Physics Stack Exchange Community Digest

Top new questions this week:

Can the collapse of the wave function be modelled as a quantum system on its own?

Imagine I have an observer $\mathcal O$, a quantum system $\mathcal S$ with Hilbert space $V_{\mathcal S}$, a Hamiltonian $H$, a self-adjoint operator $A$ acting on $V_{\mathcal S}$. The system is in ...

quantum-mechanics wavefunction-collapse quantum-measurements decoherence quantum-foundations  
user avatar asked by Lorenzo Pompili Score of 11
user avatar answered by ACuriousMind Score of 14

QM from the uncertainty principle?

In a book Quantum Mechanics with Applications (1970) by D.B. Beard and G.B. Beard, the authors wrote on page 34: "By methods beyond the scope of this text, one could state the uncertainty ...

quantum-mechanics heisenberg-uncertainty-principle history foundations  
user avatar asked by Hulkster Score of 9
user avatar answered by Andrew Steane Score of 10

About the traditional explanation of the continuity of the first derivative of a 1D wavefunction

I would like to receive some clarifications about the traditional explanation of the continuity of the first derivative of a 1D wavefunction (E.g. see the very clear answer by @ZeroTheHero ...

quantum-mechanics wavefunction schroedinger-equation differentiation observables  
user avatar asked by Valter Moretti Score of 6

Why isn't the moment of inertia of a cylindrical tube the difference of those of two cylinders?

The moment of inertia of a solid cylinder is $\frac{1}{2}mr^2$, and the moment of inertia of a composite object is the sum of the moments of inertia of the objects it consists of minus the moment of ...

user avatar asked by iTechnical Score of 5
user avatar answered by mike stone Score of 14

Tides in lakes attached to the ocean

This is research for a book I am writing and I strongly suspect the answer is no, however I can not quite get Google to spit out a direct answer. :-) If you have a lake, attached directly to the ocean ...

geophysics oceanography  
user avatar asked by Ken Score of 5
user avatar answered by David Bailey Score of 4

Is the self-dual point always a critical point?

I was studying duality maps in my Advanced Stat. Mech. class and it was told that all self-dual points need not correspond to critical point. I understand that critical points are points where ...

statistical-mechanics condensed-matter critical-phenomena duality phase-diagram  
user avatar asked by QFTheorist Score of 4
user avatar answered by Yvan Velenik Score of 8

Empirical equivalence of shifted chemical potential $\mu_i$

It is often said that, in classical thermodynamics, entropy $S$ and energy $U$ are defined only up to an additive constant proportional to the total amount of substance $N=\sum_i N_i$ (where the sum ...

thermodynamics energy potential equilibrium  
user avatar asked by Jens Score of 4

Greatest hits from previous weeks:

Why does ice have a lower density than water?

Can someone explain me why is ice less dense than water? As I know, all solids are usually denser than the liquids (correct me if I am wrong).

water physical-chemistry crystals density ice  
user avatar asked by Gil Score of 20
user avatar answered by YungHummmma Score of 21

What energy is transformed to heat when a candle is burned?

What energy is being transformed to heat when you burn a candle?

energy heat  
user avatar asked by Andy B. Score of 5
user avatar answered by Sai Score of 3

What does the magnitude of the acceleration mean?

I am a little confused as to what the magnitude of acceleration is and what it means.

kinematics acceleration terminology vectors  
user avatar asked by user40230 Score of 6
user avatar answered by Barry Score of 11

How does this "simple" electric train work?

In this YouTube video, a dry cell battery, a wound copper wire and a few magnets (see image below) are being used to create what can be described as "train". It looks fascinating but how does this ...

electromagnetism classical-electrodynamics  
user avatar asked by noir1993 Score of 53
user avatar answered by John Rennie Score of 51

Why does a remote car key work when held to your head/body?

I was trying to unlock my car with a keyfob, but I was out of range. A friend of mine said that I have to hold the transmitter next to my head. It worked, so I tried the following later that day: ...

electromagnetic-radiation everyday-life frequency wavelength  
user avatar asked by SjonTeflon Score of 91
user avatar answered by Chris Mueller Score of 85

Difference between circular motion and rotational motion

Are rotational motion and circular motion different or the same? If different then when can we say that a body is in circular motion, and when it's in rotational motion? I find several answers where ...

orbital-motion terminology rotational-kinematics  
user avatar asked by Aneek Score of 2
user avatar answered by Bill N Score of 3

What is the difference between phase difference and path difference?

The path difference is the difference between the distances travelled by two waves meeting at a point. Given the path difference, how does one calculate the phase difference?

waves terminology  
user avatar asked by Meghna Raviraj karkera Score of 14
user avatar answered by Sensebe Score of 16

Can you answer these questions?

Is really hermiticity necessary to be a physical observable? What about larger class of operators like PT invariant operators or pseudo hermitian one?

It's really necessary for an observable represented by an operator acting in a Hilbert space to be hermitian? It's known that not only hermitian operators have real eigenvalues and that also normal ...

quantum-mechanics hilbert-space observables parity cpt-symmetry  
user avatar asked by Cuntista Score of 1

Evolution of volumes in Phase-Space

Liouville's theorem states that the volume occupied by an ensemble does not change as the ensemble evolves. My question regards the volume of the smallest sphere that contains the ensemble. Is there a ...

hamiltonian-formalism phase-space time-evolution volume  
user avatar asked by Antonio Bernardo Score of 1
user avatar answered by Roland F Score of 0

Spatial separation in analogy to time separation in Lorentzian geometry?

O'Neill (Semi-Riemannian Geometry With Applications to Relativity, 1983, p. 409) defines time separation between two events as follows: "If $p, q \in M$, the time separation $\tau(p, q)$ from $p$...

general-relativity spacetime differential-geometry causality  
user avatar asked by Werner Einstein Score of 1
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