differentials”, which I thought were things like $dx,dy,dz$ etc. The Minkowski line element ...
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133 views

Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation?

In discussing this question about propelling a spacecraft with photons and their relativistic momentum, the author asked that I restate my comment as another question. If photons can really be used ...
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4k views

If nothing in the universe can travel faster than light, how come light can't escape a black hole? [duplicate]

Possible Duplicate: How does gravity escape a black hole? If nothing in the universe can travel faster than light, how come light can't escape a black hole? I mean, Einstein's relativity ...
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337 views

length contraction question

we know from eintein's theory of relativity that lets say, a ruler is travelling to a speed if light, then we can say that the ruler (from our view as observers) has shorten. but why, lets say we have ...
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664 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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200 views

On Group Theory: Symmetry Groups and Our Interest

Over the past few years, I've been doing a lot of self education in the Quantum Mechanics and General Relativity, and of course, there are mathematical elements of both doctrines that are matrices. ...
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113 views

Apparent paradox in special relativity: transmitting a message and setting off after it

I have a question about special relativity, which is set in the context of the science fiction anime Voices of a Distant Star, though it is independent of that context. Mikako goes on a spaceship ...
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186 views

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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249 views

What if a normal digital clock used to measure time in twin paradox?

Last night I was watching a youtube video about twin paradox. It still continues to baffle me :). In that video, the speaker conceptualizes a clock that measures time by reflections of light. If we ...
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51 views

Question regarding FTL information transfer between two inertial frames

Why can’t information travel faster than the speed of light, if the two endpoints to and from which the information is being sent are moving relatively to each other, as long as the information ...
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183 views

Is it really “time” that is dilating?

Consider the following variation of the twin paradox: A clock or a biological system ultimately is an electromagnetic system. First, let’s devise a new time measuring device. Imagine a tank of ...
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87 views

Relativistic Time Difference

I thought that it might be interesting to calculate the time difference between a clock placed on Earth when I was born and a hypothetical clock placed at the centre of the sun at the same time. I ...
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45 views

For a rocket travelling to a planet, which reference frame measures the dilated time?

I'm getting into some confusion with relativity. Consider a rocket and the Earth as two observers, and then the rocket travels to a distant star. Is the proper time taken measured in the frame of ...
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3answers
131 views

Why does time slow down the closer you are to a mass?

When ever i look this up all I get is sites saying how its because general relativity says "-" why does it do it though? it is because there is more motion near gravity than further away? Or is it ...
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103 views

What happens if a body free-falls at a certain speed?

It is known that a body falling to the ground is affected by gravity, and its velocity increases by 9.8 m/s per second. But when this body is falling, and it reaches the speed of 340 m/s (the speed of ...
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341 views

What happened to potential energy?

I was learning how charge can be virtue of a body's potential energy.Meanwhile,I was hung by this question. [gravitational and other forces except coulombic,are assumed to be not acting on the ...
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68 views

gamma-gamma collision seen from a relativistic rocket

This is a thought experiment. Consider two photons traveling at right angles and intersecting at some point. As seen from Earth these photons will not interact with each other because their energy is ...
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2answers
210 views

light travels a maximum speed… /? [duplicate]

Possible Duplicate: Is it possible for information to be transmitted faster than light? we know that speed of light is an unconquerable term in physics..light takes about 1 year to travel ...
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2answers
288 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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30 views

Higgs field and the null geodesic

How does coupling to the Higgs field take a particle with a spacetime interval of zero and give it a non-zero value, i.e, how does it move it off the null geodesic? [of course, the Higgs field is ...
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92 views

Doesn't the second postulate of special relativity imply the existence of “luminiferous ether”? [closed]

Einstein expressed his Second Postulate in On the Electrodynamics of Moving Bodies as: light is always propagated in empty space with a definite velocity $c$ which is independent of the state of ...
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155 views

Why does “closing speed” $>c$ not violate relativity's second postulate? [closed]

Why does closing speed $>c$ of a particle and photon or photon and photon not violate relativity's second postulate? Einstein expressed his Second Postulate in On the Electrodynamics of ...
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61 views

can interaction between a massless fermion and external sourse exist?

