# All Questions

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### Gravitational and gauge-gravitational anomalies in N=1 D=4 supergravity coupled to a SUSY gauge theory with chiral matter

When people talk about the first superstring revolution they often mention the miraculous cancellation of anomalies via the Green Schwarz mechanism. My question is whether such a string-theoretic ...
224 views

### Colder surface radiates to warmer surface

When radiation from a colder source arrives at a warmer surface there is some debate about what happens next. To make the question more concrete lets say that the colder source is at temperature 288K. ...
165 views

### String worldsheets with periodic time?

If we try to work out the details of string theory over a worldsheet with genus 1, does that mean we have periodic time on the worldsheet? But if we have periodic time, and in some portions of the ...
378 views

### What is the current status of the swampland?

What is the current status of the swampland? Have people expanded the list of swampland criteria? If let's say I wish to figure out if the Standard Model belongs to the swampland, are there any ...
511 views

### Will negatively charged strangelets be produced by the LHC?

Witten (and earlier, Bodner) hypothesized that strange matter (up, down, strange quarks) should be more stable than "regular" nuclear matter(The strange matter hypothesis). That is that the typical ...
609 views

### Software for simulating supersonic aerodynamics [closed]

Could you please suggest the software, where I can load my 3D model and see how it behave on various conditions (speed - preferably including supersonic, temperature, pressure)? Both free & ...
406 views

### Electron-hole symmetry in H and He

I'm contemplating particle-hole symmetry, and as an example I am looking at either an electron moving along a hypothetical lattice of hydrogen ions, or a hole moving along a hypothetical lattice of ...
663 views

### Is anyone studying how the general topology of spacetime arises from more fundamental notions?

Stephen Wolfram in his book A New Kind of Science touches on a model of space itself based on automata theory. That it, he makes some suggestions about modelling not only the behaviour of matter ...
2k views

### Impulse - distance question [closed]

What impulse should be applied to an object of mass m, having a known coefficient of friction u to get to a distance d ? Thanks! Update 14.02.2011: I still wasn't able to find an answer to this. ...
1k views

### What are the alternatives to the Higgs mechanism?

Can someone summarize, with references if possible, all of the alternatives to the simplest model (that requires only a single scalar Higgs field with the Mexican Hat potential) of spontaneous ...
988 views

### Why is there a search for an exchange particle for gravity?

If I understand correctly, according to Einstein's General Theory of Relativity, mass results in a distortion in space-time. In turn, the motion of the mass is affected by the distortion. A result of ...
2k views

### What are the most realistic ways of high speed space propulsion?

Liquid and solid chemical fuels in rockets are very expensive and inefficient. I have heard of solar sails but what are the most realistic space travel fuels that will be used in the future to get ...
1k views

### Give a description of M-theory your grandmother can understand

Inspired by this question, let me ask a similar question. Is it possible to do the same (give a description of M-theory your grandmother could understand)for M theory? While I know even experts don't ...
1k views

### Noether's theorem vs. Heisenberg uncertainty principle

In continuation of another question about Noether's theorem I wonder whether there exists some kind of relationship between this theorem and the Heisenberg uncertainty principle. Because both the ...
537 views

### Does string theory provide quantitative experimental predictions? [duplicate]

Possible Duplicate: What experiment would disprove string theory? We carefully observe things, observe patterns and then build theories that predict. String theory is frequently ...
184 views

### Mass into energy

The mass of a nucleus if less than the mass of the protons and nucleus. The difference is knows as binding energy of the nucleus. This nuclear binding energy is derived from the strong nuclear force. ...
1k views

### What is the 4th dimension? [closed]

I have heard before that the 4th dimension is time, however, another theory makes a lot more sense to me. This is that the 4th dimension is the third dimension stacked on top of each other in a ...
4k views

### Can I use an antenna as a light source?

Can I use a normal metal antenna to emit visible light?
2k views

### Why do stars have absorption spectra?

Absorption spectra are a result of light of a certain wavelength exciting an atom from a lower energy level to a higher one and at the same time being absorbed. However, the atom should eventually go ...
2k views

### Can black holes form in a finite amount of time?

One thing I know about black holes is that an object gets closer to the event horizon, gravitation time dilation make it move more slower from an outside perspective, so that it looks like it take an ...
2k views

### How Non-abelian anyons arise in solid-state systems?

Recently it has been studied non-abelian anyons in some solid-state systems. These states are being studied for the creation and manipulation of qubits in quantum computing. But, how these ...
373 views

### Why is the answer to this diffusion example unintuitive?

Imagine a linear decrease in concentration from left to right. Using Fick's first law, $J = -D \frac{d \psi}{d x}$ for all x, from left to right, we have the same flux amount because the decrease is ...
7k views

### How do you find the velocity function of a mechanical wave?

With the form $y(x,t)=A\sin(kx-\omega t+\phi_0)$, there are two variables, How do I find the velocity? I don't know I can apply derivative with two variables.
493 views

### Space as “flat” plane

I was watching the documentary Carl Sagan did about gravity (I believe it's quite old though) and wondered about space being "flat" and that mass creates dents in this plane as shown at about 3 ...
1k views

