Time-reversal symmetry violation

When did physicists first begin to suspect that what we experience as time emerges from quantum entanglement, much as we experience heat from the kinetic energy of molecules?

I suspect it was a long time ago, perhaps around the time of the double-slit experiment in 1909, but certainly by the 1960s. More recently some of the physicists I read have been openly speculating that time is emergent at the macro level, presumably in the context of a collapse of the wave function (measured in unit.

So it's particularly interesting that new experimental evidence of an "arrow of time" used quantum entanglement to expose T symmetry violation in kaons...

The arrow of time: Backward ran sentences… | The Economist

... The main hint that nature violates the time-reversal (T) symmetry ... —and thus that there really is an arrow of time—came from seemingly disparate discoveries about matter and antimatter. Mathematically, particles and their anti-versions differ in two ways: they have opposite electrical charges and they are each other’s mirror reflections. But in 1964 some particles called kaons were shown not to respect this charge-conjugation/parity (CP) symmetry, as it is known. Matter and antimatter are not, in other words, quite equal and opposite. However, according to another law, C, P and T symmetries, when lumped together into a single, overarching CPT symmetry, must be conserved. This means that if CP is violated, then T must be too, in order to even things out.

The obvious place to look for this T violation is where C and P are already known to misbehave. Between 1999 and 2008 a laboratory in California was set up to do just that. The old linear accelerator at Stanford was repurposed, turning it from the machine that co-discovered a particle known as the charm quark (thus winning its operators a Nobel prize) into a factory for making particles called B mesons. These are interesting because they and their antiparticles exhibit CP-violating tendencies. They are thus a promising place to look for T violations, too.

Which is what the scientists of SLAC’s BaBar experiment have been doing. Though the B-meson factory itself has been silent for four years (the accelerator is now in its third incarnation, as the world’s most powerful X-ray camera), its data live on, and the collaborators have been ploughing through them. They are looking in particular at how long it takes a B-meson to change its nature, focusing on one particular member of the extended B-meson family, the electrically neutral B0.

As with many things quantum, B0 can exist in a number of forms. These are known as B, B-bar, B-plus and B-minus. Like a subatomic werewolf, a B0 constantly shifts between them. If time truly has an arrow, though, some of these shifts will occur at a different rate when going in one direction rather than the other. In particular, CP-violation theory predicts that B-bar will turn into B-minus faster than B-minus turns into B-bar. All that remains is to measure the difference.

Unfortunately, that is not as easy as it sounds. A particle’s final state can be known by looking at what other sorts of particle it decays into. What cannot easily be known is what it was beforehand, and for how long.

In the wacky world of quantum physics, however, it is not always impossible to work out what a particle once was but no longer is. That is because B-mesons are sometimes born as quantum-mechanically conjoined twins. One twin gives away the initial state of the other and how long it lasted in that state—and all is revealed.

That revelation, which has been submitted for publication to Physical Review Letters, leaves no room for doubt: B-bars turn into B-minuses far faster than B-minuses turn into B-bars. As many as five B-minuses are produced for every B-bar. The chance of this result being a fluke is a nugatory one in 10**43...

It feels as though we're closing in on the nature of time. The next few years should be fun.

See also:

• Decoherence, Quantum Measurement and the Arrow of Time (workshop 2006)
• Planck time - Wikipedia - "The Planck time is the unique combination of the gravitational constant G, the relativity constant c, and the quantum constant h, to produce a constant with units of time."
• quantum mechanics - Can decoherence time be shorter than Planck time? - Physics (stackexchange)
• Gordon's Notes: Entanglement and the emergence of time 5/2012
• Gordon's Notes: The Tralfamadorians and the transactional interpretation of quantum mechanics 4/2007 (before I wrote this there were no hits on these strings, now there are many)
• Gordon's Notes: Quantum macro 6/2011
• Gordon's Notes: Carroll on Time: emergent or fundamental? 9/2011
• Gordon's Notes: Macroscopic quantum mechanics 4/2010
• Gordon's Notes: The Standard Model - summarized 7/2012
• Gordon's Notes: One of these things is not like the other: Gravity 4/2010

The Standard Model - summarized

In a most excellent overview of the Higgs(es?) news, The Economist manages the best concise summary of the Standard Model that I've read anywhere (emphases mine) ...

