7
votes
1answer
435 views

BPS sectors in $\cal{N}=4$ SYM

I am familiar with the idea of a BPS bound as in a lower limit on the mass of supermultiplets given by a certain function of the central charge and when I think of $\cal{N}=4$ SYM I see a complicated ...
7
votes
1answer
230 views

Are non-supersymmetric GUTs ruled out due to lack of precise gauge coupling unification?

Does there exist any good proposal on how the gauge coupling unification can be fixed in non-supersymmetric GUTs? If not, can we assert that non-supersymmetric GUTs have been experimentally ruled out? ...
9
votes
2answers
1k views

How does the period of an hourglass depend on the grain size?

Suppose I have an hourglass that takes 1 full hour on average to drain. The grains of sand are, say, $1 \pm 0.1\ {\rm mm}$ in diameter. If I replace this with very finely-grained sand $0.1 \pm 0.01\ ...
9
votes
1answer
3k views

Standard Deviation in Particle Physics

I'm familiar with sigma, and how its usually calculated and used, but would like to know how it's applied to particle physics. I recall reading that the discovery of the Higgs would only be credible ...
0
votes
1answer
448 views

Electric field of a charged spherical surface [closed]

Figure The dielectric shaped as on the figure has dielectric constant $\varepsilon=\varepsilon\left(r\right)$ and free charge density $\rho=\rho\left(r\right)$. What is the electric field and ...
0
votes
4answers
778 views

Nature of Photons

Why is it that photons are emitted in bundles? My physics teacher's answer was "it's complicated"...
5
votes
2answers
181 views

Does the Casimir effect allow to change the lifetime of a radiating atom?

Is it true that a spontaneously light-emitting atom changes its lifetime if it is put between two parallel plates that are so near that they attract each other through the Casimir effect? Thus: does ...
2
votes
2answers
628 views

What is a Kustaanheimo-Stiefel transformation?

What is a Kustaanheimo-Stiefel transformation? Which applications has it in physics? Can you point me to a reference, where this transformation is explained?
2
votes
2answers
331 views

Have CMB photons “cooled” or been “stretched”?

Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't ...
2
votes
3answers
657 views

Question on Conformal Field Theory

Since every question has to be asked in a seperate topic, I'm asking a question refering to the following topic: Beginners questions concerning Conformal Field Theory In particula I'm refering to the ...
1
vote
2answers
517 views

Give me examples of crackpots who were right after all [closed]

I am interested in examples of crackpots coming up with correct results in physics. Why do mainstream physicists look down so much upon "crackpots"?
2
votes
1answer
197 views

When do we expect to get results from the LHC?

At the current LHC luminosities, will it take years to detect the Higgs boson, superpartners, or any other forms of new physics at the LHC? What should particle physicists do in the meantime? We ...
2
votes
1answer
236 views

Are valence electrons located solely in the s and p subshells?

Or are they in all subshells??
1
vote
0answers
950 views

Damping and stiffness constants of water

I'm working on a simulation of water drops falling into a pool. I'm specifically interested in the waves generated by the impact of the drops. In order to calculate the vertical motion of the waves, I ...
3
votes
4answers
588 views

Isn't wave particle duality of light actually cheating?

When answering questions about light, I see that we conveniently shift between wave and particle nature of light to match the answer-- isn't this really cheating? Or, is it the principle that the ...
1
vote
1answer
290 views

Does the Grand Canonical Ensemble allow for exchange of particles or not?

I was doing some reading on wikipedia and found it interesting that one page says the Grand Canonical Ensemble does not allow for exchange of particles, however another page says it does. So I went on ...
5
votes
1answer
295 views

Determining Average Tidal Effects

Maximum tidal heights vary widely across the globe, from 16 m in the Bay of Fundy to mere centimeters elsewhere. These variations are due to coastline and shoreline differences. This makes it ...
4
votes
4answers
2k views

Does mass affect speed of orbit at a certain distance?

Does the mass of both the parent object, and the child object affect the speed at which the child object orbits the parent object? I thought it didn't (something like $T^2 \approx R^3$) until I saw ...
7
votes
1answer
523 views

Can observations of entangled particles affect their unobserved counterparts?

There are two experiments that are often used to explain Quantum Mechanics: the two-slit experiment and the EPR paradox. I am curious what would happen if you combined them. Imagine an experiment ...
2
votes
2answers
199 views

What are the AFS values in the Atlas experiment?

If you go to the Atlas experiment http://atlas.ch/ and click the status button, there's an AFS reading at the bottom with a current value 50ns_228b+1small_214_12_180_36bpi_8inj The 50ns seems to ...
6
votes
1answer
445 views

Expansion of multi-particle state vector as a sum of n-entangled states

Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this: $$ |\Psi\rangle = |\phi_{i_{0} i_{1} ... ...
6
votes
1answer
531 views

Is microcausality *necessary* for no-signaling?

There are proofs in the literature that QFT including microcausality is sufficient for it not to be possible to send signals by making quantum mechanical measurements associated with regions of ...
2
votes
1answer
2k views

How does Telescope lens work?

1.How does a Telescope work? 2.What factors increase the magnification of the lens?
2
votes
1answer
413 views

Do all atoms in the universe gravitate each other?

I understand that matter will gravitate toward matter. (ex: Earth gravitates a satellite toward it, and the satellite toward Earth.) Does this always apply, regardless of distance?  Take two atoms, ...
4
votes
3answers
585 views

Nomenclature: Yang-Mills theory vs Gauge theory

If you're writing about a theory with Yang-Mills/Gauge fields for an arbitrary reductive gauge group coupled to arbitrary matter fields in some representation, is it best to call it a Yang-Mills ...
2
votes
3answers
212 views

Making a “heavier-than-air” craft float

How big would a hollow rigid object need to be to float, (not in water but in air) if all of the air was vacuumed out and the container sealed?
0
votes
4answers
734 views

Voltage drop along an idealized resistance-free wire in a circuit?

