3
votes
1answer
242 views

M2-brane wrapped twice around $S^1$

M-theory wrapped around $S^1$ is type IIA, especially in the limit of zero radius. An M2-brane wrapped around $S^1$ once is a type IIA string. The zero mode anyway. In the limit of very small radius, ...
6
votes
4answers
1k views

Why are four-vectors needed in the Dirac equation, when there are 4 linearly independent 2D matrices?

I was taught that for the Dirac-equation to "work", you need matrices of the following form: $Tr(\alpha^i) = 0$. Eigenvalues +1 or -1 2 previous points together: equal number of negative and ...
8
votes
5answers
3k views

Are water waves (i.e. on the surface of the ocean) longitudinal or transverse?

I'm convinced that water waves for example: are a combination of longitudinal and transverse. Any references or proofs of this or otherwise?
2
votes
1answer
5k views

Sound - what happens with the particles when a wave passes

I'm having some problems in understanding the principles of sound propagation. The wave propagates though air (for example) exerts compression, which is followed by rarefaction. I think I got than ...
4
votes
2answers
934 views

Calculate stainless steel pole necking limit

Background Trying to determine how much weight a post can support without necking when a monitor is attached to an articulated arm: a cantilever problem. Problem There are three objects involved in ...
4
votes
1answer
219 views

Orbifolds of the $c =1$ Bosonic theory on a circle

For a $c=1$ Boson on a circle at the self-dual rdius, we get an enhanced gauge symmetry $\hat{SU}(2)_1$. It is said that we can orbifold this model by any finite subgroup of $SU(2)$ since $SU(2)$ is a ...
5
votes
6answers
780 views

Explaining Arrow of Time with Entropy

WARNING: Possibly a naive post. Hi guys. I just watched on BBC, [some show] yesterday (sunday) where the host talked about Arrow of Time, where by 2nd law of thermodynamics states that "nature" is ...
10
votes
5answers
4k views

Why are bicycle pedal threads' handedness left on the left and right on the right?

I understand the reason that bicycle pedals are oppositely threaded on either side. What I don't understand is why it works because I'm missing something. Take the right pedal for example. It's ...
19
votes
1answer
5k views

Why can you see virtual images?

In optics it is widely mentioned real images are projectable onto screens whereas virtual ones can only be seen by a person. Isn't that contradictory? I mean in order to see the virtual image it has ...
8
votes
2answers
811 views

What if LHC finds SUSY?

Here and on many other forums and blogs people ask the question "What if LHC does not find SUSY?". I would like to ask the opposite. What if it finds it? What would the implications be? Is it going to ...
6
votes
2answers
430 views

What's a good reference for the electrodynamics of moving media?

The answer to a previous question suggests that a moving, permanently magnetized material has an effective electric polarization $\vec{v}\times\vec{M}$. This is easy to check in the case of ...
6
votes
2answers
198 views

How to understand order emerging from many-body system?

Like the order behavior shown in the image, is it due to the universality of some fundamental mathematic theory? Is there some general physics explanation for it? - edit: This question comes after ...
4
votes
3answers
288 views

Is causality synonymous with continuity?

In general relativity, we use the term "time-like" to state that two events can influence one another. In fact, in order for an event to physically interact with another one, they have to be ...
8
votes
5answers
211 views

What are the chances that a deadly asteroid will hit Earth in the next decade?

What are the chances that an asteroid that will kill multiple people will hit Earth in the next decade?
3
votes
1answer
729 views

Fresnel transform

How is it possible to encrypt multiple images using fresnel transform and inverse the operation to de-multiplex those images?
1
vote
6answers
6k views

Does vacuum (empty space) exist? [closed]

Added: 5 times down vote for now! Down voter is this religion or physics, please try to explain your decision. I'm confused about this. In physics we know for a vacuum, but I think that there is a ...
6
votes
3answers
1k views

What defines the mass of elementary particle?

