5
votes
4answers
298 views

When displacement isn't possible

Stop me if i'm wrong but displacement is, for example, when you enter a bathtub the water level rises around you. What happens when displacement isnt possible? I'll give an example. I have two ...
0
votes
3answers
479 views

Should physicists abandon Popperian falsification criterion? [closed]

Many of the most brilliant ideas of modern physics are very much unpopperian. In view of this, it has become more and more difficult to hold an orthodox Popperian attitude in physics. It simply looks ...
4
votes
2answers
336 views

Is our universe a 2+1D superconformal field theory?

If our universe comes from a flux compactification of string theory over 6 dimensions with a nonzero flux, then it can't be continually deformed to another compactification with zero flux as the total ...
4
votes
2answers
671 views

Higgs Boson Mass

The WIKI Higgs boson site has an interesting diagram illustrating likely Higgs mass intervals that experiments (LEP & Tevatron) or indirect measurements have determined with a 95% confidence ...
8
votes
3answers
906 views

What is the angular momentum spectrum of an sp${}^3$ electron?

So, one thing has been annoying me ever since I learned about orbital hybridization: you explain the shape of molecules by postulating that the orbitals of multi-electron atoms are linear combinations ...
0
votes
2answers
725 views

How to model tea diffusion/osmosis?

How should I model the tea concentration as a function of time after a tea bag has been submerged? Is there a simple way of measuring the tea concentration?
11
votes
1answer
298 views

Why are all-Sky images drawn as a filled ellipse?

There is some convention? how is this 3d to 2d mapping done? here an example
4
votes
1answer
197 views

Gamma Ray Bubble at the center of our galaxy seen by Fermi Telescope

How could we measure high energy photons, whithout measuring them ? I can't understand how we can "see" those Gamma Ray Bubbles if they are not reaching here In this graph from Nasa you can see ...
2
votes
0answers
385 views

An alternative, algebraic way to introduce interactions. Are there other ways out there?

An opening paragraph: The usual approach to introducing interactions in quantum field theory is to make the constraint on the amplitude of the field towards smaller values more forceful than ...
9
votes
2answers
1k views

The Galileo thermometer: why do the bubbles float in the middle of the tube?

If the water were uniform temperature, it would have uniform density, so a bubble should either be all the way at the top (if it's lighter than water) or all the way at the bottom (if heavier). But in ...
9
votes
1answer
786 views

Bose-Einstein Condensate with T>0 in Theory and Reality

I am interested to understand how positive entropy Bose Einstein condensation for cold atoms (say) behave. The way I think about it is as follows: We have an ideal pure state where every atom is in ...
4
votes
5answers
901 views

Laws and theories

What is a physical law, a theory, and what is the relationship among them? I know this is a very basic question, so any reference to epistemology will be greatly appreciated :)
0
votes
2answers
3k views

Projectile motion without air resistance [closed]

Does the mass of projectile affect its trajectory when it is projected in no air resistance environment and why?
3
votes
1answer
449 views

III-V semiconductor compounds - band gap approximations

I'm looking for the most common and accurate approximation functions for III-V semiconductor compounds. So far, I found two (InGaAs as the sample compound): The simplest one: ...
3
votes
1answer
141 views

Identifying unrealistic traits of this exoplanet. There are a few obvious ones, but I cant find them all. Help! [closed]

I need to find the inaccuracies of this computer generated picture, the picture shows a non existent exoplanet. I need to identify the unrealistic features of the planet and its surroundings and write ...
4
votes
1answer
296 views

$B\mu$ from $\tan\beta$ and $\mu$

I'm using the SOFTSUSY package to generate the sparticle spectrum at the EW scale. One of the input parameters is the ratio of the up and down-type Higgs vevs commonly known as $\tan\beta$. The $\mu$ ...
6
votes
4answers
6k views

Where does the energy from a nuclear bomb come from?

