# All Questions

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### Why in SQCD $R_{\psi}= R_{\phi}-1$?

In SQCD = suspersymmetric QCD, in 4 dimensions and with one SUSY generator how do we determine the $R$-charge of the $U(1)_R$ symmetry of the various operators in a chiral supermultiplet? Say for ...
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### How have the duration of the martian day changed in the past?

There is a panspermia theory which claims that life might have begun on Mars and I currently read a post that the human circadian rhythm is closer to the martian day length (about 25h) than the day ...
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### How do we know that time dilation applies to objects other than light?

Here is a traditional derivation of time dilation: There's a train with a lamp in the ceiling, moving at velocity v with respect to an observer. In the frame of the observer, the path taken by the ...
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### Is it possible to calculate neutron half-life theoretically?

Is it possible to calculate neutron half-life theoretically? For example, from lattice QCD or something?
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### Gravitational coupling of tachyons

Can General Relativity stress-energy tensor be extended to include contributions from imaginary mass tachyons? what would be the expected gravitational coupling between tachyons and tardions?
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### Reversibility in classical mechanics

I am watching Susskind's 'Theoretical Minimum' videos. At one point in his course on classical mechanics (2nd video if I remember correctly) he affirms that Netwon's second law of motion makes ...
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### What will happen if I remove a nail which stops a plank from moving on a smooth floor because of a solid sphere pure rolling on it?

What will happen if I remove a nail which stops a plank from moving on a smooth floor because of a solid sphere pure rolling on it?The plank has it's upper surface which is in contact with the sphere ...
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I'm currently studying the following diagram: But I'm not entirely sure I understand what's going on. Is it just, that most exoplanets discovered, is pretty much made up of Hydrogen and Helium ? ...
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In an interview a philosopher said: "Suppose I cut the handle off your coffee mug leaving two holes. Would the coffee flow out of one hole faster than the other? If we tried to figure this out by ...
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### Why is the Luminiferous aether theory wrong? [closed]

I saw on this page about the constant speed of light that there are two ways of interpreting this constant speed: General relativity The Luminiferous aether theory I understand why the theory of ...
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### black body simulation

black body radiation is typically understood from Planck's argument of light resonance in a box, from which the density of states is computed. Now, suppose I want to simulate a black body ...
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### Many-worlds interpretation

Regarding many-worlds interpretation as an alternative explanation to Copenhagen. If we take the generation or possibility of alternative universes as an explanation for the collapse of wavefunction ...
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### wavefunction and contextuality

According to the French philosopher Michel Bitbol, the "deep-lying connection between the contextual character of observables, and the wave-like form of probability distributions was demonstrated ...
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### Charge on the remaining atom after Alpha decay

In radioactive alpha decay, a helium atom is shown to be released. However, I was told that only thing released is a helium nucleus. If so, then it should leave two of its electrons in the atom ...
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### Water level of ice in cup [duplicate]

Since ice is less dense than water, it floats on it, we all know this. Now suppose, if ice is floating in a glass cup, when the ice melts there should be some change at water level in the glass cup. ...
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### Transmissibility

An extract from a school maths mechanics textbook reads: To deal with cases in which the body is not rotating freely under gravity, we need to take into account also the work done by other ...
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### Resemblance between Coriolis force and magnetic part of Lorentz force

If we interchange velocity with charge and omega that is rotation of a system with $B$, magnetic field, we get the same thing. Is there any deeper meaning to this same mathematical form?
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### Do all isotopes have a half life? [duplicate]

I understand that some isotopes of an element have a shorter half life, and decay more quickly into other elements. Other isotopes are described as stable and no half life is stated. For elements that ...
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### Expected value of $xp$ in harmonic oscillator [closed]

I wanna find out the expected value of the $xp$ operator for the $n$-th excited state of the harmonic oscillator, i.e. calculate the value $\langle n|xp|n \rangle$. I express the position and momentum ...
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### What's the physics origin and meaning of $\delta_{ij}-k_ik_j/k^2$

The projection tensor $P_{ij}\equiv\delta_{ij}-k_ik_j/k^2$ happens frequently in fluid mechanics or field theory. What's the physics origin of this structure and what's the meaning?