The Higgs boson: Gotcha! | The Economist:

... the Standard Model, the best explanation to date for how the universe works—except in the domain of gravity, which is governed by the general theory of relativity. The model comprises 17 particles. Of these, 12 are fermions such as quarks (which coalesce into neutrons and protons in atomic nuclei) and electrons (which whizz around those nuclei). They make up matter. A further four particles, known as gauge bosons, transmit forces and so allow fermions to interact: photons convey electromagnetism, which holds electrons in orbit around atoms; gluons link quarks into protons and neutrons via the strong nuclear force; W and Z bosons carry the weak nuclear force, which is responsible for certain types of radioactive decay. And then there is the Higgs.

The Higgs, though a boson (meaning it has a particular sort of value of a quantum-mechanical property known as spin), is not a gauge boson. Physicists need it not to transmit a force but to give mass to other particles. Two of the 16 others, the photon and the gluon, are massless. But without the Higgs, or something like it, there is no explanation of where the mass of the other particles comes from.

For fermions this is no big deal. The Standard Model’s rules would let mass be ascribed to them without further explanation. But the same trick does not work with bosons. In the absence of a Higgs, the rules of the Standard Model demand that bosons be massless. The W and Z are not. They are very heavy indeed, weighing almost as much as 100 protons. This makes the Higgs the keystone of the Standard Model...

I've read elsewhere that in the absence of the Higgs particles would zip around at the speed of light. Evidently, not so! The problem is rather with the W and Z bosons. That's quite different, but there's something about this summary that feels more authoritative.

I've pasted that text into Notational Velocity/SimpleNote so I have it in my extended memory.

There's more in the article ...

...  the model requires its 20 or so constants to be exactly what they are to an uncomfortable 32 decimal places. Insert different values and the upshot is nonsensical predictions, like phenomena occurring with a likelihood of more than 100%.

... One way to look beyond the Standard Model is to question the Higgs’s status as an elementary particle. According to an idea called technicolour, if it were instead made up of all-new kinds of quark held together by a new interaction, akin to but distinct from the strong force, the need for fine-tuning disappears.

Alternatively, the Higgs can maintain its elementary status, but gain siblings. This is a consequence of an idea called supersymmetry, or susy for short. Just as all the known particles of matter have antimatter versions in the Standard Model, in the world of susy every known boson, including the Higgs, has one or more fermion partners, and every known fermion has one or more associated bosons....

Quantum action - Pusey's theorem

I'm looking forward to the discussions on this paper by Pusey et al ...

Quantum theorem shakes foundations : Nature News & Comment

... Robert Spekkens, a physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, who has favoured a statistical interpretation of the wavefunction, says that Pusey's theorem is correct and a “fantastic” result, but that he disagrees about what conclusion should be drawn from it. He favours an interpretation in which all quantum states, including non-entangled ones, are related after all.

Spekkens adds that he does expect the theorem to have broader consequences for physics, as have Bell’s and other fundamental theorems. No one foresaw in 1964 that Bell’s theorem would sow the seeds for quantum information theory and quantum cryptography — both of which rely on phenomena that aren’t possible in classical physics. Spekkens thinks this theorem may ultimately have a similar impact. “It’s very important and beautiful in its simplicity,” he says...

Pusey's interpretation is that the wave function models a physical reality. The paper allows, however, that the wave function is a predictive model [1] -- but, in that case, all quantum states are interconnected across space and time, even uncorrelated states.

This ought to be very interesting ...

[1] If you've done basic stats, you have worked with linear regression models that predict systems statistically, but once the system is understood, are found to be weakly related to the fundamental "truth". Sometimes these models do reflect fundamentals, but they don't have to. This is relatively basic math, but it gives me a way to think about statistically predictive models that don't resemble the "true" mechanistic model.

