# Tagged Questions

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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### A classical explanation of why there is a speed limit in the universe

The question is - is there any flaw in this explanation, or it is the right explanation in general language? Let me break the explanation into two parts - (1) Why there is a certain speed of ...
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### Relativity and Current in Wire

If an observer is stationary relative to a current-carrying wire in which electrons are moving, why does the observer measure the density of moving electrons to be the same as the density of electrons ...
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### Does the force between two point charges change when inertial reference frame changes?

The two point charges are as below: Then the Coulomb force between them is: $$F_1=\frac{q^2}{4\pi\epsilon_0 r^2}$$ When the inertial reference frame moves left at $v$(or the point charges move ...
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### Can a particle have an imaginary mass?

Now, I'm not very involved in the physical sciences, beyond some high-school classes - though I did listen to some college lectures for physics. I was reading "Do Tachyons Exist?" by John Baez, which ...
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### Is the energy of a collision of two photons the same as one photon hitting a 'wall'?

Special relativity says that the speed of ligt is always the same. So when a photon meets another photon he will encouter it with the speed of light and also the other one. But in case of a wall, the ...
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### Is there any description of a mechanism of curving of space-time fabric

Most of us know about famous line - "mass tells space how to curve and space tells mass how to move". There is quantitative description of the curving and its effects in Einstein's theory. Mass and ...
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### Do we know why there is a speed limit in our universe?

This question is about why we have a universal speed limit (the speed of light in vacuum). Is there a more fundamental law that tells us why this is? I'm not asking why the speed limit is equal to ...
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### Small particle rotating around neutron star

First let me say I have read the article at "users.ictp.it › lns003 › Ruoff › Ruoff.ps.gz" about a small particles orbiting a neutron star and causing excitation of different modes of gravitational ...
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### Doppler effect of matter waves

We all know that the relativistic mass of a moving object in Special relativity increases for an observer who is measuring it for a moving object. We also know the the concept of particle-wave ...
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### Conversion of energy to matter? [closed]

Now, this answer has sort of been asked before. But I haven't really found the answer that I'm looking for. Exactly what is the mechanism by which energy can be converted into matter? By ...
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### Cold Fusion and Black Holes [closed]

How does a magnetic field heat and Cool objects? Would an Atom rapidly cooled with a magnetic field release photons? Can solid magnets be used in the same manner? Einsteins cold fusion formula is ...
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### Cold Solid Matter at the End of a Black Hole's Acceleration Disk?

Is it possible that black holes magnetic field are rapidly cooling matter using a type of magneto caloric effect and cold fusion creating new matter only possible with a black hole's gravity? A type ...
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### Help understanding why can't we measure absolute velocity?

(This is probably a clone of some other question, but I haven't been able to find a satisfactory answer, so I hope this is okay.) So, I know that in special relativity, there's no such thing as a ...
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### Time and velocity

Suppose two cars are traveling at a velocity of $c/2$ ($c$=speed of light) in two straight lines parallel to each other but in opposite direction in vacuum. Then what will a person sitting in one of ...
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### Constancy of speed of light in vacuum? [closed]

Have scientists tried their best to calculate speed of light in vacuum? It seems very absurd to me that light of all frequencies have same velocity in space. Can someone find in future if this speed ...
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### Are there certain reference frames where proper length of proper time are supposed to be measured?

Let's say we have two frames: Bob on Earth and Alice in a rocketship. Let's say Alice is traveling at a relativistic speed away from Bob. With that in mind. Is there a certain frame where we should ...
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### Introduction to relativity books for an engineer [duplicate]

Possible Duplicate: Getting started general relativity I am an engineer who loves to read science fiction books especially when there's more science than fiction but usually I see that I ...
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### Why isn't a Photon justified in concluding that it is at rest and everything else is moving past it at c? [duplicate]

Why isn't a photon moving at c not justified in concluding that it is at rest and everything else is moving past it at c since relativity postulates that the laws of physics are invariant (i.e. ...
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### Visual pictures of Lorentz transformations

How can I visualize Lorentz transformations? I know it's four dimensional, but without a visual picture in my mind I can't understand any of this. For example how do: Time reflection Space ...
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### QFT: Ground State Momentum - Normalisation of States

In my notes I have, $$\left\langle \mathbf{p} \left| \mathbf{q} \right.\right\rangle = \left\langle 0 \left| {a(\mathbf{p})}\ {a(\mathbf{q})}^{\dagger} \right| 0 \right\rangle$$ I am not sure how ...
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### Show that an isolated photon cannot undergo pair production [duplicate]

I need to see the mathematical details as how the conservation of four momentum is violated.
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### Equation of motion of a free particle

We know that the equation of motion of particle can be derived from the respective action. But in the book I am reading, the author is saying: ... timelike worldline of a massive particle is ...