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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If something is not moving in space, is it moving on the time axis at the speed of light? [duplicate]

I heard this theory yesterday: If something is not moving in space, then it is moving on the time axis at the speed of light. I realize that in essence there is no object which can be considered as ...
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Why are objects at rest in motion through spacetime at the speed of light?

I read that an object at rest has such a stupendous amount of energy, $E=mc^2$ because it's effectively in motion through space-time at the speed of light and it's traveling through the time dimension ...
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What problems with Electromagnetism led Einstein to the Special Theory of Relativity?

I have often heard it said that several problems in the theory of electromagnetism as described by Maxwell's equations led Einstein to his theory of Special Relativity. What exactly were these ...
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What's wrong with this application of Thomas Precession to circular motion velocity measurements?

If you happen to have the Third Edition of Classical Electrodynamics by John David Jackson, turn to section 11.8, as that's where I'm getting all this from. If not, you should still be able to follow ...
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How can Lorentz contraction be “directly” measured?

If one is watching a relativistic object of e.g. spherical shape, which emits enough light to be detectable, it will, despite being Lorentz contracted, appear of its natural shape, although rotated. ...
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No length contraction!

Suppose a person standing on a platform were to observe and measure the length of a train passing by. Instead of the usual approach involving a clock and knowing the speed of the train, the person ...
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130 views

What wilI I observe when travelling at almost the speed of light? [duplicate]

If I and a group of friends are travelling at or just below the speed of light - can I see myself, can I see them, or they me? Would we see anything at all?
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How are light and time related?

So, from what I understand: Special Relativity says that light is always observed moving at the speed of light (c). If some object had a velocity of (3/4)c, and the object had some sort of clock ...
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Length contraction

I am trying to work out the length contraction using the Lorentz transformations. Here is how I stated the problem: Suppose a bar (whose proper length is $L$) is moving at speed $u$ (to the right) ...
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4answers
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Is time not a universal parameter, really, in special relativity?

I want to check that I get it right. The way that I have it in my mind is that, in my frame of reference and from my point of view, SR associates only one time parameter for the whole space, and not ...
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2answers
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What Did Nobelaureate Smoot Mean by “Modern Efforts to Find Violations of Special Relativity”

In George Smoot's 2006 Nobel Lecture, having won the Nobel prize for his research on the Cosmic Microwave Background (CMB), he refers to the possibility of the CMB being a special frame stating ...
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Relativistic Doppler Effect and the Sagnac effect

What I think I know about the Sagnac effect can be found here. It occurs to me that the equations for calculating the time do not take the Doppler effect into account. I'm familiar with the very ...
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How can light have the same speed for all observers? [duplicate]

I'm a little confused on this. If you're travelling at, say, 10% of the speed of light then light is travelling at 3x10^8 ms^(-1) relative to you. If you're moving at 80% of the speed of light and ...
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2answers
174 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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2answers
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Two observers moving opposite to each other will see each other moving at speeds greater than light? [duplicate]

I read this question at another forum but the thread was already closed. Here's the description: Two observers A and B are both moving at a velocity of 0.9 times the speed of light with respect to a ...
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43 views

Breaking the speed of light…? [duplicate]

I know the speed of light can't be broken, but I cannot figure out why the following scenario is not possible. I'm not a physicist myself but I know the basic stuff. Assume you're in a car ...
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Clock synchronazation in special relativity using signal other than light

I'm reading Taylor & Wheeler "Spacetime Physics" and have a question about possibility of correct clock synch using signal other then light. For example, we choose reference clock(A) and at ...
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1answer
114 views

How does EM radition depend on the reference frame?

In special relativity, magnetism is electrostatics in a different reference frame. This is how we explain the magnetic field being produced by moving charges (aka currents). Charges that move produce ...
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1answer
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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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7answers
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Why is there no absolute maximum temperature?

If temperature makes particles vibrate faster, and movement is limited by the speed of light, then temperature must be limited as well I would assume. Why there is no limits?
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Lorentz transformations an EM fields

When deriving the Lorentz transformation equations in undergraduate physics classes, teachers typically analyze the behavior of an ideal clock and a rigid bar. Once the behavior of clocks and rods is ...
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3answers
135 views

Does the Doppler effect disprove the constancy of $c$? [closed]

Why doesn't the Doppler effect disprove the relativity postulate that $c$ is constant relative to all sources or observers? It seems it does because of the following example: Suppose a ship of ...
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1answer
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Does a moving object really shrink due to length contraction? [duplicate]

Is length contraction an optical illusion? Does object really shrink? Though measurements say yes, does it really happen? Or I have to say object is really measured to shrink?
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New Supersymmetry Algebra

We know that SUSY generators commute with translation $$ [P_\mu,Q_\alpha]=0 $$ I have some questions: What is this equation physical meaning? Is it possible to make "SUSY-like" generators that do ...
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1answer
67 views

A simple coordinate transformation

I'm currently taking my first shot at reading Einstein's 'On The Electrodynamics' (with plenty of mathematical background). With a few pictures, everything has been crystal clear to my intuition, up ...
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628 views

A thought experiment in special relativity theory

We have two sets: set No.1 and set No.2 as in this picture: The observer is fixed to set No.1 . He sees set No.1 motionless and observes set No. 2 approaching with velocity 100,000 m/s. Each set ...
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A question about special relativity theory