Update: Shtetl Optimized (Scott Aaronson) hates this article, PBR's definition of statistics, and especially Slashdot... (emphases mine)

... There’s an important lesson here for mathematicians, theoretical computer scientists, and analytic philosophers.  You want the kind of public interest in your work that the physicists enjoy?  Then stop being so goddamned precise with words!   The taxpayers who fund us—those who pay attention at all, that is—want a riveting show, a grand Einsteinian dispute about what is or isn’t real.  Who wants some mathematical spoilsport telling them: “Look, it all depends what you mean by ‘real.’  If you mean, uniquely determined by the complete state of the universe, and if you’re only talking about pure states, then…”

Aaronson is a theoretical computer scientist. I don't think he's happy right now.

Carroll on Time: emergent or fundamental?

My favorite part of Sean Carroll's posts on the nature of Time was about emergence vs. fundamental time ...

Time exists...The real question is whether or not time is fundamental, or perhaps emergent. We used to think that “temperature” was a basic category of nature, but now we know it emerges from the motion of atoms. When it comes to whether time is fundamental, the answer is: nobody knows. My bet is “yes,” but we’ll need to understand quantum gravity much better before we can say for sure.

Carroll, my favorite physics blogger, confirmed that I was on the right track when I wrote entanglement and the realness of time. I wasn't just making it up! I'm willing to bet a beer that within fifteen years the consensus will be that time is emergent rather than fundamental. That's easy for me to say, I really have no idea what I'm talking about.

Reading the essay I'm reminded that in classic General Relativity Fate rules; a life history is fixed from death to birth, like the track of an ancient LP. Calvin would approve.

I wonder if Carroll holds that opinion as well, updated for an era of Quantum Gravity perhaps with a twist of the many worlds interpretation of QM.

Modern physics is so weird.

Entanglement and the realness of time

I can't find the post I was looking for.

It was written by a physicist I read. i'm still looking for it, but there were two interesting assertions. One was that "time was not real", the other was that entanglement is deeper than time.

He was being coy, but this is what I think he meant.

By "real" I think he meant "fundamental". So time is real enough, but if we really understood it we'd see it as emerging from other processes.

It's easy to understand this with "pressure". Humans presumably named the "wind" more than a hundred thousand years ago. Much more recently humans named "pressure" as the expansionary force of a heated balloon. Pressure is certainly real. It's not fundamental though. Much more recently humans figured out that "pressure" was the outcome of atoms in motion. Atomic action is more fundamental.

I gather time is thought to be like that -- an emergent outcome of something more fundamental.

So why should entanglement be the key to understanding time?

Well, physicists think quantum entanglement is very fundamental. It's close to the machinery of reality.

Entanglement is weirder than I can imagine. If I understand it correctly, one could (in theory) separate two entangled particles by a billion light years, measure one a "millisecond" apart (a very squirrely concept in this context), and find the measurements were correlated -- even though a light signal would take a billion years to cross that gap.

In other words, "entanglement" may take place outside of time or space. That's kind of interesting. So if you want to probe time and space, and expose its underlying reality, you might as well start with probing entanglement. If you get it right, you might be able to understand entanglement outside of time (and space), and also understand why we are inside of time.

I really do need to find that post ...

Update 9/1/11: I haven't found that post, but a subsequent Carroll essay suggests I'm not just making this up.

The wilfull wastefulness of the Foundational Questions Institute

The "Foundational Questions Institute" (FQXi, don't ask about the acronym) recently sponsored an essay question about the nature of reality, specifically whether it is fundamentally digital or analog. Is there, for example, a smallest slice of time? Or, if you suspect time is not fundamental but is some epiphenomena of entanglement, is there a way in which the quantum world is less digital than it seems?

Sponsored essays on speculative physics! Neat idea, and seems right up my ally. Of course FQXi's mission statement must attract a wide "variety" of thinkers (emphases mine) ...

... FQXi catalyzes, supports, and disseminates research on questions at the foundations of physics and cosmology, particularly new frontiers and innovative ideas integral to a deep understanding of reality, but unlikely to be supported by conventional funding sources...

Still, the advisory council includes Guth, Bostrom, Barrow, Rees, and Smolin. So I would have tagged them as potentially eccentric, but most likely interesting.

Would have tagged them I say - but not after I actually tried to read one of the winning essays.

It's a PDF. That's bad enough, but it's a PDF of badly scanned document.

