Belief in reversible equations

I mentioned Scott Aaronson's views on black hole firewalls, and I quote an exchange on his blog:

Michael Welford Says:

Scott

You want an isolated system showing irreversible and therefore nonunitary change? How about a perfectly insulated cavity radiator? I put some metal balls in – one of them very very hot. Through a tiny peephole I watch with amusement as details of the interior of the cavity gradually vanish from sight. Oh, no radiation is allowed in.

After shutting the peephole and allowing the interior of the cavity to reach equilibrium, I invite you in. I open the peephole and ask you to identify the metal ball that was so hot. Your reply is something like: “That’s an unfair question. I can’t see any metal balls. All I see is cavity radiation!”

I trust you to make the black hole analogies on your own.

Scott Says:

Michael Welford #8: On much the same basis, someone might object to Newton’s laws, on the ground that their form suggests the existence of perfectly reversible systems (pendulums that keeping swinging forever, etc) but we never see those in practice.

I think most people realize that the question here is not about what I could or couldn’t do in practice, but about the form of the laws of physics relevant to black holes: will the correct equations be reversible ones, in the same sense that the correct equations for a lump of burning coal (or for your metal balls in a cavity) are reversible? Or is there irreversibility, not only in practice, but even in the equations?

Now, you might object: if we only care about the form of the equations, and not about practical limitations, then why should we care about computational intractability a la Harlow and Hayden? That’s a good question. A glib answer would be: because computational intractability, while less “exalted” than outright physical impossibility, is nevertheless more exalted than mere practical difficulty. A better answer will have to await my response to Jay #10 below.

Michael Welford Says:

I need to learn to be less oracular in my comments. My main points are:
(1) It’s quite possible to have irreversible change in an isolated system ( like the interior of the cavity )
(2) Pure thermal radiation can’t tell you anything about its source except for the temperature of that source ( and the fact that the source has a well defined temperature ).
This applies to cavity radiation and to hawking radiation. ( Although Hawking seems to think otherwise. )

Anyway, if you’re trying to reconstruct a black holes history from hawking radiation, you’re too late. The informative time was when the hole was coming to equilibrium.

You mention newtonian physics. Let’s compare newtonian with quantum physics.

The newtonian rules tell us that if we know the forces on an object we can figure out its motion. The formulas for friction are ad hoc and ugly and approximate, but they give forces. We end up sacrificing the time symmetry that’s in the fundamental equations , but friction and other kinds of irreversibility still fit into the framework.

The traditional model of quantum mechanics involves intervals of unitary evolution interrupted by wave function collapse. The unitary part looks mathematically like a complicated rotation. The nonunitary collapse part looks like a geometric projection. It feels like we have two sets of rules. Furthermore, wave function collapse brings in stuff that physicists find to be not so esthetically pleasing. Things like time asymmetry, irreversibilty, information loss, nonlocality. It’s more relaxing to insist that all change is unitary, than it is to face so much unpleasantness.

Scott Says:

Now you seem to be simply denying, without argument, one of the most profound, well-established insights of 19^th-century physics! Namely, that the reversible laws governing our universe can (and do) give rise to “irreversible-looking” phenomena, ultimately because of the specialness of our universe’s initial state. Furthermore, far from being overturned by quantum mechanics, this insight is dramatically upheld by it—something that I think the Many-Worlders and the Neo-Copenhagenists actually agree about. For anyone interested in more detailed exploration of these issues, I strongly recommend Sean Carroll’s From Eternity to Here.

Michael Welford Says:

Yes, I agree that the observable universe started from a special state. However entropy increasing phenomena aren’t just irreversible-looking. They’re irreversible since we can’t bring the entropy of the universe back down.

I was trying to say, that in the traditional description of quantum mechanics irreversible change, characterized by wave function collapse, looks mathematically different from reversible change characterized by unitary evolution. This creates a temptation to (incorrectly) decide that all change is unitary.

