Thursday, November 13, 2008

Quantum Physics Through Conversation

... but it's beginning to sound more like idle chat, rather than a rational conversation.

This news article is highlighting an appearance by the author Louisa Gilde to talk about her book "The Age of Entanglement: When Quantum Physics Was Reborn". That's fine and dandy, but there's so many things that are wrong with the article itself, I don't know where to begin!

This reaction is called entanglement. Physicists have described it with words like telepathy, teleportation, ghost waves. And for more than 30 years, established physics denied that it existed.


Yowzah! Physicists have NEVER called it "telepathy". And for more than 30 years, established physics denied it? When did this happen? As far as I can tell, when EPR came up with the "paradox" for entanglement, no one denied that that is what QM tells us. Since that time, however, there was no way to make any experimental test of EPR-type phenomena until John Bell devised a cleaver way to check for a violation of local realism. That's when things took off, but before that, the discussion and debates were simply on a matter of tastes, since none of them can be tested. But who's denying what here?

Entangled particles can transmit information faster than light.


Not true. It is non-local, yes, but NOTHING is transmitted. We detect NO SIGNAL of any kind (no hidden variables either) that went from one particle to the other. So nothing gets transmitted faster than light. In fact, the whole process of entanglement cannot transmit signal faster than light. This is different than saying the process is non-local, which is not unusual in QM because one can also say that an electron in an atomic orbital is also non-local.


This tension, in fact, kept entanglement from being studied for decades. Even in the late 1990s, Gilder had never met the idea in a physics class, and it did not exist in the index of her textbook, though the first experiments that proved it were published in the 1970s.

In a philosophy of science class, Gilder read a paper by David Mermin explaining entanglement.

"I though, this is why I want to study physics. Why did my professors never tell me about this?" she said. "Clauser is eloquent on how much stigma there was and is" around the idea.


This is very strange. I don't know what she encountered, but entanglement is in any standard QM text even if it isn't called that way! For example, try setting up a 2-spin system and finding the Clebsh-Gordon coefficient. When you look at the spin state equation, those 2 spin are ENTANGLED! Or what about when one deals with a Fermi-Dirac systems? You set up a system with an asymmetric wave function, and often, the spin are aligned in such a way to preserve the asymmetry. When that happens, the spins are entangled! So entanglement is quite present in standard QM classes. She just can't find it the "index of her textbook" because it isn't always called that. But the phenomena is still the SAME and it is there!

Entanglement is a theory, Gilder makes plain, not a mystical vision.


Entanglement is NOT a theory. It is a consequence of the formalism of quantum mechanics, the same way superposition is not a theory. That was the whole point of EPR paper, to apply QM and show that it resulted in an entanglement whereby an apparent superluminal, instantaneous events can take place.

I always find it amazing that people can write whole books on something that they understand only superficially.

Zz.

8 comments:

Peter Morgan said...

Zz, perhaps the article deserved to be nailed for a few things, and you did it good. Then you went too far. The journalist has written a few bad comments in an article about a book that you haven't seen, but your last sentence nails the book, "I always find it amazing that people can write whole books on something that they understand only superficially."

Not nice, Zz. Remember what you've said about journalists in the past?

Although you finish so baldly, I admit that you start off with an only slightly reserved comment that Gilder's title is "fine and dandy", but otherwise you're fairly clear at the beginning that it's the article itself that you're tilting at.

From the article, indeed, there's some reason to take the book at least a little seriously. It looks as if "William Wootters, a professor of physics at Williams College" pretty much endorses the book, "She has been very careful in researching the subject," he added, and in explaining the theory lucidly. "I am impressed", so the book itself might be OK, perhaps, as a classic example of journalism about quantum theory? I suppose it will have a few mistakes, a few sensationalisms, it seems to have taken a biographical approach to the ideas, but perhaps it might be more-or-less OK as a whole and bring some kid or whoever to Physics.

Finally, though I could as usual go on a bit, I thought the journalist herself did a fair job in this: She found this tension between the physical and the insubstantial going back to the roots of quantum physics. Niels Bohr, whose Copenhagen school founded and dominated quantum theory until the 1990s, insisted that when scientists tried to observe a particle or a wave or a molecule, they changed it. Gilder condensed his argument to: "We can't picture it."

Einstein answered, "you won't get far if you can't picture anything," she said.
Really, it was the 1990s when suddenly the hegemony of Copenhagen collapsed, and alternative understandings of QM became possible in polite company, if they were carefully done, without some Old Guy shouting at you -- yes, they did -- and visualization is a key issue for a common kind of (limited) mathematical mind.

ZapperZ said...

Er.. come again?

You'll notice that the blog entry was NOT a review of the book. That would have been totally silly and totally out of my character to make a review of something that I haven't read and, that I've only understood superficially based on this news report. So your comment on how impressive the book is as commented by others is irrelevant. It wasn't about the book, it was about the NEWS report on the book and what the reporter wrote, including quotes from the author herself.

