I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying. This one is also not terribly focused, but nonetheless here goes:

I am wondering if there are some well-known and well-studied examples of large N matrix models (in which the fields are adjoint rather than vectors) which are of use in describing some condensed matter phenomena.

There are lots of applications of matrix models in anything between nuclear physics to number theory, and there are well-known vector models which are useful in CM physics, but off the top of my head I cannot think about matrix models which are used to solve some condensed matter problems. Quite possibly I am missing something obvious...References or brief descriptions will be appreciated.

Is it possible to counter-act g-force for a jet-pilot, by him putting on a scuba-diving suit and filling the cockpit with water? On earth we are constantly pulled down, or accelerated with one g. In this situation, if we put the jet-pilot in a pool, he would neither sink nor float.

If we could increase Earth's gravity to say 9 g's, the pilot in the pool would float even more.

Is this correct? Thanks...

in recent questions like "How are classical optics phenomena explained in QED (Snell's law)?" and "Do photons gain mass when they travel through glass?" we could learn something about effective properties of matter interacting with a force field in terms of the path integral and quasiparticles.

Surely, both approaches must be equivalent but come from a different philosophy. Widely used is the quasiparticle approach in solid state physics e.g. calculating dispersion relations of phonons.

I would really like to know if there are simple examples for explicit calculations of the properties of photon-quasiparticles coming from a rigorous approach like a matter description via QED and finding an effective action e.g. using the Wetterich equation (see e.g. Introduction to the functional RG and applications to gauge theories).

Any calculations and/or references would be very nice.
Thank you in advance, sincerely,

A stone is dropped into a river from a bridge at a height h above the water. Another stone is thrown vertically down at a time t after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second stone? Give your answer in terms of the given variables and g.

Except for Mercury, the planets in the Solar System have very small eccentricities.

Is this property special to the Solar System? Wikipedia states:

Most exoplanets with orbital periods of 20 days or less have near-circular orbits of very low eccentricity. That is believed to be due to tidal circularization, an effect in which the gravitational interaction between two bodies gradually reduces their orbital eccentricity. By contrast, most known exoplanets with longer orbital periods have quite eccentric orbits. (As of July 2010, 55% of such exoplanets have eccentricities greater than 0.2 while 17% have eccentricities greater than 0.5.1) This is not an observational selection effect, since a planet can be detected about equally well regardless of the eccentricity of its orbit. The prevalence of elliptical orbits is a major puzzle, since current theories of planetary formation strongly suggest planets should form with circular (that is, non-eccentric) orbits.

What is special about the Solar System that orbits of planets here are nearly circular, but elsewhere they are moderately or highly eccentric?

Earth's perihelion passed about nine hours ago. How accurately do we know the moment of closest approach of the Earth to the center of the sun? How do we make this measurement?

Many light sources like LEDs and lasers only emit a single wavelength of light.

Is there a light source that emits all wavelengths of visible light at the same time?

EDIT: I edited the question to reflect Moshe's objections. Please, look at it again.

It's apparently a black hole time around here so I decided to ask a question of my own.

After a few generic questions about black holes, I am wondering whether string theory is able to provide something beyond the usual semiclassical Hawking radiation talk. Feel free to provide an answer from the standpoint of other theories of quantum gravity but AFAIK none of the other theories has yet come close to dealing with these questions. That's why I focus on string theory.

So let's talk about micro black holes. They have extreme temperature, extreme curvature, and I guess they must be exceptional in other senses too. At some point the gravitational description of these objects breaks down and I imagine this kind of black hole could be more properly modeled like a condensate of some stringy stuff. So let's talk about fuzzballs instead of black holes.

What does that microscopic fuzzball model look like?
What does string theory tell us about the evaporation of those fuzzballs? Is the Hawking radiation still the main effect (as for the regular black holes) or do other phenomena take over at some point?
Also feel free to add any other established results regarding black hole decay (as Jeff did with information preservation).

