1
vote
1answer
440 views

What is discontinuity in Vector Fields

I am reading David J. Griffiths and have a problem understanding the concept of discontinuity for E-field. The E-field has apparently to components. (How does he decompose the vector field into the ...
5
votes
1answer
411 views

Distinctive properties of liquids

The molecules are closely arranged in solids, loosely arranged in liquids and are free to move in gases... But, Why are liquids (especially water) exhibiting these distinctive properties such as ...
6
votes
2answers
468 views

Is dark matter really present around the sun?

Recently I read an article that there is dark matter around the sun but if it is so, than why can we see it clearly. If it is called matter than it shall show some hindrance in radiation we receive ...
7
votes
2answers
375 views

What nonstandard theory forbids quantum computers?

What would a nonstandard model which reproduces all experimental quantum data so far but still cause quantum computers to fail when implementing Shor's algorithm look like? Would it have to be very ...
12
votes
4answers
764 views

What exactly does the holographic principle say?

Does the holographic principle say given a spatially enclosing boundary satisfying the Bousso condition on expansion parameters, the log of the number of microstates in its interior is bounded by ...
2
votes
2answers
990 views

Applying velocity Verlet algorithm

I want to implement a simple particules system using the velocity form of the Verlet algorithm as integrator. Initial conditions at $t=0$ for a given particule $p$: mass: $ m $ position: ...
9
votes
9answers
1k views

What criteria distinguishes causality from retrocausality?

The brilliant philosopher David Hume remarked that if two events are always found to be correlated to each other with one event happening prior to the other, we call the earlier event the cause and ...
1
vote
3answers
1k views

Direction of Propagation of Wave

I've always been a little uneasy with the notion of direction of wave propagation, for some reason. I guess it's always been defined 'intuitively' and I want to know the limits of the concept. To this ...
0
votes
2answers
1k views

Does effective potential for a gravitational force have a maximum below $E=0$?

The relevant figure is below (taken from Goldstein's Classical Mechanics). This figure plots the effective potential for a gravitational force. Does the effective potential $V'$ go flat below $E_2=0$? ...
0
votes
1answer
79 views

Bigger anti-matter particles

I have learned about the existence of positrons as a decay product from uranium fission - if I'm not mistaken. Is there any evidence for higher 'mass' anti-matter, or is that mere speculation or ...
0
votes
1answer
159 views

A problem on fluid flow

I am extremely weak in visualizing physical problems in mathematical context. Please help me in solving the following problem and please give as much details as possible. A fluid flows radially ...
2
votes
2answers
520 views

Special Relativity: What differential equation describes an accelerated object from a non-inertial reference frame?

I am looking for a set of differential equations (to be solved numerically for an educational program) that would describe the position and apparent time of an accelerated clock relative to a ...
5
votes
1answer
69 views

what general physical arguments discredit induced emission of nuclei?

trying to read a bit about "quantum nucleonics", i've encountered this rebuttal from people at Livermore that induced radiation stimulation of Hafnium nuclei is possible. Something that catches my eye ...
0
votes
6answers
820 views

What would be likely to completely stop a subatomic particle assuming it was possible?

Suppose that completely stopping a subatomic particle, such as an electron, could happen under certain conditions. What would be likely ways to get an electron to be perfectly still, or even just stop ...
1
vote
1answer
210 views

What is theory of Free Energy Perturbation? How is it applicable to chemical science?

What is theory behind free energy perturbation? Is it way too difficult to understand? Can someone explain it in simple terms.
0
votes
1answer
219 views

Gauss's Law in action

Need someone to tell me if I got this done correctly (a) Draw Gaussuian cylinder inside the black cylinder to find charge enclosed $Q_{en} = Q(\frac{r}{a})^2$ Apply Gauss's Law $E2\pi r \ell = ...
2
votes
2answers
856 views

What would be an appropiate shape for a parachute?

I'm trying to design a parachute that minimizes the descent velocity, but I'm not sure what shape I should use. From what I've read, ellipse-shaped parachutes are too aerodynamic and minimize drag, ...
6
votes
1answer
116 views

What causes a spark to move along rods that are not parallel?

