What state are you from?

What is the state of maximum entropy of the Universe?

• If everything were to be in a state of equilibrium. for eg: Note: My understanding of Entropy is quite limited, it's primarily from the example of mixing hot water and cold water which tends to reach natural state of a warm warm (room temprature)   But room temprature itself is an equlibrium state of external temprature & heat generated by various objects in a room, which in turn are further equilibrium states of other conditions. Taking this further on higher scales, where does it lead?   Does it go back to a singularity?

• Answer:

  It is the state of Heat Death, a proposed ultimate fate of the universe. As the stars, galaxies and black holes decay, entropy will keep on increasing. ( A Supermassive black hole decays emitting hawking radiation roughly in the order of 10^100 years. So 'at least' we should keep increasing entropy till then ). As the universe goes on expanding, its temperature ( as measured in the cosmic microwave background ) goes on decreasing. Around 3/4 of the universe's energy density is vacuum energy (Cosmological constant). This creates a cosmological event horizon and emits a black body spectrum of radiation whose temperature is determined by the cosmological constant. Now if cosmological constant is actually a constant, it would put a lower limit to the minimum temperature possible in the universe. This temperature is around the order of 10^(-30) Kelvin. This puts an upper limit to the maximum entropy possible too. So we probably approach this state of maximum entropy as black hole era (Where black holes remain the only celestial objects) ends and universe enters dark era while everything decays into sub atomic particles. (If protons decay) The high estimate for this phase is 10^1200 years from now. Through this and after this part things get even more controversial and we might have Boltzmann brains[1] appearing and we might enter Poincaré recurrence time[2] where history repeats itself an infinite number of times. Here is the timescale of events, http://en.wikipedia.org/wiki/Timeline_of_the_far_future Here are two articles about that you might find interesting http://www.mso.anu.edu.au/~charley/papers/LineweaverEganParisv2.pdf http://www.scholarpedia.org/article/Time%27s_arrow_and_Boltzmann%27s_entropy#Initial_conditions [1]http://en.wikipedia.org/wiki/Boltzmann_brain [2]http://en.wikipedia.org/wiki/Poincar%C3%A9_recurrence_theorem