I've got good news and bad news. The good news is that the Earth won't be destroyed by the inevitable heat death of the universe. The bad news is that the planet will be wiped out long before that, between 1.5 billion and 2.25 billion years from now, according to a new study by Andrew Rushby was recently published in Astrobiology.
You see, when our Sun starts running out of hydrogen fuel, it will expand until it swallows Mercury and Venus, and potentially even expands into our orbit. Obviously, this means bad things for anything left on Earth. Even if the Sun doesn't grow large enough to reach Earth's orbit, you don't want to hang around waiting for the oceans to boil away and the atmosphere to burst into flame. Trust me, you'll have a bad time.
So why study an event so unimaginably far in the future? Because it can give us a better idea of where to look for intelligent life outside our solar system. We've detected almost a thousand planets using a variety of methods around a few hundred stars in our galactic neighborhood. That's all well and good, but if the goal is to find life on other solar systems, finding planets is just the first step.
Given what we know about life on Earth, we assume that liquid water is required. That narrows down the potential billions of planets in the galaxy to only the ones that are the right size to hold an atmosphere at the right temperature and pressure for liquid water to exist. Planets that meet these conditions are said to be in the habitable zone.
At this point, it's important to note that it took a long time for life to evolve on Earth. The planet was formed about five billion years ago, it took between one and two billion years for basic microscopic life to evolve. Add another three billion years, give or take, between the rise of single-cellular life and the evolution of man, the taming of the atom and the invention of the digital watch. For simplicity sake, lets say it took 4 billion years for complex life to evolve on Earth. So, if astrobiologists want to avoid looking for life in all the wrong places, they need to consider the time that a planet will be habitable as well.
So that's why Rushby and his cohorts are studying the Sun's endgame. They're adding to the model that astrobiologists use to predicts the likelihood of the evolution of life into intelligent life, based on the long-term habitability of an exoplanet's star.
Now, with only a billion years and change left here on earth, I hope George R.R. Martin finally buckles down and finishes his Game of Thrones books.