Somehow, with all my obscurity, my central point got lost. Thermal radiation is so noisy that all it can tell you is the temperature of its source. So hawking radiation is uninformative even in principle. This principle is easily testible with cavity radiation. Keep close enough to thermal equilibrium and you won’t be able to see a difference between a cavity with an ‘X’ carved into the back from a cavity with an ‘O’. (Outside illumination is cheating, since it violates thermal equilibrium.)

SAFETY TIP: If anyone is actually going to do this experiment, I suggest buying an infrared camera and maintaining thermal equilibrium with warm water.

Scott Says:

No, I don’t think lack of clarity is the problem. You were perfectly clear; the trouble is just that (without further elaboration) you’re wrong!

The great insight of the statistical interpretation of thermodynamics was that, in theory, you could look at so-called “thermal” radiation, and work backwards to learn the original source of the heat. In other words, that there exists a clear sense in which “thermal” is just a word for our own ignorance. Our inability to reverse the heat diffusion (or unscramble the omelette, or unshatter the broken glass, whatever) is “just” a practical limitation, having to do with our failure to keep track of all the relevant microscopic details (or alternatively, to control the entire relevant Hamiltonian so that we could “set it in reverse”).

Decreasing the “entropy of the entire universe” is a different matter, since there’s no one able to stand outside the universe to pump heat out of it. But if you wait long enough for a Poincare recurrence, then sure, you’ll even see the entropy of the universe (however you choose to define it) go down as well.

Now, I don’t claim that this picture is sacrosanct. Maybe someone, someday, will give a convincing dynamical account of the origin of quantum measurement, in which case you really would have “genuine irreversibility.” (Until that happens, most physicists will continue to think about quantum measurements as “just another instance of the Second Law,” reversible in principle and only irreversible in practice.) Or maybe you want to use cosmology to argue that, once some of the information needed to unscramble your omelette is rushing away from you at the speed of light, your omelette is now unscramblable in principle, and not only in practice—assuming, of course, that you live in a deSitter universe, and not an AdS universe! I even toyed with that idea myself, in my “Ghost in the Quantum Turing Machine” essay.

My point is simply that those are cases that have to be made explicitly, if they’re made at all—clearly indicating how and why you’re choosing to depart from the conventional picture. In other words, irreversibility can’t just be asserted; you need to state the mechanism for it!

So we observe irreversibility in practice, but there is a belief that the equations should be reversible anyway, with the consequence that you will hit a firewall as you dive into a black hole past the point of no return. You just won't be able to tell anyone about it.

This discussion clearly illustrate two points of view. Many physicists, like Aaronson, have a belief in reversible equations, and that belief underlies many-worlds (MWI), unitarity, black hole firewalls, information conservation, and various other theoretical musings that have never been observed in the real world.

We do have some laws of physics that are not time reversible. The biggest examples are weak interactions (with CP violation), the second law of thermodynamics, and the wave function collapse. Time is irreversible. It is funny how physicists do not want to accept that.

I looked for evidence against collapse, and found this 2005 paper:

These developments have thus extended the domain for an application of quantum theory far into the mesoscopic and macroscopic realm, which lends strong support to assuming a universally exact and applicable Schrodinger equation. To make a physically compelling case for such a purely unitary quantum theory we must pursue two related goals. First, we ought to continue to design experiments which demonstrate the existence of quantum superpositions of macrosopically distinct states — and which, ideally, can explicitly rule out collapse models.

Second, since the assumption of a universal Schrodinger dynamics implies that superpositions of (presumably macroscopically) different observer states are both possible and inescapable if we include physical observers into the quantum-mechanical description, we must simultaneously show that environmental decoherence provides the necessary and sufficient mechanism to explain our observation of a “classical” world. The emergence of the latter can then be understood not only in spite of, but precisely because of the quantum formalism — no classical prejudice need to be imposed.

There will be a Nobel Prize for anyone who does an experiment to rule out collapse models. This has not been done yet, and may never be done.

