The quantum source of space-time • Hacker News Board

Re: The quantum source of space-time

#111

Post by typon » Wed, Nov 18, 2015, 6:18 PM UTC

lisper wrote: post #104

typon wrote: post #102

Earlier quoted context omitted.

You sound a lot like Sean Carrol in this video: https://www.youtube.com/watch?v=GdqC2bVLesQ Being so sure about your position when it isn't proven is a pretty bad way to do science. You're essentially implying that 3/4 people on that stage are wrong or idiots. I don't buy it.

I'm on the road with extremely limited internet connectivity so I can't watch a video at the moment. But may I make a suggestion? Why don't you read my paper or watch my video before you decide that I'm wrong. In fifteen years, no one who has actually read it has taken issue with it. (And, BTW, the only reason it isn't a published peer-reviewed publication is that when I submitted it, it was rejected on the grounds t…

Never said you're wrong. You may be right, I don't know. I just know that I don't believe you when you say extremely intelligent experts in the field are all wrong, except for one camp (they can even be a majority). I just have an epistemological problem with your views.

Re: The quantum source of space-time

#112

Post by lisper » Wed, Nov 18, 2015, 6:27 PM UTC

Confusion wrote: post #81

lisper wrote: post #52

Earlier quoted context omitted.

It's only disputed by people who haven't actually looked at the math. And I didn't say the state of the particle was already determined. It wasn't. Yes, of course superpositions are real. Yes, of course the Bell inequalities are violated. Yes, this eliminates all local hidden variables theories. Yes, it seems like this necessarily leads to the conclusion that there is spooky action at a distance. But that's wrong. To…

I think this is merely a terminological difference. What happens is: - before observing one particle, observations on the other particle are described and predicted by an entangled, superposition, state. - after observing one particle, observations on the other particle are described and predicted by a non-entangled, non-superposition state. The possible outcomes of the observations on the other particle, both predic…

In some sense, yes, this is just quibbling over terminology (as all pedagogical issues ultimately boil down to terminology). But the terminological quibble is very subtle and profound.

> after observing one particle, observations on the other particle are described and predicted by a non-entangled, non-superposition state.

This is the misleading part. It is not true in an absolute sense. It is only true for the observer that makes the "first" measurement (with "first" in scare quote because relativity). It is not true for the observer of the "other" particle. There is no measurement that can be made on the "other" particle that will tell you if the first particle has been measured.

> The possible outcomes of the observations on the other particle, both predicted and measured, are different after the observation on the first particle.

This too is misleading because it assumes that "possibility" is a universal property and it isn't. The "possible" outcomes for the "other" particle change for the observer of the "first" particle, but not for the observer of the "other" particle. And even this is not quite right because it depends on whether the observations are time-like or space-like separated, and whether or not there is a classical communications channel open between the two observers. It gets complicated. Read the paper.

Re: The quantum source of space-time

#113

Post by contravariant » Wed, Nov 18, 2015, 6:31 PM UTC

jessriedel wrote: post #89

semi-extrinsic wrote: post #37

Earlier quoted context omitted.

I believe Maldacena's 1999 paper [1] proving the AdS/CFT correspondence is the most cited in theoretical physics in the last 50 years. It's an incredibly nice result that is almost impossible to explain to laymen. (You did a pretty good job.) [1] https://scholar.google.no/scholar?cluster=132568844183140142...

Maldacena conjectured a correspondence. It's never been proven.

He managed to prove it quite rigorously for a specific example, which is the paper semi-extrinsic mentioned. He did indeed not prove the correspondence in general, but even this 'limited' example already turned out to be immensely useful.

Re: The quantum source of space-time

#114

Post by nhaehnle » Wed, Nov 18, 2015, 7:09 PM UTC

Retra wrote: post #109

criddell wrote: post #98

Earlier quoted context omitted.

> Mathematics is a human language for studying the structure of various experiences I think you are getting hung up on the semiotics of mathematics which is indeed a human construct. The idea of "1 + 1 = 2" is true no matter how (or if) you represent the idea. > saying that it's a "mathematical structure" is just saying that it's a structure that humans can apply mathematics to model That's not what the theory says (…

The math universe hypotheses assumes a very strict Platonist POV, which is not really a justifiable position, in my experience. >The idea of "1 + 1 = 2" is true no matter how (or if) you represent the idea. That's really a triviality, though. If you have the idea that 1+1=2, then yes, it's true. Usually people say mathematical theorems are true in "all possible universes", but the way they select which universes are…

> 1+1=2 is only true because it doesn't contradict our experiences.

