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In the dynamical laws approach, the state of any system can be described as the result of an evolution, according to dynamical laws, starting from an initial state. The initial state of a system must be provided by fiat. If we wish to explain why the initial state is how it is under the PC, we can only explain it as the result of evolution from a previous initial state. If we wish to explain that state, we again must explain it in terms of evolution from an even earlier state. Tracing this process back leads us to the initial state of the universe (or alternatively, there is no initial state of the universe and we keep tracing back forever). But what is the initial state of the universe, and why is the way that it is?

For practical purposes, that isn't a you launched a projectile, you know its angle and speed.

For philosophical purposes, it's a considerable problem because, as you say, everything traces back to an ultimate initial state that can't be accounted for. So the rationalist (old definition) dream of figuring out everything from obvious axioms (or no axioms) is not fulfilled.

I don't see how constructor theory can specify a unique initial state, rather than just cutting down the possibilities.

In fact, thats a general problem. Physics contains laws specifying that things happen necessarily, ie. deterministically , and probabilistically, ie. with different levels of possibility. I don't see how a mere distinction between the possible and the impossible could generate either.

AGI doesn't necessarily have anything to do with simulating brains, but it would count if you could do it.

Some examples of egregious falsity of Deutsch’s claim that physics is based on time evolution of initial conditions with dynamical laws:

Also, the Pauli exclusion principle is a timeless statement of impossibiliy.

Since when was politics about just one person?

Soon, it may be possible to create ‘hybrid systems’, where both gravity and quantum effects are non-negligible. In the dynamical laws approach, we do not know how such systems will behave, because we do not know what dynamical laws will be. Is there a way to reason about such systems, in the absence of dynamical laws?

We do not know what the exact dynamical laws are. I see no reason to suppose that we never will...why would it be impossible in principle?

There's a persistent problem in physics, where laws that apply at one scale are hard to reconcile with laws that apply at another. But that has nothing to do with "dynamism", in the sense of an evolution starting from initial conditions. Both GR and QM contain dynamic and non-dynamic laws

If by would the constructor approach fare better?

In the constructor approach , we do not know know how such systems will behave, because we do not know what the constructor principles will be.The

We do know what an approximate solution looks like in the prevailing approach, because there is a natural hybrid system, ie. a black hole , that we are making progress with.

Deutsch claims that some of the problems of the dynamical laws approach come from the fact that, given a set of initial conditions, this approach can tell you what will happen in a particular situation, but it is often difficult to capture notions of what is in principle possible or impossible. He gives the example of describing why a particular perpetual motion machine will not work. The dynamical laws approach would tell us that the machine won’t work because the torque on one of the axels isn’t large enough, but any physicist would just tell you that it is impossible to build a perpetual motion machine and be done with it.

Of course not. Macrsoscopic PM machines are impossible because of macroscopic laws, ie. the laws of thermodynamics, and any physicist would say so. (Microscopic PMs aren't impossible ... Atoms are PM machines, unless protons decay).

And entropy is a dynamic law, in the sense that it's dependant on an initial condition. A lower entropy state will decay into a higher one, but a high entropy state has nowhere to go..Entropy can only explain the arrow of time on the assumption that universe started in a low entropy state.

If the complete characterisation of a system consists of knowing its dynamical laws and evolution, then how do we account for emergent properties, such as information?

If they are only weakly emergent, there is no problem. A weakly emergent property is always derivable from microphysics, because it's just a coarse grained summary. A strongly emergent property, on the other hand , defies reductionism.

Note however, that just because these problems are hard to solve in the dynamical laws approach, it does not mean that physicists do not have use for these concepts. When I have discussed this before I was accused of claiming that the second law of thermodynamics is not part of physics. This is not what I am saying (or what David Deutsch is saying)! Indeed, I think that the claim being made is in fact the opposite. In practice, physicists do invoke concepts like information and entropy, and the second law of thermodynamics regularly and with great success. They seem to be important for understanding the world, and yet a description of a system in terms of its initial conditions and dynamical laws will not mention them at all.

Not explicitly, but why worry if they are entirely and unambiguously derivable from what is explicitly mentioned? If I tell you there is an elephant in the room, you can infer that there is a mammal in the room, a quadruped in the room, and so on.

There is a long-standing puzzle about whether computational properties can be unambiguously derived from physics, or whether they have a semantic component. As usual , it not obvious that this problem is caused by dynamism , or cured by construction.

"All known microscopic dynamical laws (such as those that underpin classical and quantum mechanics) are time-reversible (meaning that taking a physical evolution and ‘reversing’ the direction of time leads to an equally valid physical evolution). However, the second law of thermodynamics is time-irreversible. Since the macroscopic systems which obey the second law are composed of microscopic components, all of which must obey the reversible dynamical laws, we have reached a paradox, since it should not be possible to derive an irreversible process from time-symmetric dynamics. This is known as Loschmidt’s Paradox. "

"Some proposals claim to have solved this paradox by coarse-graining or averaging over physical states. For example, one can describe the second law in terms of the increase in entropy and entropy as a measure of uncertainty of an observer (see eg. this piece). These solutions are very elegant, but also make thermodynamics into a claim about knowledge. "

The paradox arises if one takes the microphysical laws to apply exceptionlessly at all scales. Macrophysical laws are not complete descriptions of reality, because they are coarse grained, treating microphysical behaviour as a statistical average. Microphysical laws are not necessarily complete descriptions of reality, because they might neglect large scale features such as spatial curvature.

If microphysical laws are limited and approximate , there is no reasonable expectation that they could imply macrophysical laws.

Indeed, one could take the opposite view...that microphysical laws are special cases of macrophysical ones. For instance, reversible microphysical laws are only special cases of irreversible macrophysical laws ; determinism is a special case of indeterminism; linearity is a special case of nonlinearity.

Most firms don't arise as the result of a group of people getting together with a blank slate as to how to.organise themselves; they start as one or two people who found a firm, which they continue to manage , hiring employees as they go along. Such firms are hierarchical because of the unequal status of the founders and hirelings, not because they are better ... and cooperatives are scarce because of the lack of a route to.them.

My personal experience is that unions and co-ops tend to shift compensation to those with seniority and those involved with corporate politics instead of the skilled, productive, and competent ones. This then causes more time and energy to be spent on corporate politics and drives out the most productive employees.

I've seen this happen in capitalist corporations, too. In either case, the people who decide on compensation can increase their compensation with no regard to their own productivity. Indeed under capitalism, the owner 's right to profit is based solely on ownership, not on any input.

Not talking precisely about observable reality.

Talking about what observable reality means. For instance , there is a set of observations and formulate called quantum mechanics. These might mean that we have free will, that we do n ot, that there is a parallel universe where the allies lost WWII, and so on. What it actually means can't settled by further observations, or more maths, so something else is needed...unless you give up on the question of meaning, and settle for instrumentalism.

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