Science thinks it has figured out the universe — again — and the end is nigh, but there’s plenty of time to deal with it.
In the 1990s, two important discoveries led cosmologists to believe that we were dramatically underestimating the total amount of matter and energy in the universe. The first was related to expansion. We knew the universe was expanding, but scientists discovered that the speed at which the expansion was occurring was actually accelerating. The farther we look out into space, the faster things appear to be receding away from us. This came as a complete surprise. Since gravity is an attractive force, it was thought that the initial expansion after the Big Bang should be slowing down, not speeding up. It was even thought that if gravity was strong enough, the universe might collapse back in on itself, leading to a “big crunch” where all of space would once again occupy a single point, as it did 13.7 billion years ago. But now it appears that something is applying “negative pressure” to all of space, causing it to expand, faster and faster, despite the pull of gravity. That finding got even stranger when the “something” causing the accelerating expansion was found to be space itself. Completely empty space somehow contains energy, exerting a force that acts like a kind of anti-gravity. It’s pervasive, constant and no one has the slightest idea what it is or why it’s there. This “dark” energy accounts for about 70 percent of all the energy there is. We seem to live in a universe dominated mostly by nothing.
The second big discovery of the ’90s was that another type of matter exists, and lots of it. It just happens to be invisible and the only way we know it’s there is by observing its gravitational attraction. Detailed measurements of the mass of galaxies and galaxy clusters have shown that about 90 percent of the mass in the universe is this dark matter. There’s so much of it that it’s holding the galaxies together and causes light from the distant universe to bend as though it were traveling through a camera lens. Even though we don’t know what dark matter is, we have a much better handle on it than we do dark energy. It seems to be a new kind of elementary particle that isn’t like protons or neutrons and doesn’t interact easily with normal matter.
Despite the mysterious nature of dark matter and energy, their existence has possibly solved one of the great questions of cosmology. How will it all end? The fate of the universe is determined by its geometric shape, based on the total amount of matter and energy, and with the addition of dark matter and dark energy, all the numbers are adding up to give an answer that most theorists already suspected: Space is flat and it will expand forever. As space expands faster than light and the average density of matter decreases over hundreds of billions of years, entropy will rule and life will no longer be possible. If there are intelligent beings still eking out an existence a trillion years from now, their energy states will be so low that a single thought may require a million years, but they, too, will succumb to the cold emptiness.