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What Is Spacetime, Really?

blog.stephenwolfram.com

81–90 of 122 posts

Re: What Is Spacetime, Really?

#81
post #61

I think Stephen Wolfram fell in the trap, that any continuous dynamical system can be approximated by a discrete one. His position is a bit like claiming the fundamental theory of the universe is Brainfuck. Proof: I can encode general relativity and quantum field theory in Brainfuck, at least to a arbitrary good approximation. The initial conditions are then just the program to simulate GR and QFT plus the initial co…

Why would it be a "trap"? The uncertainty principle hints that something discrete may lie at the bottom. It's clear it's deliberate, not something you fall into due to naiveness. Also, Wolfram isn't the only one in this line of thinking, and this is a topic that rears it's head time and time again in the history of physics.

It is a trap in the sense, that nothing he discusses is convincing me that it is any more than a simple application of a general theorem. ( See my example above, obviously we learn nothing about physics, we just shift the missing information from 'theory' to 'initial conditions.')

So assuming a discreet space may be fruitful, but by itself is not a step forward.

Re: What Is Spacetime, Really?

#82
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…

Tell me about it. I still remember asking my dad what came before the universe when I was a kid and he said, "No, there was no before." When I inquired again he said "Time is a property of our universe. You can't have a before without it. There wasn't nothing , there wasn't a before . You are part of this universe and cannot exist without it. There's no curtain to look behind, this is it." That realization made me fe…

I had the same realization and it terrified me.

Re: What Is Spacetime, Really?

#83
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…

I think you mean "simulate step i of Turing machine T_j"

Re: What Is Spacetime, Really?

#84

Earlier quoted context omitted.

Whether or not the brain is "really" parallel, with a fast enough computer you can simulate parallelism. So our "understanding" is either one-dimensional, or isomorphic to a one-dimensional process.

How many variables are part of this simulation? Are those not dimensions?

You can impose a one-dimensional ordering on a finite state of any size. Drawing a parabola, for instance, yields a 2-D figure. But the process that draws it (on a computer) is 1-D:

    Start at the origin
    Move right X
    Move up X*X
    Make a dot
    If X = Screen.Width Stop
    X=X+1
    Repeat
There you go: a 2-D thing from a discrete sequence of 1-D steps. I hope you can see that it generalizes to N-D things.

Re: What Is Spacetime, Really?

#85
post #63

Earlier quoted context omitted.

1. Why are the number of turing machines finite. 2. But to simulate a single step of the turing machine, you will have to simulate this turing machine too, so what you will end up doing is recursively simulating the first step of this machine to infinity. 3. Why do you assume all the programs in the world are turing computable.

1: they aren't. They don't need to be, and they cannot be. Simulate the first step of the first machine, then the first step of the second machine, then the second step of the first machine, then the first step of the third machine, then the second of the second, then the third of the first, then the first of the fourth, and so on. Every step of every program/machine is eventually reached. For the same reason that th…

Chaotic functions of continuous real variables are not computable. Computable physics assumes a discrete lattice, which the universe is not proven to be.

Re: What Is Spacetime, Really?

#86

I found this incredibly hard to read, due to Wolfram's constant need to self-aggrandize. The entire tone of the piece is, "I discovered this, then I discovered that". In reality, most of his "revelations" were discussed by others long before he arrived on set.

I really appreciated his tone. I'm incredibly fascinated by ideas like quantum physics and basic building blocks of the universe, but am often left behind when I read articles about them due to a lack of understanding of the core mathematics. His tone makes this complicated subject understandable.

He makes it feel understandable, but does it communicate anything meaningful?

Re: What Is Spacetime, Really?

#87
post #35

I found this incredibly hard to read, due to Wolfram's constant need to self-aggrandize. The entire tone of the piece is, "I discovered this, then I discovered that". In reality, most of his "revelations" were discussed by others long before he arrived on set.

