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	Podcast:		Theoretical Physics - From Outer Space to Plasma
	Episode:		Galaxy Dynamics: Stellar systems: a new state of matter
	Category:		Education
	Duration:		00:51:19
	Publish Date:		2018-01-25 03:19:10
	Description:		Prof James Binney FRS will talk about stellar systems: a new state of matter The long range of gravity means that many concepts from undergraduate statistical mechanics do not apply: energy is not extensive; there is no microcanonical or canonical ensemble. Stars and dark matter particles have long mean free paths, which means that to a very good approximation their motion is determined by the mean-field gravitational potential. James Binney will identify a hierarchy of timescales, explaining how the Boltzmann equation for the full 6N-dimensional many-particle phase space distribution function can be reduced to an evolutionary equation of a function of a mere 3 variables that is governed by the resonances among the particles' orbital frequencies.
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