Einstein was not an anti-authoritarian

TG Daily writes:

Would We Have Drugged Up Einstein? How Anti-Authoritarianism Is Deemed a Mental Health Problem In my career as a psychologist, I have talked with hundreds of people previously diagnosed by other professionals with oppositional defiant disorder, attention deficit hyperactive disorder, anxiety disorder and other psychiatric illnesses, and I am struck by 1) how many of those diagnosed are essentially anti-authoritarians; and 2) how those professionals who have diagnosed them are not. Anti-authoritarians question whether an authority is a legitimate one before taking that authority seriously. Evaluating the legitimacy of authorities includes assessing whether or not authorities actually know what they are talking about, are honest, and care about those people who are respecting their authority.

Einstein was not an anti-authoritarian. He never got kicked out of school or fired from a job for disrespecting authority. He followed all the rules to get his doctoral degree and various professorships.

His theories rarely challenged conventional wisdom. His famous 1905 papers were directly in support of the leading theorists of the day, Lorentz, Poincare, and Planck. In later life he refused to accept the new theories of quantum mechanics, when younger physicists were challenging authority. But attacking authority? Not Einstein. He was even an apologist for the authoritarian government of the USSR.

Galileo debated why ice floats

Galileo once debated why ice floats:

Galileo had a lot of self-confidence, Caruana said, which helped him stand up to the church on heliocentricity, using a strong foundation of experimental data. But the scientist’s ego also led him to propose—and vehemently defend—some curiously wrong arguments too. For example, Galileo argued that comets were optical illusions (they are most definitely physical objects) and that ocean tides were the result of oceans sloshing around from Earth’s rotation (tides have more to do with the moon’s gravitational pull). His erroneous arguments during the water debate are a useful reminder that the path to scientific enlightenment is not often direct and that even our intellectual heroes can sometimes be wrong. ...

But Galileo then went too far. Aiming at the main thrust of delle Colombe’s argument, Galileo said that the shape of an object did not affect whether the object would sink or float.

Galileo had not accounted for surface tension, however. Surface tension forces can help objects located on a liquid surface resist sinking on the basis of how much of that object is in contact with the liquid’s surface. Consider a paper clip: If it is placed flat on the surface of water it can float, but if it is placed on water standing straight up, it sinks. The difference is the higher surface tension force experienced by the paper clip lying flat on the water’s surface. So in a way, the shape of an object (in contact with the surface) does contribute to whether it sinks or floats.

On the third day of the debate, delle Colombe stole the show with a crowd-pleasing experiment, Caruana said. Delle Colombe presented a sphere of ebony to the audience. The sphere was placed on the surface of the water, and it began to sink. Then delle Colombe took a thin wafer of ebony and placed it on the surface of the water, where it floated. Because the density of both the wafer and the sphere of ebony were the same, delle Colombe announced that density had nothing to do with buoyancy and that an object’s shape was all that mattered.

That’s when “the dispute became noisy and inconclusive, and the meeting was brought to a close,” Caruana said.

To my surprise, many Slash dot commenters recognize that Galileo was not so scientific in his dispute with the Pope either:

Cause the Pope had been one of his biggest supporters and protectors. And Galileo had not been able to offer proof of his beliefs. Actually, more so that a number of his arguments in support were disproven (such as the tides sloshing about).

So basically, the Pope said you can discuss, but not advocate for the heliocentric view as a fact. Instead, Galileo, published a book arguing for it, and using some of the Pope's statements by a character named Simpleton.

This is like a venture capitalist saying "Please don't say we've discovered a cure for cancer. Until we have proved that it works. Instead, just say we are 'researching' a cure for cancer."

Then the researcher goes on the View. And well, a lot of the stuff he claims as proof of success is circumstantial and invalid. ...

Even after Galileo was placed under house arrest for publishing his work as fact instead of theory (which is what the dispute was about), the Church provided housing for him, built him an observatory, fed him, provided servents for him, paid him to do research and a host of other things. It was probably the most comfortable house arrest in history.

