6
votes
2answers
1k views

Solving the Young-Laplace equation for arbitrary axisymmetric geometry

Say I have a non-ellipsoidal soap bubble and I want to numerically analyse the pressure in the inner lobe of this bubble here: The Young Laplace equation gives the pressure difference across a ...
2
votes
1answer
95 views

Why is that the space-time associated with the Earth is not shrinking?

If we apply the Friedmann Lemaître equation to the Universe, we find a critical density $\rho_c$ : if the actual density $\rho$ is under it, the Universe will continue to expand, if it is higher than ...
0
votes
0answers
26 views

Why can radio wave travel through walls while imfrared can't? [duplicate]

Possible Duplicate: If both radio waves and gamma rays can travel through walls Does it have anything to do with the materials used to build the wall? What determines if a material can ...
3
votes
3answers
1k views

How to measure force of impact inside container?

I am in 7th grade and for my science fair project, I need a way to measure the force on a dropped object when it hits the ground. What I am trying to determine is which packing materials provide the ...
4
votes
4answers
4k views

How Felix Baumgartner has reached the speed of sound quickly

I have watched Felix Baumgartner freefall; but I wonder how Felix has reached the speed of sound quickly, in a matter of some seconds, then we had no idea of its speed? Any explanation please.
1
vote
0answers
87 views

Toolbox for Complex Networks and Graphs

Is there a toolbox which helps in visual simulation and modeling of a network (say a mesh or ring) consisting of coupled synchronized system of nonlinear equations(ODE) which represent a system of ...
1
vote
1answer
376 views

Negative probability and spin-0 scalar field in Klein-Gordon equation

Klein-Gordon equation in quantum field theory is known to suffer from the possibility of negative probability. So, the question is, despite this, Klein-Gordon describes spin-zero field. So, how can ...
1
vote
1answer
816 views

Time of a ball going up and down with air resistance

A ball is shot directly upward, and then it comes back to the place where it was shot. Suppose we have air resistance. Suppose $t_1$ is the time period from the moment that the ball was shot to the ...
1
vote
1answer
204 views

Why is there no oxidizer in space?

Just as a thought experiment. One factor in the economies of space exploration is that of fuel. This may be split as MSL - Earth Orbit Earth Orbit to Inner Solar System Beyond. In each of ...
1
vote
1answer
488 views

The equation of a ferrofluid under a magnetic field?

What is the parametric equation guiding the geometry of a ferrofluid under a magnetic field? See also this Wikipedia page. From previous research, Maxwell's Equations and Navier-Stokes Equations were ...
0
votes
1answer
653 views

State normalization in Dirac's formulation of quantum mechanics

Let us divide the time $T$ into $N$ segments each lasting $δt = T/N$. Then we write $\langle q_F | e^{−iHT} |q_I \rangle = \langle q_F | e^{−iHδt} e^{−iHδt} . . . e^{−iHδt} |q_I \rangle $ Our ...
2
votes
1answer
1k views

Schrödinger equation with complex potential

In 1 dimension what is the solution of the Schrödinger equation with potential $$ V(x) = V_r + i V_i $$ Potentials are constant.
19
votes
3answers
2k views

Why does light of high frequency appear violet?

When people are asked to match monchromatic violet light with an additive mix of basic colours, they (paradoxically) mix in red. In fact, the CIE 1931 color space chromaticity diagram shows this ...
1
vote
1answer
483 views

Time dependent Lagrangian

Suppose I have a mechanical system with $\ell + m$ degrees of freedom and an associated Lagrangian: $$L(\alpha, \beta, \dot{\alpha}, \dot{\beta}, t),$$ where $\alpha \in \mathbb{R}^{\ell}$ and $\beta ...
2
votes
1answer
162 views

Why is amplitude of a wavefunction to propagate from $q$ to $q'$ governed by $e^{-\frac{i}{\hbar}HT}$ unitary operator?

In the textbook Quantum Field Theory by A. Zee, it says: In quantum mechanics, the amplitude to propagate from a point $q_i$ to a point $q_f$ in time $T$ is governed by the unitary operator ...
2
votes
2answers
4k views

What math is needed to understand the Schrödinger equation?

