A Jewel at the Heart of Quantum Physics • Hacker News Board

Re: A Jewel at the Heart of Quantum Physics

#71

Post by redhat-reallyp » Wed, Sep 18, 2013, 4:26 PM UTC

has2k1 wrote: post #33

noonespecial wrote: post #5

Every once in a while I get the feeling that the greatest discoveries are still ahead and these next few decades might be the real "golden age of science". The "individual genius" phase is just behind us and the "collaborative brilliance" phase is just beginning.

It is possible that Gravity as we know it is an illusion. For example, the Newtonian take on Gravity was that it was a force. That according to Einstein was illusory, Gravity was really a geometric manifestation due to the curvature of space-time. With that take Gravity as we know it is different from the Gravity as was once known. However the Newtonian view that Gravity is a force can and still does facilitate usefu…

"Illusion" is a misleading way to put it.

We experience gravity as a force - we can measure it with devices designed to measure forces. It's not an illusion. However, the model of gravity as a force between massive objects does not capture certain aspects of gravity - it's an incomplete model.

That doesn't actually mean that gravity is "really a geometric manifestation due to the curvature of space-time". Gravity appears to behave that way, but what do you mean by "really" in that sentence? What we can say with confidence is that the spacetime curvature model is a more precise and complete model of gravity than the mass/force model.

Perhaps if we figure out how to unify quantum phenomena with gravitation, we'll find a different model for gravity in that context. Will you then say that gravity wasn't "really" spacetime curvature? That wouldn't make sense, because all that will have changed is that we would have another model for interpreting and understanding gravity.

When people say gravity is an "illusion" or that forces are "fictitious", what they're really getting at is that these observed phenomena are not fundamental - that they're consequences of some underlying phenomena. But they're real consequences, not illusory or fictitious.

(Of course "fictitious" is a technical term used in physics, but it doesn't mean "does not exist in reality" but rather means something more like "is not fundamental".)

Re: A Jewel at the Heart of Quantum Physics

#72

Post by vinceguidry » Wed, Sep 18, 2013, 5:01 PM UTC

redhat-reallyp wrote: post #67

vinceguidry wrote: post #60

Earlier quoted context omitted.

In other words you just spent a dozen or so paragraphs venting your bullshit detector in a space where numerous contributors that are much, much smarter than you have indicated otherwise. It's like inverse bike shedding.

Perhaps you missed the part of my very short comment where I wrote "I'm not dismissing that the work could have value, but the article makes claims that go far beyond anything that's been demonstrated." You might want to re-read my original comment and take note of the issues I commented on. If you disagree with what I'm saying, why not respond on those points? I can't help wonder if your problem is actually that I'm…

There's reasoned discussion of possible philosophical implications of the recent findings and then there's your post.

Re: A Jewel at the Heart of Quantum Physics

#73

Post by ars » Wed, Sep 18, 2013, 5:06 PM UTC

miloszf wrote: post #31

ars wrote: post #28

Earlier quoted context omitted.

> and objects move along geodesics You say that like it's so obvious. But why do they move in the first place?

In short because things move from a state of higher energy to lower energy. Not subduing yourself to gravity would take energy in opposite direction to counteract it (or the geometric slope in this analogy). Newtonian conservation of energy is a pretty good model analogy (although isn't the same thing) and the geometric one is even better. But that's all they are, however accurate - analogies, constructed on the basi…

> move from a state of higher energy to lower energy

And what's the difference between this and saying they experience a force?

Re: A Jewel at the Heart of Quantum Physics

#74

Post by ars » Wed, Sep 18, 2013, 5:08 PM UTC

textminer wrote: post #29

ars wrote: post #28

Earlier quoted context omitted.

> and objects move along geodesics You say that like it's so obvious. But why do they move in the first place?

Good discussion of your question: http://physics.stackexchange.com/questions/24359/why-do-obje...

That answers why they move along geodesics. It doesn't answer why they move.

