Britain's most eminent astronomer confronts the question of whether there will ever be an unsolvable problemby Martin Rees / November 13, 2018 / Leave a comment
The Sun formed 4.5bn years ago, but it’s got around six billion years more before its fuel runs out. It will then flare up, engulfing the inner planets. Any creatures witnessing the Sun’s demise won’t be human—they’ll be as different from us as we are from a bug. Post-human evolution could be as prolonged as the Darwinian evolution that has led to us.
And evolution is now accelerating; it can happen via intelligent design on a technological time-scale, operating far faster than natural selection and driven by advances in genetics and in artificial intelligence (AI). The long-term future probably lies with electronic rather than organic life.
In cosmological or Darwinian terms, a millennium is but an instant. So let us fast forward not for a few centuries or millennia, but for an astronomical timescale millions of times longer than that. The stellar births and deaths in our galaxy will gradually proceed more slowly, until jolted by the environmental shock of an impact with the Andromeda Galaxy, maybe four billion years hence. The debris of our galaxy, Andromeda and their smaller companions—which now make up what is called the Local Group—will thereafter aggregate into one amorphous swarm of stars. Many billions of years after that, gravitational attraction will be overwhelmed by a mysterious force latent in empty space that pushes galaxies apart from each other. Galaxies accelerate away and disappear over a horizon. All that will be left in view, after 100bn years, will be the dead and dying stars of our Local Group, which could continue for trillions of years. Against the darkening background, sub-atomic particles such as protons may decay, dark matter particles annihilate and black holes evaporate—and then silence.
As we attempt to grapple with this bleak post-human future, we must also confront the question of what humans can hope to understand. Parts of the physical world are understood. They can be observed and described by theories—but much of it cannot. Human observation bumps up against stark limits. Human reasoning is not limitless either, but it does allow us to think through what might in principle be “over the horizon.”
The By-Laws of Physics
For now, we can only see a finite number of galaxies. That’s essentially because there’s a horizon, a shell around us, delineating the greatest distance from which light can reach…