7
votes
1answer
210 views

About unitarity and R-charge in 2+1 superconformal field theory

How does unitarity require that every scalar operator in a $2+1$ SCFT will have to have a scaling dimension $\geq \frac{1}{2}$ ? Why is an operator with scaling dimension exactly equal to ...
7
votes
2answers
336 views

What happens to a single quark in lattice QCD simulations?

I understand that if a pair quark/antiquark, out of the vacuum, tries to separate then the energy increases, another pair is produced, and we finish with two mesons or generically two hadron jets. But ...
9
votes
3answers
921 views

Can black holes actually merge?

If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a ...
7
votes
1answer
1k views

Representation of the Galileo Group and Central Charges

I've arrived at this question because I've been reading Weinberg's Quantum Theory of Fields Volume I, and I'm in the second chapter about relativistic quantum mechanics. Weinberg discusses the ...
6
votes
3answers
2k views

Solar system, visible stars and deep sky objects

Since I've seen that galaxies are often called "deep sky objects", as opposed to individual stars, does this mean that all visible stars in the night sky actually only belong to The Milky Way Galaxy? ...
3
votes
1answer
106 views

What effects will the heliosheath have on the Voyager spacecraft?

I wanted to know what effects the heliosheath will have on the Voyager 1 & 2 craft. I know they used the slingshot method to travel through our solar system; so, with being way out in the ...
7
votes
3answers
695 views

Is the “Great Attractor” an indicator of the “Multiverse”?

I have heard a bit about the Great Attractor (the gravitational anomaly that seems to be "sweeping" our universe in one direction). Someone (and forgive me, I do not recall the specifics) has ...
4
votes
1answer
423 views

Invariance and forms of the Lagrangian

I have been doing Landau and due to its concise style been facing a few problems. I hope you can help me out here somehow. 1)Does the "homogeneity of space and time" essentially talk about the ...
15
votes
7answers
8k views

What is the average distance between objects in our asteroid belt?

We've all seen sci-fi movies with asteroid belts that require "great skill" to fly through, but how dense is the asteroid belt really? How much of the belt could you see from the surface of a given ...
-1
votes
1answer
126 views

What is the activity of a planet in a double star system?

If a planet is directly between two stars y distance apart (so it's y/2 from each planet), with velocity x such that x is sufficient to continue orbiting at that distance (y/2), which does it orbit, ...
1
vote
2answers
260 views

Gravititonal fields compared to electromagnetic fields - are they infinite in range?

me and my friend has a discussion last night, and he argued that both an electromagnetic field and gravititonal field are infinite in their area of effect, but with diminishing effects as you get ...
14
votes
1answer
4k views

Are all electrons identical?

Why should two sub-atomic (or elementary particle) - say electrons need to have identical static properties - identical mass, identical charge? Why can't they differ between each other by a very ...
2
votes
0answers
265 views

composition of space expansion and movement as a gauge invariance

suppose i have a space-time where we have one point-like object* which we will call movement space probe or $\mathbf{M}_{A}$ for short, and it will be moving with constant velocity $V^A_{\mu}$ in ...
18
votes
3answers
2k views

What really cause light/photons to appear slower in media?

I know that if we solve the maxwell equation, we will end up with the phase velocity of light is related to the permeability and the permittivity of the material. But this is not what I'm interested ...
3
votes
8answers
2k views

Seeking Recommendation for Celestron Firstscope Eyepiece Upgrade

I have a Celestron Firstscope telescope and like it overall for my location and the amount of observing I do. I am disappointed in my view of the planets with the scope. What would be a good eye piece ...
4
votes
4answers
388 views

Understanding Heat

Heat or thermal energy as understood is nothing but motion of molecules of the matter. If the molecules are tightly bound (in case of solids), it is to-and-fro molecular vibrations, otherwise it is ...
8
votes
6answers
424 views

Objects in Physics as a mathematician would see them

I'm a mathematician with hardly any knowledge of physics. Before I start reading volumes of physics books, I have a few questions that have been bugging me and that will help me start reading physics. ...
3
votes
1answer
185 views

Why is the local field algebra $\mathfrak F(O)$ associated with a bounded non-empty open region $O$ of space-time not irreducible?

