Saturday, October 19, 2019

Google overhyped announcement imminent

Nautilus:
News on the quantum physics grapevine, Frankfurt Institute theoretical physicist Sabine Hossenfelder tells me, is that Google will announce something special next week: Their paper on achieving quantum supremacy, the realization of a quantum computer that outdoes its conventional counterpart. ...

It’s nothing to get too excited about yet. “This” — NISQ — “is really a term invented to make investors believe that quantum computing will have practical applications in the next decades or so,” Hossenfelder says. “The trouble with NISQs is that while it is plausible that they soon will be practically feasible, no one knows how to calculate something useful with them.” Perhaps no one ever will. “I am presently quite worried that quantum computing will go the same way as nuclear fusion, that it will remain forever promising but never quite work.”
We know that the Sun gets its energy from nuclear fusion. We don't know that quantum speedups are even possible.

Thursday, October 17, 2019

Rovelli: Neither Presentism nor Eternalism

Physicist Carlo Rovelli writes in support of Neither Presentism nor Eternalism:
Shortly after the formulation of special relativity, Einstein's former math professor Minkowski found an elegant reformulation of the theory in terms of the four dimensional geometry that we call today Minkowski space. Einstein at first rejected the idea. (`A pointless mathematical complication'.) But he soon changed his mind and embraced it full heart, making it the starting point of general relativity, where Minkowski space is understood as the local approximation to a 4d, pseudo-Riemannian manifold, representing physical spacetime.

The mathematics of Minkowski and general relativity suggested an alternative to Presentism: the entire 4d spacetime is `equally real now', and becoming is illusory. This I call here Eternalism.
Other make this argument that relativity implies a eternalism philosophy of time. I disagree with this argument. You can talk about spacetime with either Galilean or Lorentz transformations. If that is eternalist, then it is either with or without relativity.

Note that Rovelli is compelled to make his relativity story all about Einstein, even tho he had nothing to do with the issue at hand. Minkowski did not reformulate Einstein's theory, as it is not clear that Minkowski was ever influenced by anything Einstein wrote. Spacetime relativity was first published by Poincare, and Minkowski cited Poincare.

Rovelli ends up wanting some compromise between presentism and eternalism, as both views are really just philosophical extremes to emphasize particular ways of thinking about time. This might seem obvious, except that there are a lot of physicists who say that relativity requires eternalism.

Monday, October 14, 2019

The hardest of the hard sciences has gone soft

Science writer Jim Baggott writes in Aeon:
So what if a handful of theoretical physicists want to indulge their inner metaphysician and publish papers that few outside their small academic circle will ever read? But look back to the beginning of this essay. Whether they intend it or not (and trust me, they intend it), this stuff has a habit of leaking into the public domain, dripping like acid into the very foundations of science. The publication of Carroll’s book Something Deeply Hidden, about the Many-Worlds interpretation, has been accompanied by an astonishing publicity blitz, including an essay on Aeon last month. A recent PBS News Hour piece led with the observation that: ‘The “Many-Worlds” theory in quantum mechanics suggests that, with every decision you make, a new universe springs into existence containing what amounts to a new version of you.’

Physics is supposed to be the hardest of the ‘hard sciences’. It sets standards by which we tend to judge all scientific endeavour. And people are watching.
Physics has become embarrassingly unscientific.

Unsurprisingly, the folks at the Discovery Institute, the Seattle-based think-tank for creationism and intelligent design, have been following the unfolding developments in theoretical physics with great interest. The Catholic evangelist Denyse O’Leary, writing for the Institute’s Evolution News blog in 2017, suggests that: ‘Advocates [of the multiverse] do not merely propose that we accept faulty evidence. They want us to abandon evidence as a key criterion for acceptance of their theory.’ The creationists are saying, with some justification: look, you accuse us of pseudoscience, but how is what you’re doing in the name of science any different?
Yes, I think it is different. The folks at the Discovery Institute try to support their ideas with evidence. Carroll has no evidence for his ideas, and denies that any evidence is needed.
Instead of ‘the multiverse exists’ and ‘it might be true’, is it really so difficult to say something like ‘the multiverse has some philosophical attractions, but it is highly speculative and controversial, and there is no evidence for it’?
No, many worlds is not some speculative idea that might be true. Saying that would suggest that there might be evidence for it. There can be no evidence for it.

