# All Questions

75 views

### How are exoplanets confirmed?

In reference to the Kepler 22b news: The Kepler team had to wait for three passes of the planet before upping its status from "candidate" to "confirmed". This is possible because the planet ...
224 views

### Relativity and predictability

My old theoretical physics professor used to say that (already) (special?) relativity shows that "the future is not predictable". Any ideas how this should be interpreted?
8k views

### How does evaporation affect the temperature of the air?

A wet object or a volume of water will decrease in temperature due to the effect of evaporation. We understand this to be because of the molecular kinetics, where the faster water molecules escape ...
909 views

### Basic Free Fall Problem [closed]

So I am trying to remember my childhood doing some Physics problems, but seems that I forgot almost everything. But it's not a big thing... that's why I'm training! My problem is pretty basic ...
433 views

### Uniqueness of eigenvector representation in a complete set of compatible observables

Sakurai states that if we have a complete, maximal set of compatible observables, say $A,B,C...$ Then, an eigenvector represented by $|a,b,c....>$, where $a,b,c...$ are respective eigenvalues, is ...
250 views

### Why doesn't our solar system run into other solar systems over billions of years?

Why doesn't our solar system run into other solar systems over billions of years. There is plenty of time for it to be attracted by gravity to other objects. So I thought, it should be a common ...
414 views

### Speed of Light, Photons or WaveSpeed?

The speed of light is almost 300 000 km/s. The photons have a speed along the wave, and the wave have a speed straight forwards. What is the speed of light? Is it the speed the photons have along ...
1k views

### What's it like in a sphere mirror? [duplicate]

Possible Duplicate: What happens to light in a perfect reflective sphere? I was working on my toy ray tracer when I pondered on this: Say we build a hollow sphere big enough to fit a ...
184 views

### Figuring out the force using Newton's 2nd Law

Here's a problem on my test review: A 12 kg crate resta on a horizontal surface and a boy pulls on it with a force that is 30° below the horizontal. If the coefficient of static friction is ...
410 views

### Sparticles: Relationship to supersymmetry and dark matter?

I was attempting to read this paper after watching a show with Brian Greene. As I understand it, sparticles are a prediction of supersymetry, so I was wondering: Wouldn't the discovery of ...
373 views

### Testing my understanding of QM - The Double Slit Experiment without the slit

First off, sorry to throw in another question from someone who hasn't studied the maths. I'd like to see if I have a correct (if very basic and non-mathematical) understanding of the wave and ...
1k views

708 views

### Would a solution to the Navier-Stokes Millennium Problem have any practical consequences?

I know the problem is especially of interest to mathematicians, but I was wondering if a solution to the problem would have any practical consequences. Upon request: this is the official problem ...
2k views

### How to calculate the temperature of a receiving point from concentrated solar power?

I'm exploring a DIY project about solar power and have found very few resources that can explain, in a not too simple but not too advanced way, how to go about calculating important values in solar ...
599 views

### Is there other uses of flow-straighteners than flow-metering?

Flow-straighteners are used before flow-meters because they remove disturbances from the flow and achieve nearly-fully developped velocity profiles. But is there any other uses of flow straighteners ...
114 views

### Spinors in more dimensions and new degeneracies?

As you more than probably know spinors dimensions go as $2^{\frac{D}2}$ in D spacetime dimensions. If we look at the peculiar case of D=2*4, spinors have 4 components and we usually say that's related ...
89 views

### Numerical Analysis of Elliptic PDEs

I am looking for an elementary reference regarding issues of stability in numerical analysis of non-linear elliptic PDEs, particularly using the finite difference method (but something more ...
103 views

### What is the best evidence/theory about the first generation of stars

In particular, during what range of years after the Big Bang did the stars form? What is the expected range of masses of these stars and what is the expected lifetime before they supernova? I assume ...
305 views

### Levitation rotation speed involving laser acceleration, pyrolytic graphite and a vacuum

The experment would involve a small NIB magnet levitating between or on the diamagnetic material pyrolytic graphite, unlike other forms of levitation this doesn't require power to run such as ...
255 views

### If LHC searches of a Higgs boson won't be a success, what consequences for the theory of electroweak interaction it can bear?

Whether it is necessary to search still for variants of an explanation of spontaneously breaking gauge symmetry, giving masses for a W, Z-bosons? Goldstone bosons are bosons that appear necessarily ...
849 views

### Time-Dependent Potentials in Quantum Mechanics

A potential that depends on time is usually solved using the time dependent perturbation theory in standard undergraduate textbooks in quantum mechanics. The reason usually mentioned is that time ...
528 views

### What is the magnetic susceptibility of NdFeB?

NdFeB is one of the most popular materials used for making permanent magnets. Yet I could find no link or reference reporting a decent value for the magnetic susceptibility of NdFeB. Magnetic ...
189 views

### Spherical magnets shooting like bullets and demagnetizing

I was playing around with a 2x chain of bucky balls and winding it around itself. Suddenly several of the little balls went shooting like bullets across the room in 3 directions and now all of the ...
162 views

### Wave propagation in anisotropic media

I'm given a wave propagation in an anisotropic medium with the following properties: \$\epsilon=\left[\begin{array}{ccc} \epsilon_{11} & 0 & 0 \\ \epsilon_{21} & \epsilon_{22} & ...
87 views

### Quantum statistics of branes

Quantum statistics of particles (bosons, fermions, anyons) arises due to the possible topologies of curves in D-dimensional spacetime winding around each other What happens if we replace particles by ...
121 views

### Conformal QFTs for D > 2

Which conformal QFTs do we know for spacetime dimension d > 2? I know that for D = 4 we have N = 4 SYM and some N = 2 supersymmetric Yang-Mills + matter models. What is the complete list of such ...
224 views

### Massive excitations in Conformal Quantum Field Theory

Single particle states in quantum field theory appear as discrete components in the spectrum of the Poincare group's action on the state space (i.e. in the decomposition of the Hilbert space of ...
1k views

### Understanding the Seebeck effect

Thermoelectricity is, as I understand it, the difference in voltage between the hot and cold ends of two dissimilar materials. If two materials are connected at two different junctions, the hot ...
2k views

### Has Chandra Varma explained cuprate superconductivity?

Chandra Varma is a theoretical physicist at University of California, Riverside. A couple years ago, he gave a talk at my institution purporting to explain superconductivity in the cuprates. It all ...
262 views

### Can stable nuclei theoretically fission through quantum tunneling?

As I understand it, an unstable nucleus is going to randomly fission because the forces binding it together are momentarily weaker than the electrostatic repulsion of the protons. Given that some ...
1k views

### Why do or don't neutrinos have antiparticles?

This was inspired by this question. According to Wikipedia, a Majorana neutrino must be its own antiparticle, while a Dirac neutrino cannot be its own antiparticle. Why is this true?