If you connected the positive terminal of a battery to the negative terminal to a battery with a wire with (hypothetically) no resistance, and are asked to give the voltage drop of a segment of wire ...
-1
votes
5answers
469 views

Is special relativity an exact description of reality?

In discussing relativity with a (somewhat mathematical) friend the other day, I ran into a problem showing why special and/or general relativity could be considered as exact descriptions of reality ...
0
votes
0answers
81 views

A question about the relativity of time [duplicate]

Possible Duplicate: Invariant spacetime - distance - Circular Motion I understand that the closer something travels to the speed of light, that time will stretch by a factor, and distance ...
12
votes
5answers
878 views

Why is the contribution of a path in Feynmans path integral formalism $\sim e^{(i/\hbar)S[x(t)]}$

In Feynman's book "Quantum Mechanics and Path Integrals" Feynman states that the probability $P(b,a)$ to go from point $x_a$ at time $t_a$ to the point $x_b$ at the time $t_b$ is $P(b,a) = ...
10
votes
2answers
1k views

Invariant spacetime - distance - Circular Motion

I understand that the closer something travels to the speed of light, that time will stretch by a factor, and distance will compress by the same factor. My question is, if something travels in a ...
5
votes
1answer
212 views

Why can you assume that the angular momentum vector of a top will always track its axis of rotation?

My favorite physics 101 textbook (Giancoli) explains precession in terms of a spinning top whose axis is tilted from the vertical. The way the book sets things up, $L$ (angular momentum) points along ...
5
votes
5answers
1k views

Is there the smallest particle that can be guaranteed to be unable to be broken down into smaller particles?

Is there the smallest particle that can be guaranteed to be unable to be broken down into smaller particles?
17
votes
6answers
3k views

Are human eyes the best possible camera?

I am not a physiologist, but whatever little I know about human eyes always makes me wonder by its details of optical subtleties. A question always comes to mind. Are human eyes the best possible ...
6
votes
2answers
235 views

Does the lack of modular nuclearity in string theory mean anything?

Nuclearity is a postulate in algebraic quantum field theory (AQFT). Basically, it says thermal states at any temperature always have a thermodynamic limit with extensive quantities. This is violated ...
4
votes
4answers
433 views

Can a disk like object (like UFO's) really fly?

UFOs as shown in movies are shown as disk like objects with raised centers that emit some sort of light from bottom. Can such a thing fly? My very limited knowledge in physics tell me that a disk ...
8
votes
1answer
800 views

Why does the water in the toilet move around so much on stormy days?

On calm days, the water in the toilet looks completely still. But when it's rainy and windy out, the water looks like it moves and pulsates. Why is this?
3
votes
1answer
385 views

The superconformal algebra

How does one derive the superconformal algebra? Especialy how to argue the existence of the operator $S$ which doesn't exist either in either the supersymmetric algebra or the conformal algebra? ...
1
vote
2answers
440 views

Is energy exchange quantized?

In the photoelectric effect there is a threshold frequency that must be exceeded, to observe any electron emission, I have two questions about this. I) Lower than threshold: What happen with lesser ...
11
votes
4answers
1k views

If all conserved quantities of a system are known, can they be explained by symmetries?

If a system has $N$ degrees of freedom (DOF) and therefore $N$ independent1 conserved quantities integrals of motion, can continuous symmetries with a total of $N$ parameters be found that deliver ...
1
vote
0answers
98 views

How to compute the heat flow for a specific material for some given boundary temperature?

Assume I have a bounded material with heat sources inside. The material is known (i.e. I know heat capacity and all relevant data) and the temperature of the boundary is fixed. I solved the (steady ...
1
vote
1answer
1k views

What is the resistivity coefficient of graphene?

What is the resistivity coefficient of graphene?
12
votes
4answers
913 views

How do I correctly interpret $\rho = \psi_1^* \psi_2$?

Summary: This turned out to be a rather trivial one indeed. As Marek mentioned in the comment, the continuity equation is trivial. And it indeed turns out be so. Godfrey Miller elaborates on this, ...
5
votes
1answer
4k views

Newton's color Disk

How does Newton's color disk work? Newton's disk - Take a circular white color disk, make 7 equal intersections and paint section with respective VIBGYOR colors, now when you spin the disk in certain ...
4
votes
1answer
108 views

Where can I get the most accurate measurements of parton distribution functions?

Where would I look to get the most accurate experimental values of parton distribution functions for the proton? I know these functions aren't measured directly, but I'd basically like to find a fit ...
5
votes
2answers
931 views

Rocket engines: air & vacuum

Could you please help me understand what is the difference between rocket engines designed to work in air (first stage) and vacuum (later stages)?
5
votes
1answer
816 views

Open shells in Quantum mechanics of multielectron atoms

This question: How do electron configuration microstates map to term symbols? And the discussion of multielectron effects here: Quantum Computing and Animal Navigation Inspired me to try to understand ...
23
votes
4answers
10k views

What's the difference between the five masses: inertial mass, gravitational mass, rest mass, invariant mass and relativistic mass?

I have learned in my physics classes about five different types of masses and I am confused about the differences between them. What's the difference between the five masses: inertial mass, ...
2
votes
1answer
622 views

Temperature vs AC energy consumption

I'm need to understand the following: to keep the room at confortable temperature (70 degree, for example), how does the amount of energy consumed by the AC grow as the outside air temperature rises ...
10
votes
3answers
500 views

What is the difference between $|0\rangle $ and $0$?

What is the difference between $|0\rangle $ and $0$ in the context of $$a_- |0\rangle =0~?$$

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