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Actor Model of Computation (2010) [pdf]

arxiv.org

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Re: Actor Model of Computation (2010) [pdf]

#11

Post by jchassoul »

Zalastax wrote: post #3

I find this resource confusing and annoying to read. When performing my thesis research I wasted a bunch of time trying to make sense of Hewitt's writing. I think a big problem is that the term "actor model" is so overloaded that it almost becomes meaningless. The actors that Hewitt is talking about is not at all the same as Erlang or Akka. As an example I consider this quote from the text nonsensical "Actor systems…

Turing machines are not very good handling uncertainty? the key pond is on physics ? yada, yada? I thought this was 101 already!

Re: Actor Model of Computation (2010) [pdf]

#13

Post by arglebarnacle »

curuinor wrote: post #4

Hewitt is now kind of a crank. When Hofstadter came over for the Symsys thing in Stanford a few years back, Hewitt handed Hofstadter a little sheet of paper saying that mere contradiction allowed axiomatic systems to transcend Godel incompleteness theorems. Hofstadter: "Thanks, Carl." and then he threw it away when Hewitt wasn't looking. I think there's a thread in Lambda the Ultimate.

You can see a flash of that in this article with "Actor systems can perform computations that are impossible by Turing Machines"

Re: Actor Model of Computation (2010) [pdf]

#15

Post by jchassoul »

arglebarnacle wrote: post #13
curuinor wrote: post #4

Hewitt is now kind of a crank. When Hofstadter came over for the Symsys thing in Stanford a few years back, Hewitt handed Hofstadter a little sheet of paper saying that mere contradiction allowed axiomatic systems to transcend Godel incompleteness theorems. Hofstadter: "Thanks, Carl." and then he threw it away when Hewitt wasn't looking. I think there's a thread in Lambda the Ultimate.

You can see a flash of that in this article with "Actor systems can perform computations that are impossible by Turing Machines"

The statement is true, Actor systems can handle uncertainty in ways that Turing Machines can not.

Re: Actor Model of Computation (2010) [pdf]

#16

Post by imode »

jchassoul wrote: post #15
arglebarnacle wrote: post #13

Earlier quoted context omitted.

You can see a flash of that in this article with "Actor systems can perform computations that are impossible by Turing Machines"

The statement is true, Actor systems can handle uncertainty in ways that Turing Machines can not.

Actor systems are no more able to handle uncertainty than Turing Machines are, either via nondeterministic TMs or by deterministic TMs. This is basic computability theory.

Re: Actor Model of Computation (2010) [pdf]

#17

Post by mindslight »

PhilWright wrote: post #7
Zalastax wrote: post #3

I find this resource confusing and annoying to read. When performing my thesis research I wasted a bunch of time trying to make sense of Hewitt's writing. I think a big problem is that the term "actor model" is so overloaded that it almost becomes meaningless. The actors that Hewitt is talking about is not at all the same as Erlang or Akka. As an example I consider this quote from the text nonsensical "Actor systems…

> "Actor systems can perform computations that are impossible by Turing Machines" As a turing machine can compute anything that is computable it is therefore impossible for an Actor to do any computation that is not possible by a turing machine. This is computer science 101 and makes me wonder about the value of anything else said in the paper.

> it is therefore impossible for an Actor to do any computation that is not possible by a turing machine

It is impossible for Actors implemented on a Turing machine to do anything that a Turing machine cannot. But the Actor model itself is larger than a Turing machine - eg nondeterminism.

Turing completeness is a lower bound on computation, not a maximum. For instance, a CPU with a hardware random number generator is a Turing machine, but a (basic/strict/pure) Turing machine cannot emulate a CPU with a hardware random number generator!

Re: Actor Model of Computation (2010) [pdf]

#18

Post by jchassoul »

imode wrote: post #16
jchassoul wrote: post #15

Earlier quoted context omitted.

The statement is true, Actor systems can handle uncertainty in ways that Turing Machines can not.

Actor systems are no more able to handle uncertainty than Turing Machines are, either via nondeterministic TMs or by deterministic TMs. This is basic computability theory.

That is wrong, Actor systems have a property called "Unbounded nondeterminism" nondeterministic TM have only bounded nondeterminism.

https://en.wikipedia.org/wiki/Unbounded_nondeterminism

Re: Actor Model of Computation (2010) [pdf]

#19

Post by carlehewitt »

For a more recent description of the Actor Model and associated work, see the following: https://www.amazon.com/Inconsistency-Robustness-Studies-Logi...

Also, those who will be in London on November 9 can come to my Code Mesh Keynote. See https://plus.google.com/+CarlHewitt-StandardIoT/posts/BXSZ7Y...

It is fair to say that the implementation of Actors is still in its infancy. There is a startup in Silicon Valley that is attempting to remedy this situation. They are looking for expert programming language and run-time implementers ;-)

Older publications are obsolete and unfortunately many of them have errors (including my own!). I wrote the Wikipedia article on the Actor Model but am no longer allowed to update it :-(

Actors are very well defined up to a unique isomorphism by axioms.

The reason that Actors can perform computations that Turing Machines cannot is that the Turing Machine model left out message passing.

Re: Actor Model of Computation (2010) [pdf]

#20

Post by carlehewitt »

curuinor wrote: post #4

Hewitt is now kind of a crank. When Hofstadter came over for the Symsys thing in Stanford a few years back, Hewitt handed Hofstadter a little sheet of paper saying that mere contradiction allowed axiomatic systems to transcend Godel incompleteness theorems. Hofstadter: "Thanks, Carl." and then he threw it away when Hewitt wasn't looking. I think there's a thread in Lambda the Ultimate.

Unfortunately, it is very common to have difficulty with paradigm shifts :-(

Those of you near Denver can come to my BLAST 2018 lecture at 5PM on August 9 at the University of Denver with the following abstract: https://plus.google.com/+CarlHewitt-StandardIoT/posts/hh5CYE...

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