Monday, December 28, 2020

Big players double down on quantum computing

Cnet reports:
For years, quantum computing has been the preserve of academics. New advances, however, are pushing this potentially revolutionary technology toward practical applications.

At the Q2B conference this month, quantum computer makers Google, IBM, Honeywell, IonQ and Xanadu detailed specific steps they expect by 2024 that will push their machines further down the road of commercial practicality. Those achievements include increasing quantum computers' scale, performance and reliability. Private sector spending on quantum computing products and services will likely more than triple to $830 million in 2024, up from $250 million in 2019, according to a forecast from Hyperion Research.

"We're in the early industrial era of quantum computing," said Seth Lloyd, an MIT professor who helped found the field in the 1990s. He says the "huge advances" are comparable to the early use of steam engines to power factories, ships and trains.

There is still no one who can make a scalable qubit, or a quantum computer that speeds up some classical algorithm.
One of the most bullish voices is Eric Schmidt, who in his former job as Google's chief executive and executive chairman approved that company's long-term quantum computing program. That work produced last year's "quantum supremacy" experiment that showed quantum computers could surpass classical computers for at least one narrow (though not practical) computing chore.

"We know this stuff is going to happen six to eight years from now," Schmidt said. "It's going to be incredible when it happens."

Where are those self-driving cars?

That technology has also been a lot slower than promises and expectations. But there are prototypes that prove that self-driving can be done, even if they are not quite reliable enough for commercial use.

We still have no such proof for quantum computing.

Thursday, December 24, 2020

The Marxist critique of Bohr’s alleged idealism

A recent paper on Niels Bohr, objectivity, and the irreversibility of measurements says:
There are three reasons (listed by Catherine Chevalley [15]) why Bohr seems obscure today. The first is that Bohr’s views have come to be equated with one variant or another of the Copenhagen interpretation. The latter only emerged in the mid-1950’s, in response to David Bohm’s hidden-variables theory and the Marxist critique of Bohr’s alleged idealism, which had inspired Bohm.
It is curious. For decades, Bohr was considered the authority on the orthodox interpretation of quantum mechanics. So much so that it was called Copenhagen. He is the one physicists who pointedly refuted Einstein, and everyone at the time was convinced that Bohr was right and Einstein was wrong.

At some point it became fashionable to badmouth Bohr. They didn't say that he was wrong, but vehemently argued that he didn't make any sense. He became "obscure".

How could he be so right that the textbooks copied him for decades, and yet others say that he was unintelligible?

Here we have an explanation: David Bohm’s hidden-variables theory and the Marxist critique of Bohr’s alleged idealism.

Wow, I thought that physicists were much too hard-headed to be swayed by the mystical ramblings of Bohm, and certainly not influence by a "Marxist critique"! But there you have it.

I have been suspicious that there is some subversive political or mystical ideology behind pilot wave theory and related matters. This confirms it. 

The above paper also has some interesting things to say about irreversibility. Maybe I will revisit that later.

Merry Christmas.

Monday, December 21, 2020

Physics does not predict rigid trajectories

Free will is mostly a philosophical issue, but some of the arguments are subject to scientific analysis. Jerry Coyne writes:
The fact that articles keep coming out assuring us that we do have free will, yet each assurance is based on a different premise, tells us that the philosophical debate will never end. Yet I consider it already ended by science: we do not have libertarian free will because our thoughts and our actions are decided by the laws of physics and not by some numinous “will” that interacts with matter in ways that physicist Sean Carroll has said is impossible. Ergo the appearance of compatibilists, who admit that yes, determinism rules, and at any one moment we can behave only one way—a way determined by physical law—but nevertheless we have other kinds of free will compatible with determinism.

That, of course, won’t satisfy the majority of people who do believe in libertarian you-can-do-otherwise free will, among these the many religionists whose faith absolutely depends on our being able to choose our path of life and our savior, and your salvation depends on making the right choice (Calvinists and their analogues are an exception). Compatibilists, when they tell us that nobody really believes in libertarian free will, are simply wrong: surveys show otherwise, and there are all those believers.

No, this is just wrong. The laws of physics are not so deterministic as to rule out libertarian free will.