For example, let's consider the electromagnetic interaction between a massless fermion and a electromagnetic externel sourse $A^\mu$, then the lagrangian is ...
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136 views

Expected result of vertical Michelson-Morley Experiment

What would the result of a vertical variation of the Michelson-Morley experiment be? I.e., if one were to compare light traveling along a horizontal arm with light traveling along a vertical arm ...
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129 views

Mass in terms of special relativity

According to special relativity mass doesnt add up like we think it does. That is, a system of 2 protons might not necessarily have a system mass of 2*(mass of one proton). If the protons are ...
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237 views

Two body particle problem with reduced mass

When we have two bodies and a central force acting towards the center of each other, we could treat the whole problem as a one body problem by introducing the relative coordinate. My question is, when ...
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1answer
192 views

What is the significance of Einsteins postulate on speed of light?

Einstein postulated that the speed of light in free space is the same for all observers, regardless of their motion relative to the light source, where we may think of an observer as an imaginary ...
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2answers
95 views

What would a person *unmoving* look like on a Minkowski diagram?

If you were to draw a person on a Minkowski diagram, that was unmoving (though time was still passing) what would that look like? (As a light cone and ignore the observer.) Also what would it look ...
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3answers
228 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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226 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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112 views

Causal reconnection

Can causally disconnected regions join up again? For example the universe is expanding faster than light creating cosmological horizon, but what if something causes the expansion to slow down and ...
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85 views

“Entangled photons never show interference in the total pattern without coincidence count” implies FTL

In my previous question, the most defended objection to the gedankenexperiment was that "Entangled photons never show interference in the total pattern without coincidence count". Here I show another ...
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107 views

Twin paradox where the twins start at different locations

Suppose we have this scenario with twins A and B: 1) Instead of the twins starting at the same location, let's say the twins start out some distance apart, in the same reference frame. 2) The ...
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2answers
51 views

Time dilation in outer space vs in a gravitational field? [duplicate]

I have been wondering how could aging process differ for a person moving close to velocity of light or for a person close to a very strong gravitational field compared to a person who is in a slow ...
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1answer
26 views

Can we measure a mass increase for a system with more energy?

This question is about whether the mass of a particle increases with its speed. Here is my related question from which this question spawned: Why is there a controversy on whether mass increases with ...
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36 views

Cheating to communicate beyond the horizons in expanding universe?

Let's say the Hubble constant is constant in the time interval we consider. So subjective "horizon" for any object has the same radius R. Let's say Bob and Charlie are just within the horizon of ...
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1answer
39 views

Relativity's effects on centripetal motion [duplicate]

I am wondering if, for a particle moving close to the speed of light (so that we must examine things relativistically rather than classically) does the centripetal force equation $F_c=m\frac{v^2}{r}$ ...
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1answer
101 views

K-factor in special relativity

A sends out a series of flashes of light to B, where the interval between flashes is denoted by T according to A's clock. Then it is plausible to assume that the intervals of reception by B's clock ...
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69 views

A question about a relation between time-like world lines

Given any Lorentzian manifold containing three distinct time-like world lines $L$, $A$ and $B$ such that $L$ and $A$ have exactly one common coincidence event, $\mathcal{E}_{AL}$, $L$ and $B$ have ...
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143 views

How is Momenergy frame independent?

momenergy = mass * spacetime displacement/proper time for that displacement What I dont understand is how can the momenergy be frame independent? The unit-4 vector always points in the direction of ...
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165 views

Symmetries of relativistic Lagrangian and Hamiltonian systems

In non-relativistic mechanics, the conserved quantities found using Noethers theorem in Lagrangian mechanics are the same as those quantities which are conserved under canonical commutation with the ...
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2k 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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1answer
210 views

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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1answer
188 views

Light orbiting a massive body [duplicate]

Possible Duplicate: Can a photon be made to orbit a known (or undiscovered theoretical) body? How massive would a black hole have to be for light to orbit it at 1km away from the ...
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1answer
146 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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29 views

Does a body curve spacetime at higher velocities? [duplicate]

Suppose we have two objects where the distance over time decreases. Now, as I understand it, general relativity says that we can observe the Universe from the perspective of both objects an get a ...