6
votes
1answer
740 views

Chiral anomalies à la Fujikawa: Why don't we just take another measure?

When deriving the chiral anomaly in the non perturbative approach for a theory of massless Dirac fermions, you start by showing that the path-integral measure is not invariant unter the chiral ...
7
votes
3answers
269 views

What's the purpose of the arbitary additive constants in Einstein's Inertia of Energy Paper?

In Einstein's paper: Does the Inertia of a Body Depend upon its Energy content? he introduces arbitary additive constants whose purpose I'm confused about. The paper has a frame $(x,y,z)$ where a ...
0
votes
3answers
2k views

Does an airplane's speed include the speed of the Earth?

After take off, does airplane's speed include Earth's movement/speed? Do airplanes turn with Earth movement/rotation?
2
votes
2answers
1k views

How much water must flow trough canal to maintain a constant water deep?

In order to maintain a constant water deep in canal, how much water must flow trought the pipe ? As shown on picture, canal have a rectangular shape. I don't know if canal length have an influence. ...
1
vote
1answer
582 views

How to represent uncertainty on the momentum operator through a variance?

The difference between the two expressions $\langle \hat p^2 \rangle_{\psi}$ and $\langle \hat p \rangle_{\psi}^2$ is defined by the squared uncertainty: $$\Delta p^2 = {\langle \hat p^2 ...
1
vote
4answers
175 views

physics , magnetic lines of a magnetic

Why magnetic lines comes from north to south out side of the magnet is any magnetic lines comes from south to north if so in which direction What is the reason of magnetic lineS
0
votes
1answer
519 views

How does the entropy of a system change when the amount of substance changes?

I am thinking of a closed system consisting only of an ideal gas. Suddenly, the amount of substance of the gas changes. No other property of the system shall change. How does this affect the entropy ...
7
votes
2answers
448 views

Will acceleration rate of expansion of space become faster than speed of light?

From watching cosmology lectures, it seems that the space between galaxies is expanding at an accelerating rate, my question is since it is the space that is (acceleratingly expanding), the special ...
0
votes
1answer
144 views

weak bosons and feynman-stueckelberg interpretation

from Wiki "The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle." Q:If each is the other's antiparticle then which is ...
1
vote
0answers
224 views

Sound Produced due to motion of air inside a tube

I'm trying to understand the sound produced by Air motion inside the respiratory system. If you have a long tube with a suction apparatus at one end , You turn on the apparatus and the air is sucked ...
3
votes
1answer
508 views

Enhance a home build spectrometer

I would like to build a home made spectrometer like it's describing here: http://coolcosmos.ipac.caltech.edu/cosmic_games/spectra/makeGrating.htm How can I improve this spectrometer? A prism from an ...
2
votes
4answers
200 views

Are physics and philosophy compatible? [closed]

Lately, there has been a war between physicists and philosophers. Some of the exchanges can be found at http://www.nytimes.com/2012/06/10/opinion/sunday/what-physics-learns-from-philosophy.html?bl, ...
2
votes
1answer
310 views

Does a complete theory of quantum gravity require anthropic post-selection?

Does a complete theory of quantum gravity require anthropic post-selection? Certainly the black hole complimentarity and causal patch conjectures highlights the essential role of observers, at least ...
4
votes
3answers
293 views

why the difference between $\langle \hat p^2 \rangle_{\psi}$ and $\langle \hat p \rangle_{\psi}^2$ is NOT zero?

Well, the difference between the two expressions $\langle \hat p^2 \rangle_{\psi}$ and $\langle \hat p \rangle_{\psi}^2$ is exactly $\Delta p^2$ , i.e. the squared uncertainty (variance) of the ...
0
votes
2answers
117 views

What is the importance of Vacua in Field Theory?

I understand that defining the Vacuum is important in Field Theory, why? Is this because it is the 'ground' state, before particles are added, so defines the 'background'? I assume its not important ...
6
votes
4answers
540 views

Is String Theory a Field Theory?

Is String Theory a Field or Quantum Mechanical Theory of the String rather than a Particle? I should know this having studied this for a term, but we jumped into the deep end, without really ...
1
vote
1answer
769 views

Which formula for entropy is correct? (OR Is the fundamental thermodynamic equality always right?)