We have two sets: set No.1 and set No.2 as in this picture: The observer is fixed to set No.1 . He sees set No.1 motionless and observes set No. 2 approaching with velocity 100,000 m/s. Each set ...
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Change in line density of electrons

We're proving that electricity and magnetism are essentially two manifestations of the same underlying phenomenon by using the toy example of a positive charge moving parallel to an infinitely long ...
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6answers
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Rotate a long bar in space and get close to (or even beyond) the speed of light $c$

Imagine a bar spinning like a helicopter propeller, At $\omega$ rad/s because the extremes of the bar goes at speed $$V = \omega * r$$ then we can reach near $c$ (speed of light) applying some ...
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1answer
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Special Relativity: Finding the Euler Lagrange of a massive particle

Knowing that $$\tag{1} L= -mc\sqrt{-\eta_{ab}\frac{d\xi^a}{d\lambda}\frac{d\xi^b}{d\lambda}}$$ we get $$\tag{2} p_a=\frac{\partial L}{\partial(d\xi^a/d\lambda)} = m\eta_{ab}u^b.$$ How come? If I ...
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If rest mass does not change with $v$ then why is infinite energy required to accelerate an object to the speed of light?

I know that as the velocity increases, the mass of the object also increases so it becomes tougher and tougher to move the object which ultimately leads to a requirement of infinite energy to ...
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2answers
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How would an electron bunch/beam look different in the rest and lab frames?

With respect to special relativity, I was wondering how the spatial dimensions would differ between the rest and LAB frame of an electron beam. System: Electron bunch/beam traveling in linear motion. ...
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1answer
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Do photons have relativistic mass?

I am conducting research on photons and was wondering if they have relativistic mass. I already know that they they have zero rest mass. Any answers are welcome!
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Can time pass for a photon if it's moving in a medium? [duplicate]

If time does not pass for a photon traveling at the speed of light, which can only occur when traveling in a vacuum, what happens when it is slowed down by traveling through non vacuum space like ...
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Is the existence of electromagnetic standing waves dependent on the observers reference frame?

If I take two plane EM waves travelling in opposite direction e.g. $E = E_0 \sin(kx-\omega t)$ and $E=E_0 \sin (kx + \omega t)$, they sum to give a standing wave with a time-averaged Poynting vector ...
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3answers
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Phase space volume and relativity

Much of statistical mechanics is derived from Liouville's theorem, which can be stated as "the phase space volume occupied by an ensemble of isolated systems is conserved over time." (I'm mostly ...
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1answer
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Why isn't time axis vertical? [closed]

Why isn't time axis vertical? I don't find any reason behind it. This graph is drawn in tree frame. Though the tree isn't moving the time axis isn't vertical. Please help me to understand it. This ...
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3answers
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What is the Andromeda Paradox?

I have been studying causality (specifically why there is no such thing as a simultaneous instant of time across all observers) recently and I keep hearing references to the Andromeda paradox. Can ...
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What does traveling close to speed of light mean?

This has been bugging me for a while. We all know in relativity that if you travel close to speed of light, all sorts of crazy things happen. But what does it mean to travel close to speed of light? ...
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Relative time/space - Two clock thought experiment [duplicate]

Please pardon my english. Here is my simple thought experiment. ...
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152 views

why do we use the equation we do for special relativity when there is a shorter, more intuitive one?

$\frac{1}{\sqrt{1-v^2/c^2}}$ is the equation physicists use to calculate time dilation.Why don't they use $\sqrt{1+v^2/c^2}$ which is faster and also more intuitive (for me at least) Although now I ...
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Velocity in relativity

We just started learning about 4-vectors in my physics class, and I'm a little confused about the relationship between the 4-velocity $U=\gamma(c,\vec{v}),$ and the velocity transformations given by ...
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4answers
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The pole and the barn paradox (stretching the pole)

The basic variant of this paradox makes sense to me but I have problems in proving mathematically variation of this non-paradox. So lets imagine that we have barn and pole which is stationary to the ...
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1answer
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Lorentz Transformation at t=0

Suppose I have two reference frames $S$ and $S'$, where $S'$ is moving with velocity $v$ with respect to $S$. The Lorentz transformation equation for time in reference frame $S$ is given by: ...
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1answer
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Are 2 time intervals the same only for same speeds?

I'm only amateur in modern phsyics having read some about relativity theory and time measurements depending on relative movement. Is it true that 2 clocks measure time the same only if the relative ...
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Special Relativity Textbooks Request [duplicate]

I have a copy of David Bohm's Special Theory of Relativity and also a copy of T.M. Helliwell's Special Relativity. I was wondering if anyone has used these texts and if they're sufficient in providing ...
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I am looking for a good primer on Special relativity [duplicate]

I am starting a course in Gravity and Quantum Field Theory this year, and I have all of the prerequisites except for a few topics in Special Relativity. I have had some SR, but only the 1-dimensional ...
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Can speed be defined in the complex plane?

This question cropped up while I was playing with the equation for time dilation. If I set the speed to be $i$ (imaginary unit) the answer from the equation still makes sense, but does that matter if ...