4
votes
2answers
3k views

Decibel level addition of multiple noise sources

If I have four computer fans of which each is said to run at 46 dB, and they run close to each other, how loud is the whole system? I somehow recall from my physics course that 10 decibel ...
4
votes
2answers
253 views

interaction at a distance: how it works

In classical physics, I know the forces due to gravity and electrostatics. I know a lot of work has been done, but don't know the status. Is there a generally accepted theory of how the force is ...
6
votes
2answers
354 views

Layman explanation for superconductivity?

I'm interested in reading an explanation of superconductivity, but though I have an undergraduate degree in engineering, I'm not sure I'm up to reading a detailed mathematical treatment of the theory. ...
12
votes
2answers
5k views

How does electricity propagate in a conductor?

On a systems level, I understand that as electrons are pushed into a wire, there is a net field and a net electron velocity. And I've read that the net electron drift is slow. But electricity ...
1
vote
4answers
344 views

Interaction of matter with EM fields

For the interaction between electromagnetic fields and matter, when do we have to include quantization of the EM field and when we can ignore it? when do we have to include quantization of atomic ...
4
votes
0answers
526 views

Cusp anomalous dimension in QCD

What is the "cusp anomalous dimension", starting from the basics? I came across this term while reading some QCD papers.
1
vote
1answer
210 views

Is the number of independent constants of a system equal to the number of degree of freedom of it?

Maybe the question is not very clear myself since I am not a physics major.But can you help me make this question clearer and then give me some comments on it? I got that this holds in gravitional ...
1
vote
0answers
403 views

how does phase-shifting principle in interferometry work?

I have been using the coherence scanning interferometry (or also known as white light scanner), where it collects images containing the fringes. The system is able to produce the depth profile for one ...
6
votes
1answer
113 views

Optimality of the CHSH strategy

The maximum achievable probability of the Clauser-Horne-Shimony-Holt game is $\cos^2(\pi/8)\approx85.355\%,$ which can be proved with Tsirelson's inequality. But I don't imagine that this remained ...
10
votes
7answers
745 views

Why regularization?

In quantum field theory when dealing with divergent integrals, particularly in calculating corrections to scattering amplitudes, what is often done to render the integrals convergent is to add a ...
1
vote
0answers
841 views

FPS to MKS usage issues

I'm currently taking a high school physics class and we're doing friction problems now. I've been doing the ones that use MKS perfectly well, but when the problems start to use the FPS system, I'm ...
4
votes
2answers
91 views

What videos should everyone watch?

Similar to this cstheory question "What videos should everyone watch?" What conferences, workshops or lectures have recordings that researchers in theoretical physics should watch?
6
votes
2answers
2k views

Physical laws prior the big bang (quantum fluctuations)

A theory among scientists says that quantum fluctuations caused the big bang and created the universe. This seems plausible to me. What I can't grasp yet is how a quantum fluctuation can even start ...
2
votes
2answers
246 views

Modeling galactic colonization

I found a really cool sounding order-of-magnitude modeling question but am a bit at a loss on how to approach this: The Milky Way contains 100 billion stars and has a radius of 250,000 light ...
1
vote
1answer
188 views

What type of symmetry specifies in presence of what each not-charged particle (for example, neutrino) should have an antiparticle?

I think that charging symmetry assumes antiparticle presence, which has an opposite charge sign . And what symmetry assumes existence of an antiparticle at a neutral particle
7
votes
1answer
116 views

Simple question on the foundations of spin foam formalism

To make it simple, take the spin foam formalism of ($SU(2)$) 3D gravity. My question is about the choice of the data that will replace the (smoothly defined) fields $e$ (the triad) and $\omega$ (the ...
0
votes
1answer
6k views

laser spectral width vs. linewidth

I have been racking my brains over the differences between laser spectral width and something called the linewidth. The linewidth was written about in detail by Henry in 1982. The spectral width is ...
6
votes
2answers
816 views

Decay from excited state to ground state

People frequently speak about an atomic system decaying from an excited state to the ground state. However, both the ground states and the excited states are defined as eigenstates of the Hamiltonian ...
3
votes
1answer
267 views