Quick question, in the lecture notes to a thermodynamic course I'm taking, $$d\underline{S}=\frac{d\underline{U}}{T}+\Big(\frac{\partial P}{\partial T}\Big)_{\underline{V}} d\underline{V}$$ But ...
5
votes
2answers
2k views

How does String Theory predict Gravity? [duplicate]

Firstly, General Relativity states that Spacetime is dynamic and is consonant with the distribution of matter/energy. How does String Theory predict gravity, when it is background dependent, that is ...
2
votes
2answers
242 views

what is the relationship between the dynamical casimir effect and virtual particles?

Since virtual particles are disturbances in a field, and not particles in any sense, as explained here, how is it that true photons arise from them when excited with kinetic energy via the dynamical ...
6
votes
3answers
575 views

What in Newton's three laws of motion is original and not a paraphrasing of his predecessors?

The three laws are: First law: The velocity of a body remains constant unless the body is acted upon by an external force. Second law: The acceleration a of a body is parallel[disambiguation needed ...
0
votes
3answers
17k views

Static Water Pressure vs Height [closed]

OK, so I have water at a known pressure, lets say 12psi. I have 2 pipes, installed vertically, one 2" diameter, the other 1/2" diameter. To what height (in feet) will the water raise to in each case? ...
1
vote
2answers
173 views

On the Existence of Interstellar Meteoroids

A meteoroid in orbit around the Sun has a heliocentric velocity in the vicinity of Earth of about 42.1 km/s. So if a meteoroid has a heliocentric velocity exceeding that, it will have an open ...
1
vote
2answers
3k views

Differences between X-Ray and Electron Diffraction

I would want to know what the differences between these two techniques in cristalography. I research on internet, but it is not clear to me what each one does. When it's better to use one and not ...
2
votes
1answer
256 views

Hairy ball theorem: references to applications

I'm looking for references to applications of the Hairy ball theorem. This is a result of mathematics (topology), but I am interested in applications. I already visited wikipedia and cited ...
4
votes
2answers
249 views

Why do we stop using optics for photons above a certain energy?

I'm reading about how the soon-to-be-launched NuSTAR is on the cutting edge of focusing x-rays, which captures 5 to 80 keV radiation by focusing them with optics that have a 10.15 meter focal length ...
2
votes
4answers
702 views

Would the rate of ascent of an indestructible balloon increase as function of it's altitude?

Assume a balloon filled with Hydrogen, fitted with a perfect valve, and capable of enduring vacuum (that is to say, it would retain it's shape and so well insulated that the extremes of temperature at ...
3
votes
1answer
294 views

What is the optical power level of common fiber optics lasers?

In the book Nonlinear Optics, it is stated that the nonlinear effects start to become a problem in WDM systems (around 1550 nm) after about 1 mW of optical power. However, I measured the optical power ...
1
vote
1answer
584 views

Relation between linear momentum and translational kinetic energy

The momentum $m v$ of a particle is formally the same as the derivative its translational kinetic energy $\frac{1}{2} m v^2$ with respect to $v$. Similarly the angular momentum $I \omega$ is the ...
5
votes
1answer
804 views

How can the Huygens-Fresnel principle be derived from the Maxwell equations?

The Huygens-Fresnel principle states that every point to which a luminous disturbance reaches becomes a source of a spherical wave. I have been trying to understand this considering a infinite screen ...
2
votes
1answer
3k views

Transforming a sound wave into a literal light wave. Is it possible? [duplicate]

Literally transforming sound into an actual light wave seems almost impossible. But transforming the sound wave into a light wave while containing a single mass? I know that sound can contain a mass ...
4
votes
2answers
341 views

Non-relativistic spinors

Even in a non-relativistic theory Spinors can arise as irreducible representations of the rotation subgroup of the symmetries of the theory. Why do people then put so much emphasize on the role of ...
7
votes
2answers
1k views

Book covering Topology required for physics and applications

I am a physics undergrad, and interested to learn Topology so far as it has use in Physics. Currently I am trying to study Topological solitons but bogged down by some topological concepts. I am not ...
8
votes
3answers
2k views

Would a fast inter-stellar spaceship benefit from an aerodynamic shape?