This is pure madness. The FQXi is a sad waste.

Quantum macro

Living in a Quantum World: Scientific American by Vlatko Vedral is the headline article for SciAm's June 2010 issue. It's behind SciAm's remarkably successful paywall, but for the moment you can find a PDF in Taiwan [1].

It's worth a read for my fellow lay fans of Quantum Mechanics. It captures the excitement of the field, where the theoretically incomprehensible is now becoming the materially incomprehensible. Some highlights of note, recognizing that this article is one physicist's personal view ...

• Until recently many popular presentations of QM, even very fine ones, confined QM to the micro realm. Decoherence, arising from "information leakage" was supposed to flip from a bizarre "binary" quantum world of entanglement to a bizarre "analog" world of gravity and black holes. Vedral and others says it's all QM from the bottom to the top. There's no "flip" between quantum and classic.
• In one experiment 10^20 atoms of lithium fluoride behaved as though, at some level, they were all entangled
• There are claims, with some evidence, that quantum effects are leveraged by navigating birds and phyotsynthesis.
• If entanglement is truly fundamental, then space and time (arrow of time) may in time be seen as side-effects of entanglement (which, I suppose, would make "spooky action at a distance" oddly easier to understand)
• Even more speculative -- gravity is not fundamental, but is emerges as a side-effect of the three (not four) fundamental forces (weak, strong, electromagnetic). Supposedly "proper" quantum treatment of those forces will yield gravity, which would explain why it's been so hard to quantize gravity.

Perhaps the most interesting bit of the article was a somewhat frustrating description of a Schrodinger Cat variant Bob and Alice thought experiment from 1961 and 1986. I've never heard this one, and I can't find it described properly on the web, so I wonder if this is partly a modern interpretation focusing on how information leakage leads to decoherence [2]. Briefly, it goes like this

• Bob, the cat, the cat poison and cesium atom are in a room. Alice is outside. The cat poison is released if the atom decays. Bob can see the cat. Alice can't.
• The cesium atom is "quantum". It is in an indeterminate state of decay or integrity. That's "rock solid" quantum physics.
• Alice puts a piece of paper under the door. She asks Bob if he can see that the cat is dead or alive, but not what state the cat is in. Just that he can tell.
• Bob writes he can tell.

So at this point the the cat is dead or alive - at least for Bob.

Here's where I don't get it at all. According to quantum theory this is all reversible. Allegedly Alice can "undo" the observation, but retain the piece of paper. If Bob remembers seeing a dead cat, but Alice makes the poison inert, he'll remember seeing a live cat. So Bob, the Cat, the poison and the Cesium ion are all entangled and indeterminate for Alice, but for Bob they're all determinate. Smells a bit like frames of reference in special and general relativity.

Unfortunately the sidebar doesn't explain how Alice can undo the observation without a bit of time travel. So I suspect the explanation has been a bit butchered, but I'll keep an eye out for a better one (Google is no help today).  Supposedly the equivalent experiment has actually been done by teams led by Blatt and Wineland, and they've shown measurement reversal in the real world (did you just feel the  universe hiccup)?

[1] If you Google on a few unique words in an article, you can usually find one copy somewhere on earth.
[2] Much of the lay physics I read these days uses an information theoretic perspective; much of physics is expressed in the language of information. Reminds me of some of my favorite mind expanding science fiction,  particularly Greg Egan's Permutation City. In that book sentient natives of a simulation with inescapably absurd physics are designed to realize that their universe must be a simulation. Except they're so brilliant they come up with a plausible "natural" explanation, and so disrupt the simulation itself ...

Quantized scent detection isn't quantum computing

Towards the end of my comments on a  BBC news article titled "quantum physics explanation for smell", I started to have second thoughts about how "quantum" these results were ...

Gordon's Notes: Quantum computing in the nose

... If these results are replicated, then Turin gets a Nobel.

If noses use these 'quantum' effects, then it's pretty much certain that neurons do as well.

Does that mean our brains are 'quantum computers'? I need help from Aaronson. This 'quantization' sites on the micro-macro boundary. Not all quantized vibrations are quantum physics....