I took my son to a science museum where they had a gadget that many of us probably saw in movies involving a mad scientist. The gadget had two metal rods about two inches apart at the bottom. The rods ...
6
votes
2answers
580 views

What law of electro-magnetics explains this?

I took my son to a science museum where they had a solenoid oriented vertically with a plastic cylinder passing through the solenoid. An employee dropped an aluminum ring over the top of the cylinder ...
2
votes
1answer
281 views

What does the notation $|x_1,x_2\rangle$ mean?

I would like clarification on an equation in the paper "Free matter wave packet teleportation via cold-molecule dynamics", L. Fisch and G. Kurizki, Europhysics Letters 75 (2006), pp. 847-853, DOI: ...
4
votes
4answers
748 views

If a pendulum is on a rotating table, will a torque be generated?

Here is the set up. Very simple. A flat (i.e. horizontal table, there is no gravity) and rounded table that spins on its axis (through the center of the table). A spring mass system is now put on the ...
8
votes
1answer
1k views

Why does a wobbly metal sheet make the sound of thunder?

In other words, what is the similarity between a lightning bolt and a wobbling sheet that make them sound alike? It seems to me that the two systems have a much different way of moving the air, and ...
3
votes
2answers
571 views

Does a fluid's temperature affect the way light passes through it?

For example, if I were to supercool water would it's refractive index still be 1.33 or would it be 1.31, the same as water-based ice even though it's still in liquid form?
1
vote
2answers
440 views

Symmetries, Generators, Commutators and Observables

I'm learning about generators and conservation laws and have derived the equation (1) $$[Q,A]=-i\hbar f(A)$$ which is satisfied by the observable generator $Q$ for a transformation group with ...
2
votes
4answers
5k views

Why is Neutron Heavier than Proton? [closed]

This is Neutron decay: $$n^o \to p^+ + e^- + \overline {\nu_e}.$$ and this is proton one: $$p^+ \to n^o + e^+ + \nu_e$$ so when the $e^+ =e^-$ and $\nu_e=\overline {\nu_e}$ why $n \not= p$? my ...
3
votes
2answers
907 views

Is there an observable of time? [duplicate]

In Quantum Mechanics, position is an observable, but time may be not. I think that time is simply a classical parameter associated with the act of measurement, but is there an observable of time? And ...
3
votes
2answers
2k views

Deriving Lagrangian density for electromagnetic field

In considering the (special) relativistic EM field, I understand that assuming a Lagrangian density of the form $$\mathcal{L} =-\frac{1}{4}F_{\mu\nu}F^{\mu\nu} + \frac{1}{c}j_\mu A^\mu$$ and ...
2
votes
2answers
313 views

A relative time dilation paradox.

Let us assume that there are two astronauts A and B who are floating in space. A sees B passing by and vice versa. A sends signals to B every minute. According to A since B is moving his clock will be ...
5
votes
1answer
1k views

Are coffee's properties different enough from water's to cause increased spillage while walking?

I recently found this article, which describes how... It just so happens that the human stride has almost exactly the right frequency to drive the natural oscillations of coffee, when the fluid is ...
0
votes
1answer
630 views

What is the particle residence time for given flow rates of gas mixture components? [closed]

For two different chemical substances there are two open valves with flow rates $$Q_1=a\frac{m^3}{h}\ \text{ and }\ \ Q_2=b\frac{m^3}{h},$$ leading into seperate cables. Next, the cables join, the ...
1
vote
1answer
913 views

Calculating capacitance of integral PCB components

I posted this question originally with Electrical Engineering Stack Exchange but nobody seems to know the answer. So I thought a physicist might find the question more approachable. Formulas for ...
9
votes
2answers
2k views

Squinting at street lights

Simple question, I've always wanted to know the answer to this. Why do you see a pair of lines radiating out from street lights when your squint at them? I can't think of a better way of describing ...
75
votes
7answers
10k views

Why do people categorically dismiss some simple quantum models?

Deterministic models. Clarification of the question: The problem with these blogs is that people are inclined to start yelling at each other. (I admit, I got infected and it's difficult not to raise ...
13
votes
4answers
1k views

$\lambda=\frac{2h}{p}$ instead of $\lambda=\frac{h}{p}$?

