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Physics : Recent Questions and Answers (Page 565)

Find answers to your questions about Physics or help others by answering their Physics questions.

Are 4-vectors covariant under general coordinate transformations?

In the context of special relativity, it is well known that 4-vectors are covariant under Lorentz transformations (which is a linear transformation in space-time), however are they covariant under general...

Asked on 02/14/2021

0 answer

Simple derivative of current confusion

Say you have some $textbf{B}$ field from an alternating current, $textbf B(t) = textbf{B}_0cos{omega ,t}$. And using Faraday law, e.m.f. $varepsilon$ = turns of a coil ...

Asked on 02/14/2021 by Chris Bolig

2 answer

Meaning of operator in ket bra notation in Hilbert space

For simplest operator $textit{M}$, I could write it as $|kranglelangle m|$.begin{equation}mathit{M} = |kranglelangle m|end{equation}When operating on a state $|nrangle$, I could write...

Asked on 02/14/2021 by Simon219

3 answer

How do the symmetries of a system constrain gauge fields?

As a simple example, take a constant magnetic field $vec{B} = (0,0,B)$. This is invariant under rotations about the $z$ axis. However, we can express $vec{B}$ as...

Asked on 02/14/2021 by DavidH

2 answer

RMOND theory and Schwarzschild metric

In a recent paper https://arxiv.org/abs/2007.00082, two authors propose a new model (RMOND) which seems succesful to explain many cosmological data. Obviously, the GR theory must have as...

Asked on 02/14/2021 by Riccardo.Alestra

1 answer

Relating the topological behaviour in the toric code to cohomology?

I've been working on the Toric Code Model (by Kitaev in his 2003 paper on quantum computation), and the model is a lattice realisation of a topological phase. The local...

Asked on 02/14/2021 by pyroscepter

0 answer

Why is the positive terminal of an ammeter connected to the positive terminal of a battery?

I always thought it's because, if we consider a circuit ABCDE with only a battery and an ammeter, if we connect the negative terminal to the positive terminal the sum...

Asked on 02/14/2021

1 answer

Bekenstein bound busted?

The ProblemLet's start with the formula in Wikipedia: I compute: $I leqslant 4.6times10^7 bits/eV...

Asked on 02/14/2021

2 answer

What is the meaning, in tensor notation, of the dot-within-a-circle $odot$? Usually shown as an exponent?

This $odot$ notation is e.g. used in this Phys.SE posts:General relativity: Why don't these two differentials commute?Why isn't there a second baryon octet?...

Asked on 02/14/2021

1 answer

When did the Big Bang happen?

Did the Big Bang happen at a point? goes through the fact that the Big Bang happened everywhere at the same time. John Rennie's answer explains this as being...

Asked on 02/14/2021

2 answer

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