Constructing a rational action?

[Fra]

I've been skimming the paper of A.N Schellekens (http://arxiv.org/abs/0807.3249) that discusses the notion of string theory landscape. He argues against uniqueness, and seems to think that the existence of a landscape of possibilities adds explanationary value and is a good thing.

Surprised linked to this paper, as part of the discussion in Tom's thread about objections about string theory: https://www.physicsforums.com/showthread.php?t=419450&page=14.

I can only conclude that there obvioulsy exists quite diverse ways of describing the problem. And repeatedly the core issues points towards some things that has to do with the physical basis of probability and it's proper context relative to a real inside observer (rather than external, or non-dynamica observer), and wether structural realism is conceptually comaptible with a view where a theory is a condensed description of the world, as seen by an inside observer, that the observer can encode?

I know I brought this up before, but here is another idea. The purpose is to stimulated a discussion about some KEY points, that are important things when analysing what a theory is, and how it is built. Comments are appreciated on the below.

If we think back to say Feynmann's path integral approach, and try to think what it means in general terms: Feynman suggest that the probability for a transition (by means of a transition amplitude; and by borns rule, but let's for a second ignore why this looks like it does) can be expressed as something contining a SUM of the set of all POSSIBLE transitions.

Also what exactly does the set of all possible transitions mean? It seems without further qualifications this notion means nothing.

Is there a first principle path to understand this? Maybe.

How about if we first question, what probability means? how do we do that? Well the normal way of answering that in physics without resorting to outdated realist ontologies, is to consider WHAT DIFFERENCE does it make? Ie. what are the impliciations of the "proability" or "expected action" beeing this or that?

Here, I propose to consider the analogy of a game, say a poker player. What difference does the expectations a given player has; about it's fellow gamers and the game itself?The difference is of course that a rational player places his bets by analysing risks and potential benefits, according to the full set of possibilities he has information about. So anything seeing how the player, places his bet can infer by induction what information he has about others in the game.

Thus, the set of all possibilities we should sum over, is not the space of mathematicall possible (whatever that even means since mathematics is certainly not unique; axioms are chosen!), it is (to be specified) the set of all physically distinguishable possible states this observer can relate to.

Also, about the maning of this subjective probability? This could be inferred by an outside observer from it's behaviour, by assumting that the system is rational. We do not konw that, but one could argue that is the only sensible assumption. There simply is no other option, that can yield a definitive action strategy. If so, what would it be?

This is a comment to something Schellenkens wrote about the landscape; that unless I am totally mistaken, reveals that he holds IMO an understanding of QM that I think is questionable. (OF course this is entirely consistent, with what whas concluded in Toms thread; namely that ST is in a sense and extension to the QFT framework; including of course the assumption that extrapolation of QM to untested domains are correct)

I guess my question here, is wether I'm the only one having this objection? Or does everything except me agree with this implicit and apparently self-evident extrapolation of QM to domains where there just is not experimental support?

A fundamental feature of Quantum Mechanics is that one must sum over all possibilities,
weighted with an exponential factor. Here \all possibilities" includes literally everything,
including physics that we know nothing about.

Also schellenkens in several places admits that the notion of probability in certain contexts escape our current understanding, but still he makes statements like this as if it's obvious.

Edit: I forgot : the counter example (by analogy) would of course be that no one would suggest that a rational poker player, places his bets consistently depending on information of which he has no possessionof ; anyone observing that would make the rational inference that the player actually HAD further information)! (I'm talking here about statistically certain actions; because of ontop of all I suggest there are still uncertainties; as the inductions only provides statistical predictions (but with a subjective meaning of this).
So it's actually the case there even if it was the case that his actions (again what ever that would mena) did depend on things not at hand (ie highly non-local behaviour) then it's not a possible rational inference of a third observer to describe it like that.

Edit2: To not make any think I'm talking about the human brain here - note that I don't mean to say it's not the experiments knowledge that is relevant, it's the systems knowledge about it's own evironment. All the experimenter(we) does when studying a subsystem is to captue the action of system + environment. (essentially observing other observers interacting; this is then the origin of the QM formalism; and the non-dynamical observer; but this can't be the full story as I tried to argeu)

Edit3: One could in principle apply this also to the actual human experimenter; then the suggested difference is the action of the experimenter! Ie. what does the physicists do, depending on what expectations it has? and how does it respong to experimental results? As we know: certain expectations makes them built strange apparatouses, looking for certain yet never seen particles. Other physiciscs with other expectations builts a second devices looking for a different but also unkonwn particle, or "phenomenon" in general. - this is rational indeed! (I don't critique this behaviour; on the contrary) I'm just trying to line out an honest description of the situation. And try to make the distinction clever that we have different levels of "observers" here. The reasoning consistently does apply to all, but at different levels.

/Fredrik

 

[AndyW]

Hello Fredrik,

Thank you for bringing up this paper and initiating a discussion on some key points about the nature of scientific theories.

I agree with Schellekens that the existence of a landscape of possibilities in string theory adds explanatory value and is a good thing. As scientists, we should always strive to explore and understand all possible avenues and explanations for a phenomenon. The concept of a landscape in string theory allows for a more comprehensive understanding of the universe and its fundamental building blocks.

I also agree with your analogy of a poker player and the concept of probability. It is important to consider what difference a certain probability or expected action makes in order to fully understand its implications. In the case of quantum mechanics, the concept of summing over all possibilities is essential in order to take into account all possible outcomes and make accurate predictions.

However, I would like to address your question about extrapolating quantum mechanics to untested domains. While it is true that there is no experimental support for these extrapolations, it is also important to note that quantum mechanics has been extensively tested and has proven to be a highly successful theory in predicting and explaining various phenomena. Therefore, it is reasonable to assume that it can be extrapolated to domains that have not yet been tested. Of course, this assumption should always be questioned and tested through further experimentation and research.

Overall, I believe that Schellekens raises some important points about the landscape of string theory and the nature of probability in quantum mechanics. It is always beneficial to critically analyze and question our theories and assumptions in order to further our understanding of the universe. Thank you again for bringing up this paper and starting a discussion on these key points.