# All Questions

3answers
1k views

### Distorted colors of Google StreetView photographs near electric power lines

This is a followup to my question: Cyclist's electrical tingling under power lines Some users presented a convincing picture that the electric shocks under power lines are primarily from the ...
1answer
295 views

### Darcy law yields extreme speed for gas flow throgh packed spheres?

The darcy law is as follows: $u=-\frac{k}{\mu}\nabla p$. Assume we have a gas, then $\mu$ is about $10^{-5}$. $k$ for packed spheres a few mm in diameter is of order $10^{-8}$ $m^2$. Say the ...
2answers
273 views

### Number of bits needed to express physical laws?

What is the minimum number of bits that would be needed to express a given physical law, like the law of universal gravitation? How many bits are needed to express each of the four fundamental forces? ...
1answer
80 views

### Could a Class A Stellar Engine Use A Brown Dwarf

Could a class A stellar engine (or maybe a class C one) be built using a brown dwarf (for argument's sake, a T-dwarf like Gliese 229B)? Would it be capable of enough thrust to move itself any ...
1answer
76 views

### Continuum model of the n-body problem?

Consider a collection of $n$ point masses evolving under the influence of gravity. For very large $n$, one might be interested in making a continuum approximation of this system (for cosmology, say). ...
3answers
443 views

### Non equilibrium statistical mechanics

A question kept bothering me about the Non-Equilibrium Statistical mechanics, can somebody give a simple description of how one approaches this subject. Is there a exact formalism, as we have for ...
4answers
2k views

### Explaining Walter Lewin's “Complete Breakdown of Intuitiion”

This Walter Lewin lecture hinges on the solenoid producing a non-conservative field. I read in the Feynman Lectures that "all the fundamental forces in nature appear to be conservative" (Vol 1, 14.5) ...
1answer
380 views

### Schmidt decomposition of coupled oscillators

Consider a system of two coupled oscillators, with Hamiltonian ($\hbar = m = 1$): \begin{align} \mathcal{H} = \frac{1}{2}(p_1^2 + \omega_0^2 x_1^2) + \frac{1}{2}(p_2^2 + \omega_0^2 x_2^2) ...
2answers
983 views

### Calculating forces in a mass suspended by four cables

As a project, I am designing a cable-controlled camera system (i.e., a home-made Skycam clone). Basically, it is a mass suspended by four cables connected to fixed points; by lengthening or shortening ...
3answers
521 views

### black body and cosmic microwave background radiation

Why is the sprectum of the cosmic microwave background radiation (or seems to be) that of a black body?
2answers
255 views

### why is there only one inertial frame that $ct$ and $x$ are orthogonal?

It is very long time ago that I took a physics lesson, so I want to refresh my memory. I think I learned that there is only one inertial frame in Minkowski spacetime (or special relativity time) that ...
1answer
109 views

### When does the “norm of quasi-eigenvectors” matter in calculations? For which physical results are these even used?

Which physical system in nonrelativistic quantum mechanics is actually described by a model, where the norm of the "position eigenstate" (i.e. the delta distribution as limit of vectors in the ...
2answers
1k views

### Do we see color with higher frequency first?

Out of the 7 colours of the rainbow, violet has the highest frequency and the smallest wavelength. Does this mean that our eye sees it first? If yes, then why? Does it travel at the same or higher ...
1answer
1k views

1answer
1k views

### Heat of vaporization of water - dependence on relative humidity?

Does the heat of vaporization of water depend strongly on the relative humidity of the gas into which it evaporates? Some context: If we want to calculate the dew point of water, we find the ...
0answers
137 views

### Separable states of maximum non-classical correlations

Although there is no standard measure of entanglement, the GHZ states $|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$ are often deemed as maximally entangled states of ...
3answers
1k views

### Why isn't light scattered through transparency?

I'm asking a question that has bothered me for years and years. First of all, let me give some context. I'm a layman in physics (college educated, math major). I've read Feynman's QED cover to cover, ...
2answers
1k views

### Can a planet have a larger diameter than Jupiter?

I have heard it said that if mass were added to Jupiter, then only its mass and density would increase but the diameter would stay about the same. Is this the case for Jupiter or some property of ...
1answer
211 views

### Why can't this speed be measured?

Superman and Supergirl were playing catch. When Superman is moving with a speed of 0.800c relative to Supergirl, he threw a ball to Supergirl with a speed of 0.600c relative to him. a. ...
0answers
71 views

### What is your prefered toolkit / program for 3D visualisations of data? [closed]

If you recorded data which represents some physical value in space (e.g. electron density) and you need to explore this dynamically in 3d (say you have a isosurface and you change the value it ...
7answers
3k views

### Changing the Half-Life of Radioactive Substances

Is there a way to extend or reduce the half-life of a radioactive object? Perhaps by subjecting it to more radiation or some other method.
2answers
374 views

### length contraction question

we know from eintein's theory of relativity that lets say, a ruler is travelling to a speed if light, then we can say that the ruler (from our view as observers) has shorten. but why, lets say we have ...
4answers
995 views

### Topology needed for Differential Geometry [duplicate]

I am a physics undergrad, and need to study differential geometry ASAP to supplement my studies on solitons and instantons. How much topology do I need to know. I know some basic concepts reading from ...
3answers
255 views

### What are some creative illustrations of the nature of dissipative forces?

I'm teaching a conceptual introduction to physics for American 13-15 year old students this summer. One of the main ideas I want to hit on is the relationship between energy conservation, ...
3answers
568 views

### waves on water generated by a falling object

Let an object of mass $m$ and volume $v$ be dropped in water from height $h$, and $a$ be the amplitude of the wave generated. What is the relation between $a$ and $h$. How many waves are generated? ...
1answer
123 views

### Sources for new experimental limits on susy models?

I know the LHC people are publishing new limits every now and then, but as a non-expert in reading experimental papers (yet), I was wondering if there's a friendly website that collects and presents ...

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