Agreed. Benoit Mandelbrot was the same; "When I discovered Fractals, which are a thing that I discovered, including the Mandelbrot Set, which is named after me, because I discovered it..." Wth some people it means I just stop listening to them, but I just ignore it here, since both Mandelbrot and Wolfram usually have interesting and insightful things to say as well.

Rather like Ms. Elk on the subject on the Brontosaurus

https://www.youtube.com/watch?v=cAYDiPizDIs

Re: What Is Spacetime, Really?

#88

I’ve come to suspect it may actually have led us on a century-long detour in understanding the true nature of space and time come to suspect? knowing theories are incomplete is science, seek questions stead answers detour? hardly, science is directed by utility and the systems inherent in the theoretical coupling that formed relativity have shown to be extremely useful and any inevitable addendum, appendage, or usurp…

i wish i knew what was so unsettling about the above opinion i'm interested in discussion

I haven't voted on your comment, but here's what stands out to me: (1) It's not written in good style. People who care about how their ideas are received by others take the time to write properly, including capitalization and punctuation.

(2) It reads like a middlebrow dismissal. It's critical but doesn't add much of substance on its own through the criticism. Wolfram certainly realizes that he hasn't proven his case, that current science is indeed incredibly useful, and that the current path will only be a "detour" if network- or automata-based models are proven correct in the end. That's why he says he "suspects" it "may" have led us to a detour. He certainly understands that the theory needs to be developed further. Put simply, Wolfram would probably agree with your overall sentiment, so the remarks are not insightful, but they're presented as if they'd likely be at odds with his position.

(3) Beyond style, the diction is unclear, such as the choice of the word "use-case". It's unclear to me what you're referring to. It's unusual to refer to physics as "use-cases". If that's intended as an analogy, then for me it doesn't connect or succeed.

(4) The ideas themselves are not clear. "... reveal those use-cases untouched by contemporary thought"; "an existence where every new finality conjures new questions". It's not clear what you're trying to convey with those phrases. You probably could say what you're trying to say in a simpler, more direct, and less critical way way. You might benefit from this advice: http://paulgraham.com/talk.html

> Here's a simple trick for getting more people to read what you write: write in spoken language. Something comes over most people when they start writing. They write in a different language than they'd use if they were talking to a friend. The sentence structure and even the words are different. [...] But perhaps worst of all [mistakes], complex sentences and fancy words give you, the writer, the false impression that you're saying more than you actually are.

If I was to try to rephrase what you've said in simple language, then I end up with something like: "The ideas need to work to be useful. We need to think up new ideas. I think we'll always have more questions to answer", which isn't that interesting. With the current phrasing it reads like a middlebrow dismissal.

Re: What Is Spacetime, Really?

#89

I’ve come to suspect it may actually have led us on a century-long detour in understanding the true nature of space and time come to suspect? knowing theories are incomplete is science, seek questions stead answers detour? hardly, science is directed by utility and the systems inherent in the theoretical coupling that formed relativity have shown to be extremely useful and any inevitable addendum, appendage, or usurp…

i wish i knew what was so unsettling about the above opinion i'm interested in discussion

I don't find it unsettling but it's not particularly interesting. You can view epicycles as detour before Copernicus, I think that's more of the sense of what Wolfram is referring to as a detour.

Re: What Is Spacetime, Really?

#90

Earlier quoted context omitted.

What is matter made of? The answer, whatever it is, cannot be matter. From what fundamental thing does 'space' arise? The answer, whatever it is, cannot be anything that would exist in a 'space' as such. And so we creep towards the idea that at a low enough level, everything is just information.

> What is matter made of? The answer, whatever it is, cannot be matter. Sure it could (in principle) be; its matter all the way down, and there is no lower-level thing of which matter is made. (Though, actually, I think the standard answer to "what is matter made of" under current way of interpreting things would be "energy", but then you could repeat the exercise with "energy" in place of "matter" and its the same i…

Greenness disintegrates: https://goo.gl/2X4288
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