Tuesday, September 4, 2012

A Ballon Producing Balloons, Producing Balloons: A Big Fractal

Think about it this way: previously we thought that our universe was like a spherical balloon. In the new picture, it's like a balloon producing balloons, producing balloons. This is a big fractal. The Greeks were thinking about our universe as an ideal sphere, because this was the best image they had at their disposal. The 20th century idea is a fractal, the beauty of a fractal. Now, you have these fractals. We ask, how many different types of these elements of fractals are there, which are irreducible to each other? And the number will be exponentially large, and in the simplest models it is about 10 to the degree 10, to the degree 10, to the degree 7. It actually may be much more than that, even though nobody can see all of these universes at once.

ANDREI LINDE, a Russian-American theoretical physicist and professor of Physics at Stanford University, is the father of "eternal chaotic inflation", one of the varieties of the inflationary multiverse theory, which proposes that the universe may consist of many universes with different properties. He is an inaugural winner of the $3 million Fundamental Physics Prize, awarded by the Milner Foundation. In 2002, he was awarded the Dirac Medal, along with Alan Guth of MIT and Paul Steinhardt of Princeton University. (...)
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Standard Big Bang theory says that everything begins with a big bang, a huge explosion. Terrorists started the universe. But when you calculate how much high tech explosives these guys would have to have at their disposal to start the universe formation, they would need 1080 tons [ed. that's 10 to the power of eighty...can't figure out how to do exponentials in blogger] of high tech explosives, compressed to a ball smaller than 1 centimeter, and ignite all of its parts exactly at the same time with precision better than 1 in 10,000.

Another problem was that in the standard Big Bang scenario, the universe could only expand slower as the time went on. But then why did the universe started to expand? Who gave it the first push? It looks totally incredible, like a miracle. However, people sometimes believe that the greater the miracle, the better: Obviously, God could create 1080 tons of explosive from nothing, then ignite it, and make it grow, all for our benefit. Can we make an attempt to come with an alternative explanation?

According to inflationary theory, one may avoid many of these problems if the universe began in some special state, almost like a vacuum-like state. The simplest version of such a state involves something called "scalar field." Remember electric and magnetic fields? Well, scalar field is even simpler, it does not point to any direction. If it is uniform and does not change in time, it is invisible like vacuum, but it may have lots of energy packed in it. When the universe expands, scalar field remains almost constant, and its energy density remains almost constant.

This is the key point, so let us talk about it. Think about the universe as a big box containing many atoms. When the universe expands two times, its volume grows eight times, and therefore the density of atoms decreases eight times. However, when the universe is filled with a constant scalar field, its energy density remains constant when the universe expands. Therefore when the size of the universe grows two times, the total energy of matter in the universe grows eight times. If the universe continues to grow, its total energy (and its total mass) rapidly becomes enormously large, so one could easily get all of these 1080 tons of mater starting from almost nothing. That was the basic idea of inflation. At the first glance, it could seem totally wrong, because of energy conservation. One cannot get energy from nothing. We always have the same energy with which we started.

Once I was invited to give an opening talk at the Nobel Symposium in Sweden on the concept of energy. And I wondered, why did they invite me there, what am I going to tell these people who study solar energy, oil, wind? What can I tell them? And then I told them: "If you want to get lots of energy, you can start from practically nothing, and you can get all the energy in the universe."

Not everyone knows that when the universe expands, the total energy of matter does change. The total energy of matter plus gravity does not change, and it amounts to exactly zero. So the energy conservation for the universe is always satisfied, but it is trivial: zero equals zero. But we are not interested in the energy of the universe as a whole; we are interested in the energy of matter.

If we can have a regime where we have some kind of instability where the initial zero energy can split into a very big positive energy of matter, and a very big negative energy of gravity, the total sum remains zero. But the total energy of matter can become as large as we want. This is one of the main ideas of inflation.

We have found how to start this instability, and how to stop it, because if it doesn't stop, then it goes forever, and then it's not the universe where we can we live. Alan Guth's idea was how to start inflation, but he did not know how to stop it in a graceful way. My idea was how to start it, continue it, and eventually stop it without damaging the universe. And when we learned how to do it, we understood that yes, we can start from practically nothing, or even literally nothing, as suggested by Alex Vilenkin, and account for everything that we see now. At that time it was quite a revolutionary development: We finally could understand many properties of our universe. We no longer needed to postulate the cosmological principle; we finally knew the real physical reason why the world that we see around us is uniform.

by Andrei Linde, The Edge |  Read more: