# All Questions

2answers
417 views

### What is an “inclined magnetic field”?

What is meant by an "inclined magnetic field"? How is it different from the usual magnetic field?
1answer
303 views

### Free/open source tools for calculating normal modes, failing that, advice

Are there any open source tools for calculating the normal modes of arbitrary objects? Input would be some 3D design format and material properties, output would be movement direction and magnitude ...
0answers
429 views

### Skin effect and currents

Here in this picture you can see I_W which is induced by H. But why I_W is not vice versa? Because of rot \, \vec B = \mu_0 \, \left( \varepsilon_0 \frac{\partial E}{\partial t} + \vec j ...
3answers
808 views

### Light bending by black holes

In the center of our milky way, it is assumed that a black hole exists with a mass of $\approx 4\times 10^6$ times our sun's mass. How much light bending (in degrees) would arise for stars that are in ...
3answers
1k views

### What happens when a black hole and an “anti-black-hole” collide?

Let's say we have one black hole that formed through the collapse of hydrogen gas and another that formed through the collapse of anti-hydrogen gas. What happens when they collide? Do they (1) ...
7answers
2k views

### References about rigorous thermodynamics

Can you suggest some references for rigorous treatment of thermodynamics? I want things like reversibility, equilibrium to be clearly defined in terms of the basic assumptions of the framework.
5answers
1k views

### Dark matter and dark energy references

I've been looking for questions about dark matter, and I've read some very interesting answers. However, I desire too look into it deeply. This is not actually a question. I'm asking the community ...
2answers
1k views

### Dynamics of moment of inertia

I'd like to be able to determine the angular acceleration of a system of two rotating masses, which are connected so as to have a variable mechanical advantage between the two. My background with ...
3answers
219 views

### Object docking in Space

How do objects dock in space? There's a recent piece of news that Keppler would dock to the ISS sometime this week. I want to know the operational aspects of it - considering the velocity of the ...
3answers
733 views

### What does it mean, when one says that system has N constants of motion?

For example for an isolated system the energy $E$ is conserved. But then any function of energy, (like $E^2,\sin E,\frac{ln|E|}{E^{42}}$ e.t.c.) is conserved too. Therefore one can make up infinitely ...
1answer
710 views

### feynman diagram - direction of arrows

http://upload.wikimedia.org/wikipedia/commons/1/1f/Feynmann_Diagram_Gluon_Radiation.svg Why does the arrow of the positron doesn't show upwards?
3answers
1k views

### Spinning Tachyons

In all examples that I know, tachyons are described by scalar fields. I was wondering why you can't have a tachyon with spin 1. If this spinning tachyon were to condense to a vacuum, the vacuum ...
3answers
497 views

### Consistent theory of continuum

Why is there a consistent theory of continuum mechanics in which one just consider things like differential elements and apply Newtons laws? Is there a deeper reason for it. Is it the nature of ...
2answers
2k views

### A pendulum clock problem

Below is a picture of a simple pendulum clock. Suppose that the bob (a rigid disk) on the end of the pendulum can spin without friction about its geometrical axis and is spinning at an angular ...
3answers
496 views

### Do extra-dimensional theories like ADD or Randall-Sundrum require string theory to be true?

What I mean is could it turn out that the world is not described by string theory / M-Theory, but that nevertheless some version of one of these extra-dimensional theories is true? I have no real ...
1answer
1k views

### Why does lambda decay violate parity?

When a lambda particle decays into proton and a pion, I am told it does not conserve parity. Why?
4answers
541 views

### What is the medium that allows magnetic fields *or any forcefield* to exist?

Magnetic fields are obvious distortions.. of.. something, but what exactly are they distortions of? Massive objects produce curvatures/gradients in space-time resulting in what we observe as ...
9answers
16k views

### What's the core difference between the electric and magnetic forces?

I require only a simple answer. One sentence is enough... (It's for high school physics)
3answers
2k views

### Is there a nice tool to plot graphs of paper citations? [closed]

I would like a tool which allows me to enter some paper citation, and then will begin drawing a graph, where each paper is linked to other papers that cite the original paper or are cited by it. It ...
2answers
962 views

### Quantum shot-noise and the fluctuation dissipation theorem

Classically, shot noise observed in the signal generated by a laser incident on a photodiode is explained as being due to the quantization of light into photons, giving rise to a Poisson process. In ...
1answer
415 views

### what does 'same energy as a ton of TNT' mean?

Very often the energy released in large-scale events (e.g., earthquakes, meteor impacts, etc) is described in terms of some number of 'tons of TNT'. This may be all well and good for those with an ...
1answer
200 views

### What keeps the sugar suspended in the tea?

At room temperature.... How long will the sugar stay suspended once dissolved ? What governs the rate of settling ? What part does Brownian motion play ? Sugar might be a bad example...please ...
3answers
2k views

### Best way to keep food cool indoors without using a fridge/freezer

I've just moved into my first place, and for reasons I do not condone or recommend I don't have any method of refrigeration right now. Luckily I now live very close to shops, so it isn't a big deal, ...
5answers
1k views

### What physics does occur at short distances in QED?

Let us take the standard QED ($e^-, e^+, \gamma$) as a model of QFT and ask what is its "short-distance" physics? They say the UV infinities appear because we do not know the real physics of short ...
1answer
172 views

### Solar neutrino predictions

The solar neutrino problem has been "solved" by discovering that neutrinos have mass and they oscillate. So how accurate are now our predictions about the number and types of solar neutrinos that ...
3answers
544 views