I asked Scott Aaronson, MIT prof of computational physics [1] and famed blogger if he'd consider a comment on the original article. Instead he replied by email, and gave me permission to quote ...

These look like *really* interesting experiments!  And it's a priori plausible that smell would involve some quantum effect -- we already know that ... photosynthesis and bird navigation do.

If true, this doesn't IN ANY WAY imply that the brain is a "quantum computer" in the sense of using quantum coherence to speed up computation.  That's a separate question, and any such suggestion would still need to overcome the problem of how entanglement could survive in the brain for any appreciable length of time.

So while we do have evidence that natural selection has made use of some aspects of quantum physics, we have no evidence (yet), that it has made use of entanglement, the spooky action that motivates research into quantum computation. So the nose may be doing quantum physics, but we have no evidence that it's doing quantum computing. [2]

[1] Born in 1981, when I left college. Sob.
[2] Incidentally, if I read Aaronson correctly, he suspects quantum computing is possible, but it won't solve radically new problems (and thus won't destroy the world economy if it works).

Quantum computing in the nose

Smell, aka the application of algorithms for molecule classification, uses "quantum" effects ...

BBC News - Quantum physics explanation for smell gains traction

... in 1996, Luca Turin, now of the Massachusetts Institute of Technology in the US, suggested that the "vibrational modes" of an odorant were its signature.

Molecules can be viewed as a collection of atoms on springs, and energy of just the right frequency - a quantum - can cause the spring to vibrate.

Since different assemblages of molecules have different characteristic frequencies, Turin proposed, these vibrations could act as a molecular signature.

The idea has been debated in the scientific literature, but presentations at the American Physical Society meeting put the theory on firmer footing.

Most recently, Dr Turin published a paper showing that flies can distinguish between molecules that are chemically similar but in which a heavier version of hydrogen had been substituted...

If these results are replicated, then Turin gets a Nobel.

If noses use these "quantum" effects, then it's pretty much certain that neurons do as well.

Does that mean our brains are "quantum computers"? I need help from Aaronson. This "quantization' sites on the micro-macro boundary. Not all quantized vibrations are quantum physics.

Update 3/25/11: I forgot to change my title when doubts crept in. My mistake!

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)

Paul Dirac on the surprising history of the Schrodinger wave equation

SciAm is republishing a terrific 1963 essay by a famed physicist, back when Scientific American graphics included serious math. Here Dirac is talking about the surprising history of the Schrodinger wave equation ...

Paul Dirac, Scientific American, 1963: The Evolution of the Physicist's Picture of Nature

... I might tell you the story I heard from Schrodinger of how, when he first got the idea for this equation, he immediately applied it to the behavior of the electron in the hydrogen atom, and then he got results that did not agree with experiment. The disagreement arose because at that time it was not known that the electron has a spin. That, of course, was a great disappointment to Schrodinger, and it caused him to abandon the work for some months. Then he noticed that if he applied the theory in a more approximate way, not taking into account the refinements required by relativity, to this rough approximation his work was in agreement with observation. He published his first paper with only this rough approximation, and in that way Schrodinger's wave equation was presented to the world. Afterward, of course, when people found out how to take into account correctly the spin of the electron, the discrepancy between the results of applying Schrodinger's relativistic equation and the experiments was completely cleared up...

This would be a good update to the history section of the Wikipedia article on the equation; it's also a lovely example for people writing about on the philosophy of science. It's all so much neater in retrospect.

Those were the glory days of Scientific American. I love the Sci Am news blog, but the magazine is very slight now. It aims for a different market.

There's so much more in this brief essay. It's required reading for the physics fanboy. Consider Dirac's discussion of "137" (Adams should have used 137, not 42):

.... There are some fundamental constants in nature: the charge on the electron (designated e), Planck's constant divided by 2 π (designated h-bar) and the velocity of light (c). From these fundamental constants one can construct a number that has no dimensions: the number h-bar*c/e^2. That number is found by experiment to have the value 137, or something very close to 137. Now, there is no known reason why it should have this value rather than some other number. Various people have put forward ideas about it, but there is no accepted theory. Still, one can be fairly sure that someday physicists will solve the problem and explain why the number has this value. There will be a physics in the future that works when h-bar*c/e^2 has the value 137 and that will not work when it has any other value...