I recently criticized Sean M. Carroll on free will.

Coyne is responding to this essay:

We need not think about the fundamental laws of physics as rails directing reality along a rigid trajectory. Rather, we can think of them as constraints on what kinds of physical transformations are possible and impossible. ...

Famous ‘free will sceptics’ like Jerry Coyne and Sam Harris are rightly worried about ditching the concept of physical determinism. In their view, the only alternative is a mysticism allowing for all kinds of silly miracles and supernatural beings. ... we still live in a universe governed by timeless, fixed laws — it’s just that these laws do not dictate by themselves how exactly the future will unfold.

..., we don’t need to accept the notion that the universe evolves according to some predetermined plan, set in stone from the beginning of time. Our best theories of physics don’t require it, and our best ethical, psychological, and political theories must reject it.

The essay refers to this 2014 paper for theoretical support. That paper is sympathetic to many-worlds theory, which is another can of worms.

Regardless, it is true that the laws of physics impose contraints on motions, and not rigid trajectories.

In a freshman physics textbook, you might see an exercise that calculates the trajectory of a cannonball, and that may seem to have infinite precision. But that is just the simplified freshman version. If you apply the laws of physics properly, you find that the forces, masses, and other parameters can only be known to be in some range of values, and the predicted trajectory is really a contraint on a range of possible trajectories.

Calvinists and academic atheists aren't the only exceptions to believing in free will. So do Moslems, and a lot of Protestant theologians.

Friday, December 18, 2020

Latest Quantum Supremacy claim starts to crumble

Scott Aaronson backtracks on quantum supremacy. After telling us for years that Gil Kalai was wrong to be skeptical about quantum supremacy, he now admits that one of Kalai's criticisms turned out to be correct.

There are now two high-prestige publications claiming quantum supremacy. Aaronson was the referee on both, and thus he got to decide that these papers were worthy of the claim.

Here is the game. Some quantum researchers do a complicated experiment, and then declare that it would be hard to simulate. But no one is particularly interested in simulating it, and we don't know how hard the problem is.

An example of a hard quantum problem is protein folding. Proteins naturally fold in milliseconds, but researchers have spent decades trying to find algorithms to predict foldings. If the protein were a quantum computer, then Aaronson would say that it has acheived quantum supremacy.

Except that Google DeepMind may have just cracked the problem. This work is very exciting, and may be worthy of next years Nobel Prize in Chemistry. They did not use quantum computers.

So it does not show quantum supremacy at all.

Maybe all these quantum supremacy experiments could be simulated by classical computers, if a team of experts spent 30 years finding a good algorithm.

Ultimately someone may find a quantum experiment that is hard to simulate. But in my mind, it won't really be quantum computation unless it computes something like Shor's algorithm that cannot be in reasonable time on a classical computer.

Update: Also amusing is Aaronson's new blog tagline:

If you take nothing else from this blog: quantum computers won't
solve hard problems instantly by just trying all solutions in parallel.

"The Far Right is destroying the world, and the Far Left is blaming me!"
The first part has been there for a while, and it refers to the facts that nearly everyone describes quantum computers as trying solutions in parallel, but they have never been shown to do that.

The new part refers to him agreeing with 95% of the Leftist agenda, but that makes him seem like a right-winger in today's academia.

Monday, December 14, 2020

Free Will v. Insanity

If somebody said that he hears voices in his head, or that he has a twin that no one can see, or believes in an invisible world, then you would infer that he is schizophrenic, or suffers some similar mental illness.

If somebody believes in Heaven, Hell, angels, and devils, and prays to an invisible god, you would infer that he is religious, but not crazy.

But what do you make of somebody with an advanced scientific degree who believes:

* You have identical twins in distant universes.

* Our world is just a simulation, running on a computer in a more advanced civilization.

* The universe constantly splits into parallel universes, where every possibility is played out for real.

* All events have been pre-determined, from the first second of the Big Bang.

* We have no free will, and all actions are controlled as with a robot or puppet.

All these things seem like symptoms of mental illness to me.

