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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Two spaceships are accelerating equally, uniformly on exactly parallel tracks. Does a rope suspended between them eventually rip?

This question is a variant of "Bell's spaceships problem". Rather than one spaceship following the other "on the same track", let the two spaceships accelerate "side by side", on exactly parallel ...
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Averaged energies in particle collisions

Let's have (in CM frame) process $x + y \to x + y + z$, where $x, y, z$ correspond to (in general) different particles with non-zero masses. The total energy of process is $E$. How to calculate ...
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Rest masses, binding energy - mechanism for negative mass

Let us have an two objects (in a box) both of mass $m_0$ far from each other. They attract each other and at some moment their distance is close and they have substantial kinetic energy. Something ...
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Is FTL communication compatible with Lorentz ether theory?

I have come to understand, that faster-than-light communication is problematic with special relativity, because it leads to the possibility of sending signals into the past. I also read about the ...
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$V_{\rm ball}=V_{\rm train}+V_{\rm ball}$?

30 years after reading Einstein's books I'm having another go at understanding astrophysics, but one thing I didn't understand back then still doesn't make sense to me. It is the example of a ball ...
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Travelling at the speed of light [closed]

more of a philosophical questions normally if you are travelling at some speed and you bump into some object, you generally would get slowed down and the force from your acceleration would be ...
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1answer
213 views

Phase velocity greater then the speed of light?

It is my understanding the the phase velocity of a wave can be greater then the speed of light. So imagine we had a wave packet consisting of a single sinusoidal wave; $$y=sin(\omega t-kx)$$ Then ...
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5answers
527 views

Can we change a photon's frequency in mid-air?

Can we have a light source emitting photons in the infrared range and after, lets say, 5 meters, these photons become a photon in the x-ray range? The only way I know we can change a photon's ...
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4answers
488 views

What is the universal speed limit relative to? [duplicate]

If all speeds are relative, then what "governing" force is that speed limit relative to? Is there some sort of fixed or absolute grid with locations everything is compared to? Does this also mean ...
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Is it possible to stop time? [duplicate]

Assuming the spacetime principle, if the space is modified the time does too. So if the velocity in the space is increase, does the time slow down? What happens if the speed is the speed of light, ...
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Special relativity: can the velocity of a free object be discontinuous relative to an accelerated observer who stops accelerating?

Suppose an observer ${\it {\mathcal O}}$ leaves point O*, origin of the Minkowski frame K*, in the $O^{*}x^{*} $ direction, with a uniform acceleration $a_{0} $ (as measured by himself) ...
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90 views

Relativistic addition of velocities in the y-direction? [closed]

I've been having some difficulty with the problem described below, please have a look: Two particles with identical masses (m) undergo a collision. Before the collision they move with velocities ...
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50 views

Length contraction alongside acceleration

Let's have a ship, a target and a ship traveler which we use as point of view. Assuming no other object are observed and we are so far from any other object that gravity distortion are negligible, I'm ...
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2answers
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Behavior of mass approaching the speed of light

I would like some clarification on the behavior of relativistic mass as it approaches the speed of light. I am a high school student with an interest in physics so chances are I will have a hard time ...
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1answer
48 views

Simultaneous observations in relativity

Consider an object which responds to two different signals A and B: it responds to signal A with blue color and signal B with red color. Also, it responds only to the signal that reached first. In ...
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40 views

The limited Computing Capabilities of Space, Increased quantized info leads to time-dilation?

