Tuesday, October 4, 2016

Constructing Stuff

Constructor theory

My friend asked me to look into constructor theory because he knows I'm interested in nonmathematical  popularizations of physics. He finds the concept quite interesting but since he's currently seeking a professorship and has a life, he lacks the time to check it out himself.  I had never heard of Constructor theory and it sounded really interesting, so I've been digging into it.  Here is my report to him.

Constructortheory.org says:   >Constructor Theory is a new approach to formulating fundamental laws in physics. Instead of describing the world in terms of trajectories, initial conditions and dynamical laws, in constructor theory laws are about which physical transformations are possible and which are impossible, and why. <

Interesting. However, too vague to be meaningful. Further digging revealed more detailed explanations.

The creator of the thory, David Deutsch says on the http://www.templetonworldcharity.org/projects/constructor-theory-of-information :
>The purpose of this project is to discover the single underlying explanation for all distinctive properties of information in Physics and beyond, which is at once the root of both the familiar properties of information, such as transcending specific embodiments, and its apparently paradoxical quantum-mechanical ones.
Our main innovative tool for addressing this is Constructor Theory, recently proposed by David Deutsch. This theory expresses all scientific theories in terms of a dichotomy between possible and impossible physical transformations - an audacious departure from existing fundamental physics (whose dichotomy is between what happens and what does not, given initial conditions).
Applying the constructor-theoretic approach to information theory, we have established the result that a simple constructor-theoretic property of the laws of quantum physics implies all the disparate features that distinguish quantum information from classical, thus revealing the hitherto mysterious connection between them. (Deutsch and Marletto, 2014)
Building on these results (Marletto, 2015), we have also addressed the issues of whether and how certain properties of living entities, such as the ability to self-reproduce and replicate, can be possible under no-design laws of physics. One shows that they can, provided that those laws allow, in addition to enough resources, information media, as characterised in the constructor theory of information.
Our work is now focussed on two projects,“Constructor Theory of Testability” and “Constructor Theory of Probability”. The latter generalises the well-known arguments to show how the Born Rule can emerge in unitary quantum mechanics, un-augmented with additional probabilistic postulates. Our constructor-theoretic generalisation depends on fewer and much simpler axioms, which are better motivated physically and are now expressed in an information-theoretic form. The Constructor Theory of Testability uses this argument to show that Unitary Quantum Theory is testable against rival theories. A new strand of research in the direction of investigating the properties of superinformation media has also emerged, using the information-theoretic tools of constructor theory to explore the information-theoretic properties of quantum media – chiefly, the possibility of teleportation  – regarding quantum systems as a special case of superinformation media.<

This sounds like Deepak Chopra; very high sounding language which seems to convey zero meaning.

So I began looking for a more practical, understandable, popularized explanation. You know, something within my range of comprehension.

Things seemed to make a lot more sense at this level.
The idea is that rather than establishing complex sets of rules and laws to predict or describe outcomes, physics should turn to a simpler, more fundamental concept which would underlie those rules and laws.  In the fact they were seeking the E = MC2 (I can't figure out how to get that two little and floating… Oh well, you know what I mean) that underlies all physics. A simple concept, easily expressed which then leads to the much more complicated world when it is applied to reality.

This is a very exciting concept. Many scientists and mathematicians are deeply enamored of the belief of beauty in simplicity. They are convinced that complex descriptions of reality must have an underlying simple and easily understood beauty and symmetry.  Constructor physics promises to be that theory of everything which starts so simple and clear and only becomes complex in application.

I must question the sweeping level of these promises. I always tend to be suspicious when you get this level of conviction.  As one advocate website has it, "Only a fool would bet against the possibility that constructor theory could also become a mainstream idea in physics that will have profound consequences for our future understanding of the universe."

Well I certainly don't want to be a fool,  but is it really foolish to engage in the usual scientific procedure of doubting any new theory until it is conclusively proven?  This kind of enthusiasm strikes me as an attempt to poison the well of anyone who dares to doubt.  It the theory is that wonderful, why the need to denigrate those who question it?

A critic ( http://motls.blogspot.com/2014/05/constructor-theory-deutsch-and-marletto.html) says, >What is this constructor theory? It's a sequence of worthless would-be smart sentences sold as a "theory of everything" and a "unifying theory of classical and quantum physics" and "all information in them" which also "defines all forms of information" and transforms all of our knowledge to "claims that some tasks are impossible"....

Some of the most experienced readers already know that
a kettle may heat water.
Fortunately, the authors allow us to formulate even such statements in a more "natural" and more "profound" way:
For instance, a kettle with a power supply can serve as a constructor that can perform the task of heating water. <

This is where the theory loses me, although supporters seem to enjoy this example with particular delight.  So,  a kettle becomes a constructor of bumps if I grab it by the handle and use it to hit someone in the head?  If he chooses to fight back, is the kettle now a constructor of fistfights?  Might it  even become the constructor of a restraining order?

Is this really physics?

The worst criticism of this concept from my point of view is that after all, it describes things that it says are impossible. However, it offers no proof that they are impossible, unless you include the laws which are supposed to be derived from this theory. In practice this means that the theory is simply describing something that the laws have already established. The laws come first, they are not derived from the theory as advertised.

As exciting as I found the idea originally, as I researched it and thought about it, my opinion has settled into believing that this is merely an elaborate linguistic construction.  I'm reminded of the endless ramblings of Wittgenstein.  It is easy to confuse reality with language, but language is only descriptor of reality, not the thing in itself.

Sadly, I have to turn away for what I thought at first was an exciting new idea. When it comes to theories that cannot yet be fully tested, perhaps not even deeply tested, I'll stick with string theory.

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