All Questions

497 views

Magnetic moment of relativistic rotating ring

Let's consider rotating charged ring. Theoretically mass of this ring has no limit as rotation speed increases. So what about magnetic moment of the ring? Is it limited by the value of speed of ...
2k views

What percentage of physics PhDs leave physics? [closed]

What percentage of physics PhDs leave physics to become quantitative analysts, work in computer science/information technology or business? Is physics that bad that so many people leave? Was it worth ...
170 views

316 views

Find drop-off rate of magnetic interference from a mass of pure iron on a magnetic compass

How can I find the magnetic interference a stationary 35000 kg block of 100% pure iron would have on a magnetic compass and what the drop off rate of the interference would be. So if said 35000 kg ...
481 views

Is holomorphy the real reason for nonrenormalization in supersymmetry?

Seiberg traced the nonrenormalization of supersymmetric theories to holomorphy of the superpotential in chiral superspace. However, this overlooks the fact that with a different number of ...
332 views

Why are some of the biggest stars known blue?

My question refers to an overview of the biggest stars we know: http://farm5.static.flickr.com/4138/4820647230_faba1c9f3b_o.jpg Why are some of those blue?
328 views

Justification of ignoring large set of entanglements

If we can think about the universe as a wave function then many particles should be entangled with many other particles in the universe. The obvious question arises why we don't see those ...
782 views

How much can AdS/CMT tell us?

I will begin my research on AdS/CMT, however I find AdS/CMT is only a phenomelogical method, so I want to know can AdS/CMT give some results the condensed matter physicists can not give, or even ...
704 views

Conservation of energy in quantum teleportation

Consider the quantum state teleportation protocol of Bennett et. al. How does one prove that this protocol would never violate the conservation of energy? At the face of it, it doesn't seem to be ...
414 views

What is the density of virtual photons around a unit charge?

It seems that virtual photons also exist in vacuum. So the precise question is: What is the additional virtual photon density due to the electric field of a unit charge? Or: How many virtual photons ...
147 views

Is the color gauge group spontaneously broken in QCD by the Savvidy vacuum?

One model for confinement in quantum chromodynamics is the Savvidy vacuum. This is a spontaneous symmetry breaking of color gauge symmetry by the gauge fields. The vacuum is divided into Savvidy ...
159 views

Are collaborations needed to be productive in physics?

If you look at most published articles, or those on the preprint server, you find the vast majority of articles have more than one authors. Are collaborations needed to be productive in physics? In ...
323 views

Is almost all entropy in our universe entanglement entropy?

Our observable universe, or a subregion of our universe many times larger than the observable universe, originated from inflating from a very tiny inflationary patch. Being so small, the initial ...
370 views

What does the Many-Body Problem say about mathematical physics?

I was interested to read the answers to the other Many-Body Problem questions on this site and was left with one nagging question of my own. What does the Many-Body Problem reveal about reality and ...
1k views

1D topological insulator

This question is inspired by another one about the simplest model of topological insulator, where 4tnemele showed a nice two band model in the answer. I read that and am wondering if we and push that ...
527 views

Order Parameters for the Higgs Phase

Phase transitions are often detected by an order parameter - some quantity which is zero in the "disordered" phase, but becomes non-zero when order is established. For example, if the phase transition ...
352 views

Calculating the deflection of an arbitrary beam of light from a thin lens

Suppose we have a lens with known focal length and are using the thin lens approximation. Is it possible to determine how an arbitrary beam of light will be deflected by it? Or, is it the case that ...
2k views

How does Newtonian mechanics explain why orbiting objects do not fall to the object they are orbiting?

The force of gravity is constantly being applied to an orbiting object. And therefore the object is constantly accelerating. Why doesn't gravity eventually "win" over the object's momentum, like a ...
2k views

How to build a laser in the garage?

So I wonder if it is any how possible to build laser at home. A powerful one to melt brick.
381 views

Withstanding charlatans: How to protect friends from buying “water structuring facilities”?

In my country it is a big business now, to sell "water structuring facilities". Promoters telling that after passing through them the water obtaining fantastic abilities basing on the fact that "water ...
875 views

Does ABS cause a force that resists turning a car into a corner?