What “I” should use in Rotational Energy formula $(I \omega^2)/2$

$\text{Rotational Energy} = \frac{1}{2} I \omega^2$. What $I$ should be used? $I$ as a inertia tensor matrix = stepRotation * inverse moment of inertia * inverse stepRotation; Or I as moment of ...
1
vote
0answers
610 views

Find equations of motion from given Lagrangian density [closed]

Could someone help me solve this probably not very hard problem? Given Lagrangian Density: $\mathcal ...
32
votes
10answers
1k views

Examples of number theory showing up in physics

My question is very simple: Are there any interesting examples of number theory showing up unexpectedly in physics? This probably sounds like rather strange question, or rather like one of the ...
5
votes
1answer
139 views

Are there any reasonable attempts at explaining the OPERA result

as there's so many papers on the opera result and it's a struggle flicking through them all combined with my limited knowledge meaning I cannot well differentiate silly nonsensical papers from ones ...
0
votes
2answers
256 views

Is existence of cosmic dark energy falsifiable yet?

Is "existence of cosmic dark energy" falsifiable yet? And what about dark matters? Let me rephrase it again(pardon me for my previous poor expression)- Is there any condition discovered which can be ...
13
votes
1answer
1k views

Difference between 1PI effective action and Wilsonian effective action?

What is the simplest ay to describe the difference between these two concepts, that often go by the same name?
0
votes
2answers
2k views

how much heat i need to reach constant temperature

Is there an equation I can use to calculate the heat required (as a function of time) to sustain water at some specif temperature? I already know how much heat I need to reach the desired temparature ...
6
votes
3answers
331 views

If the entire universe is the same age, can one assume that any potential life elsewhere is at the same stage of development as us?

There was some discussion in another question regarding whether you can consider all parts of the universe to have existed for the same length of time, and the conclusion seemed to be that, because of ...
10
votes
1answer
15k views

Why can there be fire in space while there is no oxygen?

The sun is made of fire but fire needs oxygen right? So.. Why can there be flames in space, while there's no oxygen? Same idea as with the rocket engines of the spaceship, which also produce fire ...
8
votes
1answer
106 views

Superconformal Multiplet Calculus in 6D

A convenient method for dealing with off-shell formulations of supergravity theories is provided by the superconformal multiplet calculus. This calculus was originally constructed for 4d ${\cal N}=2$ ...
3
votes
2answers
162 views

Infinitesimal input, macroscopic output

I must admit that I never got well how physicists handle infinitesimal quantities, mainly because of my education as a mathematician. So the following lines (taken from the preface of Berezin and ...
8
votes
5answers
610 views

Why is storage of spent nuclear fuel dangerous?

Just what the title states; there's a good deal of noise made about transport, and storage of spent nuclear fuel. Why all the hullabaloo when the fuel is all spent?
7
votes
1answer
105 views

How plausible is a subsurface ocean on Pluto?

According to this article on physorg.com, it's likely that Pluto has a subsurface ocean of liquid water. It suggests that the ocean would be about 165 km deep, under an equally deep crust of solid ...
5
votes
5answers
316 views

Can decoherence work when the environment itself is in a superposition without invoking collapse or splitting?

Decoherence is often presented as a program to solve the measurement problem using only the bare bones quantum mechanics framework of a Hilbert space and unitary Schrödinger time evolution. As ...
1
vote
1answer
108 views

Why don't the actinides start at neptunium?

In their physical and chemical properties, actinium, thorium, protactinium, and uranium are respectively similar to lanthanum, hafnium, tantalum, and tungsten, and thus would seem to belong ...
20
votes
2answers
2k views

Rigorous justification for rotating wave approximation

Whenever I have encountered the rotating wave approximation, I have seen "the terms that we are neglecting correspond to rapid oscillations in the interaction Hamiltonian, so they will average to 0 in ...
3
votes
2answers
2k views

why is mechanical waves faster in denser medium while EM waves slower?