Are there any approaches to Special and General Relativity using space as a computing medium? With space having a maximum computing capability and time dilation as lag? Could this idea describe the ...
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2answers
86 views

Minkowski Diagram for Time-Like Separated Events

A while ago, I asked a question if two events are always simultaneous in some reference frame. I received excellent answers. The point is that if $E_1$ and $E_2$ are time-like separated with time ...
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3answers
117 views

Doppler shift and special relativity

I have been listening to an audio course on Special Relativity. In the course the teacher repeatedly says that the "laws of physics are equally valid for all uniformly moving frames of reference". ...
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2answers
246 views

Proving the Lorentz invariance of the Lorentz invariant phase space element

I have been looking around for a satisfactory answer to prove that $$\frac{d^3\vec{p}}{2E_{\vec{p}}}$$ where $E_{\vec{p}}=+\sqrt{(|\vec{p}|c)^2+(mc^2)^2}$, is Lorentz invariant. The standard answer ...
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How did special relativity change physicists views on the two prominent inverse square laws (ie Newton grav and Coulomb's law)?

On page 107 in Hartle's Gravity -- An introduction to Einstein's General Relativity, he says the following With the success of special relativity it became apparent that the Newtonian theory of ...
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To what fraction of the speed-of-light has any multi-atom molecule (or polyatomic ion) been accelerated?

Of course photons go $c$ in a vacuum, and seems there's data on electrons getting to $0.999999999976c$ and protons to $0.99999912c$. For the twins paradox to be plausible, one of the twins must ...
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Why is the scalar product of four-velocity with itself -1?

My GR book Hartle says the scalar product of four-velocity with itself $-1$? Consider the definition of four velocity $\mathbf{u} = \frac{dx^{\alpha}}{d\tau}$. Suppose I take the scalar product of ...
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Are length contractions limited by Planck length?

While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. But we can not (even theoretically) consider length ...
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Why is the relativistic Lorentz factor defined this way? [duplicate]

My question is: why has the Lorentz factor the form $$\gamma = \dfrac{1}{\sqrt{1 - \dfrac{v^2}{c^2}}}$$ and not, for example one of those: $$\gamma = \dfrac{1}{\sqrt{1 - \dfrac{v}{c}}}$$ or ...
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2answers
115 views

What is the fastest speed that a massive object can travel at? [duplicate]

What is the fastest speed (in miles per hour) that a massive object can travel at? I have heard that an object can travel at the speed of light, but I've also heard that massive objects cannot travel ...
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63 views

Quantum relativistic effects

I was performing a thought experiment: let us assume an object is traveling so close to the speed of light that the length of the object is small enough for quantum effects to become noticeable to a ...
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6answers
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Confused about Lorentz contraction

My son asked me the following question which I can't answer in a simple way. A frame $O'$ has speed $v$ relative to $O$. A photon travelling along the $x'$-axis in frame $O'$ over a distance $L'$ ...
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Time dilation due to change in speed

I can't get something strait... Lets use the usual example: A man is flying away from earth on a very fast spaceship. So, His time is now not moving in the same "speed" like earth time but slower. But ...
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Has light been used to measure relative velocity?

Here we have 2 lasers. Both are in the same frame of reference as is top box. Laser #1 sends the light directly through the hole in the top box on one side and the light eventually exits the hole ...
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Mass-velocity-relation for tachyon

Suppose that $m = \gamma m_0$ with $$\gamma = \left(1-\frac{u^2}{c^2}\right)^{-\frac{1}{2}}$$ is valid for tachyons, where $m$ is the mass of the tachyon and $u$ its velocity. Since $u>c$, the rest ...
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Proof of Lorentz contraction?

The measurement of the flux of muons at the Earth's surface shows that many more muons are detected than would be expected, based on their mean half-lifetime of 2,2 microseconds. This is a good proof ...
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Only one invariant speed in special relativity

This is taken from Rindler's Special Relativity: Any effect whose speed in vacuum is always the same could have used to derive the Lorentz Transformation, as light was used in our derivation. Only ...
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Homogeneity of the Lorentz Transformation

The standard Lorentz transformation is linear and homogeneous. This fact implies the following: $\Delta t'= \gamma\ (\Delta t - \frac{v \Delta x}{c^2}),\ \Delta x'= \gamma\ (\Delta x - v \Delta t),\ ...
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At what velocity would a body need to travel at to experience noticeable (couple minutes) time distortion?

