Archives of In Our Time: Smolin, Gribbin and Greene

Every physics hobbyist should be familiar with the names of Smolin, Gribbin and Greene. All are literate physicists who've written excellent books and essays on tough topics, while still doing exciting research. If you're in this club, you'll love these superb In Our Time programs from the archives.

• Grand Unified Theory - 2000 - Brian Greene and Martin Rees
• Time - 1999 - Lee Smolin and Neill Johnson
• Quantum Gravity - 2001 - John Gribbin, Lee Smolin and Janna Levin

I'm a fan of Gribbin and Greene in particular. I tagged several Gribbin posts back when I was catching up with modern interpretations of Quantum Mechanics - before we started doing entanglement experiments with grossly macroscopic entities. Greene wrote the best modern physics book of the past decade (the non-string bits are the best), I'm way late to give it a review.

These gentleman turn out to be verbal gymnasts as well as physicists and writers. Really, it's not fair - but at least they share.

See also:

• Putting 'In Our Time' on your iPod (2006) - turn Real Audio stream into MP3
• In Our Time archives - EVERY EPISODE from Oct 15 1998 onwards
• Our Time: Symmetry, Moonshine, String Theory and E8
• Gordon's Notes: In Our Time (tag)

Three Shtetl-Optimized posts for livening the mind

I really need to study, so I'm noting these for future reading.

These are a set of Aaronson posts, found by tracing back from the latests, that taken together are very good reading in physics and philosophy:

• The relativity of originality
• His review of Wolfram (pdf)
• Newcomb's problem
• PHYS771 Free will

All the essays touch, more or less directly, on the question of whether "free will" (as Scott rigorously defines it) is possible. Note this is distinct from the concept of responsibility -- every reasonable thinker over the past few centuries has understood that "responsibility" is a social construction with no intellectual integrity.

By way of background scientists philosophers have gone back and forth on this since science was more or less born with Francis Bacon. Things looked particularly bad in the 20th century; in the absence of quantum mechanics general relativity seemed to predict a universe frozen in space-time, in which every moment occurred at once and invariably. Maybe this is where Vonnegut's Tralfamadorean determinism came from.

QM seemed to restore free will, but it introduced some disturbing predictions of its own. Physicists attempted to restore the concept of an observer-independent reality through the transactional interpretation, but that did in free will

More recently reality (or realism) seems to be out favor, so maybe free will is back.

Now you're prepped to read Aaronson.

PS. See also - Sean Carroll's favorite posts.

Quantum erasure and apple of the tree of knowledge

I skimmed the SciAM article on building a home "quantum eraser", but I didn't appreciate that the 1982 experiment is just one notch weirder than the what I'd read in Gribbin's 1997 book [1]. I realized how ++weird the result is upon reading Greenes description today [2].

As I dimly recall it, the "Aspect experiments" showed that the measured interference pattern that

• requires passage of a single photon through spatially separated paths simultaneously [3]

also

• requires no peeking after the photon has travelled the spatially separated paths
  

It's the "no-peeking after" part that made the experimental results so delicious. Causality (arrow of time), 1 dimensional time, and 3 dimensional space and "objective" reality all took big hits from the Aspect experiment. The discussion ever since has been which, if any, survived.

My weak understanding of Greenes' non-mathematical interpretation of the "erasure experiment was that the "no peeking after" clause is extended as follows:

and

• tricks that allow you to defer "peeking" until after the interference pattern ought to be formed don't work either (no surprise here, this is a variant of the Aspect experiment)
• if you set up a "deferred peeking" trick, but then undo it before you "peek", then the interference pattern can return. (surprise)
  

So it's the last bit that adds an additional note of sublime weirdness to the aspect experiment. It makes it just a bit easier to believe that the fundamental rule is really "no peeking". This is just something you can't know about.

It invariably reminds anyone taught by nuns of the "apple of the tree of knowledge" -- "but from the tree of the knowledge of good and evil you shall not eat, for in the day that you eat from it you will surely die.".

The universe seems to be telling us we can't watch some things too closely. Naturally, that only increases our appetite ....

[1] I really don't think Gribbin discussed this experiment, even though it was old when he wrote the book. It doesn't show up here either. I wonder why not ...

[2] Greenes is a cosmologist at heart, and he tends to shy away from the quantum weirdness Gribbin and others embrace, but he did a good job describing erasure.

