The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.

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Einstein's first postulate implies the second?

Einstein's two postulates of special relativity are as follows, 1. The principle of relativity: The laws of physics are the same in all inertial systems. There is no way to detect absolute ...
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Do GR and SR have to be considered together to determine time dilation? [duplicate]

In another related question: How to connect Einstein's Special Relativity(SR) with General Relativity(GR)? , John Rennie stated that SR is a subset (or rather can be derived from) GR, but not vice ...
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What is the relativistic mass of this spinning ball? [closed]

Relativistic Mass is: $$ m_r = \frac{m}{\sqrt{1 - v^2/c^2}} $$ So Einstein says that the faster an object moves, the more mass it gains (relativistic mass). So suppose you have a spherical ball ...
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Are some events simultaneous in all reference frames? (Einstein goes drinkin')

If simultaneity is not a universal characteristic (eg. events are not simultaneous in all reference frames), then why do some events seem to be simultaneous in all reference frames as in the following ...
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Recoil velocity and mass of particle after absorbing photon

I'm working a problem out of d'Inverno's "Introducing Einstein's Relativity", and I'm hitting a funny issue with my algebra. The problem states: An atom of rest mass $m_0$ is at rest in a ...
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Does Bell's theorem sort out local field theories?

For example the Maxwell's equations is a local theory. It's a set of differential equations that describe how should the state at a point change based on its neighbourhood. Counter example: Newtonian ...
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How is the special theory of relativity observed for these types of clocks?

I'm trying to understand Special Theory of Relativity through reading Feynman's lectures. In chapter 15 Feynman gives example of clock: rod of 1m length with mirrors at the ends. Light goes from ...
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54 views

How can we travel back to time if we go with a speed $>> c$? [duplicate]

I have read "If something attains the speed more than that of light then it can travel back to time." I want to know how it happens. Also, in relativity why can nothing acquire velocity beyond ...
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If $v_{a \dot{b}}$ transforms like a four-vector, what does $v_{a}^{\dot{b}}$ describe?

The $( \frac{1}{2}, 0)$ representation of the Lorentz group acts on left-chiral spinors $\chi_a$, the $( 0,\frac{1}{2} )$ representation on right-chiral spinors $\chi^{\dot a}$. The $( \frac{1}{2}, ...
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Proving property of lorentz transforms

I've been trying to learn relativity from Weinberg's Gravitation and Cosmology without very good knowledge of the mathematical background. I am developing it alongside, but there is one particular ...
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84 views

Conservation of relativistic momentum

I'm trying to prove that momentum, $\rho = m \, v \, \gamma(v)$, is conserved in all frames of reference. I'm having problems with the following situation that I made; momentum is not conserved to ...
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Confusion about proper time in special relativity

I have a problem understanding what proper time really means, well actually, it's the symmetry that confuses me... Suppose for convenience that particle A has a mean life-time of 10 seconds in its own ...
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Why does moving near light speed keep you young? [duplicate]

As was shown in the movie Interstellar, when you go close to a black hole or move near the speed of light in space, then your clock runs slower than a clock on Earth. In the movie, Matthew ...
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392 views

Mass in special relativity?

Is the mass of a object at rest defined by $$E=mc^2$$ where $m$ is the rest mass. I.e. does the rest mass include every thing from thermal to gravitational potential energy and every other possible ...
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In special relativity what is the energy of a macroscopic body?

Is the energy of a macroscopic body in special relativity still given by: $E=\gamma m c^2$? If so why do we not need to consider the motion of the individual particles that make it up? Is this because ...
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What is a homogeneous and isotropic frame of reference?

I have heard that inertial frames of reference in the context of special relativity are both isotropic and homogeneous. I know what isotropic and homogeneous mean in a general context, but what do ...
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The mas-energy equivalence for rest mass

It is clear that the kinetic energy can be derived as $(m-m_0)c^2$. However, why do we say that $m_0c^2$ is the rest mass energy? It seems that this mass-energy equivalence for rest mass is just a ...
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Pair production and energy conservation?

Consider the question whether a photon can decay, in the free space, into an electron and a positron - a pair production event. Such an event I don't think is possible, because both energy and ...
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67 views

Special Relativity Explanation [duplicate]

I'm in a relatively basic Physics class in university, and was reading the section in my textbook about The Principle of Relativity. It says: Einstein's Theory of Relativity ... added the ...
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Does my explanation of relativity have any validity?

I've been trying to explain relativity to myself by developing a model based upon small finite changes along one dimension. For me, as a computer programmer, this model works well as an explanation ...
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Why can a particle have a nonzero amplitude outside its forward light-cone?

I'm having trouble grasping an idea that I think that is a very basic part of  quantum field theory. Many introductory QFT resources I have consulted often pose the following question: What is ...
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Trying to understand one of Einstein's thought experiments

I try to understand Einstein's Relativity: The Special and the General Theory, chapter IX., "The Relativity of Simultaneity". Here's an online version: http://www.bartleby.com/173/9.html. ...
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Why is special relativity so special? [duplicate]

The title says it really. Why is special relativity so special? I'm just curious as to how and why the term 'special' came to describe the theory of relativity where gravitational forces are ...
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Is Minkowski space usually a vector space or an affine space?

When I visited Wikipedia's page on Minkowski space, it seemed to offer two definitions. The first defined Minkowski space a vector space. Then, in a later section, it says The section above ...
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Is a non-accelerating object far from a gravity source moving at the speed of light through time?

I'm trying to understand the Minkowski spacetime better. If an object is not undergoing acceleration, and is far from any large mass, does it travel maximally "fast" through time? Can we calculate a ...
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Why does relativistic kinetic energy (KE) equal to the total relativistic energy minus the rest mass energy?

