1
vote
2answers
18 views

Thawing of permafrost causes positive feedback loop in greenhouse effect?

This is claimed in my climate change class, which is admittedly pretty sparse in rigorous climate physics. The reason is that there are pretty large carbon deposits in glaciers which will further the ...
1
vote
1answer
11 views

Different postulates and statistical interpreations of quantum mechanics

Hi I have a query about the difference of two aspects of the statistical interpretation of quantum mechanics given in the popular introductory quantum mechanics books "Introduction to Quantum ...
0
votes
0answers
9 views

Are tides just very very very weak spaghettification?

I was wondering as to why there are two tidal bulges instead of just one on Earth, and then I saw this diagram: The oval shape that the Earth's water is transformed into in this image reminded me of ...
0
votes
0answers
2 views

How does electrical energy develop by concentrating ions on one side of a biomembrane?

In biology there is a topic called oxidative phosphorylation. In the first step of this process substrates such as isocitrate is oxidised and the electrons are transferred to coenzymes NAD+ or FAD ...
0
votes
0answers
5 views

Tractrix - velocity pointing to pulling point

It is said the tractrix is the curve described by a mass being pulled by a string, where the end of the string being pulled moves with constant speed, and the mass suffers a drag force. What is the ...
-1
votes
1answer
16 views

Global Hyperbolicity in spacetime Manifold

If space time is timelike or null geodesically incomplete but cannot be embedded in a larger spacetime then we say that it has singularity. What does incompleteness means here?
7
votes
3answers
492 views

Polarization of the lowest mode of a gaussian beam

Most introductory analyses of Gaussian beam optics work within Helmoltz scalar optics, and therefore they ignore the beam's polarisation. Because of that, I'm not clear on what are the possible ...
0
votes
2answers
29 views

What is more basic thing to explain phenomenons : Energy or Force?

You know many physical happening are explained by considering forces or we can explain these phenomenon using energy (like energy conservation, etc.). so i was wondering that explaining the physical ...
2
votes
1answer
149 views

polarization of a transverse wave travelling in ionosphere with polarization direction perpendicular to earths magnetic field

Assume a transverse electromagnetic wave entering ionosphere such that its Electric field of wave is perpendicular to earths magnetic field. Now, i read that as it will enter plasma, the wave will ...
2
votes
0answers
39 views

Adiabatic piston: why is Callen's argument flawed?

This question is related to this one. I would ask you to read that question and my answer to the question itself before answering this one. The problem is the following. In his book Thermodynamics, ...
2
votes
0answers
71 views
+50

Is it possible to determine maximum frequency of a disc using a relative circumference?

On Wikipedia there is an article that shows how to calculate the relativistic effects on a rigid spinning disc, I am referencing the formula under the "Ehrenfest's argument" section in the link. The ...
2
votes
0answers
16 views

Integrating out heavy fields while preserving symmetries

The basic a-b-c for integrating out heavy fields what one learns when making the example of Fermi theory, is that if you have a Lagrangian $L= -\frac{1}{4}F^{\mu\nu}F_{\mu\nu}+\frac{1}{2}M^2 V^\mu ...
1
vote
0answers
18 views

What to do when the fields are arranged in a matrix?

I am dealing with a Lagrangian in which the fields are arranged in an $N\times N$ matrix and i have to find the minima of the potential. Usually i would write the Lagrangian in components and then ...
0
votes
0answers
7 views

On Carnot engine and heat pollution

Suppose a power plant uses a Carnot engine to generate electricity, using the atmosphere at 300 K as the low-temperature reservoir. Suppose the power plant produces 1 × 106 J of electricity with ...
1
vote
1answer
50 views

Why is Wick contraction a $c$-number?

It is mentioned in Fetter's Quantum Theory of Many-Particle Systems (in contraction part of section 8 Wick's Theorem), that: contractions are c numbers in the occupation-number Hilbert space, not ...
0
votes
2answers
36 views

Why does the centrifugal term involve a vector originating from the center of Earth?