[3] Paradox puzzles often require one to think carefully about what words mean, so I italicized a few of the interesting ones. Spatial separation, for example, has been shown not to mean what we thought it meant. Two entangled photons a universe apart are, by some measures, not separated at all.

Gingrich's Amazon reviews

I was reviewing Gribbin's "Kittens" book, when I came across a reasonable review written by Newt Gingrich. It wasn't an in-depth review, but it's likely he at least skimmed the book. It's not an easy book.

Gingrich was profoundly wrong headed and laid the way for Rove, but it's a measure of Rove/Cheney/Bush's incompetence and willful ignorance that nowadays Gingrich looks much the lesser evil ...

The cat is undead until you open the box ...

A week or so ago I commented on recent research that both affirmed instantaneous non-local correlation of entangled quantum entities and attacked "realism". I couldn't however, really tell from the article what was meant by "realism".

This summary from a physics journal fills the gap. "Realism" is a way of saying that the "way of things" is not altered by the act of our observing them. The research seems to affirm an interpretation of quantum mechanics that gives special power to the act of perceiving, namely the power to collapse a wave function .... (emphases mine)

Quantum physics says goodbye to reality (April 2007) - News - PhysicsWeb

... Some 40 years ago the physicist John Bell predicted that many hidden-variables theories would be ruled out if a certain experimental inequality were violated – known as "Bell's inequality". In his thought experiment, a source fires entangled pairs of linearly-polarized photons in opposite directions towards two polarizers, which can be changed in orientation. Quantum mechanics says that there should be a high correlation between results at the polarizers because the photons instantaneously "decide" together which polarization to assume at the moment of measurement, even though they are separated in space. Hidden variables, however, says that such instantaneous decisions are not necessary, because the same strong correlation could be achieved if the photons were somehow informed of the orientation of the polarizers beforehand. [jf: In the transactional interpetation the "informing" can occur by meaning-free "messages" that travel back in time.]

Bell's trick, therefore, was to decide how to orient the polarizers only after the photons have left the source. If hidden variables did exist, they would be unable to know the orientation, and so the results would only be correlated half of the time. On the other hand, if quantum mechanics was right, the results would be much more correlated – in other words, Bell's inequality would be violated.

Many realizations of the thought experiment have indeed verified the violation of Bell's inequality. These have ruled out all hidden-variables theories based on joint assumptions of realism ... [reality exists when we are not observing it].... and locality ... [separated events cannot influence one another instantaneously]. But a violation of Bell's inequality does not tell specifically which assumption – realism, locality or both – is discordant with quantum mechanics.

Markus Aspelmeyer, Anton Zeilinger and colleagues from the University of Vienna, however, have now shown that realism is more [?] of a problem than locality in the quantum world. They devised an experiment that violates a different inequality proposed by physicist Anthony Leggett in 2003 that relies only on realism, and relaxes the reliance on locality. To do this, rather than taking measurements along just one plane of polarization, the Austrian team took measurements in additional, perpendicular planes to check for elliptical polarization.

They found that, just as in the realizations of Bell's thought experiment, Leggett's inequality is violated – thus stressing the quantum-mechanical assertion that reality does not exist when we're not observing it. "Our study shows that 'just' giving up the concept of locality would not be enough to obtain a more complete description of quantum mechanics," Aspelmeyer told Physics Web. "You would also have to give up certain intuitive features of realism."

This article is the best so far, but there were a few awkward phrases. I've tried to edit it minimally to clarify.

My current (weak) understanding is that locality fell a while ago. There was still hope of preserving realism, but now realism is at least partly gone. We're well into the realm of Schrodinger's "cat" being both alive and dead until an "observer" inspects the cat. I think this result may favor the "decoherence" interpretation of QM, and goes against the "transactional" interpretation favored by (among others) Gribbin.

Alternatively, there's always the reassuring possibility that mathematics is a less trustworthy guide to reality than commonly thought...

Update 5/26/2007: It turns out that in 2004 I posted on a fascinating discussion about how reality can be emergently structured that seems to fit very well with this experiment. I need to find more along the lines of that 2004 post!

