# All Questions

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### Do gravitational waves slow down as they pass through matter?

I've heard that gravitational waves travel at the speed of light, and have some parallels to electromagnetic waves. EM waves slow down as they pass through matter (speed of light in glass is slower ...
330 views

### Is spherical coordinates enough to calculate the exact position of a point with rotations included?

With "Geographic coordinate system" we only get the location, no rotations or anything. Translated into latitude and longitude. Where with "Spherical coordinate system", we should be able to get the ...
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### Violation of Lorentz symmetry on cosmological distances

This question is about the domain of validity of Lorentz symmetry. As far as I know, general relativity is a generalization of special relativity. Does that mean that Lorentz symmetry is violated on ...
1k views

### Escape velocity of a rocket standing on Ganymede (Moon of Jupiter)

I want to calculate the escape velocity of a rocket, standing on the surface of Ganymede (moon of Jupiter) and trying to leave Ganymede. My thinking was, the kinetic energy $E_{\text{KIN}}$ must be ...
314 views

### “finite” QFTs and short-distance singularities and vanishing beta functions

I am not sure that I can frame this question coherently enough - it springs from various things in QFT that I have recently been thinking and reading about. May be these thoughts are mis-directed but ...
1k views

### What is the meaning of pressure of a gas

I understand the meaning of pressure on a surface to be force acting per unit area. But when it comes to understanding pressure in the context of fluids in motion or at rest I think I am having some ...
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### Does a nonzero Poynting vector mean that there is propagation of energy?

I don't know how this "paradox" can be solved. I'm given the following system: A permanent magnet with a magnetic field given by ($\hat{a}$ are unit vectors in the x and y directions) ...
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### What's the potential of the LHC's heavy ion experiment?

RHIC has been the dominant player in heavy ion physics, producing tantalizing evidence in support of the entropy/viscocity formula from AdS/CFT. What's the potential of the LHC's Pb ion collsions? ...
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### Experimental test of the non-statisticality theorem?

Context: The recent paper The quantum state cannot be interpreted statistically by Pusey, Barrett and Rudolph (now On the reality of the quantum state, Nature Physics 8, 475–478 (2012), ...
3k views

### superconductor levitating in earth's magnetic field? [duplicate]

Possible Duplicate: Can superconducting magnets fly (or repel the earth's core)? I've seen superconductors levitating on magnets. But is it possible for superconductors to levitate on ...
136 views

### Decoherence inside black holes [closed]

I have a question about decoherence. Assume there is a macroscopic black hole floating around and you have some macroscopic object with you with a huge number of internal degrees of freedom. ...
179 views

### Inertial Mass of a scalar field

Does it make sense to talk of the inertial mass of a scalar field? By the equivalence principle, it must be equal to its gravitational mass. We know that the scalar field contributes towards the ...
82 views

### Shadow of a Jovian moon over the Great Red Spot

Where can I find pictures of the shadow of any of the Jovian moons partially covering the Great Red Spot? A series of such pictures over time would even be better. The idea is to learn more about the ...
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### How does force relate to velocity

I had originally asked this question on math overflow and it was suggested that I ask it here. So I know that a force will change the magnitude of velocity if it is at an angle other that 90 degrees. ...
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### Best time of the year to see the star Alpha Centauri in Chile, Santiago

If I'm in Chile, Santiago, what is the best time of the year to see the star Alpha Centauri at the beginning of the night?
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### What is new with quark-Gluon Plasma and the bubble formed at RHIC?

RHIC experiment results of forming Quark-Gluon Plasma and a possible bubble was news few months ago. I cannot find any follow up news after that. Does anybody know anything new in this front? I am ...
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### why do some orbiting objects have a changing position?

I know that the reason why they stay in orbit but why do some move away from the earth(the moon) or come closer and eventually fall? And why does the moon move away from earth?