[spacehome]

Yes! But the best theory is not Copenhagen or Pilot Wave.

Eliezer Yudkowski has a brilliant treatise on the Many Worlds interpretation here: http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ that really should be required reading for anyone that wants to talk intelligently on the subject.

Edit: seriously, don't even bother reading the article. It (like most science journalism) is garbage. Take the time to work through Eliezer's sequence.

[acqq]

So please explain in a few sentences what is that that Yudkowski writes, did he make any new contribution to the standard model or made something else or do you agree that the standard model is the most researched and most usable model up to now, and he just made a lot of posts where he just writes a lot of text?

I see a lot of links in the article you gave, but I don't understand what we're supposed to discover in Yudkowski's writings after trying to follow most of them. There's a lot of free text, not much physics. The standard model is a lot of smart formulas supported by the decades of expensive elaborate measurements (and vice versa), however his texts look more like writings of some philosophy student who knows a little of the math than like a physicist's material. I'd also really welcome opinions of professional physicists.

Edit: Wikipedia entry about him seems to fit my impression: http://en.wikipedia.org/wiki/Eliezer_Yudkowsky "Yudkowsky (...) is an American blogger, writer, and advocate for Friendly artificial intelligence (...) Largely self-educated."

[Sharlin]

The Standard Model does not concern itself with the various interpretations of quantum mechanics. It can, as of now, neither verify or falsify any of the interpretations which, consequently, are not scientific theories or even hypotheses, but firmly on the side of philosophy of physics. The interpretations are attempts to answer why Nature works as it does, within the framework of the Standard Model which only appears to answer the question how.

Yudkowsky certainly hasn't invented the many worlds interpretation, which was originally formulated by the physicist Hugh Everett in 1957. Even though originally scorned, in the more recent times it has gained popularity among physicists. The series of blog posts by Yudkowsky are (in my opinion, at least) a persuasive argument in its favor against the competing interpretations, and are very much recommended reading for anyone who would like to better understand the issue.

[acqq]

> the interpretations which, consequently, are not scientific theories or even hypotheses, but firmly on the side of philosophy of physics.

Thanks, that's exactly what I wanted to know.

I'm completely satisfied with the "shut up and calculate" approach. For me, until somebody shows that he/she can calculate (that is, predict) more than what physicists achieve, they are the ones the closest to "the truth" and not the "interpreter."

[spacehome]

Bring it back to the scientific method. The way to differentiate between competing hypotheses is by devising experiments that falsify some of them, and then running the experiments and either falsifying or failing to falsify them.

The issue here is subtle, and it's that the most popular interpretation, Copenhagen, isn't a complete theory because it doesn't tell you algorithmically when collapse occurs. For any possible algorithmic way to handle collapse, there's a corresponding experiment that could (at least in theory) differentiate between Copenhagen and Many Worlds. But the Copenhagen is inordinately slippery in that collapse is defined to occur ex post facto in whatever way is needed to make the experimental results match the theoretical results.

It's perhaps not so surprising that this shortcoming was overlooked in the beginning because Copenhagen was hypothesized before we really had a clear handle on the study of algorithms. But the fact that Copenhagen is still as popular as it is means that Yudkowski needs to spend a lot of time on philosophy of science, because that's what's holding back most people from seeing the problems with Copenhagen, and why at first glance it looks like philosophy.

[sriku]

spacehome suggested reading Elizer's posts on quantum physics precisely to not bother to deal with outdated statements like "the most popular interpretation, Copenhagen". Afaik, no serious physicist uses this any more, not even to explain quantum theory. To use wavefunction collapse to "explain" QM is like invoking "God" to explain the universe - i.e. it is not much of an explanation, and it raises more questions than it answers.

Text books ought to be rewritten to teach decoherence instead of outdated stuff like wave-particle duality, wavefunction collapse and such. That is the history of the development of QM and not QM as it is known today, in my limited knowledge.

If you get decoherence, much of the "mysteriousness" and "spookiness" that's talked about in such magazines just disappears and you find them all, every one of them, shallow.

[acqq]

I think I can agree with your first paragraph, even if I'd phrase it somewhat differently, but I don't see the connection between it and the next two.

[spacehome]

I certainly meant those three paragraphs to be connected; perhaps I'm just poor at explaining. As I mentioned, the shortcomings of the Copenhagen Interpretation are subtle, and I originally linked to Yudkowski's treatment because I believe he does much better job of explaining it than I ever could.

[scott_s]

Last week, I wrote a comment replying to someone asking, if we can't use experiments to determine which interpretation is better, what's the point? Rather than repeat myself, I'll just link to it: https://news.ycombinator.com/item?id=7940647

[acqq]

You say there: "How they lean will influence what sort of questions they investigate, how they investigate it, and what sort of outcomes they will look for."

