# All Questions

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### Second-order correction in Quantum-Confined Stark effect

In the wikipedia article, there is a second-order correction in the Quantum-Confined Stark Effect. I could not understand how it was solved. I did not understand the meaning of 2(0) and 1(0) and how I ...
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### 2nd law of thermodynamics - thought experiment

I have designed this simple thought experiment that seems to contradict 2nd law of thermodynamics. Could you please find a mistake in my reasoning? ...
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### Are the fundamental constants of nature independent?

Background: I am a layman and I just watched the video "Infinite Worlds: A Journey through Parallel Universes" (http://www.youtube.com/watch?v=OO4uzgiRHkE) featuring a discussion with Andrei Linde, ...
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### Definition of Force Using Momentum

When we use F = change in momentum / change in time, is that the average force applied? There could be different magnitudes of force applied over time to change the momentum (it could be instantaneous ...
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### How can I compute the average number of collisions of a particle in a spherical container?

The problem statement reads as follows: A spherical container of radius $R$ with a small hole is inmersed in an ideal gas at a tempereature T. When a gas particle enters into the spherical container, ...
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### Hamiltonian flow?

I was wondering what the Hamiltonian flow actually is? Here is my idea, I just wanted to know if I am correct about this. So let $(x(t),p(t))' = X_{H}(x(t),p(t))$ are the Hamilton's equations and ...
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### Isotropic 3D oscillator excitation levels in different eigenket basis

An isotropic 3D oscillator's excitations can be represented by combinations of raising operators $\hat{a}_i^{\dagger}$ acting on the vacuum $|0,0,0\rangle=|0\rangle$ in the $x,y,z$ basis, but also ...
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### Natural unit conversion

I'm a bit confused about different notions of "natural units" that I encounter occasionally. I'm familiar with Planck units, and in particular I can understand the conversion between, say, metres and ...
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### How do you find the projection operator onto an eigenspace if you don't know the eigenvector?

I was working on exercise 2.60 of Nielsen-Chuang which is as follows: Show that $\vec{v}\cdot\vec{\sigma}$ has eigenvalues $\pm 1$, and that the projectors onto the corresponding eigenspaces are ...
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### Analogy for the AdS/CFT Correspondence

Some time ago, I heard about a simple analogy for the AdS/CFT correspondence to something in everyday life. Consider a room filled with furniture, with the walls of the room covered in mirrors. The 2D ...
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### Quantum Monte Carlo for harmonic oscillator

I'm trying to calculate harmonic oscillator using quantum monte carlo (path integral and metropolis algorithm). It's one particle in harmonic potential. I know the theory. One divides the partition ...
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### Why don't wavefunctions for electrons in neighbouring molecules overlap?

I've come across this picture of two linked molecules. The intramolecular distances look similar to the intermolecular distances and it seems like that will be the case however you draw it because of ...
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### Minerals on Planets of our Solar System

Is there an overview (e.g. list, database, etc.) of mineral resources (raw/crude materials) available on the planets of our solar system? For Earth e.g. there is this data system of mineral ...
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### Angular and linear displacement of a turning car

My illustration is supposed to show a simplified car (with just two wheels, where the front wheel has been rotated $-90 \text{ degrees}$). Let the car travel at constant speed. This means that the ...
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### How can towtrucks tow a heavy truck on icy roads?

(This isn't hardcore physics, but bear with me. I've been watching too much Highway Thru Hell and I'm curious about this) A common problem on the Highway Thru Hell TV-show is trucks stuck on an icy ...
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### What would we see back on Earth if we shot a camera off into space and watched a live-stream?

I'm curious as to what we would see if we shot a camera off into space at, say, 50,000 mph and watched a live stream. Clearly in the beginning we'd be seeing things in more or less real time. But by ...
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### Null geodesic equation

For a null geodesic curve $X^i$, $$0=g_{ij}V^iV^j.$$ When we derive the geodesic equation from E-L equations, will this affine parametrization cause it to blow up? How is it justified to use the ...
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### Normalizing a wave function in a mixed well

So I got this potential and want to solve for the even wavefunctions http://imgur.com/GKAy4nD Since it's symmetric around the origin I need only to look at the interval [0,b] and solve for the ...
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### Where is there posted dampening coefficients for viscous dampers?

Depending on the size of the viscous dampener the coefficient will change, however i am trying to model a "physical" system with calculating everything out, so that way i can test failure before it ...
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### Relative motion at almost the speed of light

My title might not be precise but I didn't know how to decribe it better. I've been reading about the special and general theories of relativity for a short while and I started wondering. First, ...
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### Understanding view-/formfactor for radiation with a specific example

There is radiation coming from a point source (black body). How much of the total emitted energy (from the point source) hits a spherical surface given by $\phi = 0 - \pi$ and $\theta = 0 - \pi/2$? ...
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### Relative Movements Agreement on Object speed

I am confused about Relative Motion.Lets suppose we have one train and two observer.One of them inside the train and the other one is outside.Lets think the outside observer see the train moves a ...
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### What is happening kinematically to a car on an icy turn? [on hold]

I am stumped on a conceptual homework question that involves rotational kinematics and friction. Consider a car traveling along a road that encounters a turn covered in an unseen layer of ice. ...
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### Understanding the AdS/CFT Correspondence [duplicate]

I am beginning to learn about the AdS/CFT correspondence, but I can't find a comprehensive introduction that includes the relevant gravitational/string theory physics. What specific areas of general ...
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### Can I Weyl-order the following Hamiltonian?