Dirac gets numerological about 137. He really doesn't like square roots ...

.... Only two of them can be fundamental, and the third must be derived from those two. It is almost certain that c will be one of the two fundamental ones.... If h-bar is fundamental, e will have to be explained in some way in terms of the square root of h-bar, and it seems most unlikely that any fundamental theory can give e in terms of a square root, since square roots do not occur in basic equations. It is much more likely that e will be the fundamental quantity and that h-bar will be explained in terms of c^2. Then there will be no square root in the basic equations...

Genius is sometimes close to dysfunction [1]; it's common in science that elder genius takes odd directions. This stuff is great fodder for crackpots, but there's always the tantalizing possibility that some of it will be borne out one day.

[1] I've lost a recent developmental neurobiology reference that put the old "genius is close to madness" cliche on firm ground. It wasn't this review article, but it was of the same genre. The same mechanisms that make a person creative do seem to make them more prone to "strange loops", perhaps particularly as they age. (Yeah, I'm being self-referential.)

Macroscopic quantum mechanics

In Greg Egan's Teranesia [1] one story I can't currently locate (h/t Mel Anderson, comments), the protagonist is fighting the ultimate infection. It seems impossibly mutable. Turns out it has evolved to exploit quantum effects, and it's finding the perfect mutation by exploring all the many worlds of variation.

That wasn't the only science fiction story of the past decade to imagine that biological organisms, operating at atomic scales, might exploit quantum effects. Alas, science fiction memes don't last long these days. Protein exploitation of quantum effects has become a mainstream research topic. This Nov 2009 Sci Am news article is a good overview of the underlying physics; note especially the resolution to the old debate about how the quantum/classical transition happens ...

How Noise Can Help Quantum Entanglement: Scientific American

... In the modern view that has gained traction in the past decade, you don’t see quantum effects in everyday life not because you are big, per se, but because those effects are camouflaged by their own sheer complexity. They are there if you know how to look, and physicists have been realizing that they show up in the macroscopic world more than they thought...

... This work suggests that, contrary to conventional wisdom, entanglement can persist in large, warm systems—including living organisms. “This opens the door to the possibility that entanglement could play a role in, or be a resource for, biological systems,” says Mohan Sarovar of the University of California, Berkeley, who recently found that entanglement may aid photosynthesis ... In the magnetism-sensitive molecule that birds may use as compasses, Vedral, Elisabeth Rieper, also at Singapore, and their colleagues discovered that electrons manage to remain entangled 10 to 100 times longer than the standard formulas predict...

A quick search on scholar.google.com finds many references on how quantum effects might alter molecular behavior in neurons.

It's a small, small world after all.

[1] See also: Mind expanding books: a list and my comments there on Egan's Incandescence.

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One of these things is not like the other: Gravity

In this popular account from 1860 [1]) the observation that "electricity" traveled through a medium implied that "other" fundamental forces such as light and gravity must also travel through a medium (emphases mine) ...

April 1860 -Scientific American - Electrical Theory

... The results of the experiments instituted by Sir William Grove are exceedingly curious, and must be regarded as all but proving the truth of the modern theory, which assumes that electricity is not, in any sense, a material substance but only an affection (state) or motion of the particles of ordinary matter.

If electricity is unable to pass over or through a vacuum, it is probable that all the other so-called imponderable forces—light, heat, magnetism, and possibly attraction—obey the same law, and as these agencies freely travel the interplanetary spaces, the supposition of Newton that such spaces may be filled with an ethereal form of matter receives an indirect but powerful support....

There is no ethereal form of matter in the 19th century sense however. Electricity has a relationship to fundamental electromagnetic forces, but it is not the same sort of thing. Once electricity was divided from "light" it was possible to find common models for light and magnetism.

In 2010 some people are trying to deal with the unquantifiability of gravity through a similar approach ...

arXiv blog: Gravity Emerges from Quantum Information, Say Physicists..

One of the hottest new ideas in physics is that gravity is an emergent phenomena; that it somehow arises from the complex interaction of simpler things.

