Sunday, July 06, 2008

To string or not to string, 4D vs 11Dimensions


String theory made the universe extremely fun for scientists, mathematicians and mystics alike.

I heard before about alternatives to the string theory in the quest for unifying the theory of all things (integrating the four forces: strong and weak interaction, electromagnetism and gravity, into one nice beautiful equation) that would shed a much more "normal" 4D universe. Apparently, the alternative has to do with a structurally different conception of space-time, which instead of being a continuum would consist of discrete tiny building blocks.

Only a few days ago, reading the article "Using Causality to Solve the Puzzle of Quantum Spacetime" I could understand more what this alternative is about:
"if we think of empty spacetime as some immaterial substance, consisting of a very large number of minute, structureless pieces, and if we then let these microscopic building blocks interact with one another according to simple rules dictated by gravity and quantum theory, they will spontaneously arrange themselves into a whole that in many ways looks like the observed universe. It is similar to the way that molecules assemble themselves into crystalline or amorphous solids."

Computer simulation software is essentially what they use to produce different universe creations starting from small building blocks. Usually they start out with blocks called simplex. What was introduced in this particular approach is an added rule of causality (or time direction):
"Instead of disregarding causality when assembling individual universes and hoping for it to reappear through the collective wisdom of the superposition, we decided to incorporate the causal structure at a much earlier stage. The technical term for our method is causal dynamical triangulations. In it, we first assign each simplex an arrow of time pointing from the past to the future. Then we enforce causal gluing rules: two simplices must be glued together to keep their arrows pointing in the same direction. The simplices must share a notion of time, which unfolds steadily in the direction of these arrows and never stands still or runs backward. Space keeps its overall form as time advances; it cannot break up into disconnected pieces or create wormholes."

It's interesting that if they impose this arrow of time when building their universe they end up with a universe like the one we can perceive: a 4 dimensional one with an arrow of time. Simple ... and makes sense ... although it makes me wonder, are we limiting this way our conception of the world to our human perception? If we were other type of less evolved organism with no sense of time, would we end up building a 3D world just to conform to what our senses would tell us?

Scientists continue to try to find experiments that can shed light over this incredible questions about the nature of the universe. In the words of Janet Conrad: “There’s this cycle in physics,” she says, “where experiment pushes theory and then theory pushes experiment, and I really like the moment in which experiment is pushing theory”—which is what is happening now in the area of neutrinos.
She's basically referring to the Mini-Boo Neutrino Experiment which is studying one of the most elusive particles ever the neutrino. These particles are ubiquitous, actually according to this article: 100 trillion of these tiny particles just passed through your body in the last second. They might be accountable for some amount of lost mass that physicist expect to find in the universe. One of the explanations for this weird neutrino behavior involves more dimensions.

This seems to be a century of questions, not so sure it is one of answers even considering science can only provide tentative relativistic answers.
Long live to the mystery!

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