I am trying to perform a path integral but I am having trouble with the Weyl ordering of my Hamiltonian. The Lagrangian of the system in question is $$L~=~\frac{1}{2}f(q)\dot{q}^2,$$ where $f(q)$ ...
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### Mirror question [on hold]

A man stands in front of a plane mirror. The vertical distance between his eyes and the top of his head is 8 cm. Find the minimum height of the mirror so that the man can see all his body.
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### Why are complex fields in the Lagrangian?

I know that a complex field has twice the number of degrees of freedom of a real field, and that fields (in QFT) aren't observables so we don't really care if they are real. But why the need for ...
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### Vertical wall at 3 different temperatures - do the same natural convection coefficient correlations apply?

I have an vertical enclosure that consists of 3 shelves, each with its own temperature and are thermally isolated from each other. We will call the shelves A, B, and C with A being the base shelf. The ...
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### When was the temperature of the CMB between 0°C? When was it 100°C? [duplicate]

The current temperature of the CMB is something like 3°K. When was the CMB temperature between 0° and 100° Celsius?
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### Why isn't everthing in a superposition state?

I know that a superposition is a state in which there are 50% and 50% (other % also) chances of two things to happen so why am I not in a superposition state? Example, I am at rest and i now choose to ...
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### Why can't a classical bit behave like a qubit?

For example i have a 2 qubits which can have 4 possibilities i.e. 00, 01, 10, 11 so this shows that the 2 qubits can contain four bits of information as they are superpositioned but i think 2 ...
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### Symmetries and quantum numbers $n$, $l$, $m$, $s$ [on hold]

I would like to better understand the symmetries and groups underpinning the quantum numbers $n,l,m,s$ for a bound electron. My understanding is that: $n$ is the principal quantum number, and is ...
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### Non-abelian current transformation

This is my firs post ever here and I just registered on this site but I want to say that this site has helped me a lot and you guys are great! On to the question: I have the equation of motion that ...
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### Explanation to; Energy loss from a vertically bouncing mass on a spring [on hold]

Basically i have been assigned this title in my physics coursework of the (IB) and im struggling to get started. I have read my way through the internet, with ought any success. I hope one of you ...
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### Interpretation of Virial theorem in the case n=-2

For potentials $V$ that fulfil $V(\lambda \vec{r}_1, \lambda \vec{r}_2, \ldots, \lambda \vec{r}_N) = \lambda^n V(\vec{r}_1,\vec{r}_2,\ldots, \vec{r}_N)$ one can rewrite the virial theorem as ...
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### When trying to see what symmetries an operator generates, how do you “decide” what coordinate to apply it to?

Suppose I have $\hat{O}_{1}=-i\hbar\partial_{x}$ then \begin{eqnarray} e^{-i\gamma\hat{O}_{1}/\hbar}x\,e^{i\gamma\hat{O}_{1}/\hbar}=x+\gamma \end{eqnarray} and \begin{eqnarray} ...
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### Is a Super-luminal Laser spot possible? [duplicate]

Note:This is not the same as Is the "How to break the speed of light" minute physics video wrong? because a larger distance is used in a different direction so that the time of flight of the ...
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### Fluctuation operator and partial wave

Can someone please explain to me why the expression $[-\Box + U''(\Phi(r))]$ is called the fluctuation operator? I was also wondering how to derive the following for the $l^{th}$ partial wave of the ...
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### The definition of mutual capacitance

I am not sure I completely understand the definition of mutual capacitance. Let's say we have two conductors, $A$ and $B$, so that the following holds: Both conductors are isolated. $A$ is isolated ...
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### Effective field theory of inflation in the slow roll case

I'm reading this set of notes by Daniel Baumann on the effective field theory of inflation but I can't quite understand one step in section 3.1.1 concerning slow roll inflation. Basically, the author ...
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### What is the Anomalous Dimension Matrix in QCD?

I read a lot about the calculation of the Anomalous Dimension Matrix in QCD but wasn't able to find any comprehensible explanation of what this matrix actually describes. I would be happy about all ...
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### How to calculate the self diffusion of carbon in diamond? [on hold]

What is self diffusion and How to calculate the self diffusion of carbon in graphite and carbon in diamond ?
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### dipole field on axis twice the field on perpendicular bisector

Why is the dipole field on axis twice the field on perpendicular bisector? For the perpendicular bisector: Lets assume -q is right from of the origin and +q is left from the origin, both a distance a ...