1
vote
1answer
206 views

Time-reversed twin paradox

This started with wondering about the nature of certain physical quantities under time-reversal - chiefly, that acceleration retains its magnitude and direction at a given time regardless of the ...
1
vote
1answer
55 views

Wigner's Theorem and discrete Symmetries

According to my skript: A pure state is a ray: $\quad$ $\{λψ\}$, where $ψ ∈ \mathcal H$, $||ψ|| =1$ fixed and $λ ∈ \mathbb C$, $|λ| = 1$. Pure states are uniquely given by 1-dimensional orthogonal ...
2
votes
1answer
59 views

Why there's any voltage on P-N junction in diodes?

If all electrons here have their counterparts in protons, on both, P and N sides, then why there's any voltage (built-in voltage, on the bottom of the image)? Both sides should be neutral, shouldn't ...
0
votes
1answer
52 views

What is the relation between Rössler attractor and thin accretion discs (like in the movie Interstellar)?

Is there any relationship between the Rössler attractor and thin accretion disks, like the accretion disk(s) in the movie Interstellar?
1
vote
1answer
94 views

Electric force vs. Magnetic force

$E$, electric field $\to$ $H$, magnetic field $D$, electric flux density $\to$ $B$, magnetic flux density $D=\epsilon E$ $\to$ $B= \mu H$ Electric force calculation is based on electric field: ...
0
votes
2answers
301 views

Is it possible to have both a conduction current and a displacement current at the same time?

According to Ampere's law, is it possible to have both a conduction current and a displacement current at the same time? In the classical derivation of the displacement current using a parallel plate ...
0
votes
3answers
96 views

Which formula is correct for the velocity of a mathematical pendulum?

Suppose I have a mathematical pendulum swinging in a plane, and the angle between the vertical direction and the pendulum is $\phi(t) = \phi_0 \cos\omega_0t$. The length of the pendulum is $l$, its ...
0
votes
0answers
22 views

Chain links weight limit?

I have a back helping/crunch bench that rotates around and is stopped by a series of chains linked. My weight is around 66 kg, other people that might use it weight around 91 kg, designated as $M$. ...
7
votes
2answers
438 views

Floquet and Bloch's theorems : connection?

It is often stated that Bloch's theorem and Floquet's theorem are equivalent, even the Bloch's theorem is often referred as Floquet-Bloch theorem. However, it seems quite confusing to me since the ...
1
vote
1answer
54 views

Probabilities of pure states and density operators

According to my skript: A pure state is a ray: $\quad$ $\{λψ\}$, where $ψ ∈ \mathcal H$, $||ψ|| =1$ fixed and $λ ∈ \mathbb C$, $|λ| = 1$. Pure states are uniquely given by 1-dimensional orthogonal ...
3
votes
1answer
118 views

Superposition of electromagnetic waves and energy localization

Sorry for the long question. I didn't know how to make it shorter. I'm trying to understand how energy is spatially localized in an electromagnetic wave. My premises are: Electromagnetic energy is ...
1
vote
2answers
73 views

Is there a portable method of preventing all IR radiation from being emitted?

Me and some friends were recently disuccing "How cool it would be to be invisible", from a military viewpoint, I said that Camouflage, when done correctly, works surprisingly well, so invisibility was ...
1
vote
0answers
169 views

Law of reflection for a moving mirror

An elementary fact that people learn about mirrors is the law of reflection, that the angle of incidence of a light beam striking the mirror (as measured with respect to a normal) equals the angle of ...
0
votes
1answer
185 views

Efficiency larger than one?

The efficiency of a heat engine is the work we can do divided by the heat we take out of the hot reservoir. This quantity is always $ \le 1$. The efficiency of a heat pump is the heat we can release ...
1
vote
2answers
122 views

Heating of two identical balls [closed]

You are given two identical steel balls of radius (say) 5 cm. One ball is resting on a table, the other ball is hanging from a string. Both balls are heated (with a blow torch) until their radii have ...
4
votes
1answer
97 views

Fifth force in string theory [closed]

I can't seem to get a clear description of what the "fifth force" in string theory is. What is the fifth force in string theory? What does it do? What mediates it?
1
vote
0answers
16 views

Are there any pigments which can be altered via the use of electricty?

