What is Constructor Theory and how is it different now than in its original formulation by David Deutsch?

So Constructor Theory is a new way of formulating the laws of physics and this was originally proposed by David, I think back in 2011, something like that, as a new mode of explanation.

So he wrote a paper that had a very strong philosophical component, which laid the foundations of the theory in the form of a

program in a sense. And the key idea there was to modify the way we formulate laws of physics

and so the fundamental laws of physics. So instead of using things like dynamical equations, so laws of motion

and initial conditions, which is what most fundamental theories do, switch to a different mode where

the basic fundamental statements are constraints about which transformations can be performed

and which transformations cannot be performed and why.

So what is possible and what is impossible.

And then consider dynamics and initial conditions as kind of emergent consequences of these principles.

So it's really like a switch of perspective into thinking what is the fundamental element

in a physical theory. And this was there, I think that's the key idea. And David was really

inspired to do this by the quantum theory of computation,

which is a theory that he himself pioneered in the 80s,

when he with other people proposed the idea of a universal quantum computer.

There, I think it's really important in that theory,

to think of what can be performed by a universal Turing machine and what cannot be performed by it under given laws of physics.

So in the case of classical physics, you have a classical universal theory machine that can do

certain things and not others. And then you have a quantum universal theory machine that can do certain things and not others.

And then you have a quantum universal theory which uses the laws of quantum theory, not classical physics.

And there you have new different modes of computation available.

And this was a key insight in developing this idea of the universal quantum computer.

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