# All Questions

444 views

### Transition between 2D and 3D quantum systems

Quantum Hall effect and anyonic particles are examples that occur in a two-dimensional system. However, experiments for such systems can only be realized in a pseudo-2D environment, where the third ...
3k views

### How exactly is the propagator a Green's function for the Schrodinger equation

Sakurai mentions that the propagator is a Green's function for the Schrodinger equation because it solves \left(H-i\hbar\frac{\partial}{\partial t}\right)K(x,t,x_0,t_0) = ...
386 views

### In What Frame of Reference does the Special Theory of Relativity Operate? [duplicate]

Possible Duplicate: Time Dilation - How does it know which Frame of Reference to age slower? This has bugged me for years. According to the theory of relativity, the faster an object ...
1k views

### Inductor with controlled temperature coefficient

Let's assume we have an air-spaced inductor made of copper wire. As temperature changes, due to thermal expansion of physical dimensions of the coil, its inductance changes too. 1) Is there a way to ...
1k views

### Black Hole Photon Sphere

The photon sphere is a spherical region in space where photons are forced to travel in an orbit at $r = \frac{3GM}{c^{2}}$. Is it possible to detect these spheres? What happens if I fall through ...
3k views

### Are quantum mechanics calculations useful for engineering?

I heard it's is pretty tough to get results for more than a few quantum particles. Are quantum mechanical calculations useful at all for any technology that is being sold? Or do they use ...
901 views

### Difference in timbre between 'quiet' and 'far away'

I'd like to know what are the differences in timbre - or the acoustic properties of a sound - that allow us to differentiate between a sound which is quiet (but close-by) and one which is far away. ...
7k views

### Lowest gravity on Earth's surface?

I am trying to determine which on Earth's surface has the lowest gravity. Googling is not finding anything concrete. My natural inclination would be to think of Mount Chimborazo in Ecuador, being on ...
361 views

### Advantage of string theory over other theory-of-everything candidates

I am getting curious over why string theory, especially M-theory, is the most popular candidate for the theory of everything. It seems that all candidates of the theory of everything lack substantial ...
213 views

### How important are electromagnetic tidal effects in QFT? Can they be used to determine whether a particle is point-like?

I just did a back-of-the-envelope calculation, which surprised me. I calculated the difference in acceleration (due to repelling like-charges) experienced by two sides of an electron the size of the ...
460 views

### Why is Jupiter so sharply defined?

In photographs of Jupiter, the limb seems extremely definite. Being a gas giant, my naive self thinks that the atmosphere should have a more gradual cut off, creating a hazy effect similar to that on ...
678 views

### How do magnets work?

I've read a classbook on the field theory (including EM): it perfectly describes quantitive patterns in EM-theory, but I have no luck understanding how and why it works. I mean, magnetic substances ...
1k views

### Using 'Euler's Homogeneous Function Theorem' to Justify Thermodynamic Derivations

I've been working through the derivation of quantities like Gibb's free energy and internal energy, and I realised that I couldn't easily justify one of the final steps in the derivation. For ...
340 views

### A question about definition of Fermi energy

Wikipedia states the definition of Fermi energy as for "a system of non-interacting fermions". If we have to assume free electrons in a solid behave this way before we are able to calculate Fermi ...
75 views

### wind versus compressed air

What would the calculation look like when computing the wind pressure of a moving vehilce versus compressed air pressure pushing against the the moving vehicle, how much compressed air pressure would ...
124 views

### What is a qualitative explanation for order of values of standard entropies of formation for isomers of hexane?

I have literature values for the standard enthalpy and Gibbs energy changes of formation at 298 K, $\Delta H_\text{f}^o$ and $\Delta G_\text{f}^o$, for product in the ideal gas state. Since $G=H-TS$ ...
479 views

### Why does the homogeneity of the universe require inflation?

They say inflation must have occured because the universe is very homogeneous. Otherwise, how could one part of the universe reach the same temperature as another when the distance between the parts ...
479 views

### Gauge invariance and the form of the Rarita-Schwinger action

in Weinberg Vol. I section 5.9 (in particular p. 251 and surrounding discussion), it is explained that the smallest-dimension field operator for a massless particle of spin-1 takes the form of a field ...
310 views

### What is 'tilt locking' of a laser cavity?

In another question, jasonh mentions a scheme for locking a laser to a resonant cavity called 'tilt locking': The signal is used for locking the frequency of a laser to a high finesse cavity. The ...
799 views

### Can black holes be created on a miniature scale?

A black hole is so powerful to suck everything into itself. So is it possible that mini black holes can be created? If not then we could have actively disproved the rumors spread during LHC ...
2k views

### How does a train, airplane measure its speed? [closed]

I always get the doubt about this. I know that a bike measures its speed based on the motion of its front wheel. So what is the case with train? Is it same principle? Then what about an airplane? Is ...
322 views

### Hamilton's equations in terms of initial conditions

I'm trying to understand the way that Hamilton's equations have been written in this paper. It looks very similar to the usual vector/matrix form of Hamilton's equations, but there is a difference. ...
308 views

### How many photons does it take to measure a linear polarization?

A star emits perfectly (100%) linearly polarized light at an arbitrary angle. How many photons must you detect to measure this angle to a precision of n binary digits? (with greater than 50% ...
38 views