I was looking at alternative visual output methods for computer, phone and the like and was wondering, are there pigments, Red, Green and Blue preferably, that can have their intensity/opacity ...
3
votes
3answers
114 views

Entropy of loops in the PV plane

The change in entropy of the Carnot and reversible cycles is said to be 0. Several other loops are supposed to have a non-negative change in entropy. This presents 2 problems which I cannot ...
2
votes
1answer
132 views

Can a fuzzball collapse into a singularity?

I've been reading Kip Thorne's Black Holes and Time Warps and got curious about extreme states of degenerate matter; a little research reveals that since the book was written quark and preon ...
1
vote
3answers
573 views

Example of law of conservation of energy

Law of conservation of energy states that "Energy of the universe remains constant. Energy can neither be created nor be destroyed, but it can be transformed from one form to another". So I ...
2
votes
1answer
96 views

Do electrons have a location before they are observed/measured? [closed]

Is this in all interpretations of QM? What about interpretations that are realist (MWI, penrose, ect)?
2
votes
3answers
249 views

Cosmic Background Radiation and redshift vs. temperature

I get that the CMB has gone from high energy photons, to low microwave photons today. And that is probably due to the redshift from the expanding Universe. But, since CMB is a black body it is ...
1
vote
2answers
93 views

What is the initial angular momentum of a rigid body given an offset impulsed force?

What is the imparted angular momentum to a rigid body if the impulse force is offset by a distance $h$ from the center of mass and the imparted momentum from the center of mass is $mv$? For a ...
5
votes
1answer
64 views

Spin, statistics and neutron stars

So a thought occurred to a friend of mine the other day: in a neutron star, neutrons are prevented from sitting directly on top of one another due to the Pauli exclusion principle, what with neutrons ...
-1
votes
1answer
116 views

In Quantum mechanics, what is realism? [closed]

Some interpretations of QM are realist and some are anti-realist. But, it is the idea that something exists before it is measured, correct?
4
votes
1answer
67 views

How can we see that the Riemann curvature tensor is covariant?

The Riemann curvature tensor, using the conventions of wikipedia, is written in terms of Christoffel symbols as: $$ \tag{1} R^\lambda_{\,\,\mu \nu \rho} = \partial_\nu \Gamma^\lambda_{\,\,\rho \mu} - ...
0
votes
2answers
167 views

Thermodynamic equilibrium of an isolated system

When an arbitrary system is isolated and left to itself, its property will in general change in time. ....after a sufficiently long time,the temperature will become the same at all points and then ...
2
votes
1answer
510 views

How does reflection of light at normal incidence angle happen?

I was wondering few scenarios pertaining about reflection of light at a normal incidence angle (perpendicular to the mirror) in that case how can a wave-of-light reflect of? As the reflected waves ...
2
votes
1answer
1k views

Fresnel half-period zone

I am following this set of lecture notes (see below). I understand that the idea is to evaluate the Fresnel integral for the circular aperture using the graphic method. However I don't understand at ...
3
votes
0answers
154 views

Quantum vs classical degrees of freedom

It is sometimes stated that any classical underpinnings (rightly non-local) of a general quantum system are unrealistic or unphysical because these require exponentially more information to store what ...
-8
votes
1answer
122 views

Is this even possible to understand this proof? [closed]

Can someone explain what kind of sorcellery is this proof about Maxwell's equations: http://proofs.wiki/Maxwell%27s_equations_predict_that_the_speed_of_light_is_constant. Is this a joke?
1
vote
1answer
70 views

Obtaining momentum operator $P^\mu$ from Lagrangian and energy-momentum tensor $T^{\mu\nu}$

I am pretty new to quantum field theory. Given the Lagrangian density, $$ \mathcal{L} = \frac{1}{2} ( \partial_\mu \phi ) ( \partial^\mu \phi ) - \frac{1}{2} m^2 \phi^2 $$ and its energy-momentum ...
2
votes
1answer
207 views

Coherence length requirement for interference

One property of light sources that is usually stated, which is of particular importance when trying to create interference fringes, is the coherence length (or coherence time). The equation for the ...
19
votes
1answer
3k views

What happens if you remove the polarization filter from a computer monitor?