A few month's ago, Erik Verlinde at the the University of Amsterdam put forward one such idea which has taken the world of physics by storm. Verlinde suggested that gravity is merely a manifestation of entropy in the Universe. His idea is based on the second law of thermodynamics, that entropy always increases over time. It suggests that differences in entropy between parts of the Universe generates a force that redistributes matter in a way that maximises entropy. This is the force we call gravity.

What's exciting about the approach is that it dramatically simplifies the theoretical scaffolding that supports modern physics. And while it has its limitations--for example, it generates Newton's laws of gravity rather than Einstein's--it has some advantages too, such as the ability to account for the magnitude of dark energy which conventional theories of gravity struggle with.

But perhaps the most powerful idea to emerge from Verlinde's approach is that gravity is essentially a phenomenon of information.

Today, this idea gets a useful boost from Jae-Weon Lee at Jungwon University in South Korea and a couple of buddies. They use the idea of quantum information to derive a theory of gravity and they do it taking a slightly different tack to Verlinde.

At the heart of their idea is the tricky question of what happens to information when it enters a black hole. Physicists have puzzled over this for decades with little consensus. But one thing they agree on is Landauer's principle: that erasing a bit of quantum information always increases the entropy of the Universe by a certain small amount and requires a specific amount of energy.

Jae-Weon and co assume that this erasure process must occur at the black hole horizon. And if so, spacetime must organise itself in a way that maximises entropy at these horizons. In other words, it generates a gravity-like force.

That's intriguing for several reasons. First, Jae-Weon and co assume the existence of spacetime and its geometry and simply ask what form it must take if information is being erased at horizons in this way.

It also relates gravity to quantum information for the first time. Over recent years many results in quantum mechanics have pointed to the increasingly important role that information appears to play in the Universe.

Some physicists are convinced that the properties of information do not come from the behaviour of information carriers such as photons and electrons but the other way round. They think that information itself is the ghostly bedrock on which our universe is built.

Gravity has always been a fly in this ointment. But the growing realisation that information plays a fundamental role here too, could open the way to the kind of unification between the quantum mechanics and relativity that physicists have dreamed of..

In short, one way to deal with the gravity problem is to make gravity go away. It's merely a confusing epiphenomena.

Hey, it worked for electricity ...

[1] Just prior to the American civil war. In a few years the SciAm "150 year back" article excerpts will be all about military science relevant to the most bloody battles of the 19th century. That should be interesting.

Subversive theophysics - Greg Egan

I've been composing a post about Greg Egan's Permutation City for a while. I'm afraid I'll never get to the whole thing, so I'm going to toss off the short version. (Warning, contains spoilers)

Greg Egan is usually said to write "hard" science fiction. That's inadequate. He writes neutronium grade science fiction. His mathematical physics bent has become so extreme that his latest book is a thin layer of fiction around a core of speculative physics (Amazon promises me a copy in 3-4 weeks, apparently they have to retype it. Egan has put a prequel to the story on his web site).

Permutation City is one of his best works. Despite the math science bent several of the characters have stuck with me.

The best part though, is the fusion between theology and physics -- theophysics. In Permutation City reality is fundamentally mathematical, much as imagined by Stephen Wolfram and many more conventional physicists. A group of experimental modelers creates an artificial world with a different sort of mathematical reality.

No wait, hang in here for a minute. I'm really going somewhere.

The creatures of this new world are fantastically alien, but like us they're compelled to understand their world. Problem is, their world is fundamentally incomprehensible. It was created by omniscient and omnipotent Creators. Gods.

So the alien critter(s) is(are) "anguished". They are compelled to understand, but they cannot understand. The human Creators are sympathetic, and decide to manifest themselves in the alien world. The Truth shall be known, and the aliens will understand.

Except, the aliens come up with their own Theory of Everything; their equivalent of quantum gravity. It looks crazy and absurd, but it's internally consistent. It explains everything but the appearance of the Creators, and that detail can be quickly forgotten.

The Creators suddenly find themselves written out of the script, but that's a different story. I'm telling the story of the subversive aspects of Egan's fiction.

Obviously, the invented aliens of Permutation City aren't alone. We too are compelled to comprehend, and modern physics is getting pretty damned absurd...