I am studying quantum physics and there is something I don't understand: I know that for any particle $E=hf$ (Einstein relation) and $v=\lambda f$ ($v$ is the speed of the particle). I also know ...
3
votes
1answer
375 views

gamma ray lasers?

Is it really possible in the foreseeable future to create a gamma ray laser? I've read these two articles on Wikipedia: the Hafnium controversy Induced gamma emission It sounds pretty amazing, ...
3
votes
1answer
491 views

Phase space suppression

In talking about production/decay processes, I've heard people speaking of decay modes or cross sections being 'phase space' suppressed. For example, a two body final state is more likely to occur ...
5
votes
2answers
746 views

relativistic acceleration equation

A Starship is going to accelerate from 0 to some final four-velocity, but it cannot accelerate faster than $g_M$, otherwise it will crush the astronauts. what is the appropiate equation to constraint ...
7
votes
2answers
689 views

Mars Curiosity Power System

Curiosity's power source comes from a radioisotope thermoelectric generator (RTG) rather than from solar panels like the two Mars Rovers. 2,000 watts of thermal power from alpha particle emission in ...
0
votes
1answer
103 views

Density and statistical models for visible air dust

If a laser beam is looked at from the side versus a dark background, a sparkling effect can be seen caused by dust particles in the air hit by the beam. Is there any simple model or coarse ...
6
votes
3answers
815 views

How are the masses of unstable elementary particles measured?

I am interested in knowing how (Q1) the particle's masses are experimentally determined from accelerator observations. What kind of particles? They must be as far as we know elementary and unstable ...
1
vote
0answers
94 views

Some questions about flavour and R-symmetry in $2+1$ ${\cal N}=3$ theory

I have heard this fact that for ${\cal N}=3$ theories in $2+1$ with $N_f$ ${\cal N}=3$ matter fields the flavour symmetry group is $USp(N_f)$, $U(N_f)$ or $SO(2N_f)$ depending on whether the gauge ...
2
votes
4answers
1k views

Which Schrödinger equation is correct?

In the coordinate representation, in 1D, the wave function depends on space and time, $\Psi(x,t)$, accordingly the time dependent Schrödinger equation is $$H\Psi(x,t) = ...
2
votes
2answers
290 views

Wave Function Statistical Interpretation vs Oscillation Interpretation

Can the wave function solution to Schrodinger's Equation be interpreted as an oscillation between all possible measurements (obviously with some type of weighting that would describe the shape of the ...
1
vote
3answers
2k views

How can there be heat in a vacuum?

I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc. If heat is caused by thermal energy being radiated from particles ...
4
votes
2answers
8k views

How can an object's instantaneous speed be zero and it's instantaneous acceleration be nonzero?

I'm studying for my upcoming physics course and ran across this concept - I'd love an explanation.
3
votes
2answers
123 views

A problem of approximation [duplicate]

Possible Duplicate: Why are continuum fluid mechanics accurate when constituents are discrete objects of finite size? When we apply differentiation on charge being conducted with respect to ...
0
votes
1answer
221 views

Impact of Apophis

I read about the near-earth asteroid 99942 Apophis. It is in the first place of Potentially Hazardous Asteroids (visiting earth at an altitude of about 36,000km on 2028). But, scientists have ...
21
votes
1answer
2k views

In 't Hooft beable models, do measurements keep states classical?

This is a questions on 't Hooft's beable models (see here: Discreteness and Determinism in Superstrings?) for quantum mechanics, and the goal is to understand to what extent these succeed in ...
4
votes
5answers
547 views

Space Expansion vs. Relative Motion

Given 2 objects moving at some velocity $v$ relative to one another, is it possible to determine whether they are moving or whether the space between them is expanding?
0
votes
1answer
107 views

mathematical explanation for UV divergences and $ \delta ^{(n)}(0) $

is there any mathematical explanation for the UV divergences ?? i have read that in the framework of Epstein-Glser theory :D these UV divergences appear from the product of distributions anyone does ...

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