Another tipoff is having crazy ideas about randomness. Insane people sometimes think that nothing is random, and every coincidence is a manifestation of some bizarre conspiracy of causes. Or they think that randomness is one of the fundamental forces in the universe, disrupting everything. Either way, the insane man is troubled by imaginary demons that are sabotaging his life.

So how am I supposed to think about respected physics professors who believe in this crazy stuff? I do not have a good answer for this.

I have reviewed some debates on free will, from respected professors. I think that they are all insane. I wonder how they can even function in their daily lives with such peculiar beliefs.

As an example, see Sean M. Carroll's most recent podcast. He is pretty good at explaining physics, but he also believes in a lot of wacky stuff. He believes in the many-worlds multiverse. He claims to believe in free will, but he also believes in a deterministic multiverse. At 2:10:40, he gets a question about free will and determinism. He concedes that our branch of the multiverse may not be deterministic, but he adamantly argues:

There is a question about whether or not the laws of physics are deterministic or indeterministic, but that has zero to do with the question of free will. The strong sense of free will, the libertarian sense of free will, has to do with whether or not you personally can violate the laws of physics, just by thinking about it. And I don't think that's true, but whether or not it's true, has nothing to do with whether the laws are deterministic or indeterministic.
This is just nutty on multiple levels.

What does he mean by "laws of physics"? He includes many-worlds multiverse, even tho it makes no predictions and has no relation to reality. It is just a fantasy game, where he pretends that all possibilities are happening in some parallel universe. He does not include strong or libertarian free will, as he thinks that means willing a law violation.

If a law of physics is violated, then it is not really a law of physics. Defining free will as a violation does not solve anything.

Part of his problem is that he is always talking about what is "fundamental" or not. Some laws of physics are, and some are not. Some are emergent. Many of these opinions are based on what he thinks will be in some hypothetical Final Theory, from which all else will be derived.

My personal opinion is that consciousness and free will are real, and consistent with the laws of physics. We may or may not get better theoretical understandings of them in the future, but personal experience today convinces me of the nature of consciousness and free will. It is not contrary to any known law of physics.

But Carroll says free will has zero to do with determinism. He doesn't believe that he has any ability to make any choices, as they are all determined. There could be parallel universe branching to confuse matters, but that does not affect his view that all his choices are just illusions.

Elsewhere in the podcast, he explains his belief in eternalism. The present time is just another illusion, and all times are equally valid. Our minds just remember the past instead of the future, because entropy is increasing in the brain.

I think that Carroll would be considered insane, except that he is also able to explain coherently a lot of textbook physics.

On the subject of what is fundament, the "Ask a Physicist" blog tries to explain Carroll's many-worlds nonsense, without much success, and notes:

Very, very frustratingly, without declaring a measurement scheme in advance, you can’t even talk about quantum systems being in any particular set of states. For example, a circularly polarized photon can be described as some combination of vertical and horizontal states, so there’s your two worlds, or it can described as a combination of the two diagonal states, so there’s your… also two worlds. This photon is free to be in multiple states in multiple ways or even be in a definite state, depending on how you’d like to interact with it. For the world to properly “split” a distinction must be made about how the photon is to be measured, but that isn’t something intrinsic to either the photon or the universe.
It is this sort of argument that makes me doubt whether it is useful to even talk about something being fundamental. Which type of polarization is the fundamental one? It is impossible to say, as each type appears non-fundamental when viewed in the context of the other. You are apt to think one is fundamental if it happened to be explained first in whatever textbook you used.

Much of Physics is this way. Things seem fundamental when explained one way, but there is often an equivalent theory where something else is fundamental. For example, some people think particles are fundamental and fields are derived, while others think fields are fundamental and particles are derived.

Wednesday, December 9, 2020

Einstein plagiarized Kaluza-Klein

A reader named Peter writes:
It is possible that Einstein had some character flaw because totally unnecessarily already after his Nobel prize and when he was more famous than any other physicist before him in 1927 he plagiarized 1926 paper of Oscar Klein that lead to the Kaluza-Klein theory. But he was caught and the editor of the journal forced Einstein to write a statement that everything he showed was done year earlier by Klein.
I did not know that story when I wrote my book, but I am not surprised. Yes, Einstein had a character flaw where he avoided crediting anyone. As Peter says, the Einstein collected works acknowledge that Einstein knew of the Kaluza-Klein work, and deliberately omitted any citation.

