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What Is Spacetime, Really?

blog.stephenwolfram.com

41–50 of 122 posts

Re: What Is Spacetime, Really?

#41
post #37

Earlier quoted context omitted.

It seems to me that the fundamental thing that Wolfram is saying is that reality is non-local. Locality itself is an emergent phenomenon. This is his clever way of getting around Bell's Theorem. His networks don't require space to exist, they are space. When we think of spacetime, we think of a manifold, and he's saying that what looks like a manifold at a macro level is really just a discrete network at a micro leve…

But a theory is supposed to model something that actually exists, yes? So for instance when philosophers made the conjecture for the existence of the atom, their theory was either correct or not, on the basis of whether the atom actually existed in nature. So if Wolfram is correct, then there exists at the lowest level of nature a network, upon which everything else follows. Wolfram is trying to describe reality, som…

This is a classic debate in the philosophy science. Should theories describe the world, or merely make predictions about it? Because no one these days believes that quantum mechanics really describes the world, we live firmly in the realm of theories being things that make predictions.

The existence of the atom, however, is not what is being predicted. A theory should predict the sensor readings of particular instruments during particular experiments. Those sensor readings are what is real; "The Atom" is the abstraction.

The very idea that "things exist" is an abstraction. A thing exists if we can model it, and that model corresponds with reality.

Re: What Is Spacetime, Really?

#42
post #22

Things like this always leave me feeling stupid. How is one supposed to wrap their mind around the idea of space emerging from an underlying "network"? What exactly is being networked; what is the "stuff" of the network? He describes the network in terms of connections, which in my mind requires a topology, or space within which to exist; yet space does not apparently exist at this level. If there is no space, then w…

Wolfram is proposing a radically different way of interpreting the universe. His main argument is that if his cellular automatons can achieve emergent behaviour similar to real physics, then it is evidence for it being the underlying mechanism in the universe.

For a (really long) discussion on how this simulation parallels physics, check his book, A New Kind of Science, out.

Then maybe you would want to read Aaronson's review of it, just for a balanced perspective.

Re: What Is Spacetime, Really?

#46
All of our theories are single-threaded in the sense that the reader begins at the beginning of the paper and reads it through to the end. Theoretical physics at this level has always seemed to me a kind of weird mirror of this fundamental constraint on the 1-D nature of theories themselves.

Re: What Is Spacetime, Really?

#47
post #16

If you want a second opinion, Cosma Shalizi reviews A New Kind of Science by Stephen Wolfram: http://bactra.org/reviews/wolfram/

Serendipity. This morning, in another context, I learned for the first time about E.T. Jaynes' work and downloaded a copy of his unfinished tome. And now, this afternoon, in Shalizi's review, I again see it honorably mentioned. Thanks for this link.

Re: What Is Spacetime, Really?

#48
post #36

If the answer is "there is such a program that reproduces the universe," then I have already found one such program that does it. Here it is: interleave the simulation of individual steps of every Turing machine in lexicographic order. That is, if the Turing machines are enumerated T_1, T_2, T_3, ... you do the following: i = 1 while True: j = 1 while j If there is some program, it will be in the list. This is the pi…

Does this set of all turing machines contain the given turing machine? If yes, then it would seem that you can never simulate even a single iteration of the inner loop. If no, then you are not actually simulating all the programs are you?

This goes a little beyond NP hard complexity, I believe.

Re: What Is Spacetime, Really?

#49

In the beginning was a graph, more like diamond than graphite. Every node in this graph was tetravalent: connected by four edges to four other nodes. By a count of edges, the shortest path from any node back to itself was a loop six edges long. Every node belonged to twenty-four such loops, as well as forty-eight loops eight edges long, and four hundred eighty that were ten edges long. The edges had no length or shap…

Thank you, I had forgotten how much I loved that book. Time for a new Greg Egan kick!

Re: What Is Spacetime, Really?

#50
post #36

If the answer is "there is such a program that reproduces the universe," then I have already found one such program that does it. Here it is: interleave the simulation of individual steps of every Turing machine in lexicographic order. That is, if the Turing machines are enumerated T_1, T_2, T_3, ... you do the following: i = 1 while True: j = 1 while j If there is some program, it will be in the list. This is the pi…

Does this set of all turing machines contain the given turing machine? If yes, then it would seem that you can never simulate even a single iteration of the inner loop. If no, then you are not actually simulating all the programs are you? This goes a little beyond NP hard complexity, I believe.

This set of Turing machines is the set of all Turing machines. But you misunderstand, I am only simulating a single step (constant time) of a finite number of Turing machines in any given iteration of the inner loop.

It goes arbitrarily far beyond NP hard complexity, which is my point. Wolfram ignores complexity entirely, and that means this algorithm is fair game.

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