Re: A Jewel at the Heart of Quantum Physics

#75

Post by wbhart » Wed, Sep 18, 2013, 5:16 PM UTC

The article states about unitarity and locality that "both are suspect". I'm happy for locality to be suspect, but in what sense is unitarity suspect? Surely only in the sense that it is apparently a consequence of more fundamental things. And when you think about it, that's philosophically amazing, that probabilities summing to one may have an underlying (timeless?) explanation. Or maybe I should infer that there has been some exaggeration!?

Re: A Jewel at the Heart of Quantum Physics

#76

Post by redhat-reallyp » Wed, Sep 18, 2013, 5:25 PM UTC

loup-vaillant wrote: post #70

redhat-reallyp wrote: post #13

Earlier quoted context omitted.

"it contains signs of a genuine conceptual breakthrough." It contains claims of such signs, which seems to be the point of this fluff piece. Alarm bells should go off when you read statements like this: "...giving up space and time as fundamental constituents of nature and figuring out how the Big Bang and cosmological evolution of the universe arose out of pure geometry." Ah yes, well that solves the mystery, doesn'…

> Ah yes, well that solves the mystery, doesn't it. The universe arose out of pure geometry. That was a serious hypothesis before this. Heard about Tegmark's level IV multiverse? It's the idea that every mathematical structure just "exists", like "poof magic", and the simpler ones would, like, have greater weight. Kind of a literal interpretation of Occam's Razor, really. A corrolary is, the simpler the laws of physi…

> That was a serious hypothesis before this. Heard about Tegmark's level IV multiverse?

Of course, I love Tegmark's speculative work. But that's all it is, speculative. It's like reading science fiction, one shouldn't confuse it with reality, at least not without evidence to justify that.

> It's the idea that every mathematical structure just 'exists', like 'poof magic', and the simpler ones would, like, have greater weight.

There's no evidence that this is how reality works, and there's no particular reason to think that it should work this way.

> A corollary is, the simpler the laws of physics are, the more probable the above hypothesis is. And suddenly we learn that the true laws of physics might be much simpler than we anticipated? This is huge. Or not.

All current evidence is that it's a fantasy, one which happens to be so attractive to some people that they're willing to suspend critical thinking to favor it, much as people do with belief in supernatural beings.

There are certainly cases where basic mathematical principles are expressed in a very direct way in the universe. Probability in quantum mechanics is one example, Noether's Theorem is another. But even in these cases, saying that some property of the universe arises from pure mathematics is misleading.

To boil down the objection, mathematics is a way to describe and model these phenomena, and shouldn't be confused with the phenomena themselves. Doing so is a map/territory style confusion.

If you want to say that the universe arises from pure mathematics, you then have to explain what sort of phenomenon pure mathematics is, that it is capable of producing such effects. To use my analogy, it would be a bit like saying "The topography of Earth arises from a pure map."

> The idea of a timeless universe, where our subjective notion of time just arise from its structure has been around for quite some… time.

That's a little different from the idea that reality is an incarnation of pure mathematics. In case, the fact that ideas have been around for some time has little bearing on their validity. Consider astrology.

> Likewise, Occam's Razor itself suggests that the true laws of physics are simpler than we think.

It does not actually suggest that in general. It can mean that in cases where an explanation contains unnecessary elements, but it says nothing about explanations necessarily being simple, or simpler than they already are.

> Plus, current human laws of physics are either false or incomplete.

I prefer to think in terms of models than laws, and models are always incomplete. The only complete model is the thing being modeled itself.

> I fully expect future physics to be further simplified. Claims of massive simplification are therefore not that surprising.

By your premise, actual simplification would not be surprising, but claims have no necessary correlation to actual simplifications.

Sorry to be picky!

Re: A Jewel at the Heart of Quantum Physics

#77

Post by redhat-reallyp » Wed, Sep 18, 2013, 5:30 PM UTC

vinceguidry wrote: post #72

redhat-reallyp wrote: post #67

Earlier quoted context omitted.