### What is the physical meaning of enhanced gauge symmetries in string compactifications?

For some very special cases of string compactification backgrounds, we get mysterious enhanced gauge symmetries. What is their physical meaning, and why do they arise? Is there any geometrical ...
2answers
223 views

### If we are willing to accept tachyonic string modes, are there valid projections other than the GSO projections?

One reason superstring theory has often been touted as being an improvement over bosonic string theory is that we can impose GSO projections to remove the tachyonic mode. If we insist upon the no ...
3answers
362 views

### Has every possible interaction between elementary particles been observed?

There are some interactions that are forbidden by conservation laws, e.g. an electron cannot turn into a positron by conservation of charge and a photon cannot turn into a positron electron pair by ...
3answers
3k views

### Why does my body accumulate charge?

If I wander outside in cold weather for 10-20 minutes my body accumulates charges. I get electric shock if I touch metal, e.g., door knob, car door etc. Now I've two questions: Why does human body ...
1answer
697 views

### Quantization of Gravitational Field: Quantization conditions

I'm begining to study Quantization of field with the second quantization formalism. I've studied phononic field, electromagnetic field in the vacuum and a generic relativistical scalar field. I ...
4answers
1k views

### Wavefunction collapse in relativity

It is well accepted that quantum theory has well adapted itself to the requirements of special relativity. Quantum field theories are perfect examples of this peaceful coexistence. However I sometimes ...
2answers
14k views

### Why do car keys have longer range when held next to your head?

I first saw this on Top Gear, and assumed it was a load of rubbish, but today I tried it out and it actually works, if you walk away from the car continuously unlocking/locking it until it stops, and ...
2answers
636 views

### Is there a different behavior between proton and antiproton beams at the Tevatron?

This question has its origin to the reference on the Aegis experiment at CERN where they aim to produce super cooled antihydrogen and detect whether its reaction to gravity is negative. It set me ...
1answer
407 views

### If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal?

Free field theories are definitely local in . In the interaction picture, we can decompose the fields into creation operator modes and annihilation operator modes. The product of operators can be ...
1answer
799 views

### Dual conformal symmetry and spin networks in ABJM

In this question, I would love to hear some independent opinions on an issue I asked Juan Maldacena, Nathan Berkovits, Dan Jafferis, and others, but all the physicists may be missing something. The ...
7answers
8k views

### How to learn physics effectively and efficiently [closed]

How do you effectively study physics? How does one read a physics book instead or just staring at it for hours? (Apologies in advance if the question is ill-posed or too subjective in its current ...
3answers
328 views

### Information about an expanding event horizon

Assume an observer sent a beam of photons close to an event horizon, say at some distance x (a distance far enough to avoid the photons falling in.) This light would still be observable, albeit red ...
1answer
405 views

### NASCAR drafting at Daytona

This year, the racetrack at Daytona has been repaved. The track was always faster than other tracks NASCAR raced at and several cars in a "train" were faster than single cars or smaller trains. This ...
5answers
5k views

### What does it take to become a top physicist? [closed]

What does it take to become a top physicist? Why do so many extremely talented young upstarts totally flop as they move to more advanced physics?
1answer
346 views

### Are strange metals described by a quantum critical theory?

Are strange metals described by a quantum critical theory?
1answer
536 views

### Astronomical detection significance from magnitude error

At this website: http://heasarc.gsfc.nasa.gov/docs/swift/analysis/threads/uvot_thread_afterglows.html The passage at the bottom states that a V-band magnitude of 17.62, with an error $\pm$0.02 is a ...
1answer
173 views

### Would it be worthwhile to work out a manifestly supersymmetric superspace formalism for 16 and 32 real SUSY generators?

For 4 real SUSY generators, the superspace formalism has been worked out a long time ago. For 8 real SUSY generators, some brilliant theoreticians have worked out the details of harmonic superspace. ...
10answers
4k views

### Is Mach's Principle Wrong?

This question was prompted by another question about a paper by Woodward (not mine). IMO Mach's principle is very problematic (?wrong) thinking. Mach was obviously influenced by Leibniz. Empty space ...
1answer
549 views

### Supersymmetry breaking and Goldstino

I would be glad if someone can explain to me the argument as to why supersymmetry breaking is necessarily accompanied by appearance of a massless fermion, namely the goldstino. (and also why this is a ...
4answers
3k views

### Is the Woodward effect real?

Did anyone ever heard about this?I've never seen any serious physicist talk about "mass fluctuations". Here is the man in his own words: http://www.intalek.com/Index/Projects/Research/woodward1.pdf ...
3answers
810 views

### What does the fine structure constant describe?

Feynman says in his book "QED" that the square root of the fine structure constant is the probability for a charged particle to emit a photon. But for which wavelength? Or is it an average over all ...
5answers
2k views

### Why do particles move? [closed]

Is all particles moving and forever? Can the movement of particles be stoped ?
1answer
573 views

### Does the potential energy for a given photon increase or decrease in quanta?

As a photon leaves a strong gravitational field, it loses energy and redshifts. Is the exchange in potential energy of a photon characterized by energy quanta?
8answers
7k views

### The speed of gravity?

Sorry for the layman question, but it's not my field. Suppose this thought experiment is performed. Light takes 8 minutes to go from the surface of the Sun to Earth. Imagine the Sun is suddenly ...
3answers
979 views

### What is physical in the principle of local gauge invariance? [closed]

Modern theories of interactions in particle physics are gauge ones. I know how the gauge fields are introduced in equations ($D = \partial + A$). I just do not see any physical motivation in it. I am ...

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