If Galileo had stuck to established science, he would not have had trouble.

Firewalls can only be settled by debate

Matthew R. Francis writes in Slate:

The wild-haired German's latest foe comes to us courtesy of a story in the New York Times by Dennis Overbye. The very first sentence reads: “This time, they say, Einstein might really be wrong.” Specifically, a debate over the nature of black holes could challenge “the basis of his general theory of relativity … on which our understanding of the universe is based.”

Sounds dire, no? Poor Einstein could be refuted at last, more than 50 years after his death, his legacy shredded by the very black holes his theory predicted. But this framing presents a distorted view of the process of science. ...

Newer theories supplant older ones conceptually, but every theory is provisional, constantly tested by experiments and observations. Einstein, important as he was in 20^th-century physics, is not the ultimate authority even on his own theories, and refinements to his work should not be framed as proving him right or wrong. Rather than saying things like “Einstein survives to fight another day” or “[throwing] Einstein under the bus,” as Overbye does, we should frame scientific discovery as a process, not a clash between people. Black hole firewalls are part of the process, which ultimately won't be settled by debate. Let's let Einstein sit this one out.

I already commented on Overbye's raticle. Overbye is an Einstein biographer and idolizer, but other science writers do the same.

It is rare for anyone to even mention relativity without tying in some Einstein worship. I cannot think of any other scientific theory that is so universally tied to the beliefs and personality of one man.

In this case, Einstein is particularly inappropriate because he did not even believe in black holes or quantum mechanics. So we have no idea what he would think about some alleged contradiction between the two.

I agree with much of what Francis says, but not his conclusion that "Black hole firewalls ... ultimately won't be settled by debate." The issue can only be settled by debate. There is no experiment that can be done to decide the issue. It is not really a scientific question.

Leo Susskind wrote a whole book on how debate supposedly settled a closely related issue, the Black hole information paradox. He is a big believer in paradigm shift theory, and he has no evidence in the usual scientific sense. He claims victory based on opinion polls of his colleagues, not any scientific theory or experiment. He is an example in my book of how How Einstein Ruined Physics.

Update: Freeman Dyson recently wrote:

Permanent free fall was a new idea, counterintuitive and profoundly important. It allows a massive star to keep falling permanently into a black hole without ever reaching the bottom.

Einstein never imagined and never accepted this consequence of his theory.

So yes, Einstein was not the authority on black holes.

Black hole fuzz or fire

Computer complexity theorist Scott Aaronson

Hi from Santa Barbara. I’m at the KITP firewall workshop ...

It’s true that most of the talks have surprisingly little math in them (and, of course, zero input from any recent experiment): it’s mainly just conceptual arguments illustrated by simple cartoons. ...

As I understand it, the issue is actually pretty simple. Do you agree that
(1) the Hawking evaporation process should be unitary, and
(2) the laws of physics should describe the experiences of an infalling observer, not just those of an observer who stays outside the horizon?
If so, then you seem forced to accept ...

How is this even considered science? No experimental evidence and little math -- just cartoons.

I don't see why the laws of physics should tell us about the inside of a black hole. There is no experiment that can tell us anything about what is inside the Schwarzschild radius.

I have argued before (such as here, here, here, and here) that unitarity is a mathematical convenience with no proven physical significance. It is violated by wave function collapse, altho there is no agreement on whether the collapse is real or is an illusion.

Update: A new thesis on wave function collapse has just been posted. It starts with this J.S. Bell quote:

The continuing dispute about quantum measurement theory... is between people who view with di fferent degrees of concern or complacency the following fact: so long as the wave packet reduction is an essential component, and so long as we do not know exactly when and how it takes over from the Schrodinger equation, we do not have an exact and unambiguous formulation of our most fundamental physical theory.

As long as there is this disagreement, there is no agreement that any process is unitary.

