Constructor Theory Solves the Riddle of Life

>In constructor theory, physical laws are formulated only in terms of which tasks are possible (with arbitrarily high accuracy, reliability, and repeatability), and which are impossible, and why – as opposed to what happens, and what does not happen, given dynamical laws and initial conditions. A task is impossible if there is a law of physics that forbids it. Otherwise, it is possible – which means that a constructor for that task – an object that causes the task to occur and retains the ability to cause it again – can be approximated arbitrarily well in reality.

This seems to be false, as there is no physical law preventing entropy from decreasing but there is a physical law which prevents the existence of a 'constructor' capable of decreasing entropy.

>Moreover, it is a fundamental idea of constructor theory that any transformation that is not forbidden by the laws of physics can be achieved given the requisite knowledge. There is no third possibility: either the laws of physics forbid it, or it is achievable.

Either they are saying something is achievable if and only if there is a constructor for it, which is false (see previous point), or they are claiming something is achievable if and only if the laws of physics don't forbid it, which makes this 'fundamental idea' vacuous.

A constructor is like a program. In this case, the rules of the language are physics itself. We're familiar with writing simple programs in C. We can imagine programs, like the halting problem solver. It turns out that program can't exist, but you kind of have to think about it for a while to understand why.

A constructor (as i understand it) is sort of hand rolled assembly (matter) running right on physics. Perhaps there are space unicorns on the dark side of the moon. We can imagine that. It's not really clear if physics actually allows that though. My gut says no, but the rules of the game, much like the rules of the language may allow such a collection of matter to exist.

I mean, quines are pretty weird. I wouldn't have thought that was even possible.

The author appears to be one of the primary proponents of so called 'constructor theory'. I dug a bit into their research and it's setting off all of my skeptic alarms. Their primary research papers appear to be typeset in Word for christ sake.

To nitpick some particular aspects of the theory and article:

From the wikipedia article on constructor theory:

"Current theories of physics based on quantum mechanics do not adequately explain why some transformations between states of being are possible and some are not. For example a drop of dye can dissolve in water but thermodynamics shows that the reverse transformation, of the dye clumping back together, is not possible. We do not know at a quantum level why this should be so" [1]

An egregiously incorrect statement. This is basic statistical mechanics. The dye dropped into a solution diffuses and doesn't return back into the original drop is very simple: there are very few configurations of the dye/solution system where the dye is in a concentrated drop and a mind bogglingly large number of configurations where the dye is diffused throughout the solution. Nothing in physical law forbids the formation of a concentrated drop from a diffused solution - it's just ridiculously implausibly unlikely.

In fact, due to time reversal symmetry we know that the formation of the concentrated drop is explicitly allowed. Here's a little gedanken experiment: put a drop of dye in the solution and let it diffuse. After some time t, reverse all of the momenta of all of the atoms in the solution (you are God). At time 2t the dye will reform in the original concentrated droplet. But here's the zinger: keep watching and that droplet will again diffuse across the solution! Keep letting the clock run backwards and you'll probably never see the drop reform again.

One more note on that quote: the last sentence says that this is somehow forbidden by quantum mechanics. Again, this is bogus. Ensembles of large number of particles is the domain of statistical mechanics! Long discussion in of itself but the (semi)classical view is a very useful and valid perspective for many problems!

Now a comment about the article:

"Here’s where the puzzle arises. Biological replication and self‑reproduction are in fact such stupendously well‑orchestrated physical transformations that one must explain how they are possible under the simple, no‑design laws of physics such as ours. This additional explanation, which was not included in the theory of evolution, is essential for that theory to properly explain how living things arise without intentional design – to close the explanatory gap"

1. Absolute bullshit that one needs to 'justify' how certain physical states that _seem_ improbable are realized. Total garbage. Another core tenet of statistical mechanics is ergodocity [2] which states that ALL states of a system are will eventually be visited (if you have infinite time).

2. My major gripe: (non-equilibrium) statistical mechanics accounts can explain the formation of complexity (such as life)!! It is not mysterious or outside of the scope of our current framework!! By analogy consider a pot of water being heated by a hotplate from underneath: if the hot plate is on low the heat will diffuse up through the water in a disorganized manner; but, at some critical temperature convection rolls will form spontaneously in the water. They form because the increase in energy dissipation wins out over the reduction in entropy induced by their formation.

This is exactly the mechanism driving the formation of life! The existence of life is not mysterious, it's inevitable!

This article is complete and utter bullshit.

[1] https://en.wikipedia.org/wiki/Constructor_theory#Motivations

[2] https://en.wikipedia.org/wiki/Ergodic_hypothesis

And thing is that laws of physics don't have it in themselves to give birth to processes when by 'process' we mean something more in line of a function, something that would not allow us to say that the Sun is a living organism, although there's processes happening inside a star.

To take this further: you can physically do this with a similar system (replace diffusion with stirring) for very low Reynolds number flows, which are time-reversible. It's called the Taylor-Couette experiment, you can see it in action here: https://youtu.be/k7ZZtxdtmeQ