### Do derivatives anticommute with Grassmann variables and complex numbers in a many-body path integral?

I'm trying to learn how to do a many-body path integral for both fermions and bosons, and I'm stuck. I'm following Altland and Simons - Condensed Matter Field Theory, chapter 4. On page 167, equation ...
719 views

### CFTs and formalizing quantum field theory

Moshe's recent questions on formalizing quantum field theory and lattices as a definition of field theory remind me of something I occasionally idly wonder about, and maybe this site can tell me the ...
6k views

### Mathematical background for Quantum Mechanics [duplicate]

What are some good sources to learn the mathematical background of Quantum Mechanics? I am talking functional analysis, operator theory etc etc...
2k views

### trying to understand Bose-Einstein Condensate (BEC)

I am a computer scientist interested in network theory. I have come across the Bose-Einstein Condensate (BEC) because of its connections to complex networks. What I know about condensation is the ...
2k views

### “Velvet way” to Grassmann numbers

In my opinion, the Grassmann number "apparatus" is one of the least intuitive things in modern physics. I remember that it took a lot of effort when I was studying this. The problem was not in the ...
198 views

### Vanishing of field strength in gauged WZW model

Consider gWZW action $S_{gWZW}(g,A)=S_{WZW}(g)+S_{gauge}(g,A)$, where $S_{WZW}$ is usual WZW action being sum of sigma model and WZ terms for field $g$ taking values in group $G$ and \$S_{gauge}=\int ...
3k views

### Pressure drop in a pipe due to cooling

I’m trying to better my understanding of the thermodynamics and momentum balance of pipe flows. The following situation, however, is making me scratch my head and I’ve found no help in my books. ...
655 views

### Pedagogical explanations of critical dimensions of string theories

Once you understand the formalism, I think it's clearest to say the critical dimension of the space-time arises because we need to cancel the central charge of the (super)conformal ghosts on the ...
3k views

### Chaos theory and determinism

My professor in class went a little over chaos theory, and basically said that Newtonian determinism no longer applies, since as time goes to infinity, no matter how close together two initial points ...
2k views

### What is a D-brane?

I know that in string theory, D-branes are objects on which open strings are attached with Dirichlet boundary conditions. But what exactly is a brane? Are they equally fundamental objects like string? ...
301 views

### Could ball lightening be a form of plasma?

With regard to the recent arXiv article: J. D. Shelton, Eddy Current Model of Ball Lightening http://arxiv.org/abs/1102.1224 I wonder if this is a reasonable explanation of ball lightening, or if ...
2k views

### Bose-Einstein condensate in 1D

I've read that for a Bose-Einstein gas in 1D there's no condensation. Why this happenes? How can I prove that?
698 views

### Do symmetries increase the number of conserved quantities? [closed]

Let us consider a classical mechanical system of N particles in a constant external field. We have 3N coordinates and 3N velocities, so totally 6N unknown variables. We have 6N ordinary differential ...
520 views

### Why (in relatively non-technical terms) are Calabi-Yau manifolds favored for compactified dimensions in string theory?

I was hoping for an answer in general terms avoiding things like holonomy, Chern classes, Kahler manifolds, fibre bundles and terms of similar ilk. Simply, what are the compelling reasons for ...
724 views

### Is quantum field theory defined by its lattice regularization?

One statement I've heard many times is that QFT is "defined" by the lattice, or that the "only" definition of QFT is on the lattice (when such definition exists, e.g in pure Yang-Mills theory). I've ...
4k views

### Can Noether's theorem be understood intuitively?

Noether's theorem is one of those surprisingly clear results of mathematical calculations, for which I am inclined to think that some kind of intuitive understanding should or must be possible. ...
200 views

### Open/Closed Branes

Hello this is my first question. For an open string you can pick different boundary conditions for the endpoints along different directions of space time. For example, you can choose Dirichlet ...
460 views

### Can the work done between two non-equilibrium states be calculated?

The work done during a process between two equilibrium states can be described by thermodynamics. Even when process itself is out of equilibrium, the thermodynamic laws can still be used, though ...
959 views

### Does van Eck phreaking really work, or is it an urban myth?

Van Eck phreaking, the ability to reconstruct distally the text on a CRT or LCD screen using the leaking em from the target computer, was in the news about five to ten years ago. It is talked about as ...
1k views

### What is the need for the Higgs mechanism and electroweak unification?

The Higgs mechanism allows massless fields to acquire mass through their coupling to a scalar field. But if the masses cannot be predicted because the couplings have to be fixed, what really is the ...
1k views

### Is there a relativistic (quantum) thermodynamics?

Does a relativistic version of quantum thermodynamics exist? I.e. in a non-inertial frame of reference, can I, an external observer, calculate quantities like magnetisation within the non-inertial ...
848 views

### Does Wick rotation work for quantum gravity?

Does Wick rotation work for quantum gravity? The Euclidean Einstein-Hilbert action isn't bounded from below.
6k views

### What does it mean for a Hamiltonian or system to be gapped or gapless?

I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean? Edit: Is an XX spin chain in a magnetic field gapped? Why or why not?
614 views

### Why do Faddeev-Popov ghosts decouple in BRST?

Why do Faddeev-Popov ghosts decouple in BRST? What is the physical reason behind it? Not just the mathematical reason. If BRST quantization is specifically engineered to make the ghosts decouple, how ...