The electron is particle. The mass of electron is $9.10938215(45)\times 10^{−31}\, {\rm kg}$. But why is the mass exactly what it is? What in physics defines the mass of elementary particle?
-1
votes
1answer
393 views

Finding the mass of bed/Patient [closed]

One of my friends has a problem and we don't know how to get this done, We want to to know the mass of a patient who is laying on a bed. One scales was put under the foot of a bed and weighed 232kg ...
6
votes
2answers
536 views

Calculate the electric field of a moving infinite magnet, without boosting

Consider a rectangular slab of permanently magnetized material. The slab's dimensions are $L_x$, $L_y$, and $L_z$, and the slab is uniformly magnetized in the $\hat{x}$-direction. The slab is not ...
1
vote
0answers
163 views

can someone review a 8 page essay for me for accuracy? essay is in cosmology [closed]

I am a bio-chemist by profession and recently written an essay for a book which is related to the subject of cosmology. This is not my area of expertise. Is there a cosmologist out there who will be ...
6
votes
1answer
310 views

Construction of the $\cal{N}=3$ supersymmetric Yang-Mills Chern-Simons theory in $2+1$ dimensions

I am stuck with understanding the following construction. I am breaking it up into segments which I think can be separately answered. This is related to an earlier question of mine. Note that this ...
9
votes
4answers
1k views

Is there an accepted analogy/conceptual aid for the Higgs field?

Is there an accepted analogy / conceptual aid for the Higgs field? In Physics there are many accepted conceptual aids such as * Schrödinger's cat * Maxwell's Demon * I'm sure I'm missing ...
5
votes
4answers
3k views

“The Schwarzschild Proton” paper - Is the science valid?

I'm a layman without a university background in physics / math. Since I don't have a background, reading a paper is more of an effort. Consequently, when I come across an interesting paper, I can't ...
4
votes
1answer
518 views

Electric Potential

A nonuniform linear charge distribution given by $\lambda = bx$, where $b$ is a constant, is located along an $x$ axis from $x = 0$ to $x = L$. What is the electric potential at a point on the $y$ ...
2
votes
2answers
149 views

Mathematical Elegance in a Cosmological Theory Considered Necessary?

In general, it seems cosmological theories that encompass more and more of the phenomena of the universe are expected to be more and more mathematically elegant, in conception if not in detail. Our ...
26
votes
4answers
5k views

What if the LHC doesn't see SUSY?

A question in four parts. What are the main problems which supersymmetry purports to solve? What would constitute lack of evidence for SUSY at the proposed LHC energy scales (e.g. certain predicted ...
2
votes
1answer
275 views

Can the geodesic propagators in the Euclidean BTZ black hole can be written in terms of meromorphic functions on its conformal boundary?

I'm interested in knowing if ,in the context of $AdS_{3}/CFT_{2}$, we can (and how to) express the geodesic propagators on the bulk space of the Euclidean $AdS_{3}$ black holes, in terms of ...
5
votes
3answers
481 views

Cosmic ray hazards

The Pierre Auger Observatory site mentions the detection of a 3E20 eV (48 J) cosmic ray whose energy, well above the GZK cutoff, was based on an analysis of its atmospheric shower. This was equivalent ...
3
votes
1answer
461 views

Gravitational redshift of virtual photons

There is well known gravitational redshift of real photons. What about gravitational redshift of virtual photons of charged neutron star? Is electrostatic force become weaker while mass of ...
3
votes
3answers
598 views

Snell's law starting from qft? [duplicate]

Can one "interpret" Snell's law in terms of QED and the photon picture? How would one justifiy this interpretation with some degree of mathematical rigour? At the end I would like to have a direct ...
15
votes
1answer
1k views

Good introductory text for matrix string theory

Where can I find a good introductory text for matrix string theory? Most textbooks don't cover it, or only cover it very superficially. What is the basic idea behind matrix string theory? How can ...
7
votes
1answer
203 views

Statistics and macrolocality in string theory

Take two identical closed strings, both tracing out exactly the same path in space. These two strings are coincident everywhere. Call this state I. Take a single closed string following exactly the ...
5
votes
3answers
560 views

Electric engine transmission

If we compare a petrol engine and an electric engine car, it is sufficient for the electric engine car (e.g Tesla Roadster) just to have 1 gear (forward), whereas petrol engine can have up to 7. Why ...
6
votes
1answer
194 views

Can long strings always snap?