Trying to prove the world is random and nonlocal

MyCQstate blog explains entanglement and cryptography, and says:

Although it was explicitly made only relatively recently (see Chapter 5 in Roger Colbeck’s 2009 Ph.D. thesis), the sole violation of any Bell inequality already has one striking consequence: any physical process whose input/output behavior generates said violation cannot by definition satisfy all three basic assumptions (*). Provided that we believe in free will (inputs in the experiment are chosen independently of the system’s internal state) and e.g. special relativity (as a way to enforce the no-signaling condition between the system’s two parts), then I claim that the physical process — whatever it is, quantum mechanical or not — must generate randomness on the fly. ...

Note how we have discovered a very simple test which if verified all but proves that the universe is intrinsically random, based on only very weak physical assumptions. (We do need to assume something, as in principle nothing prevents the whole universe from being fully deterministic.) I think this conclusion deserves to be much more widely known — as Avi Wigderson (almost) suggested recently, it should even be taught in high school! Of course we know (well, maybe not yet in high school) that the laws of quantum mechanics predict that the world is random: they claim that measuring the state ... results in each of the two possible outcomes being obtained with probability 50%.

This is a dubious argument. What could it possibly mean to prove that processes generate randomness on the fly, if you also concede that the universe might be fully deterministic?

Generating randomness is an essential step towards quantum cryptography. They want to say, for example, that an eavesdropper will just get random bits.

In fact there is no proof that anything in nature is truly random. All we can say is that according to quantum mechanics, certain observables are uncorrelated with various other variables of interest. With a little more cleverness and assumptions, we can show that the observables are uncorrelated with hypothetical hidden variables. But that is not really saying much, as the consensus is that hidden variables are impossible anyway.

It sure appears that the radioactive decay of Potassium-40 is random, with known half-life and other statistical properties. Maybe K-40 has a mind of its own and decays when it wants to decay. Or maybe its quarks are vibrating in a chaotic system that would be perfectly predictable if the initial conditions of a billion years ago were perfectly known.

The claims of provable security in quantum cryptography depend on arguments like provable randomness. But no such thing is provable.

The blog recommends an article on The Joy of Entanglement:

Why is the EPR claim "the reasonable thing"? It is reasonable insofar as it follows from a principle that has long guided physicists: the principle of locality -- no action at a distance. Locality implies that particles cannot communicate over spacelike separations. The GHZ thought experiment, however, shows that -- in some sense -- particles do communicate over spacelike separations. Hence quantum mechanics is nonlocal.

In Sect. 2, we stated that such nonlocality seems incompatible with the theory of relativity. Now we have to look more carefully at the apparent incompatibility. Can Alice, Bob and Claire use the GHZ experiment to exchange superluminal signals? Let Alice, say, ... The particles may communicate, but Alice, Bob and Claire cannot. Quantum nonlocality violates the spirit, but not the letter, of relativity theory.

I guess that this is a common view, but I don't think that it is a useful one. It is saying that quantum mechanics requires some sort of strange nonlocality that we can never observe directly.

Assuming lcoality makes more sense to me. The evidence is against local hidden variables, but quantum theory rejects hidden variable anyway. Nonlocality is just an unscientific belief.

Another recommended 2013 survey starts:

Bell's 1964 theorem, which states that the predictions of quantum theory cannot be accounted for by any local theory, represents one of the most profound developments in the foundations of physics. ... We review the main concepts and tools which have been developed to describe and study the nonlocality of quantum theory, and which have raised this topic to the status of a full sub-field of quantum information science.

This is nonsense. The predictions of quantum theory are accounted for by quantum theory, a local theory. Bell's theorem actually says that the predictions of quantum theory cannot be accounted for by any local theory of hidden variables. The theorem is only so profound when it is misstated.

Goedel's Lost Letter blog speculates about a world without randomness. I guess that is what the determinists believe in, but it would be a strange world.

