2
votes
1answer
1k views

Nanotech - zero dimensional fullerene

Not really a physics junkie, and I think this is a chemistry question, but since there's no chemistry.stackexchange.com (yet) I think here is the best place. I was just reading up on nanotech and ...
1
vote
1answer
248 views

Maxwell's Demon bug, trapdoor space and time

What about the size of the door (space) and how long has it to be opened (time)? I think Maxwell's demon would have a problem with space, if the door is too wide (more than one particle size), then ...
3
votes
1answer
340 views

Effects of parallel superconducting plates

Assuming the existence of virtual particle field ( zero point energy field) Casimir force is produced by 2 parallel conducting plates excluding some of the frequencies between the plates, if these 2 ...
4
votes
2answers
284 views

Generalisation of Reversible Equation to Non-Reversible Situations Because it Only Contains 'Properties of the System'

I've just been reading through Van Ness' Understanding Thermodynamics, and I'm having a little trouble following his argument at one point. He is deriving the useful differential equation: $$dU=T \ ...
-1
votes
1answer
168 views

frames of reference [duplicate]

Possible Duplicate: Help Me Gain an Intuitive Understanding of Lorentz Contraction Frames k and k' are inertial frames. Frame k' is moving at a velocity of magnitude v relative to frame k ...
2
votes
1answer
513 views

Einstein Relative Motion and Time Order of Events

According to Einstein, do observers in relative motion agree on the time order of all events? I don't think they would agree on the timing of events, but I am having trouble figuring out why they ...
3
votes
1answer
169 views

Can a solar thermal collector designed for use in homes ever power a stirling engine designed for use in homes?

Can a solar thermal collector common on private roofs today designed for collecting heat for the household ever collect enough heat to power a stirling engine of say this model: ...
8
votes
4answers
2k views

Can gravity be shielded, like electromagnetism?

If I remember well, they said that it can't, but I do not know why. Yes, I meant if gravity can be shielded using something like a Faraday cage (or something else?). Thank you.
0
votes
1answer
978 views

Temperature change effected by electric heater [closed]

A 40-gallon electric water heater has a 10kW heating element. What will the water temperature be after 15 min of heating if the start temp is 50F degrees. There must be an equation. I can't find it ...
1
vote
2answers
259 views

Where to find cross section data for e- + p -> p + e-?

Where to find cross section data for e- + p -> p + e-? PDG's cross section data listing does not include it.
0
votes
2answers
275 views

light travels a maximum speed… /? [duplicate]

Possible Duplicate: Is it possible for information to be transmitted faster than light? we know that speed of light is an unconquerable term in physics..light takes about 1 year to travel ...
2
votes
2answers
726 views

Basic question about law of gravitation [duplicate]

Possible Duplicate: Radial fall in a Newtonian gravitational field This is how Wikipedia defines Newton's law of Gravitation: Every point mass attracts every single other point mass by ...
4
votes
2answers
515 views

Conceptual puzzles when using Coulomb's potential in solving the hydrogen atom in non relativistic QM

When solving the hydrogen atom in non relativistic quantum mechanics we use Coulomb's potential, $\sim1/r$, to describe the interaction between the proton and the electron. I am worried about two ...
10
votes
1answer
196 views

Are Uranus and Neptune too big for their location?

So I was watching some TV, and I heard Dr. Plait mention that the planets Uranus and Neptune are too big to be located so far out in our solar system. Now, I heard his explanation on the show as to ...
8
votes
2answers
1k views

Some questions about Wilson loops

Let $G$ be the gauge group whose Yang-Mill's theory one is looking at and $A$ be its connection and $C$ be a loop in the space-time and $R$ be a finite-dimensional representation of the gauge group ...
7
votes
4answers
2k views

Can Planck's constant be derived from Maxwell's equations?

Can mathematics (including statistics, dynamical systems,...) combined with classical electromagnetism (using only the constants appearing in chargefree Maxwell equations) be used to derive the Planck ...
3
votes
1answer
412 views

An odd relation with the epsilon/delta invariant tensors of SO(3)

The rotation group SO(3) can be viewed as the group that preserves our old friends the delta tensor $\delta^{ab}$ and $\epsilon^{abc}$ (the totally antisymmetric tensor). In equations, this says: ...
-2
votes
2answers
343 views

Occam's razor on spin statistics theorem?

