What Is Spacetime, Really? • Hacker News Board

Re: What Is Spacetime, Really?

#101

Post by hyperion2010 » Thu, Dec 03, 2015, 7:26 AM UTC

javajosh wrote: post #84

nitrogen wrote: post #78

Earlier quoted context omitted.

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.

I think the question here, which has been raised in other parts of the comments here, is what the complexity of the operation to serialize/deserialize is and how one might think about translating between computational complexity and dimensionality.

Re: What Is Spacetime, Really?

#102

Post by iofj » Thu, Dec 03, 2015, 8:54 AM UTC

chengiz wrote: post #44

If all you have is cellular automata, everything starts looking like a network.

Same can be said about string theory. In fact, there's an (in)famous book about exactly that statement :

http://www.amazon.com/Not-Even-Wrong-Failure-Physical-ebook/...

(Word of warning: do not indicate to your promotor that you're interested in this book's subject, or even have read it, unless you're damn sure where he stands on the subject, unless you want get a very effective demonstration that physics might be value-free, professors definitely aren't)

Re: What Is Spacetime, Really?

#103

Post by memracom » Thu, Dec 03, 2015, 9:46 AM UTC

Let's see, everything is just nodes and connections.

Category theory says everything is just objects and morphisms.

Brown's Laws of Form starts with "drawing a distinction".

Could this last be the starting point? Is it consistent with either the network or with Category Theory?

Lots to think about...

Re: What Is Spacetime, Really?

#104

Post by interpol_p » Thu, Dec 03, 2015, 11:32 AM UTC

The thing that bugs me about his theory is that it just assumes the existence of time. That patterns within the network are replaced according to certain rules. And it seems that this replacement rule corresponds to time at the high level.

His low level model seems to require propagation / evolution without being able to model it. Whatever enacts the replacement rule is an external force that acts upon his network, and so falls outside his definition of the universe.

I guess it's a limitation of the cellular automata model. You have to assume that something outside of the system "steps" the simulation forward.

Re: What Is Spacetime, Really?

#105

Post by yetihehe » Thu, Dec 03, 2015, 1:46 PM UTC

euyyn wrote: post #96

hcarvalhoalves wrote: post #72

Earlier quoted context omitted.

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.

> The uncertainty principle hints that something discrete may lie at the bottom. Not necessarily. The uncertainty principle is a direct consequence of some quantities being "the Fourier transform" of each other. You can't play a pure tone unless it extends infinitely in time, and vice versa: You can't play an infinitesimally short sound unless you ring all frequencies. That's all. And actually, if something discrete…

There IS known max energy, it's called Planck scale (https://en.wikipedia.org/wiki/Planck_scale).

Re: What Is Spacetime, Really?

#106

Post by FiatLuxDave » Thu, Dec 03, 2015, 2:04 PM UTC

codeulike wrote: post #10

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…

I haven't read Schild's Ladder, but that section strongly reminds me of a lecture I attended by David Finkelstein (https://en.wikipedia.org/wiki/David_Finkelstein) given to a physics department composed largely of condensed matter physicists. He basically said that he was going to attempt to explain space-time as a crystal structure, and he said that structure was most analogous to diamond. Then he used condensed matter formalisms to explore the crystal structure and explain how this created the properties of space-time that we see. This was back in 1996 or so.

Re: What Is Spacetime, Really?

#107

Post by j2kun » Thu, Dec 03, 2015, 2:28 PM UTC

infogulch wrote: post #83

j2kun wrote: 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 "

Quite right. It's sad I can't edit even slightly old comments.

Re: What Is Spacetime, Really?

#108

Post by j2kun » Thu, Dec 03, 2015, 2:30 PM UTC

knughit wrote: post #85

drdeca wrote: post #63

Earlier quoted context omitted.

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.

There's also no proof (or even evidence) that the universe is not discrete.

Re: What Is Spacetime, Really?

#109

Post by amelius » Thu, Dec 03, 2015, 3:06 PM UTC

grkvlt wrote: post #33

amelius wrote: post #14

Same topic, different approach: [1] [1] https://www.youtube.com/watch?v=W2XdhzCORbo

FYI - "The first lecture in a series given by Dr Peter Rowlands of the University of Liverpool on the Foundations of Physical Law. Further lectures will be uploaded after they have been given."

Actually, there are more lectures available already.

Re: What Is Spacetime, Really?

#110

Post by AnimalMuppet » Thu, Dec 03, 2015, 5:31 PM UTC

GFK_of_xmaspast wrote: post #60

AnimalMuppet wrote: post #51

Earlier quoted context omitted.

Dijkstra's ideas survive, but are (mostly) not used...

There's a whole lot of structured programming going on these days.

Ah, yes, I had forgotten structured programming. Yes, it won and goto lost, and the world is better for it.

What I was referring to, though, was what I think was Dijkstra's main idea: That programming should be done by a particular approach (the "postulational method") that allows/requires mathematical reasoning about code, and that code should be mathematically proven to be correct. That idea is used very little.