Whether she understood what she wrote is definitely questionable. Based on what she said, I don't think so. I don't trust anyone who haven't worked through the intricate details of QM to actually have a feel for it (including all its weirdness and subtleties) beyond just a superficial understanding of it. So is this out of line?

I have already written a blog entry on why QM is so difficult, and why the overemphasis on "visualization" can often lead to misunderstanding, especially among those who haven't studied it. Just because someone can "visualize" some aspect of QM doesn't mean that the visualization is accurate! I've seen a lot of visualization that are often rife with outrageous assumption and extrapolation. I'd rather they have no visualization at all then have something that bad.

Zz.

Peter Morgan said...

I come again.

Your final comment, Zz! "I always find it amazing that people can write whole books on something that they understand only superficially."

Is that not a comment on the book? Most of your post is certainly about the article, I go out of my way to accept that, but then this. My "comment on how impressive the book is" would not, I think, warm the author's heart. My impression is that Wootters' comment may well be coded.

In your comment on mine, I think you segue from the author of the article to the author of the book, based on what the author of the article chose to quote, which I suppose is part of what the author of the book said that the author of the article understood.

The Amazon page on the book is kinda interesting. It looks like the book has a quite striking jacket (indeed, the jacket has roused some strongly positive response at "http://nytimesbooks.blogspot.com/2008/10/age-of-entanglement-when-quantum.html"). The reviewers listed will make you suspicious, if you're like me, but unsurprisingly they say glowing things.

When an author reportedly spends 8 years of her life on a biography of Physics, as this perhaps might be called, particularly after reading the Amazon blurb, would we rather have no comment in a local newspaper on a local event because a journalist who understands every last subtlety of QM cannot be found? Would then Physics die of its isolation in esoterica? It seemed to me, anyway, that not everything written by this journalist was beyond hope, even though I agreed with you that she should be nailed for a few things.

OK. Now the killer. Google is great. You can really see where she's from in an hour-long video, http://video.google.com/videoplay?docid=-2670407799997768291.
OMG. Zz. Note the amazing venue, then skip the first two minutes, then Kill Me Now. I made it to ten minutes in the interests of research.

I agree with your excoriation of visualization, albeit without the blood pressure.

ZapperZ said...

That comment "I always find it amazing that people can write whole books on something that they understand only superficially." is the comment on the author, NOT the book. As I've stated both in the blog entry and in my first reply, it is my impression that the author has only a superficial knowledge of QM based on what she has said in the news report/interview. How else can one explain why she didn't realize that "entanglement" is done in a standard QM text, even when it isn't called that, and that she thought entanglement is a "theory"? Thus, I think I have strong evidence, accompanied by her academic background, that she has only a superficial knowledge of QM, but still thinks that she can write a book about it. That statement isn't a review of her book, but about her.

Zz.

George said...

Read the book and you will find Louisa agrees with virtually all your comments, but she puts them into more vivid historical context than anyone else has before her. When she began the book, John Bell was virtually unknown. By the time she finished he was the most quoted physicist in the professional literature. If you read Bell (and Louisa) you will know why.

George Gilder

ZapperZ said...

Er.... When did she started writing her book? In the 1980's? When was Aspect's first experiment? Are you telling me that her book was the one responsible for Bell being well known, and not Aspect's experiment?

And since when is Bell "... the most quoted physicist in the professional literature..."? What citation index did you use to come up with that claim? Until recently, the BCS paper was the most, if not one of the most, cited paper in physics. That "B" in BCS isn't "Bell".

Zz.

George said...

Obviously I am not saying that she made Bell famous. Knopf just published her book last week. But Bell became famous (most quoted physicist according to a reputable index) long after she identified the significance of his inequality as an undergraduate physics student at Dartmouth in 2000. She is a 30 year old writer of history, not a professional physicist. As a professional physicist, you know about Clauser, Aspect, Zeilinger, Gissin, Horne, Bertlmann, Holt, Shimony, and the scores of other key figures she interviewed at length for her history. But most of the world doesn't. That's why she wrote the book. She wanted to convey the excitement and controversy surrounding the pursuit of truth in physics. It is for others to judge her success. But the article you quote does not accurately represent the quality of the research in the book.

Overall, fascinating blog.

GG

George said...

That's intriguing. Bardeen, Cooper, Schriefer (is that the right spelling?) ranked behind EPR as I understand it. Or is it only that EPR is Einstein's most quoted paper, which is a remarkable testament to the increasing centrality of entanglement in physics, Louisa's point in her history.

As for Bardeen, beyond his quotable role in superconductivity, he is one of the most quoted in the semiconductor industry as well, as an inventor of the point contact transistor and theoretician of transistor action.

GG