Relativity as a consequence of quantum entanglement

Useful at parties ...

Relativity as a Consequence of Quantum Entanglement: A Quantum Logic Gate Space Model for the Universe

Everything in the Universe is assumed to be compromised of pure reversible quantum Toffoli gates, including empty space itself...

The nature of time - essential reading for reality hobbyists

Are you an amateur epistemontologist? Curious about the nature of reality? Not willing to accept the illusions of the senses?

Then you've got reading ...

The Envelope Please… | Cosmic Variance | Discover Magazine

The results are in for the Foundational Questions Institute essay competition on “The Nature of Time,” which we discussed here. And the winners are:

... Julian Barbour on “The Nature of Time”

... Claus Kiefer on “Does Time Exist in Quantum Gravity?”

... Sean Carroll on “What if Time Really Exists?”...

Love it.

Quantum madness. Chapter IX.

Lovecraft was wrong.

Madness is not to be taught at Nyarlathotep Academy, it to found in the contemplation of the quantum ...

Quantum physics and reality | I'm not looking, honest! | The Economist

... In the 1990s a physicist called Lucien Hardy proposed a thought experiment that makes nonsense of the famous interaction between matter and antimatter—that when a particle meets its antiparticle, the pair always annihilate one another in a burst of energy. Dr Hardy’s scheme left open the possibility that in some cases when their interaction is not observed a particle and an antiparticle could interact with one another and survive. Of course, since the interaction has to remain unseen, no one should ever notice this happening, which is why the result is known as Hardy’s paradox.

This week Kazuhiro Yokota of Osaka University in Japan and his colleagues demonstrated that Hardy’s paradox is, in fact, correct...

Update: To be fair to physics, I dimly believe that "unseen" is a bit of an overstatement -- just about any interaction with the universe will collapse these indeterminate states.

SciAm's quantum weirdness day: Nonlocality

Almost exactly two years ago a Wired magazine article inspired me to catch up on the past 15 years of popular physics. I've had a great time since then, but I particularly appreciated Gribbin's willingness to meet quantum weirdness head on.

I'm thus pleased to report that SciAm has an article and a few blog posts on one of my favorite topics -- non-locality ...

• Was Einstein Wrong?: A Quantum Threat to Special Relativity: Scientific American
• Bell's theorem and the physical world
• Nonlocality from Newton to Maxwell

To be clear, I'm over any childhood pretensions to novel insights into modern physics. I'm strictly a non-participatory fan, and very grateful to physicists who try to translate their world into our world.

A quantum state eternally evolving in an infinite-dimensional Hilbert space

It's time for your morning exercise ...

FQXi Community: Articles, Forums, Blogs, News

.... The arrow of time finds a plausible explanation in a 'Heraclitean universe,' described by a quantum state eternally evolving in an infinite-dimensional Hilbert space....

Sean Carroll of Cosmic Variance fame has entered an essay contest on the nature of time.

I've asked Sean to tell us what the other good ones are.

The wikiepdia entry on Heraclitus might be of assistance.

Cosmology and Complexity - almost understandable

This Aaronson lecture is surprisingly readable. Thank you scribe!

PHYS771 Lecture 20: Cosmology and Complexity

...But that's only one thing that's wrong with the simple "spherical/flat/hyperbolic" trichotomy. Another thing wrong with it is that the geometry of the universe and its topology are two separate questions. Just assuming the universe is flat doesn't imply that it's infinite. If the universe had a constant positive curvature, that would imply it was finite. Picture the Earth; on learning that it has a constant positive curvature, you would conclude it's round. I mean, yes, it could curve off to infinity where you can't see it, but assuming it's homogenous in curvature, mathematically it has to curve around in either a sphere or some other more complicated finite shape. If space is flat, however, that doesn't tell you whether it's is finite or infinite. It could be like one of the video games where when you go off one end of the screen, you reappear on the other end. That's perfectly compatible with geometric flatness, but would correspond to a closed topology. The answer, then, to whether the universe is finite or infinite, is unfortunately that we don't know....

Very fun topic. I finally have a personal story for the limits of information -- when bits become a black hole.

Curious relationship between computation and the cosmological constant.