If I understand you, we can expect that somebody is maybe going to be the first to discover something new thanks to the way he's used to think about the subject. Still, before that happens, what do we have?

Edit: Only real hard science. The discoverer we expect of course must decide from which side to attack the matter to reach the new discoveries.

[scott_s]

I don't know, but I'm not sure what you're asking. Kuhn's point (and mine, by transitivity) is that scientists are human with unavoidable biases, and these biases will influence what work they do.

The reason I don't know how to answer your question is that I interpret it to mean: what tangible result do we have before we have our first tangible result?

Of course, if that's not what you mean, then please clarify. You may want to read his book, though, as this concept is central to some of it. If you're saying, "what is the effect of such paradigms before they change," then it's best to read his book. One point he makes is that everyone operates under a paradigm, whether conscious of it or not. That is, we must think about our scientific work in some way, and whatever way we think about it will influence what scientific work we do. It is generally the case, though, that many people have some form of agreement on that "some way." When we do, that sets informal bounds on what is "acceptable science."

He does use quantum mechanics as an example, but that's loaded because we're still hashing it out. Another example he uses is phlogiston chemistry (http://en.wikipedia.org/wiki/Phlogiston_theory), which has thoroughly been supplanted. Those who first encountered oxygen were unable to recognize what it was because the paradigm in which they operated didn't contain the concept.

[GregBuchholz]

If you can get the same answers, with a simpler or more elegant theory, you might consider that a "better" theory. IIRC, initially the heliocentric theory of the solar system gave worse approximations of planetary positions than the highly refined epicycles of the geocentric models.

[danbruc]

IMHO the many worlds interpretation is one of the least appealing interpretation - millions of millions of millions of universes for nothing. What do you think about the following similar argument? Why are the laws of physics and the physical constants the way they are? There is a universe for every possible set of laws and constants and our universe just happens to be compatible with life. You can just render almost every interesting question moot with similar arguments - I would really prefer something more interesting at the heart of the universe.

[acqq]

On that level I don't have any problem with "many worlds" as it can be seen just a one more extrapolation of "we're not in the designed special position" principle: first we're not the center around which the planets circle, then our Sun also isn't the center of our set of stars, then our set of stars is one of many other galaxies... if our physical universe is just a lucky variant of other possible (and mostly uninteresting) universes, it at least doesn't appear surprising.

[danbruc]

But there is an important difference - you can observe the other stuff in our universe and therefore know that we are not (exceptionally) special in our universe. Other universes are usually per definition completely outside of our reach, as hard to grab as a god or Russell's teapot.

[acqq]

> completely outside of our reach, as hard to grab as a god or Russell's teapot.

I agree! As in my other comments here, as long as there isn't any scientific result, I also won't regard the products of the proponents of such "interpretations" better than you.

[spacehome]

Well, they're not completely outside our reach. Interference between our worlds and nearby ones is very testable, and the reason the theory exists.

[DavidPlumpton]

What's more likely? That quantum interference appears because many worlds perpetually exist, or because they seem to exist but somehow don't, or because they sometimes briefly come into existence, hang around for a bit and then randomly collapse breaking all sorts of laws (Liouville thereom, CPT invariance etc.)?

Many Worlds is much tidier than all the alternatives.hh

[eli_gottlieb]

Actually, I'd say the "illusion" option is the simplest and tidiest. It is more likely that we interpret a complicated reality from incomplete information than that reality truly is complicated.

[Jach]

Have you read Feynman's QED? It's a bit like that, in that it's meant for a layman, but with more algebra. Instead of abstract arrows, EY goes straight to complex numbers. It goes through a basic approach to quantum mechanics (taking diagrams from here for instance: http://www.qi.damtp.cam.ac.uk/node/60) in a modern way and tries to build an intuitive understanding of the subject, especially demolishing a lot of confusions one may have gained through popular media. He then departs from the basic theory to elaborate on why the collapse interpretation is ridiculous and why Many-Worlds makes more sense. You can stop when you get to the Timeless stuff.

You're not really going to find anything ground-breaking, but it may help your intuitions about QM even if you're a physicist. As a chapter from the Aaronson book (http://www.scottaaronson.com/democritus/lec9.html) I linked to in a cousin comment says in the first two paragraphs:

There are two ways to teach quantum mechanics. The first way -- which for most physicists today is still the only way -- follows the historical order in which the ideas were discovered. So, you start with classical mechanics and electrodynamics, solving lots of grueling differential equations at every step. Then you learn about the "blackbody paradox" and various strange experimental results, and the great crisis these things posed for physics. Next you learn a complicated patchwork of ideas that physicists invented between 1900 and 1926 to try to make the crisis go away. Then, if you're lucky, after years of study you finally get around to the central conceptual point: that nature is described not by probabilities (which are always nonnegative), but by numbers called amplitudes that can be positive, negative, or even complex.

