Marshall, I would keep in mind that good intentions are not sufficient for getting your comments up-voted. They need to contribute to the discussion. Since your account was deleted, we can't to judge one way or the other.

I think there is some truth to Marshall's critique and that the situation could be easily improved by making it clear (either on the "about" page or in some other high-visibility note) what the guidelines for voting are. That means guidelines would have to be agreed upon. Until that happens, I suspect people will continue to just vote up comments they agree with, stifling debate.

I've previously suggested a change to the voting system, but this might require more man-power to implement than is available.

I'm confused. What is the relationship between Alcor and the Cryonics Institute? Is it either-or? What is the purpose of yearly fees to them if you can just take out insurance which will cover all the costs in the event of your death?

Eliezer, I believe that your belittling tone is conducive to neither a healthy debate nor a readable blog post. I suspect that your attitude is borne out of just frustration, not contempt, but I would still strongly encourage you to write more civilly. It's not just a matter of being nice; rudeness prevents both the speaker and the listener from thinking clearly and objectively, and it doesn't contribute to anything.

G端nther: Of course my comments about Barbour were (partially) ad hominem. The point was not to criticize his work, but to criticize this post. Very few people are qualified to assess the merit of Barbour's work. This includes, with respect, Eliezer. In the absence of expertise, the rational thinker must defer to the experts. The experts have found nothing of note in Barbour's work.

Albert Einstein was not performing philosophy when he developed GR. He was motivated by a philosophical insight and then did physics.

You've drawn many vague conclusions (read: words, not equations or experimental predictions) about the nature of reality from a vague idea promoted by a non-academic. It smacks strongly of pseudo-science.

Julian Barbour's work is unconventional. Many of his papers border on philosophy and most are not published in prominent journals. His first idea, that time is simply another coordinate parameterizing a mathematical object (like a manifold in GR) and that it's specialness is an illusion, is ancient. His second idea, that any theory more fundamental than QM or GR will necessarily feature time only in a relational sense (in contrast to the commonly accepted, and beautiful, gauge freedom of all time and space coordinates) is interesting and possibly true, but it is most likely not profound. I can't read all of his papers, so perhaps he has some worthwhile work.

This post, however, appears to be completely without substance. What is the point?

That the universe as we understand it is best described by a timeless mathematical object (e.g. a manifold equipped with some quantum fields)? This viewpoint, taken by most physicists, has been around since at least the 1920's. While profound, it has little to do with Barbour's work, which seems to be the focus of this post.

That the next theory of physics should be expressed with a "relational approach"? This is a nice idea, but one which has (to my knowledge) produced no objective progress in formulating a successor to GR or QM. There are a thousand approaches out there with similar promise...and similar results.

I can't help but feel that you are wading into waters which are above your expertise.

I definitely agree that there is truth to Max Planck's assertion. And indeed, the Copenhagen interpretation was untenable as soon as it was put forth. However, Everett's initial theory was also very unsatisfying. It only became (somewhat) attractive with the much later development of decoherence theory, which first made plausible the claim that no-collapse QM evolution could explain our experiences. (For most physicists who examine it seriously, the claim is still very questionable).

Hence, the gradual increase in acceptance of the MW interpretation is a product both of the old guard dying off and the development of better theoretical support for MW.

Psy-Kosh: Oh, I almost forgot to answer your questions. Experimental results are still several years distant. The basic idea is to fabricate a tiny cantilever with an even tinier mirror attached to its end. Then, you position that mirror at one end of a photon cavity (the other end being a regular fixed mirror). If you then send a photon into the cavity through a half-silvered third mirror--so that it will be in a superposition of being in and not in the cavity--then the cantilever will be put into a correlated superposition: it will be vibrating if the photon is in the cavity and it will be still if the photon is not. Of course, the really, really super-hard part is getting all this to happen without the state decohering before you see anything interesting.

Robin Z: The motivation for suspecting that something funny happens as you try scale up decoherance to full blown many-worlds comes from the serious problems that many-worlds has. Beyond the issue with predicting the Born postulate, there are serious conceptual problems with defining individual worlds, even emergently.

The motivation for doing this experiment is even more clear: (1) The many-worlds interpretation is a fantastically profound statement about our universe and therefore demands that fantastic experimental work be done to confirm it as best as is possible. (For instance, despite the fact that I very confidently expect Bell's inequality to continue to hold after each tenuous experimental loophole is closed, I still consider it an excellent use of my tax dollars that these experiments continue to be improved). (2) Fundamental new regimes in physics should always be probed, especially at this daunting time in the history of physics where we seem to be able to predict nearly everything we see around us but unable to extend our theories to in-principally testable but currently inaccessible regimes. (3) It's just plain cool.

Psy-Kosh: It is an awesome experiment. Here are links to Bouwmeester's home page , the original proposal, and the latest update on cooling the cantilever.(Bouwmeester has perhaps the most annoying web interface of any serious scientist. Click in the upper left on "research" and then the lower right on "macroscopic quantum superposition". Also, the last article appeared in nature and may not be accessible without a subscription.)

Obviously, this is a very hard experiment and success is not assured.

Also, you might be interested to know that at least one other group, Jack Harris's at Yale, is doing similar work.

Excellent post Eliezer. I have just a small quibble: it should be made clear that decoherance and the many worlds interpretations are logically distinct. Many physicists, especially condensed matter physicist working on quantum computation/information, use models of microscopic decoherance on a daily basis while remaining agnostic about collapse. These models of decoherance (used for so-called "partial measurement") are directly experimentally testable.

Maybe a better term for what you are talking about is macroscopic decoherance. As of right now, no one has ever created serious macroscopic superpositions. Macroscopic decoherance, and hence the many worlds interpretation, rely on extrapolating microscopic observed phenomena.

If there's one lesson we can take from the history of physics, it's that everytime new experimental "regimes" are probed (e.g. large velocities, small sizes, large mass densities, large energies), phenomena are observed which lead to new theories (special relativity, quantum mechanics, general relativity, and the standard model, respectively). This is part of the reason I find it likely that the peculiar implications of uncollapsed hermitian evolution are simply the artifacts of using quantum mechanics outside its regime of applicability.

Here at UC Santa Barbara, Dirk Bouwmeester is trying to probe this macroscopic regime by superposing a cantilever that is ~50 microns across--big enough to see with an optical microscope!