When a person experiences higher speeds, the light must travel a greater distance to reach the person whom is moving compared to that whom is staying still. Right? So therefore, light takes slightly ...
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Why does the thought experiment of a photon bouncing of a mirror imply anything for other objects?

Okay, so I am reading a book, "The Elegant Universe" by Brian Greene, which talks about motion and its effect on time. Greene makes the point that time changes with motion by saying that if you have ...
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2answers
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I'm having trouble interpreting the Lorentz transformations

There are two frames which I will call O and O'. Suppose I'm someone in O. Are the lorentz transformations a means by which to calculate coordinates on O' in a way that only frames like me would ...
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4answers
458 views

What is Minkowski spacetime?

I was browsing through an article on spacetime when I caught the words Minkowski Spacetime. A Wikipedia search brought me an article too complex for me to totally understand. So what is Minkowski ...
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1answer
152 views

Special Relativity & QuickSilver from X-Men

In the movie X-Men: Days of Future Past, the mutant character Quicksilver possesses the ability to move very fast. A particularly memorable scene in the movie is one where he runs around very quickly ...
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Do tachyons move faster than light?

I am trying to understand whether or not tachyons travel faster than light. The linked Wikipedia page shows some seemingly contradictory statements, and they are confusing. For instance, the first ...
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Simple relativity question

I have a simple question in foundation SR that I hope someone can clarify. Given a mirror of length l travelling at a relativistic speed wrt a 'stationary' frame of reference containing two laser ...
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2answers
154 views

Origin of the Lorentz force from the point view of relativity?

I'm a physicist, when I'm working on the quantum spin hall effect, I recollected the high-school knowledge on Lorentz force and try to explain the origin of it, but didn't get it in the first glance. ...
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Does matter become energy at the speed of light? [closed]

According to modern physics, we can't push matter to the speed of light. It would slow down (relative to its environment). But theoretically, if matter were to travel the speed of light, would it ...
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1answer
125 views

States in light cone string theory

Currently I'm trying to understand string theory in the light cone quantization. I just have had a look into Polchinski (Vol. 1, Introduction to the bosonic string), because – as far as I could see – ...
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1answer
53 views

Can relative speed be faster than c [duplicate]

If there are two spaceships moving away from each other(in opposite directions) at a speed 0.6c, then wouldnt that make the relative speed of one from the other's frame of reference 1.2c? Does this ...
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A theoretical speed of light question [duplicate]

This is a hard question to explain so bear with me. Let's say that Earth is moving at 1/3 the speed of light to the 'right' (obviously I realize there is no constant left or right). If I were to ...
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2answers
68 views

During relativistic effects what would a person feel experiencing length contraction?

It has been determined that when accelerating a mass towards light speed it gains mass, experiences length contraction, and time dilation. During such a period of special relativity what would a ...
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2answers
65 views

How fast does an object have to be going to turn into energy [closed]

Albert Einstein's equation, $E=mc^2$, says that an object has to be going at the speed of light squared to turn into energy. How fast would this be in miles per hour?
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Is it possible that the geometry of spacetime isn't Minkowskian, if we only take special relativity into account? [duplicate]

If you don't consider general relativity, could you say that the geometry of spacetime might be different from how it's specified by the Minkowski metric? Or is Minkowski spacetime the only geometry ...
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1answer
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Is there experimental evidence of time order inversion for spacelike events?

The title sums up the question. Given two events separated by a spacelike interval, say one takes place after the other in an inertial frame, then by a suitable boost we may invert the time order of ...
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Can surrounding masses influence the speed of time (excluding the time dilation due to gravity)?

https://www.youtube.com/watch?v=ev9zrt__lec @6:22-7:22 If you removed the middle and front spaceships, will the time of the last spaceship flow differently? As this is what it appears to suggest.