Highly related to A reading list to build up to the spin statistics theorem I see 2 parts to the spin statistics theorem: (spin $n$ or $n+\frac{1}{2}$) step 1 given that a spin is integral or ...
-1
votes
3answers
187 views

Earth's stationary iron core

Why is the earth's iron core stationary, while the liquid matal circles around it creating the magnetic shield. Don't understand how can the entire planet rotate where as the planet's center is ...
3
votes
1answer
203 views

Feynman Diagram for Bragg Equation

Did Feynman ever derive the Bragg equation as a particle representation using Feynman diagrams? And where is it available? I spoke to Freeman Dyson and he couldn't recall.
-3
votes
3answers
2k views

Should linear algebra and vector calculus from traditional courses be replaced with `geometric algebra`? [closed]

geometric algebra gives geometric meaning to linear algebra and much more. it can provide a coordinate free geometric interpretation of spaces. those who learn of ...
4
votes
2answers
290 views

What specifically are the measurements that correspond to fixing the infinite number of counterterms in quantum gravity?

I understand that quantum gravity is nonrenormalizable because there are an infinite number of counterterms. In QED the counterterms correspond to the loop corrections to the vertex function as well ...
6
votes
3answers
676 views

Axiomatic statistical mechanics

Ive read a few courses on statistical mechanics, and while their textual explanations and example choices differ, the flow of information from microscopy to macroscopy seems the same, and reading ...
28
votes
3answers
3k views

What's the interpretation of Feynman's picture proof of Noether's Theorem?

On pp 103 - 105 of The Character of Physical Law, Feynman draws this diagram to demonstrate that invariance under spatial translation leads to conservation of momentum: To paraphrase Feynman's ...
-2
votes
1answer
73 views

To what extent `should` raw `data` from `publicly funded` research be made `available for download` `?` [closed]

When taxpayers pay money for expensive research (irrespective of the partition-function ...
1
vote
1answer
309 views

How can I turn a pinewood derby project into a physics lesson?

My 8yo son is in the Cub Scouts. He has a pinewood derby coming up next month and I would like to take this project and turn it into a fun, physics lesson for him. For those not familiar, a ...
1
vote
5answers
420 views

How do electrical devices suck electricity?

If the electric potential is 220V and some device needs 1500watts then how does it suck exactly that amount of electrical energy from outlet?
2
votes
1answer
2k views

Rotating fluid under gravity, fluid dynamics question

An incompressible inviscid fluid is rotating under gravity g with constant angular velocity $\Omega$ about the z-axis, which is vertical, so that $u = (−\Omega y, \Omega x, 0)$ relative to fixed ...
4
votes
1answer
181 views

How can there be a path to ground with thick shoes and a carpet?

I'm connecting a test light to one pin of an halogen lamp. When I touch the metallic part on the back of the test light, the light glows, as it is supposed to. However, I have thick shoes and I am ...
2
votes
1answer
14k views

Torque Required For a Motor to Move an Object on Wheels?

I've been attempting to calculate how much torque a motor needs to produce in order to start a stationary object on wheels moving. (The torque is being applied to the rear 2 wheels, the front 2 are on ...
3
votes
3answers
1k views

What is the meaning of speed of light $c$ in $E=mc^2$?

$E=mc^2$ is the famous mass-energy equation of Albert Einstein. I know that it tells that mass can be converted to energy and vice versa. I know that $E$ is energy, $m$ is mass of a matter and $c$ is ...
4
votes
1answer
314 views

What are conditions for the existence of a critical value (for a phase transition)?

