Coleman Fest: Day 2
Lubos, Peter and David very well summarized the second day so I don't need to spend your and my time. Instead I want to focus on another question, Gross briefly and Witten extensively talked about. Can we make spacetime emergent?
I think the question needs better definition. What they are giving as examples right now is indeed extremely interesting. Two theories living in two different spacetime dimensions can be "dual". This means that every calculation done in one way, can be done in the other and give the same result. I personally would not call these dual theories as emergent. Material continuum is an emergent realization of atoms. So if you want to make a theory with emergent spacetime I would think that dimensions are build from discrete geometries or some other totally different mathematical structure which effectively geometric at large "distances", whatever it means in this case. My humble intuition for the current situation is that it is a manifestation of the gauge redundancy in our theories. They can be reduced (somehow) not only by changing the field degrees of freedom but a combination of spacetime and gauge degrees, since the former is also dynamical in the gravitational theories. But you may need to introduce new redundancies in the second theory. Zee speculates in the last chapter of his marvelous book that our gauge language may not be the best one to represent nature since it includes unavoidable redundancies. Most probably dual theories will have the same or trivially related representations in the ultimate language when we find it.
I don't want to alert anybody out there unnecessarily. I should say that everything Gross and Witten said is accurate for our current understanding, but the word emergent might be confusing since it is used in many different contexts these days. And there is no sign of inaccuracy of the gauge language; it is just hard to play with for the human mind despite its all elegancy.
I also had an opportunity to eat the lunch with David Gross, Frank Wilczek, Stephen Wolfram (Mr. Mathematica), Leonard Parker (who wrote the apparently useful but ridiculously expensive Mathematica package MathTensor) and Jack Ng (who wrote interesting papers on unimodular gravity which I am currently interested in). Wolfram was trying to convince Gross and Wilczek for the enumerability of the physical laws. (Well, they were not amused.) He would like to give brute force search. I am quite skeptical that we can recognize even if we hit the right one. Wolfram is unquestionably a smart guy. I can't say that I buy his cellular automaton ideas but community might be too harsh on him. We always need someone outside the crowd. He also announced us the latest upcoming service from the Wolfram companies but probably I should not say it hear. One teaser: it is about cell phones!
Lively debate (clockwise): Ng, Parker, Gross, Wilczek, Wolfram, Cabi
It was sad to hear that Coleman does not feel well. Shame on me that I have not read his book yet. This week should be the time.
I think the question needs better definition. What they are giving as examples right now is indeed extremely interesting. Two theories living in two different spacetime dimensions can be "dual". This means that every calculation done in one way, can be done in the other and give the same result. I personally would not call these dual theories as emergent. Material continuum is an emergent realization of atoms. So if you want to make a theory with emergent spacetime I would think that dimensions are build from discrete geometries or some other totally different mathematical structure which effectively geometric at large "distances", whatever it means in this case. My humble intuition for the current situation is that it is a manifestation of the gauge redundancy in our theories. They can be reduced (somehow) not only by changing the field degrees of freedom but a combination of spacetime and gauge degrees, since the former is also dynamical in the gravitational theories. But you may need to introduce new redundancies in the second theory. Zee speculates in the last chapter of his marvelous book that our gauge language may not be the best one to represent nature since it includes unavoidable redundancies. Most probably dual theories will have the same or trivially related representations in the ultimate language when we find it.
I don't want to alert anybody out there unnecessarily. I should say that everything Gross and Witten said is accurate for our current understanding, but the word emergent might be confusing since it is used in many different contexts these days. And there is no sign of inaccuracy of the gauge language; it is just hard to play with for the human mind despite its all elegancy.
I also had an opportunity to eat the lunch with David Gross, Frank Wilczek, Stephen Wolfram (Mr. Mathematica), Leonard Parker (who wrote the apparently useful but ridiculously expensive Mathematica package MathTensor) and Jack Ng (who wrote interesting papers on unimodular gravity which I am currently interested in). Wolfram was trying to convince Gross and Wilczek for the enumerability of the physical laws. (Well, they were not amused.) He would like to give brute force search. I am quite skeptical that we can recognize even if we hit the right one. Wolfram is unquestionably a smart guy. I can't say that I buy his cellular automaton ideas but community might be too harsh on him. We always need someone outside the crowd. He also announced us the latest upcoming service from the Wolfram companies but probably I should not say it hear. One teaser: it is about cell phones!
Lively debate (clockwise): Ng, Parker, Gross, Wilczek, Wolfram, Cabi
It was sad to hear that Coleman does not feel well. Shame on me that I have not read his book yet. This week should be the time.
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