Let us consider a Wightman field theory for the free scalar neutral field $\phi$, and let $O\mapsto\mathfrak F(O)$ be the net of local von Neumann field algebras. If we take a non-empty bounded open ...
10
votes
5answers
935 views

How is it possible for astronomers to see something 13B light years away?

In a NPR News story from a few years back: "A gamma-ray burst from about 13 billion light years away has become the most distant object in the known universe." I'm a layman when it comes ...
13
votes
7answers
1k views

Can energy be taken out of the QFT vacuum?

There have been recent questions about the vacuum. In my simplified knowledge the vacuum is like a ground state energy level, and also that there might even exist other lower energy levels than the ...
6
votes
4answers
7k views

Derivation of self-inductance of a long wire

Currently I am stuck, trying to derive the self-inductance of a long wire. According to literature it should be $$L=\frac{\mu_r\mu_0l}{8\pi}$$ and in literature its derived by looking at the energy ...
1
vote
1answer
249 views

Linear polarizer and the angle of incidence

It is known that when a beam of lineary polarized light falls perpendicularly on a linear polarizer, the intensity of polarization changes according to Malus' law and the direction of polarization ...
-1
votes
1answer
271 views

What the theta in schwinger function and what is theta formula?

What the theta in schwinger function and what is theta formula? is theta formula general solution of klein gordon equation? if so, what is its coefficient of $\exp\left(-ipx\right)$?
7
votes
4answers
415 views

Applying the Maxwell–Boltzmann statistics to astrophysical objects

Quoting Wikipedia: In statistical mechanics, Maxwell–Boltzmann statistics describes the statistical distribution of material particles over various energy states in thermal equilibrium, when the ...
2
votes
2answers
1k views

How to calculate concentration of vapor at the surface of a water drop

I'm reading a paper that examines the evaporation rates of water. In the final formula, it has the following constant: $c_s - c_\infty $ where $c_s$ is the concentration of the vapor at the sphere ...
5
votes
2answers
2k views

how does a helicopter get forward thrust?

Just passed a helicopter on my way to work. We have read in some detail how an airplane gets forward thrust and lift by deflecting air. How does a helicopter with horizontal fans achieve that ?
1
vote
0answers
112 views

Show that the electric field E in the system at rest is $E=\frac{Q}{4 \pi \epsilon_0 \sqrt{(x^2+y^2+z^2)^3}} (x,y,z)$ [closed]

A body point charge $Q$ moves in relation to the reference system $\Sigma$ according to the law of motion $x(t)=v_0 t$, $y(t)=0$, $z(t)=0$.
7
votes
5answers
755 views

Whats the range of dimension exponents in the SI Units system?

I am working on a software library for Units of Measure. To represent dimensions, I need to know the required range of exponents for each of the seven base units (precisely, I need to know the ...
2
votes
4answers
2k views

Doppler effect from an accelerating frame of reference

The standard equation for the doppler effect from a frame of reference with constant velocity is $f_0$ initial frequency; $v$ is the velocity of waves in the medium; $v_r$ is the velocity of the ...
6
votes
1answer
127 views

Stellar Viscosity in Galaxies

Is there such as thing as the viscosity of stars in a galaxy, along the lines of gravitational attraction between stars changing the dynamics. If so, how is that put in terms of the Virial Theorem?
8
votes
2answers
221 views

Finding the spectrum of a polynomial of the creation and annihilation operators

Is there a general algorithm to find the spectrum of $S S^\dagger$, where $S$ is a homogenous polynomial (of degree $n$) of the annihilation operators (of $d$ variables)?
3
votes
1answer
2k views

what is uniform velocity?

i have a very basic question from school days. what does it mean to say an object is moving with uniform speed? it seems to me now that it should be an unit dependent concept. for example if speed is ...
7
votes
2answers
661 views

Does a static electric field and the conservation of momentum give rise to a relationship between $E$, $t$, and some path $s$?

For a static electric field $E$ the conservation of energy gives rise to $$\oint E\cdot ds =0$$ Is there an analogous mathematical expression the conservation of momentum gives rise to?
18
votes
5answers
240 views

Given a photo of the Moon, taken from Earth, is it possible to calculate the position of the photographer's site?

