Vacuum has friction from an effect similar to the Casimir effect | Hacker News Reader

Vacuum has friction from an effect similar to the Casimir effect

nextbigfuture.com

27 pointscwan12 comments

Only for accelerating systems. The system here is spinning, which is an acceleration.

vacuum can have temperature? am i reading it wrong or....?

I believe the temperature reference is in regards to the object's temperature.

In physics, "temperature" is the same thing as "speed". The faster the movement of particles in a given amount of space, the "hotter" it is. The terms are interchangeable.

There is also a common misconception that you would freeze almost instantly if you jumped out of an airlock in space. Quite the contrary. A vacuum is actually an incredibly efficient insulator. Hence vacuum thermoses. Your body would not lose heat very fast. Not having a helmet on, though, would be very bad for your health.

> Not having a helmet on, though, would be very bad for your health.>

NASA accidentally tested it in 1966: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.h...

This link just shown me how many misconceptions I have about vacuum exposure. Thank you! I've learned a lot from it.

The speed in your definition would refer to the temperature of the particle, and not the temperature of the vacuum. This paper has both the vacuum and the particle not in thermal equilibrium, so the temperature of the vacuum is not due to the speed of the particle moving within it.

You can also have temperature from a photon flux.

> Common misconception... a vacuum is actually an incredibly efficient insulator

Yes, it is even a very real problem for EVAs and spacecraft. One of the first things the Shuttle does is open up its radiators to help get rid of its internal heat. The astronauts doing EVA have a problem with heat too, they have to wear an internal cooling suit with fluid piped around their bodies.

Yeah, because the electromagnetic field contains energy, which can be converted into other forms. A system's temperature is 'how readily it gives off energy'. It need not have anything to do with particles or speed.

http://physics.about.com/od/glossary/g/temperature.htm http://en.wikipedia.org/wiki/Temperature "n the classical thermodynamic approach to temperature, temperature of an object varies with the speed of the particles it contains, raised to the second power. Therefore, temperature is tied directly to the mean kinetic energy of particles moving relative to the center of mass coordinates for that object. Temperature is an intensive variable because it is independent of the bulk amount of elementary entities contained inside, be they atoms, molecules, or electrons. In order for the temperature of a system to be defined, the system must be in thermodynamic equilibrium. Temperature may be considered to vary with position only if, for every point, there is a small neighborhood around that point can be treated as a thermodynamic system in equilibrium (i.e. local thermodynamic equilibrium). In the statistical thermodynamic approach, degrees of freedom are used instead of particles."

I'm afraid you've been misled by an oversimplified definition. That is not fundamenatally what temperature is, though it works out that way for many common systems. Temperature is a way to measure which way energy will flow between two objects at equilibrium. Equilibrium in this case means a maximum entropy distribution. Which way will energy flow so as to maximize this. Well, we just take the derivative of entropy with respect to energy transfer, and we get the equilibrium condition. T is (partial S / partial E)^(-1)

When you accelerate through it, yes.

http://en.wikipedia.org/wiki/Unruh_effect

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