Why in every mechanics/dynamics book I look the centrifugal force due to Earth's rotation is measured from "the center of Earth"? For example in Marion's dynamics, the fixed inertial axes are placed ...
0
votes
4answers
26 views
3
votes
1answer
686 views

Homopolar motor and Lorentz force

My second grader thought making a homopolar motor for her science experiment would be fun. And, it was. Now I am trying to explain how it works and the Lorentz force. Please help me by giving me a ...
12
votes
3answers
353 views

Why does LIGO do blind data injections but not the LHC?

The LIGO group has a team that periodically produces fake data indicating a possible gravitational wave without informing the analysts. A friend of mine who works on LHC data analysis told me that ...
5
votes
3answers
10k views

Pressure of sealed in liquid nitrogen

If you take a container of great strength, fill it to the brim with liquid nitrogen, seal the container, and heat it to room temperature. What will the pressure be inside? Bonus: The same with ...
-2
votes
0answers
31 views

Eigenvalue equation with position operator

I have done a little run through of a basic QM eigenvalue equation for a particle on a 2D plane from bra-ket notation in the spirit of a complex position operator, although I have solved the SE, ...
1
vote
0answers
11 views

Very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth

I need a very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth. Currently, thanks to the algorithm which generates the position ...
0
votes
0answers
21 views

Noether current for a transformation for the Klein-Gordon Lagrangian

I have this Lagrangian density $$\mathcal{L} = \frac{1}{2}(g^{\mu\nu}\partial_\mu\phi\partial_\nu\phi^* - \mu_0^2\phi^*\phi)$$ with $g_{\mu\nu} = g_{\mu\nu}(x^\alpha)$ and I need to get the Noether ...
-3
votes
0answers
14 views

Books for students [duplicate]

Can any one please suggest me books for physics. I need a book for good theory and concept . And a book for practice , it should contain some solved questions. The both the books should contain ...
1
vote
0answers
8 views

What is exactly the difference between an active and passive frequency standard?

In the case of passive atomic frequency standard, we take an atomic reference which has a resonant frequency response centered at certain particular frequency. Then we take a local oscillator and tune ...
4
votes
2answers
273 views

Why does Srednicki insist on $\phi$ having zero VEV?

Let $\phi$ be a scalar field in an interacting theory ($\phi^3$ or $\phi^4$, for example). If $|0\rangle$ is the vacuum of the interacting theory and $P^\mu$ is the four-momentum operator, we have ...
0
votes
1answer
29 views

Are pure Dirac fermions (electrons, quarks, …) allowed to have effective Majorana mass?

Charged particles such as electrons and quarks are not allowed to have a hard Majorana mass (see here). With 'hard' I mean an explicit mass term in the Lagrangian which would break the corresponding ...
0
votes
1answer
31 views

Scattering in Schrödinger picture

If we look at a scattering process in the Schrödinger picture for a Hamiltonian $H = H_0(t) + V(t)$ where $H$ is independent of time (because we examine a theoretical situation after accelerating ...
-2
votes
0answers
13 views

Mathematical formula for maximum sound pressure level [on hold]

I googled a math equation for calculating Maximum Sound Pressure Level but couldn't help myself. What is it?
1
vote
1answer
406 views

Bernoulli's Equation for flow of gas and changing area

My task is to determine the size of piping needed in a system. In this system, hydrogen gas flows horizontally in a $\frac{3}{4}\,\mathrm{inch}$ pipe and into a vertical pipe of a larger diameter. My ...
-3
votes
1answer
41 views

What is hyperbolic metamaterial?

What is hyperbolic metamaterial? Could you explain in a few words what is hyperbolic metamaterial?
1
vote
4answers
49 views

Question about levers

Suppose we have a lever $AB$ of length $1m$ and that the fixed point is $O$ and $AO=0,3m$. If in $B$ I have a down vertical force of $F_1=5N$, find the force $F_2$ applied in A that guarantees the ...
7
votes
3answers
984 views

If water is essentially incompressible, why are there tides?

So recently we were taught in school that tides are formed because the moon 'cancels out' some of the earth's gravity, and so the water rises because of the weaker force. But if water is not ...
1
vote
1answer
142 views

Specific Internal Energy Decreases with Increasing Pressure?