I'll break this down to two related questions: With a fission bomb, Uranium or Plutonium atoms are split by a high energy neutron, thus releasing energy (and more neutrons). Where does the energy ...
1
vote
0answers
293 views

Kinematics textbook illustration

I have trouble interpreting this illustration. I see why r (position) and a (acceleration) are the way they are, but what happened to v? Why is it smaller than its coordinates? Is this another error ...
9
votes
2answers
525 views

Some Majorana fermion identities

I have been struggling with these Majorana fermion identities for quite sometime now. I would be grateful if someone can help me with them. Let $\lambda$,$\theta$ and $\psi$ be $4$-component ...
0
votes
1answer
536 views

What role does gravity have on flame composition?

In 2000, Nasa conducted an experiment and found that gravity plays an indirect role in flame formation and composition (see the wikipedia article). What role does gravity play? Why does a flame ...
3
votes
1answer
175 views

Gribov ambiguities for splitting strings in the BRST conformal gauge

The standard textbook treatment of the conformal gauge for a free string with BRST ghosts is fine, but when a string splits into two, we have Gribov ambiguities for the conformal gauge. We can impose ...
4
votes
5answers
633 views

Eigenvalue Postulate and Experiment Outcomes in QM

In Nielsen and Chuang's text on Quantum Information and Computation, the measurement postulate is stated by using a collection of measurement operators and the outcomes are the indices of the ...
27
votes
5answers
4k views

Does a photon interfere only with itself?

I sometimes hear statements like that: Quantum-mechanically, interference pattern occurs due to quantum interference of wavefunction of a photon. Wavefunction of a single photon only interferes ...
0
votes
5answers
2k views

Use of the mathematical concept 'function' in theoretical physics

The mathematical concept of function is used in physics to represent different physical quantities. For example the air pressure variation with time and space is called an acoustic wave. We use a ...
7
votes
2answers
8k views

Grip of the train wheels

How do the wheels of a train have sufficient grip on a metal track? I mean both of the surfaces are smooth (and not flexible) and it is okay if there is no inclination, but how about on an inclined ...
2
votes
3answers
2k views

Gravitational pull vs. acceleration due to gravity

It might seem obvious but i can't imagine how is gravitational pull is different from acceleration due to gravity?
16
votes
16answers
5k views

Can a car get better mileage driving over hills?

Two towns are at the same elevation and are connected by two roads of the same length. One road is flat, the other road goes up and down some hills. Will an automobile always get the best mileage ...
1
vote
2answers
2k views

Extracting heat energy from a material

Does it violate any physical laws to take a portion of the energy out of a system and use it? Specifically I'm referring to heat. (Kinetic energy). For example, if you have a material which has a lot ...
2
votes
3answers
265 views

What's the worst thing about the tomographic approach to QM?

I saw a paper on arXiv that referenced this approach to an ontology of QM: Phys.Lett. A213 (1996) 1, S. Mancini, V. I. Man'ko, P.Tombesi Symplectic tomography as classical approach to quantum ...
5
votes
3answers
631 views

Paradoxical interaction between a massive charged sphere and a point charge

Suppose we have a sphere of radius $r$ and mass m and a negatively charged test particle at distance d from its center, $d\gg r$. If the sphere is electrically neutral, the particle will fall toward ...
17
votes
6answers
4k views

Where should a physicist go to learn chemistry?

I took an introductory chemistry course long ago, but the rules seemed arbitrary, and I've forgotten most of what I learned. Now that I have an undergraduate education in physics, I should be able to ...
5
votes
3answers
3k views

Best inflation pressure of car tire in the rain- higher, same, lower than normal?

If I am driving a car in the rain, and want to increase the available traction, should I: Increase pressure in the tires Decrease pressure Leave the pressure set to optimum dry pressure Increase or ...
4
votes
1answer
494 views

Building an Afocal Zoom System with only one stage

Can you build an afocal zoom system with only one stage. It looks like you would have to use more than three lenses. You would probably have to have all but one of the lenses be fixed; but it might ...
14
votes
2answers
3k views

Does $E = mc^2$ apply to photons?