Gribbin, Wittgenstein, Amazon and the reasonable ineffectiveness of mathematics

The serendipity of modern life, abetted by the evolution of the podcast, the USB-equipped car stereo, and emergent algorithmic connections [1], has meant that I am simultaneously listening to a 2003 In Our Time podcast on Wittgenstein, reading a 1994 book by John Gribbin, and sluggishly pondering the limits to reason.

There's something in there I am not clever enough to tease apart, something about what mathematics can and cannot tell us about "the real" [2], and how our forms of expression (language, mathematics, visualization, etc) match up to the challenge of describing "the real".

The common thread, just on the tip of the cognitive tongue, feels like a extended debate about whether it is "true" (whatever that means) to say that mathematics is "unreasonably effective" at describing "the real", or whether a combination of metaphor, intuition and empirical intuition is a better guide.

If we go with the latter, then mathematics is "merely" a self-consistent (but limited and tricksy) toolkit with which an almost unlimited number of models of "the real" may be extended or manipulated. It is thus not "unreasonably effective" but rather "reasonably" (as in understandably) ineffective (and effective too).

Sigh. If I were to try to toss in 'Strange Loop' (Hoftstader) [3], Wolfram and (inevitably) Godel my head would probably explode, but if I had three times my currently declining intellect perhaps it would all make sense. Maybe if I keep rereading Gribbin (who is much underestimated I think) and replaying Wittgenstein I'll make a bit more progress. Or not.

Notes and asides

[1] Amazon, Google and Wikipedia all played their role in producing a never ending web of relationships. This blog, posting, in its own small way, will be one more bit of noise for our friendly reinforcing neural network. Of course we all know about Google and Wikipedia, but Amazon is continuing to add new layers of reinforcing connections between its artifacts, one of which led to this book: A World Without Time: The Forgotten Legacy of Godel And Einstein. Amazon's link to used books (how do they make money from that?) means I was able to pick it up for $5 impulse purchase. Hence Amazon gets in the post title.

[2] In parens since reality is starting to feel very different from our historical sense of it.

[3] Speaking of strange loops and the arrow of time, while writing this a funny stutter in the relationship between Blogger and my browser cache switched the post transiently back to an earlier version. Which did produce a weird sensation ...

Bell's theorem: My reading of it (at last)

It was a supercilious Wired magazine article from earlier this year that inspired me update my 27 you QM knowledge.

Ultimately, the answer is bound to be unnerving: According to a famous doctrine called Bell’s Inequality, for entanglement to square with relativity, either we have no free will or reality is an illusion. Some choice.
- Lucas Graves, New York City-based writer

I turned to the Wikipedia article, but I couldn't make sense of it. Now that I've read a bit more, I think the article is actually quite a mess. It feels like the battleground of a religious conflict, a not implausible scenario. I didn't dare edit it, but I added this as a comment:

I'm not a physicist, so I'm loathe to edit the original article. Based on my slow reading of Gribbin (Schrodinger's Kittens, 1994), however, this comes across as a particularly messy article.

For example, the article refers to von Neumann's proof against local variables, but Gribbin claims that proof was demolished by Bell. If that is true, it should not be mentioned here as it would be of only historic significance.

I'll paraphrase below how Gribbin describes Bell's Theorem and its modern consequences. If this makes sense I suggest it be incorporated with a citation to Gribbin (Schrodinger's Kitten). I think I can see pieces of Gribbin's lucid summary in the article, but the message is fragmented and expressed in unnecessarily formal language.

Bell's Theorem showed that if non-locality ("spooky action at a distance", instaneous correlation of polarization states, etc) were found to occur, irregardless of any interpretation of quantum mechanics, then physics had to abandon one of two cherished beliefs:

1. That the world exists independently of our observations of it.
2. That there is no communication faster than the speed of light.

Subsequently non-locality has been shown, several times, to occur. That means we have to give up on either the "persistent world" or faster than light communications. Not surprisingly, physicists have decided the lesser evil is to accept a faster than light communication -- as long as that communication carries no "meaning". In other words, "meaning" cannot travel faster than light.

How does this translate to Lucas Grave's choice between free will and "reality is an illusion"? The illusion part is easy, that's the #1 choice.

I think the "free will" issues comes as a consequence of "faster than light" communication. In physics "faster than light" has usually been thought to be the equivalent of "traveling backwards in time". If a message is sent from the future and measured in the past, then it seems the future is predestined. The message cannot fail to be sent.

