….oh wait this was supposed to go over on the poetry thread….

Elliot

Exactly.

Moshe: I’m sorry if my tone was too aggressive. I did get carried away on my high horse. Still, I stand by everything I said. Fyodor has expressed it perhaps more succinctly than I did. Good luck with the war on reality.

Fyodor: I believe that the answer from string theory would be the following. The observer would wave his arms around and count a certain number of dimensions. Then he would learn string theory and do experiments with an LHC and conclude from the particle spectrum that there are extra dimensions that he didn’t count while waving his arms around. Some observers would be able to count all the dimensions by waving their arms and others would have a very difficult time finding them. What is indistinguishable is the final string-theoretic description of the world that the two would reach (which is what string theorists would call the real world), and the differences in the respective worlds that they see around them would be attributed to the fact that the observers would regard themselves as embedded in the stringy world in different ways. An observer imprisoned in a D-brane would be able to wave his arms in fewer directions than an observer who wasn’t so imprisoned.

My virtual existance, one day reached a singularity. To become real, meant I had to escape from the edge of an horizon and fall into a black hole, at the same time. This was not to live forever, I did this… Just to be born. When I was born, you all! Was already dead. For you all to have existed, would mean I had no choice, other than to escape, I did and I did become real and I was born.

Teddy bears dont work, Quantum physics is nonsense, there are no magic boxes, CATS SEE WITH TWO EYES and one day I will die!!

First, I emphasize I did not mention string theory at all when talking about observables of quantum gravity, whether in 4 dimensions or in higher dimensions. If you define “observables” as those things that can be observed, where observation includes and actual observer and a measuring device, the only things that we know exist are S-matrix elements. Those include everything we ever measured. Now this was not a statement about string theory at all, and please try to contain your passion and wait for me to actually make an arrogant and ill-informed statement. Yes “string theory observables” is a term you made up yourself rof.

Second, since the beginning of quantum theory physics is defined as the attempt to describe and predict results of measurments, I have no interest in “reality” beyond that, whatever that may mean. That is precisely why I caution talking about all kinds of comfortable notions one may have, and try to concentrate on precise statements about results of measurments.

All I had to say about T-duality was in the context of string theory, where this thing exist. It was not a statement about the real world where we don’t have experimental evidence for T-duality. If string thoery describes the world and it has a compact circle, there are no measurements that will distinguish a small circle from a large one. Since I am only interested in results of measurments there is no reason for me to choose.

I think I will leave it at that, there is too much war on reality to do this week.

Perhaps you can justify this apparently strange assertion?

Let me explain. If you look at the history [say 1930] of Kaluza Klein theory, you will find that there were two schools of thought. One said that the 5th dimension was real, the other that it was just a mathematical formalism. Of course, nobody disputed that the KK equations were *exactly equivalent* mathematically to the Einstein-Maxwell system, but nobody assumed that *exact mathematical equivalence* was the same thing as “equally real”. Similarly, string theorists circa 1985 surely knew that a purely formal interpretation of Calabi-Yau compactifications was possible, but evidently nobody felt moved to attach any importance to this observation.

Now you want to assert that mathematically indistinguishable situations are *equally real*. Maybe you can persuade us, but you won’t do it by means of analogies with special relativity. You will do it by describing *precisely* how an observer who waves his arms about can possibly describe his experiences in terms of two different dimensionalities. More generally, a string-theoretic analysis of the concept of “reality” would do the trick nicely.