If I now see the Schrödinger equation, I just see a bunch of weird symbols, but I want to know what it actually means. So I'm taking a course of Linear Algebra and I'm planning on starting with PDE's ...
3
votes
2answers
426 views

Does air resistance ever slow a particle down to zero velocity?

If a particle moves in a place with air resistance (but no other forces), will it ever reach a zero velocity in finite time? The air resistance is proportional to some power of velocity - $v^\alpha$, ...
2
votes
6answers
20k views

What is a microstate, macrostate and thermodynamic probability in statistical mechanics?

Currently I am learning Maxwell-Boltsmann distribution (MBD) and in that I am learning about microstate, macrostate and thermodynamic probability (TDP). I understood the derivation of MBD but I am ...
10
votes
3answers
1k views

Grassmann paradox weirdness

I'm running into an annoying problem I am unable to resolve, although a friend has given me some guidance as to how the resolution might come about. Hopefully someone on here knows the answer. It is ...
5
votes
1answer
266 views

Curvature and edge state

If the boundary of quantum hall fluid has non-constant curvature, how will it affect the edge state which is usually described in chiral Luttinger fluid?
4
votes
1answer
574 views

The Universe is a Hologram

First my background: no physics, but Ph.D. in math. I was reading this article on Slashdot. It links to this Wikipedia page. The content of the Slashdot article is that some physicists believe the ...
7
votes
2answers
582 views

Is Dyson Sphere a stable construction?

Suppose that a star is encompassed by a Dyson Sphere. Do we need a position control system for the Dyson Sphere to keep its origin always aligned with the center of the star? Will it stay aligned ...
0
votes
0answers
47 views

Reflection of light [duplicate]

Possible Duplicate: What is the difference between a white object and a mirror? When I look at a red object under white light, I see it as red because it absorbs the other colours and ...
2
votes
2answers
2k views

Is there still light in practical darkness? Do photons penetrate everywhere?

I always thought that, even in darkness, there would still be some light, making complete darkness, i.e. complete absence of photons as far as I know, just a theoretical thing. When I tried looking up ...
1
vote
2answers
882 views

Charge, velocity-dependent potentials and Lagrangian

Given an electric charge $q$ of mass $m$ moving at a velocity ${\bf v}$ in a region containing both electric field ${\bf E}(t,x,y,z)$ and magnetic field ${\bf B}(t,x,y,z)$ (${\bf B}$ and ${\bf E}$ are ...
2
votes
2answers
254 views

numerical formulation of Dirac equation plus electromagnetic field

I have the following equations describing the electron field in a (classic) electromagnetic field: $$ c\left(\alpha _i\right.{\cdot (P - q(A + A_b) + \beta mc) \psi = E \psi } $$ where $A_b$ is ...
11
votes
3answers
2k views

What are some of the best books on complex systems?

I'm rather interested in getting my feet wet at the interface of complex systems and emergence. Can anybody give me references to some good books on these topics? I'm looking for very introductory ...
4
votes
1answer
204 views

How does a 2D MEMS based optical cross-connect control its mirrors?

Concerning fiber optics, I'd like to know how a 2D MEMS based optical cross-connect is able to switch optical signals. I've read that these mirrors are controlled with electrical signals to be either ...
3
votes
3answers
409 views

Can a wavefunction be solved to any arbitrary precision, given enough computer time?

I learned that the wavefunction for the hydrogen atom can be solved analytically (we did the derivation in class), but that for more complicated atoms it is "impossible" to solve and that only ...
7
votes
4answers
9k views

What equation of state is needed for liquid states?

I'm familiar with the ideal gas law $$PV=nRT$$ but I don't think it applies to liquids like water. If I'm wrong, please correct me! If I'm right, then what equation of state applies to liquids such ...
4
votes
1answer
158 views

Rotation of Spacetime => Change in orbit/path

Along the idea of frame-dragging; Will the rotation of a black hole, which has some velocity v and angular momentum, influence its path in 3D space? I've seen the fact that depending on the ...
11
votes
5answers
4k views

Why would a fat skydiver fall first in free fall?

I was having one of those obnoxious conversations with a friend where he was arguing that a fat skydiver would reach the ground faster than a skinny skydiver. To me it seemed as obvious that the world ...
1
vote
1answer
116 views

Does (will) wind affect plasma (electical spark passing through a gap)?

