# All Questions

63 views

### A parameter to quantify instability in flight

Suppose I have plotted the body angles of a flying aeroplane.I have two such plots. One of a normal plane, and the other plot in which a primary sensor of the aeroplane is removed. So with the absence ...
140 views

### If reality is relative, then what about Newton's bucket argument?

There is nothing outside the universe. - Lee Smolin So, there can't be any absolute frame. Everything must be measured relative to an entity that exists in the universe. Thus, space ...
78 views

### Is the speed of photon always $c_0$? [duplicate]

The propagation of light in medium is sometimes interpreted as the photons moving with $c_0$ (the speed of light in vacuum), occasionally absorbed by particles and released again by transition, ...
47 views

### does electron - positron pair annihilation occur when E is negative?

Suppose I release an electron-positron pair from rest at a distance of $r$. Then the particles attract each other and collide. The total energy $E$ is $$E = 2m_ec^2-\frac{e^2}{4\pi\varepsilon_0r},$$ ...
38 views

### Does the holographic principle imply that objects exist twice?

The surface area that surrounds a volume of space contains the same information that the volume has. My question is if we have Alice in a 3D space the 2D boundary should have all of her information. ...
39 views

### Does Poincare recurrence imply that a photon shot into a box will exit the way it came in?

If you have a big closed cube that has perfectly mirrored surfaces on the smooth flat walls or faces of the cube and only one corner has a tiny 'entrance' , a narrow hole at a specific angle , say ...
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### Chrial multiplet's fundamental and anti-fundamental representation

Here i follow the notation in arXiv 9312104v1 (Witten's Verlinder algebra ~ paper) The usual kinetic energy for a chiral multiplet is given as (In 2 dimensional $N=(2,2)$ supersymmetry theory) ...
480 views

### How can a negative charge move towards a position of a higher electric potential but lose electric potential energy?

I understand that the equation is: change in electric potential = (negative)change in electric potential energy / unit charge. And I understand that if q is negative, then the change in electric ...
58 views

### Why $2j+1$ number of states?

In this statement from Modern Quantum Mechanics by J.J. Sakurai: If $j$ is an integer, all $m$ values are integers; if $j$ is a half-integer, all $m$ values are half-integers. The allowed ...
162 views

### charge distribution on three conducting plates [closed]

There are three parallel plates identical and equidistant. A charge q is given to the first plate.And then the second and third plate are connected with wire.Then how to find its charge distribution. ...
27 views

### If neutron would be lighter by 1 MeV, how stability of Hydrogen could be changed?

In current Universe proton is stable and the following reaction does not go $p + e \rightarrow n + \overline{\nu_e}$ Currently proton is lighter than neutron by 1.293 MeV. If neutron would be ...
80 views

### Boy , Table and the Newton [duplicate]

Suppose a boy is trying to stand on a table. If the table can hold upto a particular force, the boy would fall on to earth. If he stands on the table and providing greater force than the table can ...
70 views

### What is the implication that the Schrodinger equation be solved by both real and imaginary part of the wave function? [closed]

Suppose $\psi = \psi_{real} + i \psi_{imag}$ be the wave function, then both $\psi_{real}$ and $\psi_{imag}$ can be used to solve the Schrodinger's equation This can be demonstrated by plugging ...
143 views

### Connections between classical mechanics and quantum mechanics [duplicate]

I've been studying quantum mechanics and classical mechanics for a little while now, and I still don't feel as though I fully understand the motivation for some of our choices in Heisenberg mechanics. ...
416 views

### In physics, what is the importance of distinguishing between a matrix and a group? [closed]

On the topic of Pauli matrices, I have noticed that some authors tend to use the term matrix and group interchangeably. I am asking because I do not see see any profound difference referring to the ...
292 views

### How do we know that electron wave function extends to infinity?

Why do physicists assume this? Is it a proven fact that wave function extends to infinity or just a theory? Would it make sense if they didn't extend to infinity?
104 views

### Flow rate of gas down a pipe at low pressures

I'm trying to understand an 'approximate derivation' of the flow rate of gas down a pipe at low pressure from my book (an example problem). It uses the result that the flux of a gas is given by ...
28 views

### 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 ...
53 views

### 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 ...
359 views

### 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 ...
62 views

### 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?
143 views

### 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?
73 views

### 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 ...
75 views

### 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 ? ...
247 views

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 ...
275 views

### 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 ...
119 views

### 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 ...
151 views

### 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 ...
187 views

### 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 ...
91 views

### 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. ...
55 views

### 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 ...
134 views

### 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?
242 views

### 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 ...
166 views

### 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 ...
143 views

### 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?
103 views

### A Theory of Almost Everything? [closed]

Before I present this theory, I ask that you take the time to read this disclaimer. I do not claim to have an excellent knowledge of physics, it is actually rather limited. Therefore, I am not ...
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### What is the difference between Newton's first & third law?

Newton first law states that object stays in fixed state, unless external force is applied. Newton third law states that: if there is action then there will be opposite & equal reaction. So if ...
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### Why is the Earth self-rotating? [duplicate]

What drives this happen? Would it be the internal energy or by an external force? I did try to Google the answer, but could not find a good one.
43 views

### What is the best laser wavelength to melt a certain material to the point of 'welding' together

Assume the material is enough of a heat sink that you can hold the torch to the material and the spread of the red-hot metal is not moving - is stabilized, but you can still melt the material in the ...
130 views

### thermodynamics poisson's ratio of mixtures

air consists of 79% nitrogen and 21% diatomic gas(say) . to perform calculations on ΔH on adiabatic expansions, instead of taking as parts , can i take it as a uniform gas with some γ(poission's ...
48 views

### Is there a well-defined partition function of 4d Yang-Mills?

So I've looked everywhere to find a resource on 4 dimensional Yang-Mills partition functions, but have only managed to find examples using supersymmetry. Is there a resource describing the partition ...
142 views

### Electrons and Magnetism

Electron at rest generates Electric field. Electron moving without acceleration produces electric and magnetic field. Electron moving with acceleration produces electromagnetic waves. Please explain ...