Can there only be a critical temperature if there is some natural unit for an observable in the model, i.e. if there is a natural scale for something? Otherwise I don't see how for a system there ...
5
votes
2answers
4k views

Calculating gravity when taking into account the change of gravitational force

This is a problem that has bothered me for a couple of weeks now, and I can't seem to wrap my head around it and understand it. Let's say we have a planet with a mass of m. We also have an object of ...
1
vote
2answers
399 views

Simple conservation of momentum

Imagine a particle moving right at 10 mph. It enters a cylinder with an open left end and closed right end. The cylinder is moving right at 1 mph. In the frame of reference of the cylinder, the ...
2
votes
1answer
529 views

Symbolic tool for doing 2nd quantization operator calculations

I think everyone who has attended a lecture introducing second quantization appreciates what a pain it can be to compute expressions involving commutators or anticommutators with lots of operators. ...
1
vote
1answer
263 views

Inverting Generalized Coordinates

In Corben's classical mechanics on pg. 9, it says that given generalized coordinates $q_m = q_m(x_1, ..., x_n,t)$, then if the Jacobian is non-zero everywhere, you may express $x_i = ...
1
vote
0answers
390 views

Style in Physics vs Mathematics [closed]

I'm a mathematics major who has taken a few physics courses and the presentation in physics texts bothers me. In mathematics, the standard format is a theorem-proof repetition with some discussion. ...
2
votes
1answer
523 views

Origins of the principle of least time in classical mechanics

Is it possible to derive the principle of least time from the principle of least action in lagrangian or hamiltonian mechanics? Or is Fermat's principle more fundamental than the principle of least ...
1
vote
1answer
143 views

What is an isoscalar factor?

I need to find a definition for "the isoscalar factors of 3j-symbols for the restriction $SO(n)\supset SO(n-1)$...denoted by brackets with a composite subscript $(n: n-1)$..." They are given as: $$ ...
5
votes
1answer
501 views

Source term of the Einstein field equation

My copy of Feynman's "Six Not-So-Easy Pieces" has an interesting introduction by Roger Penrose. In that introduction (copyright 1997 according to the copyright page), Penrose complains that Feynman's ...
8
votes
1answer
705 views

Relativistic center of mass

Recently I realized the concept of center of mass makes sense in special relativity. Maybe it's explained in the textbooks, but I missed it. However, there's a puzzle regarding the zero mass case ...
18
votes
3answers
879 views

Has the concept of non-integer $(n+m)$-dimensional spacetime ever been investigated by theoretical physicists?

The following image serves to aid the reader in understanding the "privileged character" of $3+1$-spacetime. The wikipedia article on spacetime, and the sub-article "The priveleged character of ...
4
votes
1answer
824 views

How does Newton's 2nd law correspond to GR in the weak field limit?

I can only perform the demonstration from the much simpler $E = mc^2$. Take as given the Einstein field equation: $G_{\mu\nu} = 8 \pi \, T_{\mu\nu}$ ... can it be proved that Newton's formulation ...
9
votes
5answers
700 views

sun-moon-earth anomaly

When one looks at the sun and the moon in the sky together, why is it that the illuminated crescent of the moon does NOT "point" at the sun? (More correctly the perpendicular bisector of the straight ...
3
votes
1answer
578 views

Feynman rule 4-point vertex WW -> ZZ

I am looking for the Feynman rule of the 4-point gauge boson interaction of W+ W- -> Z Z. I am guessing it looks like the Yang Mills 4-point vertex for gluons, but with helicity included. Equation ...
5
votes
2answers
115 views

Significance of massive states in string theory

A free superstring has an infinite tower of states with increasing mass. The massless states correspond to the fields of the corresponding SUGRA. In "Quantum Fields and Strings: A Course for ...
2
votes
3answers
786 views

Hilbert space and Lie algebra in quantum mechanics

We are looking for a publication or website that explains the Standard Model in terms of Hilbert space and Lie algebra. We are reading Debnath's Introduction to Hilbert Spaces and Applications and ...
1
vote
1answer
201 views

Where does the photon's energy come from in X-ray bremsstrahlung?

In an X-ray tube, bremsstrahlung is generated by accelerating electrons toward a target metal. As a photon is emitted, something loses energy. I suppose that the target metal remains fixed and is ...
6
votes
1answer
1k views

What software programs are used to draw Mechanics, Electricity & Magnetism, Waves, Thermodynamics, Optics & Modern Physics diagrams? [duplicate]

For training students in competitive exams & physics olympiads, I want to illustrate deeper meanings in problem solving through diagrams. I have my teaching material hand drawn in OneNote. I want ...
20
votes
3answers
1k views

Quantum field theory variants

Wikipedia describes many variants of quantum field theory: conformal quantum field theory topological quantum field theory axiomatic/constructive quantum field theory algebraic quantum field theory ...

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