Across the Universe
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On his theories about the origin of the universe:
We now have good reasons to believe that most of the universe is in the state of explosive, accelerated expansion, called inflation. The expansion is so fast that in a tiny fraction of a second a region the size of an atom is blown to dimensions much greater than the entire currently observable universe. In our local neighborhood, inflation ended about 14 billion years ago, and the energy that drove the expansion went to ignite a hot fireball of particles and radiation. This is what we call the big bang. As the fireball continues to expand, it cools down, galaxies are gradually pulled together by gravity, and cosmic space lights up with stars.
While all this is happening in our local region, inflation still continues in remote parts of the universe, and other regions like ours are constantly being produced. This never ending process is called eternal inflation. The big bang in this scenario is no longer a one-time event in our past: multiple bangs went off before it in distant parts of the universe, and countless other bangs will erupt in the future.
This new worldview has a somewhat bizarre consequence. The process of eternal inflation creates an infinite number of regions like ours. Each of these regions has its own history, from the big bang till present, but it follows from quantum mechanics that the number of possible histories is finite. It is an unimaginably large number, 10 to the power 10 to the power 150, but the important point is that it is finite. Now, if you have a finite number of histories that are unfolding in an infinite number of regions, it follows that every history that can possibly happen will happen and it will happen an infinite number of times. So there are an infinite number of regions where we have exactly the same planet, like our Earth, with exactly the same people and we are having exactly the same conversation. This is not something that would affect your daily life, but it's something to ponder.
I, for one, was very depressed by this conclusion for a while, because I thought it robs us of our uniqueness. I thought, you can think of our civilization as being good or bad, but it is unique and for that reason alone you would treasure it as a work of art, right? But now this picture of the universe tells us that there are an infinite number of civilizations which are identical to ours scattered in the universe. There are also all possible variations. You have regions where Elvis is still alive and regions where dinosaurs still roam the earth.
On why the study of the origin of the universe is important:
If you look at different ancient civilizations and ask what we remember them for, the philosophy and art and the useless things like pyramids are the things that strike us most. Satellites exploring the cosmos and huge particle accelerators are the pyramids of our age. I think this is what our civilization will be remembered for, our technology and scientific achievement.
On whether there is a final answer to questions concerning the origin of the universe:
I wish I could answer that. I don't know. It's possible that underlying the universe is just one equation. You just have to figure it out. But even then, from knowing the equation and being able to work out its consequences is a huge distance. There would still be a practically infinite number of phenomena that need to be studied. So I think there is no danger that physicists will be out of work any time soon.
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Interview by Georgiana Cohen, Office of Web Communications
Photo by Jodi Hilton for Tufts University
This story originally ran on Nov. 12, 2007.