Have a look at this youtube video (and some extra footage here). Here I will post a gif showing in short what it is about: It shows that if you remove the polarizing filter from a pc's monitor and ...
0
votes
2answers
19 views

Exothermic heat release mechanism in gases

How is heat released when bond formation occurs in gases? For example, when atomic oxygen and molecular oxygen combine to form ozone?
2
votes
1answer
151 views

Time dilation simple derivation

In a special theory of relativity we have a phenomenon known as time dilation. There is a simple explanation of this, with a thought experiment with a train and a flash light: We flash a light in a ...
2
votes
1answer
51 views

How are specific volumes accurately measured experimentally?

In every thermodynamics textbook there are tables containing the specific volume of various fluids at different temperatures and pressures. My question is, how is this data obtained experimentally? ...
2
votes
1answer
46 views

Is there any difference in radiation pressure for two observers in different gravitational potential?

Suppose that a light beam is shone upwards from surface of a planet. So, due to gravitational redshift, the frequency of the light perceived by observer far from the surface will be lower than that ...
11
votes
3answers
986 views

Validity of Maxwell's equations with no aether or relativity?

In From Paradox to Reality: Our Basic Concepts of the Physical World by Fritz Rohrlich page 55 it states that [...] just doing away with the ether would not have resolved all problems. The ...
1
vote
0answers
46 views

Why is information transfer usually done through frequency modulation but not amplitude modulation [closed]

For example, if we were to transmit a sequence of code, we could do so by alternating the flash rate of the source, or alternate the strength of the source. Both methods can represent a large amount ...
0
votes
0answers
33 views

Why do thermal noise exist in the $\mu V$ range?

I am not familiar with thermal physics. I am conducting an experiment where I have to use muscle signal to control a car. I have noticed that in the literature a lot of thermal effects such as ...
5
votes
1answer
148 views

Can I fix a point in Minkowski space to give it a vector space structure?

I looked up the term Minkowski space on Wikipedia. It said There is an alternative definition of Minkowski space as an affine space which views Minkowski space as a homogenous space of the ...
1
vote
2answers
202 views

Could a really tall tube suck garbage in to space?

When I was around 10 years old, I had this idea that was supposed to solve our waste problems; I imagined having tubes miles high that would stretch in to space. Every tube would have a door at the ...
2
votes
1answer
110 views

Am I correct in saying this about a battery?

I recently answered this: Q When a battery, by performing work on a charge, moves it to the higher potential, why doesn't the charge move through the battery and return to the low potential, ...
1
vote
1answer
35 views

Why are crystals so useful for quantum isolation?

Some implementations of quantum gates (in the hopes of building a quantum computer one day) use crystals to isolate the qubits (to prevent decoherence). Why is a crystal so much better than an ...
0
votes
1answer
35 views

magnetostrictive effect due to earth's magnetic field

is there any magnetic field sensor,which produces stress or strain as output,when that sensor is sensing earth's magnetic field on the surface of earth(0.25 gauss to 0.65 gauss)?or any ...
2
votes
0answers
97 views

Kleppner derivation of Lorentz transformation

I am reading Kleppner.(Lorentz transformations) He said,we take the most general transformation relating the coordinates of a given event in the two systems to be of the form $$x'=Ax +Bt, y'=y, z'=z, ...
8
votes
3answers
507 views

What information is contained in the quantum spectral density?

Consider a harmonic oscillator system with Hamiltonian $$\hat{H} = \frac{1}{2} A \hat{u}^2 + \frac{1}{2} B \hat{v}^2 \qquad [\hat{u}, \hat{v}]=i \gamma $$ where $A$, $B$, and $\gamma$ are all real. ...
0
votes
1answer
79 views

How can I write the anderson hamiltonian as a matrix? [closed]

How can I write this Hamiltonian: $$ H = \sum E_d \hat{n}_d + \sum_k \epsilon_k\hat{n}_k + \sum_k V_{kd} (\hat{a}^\dagger_k \hat{a}_d + \hat{a}^\dagger_d \hat{a}_k) $$ in matrix form using its ...
1
vote
2answers
223 views

Is time infinitely divisible? [duplicate]

Simple question (I think). Is time infinitely divisible? I heard that it was, although not from a particularly explanatory source. If so, are we sure that it is, without a shadow of a doubt?

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