Saturday, January 21, 2006

Yet another Interview

I recently had a conversation with my father. He has a degree in Nuclear Physics and was a teacher for over 20 years. Although he is now retired he still keeps up with the latest developments in physics and keeps up a blog on physics called Stings of Ideas. We talked about String Theory, the Big Bang Theory and other things …

Mad Scientist: Could you briefly explain string theory (ST)?

Man from Zohra: Basic idea: everything - quarks, electrons, photons - are made of tiny strings.

MS: Why do many believe that ST is the key to deducing the grand unifying theory?

MfZ: By accident, when it was proposed as a theory for the nuclear force, the graviton appeared in the theory. Up until then gravity was a force outside the scheme that Quantum Mechanics has for all the other forces.

MS: So the elusive graviton can be predicted by ST ...

MfZ: Absolutely, if it were discovered, it would be a great boost to ST.

MS: It is often said that ST can predict 10^500 different types of universes, what strategy do String theorists have to figure out which theory belongs to our present universe?

MfZ: ST relies on mathematics that employs 10 dimensions. The main problem in ST is to go from 10 dimensions ( 9 spatial plus time) to 3 spatial plus time. In other words, we get too much information, and the trick is to try to weed out the useless information. Now what has been identified are Calabi-Yau manifolds which divide higher dimensional space neatly into 4 and six.

MS: So what in our universe is represented by a Calabi-Yau manifold?

MfZ: Nothing that I know, right now it is basically a mathematical structure that theorists are using to break down a 10-D equation into a 4- and 6-space.

MS: So is our universe a Yau-Calabi manifold floating in a 10D reality?

MfZ: Too soon to tell.

MS: What does ST have to say about the cosmological constant?

MfZ: Cosmology theories are separate but ST also might include supersymmetry, which would have a lot to say about the fundamental particles and how the universe was formed in the early stage, but that is another story.

MS: What is supersymmetry and why is it so important for ST?

MfZ: A good definition of supersymmetry can be found here. It is not vital to ST, but a main concern is the Higgs field, in which particles acquire mass. Supersymmetry would be nice if it turned out to be true.

MS: An alternative to the big bang theory has been floating around recently, could you explain what this is all about?

MfZ: The cyclic theory incorporates the big bang theory but it proposes no beginning. The Universe undergoes an endless sequence of cycles in which it contracts in a big crunch and re-emerges in an expanding big bang, with trillions of years of evolution in between.

MS: So the universe is contracting and expanding indefinitely.

MfZ: The seeds for galaxy formation were created by instabilities arising as the Universe was collapsing towards a big crunch, prior to our big bang.

MS: How do they explain that the expansion in our universe is accelerating? Shouldn't it be slowing down?

MfZ: In the initial phase, think of a spring compressed and released, it would accelerate then slow down. If the spring is attached to a wall, it will then reverse direction. The universe is believed to behave in that fashion.

MS: But if gravity acted as the accelerating force during the big crunch, shouldn't it be the deaccelerating force during the expansion?

MfZ: Dark energy would fueling our expansion. Eventually, we will slow down as gravity caught up. For the next trillion years or more, the Universe undergoes a period of slow cosmic acceleration (as detected in recent observations), which ultimately empties the Universe of all of the entropy and black holes produced in the preceding cycle and triggers the events that lead to contraction and a big crunch. Note that dark energy is not simply added on -- it plays an essential role.

MS: So what is this dark energy?

MfZ: If I knew, I would win the nobel price.

MS: Do they have any idea at how far out the universe will expand before the forces of gravity start to over come the dark energy and start contracting the universe?

MfZ: No, this is beyond our measuring capacity. According to the latest theory, the universe would be expanding for trillions of years, who knows how far it will reach is anyone's guess.

MS: One last question ... what will be the next big idea in cosmology? (if you were to guess)

MfZ: That a trick question?

MS: No - it's the big guess question. BGQ

MfZ: Maybe our latest probe to Pluto might tell us we are wrong on gravity???

MS: Wow.

MS: Ok thanks for the interview.

MfZ: Bye.