Properly crediting Kaluza-Klein theory is tricky. It appears that mathematician H. Weyl clearly understood that you could get general relativity and Maxwell's equations from and appropriate curvature on a 5-dimensional manifold. One dimension is time, and one is electromagnetic phase. Surely others understood this also. However I cannot find where anyone wrote it down clearly until many decades later, where it uses a connection on a circle bundle over a spacetime.

Another example that was new to me was his refusal to credit Gerber for the Mercury precession formula. Einstein claimed to not know that Gerber published the formula before, but even said that he would not have cited Gerber even if he had known.

I mostly judge Einstein for his Physics, not his personal ethics. But it is sometimes hard to figure out what he rediscovered, and what he stole.

Peter also says:

When Einstein derived (did not show details) the superposition of velocities he stated that the operation constitute a mathematic group. Interestingly pretty much the same phrase was in Poincare 1905 paper. Somehow I have difficulty believing that Einstein would use such a cool and fairly modern at that time mathematical concept which obviously was natural for Poincare.
Yes, I agree with that. At best, Einstein was saying that the one-dimensional set of transformations in one direction form a group, as there is no sign that he grasped the significance of all Lorentz transformations forming a group. He likely got the term "group" from Poincare's paper.


It is interesting that in many textbooks Michelson precedes STR that is present as explanation of Michelson but it never is stated that Einstein did not use or was aware of Michelson. What motivated Einstein work, which experiments?
Historians have debated this, and I have my own theory. I say that Einstein was not directly influenced by any experiment.

Michelson-Morley and other experiments clearly influenced Lorentz's 1895 paper, and Poincare's work. The purpose of Einstein's 1905 paper is just to give an alternate derivation of Lorentz's formulas, and not to give an empirical argument. There was no reason to rely on any experiment directly.

Einstein's comments on this seem confusing, but I think he was simply saying that Michelson-Morley was important to the history of special relativity, but not to his own 1905 paper. Those things are true. They are not confusing if you understand that special relativity had a history before Einstein.

Monday, December 7, 2020

Difference between Mathematicians and Physicists

For the last 50 years, physics has gotten so mathematical that many people view mathematics and physics as two variants of the same field. The star of this view is Ed Witten, who is widely for both his mathematics and physics.

This is mistaken. Mathematics and Physics are not so similar. Yes, they both use numbers and fancy symbols, but here are three big differences.

Proof v experiment. Mathematics is all about what can be proved from the axioms, like ZFC. The mathematician seeks 100% certain knowledge, and settles for nothing less. The physicists gains validation by doing experiments. Truth is just a tentative shorthand for explaining some observations.

Infinity. All the interesting mathematics uses infinities. The concept is essential to everything. There are no infinities in the natural world. While they occasionally crop up in some physics theories, they are not essential to anything, and there is no reason for a physicist to believe in them.

Spin. Mathematicians are like fermions, and physicists like bosons. Each mathematician is like a unique piece to a giant jigsaw puzzle of knowledge. Physicists do not see things that way at all, as they replicate the work of others and are susceptible to groupthink.

These are huge differences. They are so large that I don't think that it makes sense to say that the fields overlap.

Sure, math gets applied to physics, and there are some mathematical physicists who are really mathematicians in their outlook. But mostly, mathematicians and physicists are different animals.

Dr. Bee writes on whether infinity is real:

Infinity and zero are everywhere in physics. Even in seemingly innocent things like space, or space-time. The moment you write down the mathematics for space, you assume there are no gaps in it. You assume it’s a perfectly smooth continuum, made of infinitely many infinitely small points.

Mathematically, that’s a convenient assumption because it’s easy to work with. And it seems to be working just fine. That’s why most physicists do not worry all that much about it. They just use infinity as a useful mathematical tool.

But maybe using infinity and zero in physics brings in mistakes because these assumptions are not only not scientifically justified, they are not scientifically justifiable. And this may play a role in our understanding of the cosmos or quantum mechanics. This is why some physicists, like George Ellis, Tim Palmer, and Nicolas Gisin have argued that we should be formulating physics without using infinities or infinitely precise numbers.

