I didn’t read the whole post, but wanted to chime in on the Constructor theory in physics. As a trained (but not practicing) physicist I make a categorical pronouncement that it is a load of bunk. (Were I a practicing physicist, I would make a much more careful and qualified statement.) David Deutsch is a genius with a lot of fantastic contributions to science, but that part is one of those where a genius goes off the deep end. Roger Penrose, Albert Einstein, Isaac Newton and many other top-notch physicists have or had their own pet ideas that are… not very well connected to reality.
Why I think it is bunk:
There have been zero interesting contributions from the constructor theory to our understanding of physics, let alone new testable ideas.
The main claim that physics is based on “dynamical laws and initial conditions” is patently false. Like, completely false. General relativity, Maxwell equations, Fermat principle, any least action principle are timeless and initial-condition-free.
As you say
Deutsch claims that there are certain problems in physics which are difficult or impossible to solve using the dynamical laws approach.
Indeed there are. And they are solved, but not that way, instead other approaches are used.
Some examples of egregious falsity of Deutsch’s claim that physics is based on time evolution of initial conditions with dynamical laws:
The first ever exact solution of the Einstein equation, the Schwarzschild metric, was found purely through symmetries, without any reference to initial conditions and subsequent time evolution. In fact, it is static and timeless, despite time being a variable in it. It took some half a century to even figure out an approximate approach to constructing it using initial conditions (stellar collapse).
The Godel metric, one that contains closed timelike curves everywhere and cannot be described as time evolution from initial conditions even in principle, no matter how much you try.
Simulated annealing-type approaches where each successive step is “unphysical”, but the result corresponds to a physically realizable configuration.
S-matrix approaches, where the calculation is non-local to begin with.
I have no idea about the constructor theory-like approaches in AI alignment, but my credence of it being a useful contributor to physics some day is at the noise level. That is, lost among a multitude of other unpromising ideas.
Thanks for writing this. I wanted to write something about how Deutsch performs a bit a of motte-and-bailey argument (motte:‘there are some problems in physics which are hard to solve using the dynamical laws approach’. bailey:‘these problems can be solved using constructor theory specifically, rather than other approaches’). Your comment does a good job of making this case. In the end I didn’t include it, as the piece was already too long. I just wrote the sentence
Pointing out problems in the dynamical laws approach to physics and trying to find solutions is useful, even if constructor theory turns out not to be the best solution to them.
I didn’t read the whole post, but wanted to chime in on the Constructor theory in physics. As a trained (but not practicing) physicist I make a categorical pronouncement that it is a load of bunk. (Were I a practicing physicist, I would make a much more careful and qualified statement.) David Deutsch is a genius with a lot of fantastic contributions to science, but that part is one of those where a genius goes off the deep end. Roger Penrose, Albert Einstein, Isaac Newton and many other top-notch physicists have or had their own pet ideas that are… not very well connected to reality.
Why I think it is bunk:
There have been zero interesting contributions from the constructor theory to our understanding of physics, let alone new testable ideas.
The main claim that physics is based on “dynamical laws and initial conditions” is patently false. Like, completely false. General relativity, Maxwell equations, Fermat principle, any least action principle are timeless and initial-condition-free.
As you say
Indeed there are. And they are solved, but not that way, instead other approaches are used.
Some examples of egregious falsity of Deutsch’s claim that physics is based on time evolution of initial conditions with dynamical laws:
The first ever exact solution of the Einstein equation, the Schwarzschild metric, was found purely through symmetries, without any reference to initial conditions and subsequent time evolution. In fact, it is static and timeless, despite time being a variable in it. It took some half a century to even figure out an approximate approach to constructing it using initial conditions (stellar collapse).
The Godel metric, one that contains closed timelike curves everywhere and cannot be described as time evolution from initial conditions even in principle, no matter how much you try.
Simulated annealing-type approaches where each successive step is “unphysical”, but the result corresponds to a physically realizable configuration.
S-matrix approaches, where the calculation is non-local to begin with.
I have no idea about the constructor theory-like approaches in AI alignment, but my credence of it being a useful contributor to physics some day is at the noise level. That is, lost among a multitude of other unpromising ideas.
Thanks for writing this. I wanted to write something about how Deutsch performs a bit a of motte-and-bailey argument (motte:‘there are some problems in physics which are hard to solve using the dynamical laws approach’. bailey:‘these problems can be solved using constructor theory specifically, rather than other approaches’). Your comment does a good job of making this case. In the end I didn’t include it, as the piece was already too long. I just wrote the sentence
and left it at that.
Also, the Pauli exclusion principle is a timeless statement of impossibiliy.