Given a photo of the Moon, taken from Earth, is it possible to calculate the position (Earth longitude and latitude) of the photographer's site? I am thinking about photos taken with a normal camera ...
10
votes
1answer
473 views

how does dynamic casimir effect generate correlated photons

There is a recent paper on arxiv receiving lot of acclaim http://arxiv.org/abs/1105.4714 The authors experimentally show that moving a mirror of a cavity at high speeds produces light from high ...
8
votes
2answers
2k views

maximum rotational speed

I am wondering if there is a limit to rotational speed of an object just like there is one for translation speed ? what are the implications of general relativity for rotating objects ?
4
votes
2answers
492 views

Landau's ambiguous statement about the existence of inertial frames

Landau writes "It is found, however, that a frame of reference can always be chosen in which space is homogeneous and isotropic and time is homogeneous." Does he mean that we can prove the existence ...
9
votes
4answers
3k views

What is the strongest evidence that anti-matter exists?

Every space show I watch mentions that anti-matter used to exist, or still does and we just can't detect it. I think some shows even say we can create a small amount of anti-matter. It is not ...
-5
votes
1answer
246 views

What is a simple physics application of the reciprocal of a square root? [closed]

I learned yesterday that the inverse of square roots is used to calculate the vectors of surface normals in 3d graphics. It seems like such a mind-bogglingly simple idea, and it leads me to wonder if ...
10
votes
4answers
4k views

Does it matter how you order your tug-of-war participants?

In a tug-of-war match today, my summer camp students were very concerned about putting the biggest people at the back of the rope. Is there any advantage to this strategy?
4
votes
1answer
601 views

Wave function normalization

A book by C. J. Ballhausen led me to believe that a quick way to check that I performed step operators properly was by observing that the "wave function should appear normalized," but I have found ...
2
votes
2answers
80 views

In a gas of particles, how is the displacement vector related to the number density?

Suppose I have a gas of particles that is initially uniformly distributed so that the number density is $n_0$ (number of particles per unit volume), and then I displace the particles by the vector ...
8
votes
5answers
2k views

On a bicycle, why does my back tyre wear so much more quickly than the front?

This question is cross-posted from Bicycles.SE, but it is really one for those that know a bit about physics. Why does the back tyre of a bicycle wear out quicker than the front tyre? I have my ...
1
vote
2answers
3k views

How do I calculate the power consumed by a lightbulb?

I'm studying a lightbulb and its variable resistance, given by the expression: $R(T) = Ro[1 + α(T-T_0)]$, where $R_0$ is the resistance of the lamp at $T_0$. In this case, $R$ is not given by Ohm's ...
2
votes
1answer
1k views

What makes some aluminium alloys so strong while remaining light?

Compared to cast iron, for example, certain alloys of aluminum have both strength and weight advantages. How can aluminum be so strong while being so light?
1
vote
1answer
679 views

Can a photon exiting from a gravity well ever reach a frequency of zero / wavelength of $\infty$?

In reading another question about gravity's effects on a photon, I wondered if it were possible for a photon to ever be redshifted to zero wavelength. I know that black holes have a gravity field ...
2
votes
2answers
2k views

Stress vs Strain for mild steel

After Yield point on stress strain diagram the under curve occurs what does it mean what will happen for the mild steel at that particular time and again why the curve goes to up and reaches ...
2
votes
0answers
133 views

Argument for quantum theoretic conformality of $\cal{N}=2$ super-Chern-Simon's theory in $2+1$ dimensions -Part 2

This is in continuation to what I was asking here earlier - Argument for quantum theoretic conformality of $\cal{N}=2$ super-Chern-Simon's theory in $2+1$ dimensions Or one can look at this ...
0
votes
3answers
728 views

What makes waves at beaches to come with high velocity and frequency at nights?

When we are in beach we can see waves coming when the sun light goes of the waves amplitude will increase what is the reason Some people said me that for moon light the frequency and velocity of ...
1
vote
1answer
93 views

dynamic viscosity in the minute scale

The dynamic viscosity of air is $1.78\cdot 10^{-5}Pas = 1.78\cdot 10^{-5}\frac{kg}{ms}$. How do I convert this to the minute scale? I see a reason for multiplying the value with 60 (because of the ...

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