Scientists who are tracking atomic time say the days on Earth are getting longer by milliseconds all the time -350 million years ago, each day lasted only 22 hours. This is not necessarily good news, even for worn-out, two-career couples. It’s due to the fact that the moon and Earth exert subtle gravitational effects on each other. The moon is gradually moving away from us, and its orbit is slowing, which is slowing Earth’s rotation in turn. Perhaps as soon as 10 billion years from now the moon and Earth will be locked in synchronous orbit around the sun, says Alan Harris of the Jet Propulsion Lab in Pasadena, Calif. By then, days and nights on Earth could each last 50 of our current days, severely altering the balance of plants and animals. That may not be completely fatal, since Earth’s atmosphere will provide some protection from the extremes of heat and cold. Harris, for one, is optimistic that some large mammals could evolve accordingly. “Something would manage to live,” he predicts, “and actually enjoy it.”
Our Milky Way and its closest neighbor, the Andromeda galaxy, are hurtling toward each other at about 125 kilometers per second. At that rate, they will close the 2 million light-years that separate them and collide in 5 billion to 10 billion years. Since Andromeda is two to three times bigger than the Milky Way, the collision will be “analogous to a hostile takeover,” says astronomer Lars Hernquist at the University of California, Santa Cruz. “Our galaxy will be consumed and destroyed.” Even if Earth managed to survive somehow, given all the empty space in the galaxy, the collision could send more comets, asteroids and other debris pounding into our solar system.
By then, Earth may well be cooked by our own evolving star. The sun, now about 4.5 billion years old, is gradually getting bigger and more luminous. It won’t undergo any really dramatic changes for another 5 billion years or so, says astrophysicist Icko Iben of the University of Illinois, but Earth will start feeling the effects long before that. In about 2 billion years, winter temperatures in Massachusetts will hit 90 degrees Fahrenheit. In 7 billion years, the sun will become a Red Giant and start expanding rapidly. When the Sun is twice its current diameter, the Earth’s oceans will boil. In another billion years, when the sun is 15 times brighter, Earth’s surface temperatures will reach 600 degrees Kelvin and its crust will melt. A mere 250 million years after that, the sun will be 2,000 times more luminous and will fill up half the distance to us. Eventually, it will ignite in a giant helium flash visible for several billion years until it burns up all its hydrogen and evolves, pathetically, into a has-been White Dwarf.
Remember little Alvy Singer (Woody Allen) in the movie “Annie Hall,” who was too depressed to do his homework because the universe is expanding? Alvy was right, of course-the key question is, how fast? Once astronomers determine the rate of expansion (also known as Hubble’s constant), they may be able to pinpoint the precise size and age of the universe-and they’ll have a better idea of how it will end. The answer also depends on something called “dark matter,” which makes up most of the universe but is not observable in the electromagnetic radiation spectrum we know as lightwaves. If there is a limited amount of dark matter out there the universe will keep expanding forever into cold emptiness. If there is more dark matter, its gravitational pull will bring the universe collapsing back on itself in a dense fireball-like the big bang in reverse. Fire or ice? It’s the age-old quandary. Either way, we’ll be toast.
If the universe does contract into itself, another expansion might follow-what some experts call “the Big Bounce.” The whole cycle could conceivably repeat itself every 100 billion years or so. But short-circuited by still another threat-this time from deep within. Some scientists believe that protons, of which all matter is made, may someday disintegrate, turning everything in the universe into a poof of radioactive energy. After that, there will be “nothing but radiation filling the universe, getting colder and colder,” says physicist Steven Weinberg at the University of Texas. This notion is still highly theoretical. To date, no one has actually observed a proton decaying, though huge underground detectors have been watching for more than a decade. Proponents concede it will take a long time: the average life of a proton may be 10 to the 33rd power years. How long is that? The universe is about 10 billion, or 10,000,000,000, years old. 10 to the 33rd power has 23 more zeros. But it’s never too soon to start worrying.