Today, in the quantum information age, the fact that all the physicists had to learn quantum this way seems increasingly humorous. For example, I've had experts in quantum field theory -- people who've spent years calculating path integrals of mind-boggling complexity -- ask me to explain the Bell inequality to them. That's like Andrew Wiles asking me to explain the Pythagorean Theorem.

(And on EY himself, just read the million or so words of the Sequences and you'll see he is actually really smart across multiple domains. ;))

[acqq]

I never claimed that EY isn't smart, only that what he writes is not actually physics.

As much as I remember Feynman's lectures, he introduced the amplitudes very early?

[Jach]

Fair enough. I agree a large part of it isn't strictly physics, though I think in the beginning it's like the first couple weeks of a high school Mechanics class. Low on math, but you get to do or hear about experiments and how they ought to shape your view of what's going on. (Thinking of masses and acceleration and forces, thinking of complex amplitudes and decoherence.)

[sriku]

Yudkowsky's contribution is pedagogical rather than anything fundamentally new. He explains quite well in short the process of "decoherence" and links it well to the many worlds interpretation. He makes a case for why the "many worlds interpretation" is not really an "interpretation", but is just stating what the mathematics says on its face anyway .. and hence is the one we should adopt. In particular, he does a good job of connecting this to "timeless physics" - i.e. the Weyl equation for the "wavefunction of the universe" which does not have time in it.

[sriku]

edit: Sorry! Tongue of the slip. I was referring to the "Wheeler-DeWitt equation" [1] and not the "Weyl equation" [2].

[1] http://en.wikipedia.org/wiki/Wheeler%E2%80%93DeWitt_equation

[2] http://en.wikipedia.org/wiki/Weyl_equation

[DavidPlumpton]

Yudkowsky is more of an expert in reasoning than in Physics. For example, imagine you are a world class expert in Quantum Mechanics and you are asked to give a talk at a science club. You cover a lot of stuff and think "that was great". But somebody else tells you "that was terrible, you mumbled, you wrote illegible stuff on the board etc." and you realise it wasn't about QM, it was about public speaking.

Similarly physicists have done amazing work over the decades, and now it's time to draw conclusions from all that evidence. But it turns out that physicists are not domain experts in drawing conclusions from evidence. That kind of skill is a separate domain in its own right.

[gohrt]

The Standard Model is a model, not an interpretation. Whether Yudkowsky is right or wrong, anyone's interpretation is going to be text, not physics.

[X4]

May I add David Deutsch's (not yet peer-reviewed, but promising) paper on the Contructor Theory of Information?

The Physics arXiv Blog writes about it here: https://medium.com/the-physics-arxiv-blog/deeper-than-quantu...

For the curious, the link to the paper can be found at the end of the article.

I remember being downvoted by circle of HN folks who weren't comfortable with Information transfer using Quantum Teleportation. Depite efforts to refute it, here's a team that suceeded doing exactly this => http://phys.org/news/2014-05-team-accurately-teleported-quan...

[Jach]

While we're giving suggestions, I'd again point to Scott Aaronson's http://www.scottaaronson.com/democritus/default.html (also available in book form) and his blog in general (especially when quantum computers are in the news). His approach is unique to me in that it's a strongly computer science point of view.

Edit: Another link I remembered that's strongly in the vein of QM for programmers is (suitably titled) here: http://oyhus.no/QuantumMechanicsForProgrammers.html

[thedufer]

I'm skeptical, if only because this should be a big deal and hasn't gotten much press.

> We're able to set the spin (rotational direction) of these particles in a predetermined state, verify this spin and subsequently read out the data.

This is terribly unclear. I don't have access to the article - maybe its better explained there?

The problem with using quantum entanglement for information transfer is that you can't cause a particular spin at either location - they're just both reading random data that correlates. Nothing about this allows any actual transfer of information. Why are they not explaining how they got around this? That's the interesting bit, as far as I can tell.

[X4]

Paper in short: http://download.repubblica.it/pdf/2014/scienze/science-xpres...

Paper in full: http://arxiv.org/abs/1404.4369

To the physicists among the us, please share your opinion on the paper with the rest of us.

