# All Questions

203 views

### How could pinion in automatic quartz watch be rotated at 100K RPM?

Wikipedia article on automatic quartz watch describes the watch mechanism as follows: a rotating pendulum is attached to a pinion and when the wearer moves his hand the pinion is rotated at up to 100 ...
391 views

### Cosmic Microwave Background (CMB) and its relation to Inertial Frames

We know that the CMB is isotropic when viewed outside of the spinning and revolving earth. Is it homogeneous? Can we relate the CMB to an inertial frame in the Newtonian sense (in which space and ...
244 views

### Is the Assumption That Space-time Has to Be a Continuum Just a Matter of Mathematical Taste?

Is the assumption that space-time has to be a continuum just a matter of mathematical taste? Isn't there any physical significance associated with it?
2k views

### A spinning bullet

I know the rifling in a gun or rifle puts a spin on the bullet along the axis of trajectory. Now I don’t understand exactly what does it make the trajectory more stable and the travel grater?
226 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 ...
363 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 ...
1k 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 ...
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 ...
1k 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? ...
111 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 ...
843 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 ...
455 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 ...
10k 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 ...
129 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, ...
272 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 ...
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 ...
272 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 ...
3k 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 being related to the permeability and the permittivity of the material. But this is not what I'm ...
3k 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 ...
416 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 ...
493 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. ...
204 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 ...
1k 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 ...
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 ...
8k 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 ...
287 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 ...
277 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 $\exp\left(-ipx\right)$?
503 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 ...
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 ...
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 ?
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 $x(t)=v_0 t$, $y(t)=0$, $z(t)=0$.
949 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 ...
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 ...
136 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?
233 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)?
1k 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 ...
732 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?
272 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 ...
502 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 ...
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 ?
526 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 ...
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 ...
253 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 ...
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?
627 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 ...
82 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 ...
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 ...
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 ...