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What Is Spacetime, Really?

blog.stephenwolfram.com

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Re: What Is Spacetime, Really?

#71

Post by brazzledazzle »

tux1968 wrote: 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 feel pretty stupid and caused a minor existential crisis.

Re: What Is Spacetime, Really?

#72

Post by hcarvalhoalves »

yk wrote: 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.

Re: What Is Spacetime, Really?

#73

Post by dnautics »

gohrt wrote: post #27
amelius wrote: post #15

Earlier quoted context omitted.

IANAP either, but wasn't the hidden variable problem resolved by the pilot wave theory?

It wasn't resolved. Pilot Waves have nonlocality, which contradicts Relativity. (I don't know, it may be correct that quantum mechanics is non-local, but Relativity-minded folk are rightfully suspicious of such a model.)

There are other formulations of relativity which aren't nonlocal!! Like the Tangherlini transformations.

I like this quote:

"Alice wants to synchronize her clock with Bob's, so this is how it might go:

At 12:00:00 pm Alice time, Alice sends out a beam of light to Bob, as a signal for Bob to tell Alice what time he has.

Once Bob receives the beam of light, Bob immediately sends Alice a beam of light telling her the time he has.

At 12:00:02 pm Alice time, Alice receives Bob's time, say 11:41:23 am.

At this point, how should Alice synchronize clocks? Clearly, 12:00:01 pm Alice time is 11:41:23 Bob time. We're done.

But we've unknowingly introduced an assumption here, namely that the speed of light travelling from Alice to Bob is identical to the speed of light travelling from Bob to Alice."

Re: What Is Spacetime, Really?

#74

Post by brazzledazzle »

tux1968 wrote: post #64
drdeca wrote: post #57

Earlier quoted context omitted.

I don't understand why you feel that there needs to be a space in order to have a collection of nodes and edges that connect the nodes. It isn't as if there is an actual line connecting two dots across space. It's just, there's a set of "points" (there doesn't need to be any things about these "points" other than that they are distinct. You could think of them as urelements I guess.), and another set of "edges", whic…

This conversation has given me lots to think about and I was ready to let it trail off. But wanted to answer you just out of respect. My mistake was thinking that he was proposing something about the nature of physical reality. Ie. that physical reality was literally a network of interconnected nodes at its fundamental level. Something along the lines of macroscopic -> atomic -> sub atomic -> wolfram-nodal. A la, str…

I'm as dumb as they come, so take this with a grain of salt: I think he is describing (a theory about) physical reality. To give you a different perspective: You position his theory of the universe as a network of nodes along with distances/measurements. But if you think for a moment about the void that you have to cross to get from one object to another (like from our star system to another) what is it? If you put it under an electron microscope it doesn't reveal itself.

It's "nothing" as far as we're concerned but despite being intangible, despite being nothing, it has rules and laws that govern matter that traverses it just like every other part of our universe. So what is space itself? What is it composed of? You can't take a quick step outside of the universe to get a look under the hood because you are part of the universe. You can only talk about it in terms of it's rules and behavior–in the abstract.

Re: What Is Spacetime, Really?

#75

Post by JabavuAdams »

tux1968 wrote: post #64
drdeca wrote: post #57

Earlier quoted context omitted.

I don't understand why you feel that there needs to be a space in order to have a collection of nodes and edges that connect the nodes. It isn't as if there is an actual line connecting two dots across space. It's just, there's a set of "points" (there doesn't need to be any things about these "points" other than that they are distinct. You could think of them as urelements I guess.), and another set of "edges", whic…

This conversation has given me lots to think about and I was ready to let it trail off. But wanted to answer you just out of respect. My mistake was thinking that he was proposing something about the nature of physical reality. Ie. that physical reality was literally a network of interconnected nodes at its fundamental level. Something along the lines of macroscopic -> atomic -> sub atomic -> wolfram-nodal. A la, str…

No, I don't think that's it. He is saying that physical reality is literally a network of interconnected nodes at its fundamental level. I think you're still assuming that these graphs have to be embedded in some space to be real.

If we get fundamental enough, we can go below geometry, into algebra.

For a less abstract example, what's the radius of an electron in modern physics?

Re: What Is Spacetime, Really?

#76

Post by hcarvalhoalves »

tux1968 wrote: 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…

You can describe things in two ways:

1) Decompose into smaller components and put back together 2) Look at it's structure

It's the diference between describing a cardboard box and a cube (platonic solid).

To describe the first, I have to describe what is cardboard, what is cellulose, what is a cell, what is matter, ... all the way down, and then I hit a wall.

To describe the second, I just need topology.

This definition of space is that space "just is", resembles a network, and that the "stuff" in it is just how we perceive particular local structures.

The network is only a geometrical analogy, there's no "space" between the nodes because the nodes don't represent anything concrete. You can describe the same network algebraically, but then you're left with no pictures to illustrate the article.

Re: What Is Spacetime, Really?

#77

Post by Xcelerate »

iandanforth wrote: post #45

At the risk of humor, this cartoon exactly summarizes my reaction to this post: http://www.smbc-comics.com/index.php?id=3805

I mean... I think deep down most (scientific) people think that's probably the fundamental truth. The challenge is in reifying the notion.

Let there be math, and then the laws of physics fall out as trivial tautologies.

Re: What Is Spacetime, Really?

#78

Post by nitrogen »

javajosh wrote: post #69
hyperion2010 wrote: post #68

Earlier quoted context omitted.

I would say that the physical processes that underlie our mental representations of concepts are fundamentally not serialized (part of why it is often so hard to put thoughts into words). They are non local in the sense that many different actors can operate on the data at the same time to create or modify some higher dimensional state and are not necessarily contingent on prior state in the way parsing is. You can't…

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?

Re: What Is Spacetime, Really?

#79

Post by justifier »

justifier wrote: post #70

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

Re: What Is Spacetime, Really?

#80

Post by FeepingCreature »

Pharaoh2 wrote: post #56
j2kun wrote: post #50

Earlier quoted context omitted.

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.

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.

https://en.wikipedia.org/wiki/Dovetailing_%28computer_scienc...
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