My sense is most physicists have opted for choice #2, but since nobody's figured out a way to send a meaningful or actionable message faster than light, #2 has been expressed (my words) as "Meaning cannot travel faster than light".

I don't know if this gives any options for "free will", but I think that is how the Wired quote came about. A predestined universe seems a bit claustrophobic, so maybe physicists will figure out a way that a meaningless (infinite entropy) message can travel faster than light without implying a retro-temporal signal.

Yech. We need some more options.

The peculiar scarcity of books on quantum entanglement

I've been blogging periodically about the weirdness of a universe where quantum entanglement is real, but it was a somewhat supercilious essay in Wired magazine that convinced me I needed to read a real book ..

Wired 15.02: What We Don't Know

How do entangled particles communicate?

... In 1997, scientists separated a pair of entangled photons by shooting them through fiber-optic cables to two villages 6 miles apart. Tipping one into a particular quantum state forced the other into the opposite state less than five-trillionths of a second later, or nearly 7 million times faster than light could travel between the two [jf: probably instantaneously]. Of course, according to relativity, nothing travels faster than the speed of light - not even information between particles.

Even the best theories to explain how entanglement gets around this problem seem preposterous. One, for example, speculates that signals are shot back through time. Ultimately, the answer is bound to be unnerving: According to a famous doctrine called Bell’s Inequality, for entanglement to square with relativity, either we have no free will or reality is an illusion. Some choice.
- Lucas Graves, New York City-based writer

I was sure I'd find a lot of books on the topic, but the best I could do was 'Schrodinger's Kittens' -- written about 13 years ago! I did find some a more recent text, but it belonged to what a Wikipedia article calls Dirac's "shut up and calculate" school [1]. The other relatively recent texts I found were either fluffy or preferred to deal with familiar topics like modern cosmology.

So what gives? Is this such a scary topic that almost no-one dares to explore what it means?

I'm write some more as I work my way through the Kittens ...

[1] Easy for Dirac to say -- he died before we were doing quantum teleportation, quantum encryption, and irrefutable entanglements.

Update 2/15/07: After finishing the last chapter of Schrodinger's Kittens I understand why Graves setup the choice of 'reality is not what we think' versus 'no free will'. The 'transactional model' preserves our familiar "reality" of time and relativity, but the handshakes between past and future seem to constrain the future. In the enhanced (Wheeler) slit model, for example, the photon assumes its wave or particle behavior as it crosses the slit based on a handshake with the future absorbed photon. The nature of the future absorbed photon however, is based upon an observer choosing whether or not to "drop the screen". Since the photon adopts its configuration before the screen is dropped, however, the observer cannot really be choosing whether or not to drop the screen. The choice must be made in a way that's consistent with the form of the photon. Gribbin tries to dodge this trap with some handwaving about micro vs. macro causality, but it's obvious his heart isn't in it.

Hmmm. I'm beginning to see why Feynman warned us about 'going down the [quantum] drain', and why there are so many books on cosmology and so few on Bell's theorem. Next thing you know I'll be ready to start believing that our universe is both simultaneously vast and unbelievably small, that all things that will happen have happened, and that time's arrow really is an illusion ...

There is an escape clause. Gribbin's framed the transactional model as being dependent upon a closed universe. We appear to live in an open (perhaps excessively open) universe (but see below). In an open universe, might we get a true arrow of time and the possibility of choice? Maybe one day, if we ever "understand it all", we'll learn that you can determine whether a universe is open or closed by testing for action-at-a-distance.

Update 3/4/07: I'm reading through Gribbin from page one, and since I'd read the last chapter first I know to watch for references to a closed universe. I've found a few, it seems that more than a few of the foundations of QM, and even QED, do assume a closed universe. I'd thought that the universe is now thought to be "open", so I wrote Professor Gribbin asking if he'd written any updates. He graciously replied:

... It is entirely possible for the Universe to be closed but with accelerating expansion! All we know for sure is it is indistinguishably close to flat, and it is probably on the closed side of flat, pushed there by inflation.

Which reminds me of my old post about the respiratory rate of the universe ...

I'll just keep on reading, reading, reading ...

Update 5/13/07: My Amazon review of Gribbin's book. Five stars, despite being 12 years old.