Here's an proposal on how to get from point A to point B in zero-gravity without using any propellant and the question why it wouldn't work:

A closed tube, filled with water and a round (solid) object. If you need equations, the volume of enclosed water is the same as the round object, but the round object is 10 times lighter. (imagine a glass with water plus a ping-pong ball).

On earth the round object will float on the water inside the tube (subject to one G).

In zero-gravity the round object has no preferred position.

If we accelerate the tube in zero-gravity by one G, the situation is the same as on earth, the round object "floats". In this example we are accelerating the tube from the left side to the right side. The round object will consider floating to the right AS LONG AS THERE IS acceleration.

Now consider adding a pipe to the bottom of the tube and connecting it to the top, a loop. Inside the pipe is a small water pump.

If we give this apparatus a push, say one G in a zero-g environment, the round object will move "up", but now we start the water pump and spray the water on the round object, we try to submerge it. It will resist and impart a impulse on the water. like trying to hose down a air balloon floating on the pool. The pump will feel a resistance and hence the whole apparatus will move.

Just running the pump at constant speed, same volume of water per second, will do nothing. but if we run the pump faster and faster the whole apparatus will start moving:

the amount needs to be geometrical. The point is that we need to keep the apparatus feeling an acceleration, since only then will the round-object "float" and resist the incoming water at the top, hence we have something to "push on".

Before you blow the "foul whistle": consider the situation if there were no round floating ball in the apparatus.

(the pump runs on solar power or pre-charged battery)

(disclaimer: i know standing on a sailboat and blowing into the sail will not get me anywhere, action<->reaction)

thanks a bunch Sklivvz for the edit. sometimes the idea just needs to get out, never the mind how it looks like : P

I don't know much about light-emitting diodes, but I imaging if you had a panel of RGB diodes you could produce any wavelength of color within the visible light spectrum. However, if I also wanted to generate specific wavelengths of UVA or UVB (anywhere from 290 to 400nm), could I also accomplish this using diodes? Essentially, I am interested in making a small panel of diodes in which I could produce any specific wavelength of visible light, UVA, or UVB.

Thanks in advance.

What is the significance about the bell shape, when its hit at the rim it rings/produces sound better than other shaped objects? If so could anyone explain a little bit on it.

EDIT: From the suggestions in the comments, clarification for the term "sound better": Sound more effective for the purpose which bells are created for. (Thanks Justin)

I know that string theory is still under heavy development, and as such it still can't make predictions (or not that many predictions anyways).

On the other hand, it is clear from the number of years this theory has been under development and from the large number of theoretical physicists studying it, that it is considered a good and viable candidate as a quantum gravity theory.

So, what is the evidence that this is true? Why is it considered such a good candidate as the correct quantum gravity theory?

Without wanting to sound inflammatory in the least, it has been under heavy development for a very long time and it's still not able to make predictions, for example, or still makes outlandish statements (like extra dimensions) that would require a high amount of experimental evidence to be accepted. So - if so many people believe it is the way to go, there have to be good reasons, right? What are they?

I read an article which tells power consumption by many devices. It say that a desktop computer (computer and monitor) use 400 to 600 watt.
While when i checked my computer and monitor with meter, it was about 60 + 60 = 120 watt (computer + 17" CRT monitor) after loading windows xp and running an application. The voltage is 220V here.
Which one is correct? How much power does it consume?

Q9

Provided the amplitude is sufficiently great, the human ear can respond to longitudinal waves over a range of frequencies from about 20.0 Hz to about 20.0 kHz. (a) If you were to mark the beginning of each complete wave pattern with a red dot for the long-wavelength sound and a blue dot for the short-wavelength sound, how far apart would the red dots be? m How far apart would the blue dots be? cm (b) In reality would adjacent dots in each set be far enough apart for you to easily measure their separation with a meterstick? Yes No (c) Suppose you repeated part (a) in water, where sound travels at 1480 m/s. How far apart would the red dots be? m How far apart would the blue dots be? cm Could you readily measure their separation with a meterstick? Yes No

What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and energy into the black hole?