Does (will) wind affect plasma (electical spark passing through a gap) in a way such as it affects fire? My guess is no because it's like light, but still thought its worth asking. Thanks
3
votes
2answers
7k views

Calculating torque adjustment for offset of pivot point

I'm trying to figure out how much to adjust torque, on a torque wrench when using an extension that offsets the pivot point. See this calculator for a diagram of what I'm talking about: The trouble ...
2
votes
1answer
1k views

Anti-matter black hole and time

I have recently read some hard science-fiction story based on an assumption that if time stops (from external observer's perspective) on the event horizon of black hole, then in an anti-matter black ...
6
votes
1answer
438 views

Electromagnetic 4-potential and basic index contraction

I'm trying to learn about relativistic electrodynamics on my own, and I am struggling with derivatives of the 4-potential and index (Einstein) notation. I think I understand expressions such as ...
3
votes
1answer
400 views

Do communicating vessels work when water is moving?

I want to know if the water level equalize in communicating vessels, when in one of the vessels there is a vortex, or any other water movement, and if the level does equalize, what will be the level? ...
6
votes
4answers
1k views

Entangled electron-positron pair

Usually when we talk about entanglement, we mean entangled spin states (of electrons) or polarizations (of photons). My questions are: Does pair production guarantee the product electron and ...
0
votes
1answer
1k views

energy production in the nuclear fission

according to this image of nuclear fission, before fisson reaction, the total mass of uranium and the slow neutron is 236 amu. and after adding the masses of Barium, krypton and the 3 neutrons after ...
8
votes
1answer
233 views

Are Born-Oppenheimer energies analytic functions of nuclear positions?

I am looking for references to bibliography that explores the smoothness and analyticity of eigenvalues and eigenfunctions (and matrix elements in general) of a hamiltonian that depends on some ...
2
votes
2answers
699 views

Why can't collisions be elastic?

I understand that in inelastic collisions thermal energy is given out, but why does that happen? Why can't they simply rebound without giving off energy? Also, why in some collisions more heat is ...
5
votes
2answers
4k views

Differences between classical, analytical, rational and theoretical mechanics

Can you explain me what are the differences between the four following subjects? analytical mechanics rational mechanics classical mechanics theoretical mechanics
1
vote
2answers
261 views

Measurement of the energy of an atom using a cold substance

An atom was prepared in a superposition of ground state and excited states.I propose to measure the state by coupling the system to a cold enough substance. By cold enough I mean $$kT\ll E_1,$$ where ...
4
votes
1answer
64 views

Does a “reflected” hologram produce a caustic in the shape of the original object?

Imagine you make a transmission hologram, ala the standard picture. Now you take your photographic plate, and everywhere it is transparent, you put a thin reflective layer on, and everywhere it is ...
5
votes
2answers
331 views

Xray compression of secondary in hydrogen bomb

Accounts of the "secret" of the hydrogen bomb describe Xrays from a primary fission explosion reflecting off of the bomb case (occasionally passing through polystyrene foam) and compressing and ...
5
votes
1answer
342 views

Does the color of a quark matter in a meson?

QCD and confinement specify that hadrons must be color-neutral. My understanding is that this means you can have mesons (quark + antiquark) or baryons with 3 quarks, one of each color: ...
3
votes
2answers
1k views

Necessary air pressure in flexible vessel to lift a certain mass

I have the following situation in mind: A big airtight bag of arbitrary shape with a person standing on it. The bag gets inflated with air to lift the person. Assuming that the bag is much larger ...
1
vote
0answers
451 views

What direction a flag on an object moving in the wind shows?

"The flag of a ship that is moving northward with 10 km/h, points exactly southwestward. The windsock at the lighthouse points under 30 relative to the western direction southward. Calculate the ...
11
votes
6answers
2k views

Paradox with Gauss' law when space is uniformly charged everywhere

Consider that space is uniformly charged everywhere, i.e., filled with a uniform charge distribution, $\rho$, everywhere. By symmetry, the electric field is zero everywhere. (If I take any point in ...
3
votes
3answers
435 views

What if $\gamma$-rays in Electron microscope?

I was referring Electron microscopes and read that the electrons have wavelength way less than that of visible light. But, the question I can't find an answer was that, If gamma radiation has the ...

15 30 50 per page