Sabine Hossenfelder writes:
Right, as I say in my public lecture, physicists know they shouldn't make these arguments, but they do it nevertheless. That's why I am convinced humans will go extinct in the next few hundred years.
Extinct? Maybe rational humans will die out, and be replaced by intelligent robots and an uneducated underclass.

Wednesday, October 9, 2019

Preskill explains quantum supremacy

Physicist John Preskill writes in Quillette:
In 2012, I proposed the term “quantum supremacy” to describe the point where quantum computers can do things that classical computers can’t, regardless of whether those tasks are useful. ...

The words “quantum supremacy” — if not the concept — proved to be controversial for two reasons. One is that supremacy, through its association with white supremacy, evokes a repugnant political stance. The other reason is that the word exacerbates the already overhyped reporting on the status of quantum technology.
This is funny. A few years ago, supremacy might have invoked thoughts of kings, empires, popes, and laws, but not white people. Now rationalist internet forums get frequented by misogynists and white nationalists. Preskill seems to be referring to this gripe about white supremacy.
The catch, as the Google team acknowledges, is that the problem their machine solved with astounding speed was carefully chosen just for the purpose of demonstrating the quantum computer’s superiority. It is not otherwise a problem of much practical interest. In brief, the quantum computer executed a randomly chosen sequence of instructions, and then all the qubits were measured to produce an output bit string. This quantum computation has very little structure, which makes it harder for the classical computer to keep up, but also means that the answer is not very informative.

However, the demonstration is still significant. By checking that the output of their quantum computer agrees with the output of a classical supercomputer (in cases where it doesn’t take thousands of years), the team has verified that they understand their device and that it performs as it should. Now that we know the hardware is working, we can begin the search for more useful applications.
The term "quantum supremacy" suggests a major accomplishment. But all we really know is that the hardware is working.

We also know that they did a quantum experiment that is hard to simulate. But so what? The weather is hard to simulate. A lot of things are hard to simulate.

Here is Preskill's 2012 paper on quantum supremacy, and 2018 paper on NISQ. The latter says:
I’ve already emphasized repeatedly that it will probably be a long time before we have fault-tolerant quantum computers solving hard problems. ...

Nevertheless, solving really hard problems (like factoring numbers which are thousands of bits long) using fault-tolerant quantum computing is not likely to happen for a while, because of the large number of physical qubits needed. To run algorithms involving thousands of protected qubits we’ll need a number of physical qubits which is in the millions, or more [56].
So a quantum computer that tells us something we didn't already know is decades away. Or impossible.

Monday, October 7, 2019

Many-Worlds does not solve measurement

Dr. Bee has a podcast on The Trouble with Many Worlds:
The measurement process therefore is not only an additional assumption that quantum mechanics needs to reproduce what we observe. It is actually incompatible with the Schrödinger equation.

Now, the most obvious way to deal with that is to say, well, the measurement process is something complicated that we do not yet understand, and the wave-function collapse is a placeholder that we use until we will figured out something better.

But that’s not how most physicists deal with it.
Actually, I think it is. Quantum mechanics was created by positivists, and their attitude is to go with what we've got, and not worry too much about purely philosophical objections.
Most sign up for what is known as the Copenhagen interpretation, that basically says you’re not supposed to ask what happens during measurement. In this interpretation, quantum mechanics is merely a mathematical machinery that makes predictions and that’s that. The problem with Copenhagen – and with all similar interpretations – is that they require you to give up the idea that what a macroscopic object, like a detector does should be derivable from theory of its microscopic constituents.

If you believe in the Copenhagen interpretation you have to buy that what the detector does just cannot be derived from the behavior of its microscopic constituents.
The positivists would go along with saying that the theory is all about the predictions, but would never say that you are not supposed to ask about the measurement process. Positivists do not tell you what not to do. They talk about what works.

She is completely correct that the collapse is observed. Some people complain that Copenhagen is goofy because the collapse is unnatural, but all interpretations have to explain the apparent collapse somehow.
The many world interpretation, now, supposedly does away with the problem of the quantum measurement and it does this by just saying there isn’t such a thing as wavefunction collapse. Instead, many worlds people say, every time you make a measurement, the universe splits into several parallel words, one for each possible measurement outcome. This universe splitting is also sometimes called branching. ...

And because it’s the same thing you already know that you cannot derive this detector definition from the Schrödinger equation. It’s not possible. What the many worlds people are now trying instead is to derive this postulate from rational choice theory. But of course that brings back in macroscopic terms, like actors who make decisions and so on. In other words, this reference to knowledge is equally in conflict with reductionism as is the Copenhagen interpretation.

