# Questions tagged [special-relativity]

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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### Lorentz Invariance of kinetic terms for Weyl Spinors

Just to preface things, this exact question has been asked before here, but I don't feel like the answer really clarifies things for me. The core issue is that we want to construct a 4-vector that we ...
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### Time and measurement relation to displacement

Is there any other way to measure time without using any type of periodic motion. I think it's a no. A clock is essentially a periodic motion in which we measure some type of periodic displacement. I ...
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### Connection between kinetic and gravitational time dilation [duplicate]

I am learning about relativity and am interested in time dilation. I now exactly understand where the formula of kinetic time dilation comes from and wondered about gravitational time dilation. I have ...
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### Finding the Lorentz Velocity for Relativistic Electrodynamics

I'm trying to understand something from my Special Relativity notes. Assume here that $\vec{E}$ and $\vec{B}$ are perpendicular and $|\vec{E}|>|\vec{B}|$. Show that there is a frame $\bar{\Sigma}$ ...
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### Are there non-smooth metrics for spacetime?

I found this statement in a discussion about the application of local Lorentz symmetry in spacetime metrics: Lorentz invariance holds locally in GR, but you're right that it no longer applies ...
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### Can FTL be done in a way that it dosen't break causality? [closed]

So I was wondering if we could travel faster than the speed of light without creating time paradoxes?could we achieve FTL in a certain way that it dosen't break causality?or does FTL always break ...
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### Does Relativity Theory Allow Cyclic Time Travel? [closed]

In the H.G. Wells novel "The Time Machine" and original 1960 movie we saw that the protagonist traveled from his present time to the future and back again to the present just within a few ...
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### Tensionless string in Nambu-Goto action

I am studying string theory from the book "String theory and M-theory", written by Becker, Becker and Schwartz. My question is: We are taught that one of the advantages of introducing a ...
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### Proper acceleration along perpendicular directions

Let's take an object (all times mentioned in this problem are proper times). There is a constant proper acceleration "$a$" on this object in the x-direction for time $t, 0\leq t \leq \tau$. ...
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### Can you translate between Newtonian physics and special relativity physics? [closed]

I am asking for clarification on a question on a test I had recently on special relativity. The question was: "An astronaut is travelling at a velocity of 0.866c. This gives a Lorentz factor of 2....
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### Is the law of the lever equation the same in classical physics as in relativity ? Why?

In classical mechanics the balancing lever equation (law of the lever) is $$M_1 a = M_2 b$$ Where $M_1$ is the mass at a distance $a$ from the fulcrum and $M_2$ is the mass at a distance $b$ from the ...
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### In this time dilation explanation, shouldn't gravity and mass affect the example?

recently i've started "exploring" general relativity, and found this example explaining time dilation caused by velocity: The example was taken from https://en.wikipedia.org/wiki/...
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### What is the covariant version of the dipole moment?

Magnetic dipoles in a rest frame behave as a mixture of dielectric dipoles and magnetic dipoles in another moving frame. However this is sometimes controversial due to Mansuripur's paradox (see ...
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### What's the difference between Lorentz transformation properties of Hermitian and Dirac adjoint lepton doublets?

If the lepton doublet transforms like a left-handed Weyl spinor under Lorentz transformations, $$L \longrightarrow exp\left[\frac{1}{2}(i\theta_j\sigma^j - \beta_j\sigma^j)\right]L = \Lambda_{sL}L,$$...
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### Dimension of a vector space of all tensors of rank $(k,l)$ in 4D

Dual vector space is the set of all linear functionals defined on a given vector space. The vector space and dual vector space is isomorphic and hence have the same dimension. A rank $(k,l)$ tensor is ...
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