The play “Rosencrantz and Guildenstern are Dead” opens with 157 heads in a row. By multiverse theory there exists a world where that really happened. Playwright Tom Stoppard could have been more subtle and had the coin flips trace out the sequence of prime numbers, in the manner of the novel Contact, or the binary expansion of π. Since the latter are low-complexity deterministic sequences, by Levin’s measures they are scarcely different from all-heads as outcomes. In an unrestricted multiverse, there are worlds where those sequences occur too, for as long as is relevant. Any of those worlds could be our world.

That is another reason to disbelieve in the multiverse.

The word "random" is also used in the sensational reporting of a racist murder:

It comes as Edwards, who has been charged with first-degree murder, posted racist tweets saying he hated white people in the months before the shooting. ...

Authorities allege Lane, a 22-year-old baseball player who had a scholarship with an Oklahoma college and was visiting his US girlfriend Sarah Harper in Duncan, was jogging along Country Club Road when he was shot in the back in a random drive-by shooting.

CNN also reported:

“It does appear random,” Spokane police Lt. Mark Griffiths told reporters. “It appears he was assaulted in the parking lot and there was no indication that he would have known these people prior to the assault.”

It’s the second time in a week that a seemingly random attack by teenagers has claimed a life.

On August 16, a 23-year-old Australian baseball player attending college in Oklahoma was gunned down in the town of Duncan.

One of three teens police arrested in that shooting said they carried it out because “we were bored and didn’t have anything to do.”

The randomness of the two attacks was not lost on Ted Denison, who’s been friends with Belton for a long time.

“It’s really depressing,” Denison told CNN late Thursday night. “Seems that all there is is bad news.”

By comparison, the word in not used in the reporting of this murder:

The jury of six men and six women will reconvene Sept. 4 to determine if Naso gets the death penalty for killing the four women with alliterative names: Roxene Roggasch in 1977, Carmen Colon in 1978, Pamela Parsons in 1993 and Tracy Tafoya in 1994.

I am not sure what makes one crime more random than another.

Celebrating the quantum cat

A Google doodle celebrates Schrödinger's cat. Time magazine explains:

Put a cat in a box, he proposed, and rig up a Rube Goldberg contraption involving a hammer, a vial of poison and a quantum triggering device. If an electron is in one position, the hammer will remain safely cocked. But if the electron moves into the opposite location, the hammer will drop, smashing the vial and killing the cat. The laws of quantum mechanics hold that as long as the electron remains undisturbed, it hangs in limbo, occupying both its possible states. The cat, by extension, is both dead and alive.

This is always presented as some profound quantum mechanical truth, but the pre-quantum explanation is not any different from the quantum explanation. There is not a shred of empirical evidence that a cat can be half dead and half alive. For all we know, the above ket (wave function) is just a mathematical shorthand for our lack of knowledge about whether the cat is dead or alive. Some people say that the cat is dead in one world, and alive in another. But that explains nothing. In quantum mechanics, a state is often written as a superposition of possibilities, even tho a measurement would constrain the state to one of those possibilities. The Schroedinger cat is just an analogy for thinking about such superpositions. But it is not to be taken too seriously.

Cosmologist Sean M. Carroll has put his Quantum Mechanics Made Easy online. It is not bad. He is interested in the arrow of time, and he notes that collapse of the wave function is irreversible. There is no agreement on what the collapse means, or whether the wave function really collapses. He also encourages describing quantum mechanics in 5 words:

Interfering probability theory.
Everything is waves, until measured.
representation theory of Poincaré group
unintuitive doesn't mean not comprehendable
You understand it? Me, neither.
multiple outcomes to single measurement
Probabilities on orthomodular proposition lattices
Imperfectly predictable and unpredictably perfect.
Schizophrenic states waiting for measurement.
nonrelativistic particles with discrete energies.
They're everywhere. Until you look.
Everything not forbidden is mandatory.
All knowledge is precisely uncertain.
Stop dictating to God, Einstein!

I like the "waves until measured".