It's not easy to digest the paper. The finding is not only going to change finance, but also the whole data economy will speed up. Now 'Quants' can be located anywhere and everyone has can enjoy same advantage of datacenter-closeness, evening out the prestigious role of the select few. Well, not really. It's going to take quite some time until the mid-class can access this technology unless, someone finds out a way for mass-production. That would be stellar.

That's it. I hate nobody with a rational mind of whatever kind, but naysayers really itch me.

[millstone]

Luboš Motl reviewed it. http://motls.blogspot.com/2014/05/constructor-theory-deutsch...

He didn't like it, as if there were any doubt.

[Jach]

Not a physicist, but I don't think this is much to get excited about... There's no faster-than-light communication happening -- you'll note in the second paragraph that Alice must send the outcome of her measurement to Bob. It's a step towards impressive quantum computers, which will be cool to have so we can do things like Shor's algorithm or Grover's algorithm, but there's still a long way to go.

[thedufer]

> Alice sends the outcome via a classical communication channel to Bob, who can then recover the original state by applying the corresponding local transformation.

This seems to be the key point - there is absolutely no FTL information transfer going on, which is pretty much what I expected. As I said before, it would've been much bigger news if there was. The press article was clearly written by someone who didn't understand what was going on (or was intentionally deceitful, but that seems unlikely).

[im3w1l]

I'd like to propose a thought experiment that in my opinion speaks for a many world interpretation.

Imagine Schrödingers Cat. Only we have a physicist in the box instead! Also inside the box is a photon emitter programmed to send a photon after 30 seconds. Our dear physicist has been instructed to, if he is still alive after 20 seconds (adjusted to have 50% prob) to move the emitter just a tiny little bit to the left. Now according to the quantum laws, the photon from the original position should create an interference pattern with the photon from the slightly moved position... provided we succeeded in creating a superposition of dead/alive physicist. Of course, every single experiment would just give one detection, so we would have to do it many times, to really verify that it worked.

The experiment could of course be scaled up, so that we instead proved that we had superpositions of planets being blown up or something. At some point, when the system in superposition is large enough - or significant enough -, I don't see how you could refrain from calling that many worlds.

[ars]

https://en.wikipedia.org/wiki/Quantum_suicide

[im3w1l]

Since you only post a link with no comment text I don't really know what you mean to say with it.

Anyway, I think my proposal had a key advantage. The interference pattern could in theory be measured. We could get tables and graphs and sigma values.

[ars]

It was just a link to something that seemed very similar to what you said.

[jostylr]

The clearest version of Many Worlds that I have seen is from the "Bohmians": http://arxiv.org/pdf/0903.2211.pdf

Basically, you get a mass density on physical space by integrating over the wave function. Then you have correlations of changes in the mass density. Reality becomes a bit like fuzzy tv reception with overlapping channels.

There is no splitting of the universe or any other nonsense.

I still don't like the theory, but at least it is a well-defined theory.

[SilasX]

I want to upvote out of agreement, but I really, really hate when people recommend a very long work they expect me to read on faith without a summary of what it offers so I can know Of it's worthwhile.

Here's what I would have added: Yudkowsky explains quantum mechanics in terms of the decoherence interpretation and how it makes logical sense as following from a simple rule that nonetheless contradicted widely held philosophical assumptions that kept its simple truth from being appreciated.

[deutronium]

And why should we read Yudkowski instead, rather than other physicists on this matter, as far as I know he's not in a position of authority in this area.

[spacehome]

I would never say instead of. Read whomever you like; read them all. Though, I would suggest that anyone who still takes Copenhagen seriously really needs to digest that sequence.

Eliezer is a smart guy with great insights into how to think about questions. His "position of authority" is that he writes in a way that's clear and conveys meaningful novel insights. If you think that only Ph.D.s have insights worth reading you're missing out. There's nothing "new" or "publishable" in the sequence, but Eliezer collates a lot of good ideas and presents them well.

For what it's worth, I personally feel like I've learned a lot from reading him. I was just trying to share it in the hopes that someone else on HN may find him as insightful as I do, and the quantum physics sequence is one of his better works. It was just a friendly pointer. If you're not interested, disregard.

[SilasX]

>>And why should we read Yudkowski instead

>I would never say instead of.

When you recommend something, you're implicitly advocating that it be read in preference to other works on the matter.

It makes no sense to say "I recommend this, but it's no better than anything else."

[prutschman]

"I recommend this. Reading it is better than not reading it, and you may not have been aware of its existence."

The recommender is in no position to know whether your next-best alternative was reading another work on the subject or reloading hacker news or taking a nap.

[SilasX]

The recommendation and its follow-up question were about alternatives in the context of learning about quantum mechanics.