Not quite. In the mathematical sense, 1+1=2 is true because (a) it is a well-formed sentence in a certain formal system and (b) there exists a proof of it in that formal system. The formal system consists of a grammar for well-formed sentences as well as rules for deriving true sentences.

The key point here is that the definition of "true" is part of the definition of the formal system. Unlike in philosophy, we have a clear and unambiguous definition of what "true" means, and its evaluation does not depend on properties of our physical universe.[0]

So when people say that "mathematical theorems are true in all possible universes", they're well-intentioned but I would argue that they are misleading. The deeper (philosophical) truth is that the (mathematical) truth of mathematical theorems is independent of universes[1].

[0] The fact that our minds are drawn to thinking about the specific type of formal systems that are usually considered to be reasonable foundations for mathematics may well be a consequence of the properties of our physical existence.[2] However, if by some magic the definitions of formal systems studied by alien civilizations in a different physical universe were to be transmitted to us, we would be able to arrive at the same conclusions about those systems as the aliens, and vice versa. There would be no disagreement about what sentences are true in such an alien formal system.

[1] Where I use the word "universe" in the physical sense and not in the sense that is found in set theory and its ilk.

[2] However, I personally don't think so. I believe (though I cannot prove it) that something like the Church-Turing hypothesis also applies to foundational formal systems at least up to basic set theory (possibly minus the axiom of choice). It is conceivable that some alien civilization in a much stranger universe would consider a certain extension of our set theory as the natural choice for mathematical foundations, but they would recognize our set theory as a subset of what they're studying.

Re: The quantum source of space-time

#115

Post by duaneb » Wed, Nov 18, 2015, 8:11 PM UTC

criddell wrote: post #93

duaneb wrote: post #74

Earlier quoted context omitted.

Why do you (and others) tend towards arguments suggesting simulations? To me, the language here is important. Both simulation and computation imply (to me) a tool and a user of the tool. Even a broader interpretation of computation as, umm, the efficient transfer of precise information through spacetime in certain shapes (which is easily providable by our understanding of physics today) requires an observer to extrac…

What do you feel about the mathematical universe hypothesis[1]? If I understand it correctly (and I probably don't), it says that the universe is literally mathematics. Not that it's a manifestation of mathematics or can be modeled by mathematics, but is 100% mathematics. I think that fits the computation model and doesn't require an observer or operator. [1]: https://en.wikipedia.org/wiki/Mathematical_universe_hypot…

I actually love that theory because it makes me feel warm and fuzzy. However, it is.... Highly hard to defend, to say the least.

Re: The quantum source of space-time

#116

Post by Retra » Wed, Nov 18, 2015, 10:18 PM UTC

nhaehnle wrote: post #114

Retra wrote: post #109

Earlier quoted context omitted.

The math universe hypotheses assumes a very strict Platonist POV, which is not really a justifiable position, in my experience. >The idea of "1 + 1 = 2" is true no matter how (or if) you represent the idea. That's really a triviality, though. If you have the idea that 1+1=2, then yes, it's true. Usually people say mathematical theorems are true in "all possible universes", but the way they select which universes are…

> 1+1=2 is only true because it doesn't contradict our experiences. Not quite. In the mathematical sense, 1+1=2 is true because (a) it is a well-formed sentence in a certain formal system and (b) there exists a proof of it in that formal system. The formal system consists of a grammar for well-formed sentences as well as rules for deriving true sentences. The key point here is that the definition of "true" is part of…

If you received a formal statement from an alien in another universe, it might not even look formal from your perspective. Mathematical theorems are not necessarily independent of universes, because those factors we consider necessary for formalization may not apply in other universes. You don't know if contradictions in this universe must be contradictions elsewhere.

Re: The quantum source of space-time

#117

Post by semi-extrinsic » Wed, Nov 18, 2015, 11:28 PM UTC

lisper wrote: post #71

semi-extrinsic wrote: post #66

Earlier quoted context omitted.