I was looking at "Properties of Compressed Liquid Water" (Table A-5) in Fundamentals of Engineering Thermodynamics by Moran. Table A-5 shows that the specific internal energy $u$ of compressed liquid ...
21
votes
4answers
1k views

Difference between sunrise and sunset?

Other than knowing which direction is east and which direction is west, or observing for a sufficient timespan (to determine the direction of motion), is there any way of telling whether what one is ...
1
vote
1answer
29 views

Why do quasi-free states satisfy the positivity condition?

In LQFT, a state, $\omega$, is a linear map $\omega:A=:CCR({\cal{S}},\Omega)\rightarrow \mathbb{C}$ satisfying: $\omega(aa^{*})\geq 0$ for all $a\in A$. $\omega(I)=1$ where $I$ denotes the identity ...
-3
votes
0answers
26 views

Non-locality Vs deterministic correlated states [on hold]

Take this scenario: 2 pair were entangled (P1,P2) Take P2 and entangle it with P3 Destroy P2 Now we have P1 & P3 correlated although they never met each other. P2 transferred it's ...
0
votes
0answers
8 views

does changing air velocity change the frequency of sound coming out of a whistle?

If I use an air compressor and vary the velocity of the air coming out, does the frequency of the whistle change too?
0
votes
1answer
160 views

Internal Resistor in a Diode

When we talk about the resistance of a diode (of the P and N region), is this resistance like the one inside an Electro-Motive Force or it acts like a normal resistor (external electric field exist)? ...
0
votes
1answer
26 views

Can we perform matrix operations of CNOT on 2 qubit systems? [closed]

I am trying to get started on quantum computing. I find that 2x2 matrices like Pauli X,Y,Z,or gates like H,S can be used to perform operations on single qubits as direct matrix multiplication. For e.g ...
5
votes
3answers
385 views

Terminal velocity after vertical launch

If an object is launched directly up at its terminal velocity, will it have enough time/energy to reach its terminal velocity again before it hits the ground, or will drag prevent this? In this case, ...
1
vote
1answer
20 views

What is the gravitational/electric/inverse-square field inside a cylinder?

I've read from the shell theorem that an inverse-square potential has zero field inside a spherical shell. What about the field inside a cylinder? Are objects inside a long cylinder attracted to the ...
1
vote
0answers
26 views

World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
0
votes
0answers
18 views

Is the magnetic field caused by the lenght contraction, as seen by us, in the frame of a fast moving charged particle?

If for example an electron moves very fast relative to us, then the length contraction as seen by us, causes the electric field lines to compress themselves in the direction of motion. Is this the ...
3
votes
3answers
323 views

Fringe width and spacing and number of slits in diffraction experiments

In a single slit experiment, the fringes are not equally spaced and aren’t of equal widths—the central maximum is the widest, the secondary maxima grow narrower and narrower outward, and the minima ...
0
votes
2answers
108 views

Why doesn't current induced by changes in flux affect the flux, while current induced by a battery does?

Faraday's law states $V=-\frac{\mathrm{d}F}{\mathrm{d}t}$, where $F$ is flux. Since $V=IR$ for passive circuits, $I = V/R = -\frac{1}{R}\frac{\mathrm{d}F}{\mathrm{d}t}.$ But by the Biot-Savart law, ...
3
votes
1answer
47 views

Schrödinger-Pauli Equation Solutions

The Schrödinger-Pauli equation is the non-relativistic limit of the Dirac equation, and therefore describes spin-1/2 particles in an external electromagnetic field. It is given by: ...
-1
votes
0answers
19 views

Is the change in viscocity of water at 1C vs 99C discernable visually?

Waters viscosity varies from 1.7 at 0C to .3 at 100C. Is this visually confirmable?
0
votes
0answers
19 views

High School Physics What to Do [duplicate]

I am an aspiring physicist in high school and I would like to know ways to get involved. Of course, it would look great for potential physics colleges, but I really want to understand physics better. ...
0
votes
0answers
15 views

Can a Van de Graaff Generator be used to put plasma at high potential?

Lets say hypothetically, we use a sphere of plasma (ofcourse lab-plasma, stabilized somehow) instead of a sphere of metal in a van de graaff generator. Now can we use it to put a large amount of ...

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