ABS systems work by allowing a tire to continue to rotate rather than "locking-up" (stop turning) due to loss of traction with the road surface. A rotating tire can influence the direction of the ...
140 views

What are wimpy particles?

Can anyone give a brief overview of what a wimpy particle is?
6k views

Phase diagram for oxygen

Do you know where can I find simple diagram (solid, liquid, gas) for for oxygen? EDIT: I made a mistake. I wanted oxygen instead of water. sorry.
5k views

How can super massive black holes have a lower density than water?

I heard on a podcast recently that the supermassive black holes at the centre of some galaxies could have densities less than water, so in theory, they could float on the substance they were gobbling ...
2k views

What is the effect of polarization on diffraction by a narrow slit?

Consider the well known demonstration of diffraction by a narrowing slit. (See for example the demonstration at the 30 minute mark of this lecture at MIT by Walter Lewin) It is my (possibly mistaken) ...
863 views

What type of electromagnetic wave can pass through silver or aluminium standard mirror?

I have been told (not sure if it is true), that mirror (and glass) do not allow to pass the electromagnetic signals of mobile signals. but for a standard mirror what type of wave can pass through ...
9k views

How does a honeycomb grid affect the travel of light?

A light modifier that is commonly used in studio photography is a honeycomb grid. It narrows the beam of light to a circle with soft edges, as it can be seen here: My question is: how is this ...
4k views

Convert running speed uphill to equivilent speed on flat

Given a certain running pace uphill, I want to be able to determine an equivalent pace running with no elevation change. Assumptions: similar effort in both cases (say for example running at 90% max ...
654 views

Can a functional derivative be calculated if we have a function of more than one variable?

Can a functional derivative be calculated if we have a function of more than one variable? The functional derivative of, for example, $F[b(x)]=e^{\int_0^{x'} dx a(x,y) b(x)}$ is ...
537 views

Conjectures that have been disproved with extremely large counterexamples

I would like to migrate this Math Question into physics. The question is: Are there conjectures in Physics which have been disproved with extremely large counterexamples? If yes, i would like to ...
1k views

Do all light rays from a point passing through a thin lens converge at the image?

I have often seen diagrams, like this one on Wikipedia for a thin convex lens that show three lines from a point on the object converging at the image. Do all the other lines from that point on the ...
177 views

A particular supersymmetry transformation

While reading a paper I ran into this particular way of writing a $\cal{N}=3$ fields (in a theory with $N_f$ hypermultiplets) that I couldn't relate to anything I had seen before in the text-books ...
3k views

How can I find the potential difference of a plastic sphere in a capacitor?

A thin spherical shell made of plastic carries a uniformly distributed negative charge of -Q coulombs. Two large thin disks made of glass carry uniformly distributed positive and negative charges S ...
569 views

Probabilistic quantum cloning

I have a question with regard to probabilistic quantum cloning - see for example http://prl.aps.org/abstract/PRL/v80/i22/p4999_1. It does seems like I can use the proof for no-cloning theorem to ...
609 views

When lasers are used to cool atoms or ions, etc where does the heat go?

According to the first law of thermodynamics, sourced from wikipedia "In any process in an isolated system, the total energy remains the same." So when lasers are used for cooling in traps, similar ...
3k views

Pressure vs wind speed, on a rectangular surface

How do I go about finding the pressure exerted on a rectangular surface in a free flowing air stream? I wouldn't imagine that this is directly related to the airspeed / surface area, but have no idea ...
1k views

Measuring the spring constant in a system with hydrostatic buoyancy

I have a physics lab tomorrow and I would appreciate it if you could give me your opinion on whether my reasoning is correct for this situation or not: http://i.stack.imgur.com/WMzA7.jpg The title ...
929 views

What is more efficient: Add milk, and then heat up coffee in the microwave, or microwave than milk?

Adding milk first increases the volume to heat and lowers average temerature, but adding it afterwards seems to have similar effects. How can you compare the two?
302 views

Creating the proper suction

I'm a bit rusty on my fluid dynamics. I'm experimenting with creating my own leaf vacuum. How would I determine how much suction a fan creates? Bernoulli's equation would apply correct? I would ...