Photons are massless, but if $m = 0$ and $E=mc^2$, then $E = 0c^2 = 0$. This would say that photons have no energy, which is not true. However, given the formula $E = ℎf$, a photon does have energy ...
1
vote
0answers
447 views

Fermi level in disordered amorphous and/or organic semiconductors

So, the Fermi level in crystals is pretty easy to understand. Been using it and talking about it in terms of the highest occupied level forever. However, I'm now reading about disordered systems. A ...
34
votes
3answers
3k views

Do two beams of light attract each other in general theory of relativity?

In general relativity, light is subject to gravitational pull. Does light generate gravitational pull, and do two beams of light attract each other?
8
votes
2answers
487 views

Explaining valence with quantum mechanics

Can anyone give me a quantum mechanical explanation of the theory of valence? (i.e. why atoms bond just enough to have a complete orbital) EDIT: To clarify, I already have an idea of why atoms bond, ...
1
vote
1answer
297 views

Simple kinematics excercise, throwing something upwards [closed]

I am trying to solve this simple excercise: Question You throw a small coin upwards with $4 \frac{m}{s}$ . How much time does it need to reach the height of $0.5 m$ ? Why do we get two results? ...
5
votes
1answer
2k views

How fast do electrons move through a conductor?

If I apply $1 \text{ V}$ across a $1 \text{ }\Omega$ resistance, I'd get $1 \text{ A}$ flowing. $1 \text{ A}$ is defined as $1 \frac{\text{C}}{\text{s}}$, and $1 \text{ C}$ is equivalent to ...
7
votes
3answers
311 views

If I take a handful of salt and wait for an infinite time will it become a single crystal?

That pretty much says it. Suppose I have some powder of $NaCl$. It is kept in contact with itself in vacuum. You are free to remove all the disturbances that bother you. Is that true that, well, ...
1
vote
1answer
266 views

Inflation and string theory in general relativity

How can we relate inflation and string theory? We study some inflationary cosmological model or some string cosmological model under some specific assumptions or conditions. Is their any relation or ...
16
votes
4answers
3k views

Quantum Hall effect for dummies

In the past few days I've become increasingly intrigued by the QHE, mainly thanks to very interesting questions and answers that have appeared here. Unfortunately, I am as of yet very confused by all ...
0
votes
2answers
368 views

How did these guys get the masses from Heim Theory?

How did these guys get the masses from Heim Theory? I won't even bother to ask about validity as I read the other post on this. So I know how we all feel about that. I hadn't even heard of it till ...
7
votes
5answers
953 views

Time Dilation - How does it know which Frame of Reference to age slower?

Okay, I'm asking a question similar to this one here: Time Dilation - what happens when you bring the observers back together?. Specifically, I am curious about a specific angle on the second part of ...
0
votes
1answer
184 views

Standing Wave: How to show that $\frac{\mathrm df}{f}=0.5\frac{\mathrm dF}{F}$ where $f$ is frequency and $F$ is tension of the string?

How to do this? Show that if the tension $F$ in a string is changed by a small amount $\mathrm dF$, the fractional change in frequency of a standing wave, $\frac{\mathrm df}{f}$ is given by: ...
7
votes
4answers
917 views

Special Relativistic Time Dilation — A computer in a very fast centrifuge

Ok, I've stumbled onto what I think is a bit of a paradox. First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on ...
3
votes
3answers
138 views

Neutron star references?

I'm looking for contemporary reviews on neutron stars. Seems like this area is pretty active, so even reviews from five or ten years ago are somewhat lacking, though certainly not worthless. Does ...
3
votes
1answer
461 views

Einstein's relation and osmotic pressure

How can I derive the Einstein's relation $D=k_{b}TB$, where $D$ is the diffusion coefficient and B is the mobility coefficient, from the concept of osmotic pressure?
28
votes
15answers
9k views

Comprehensive book on group theory for physicists?

I am looking for a good source on group theory aimed at physicists. I'd prefer one with a good general introduction to group theory, not just focusing on Lie groups or crystal groups but one that ...
7
votes
2answers
230 views

Is there a meaning to the E,B analogues of other gauge fields?

From the gauge field $A_\mu$ and the QED lagrangian we can derive maxwell's equations in terms of electric and magnetic fields. Are there any situations where similar derivations using the other gauge ...

15 30 50 per page