Universal death - 2

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Entropy and the heat death

The Second Law of Thermodynamics

Entropy measures the disorder of a system. Fighting disorder, to create order (as in living creatures) requires energy. The second law of thermodynamics basically says that eventually we're going to run out of energy.
Or, as Flanders and Swann put it,
Heat can't flow from a cooler to a hotter
You can try it if you like, but you're far better not to
'Cause the cold in the cooler will get hotter as a ruler
As the hotter bodies heat gets passed to the cooler
[First Law] Heat is work and work is heat...

The end of the world... as we know it

The planetary nebula, NGC 6543

All intermediate mass stars, like the Sun, eject at least half of their mass when they become planetary nebula. Higher-mass stars which undergo supernova explosions return up to 90 % of their mass to the interstellar medium. That material is swept up in spiral arms, collected into large gas clouds, and recycled to form new stars.

The Orion nebula - an active, star-forming region

But each time a planetary nebula is born, or a supernova occurs, some fraction of the total mass is locked up as a stellar remnant

1. a white dwarf, for stars less massive than 8 x Sun
2. a 10-km diameter neutron star, for stars between 8 and ~25 Suns
3. a black hole, for the most massive stars

The view from a red dwarf planet (W. Hartmann)

The lifetime of a star depends on its mass:
high mass stars have lots of fuel, but exhaust their resources in profligate fashion
low mass stars have less fuel, but are parsimonious in their use.
The longest-lived stars are red dwarfs, with masses ~one-tenth that of the Sun, and luminosities of less than one ten-thousandth that of the Sun: their lifetimes can exceed 1,000 billion years (10¹² years), one hundred times that of the Sun.
They'll be the last stars shining - but the story doesn't stop there.

Fred Adams and Greg Laughlin have divided the evolution of the universe into five eras (see their book, The Five Ages of the Universe), measuring time in `cosmological decades' - a logarithmic scale.
An age of 100 = 10² years is the second decade
an age of 1,000,000 = 10⁶ years is the sixth decade
an age of 1,000,000,000 = 10⁹ years is the ninth decade
and so on

1. The Primordial Era: <5th decade - the formative stages of the Universe
2. The Stelliferous Era: 6th decade to 14th decade - the present era, when the Universe is dominated by starlight. The last stars, red dwarfs, will grow to become yellow giants and fade to white dwarfs at the end of this era.
3. The Degenerate Era: 15th to 39th decade - not the Edwardian phase of universal existence, but the period when brown dwarfs (failed stars) and stellar remnants (white dwarfs, neutron stars, black holes) are the only remaining constituents in galaxies throughout the universe. White dwarfs continue to shine very faintly, with energy supplied by proton decay - about 400 Watts per white dwarf. Eventually, all the material in white dwarfs and neutron stars "evaporates" into elementary particle.
4. The Black Hole Era: 40th decade to 100th decade - black holes gradually evaporate (through emission of Hawking radiation). Galaxies, invisible to the eye (were there an eye around to see), gradually disperse, as both `dark matter' and black holes disappear.
5. The Dark Era: after the 100th decade - elementary particles and shards of radiation are all that survive.

This scenario assumes that the Universe is `open' - that it will continue to expand forever. A `closed' universe might collapse, and recycle at some point during one of the last four Eras

What about life?
It can probably find suitable environments for survival throughout the stelliferous era - but after that.....?

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