(Not constructive, but OK: Obviously a blog is not a journal paper, but it doesn't try to look like one either. It does have references to the journal papers it discusses though. As for the Cerf and Adami paper you linked above: from my searching it appears this is not published anywhere, it's just a 15-year-old preprint on the arXiv.) So, to be clear: you are advocating some interpretation of quantum mechanics (for…

> I believe this interpretation fails to explain experiments where people have entangled particles with timelike separation [1] I don't have time to read that paper right now, but it sounds like simple entanglement transfer, not unlike what is done for "quantum teleportation." In any case, the math behind QIT is simply the math of QM, so anything that QM can explain, QIT can explain. [UPDATE:] There was a published v…

I'm not sure what you mean by "There is essentially no dispute over the facts any more." As far as I understand, no-one has been able (yet) to make a prediction based on the many-worlds interpretation that could (even in theory, with infinite resources and time) be tested experimentally. Same goes for the Copenhagen interpretation. Thus neither of these are proper scientific theories (in the sense of Popper), and so we call them "interpretations". In light of this I don't understand how you can claim it is settled in favor of one side or the other?

Re: The quantum source of space-time

#118

Post by criddell » Wed, Nov 18, 2015, 11:41 PM UTC

Retra wrote: post #109

criddell wrote: post #98

Earlier quoted context omitted.

> Mathematics is a human language for studying the structure of various experiences I think you are getting hung up on the semiotics of mathematics which is indeed a human construct. The idea of "1 + 1 = 2" is true no matter how (or if) you represent the idea. > saying that it's a "mathematical structure" is just saying that it's a structure that humans can apply mathematics to model That's not what the theory says (…

The math universe hypotheses assumes a very strict Platonist POV, which is not really a justifiable position, in my experience. >The idea of "1 + 1 = 2" is true no matter how (or if) you represent the idea. That's really a triviality, though. If you have the idea that 1+1=2, then yes, it's true. Usually people say mathematical theorems are true in "all possible universes", but the way they select which universes are…

> I would put words in whatever order was most useful to them to employ for the construction and manipulation of tables. Anything else would be meaningless

Is your objection to the mathematical universe mostly that it's not useful to know everything is just mathematics? That our reality is essentially the same as if it were a simulation is just trivia but doesn't help you make a table?

Re: The quantum source of space-time

#119

Post by Retra » Thu, Nov 19, 2015, 3:32 AM UTC

criddell wrote: post #118

Retra wrote: post #109

Earlier quoted context omitted.

The math universe hypotheses assumes a very strict Platonist POV, which is not really a justifiable position, in my experience. >The idea of "1 + 1 = 2" is true no matter how (or if) you represent the idea. That's really a triviality, though. If you have the idea that 1+1=2, then yes, it's true. Usually people say mathematical theorems are true in "all possible universes", but the way they select which universes are…

> I would put words in whatever order was most useful to them to employ for the construction and manipulation of tables. Anything else would be meaningless Is your objection to the mathematical universe mostly that it's not useful to know everything is just mathematics? That our reality is essentially the same as if it were a simulation is just trivia but doesn't help you make a table?

Pretty much. You say it's all mathematics, I'll say it's a simulation. Or maybe it's a dream. Or a the manifestation of another being's will. Or something completely incomprehensible.

Why should anyone care that it's mathematics? It's certainly not like any mathematics that we know; we can't do it some other way if we don't understand it. It's too big to fit in a brain, and too complex to simplify accurately. Since we don't understand its axioms, how do we know they form a mathematical structure?

Re: The quantum source of space-time

#120

Post by criddell » Thu, Nov 19, 2015, 4:07 AM UTC

Retra wrote: post #119

criddell wrote: post #118

Earlier quoted context omitted.

> I would put words in whatever order was most useful to them to employ for the construction and manipulation of tables. Anything else would be meaningless Is your objection to the mathematical universe mostly that it's not useful to know everything is just mathematics? That our reality is essentially the same as if it were a simulation is just trivia but doesn't help you make a table?

Pretty much. You say it's all mathematics, I'll say it's a simulation. Or maybe it's a dream. Or a the manifestation of another being's will. Or something completely incomprehensible. Why should anyone care that it's mathematics? It's certainly not like any mathematics that we know; we can't do it some other way if we don't understand it. It's too big to fit in a brain, and too complex to simplify accurately. Since w…

> Why should anyone care that it's mathematics?

Well, if the universe is a simulation, then you can start poking around for the limits of the simulation and finding out new things is something that lots of people enjoy.

http://www.technologyreview.com/view/429561/the-measurement-...