Infinity and zero are everywhere in mathematics, so if you are applying math to physics, they will be there. But they are only mathematically real, and do not exist in the natural world.

Friday, December 4, 2020

Quantum Supremacy claimed again

SciAm reports:
For the first time, a quantum computer made from photons—particles of light—has outperformed even the fastest classical supercomputers.

Physicists led by Chao-Yang Lu and Jian-Wei Pan of the University of Science and Technology of China (USTC) in Shanghai performed a technique called Gaussian boson sampling with their quantum computer, named Jiŭzhāng. The result, reported in the journal Science, was 76 detected photons—far above and beyond the previous record of five detected photons and the capabilities of classical supercomputers. ...

This is only the second demonstration of quantum primacy [supremacy], which is a term that describes the point at which a quantum computer exponentially outspeeds any classical one, effectively doing what would otherwise essentially be computationally impossible.

The article uses "primacy" instead of "supremacy", because of George Floyd. Or maybe Donald Trump or George Washington, I am not sure.

Scott Aaronson brags about it, as they needed to get his approval to call it quantum supremacy. He didn't invent the term, but he owns it now.

Okay, I am going to have to study this. What was really computed?

The setup for boson sampling is analogous to the toy called a bean machine, which is just a peg-studded board covered with a sheet of clear glass. Balls are dropped into the rows of pegs from the top. On their way down, they bounce off of the pegs and each other until they land in slots at the bottom. Simulating the distribution of balls in slots is relatively easy on a classical computer.

Instead of balls, boson sampling uses photons, and it replaces pegs with mirrors and prisms. Photons from the lasers bounce off of mirrors and through prisms until they land in a “slot” to be detected. ...

Even so, she acknowledges that the USTC setup is dauntingly complicated. Jiŭzhāng begins with a laser that is split so it strikes 25 crystals made of potassium titanyl phosphate. After each crystal is hit, it reliably spits out two photons in opposite directions. The photons are then sent through 100 inputs, where they race through a track made of 300 prisms and 75 mirrors. Finally, the photons land in 100 slots where they are detected. Averaging over 200 seconds of runs, the USTC group detected about 43 photons per run. But in one run, they observed 76 photons — more than enough to justify their quantum primacy claim.

It is difficult to estimate just how much time would be needed for a supercomputer to solve a distribution with 76 detected photons—in large part because it is not exactly feasible to spend 2.5 billion years running a supercomputer to directly check it. Instead, the researchers extrapolate from the time it takes to classically calculate for smaller numbers of detected photons. At best, solving for 50 photons, the researchers claim, would take a supercomputer two days, which is far slower than the 200-second run time of Jiŭzhāng.

It appears to me that they didn't compute anything. They just concocted a complicated setup that would be hard to simulate. It is hard for me to see how anything like this could be applied to a useful computation.

But I should study this more before jumping to conclusions. I am still trying to figure out what is so impressive about observing 76 photons in one run.

Wednesday, December 2, 2020

Einstein's God

Nautilus essay:
In 1929, Einstein received a telegram inquiring about his belief in God from a New York rabbi named Herbert Goldstein, who had heard a Boston cardinal say that the physicist’s theory of relativity implies “the ghastly apparition of atheism.” Einstein settled Goldstein down. “I believe in Spinoza’s God, who reveals himself in the lawful harmony of the world,” he told him, “not in a God who concerns himself with the fate and the doings of mankind.”

What that amounted to for Einstein, according to a 2006 paper, was a “cosmic religious feeling” that required no “anthropomorphic conception of God.” He explained this view in the New York Times Magazine: “The religious geniuses of all ages have been distinguished by this kind of religious feeling, which knows no dogma and no God conceived in man’s image; so that there can be no church whose central teachings are based on it. Hence it is precisely among the heretics of every age that we find men who were filled with this highest kind of religious feeling and were in many cases regarded by their contemporaries as atheists, sometimes also as saints. Looked at in this light, men like Democritus, Francis of Assisi, and Spinoza are closely akin to one another.”

So, as Einstein would have it, there is no necessary conflict between science and religion — or between science and “religious feelings.”