In quantum chromodynamics, long flux tubes will always snap because a quark-antiquark pair gets created from the vacuum, and hadronization results with a quark attached to each new end. In string ...
2
votes
1answer
270 views

Axion related questions

I have several question regarding axion. Could anyone give me some brief introduction to what is a axion string, axion field and how is this related to fermion zero mode and chiral zero mode?
5
votes
1answer
2k views

How does one prove Fierz identities?

Fierz identities are discussed in the wikipedia article: http://en.wikipedia.org/wiki/Fierz_identity but the article doesn't give any derivation. The article implies that they arise from the blade ...
3
votes
1answer
164 views

2D CFTs and permutation orbifolds

Suppose we have 2 systems with the same partition function, does this mean the 2 systems are the same? For example, in 2D CFTs, would the equality of two partition functions imply that the underlying ...
3
votes
1answer
540 views

What's a better phrase than “speed of light” for the universal spacetime speed constant? [closed]

The phrase "speed of light" is commonly used for the constant c =3E8 m/s, a feature that's "hardcoded" into the structure of spacetime. All massless waves and particles move at this speed, and it's a ...
16
votes
4answers
3k views

Are tidal power plants slowing down Earth's rotation?

Are tidal power plants slowing down Earth's rotation to the speed of the orbiting moon? (1 rotation per 28 cca days) Are they vice versa increasing the speed of moon orbiting by generating some ...
3
votes
2answers
2k views

Low frequency electromagnetic waves

Some frequencies of electromagnetic waves are used for transmission of information, like radiowaves, microwaves, light, but some not.. What about Low Frequencies?: Perhaps low frequencies aren't ...
5
votes
1answer
224 views

Can a $CFT_2$ which can't be factorized into chiral and antichiral parts and/or have a central charge not a multiple of 24 have AdS duals?

In the article Three dimensional gravity reconsidered by Ed Witten, he remarked that the CFT dual to three dimensional quantum gravity has to admit a holomorphic factorization and have a central ...
2
votes
3answers
1k views

How could this person have discovered the resonant frequency from this string of magnets?

I stumbled onto this page http://mylifeisaverage.com/story/1364811/ and the post states that they were all making strings and shapes with these sets of 216 really small spherical earth ...
1
vote
1answer
100 views

Physics II Video Courseware Recommendations

I'm looking for something to supplement my Physics II class. Last year I started using these video lectures to supplement my Calculus class and it helped tremendously. I also turned to this ...
5
votes
1answer
305 views

A “global warming” problem

Suppose that a someone decided to calculate, for a given amount of heat added into a planet's atmosphere(an ideal gas), how much is the corresponding temperature rising of the atmosphere, $\Delta T$. ...
17
votes
3answers
1k views

Why does dilation invariance often imply proper conformal invariance?

Why does a quantum field theory invariant under dilations almost always also have to be invariant under proper conformal transformations? To show your favorite dilatation invariant theory is also ...
6
votes
1answer
328 views

LHC Big Bang Temperatures

It's been claimed that the LHC's 14 TeV energy produces temperatures comparable to that which occurred very soon after the Big Bang. The well-known $E=1.5kT$ formula from classical statistical ...
1
vote
7answers
6k views

I need help with finding distance traveled

How do I find the distance traveled of an object if the speed is not constant?
2
votes
2answers
406 views

Specific heat and temperature

This is a two-part question... Firstly, models of the specific heat capacity $C$ (i.e. Debye, Einstein) in relation to the temperature $T$ give $C$ as steadily increasing with $T$. I assume that the ...
2
votes
3answers
264 views

Tachyonic complex structure directions in flux vacua

In flux compactifications to 4D, e.g. Type IIB on a CY orientifold $X$, one uses fluxes to stabilize the axio-dilaton $\tau$ and the complex structure moduli $z_a$ - the periods of the holomorphic ...
1
vote
2answers
249 views

Double slit experiment and perforated walls' properties

I have a doubt about how double slit experiment is made. Let's think about the perforated wall, what are the requirement for it? Can a photographic plate could be used as a wall ? I see a problem ...

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