The Last Day on Earth

Around 5 billion years from today, the sun will begin to exhaust its hydrogen fuel, and it's own energy production will lose the ancient tug of war it plays with gravity. The sun will expand as it becomes a red giant star for a brief couple millenia, and it will engulf the earth whole.

It will slowly receed and collapse into itself, forming a white dwarf barely the size of this planet, and emitting almost no more light than one of the distant stars we see in the sky.

However, that will not be the last day on earth. Earth will continue on, devoid of any life whatsoever, until about 10⁸⁰ years from now, when ultimate entropy will kick in, and the very fabric of matter itself will begin to fall apart. While "days" will continue to elapse, the matter that had comprised earth will be part of the huge universe sized atoms floating around at an excruciatingly slow speed. So, really, it won't be earth any more. But the atoms that used to be earth will continue to see days pass. Ad infinitum.

So anyway, who wants ice cream?

Just how long does it take for the old obsolete theory to die out? xmatt's theory doesn't take into account these factors:

• Alpha Centauri system approaches the Solar system, and will bypass it in 800000 years.
• The Sun is brightening.
• The gravity of the Sun will weaken as is expands.

The first thing is Alpha Centauri. The gravity of the system will hit the Solar Oort Cloud, so that comets, asteroids and mini-planets of all size will be thrown towards the Sun, reaching the inner Solar system, where we are. Jupiter can deflect or absorb most, but not all of the matter. There will be a massive meteor shower.

The Sun has brightened 10% since the Earth formed. It will continue to brighten, reaching 30% before the expansion. The core is getting more compressed already. In one billion years it has brightened so hot that the oceans will boil, the steam will rise to high atmosphere and dissociate to hydrogen and oxygen because of the ultraviolet radiation. The Earth will be as dry and dead as the Moon.

In a simulation it was shown that the Sun loses a lot of mass as it expands. Its gravity will weaken so much that the orbit of Earth will be in the place where Mars orbits today. Still, it's so hot that the crust of the Earth will completely melt. Then the Sun will blow its outer layers out. The white dwarf in the center will eventually cool down to a cold ball of iron.

So, this new scenario is much worse than the old one! First the meteors, then oceans boil, and then the crust will melt. And only 800000 years to begin! The Last Day will be in the far future, when the remains of the Sun drift with to another star or a black hole. For the humans, the Last Day is coming much faster.

Source: Tiede. http://www.tiede.net/