Some (generous) assumptions: We have a spaceship that can reach a reasonable fraction of light speed. The ship is able to withstand the high energies of matter impacting at that speed. Given the ...
1
vote
0answers
75 views

How to apply Guass Law to Voltages

So, I know $\oint E\centerdot dA = 4\pi Q_{enc}$ I'm trying to solve for a TEM mode with two concentric (infinite) cylindrical wave guides of radius a and b, $a<b$. I know that for TEM modes, I ...
3
votes
2answers
665 views

How were the heavy elements from iron to uranium made? [duplicate]

Possible Duplicate: Age of the Earth and the star that preceded the Sun How were the heavy elements from iron to uranium made? References: ...
0
votes
1answer
888 views

Linear charge density, surface charge density and volume charge density

What is the difference among: linear charge density, surface charge density, and volume charge density?
1
vote
1answer
545 views

Does a magnetic field induce an emf in a loop of wire

Is it true that any magnetic field induces an emf in a loop of wire? If It it is true then kindly explain me with an example
4
votes
3answers
429 views

Can anyone estimate what proportion of water remains after I flush a toilet?

Imagine I have a clean toilet with some amount of water in the bowl. When I flush the toilet much of that water will be displaced by the tank's water. I want to work out (or model really) what amount ...
5
votes
0answers
210 views

The ${\cal N} = 3$ Chern-Simons matter lagrangian

This question is sort of a continuation of this previous question of mine. I would like to know of some further details about the Lagrangian discussed in this paper in equation 2.8 (page 7) and in ...
1
vote
0answers
59 views

is cosmic expansion related with IR divergencies?

This question is related to renormalization, but in the IR limit. It is assumed that unitarity does take care of IR divergencies in interacting theories like QED. But how would one interpret ...
4
votes
3answers
248 views

How many stars within 5 parsecs?

I've ran some scripts on some star catalogs, which counted the number of stars with a parallax greater than 200 mas, which should mean everything closer than 5 pc. The results are as follows: ...
11
votes
6answers
32k views

Gravity on the International Space Station

We created a table in my physics class which contained the strength of gravity on different planet and objects in space. At altitude 0(earth), the gravitational strength is 100%. On the moon at ...
2
votes
2answers
3k views

Determine the acceleration and angular acceleration of a disc

The question is: A 90kg disc is floating in a frictionless vacuum. A 150N force is applied to the outer rim of the disc. The disc has a radius of 0.25m and a radius of gyration of 0.16m. What ...
4
votes
5answers
1k views

Why isn't the symmetric twin paradox a paradox?

Two twin sisters synchronize their watches and simultaneously (from the earth frame) depart earth in different directions. Following a predetermined flight plan, each sister accelerates identically to ...
1
vote
0answers
41 views

bond energies database [closed]

I’m looking for a public database of bond energies of biochemical compounds. Do you know about any? Otherwise, which is the standard computational methodology to calculate them? Any references would ...
4
votes
3answers
542 views

Is Schrodinger's Cat a real conceptual problem or just a problem with approximations?

In this thought-experiment a cat is placed in a box set with a bottle poison that will release and kill it depending on whether or not a certain radioactive particle decays. The box is kept closed and ...
0
votes
3answers
165 views

How is extra information encoded in digital radio?

Earlier today, I was listening to my digital radio, and was intrigued as to how they are able to encode the information displayed on the LCD screen (which was basically a short string of text giving a ...
1
vote
0answers
78 views

Unitarity and quantum cosmology

By studying quantum cosmology I was asking myself if the fact that the universe is expanding, so space is expanding and with it I would say that phase space is also expanding, so it's a non-unitary ...
2
votes
3answers
11k views

How can I theoretically describe the potential between two capacitors in series?

Suppose to have two capacitors in series: The voltage in the middle point will be: $$ V_X = V_1 \frac{C_1}{C_1+C_2} $$ How can this be explained? It's been asked in electronics, and explained in ...
1
vote
1answer
354 views

Two identical rockets, time dilation, and possible weirdness [duplicate]

Possible Duplicate: Why isn't the symmetric twin paradox a paradox? Suppose there are two identical rockets, each carrying one of two identical clocks and one of two identical ...

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