Why is it that mechanical waves/longitudinal waves/sound travel faster in a denser/stiffer medium as in steel compared to say air, while EM waves/trasverse waves/light travels slower in a (optically) ...
12
votes
5answers
1k views

Is it possible to recover Classical Mechanics from Schrödinger's equation?

Let me explain in details. Let $\Psi=\Psi(x,t)$ be the wave function of a particle moving in a unidimensional space. Is there a way of writing $\Psi(x,t)$ so that $|\Psi(x,t)|^2$ represents the ...
3
votes
1answer
2k views

How to modify the bullet trajectory based on the ballistic coefficient?

I am new to the physics surrounding bullet trajectory and how it is calculated. I am a software developer and I am working on a ballistics calculator for rifles. I am using wiki for the trajectory ...
2
votes
3answers
172 views

How can I modify the bullet trajectory based on the ballistic coefficient? [duplicate]

Possible Duplicate: How to modify the bullet trajectory based on the ballistic coefficient? I am new to the physics surrounding bullet trajectory and how it is calculated. I am a software ...
2
votes
0answers
889 views

How to calculate the electric field and potential inside a dielectric surface placed into a homogenous field

In an experiment we placed a long dielectric cylindrical shell (cylindrical tube)(with inner and outer radii r1 and r2, respectively) in a homogenous field such that its axis was orthogonal to the ...
1
vote
3answers
2k views

Analytic solutions to time-dependent Schrödinger equation

Are there analytic solutions to the time-Dependent Schrödinger equation, or is the equation too non-linear to solve non-numerically? Specifically - are there solutions to time-Dependent Schrödinger ...
3
votes
3answers
3k views

Does stirring water in a bucket in whirlpool keeps it warm?

I did an experiment when I was a teenager. I want to prove/see what really went on in that experiment. When taking a bath, take a warm water in bucket and start taking a bath. You will notice that ...
0
votes
3answers
368 views

Has anyone theorized a connection between entropy and quantum uncertainty?

I apologize if this kind of idle theorizing is frowned upon here, but I was wondering if it is possible that the Second Law of Thermodynamics is a consequence of quantum uncertainty. I've heard ...
4
votes
3answers
2k views

How can a sine wave represent a longitudinal wave?

I envision a longitudinal wave as a series of vertical lines like that drawn on the board in an introductory physics class. This image contains no angles. Sound is a longitudinal wave. Some ...
3
votes
1answer
88 views

Did Penzias and Wilson use Wein's law (or data based on it) to determine the temperature of CMB?

I'm writing a paper and I used them as an example, but then reconsidered . . . maybe I'm not getting it right! thanks!
1
vote
0answers
290 views

How to model an accelerometer measurements on a car wheel?

I am working on kinematically modelling an accelerometer on a car wheel. When working on the initial conditions, I am confused whether or not I should use the gravitational acceleration since there ...
3
votes
2answers
4k views

Testing the temperature of an open flame

How, and what device do you need, to obtain the exact temperature of an open flame? For the purpose of this question, you wanted to maintain 375 degrees. You can control the flame, but have no idea ...
3
votes
2answers
671 views

What are some interesting coupled harmonic oscillators problems?

That I could create as a classical mechanics class project? Other than the classical examples that we see in textbooks.
8
votes
2answers
638 views

Quantum Computing, Qubit Creation/Entanglement

I am currently a high school student researching quantum computing. I was referred to this site by Google and a friend. Currently I am researching the qubit part of quantum computing. My question is ...
1
vote
2answers
230 views

curvature tensor component capable of doing work on $T_{\mu \nu}$

I'm wondering what part of the curvature tensor is able to do work (and hence transfer energy) in matter. I'm wondering if this tensor: http://en.wikipedia.org/wiki/Stress-energy-momentum_pseudotensor ...
2
votes
2answers
7k views

Relationship between inductance and number of turns in a coil in loudspeaker

I am in the process of designing a loudspeaker and have a question regarding the number of turns in the multilayered solenoidal coil and the speaker impedance of $8\:\Omega$. I understand that the ...

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