Last chance to join our Costa Rica Star Party! Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas. The Big Freeze. Astronomers once thought the universe could collapse in a Big Crunch.
Now most agree it will end with a Big Freeze. If the expanding universe could not combat the collective inward pull of gravity, it would die in a Big Crunch, like the Big Bang played in reverse.
However, the cosmos is ballooning up at an ever-increasing rate, which makes most astronomers think the universe will die in a Big Freeze, where any lingering particles are separated by distances greater than the current observable universe. How will the universe end?
Humanity has pondered this question for thousands of years. And now science actually has the knowledge and tools to attempt an answer. Until rather recently, astronomers thought the cosmos would repeatedly expand and collapse in an infinite cycle of cosmic death and rebirth. But the best evidence points to a distant Armageddon filled with more existential dread than the Book of Revelation. Trillions of years in the future, long after Earth is destroyed, the universe will drift apart until galaxy and star formation ceases.
Slowly, stars will fizzle out, turning night skies black. Finally, the last traces of heat will disappear. Roughly a century ago, astronomers thought that our Milky Way Galaxy was the entire universe. Our cosmos appeared static — it had always been, and would always remain, roughly the same. However, as Albert Einstein formulated his theories of relativity, he noticed signs of something strange. His equations implied a universe in motion, either expanding or contracting. So Einstein added a fudge factor — a cosmological constant — that held the universe in a more appealing steady state.
However, around the same time, astronomers began to accept that some of the fuzzy spiral-shaped nebulae they observed through their telescopes were not collections of stars in our galaxy. They were other galaxies entirely. And when Edwin Hubble meticulously measured their motions, he showed these galaxies were indeed moving away from our own. Humanity had discovered that the universe is expanding. Pressing rewind on that expansion ultimately revealed that the entire universe was born in a violent Big Bang some With its foundations firmly fixed, cosmology turned to the next great question: How will the universe end?
There are two main ways for an expanding universe to die: The cosmos could eventually collapse back in on itself, or it could continue inflating forever. Quantum physics also forces inflation theories into very messy territory. Nothing is ruled out that is physically conceivable.
Steinhardt, who was one of the original architects of inflationary theory, ultimately got fed up with the lack of predictiveness and untestability. We have to look for a better idea. Rather than being a beginning, the Big Bang could have been a moment of transition from one period of space and time to another — more of a bounce Credit: Alamy.
The problem might have to do with the Big Bang itself, and with the idea that there was a beginning to space and time. But rather than being the beginning of space and time, that was a moment of transition from an earlier phase during which space was contracting.
With a bounce rather than a bang, Steinhardt says, distant parts of the cosmos would have plenty of time to interact with each other, and to form a single smooth universe in which the sources of CMB radiation would have had a chance to even out. Our expanding universe could start to contract, returning to that dense state and starting the bounce cycle again. Steinhardt and Turok worked together on some early versions of the Big Bounce model, in which the Universe shrunk to such a tiny size that quantum physics took over from classical physics, leaving the predictions uncertain.
This Big Bounce model says this is how the Universe must be. It is not random. It's incredibly ordered and regular and requires very few numbers to describe everything. Our forward-time flowing universe could have a perfect reflection that also extends out in reverse from the event we call the Big Bang Credit: Alamy.
With this in mind, Turok sees no place for a multiverse, higher dimensions, or new particles to explain what can be seen when we look up at the heavens.
The remainder seems to be made up of something we cannot currently see — dark matter. While particle physicists have yet to directly see any of these particles, they are pretty sure they exist. And it is these that make up dark matter, according to those who support the Mirror Universe theory. Like the Big Bounce, it involves a universe that might have existed forever. But in CCC, it never goes through a period of contraction — it only ever expands.
Penrose says at this point, the Universe begins to look much as it did at its start, setting the stage for the start of another aeon. One of the predictions of CCC is that there might be a record of the previous aeon in the cosmic microwave background radiation that originally inspired the inflation model. Recent observations confirm that Andromeda is heading straight toward us at about 60 miles per second, and will traverse the 2.
While the collision of two galaxies might conjure up images of mass devastation, the event will be largely imperceptible to our descendants, if any are still around. They will have had to find another home: By that time, the increasing luminosity of our sun will have rendered Earth uninhabitable. Galaxies are mostly empty space, so almost no stars or planets will actually collide.
Nonetheless, the Milky Way as we know it will cease to exist. Initially, the two galaxies will slide past each other and draw apart until gravity hits the brakes and pulls them back together. If the size of the universe were to remain unchanged, the mutual gravitational attraction among galaxies eventually would cause all of them to merge together. Throughout much of the 20th century, the big question in cosmology circles was: Is there sufficient mass in the universe to enable gravity to halt this expansion?
Or will distant galaxies continue to move apart, slowing down but never quite stopping? Then came the discovery that presented a third, unforeseen option: The expansion of the universe is not slowing down, as any sensible universe should be doing, but speeding up.
0コメント