OK, I understand why $KE=\gamma mc^2-mc^2$, but why is it also equal to $E-E_0$?
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Successive measurment of incompatible variables on an entangled state

Suppose I have 2 particles in an entangled state with opposite spins far away from each other, both stationary with respect to the lab. At time t=0 I measure the spin of both particles in the x ...
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Muon decay why proper length in the earth frame?

Consider the two diagrams below (ignore the velocities), Consider the situation in the right hand picture where we have a rod connected to the earth. Let us now say that the muon is created at the ...
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Time difference between two moving inertial frames of reference [closed]

This is a question I am trying to solve: Let S and S' be two inertial frames of reference and S' is moving relative to S at a velocity of 0.6c. When x = x' = 0, t = t' = 0. At t = 2 x 10-7 s, an ...
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Photon energies after neutral pion decay

I am trying to find the photon energies of the decay $\pi_0 \rightarrow \gamma\gamma$ and their dependence on the pion energy $E_{\pi}$, its initial velocity $\beta$ and the scattering angle between ...
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327 views

The cap on massive particles's speed is below the speed of light due to Planck length?

This answer http://worldbuilding.stackexchange.com/a/8525/1991 claims that no particle can accelerate further after its de Broglie wavelength becomes Planck length. Given that speed at this point is ...
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Two particle collision - excited particle emits photon absorbed by the other particle

Part (a) Doing everything in the lab frame: 4-vector before collision: $(Mc,0)$ Let $E$ be energy of photon emitted, p be momentum of de-excited particle. 4-vector after collision: ...
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Why does the Michleson-Morley experiment only contradict the aether?

This question is related to Validity of Maxwell's equations with no aether or relativity? (so please read this first). In this question, the answers seem to suggest that getting rid of the aether ...
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Special relativity and the electromagnetic field tensor [closed]

Ok, I've got an exam for general relativity in the next week and I'm working through a (special) relativity problem at the moment and I just cant seem to get the solution indicated at all and was ...
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why do x Schwarzschild radii equal time dilation effects of speed of light going y times faster than an object^2?

let me walk you through the math. First you start with the gravitational time dilation formula where: $$ T_1=T\sqrt{1-\frac{2GM}{rc^2}} $$ and rather than entering $r$ for the radius we replace $r$ ...
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Possible Answer To The Double-Slit Experiment [closed]

I think I might have figured the double-slit experiment out. I am not going to explain it here, Google it if you don't know it. If I am wrong please tell me why: Matter are relative to observers ...
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How does a frame of reference work in relativity? [duplicate]

I am struggling to understand what frame of reference means in relativity. Imagine the twin scenario. Twin A is at rest, while twin B travels somewhere and back at near the speed of light. If one ...
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Why does the speed of light totally prevent instantaneous information exchange?

Based on the classical light-cone approach it's easy to see you can't transmit information faster than $c$ but why does the speed of light (as far as I know) treat information transmission in this way ...
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Does coordinate time have physical meaning?

I have always been a little confused by the meaning of the "$t$" which appears in spacetime intervals or metrics in general relativity. I concluded that $t$ was just a mathematical thing which allow ...
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Michelson-Morley experiment revisited under the light of special relativity

Taking into account the composition of speeds in special relativity, lets suppose that a Michelson-Morley interferometer is moving at a speed of $\vec{v}$: the speed of Earth relative to the local ...
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Do charges attractions cause time dilation? [duplicate]

I was pondering whether charges will cause time dilatation? Let me explain more, well we know that gravity causes time-dilatation because of gravitational acceleration which is equal to: $$a = ...
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Time Dilation Back to Original Frame is Inconsistent?

I am watching someone jog at nearly the speed of light, and they snap their fingers. In my frame (A), it takes $\Delta t$ seconds. Using $\Delta \bar{t}=\frac{\Delta t}{\gamma}$ to bring you from ...
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What is the slowest possible speed?

According to special relativity, nothing can go faster than the speed of light, and nothing can be distinguished to be in a state of absolute rest. So it makes me wonder: is there a slowest ...
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What would an relativistically expanding sphere look like for an external observer?

Consider a reflecting sphere, whose radius is increasing at constant rate V close to light speed. What would the collision look like for a remote observer stationary relative to the centre of the ...
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Why is the speed of light in vacuum constant? [duplicate]

Are there any proof of the speed of light in vacuum being constant? All I hear is that light in vacuum travels at a constant speed because that's an observation and that it fits in a coherent theory ...
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1answer
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Calculating time dilation for photon traveling towards a moving spaceship

Suppose a spaceship is moving away from the Earth at $0.5c$. When the spaceship is one light-year away from Earth, an observer on Earth sends a photon toward the spaceship. According to the observer ...
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Non-reciprocal time dilation

Is this report describing Absolute Lorentz Transformation legitimate or pseudoscience? The reporting sounds like the kinds of things I see in newbie's questions on the twin paradox, or crackpot ...
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What does the temperature of the early universe tell me?

I am re-reading Weinberg's book "The First Three Minutes". In the Introduction he makes this statement: "At about one-hundreth of a second, the earliest time about which we can speak with any ...
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Does the stationary object deform more than the moving one after a collision?

Given two identical clay disks on an air track, one is stationary and another is moving at "high" speed. After colliding, does the stationary disk deform more than the moving one? If it matters, the ...
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Why can you treat coordinates as vector in flat spacetime?

In a manifold there is a distinction between points and vectors, but in flat spacetime this seems to disappear. For example in Minkowski spacetime you can define a coordinate 4-vector ...