# All Questions

1answer
90 views

### Does an antiDeSitter space compensate the vacuum energy?

Sometimes I read here or there that a problem with the electroweak vacuum is that it implies a huge positive cosmological constant. On other side, I also read that AdS spaces are not useful anymore ...
9answers
2k views

### What is the difference between translation and rotation?

What is the difference between translation and rotation ? If this were a mathematics site, the question would be at best naive. But this is physics site, and the question must be interpreted as a ...
1answer
222 views

### Two Loop ultraviolet divergence of $\phi^4$ theory

During the renormalization procedure of a massive $\phi^4$ theory at two loop level, one finds that the quantity $K_{\Lambda}(k^2,m^2)-K_{\Lambda}(0,m^2)$ that appears in the bare $\Gamma^{(2)}$ ...
1answer
107 views

### What is the necessary amount of energy to propel a 100g from ground to orbit ? (Slingatron)

I would like to know what is the energy needed considering the air resistance to shoot from ground to the orbit a 100g object (even if it vaporizes in the process). Variables to make approx ...
2answers
145 views

### Inverting the laws of physics [closed]

Are there any good theories on inverting the law of physics? To make physics work the opposite way of what it does. Please ask question if this is unclear! I'll answer as well as I can. Ok, I'll ...
4answers
1k views

### Maximum acceleration for wheel-driven vehicle from standstill

Once I discussed cars and there was a question about rate at which the car gains its speed ($100\:\mathrm{km/h}$) from standstill (i.e. acceleration). At some point of conversation it came up that ...
1answer
86 views

### Electron inside a conducting shell

Suppose I keep a single electron inside a hollow metallic/conducting shell,what will the charge distribution on the surfaces of the shell? Now in principle from Maxwell's equations,it simply should ...
3answers
208 views

### If there's no atmosphere in space shielding from particles, why is not dangerous for spaceships/humans?

Some time ago I was thinking about this. We know that space is almost matter-free, and also is plenty of particles and objects orbiting around all planets and sattellites. If objects orbit around ...
0answers
79 views

0answers
220 views

### What different approximations yield Gravitoelectromagnetism and Weak Field Einstein Equations?

This question is inspired by this answer, which cites Gravitoelectromagnetism (GEM) as a valid approximation to the Einstein Field Equations (EFE). The wonted presentation of gravitational waves is ...
1answer
73 views

### Input parameters for the reconstruction algorithm in Digital Holography

I've been browsing some Digital Holography papers these days, and have come across this fundamental question. When you reconstruct the complex amplitude for the object image, you use e.g. Fresnel ...
1answer
231 views

1answer
210 views

### Blasius boundary layer solutions

I'm trying to understand the Blasius boundary layer solution, but I'm having some difficulties. Using wikipedia, I wonder how they get the first formula: ...
3answers
3k views

### Which color of an umbrella is more effective against sunlight?

It's usually said that black umbrellas are best against sun, since black absorbs most of the radiation . The common umbrellas in market(atleast in India) are painted black outside and silvery inside. ...
2answers
260 views

### Unpolarized light vs. randomly rotating polarized light?

I am confused with physical picture about unpolarized light. Is unpolarized light very fast rotating polarized light? or co-existing state of two orthogonal polarization? (or something else?) If ...

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