Perhaps you missed the part of my very short comment where I wrote "I'm not dismissing that the work could have value, but the article makes claims that go far beyond anything that's been demonstrated." You might want to re-read my original comment and take note of the issues I commented on. If you disagree with what I'm saying, why not respond on those points? I can't help wonder if your problem is actually that I'm…

There's reasoned discussion of possible philosophical implications of the recent findings and then there's your post.

At https://news.ycombinator.com/item?id=6406551 I'm having a reasoned discussion with someone who responded more substantively to what I wrote. Your petty sniping is not reasoned discussion.

Re: A Jewel at the Heart of Quantum Physics

#78

Post by redhat-reallyp » Wed, Sep 18, 2013, 5:53 PM UTC

ars wrote: post #73

miloszf wrote: post #31

Earlier quoted context omitted.

In short because things move from a state of higher energy to lower energy. Not subduing yourself to gravity would take energy in opposite direction to counteract it (or the geometric slope in this analogy). Newtonian conservation of energy is a pretty good model analogy (although isn't the same thing) and the geometric one is even better. But that's all they are, however accurate - analogies, constructed on the basi…

> move from a state of higher energy to lower energy And what's the difference between this and saying they experience a force?

You hit the nail on the head. The real issue is that the force is not considered fundamental, because it is explained by some other model such as spacetime curvature.

Re: A Jewel at the Heart of Quantum Physics

#79

Post by stan_rogers » Wed, Sep 18, 2013, 6:01 PM UTC

wbhart wrote: post #75

The article states about unitarity and locality that "both are suspect". I'm happy for locality to be suspect, but in what sense is unitarity suspect? Surely only in the sense that it is apparently a consequence of more fundamental things. And when you think about it, that's philosophically amazing, that probabilities summing to one may have an underlying (timeless?) explanation. Or maybe I should infer that there ha…

It's that "only" in "... only in the sense that ..." upon which the whole thing hangs. Presupposing unitarity (and locality) and constraining models to conform to that presupposition may be that complication, that blinder, that prevents discovery of the simpler underlying rule from which either or both emerge. And either or both may be necessary consequences of the much simpler, underlying rule (if there is one to be found), at least on the observable side of any predicted phenomena, but that can't be determined unless one is willing to first throw away the constraints that keep you from finding it. (In effect, it's analogous to simply adding two natural numbers directly rather than using Peano arithmetic and checking at each iteration that an increment occurs. Either way you will arrive at the same answer, but the unconstrained rules for addition allows for negative numbers and fractions.)

Re: A Jewel at the Heart of Quantum Physics

#80

Post by tokipin » Wed, Sep 18, 2013, 6:56 PM UTC

crntaylor wrote: post #27

Xcelerate wrote: post #25

This is really cool. I didn't understand most of it, even though I'm taking QFT right now. Shows you how deep the subject goes. On another note, if I see the word "illusion" or "illusory" one more time in these science blogs, I'm going to have a fit. This must be the meaningless new buzzword of the day. 1) Spacetime is not an "illusion" 2) Gravity is not an "illusion" 3) is not an "illusion". That doesn't even make s…

I think what they mean is that the force we call gravity is an illusion that we experience because we perceive spacetime as flat. In a curved spacetime, you don't need to posit a force to explain motion due to a nearby mass - the mass curves spacetime, and objects move along geodesics in the curved spacetime. So while it would be incorrect to say "gravity is an illusion" I think it makes sense to say "the force of gr…

He's probably quite aware of what the intended meaning is. The point is that since we're in effect always talking about 'verisimilitudes', calling this or that an "illusion" is silly, because it implies that we didn't realize our models are just models ("You mean to tell me the Standard Model isn't a 1-to-1 mapping from reality to our brains??? NOOOOO * worldview shattered * ").

For example, the spacetime explanation for gravity is also a model, and is also likely to be an "illusion." Making note of that is theoretical physics 101... or at least it should be.