### Low-energy gluodynamics as a string

Does anyone know of a (most likely heuristic) derivation of the use of the string sigma model action to model the soft gluonic interactions between color charges? I'm familiar with the classic ...
875 views

### How can I visualize a gas giant?

From wikipedia Gas giants are commonly said to lack solid surfaces, but it is closer to the truth to say that they lack surfaces altogether since the gases that make them up simply become ...
707 views

### Do “shape” and “volume” in “space” have any meaning for an electron?

The Standard Model (SM) predicts an "aspherical" electron due to its possesing a non-zero electron electric dipole moment (EEDM). An experiment by Hinds (2011) placed an upper bound on the ...
962 views

### How is contact resistivity defined for a Schottky contact, or the Schottky barrier height for an ohmic contact?

Based on the transfer length method (TLM), one can accurately calculate the contact resistivity for an ohmic contact, by evaluating the absolute resistance measured through the test structure and ...
2k views

### Question Based On Units And Measurements Involving Lengths [duplicate]

The below is the sixth question of the very first chapter from halliday and resnicks fundamentals of physics text,which i'am not able to comprehend. Harward Bridge,which connects MIT with its ...
672 views

### Why is quantum physics needed to explain photosynthesis?

Why is quantum physics needed to explain photosynthesis? In what aspect does the corresponding classical theories for photosynthesis fail?
3k views

### How does string theory reduce to the standard model?

It is said that string theory is a unification of particle physics and gravitation. Is there a reasonably simple explanation for how the standard model arises as a limit of string theory? How does ...
2k views

### Strategies against 50 Hz mains hum on detector signals?

I'm having problems with a strong 50 Hz mains hum on signals created by photodetectors. I assume that they are due to ground loops and I realize that the best option would be to remove those. What are ...
199 views

### $2+1$ dimensional physics theory of our universe?

Is there any physics theory that depicts our universe as $2+1$ dimensional? I heard that black holes seem to suggest that the world might be $2+1$ dimensional, so I am curious whether such theory ...
326 views

### What really is the future about the Standard Model

The fact that the bosons of the weak force have mass is something that I think technically poses many problems. To avoid this and other problems with the masses of the particles devised a mechanism ...
624 views

### Measuring extra-dimensions

I have read and heard in a number of places that extra dimension might be as big as $x$ mm. What I'm wondering is the following: How is length assigned to these extra dimensions? I mean you can ...
521 views

### Multiplication of 3-vector operators

I've started reading "Quantum Mechanics: A Modern Development" by Leslie E. Ballentine and have some trouble understanding how to handle 3-vector operators (i.e. an operator $\mathbf{A}$ with ...
190 views

### Event-by-Event Simulation of Quantum Phenomena

I just recently stumbled over http://rugth30.phys.rug.nl/dlm/ and http://www.sbfisica.org.br/bjp/files/v38_26.pdf As the title suggests these are presentations of mathematical models capable of ...
475 views

### Special Relativity - Relativistic Dynamics

I've been wrestling with this problem but to no avail. I'm hoping that someone here can give me a little nod in the right direction. Problem statement: A thrust-beam space vehicle works bearing a ...
335 views

### Magnetic force and work

If the magnetic force does no work on a particle with electric charge, then: How can you influence the motion of the particle? Is there perhaps another example of the work force but do not have a ...
625 views

### How can people do music with Tesla coils?

I saw a lot of videos of Tesla coils doing music on YouTube. And I wonder how can they do that sort of things. How they can calculate what tone it is going to do? And what are the factors to ...
98 views

### Sky projections in sky view software

I'm playing with an idea of making a little program to draw the sky. Nothing fancy, just for fun. And I'm reading about projections. Now I know that I must use different projections depending on my ...
190 views

### What chemistry course to take for a physics undergraduate [closed]

This question is mainly aimed at people who know about the science market in the UK, but any suggestions would be much appreciated. I am a third year physics undergraduate, studding for an MSci ...
478 views

### What is the total kinetic energy per second of the particles accelerated by the LHC

Related: how many protons per second can the LHC accelerate?
2k views

### What will happen if a gamma-ray burst hits the Earth?

Is there any probability that a gamma-ray burst (GRB) could affect the Earth?
524 views

### Is the quantization of the harmonic oscillator unique?

To put it a little better: Is there more than one quantum system, which ends up in the classical harmonic oscillator in the classial limit? I'm specifically, but not only, interested in an ...
201 views

### Interpreting range of conductivity diagram

I have found the following diagram (unfortunately in german) about the range of conductivity of conductors (Leiter), semiconductors (Halbleiter) and insulators (Isolatoren). How should one interpret ...
261 views

### Hygiene thermodynamics 2

Two kinda related questions here: Is evaporation rate and temperature difference related? There is an experiment of pouring cup of hot water out the window during winter. The water evaporates almost ...
21k views

### Do salt lamps really produce negative ions?

Do salt lamps really produce negative ions? Do you know about any scientific study that could support this assertion or disprove it?
3k views

### Sauna thermodynamics

Why does it get hotter (feel hotter) in a sauna when one pours water over the hot stones? Wikipedia says that the water condenses onto the skin, but the actual air humidity is so low that I doubt ...