And that’s why the many worlds interpretation does not solve the measurement problem and therefore it is equally troubled as all other interpretations of quantum mechanics.
She is right that Many-Worlds does not solve the measurement problem, and really has to have its own sneaky collapse postulate like Copenhagen, even tho the whole point of Many-Worlds was to avoid that.

However the situation with Many-Worlds is worse than that. Any physical theory could be turned into a Many-Worlds theory by simply introducing a universe splitting for each probabilistic prediction. This can be done with Newtonian celestial mechanics, electromagnetism, relativity, or anything else.

With any of these Many-Worlds theories, you can believe in them if you want, but the split universes have no observable consequences except to reduce or kill the predictive power of your theory. Any freak event can be explained away by splitting to another universe.

So Many-Worlds does not, and cannot, explain anything. It is just smoke and mirrors.

A reader asks:
What is your explanation as to why many people who are obviously very smart, such as Max Tegmark, David Deutsch, Sean Carroll, etc, subscribe to the many-worlds interpretation?
Why do so many smart people tell lies about Donald Trump every day?

I wrote a whole book on how Physics has lost its way. There is now a long list of subjects where prominent Physics professors recite nonsense. I hesitate to say that they are all con men, as many appear to be sincerely misguided.

Friday, October 4, 2019

Google scooped by unconventional p-bit computer

It is funny how quantum computing evangelist Scott Aaronson is flummoxed by being scooped by a rival technology:
Nature paper entitled Integer factorization using stochastic magnetic tunnel junctions (warning: paywalled). See also here for a university press release.

The authors report building a new kind of computer based on asynchronously updated “p-bits” (probabilistic bits). A p-bit is “a robust, classical entity fluctuating in time between 0 and 1, which interacts with other p-bits … using principles inspired by neural networks.” They build a device with 8 p-bits, and use it to factor integers up to 945. They present this as another “unconventional computation scheme” alongside quantum computing, and as a “potentially scalable hardware approach to the difficult problems of optimization and sampling.”

A commentary accompanying the Nature paper goes much further still — claiming that the new factoring approach, “if improved, could threaten data encryption,” and that resources should now be diverted from quantum computing to this promising new idea, one with the advantages of requiring no refrigeration or maintenance of delicate entangled states. (It should’ve added: and how big a number has Shor’s algorithm factored anyway, 21? Compared to 945, that’s peanuts!)

Since I couldn’t figure out a gentler way to say this, here goes: it’s astounding that this paper and commentary made it into Nature in the form that they did. This is funny. While Google is keeping mum in order to over-dramatize their silly result, a rival group steals the spotlight with non-quantum technology.

Aaronson is annoyed that this is non-quantum technology making extravagant claims, but exactly how is the Google quantum computer effort any better?

Apparently Google refuses to compete in any meaningful way, as Aaronson says
How large a number Google could factor, by running Shor’s algorithm on its current device, is a semi-interesting question to which I don’t know the answer. My guess would be that they could at least get up to the hundreds, depending on how much precompilation and other classical trickery was allowed. The Google group has expressed no interest in doing this, regarding it (with some justice) as a circus stunt that doesn’t showcase the real abilities of the hardware.
A circus stunt? Obviously the results would be embarrassingly bad for Google.

Others have claimed to use quantum computers to factor 15 or , but those were circus stunts. They failed to show any evidence of a quantum speedup.

An interesting quantum computer result would factor numbers with Shor's algorithm, and show how the work scales with the size of the number.

Also:
But as I explained in the FAQ, running Shor to factor a classically intractable number will set you back thousands of logical qubits, which after error-correction could translate into millions of physical qubits. That’s why no can do it yet.
And that is why we will not see true quantum supremacy any time soon. All Google has is a fancy random number generator.

Thursday, October 3, 2019

How there is mathematical pluralism

Mathematics is the study of absolute truth.

It is common for non-mathematicians to try to deny this. Sometimes they give arguments like saying that Goedel proved that mathematical truth is not possible. Goedel would never have agreed to that.

Mathematician Timothy Chow writes:
I would say that virtually all professional mathematicians agree that questions of the form “Does Theorem T provably follow from Axioms A1, A2, and A3?” have objectively true answers. ...

On the other hand, when it comes to the question of whether Axioms A1, A2, and A3 are true, then I think we have (what I called) “pluralism” in mathematics.
That is correct.

There are some axioms for the existence of very large cardinals, and some disagreement among mathematicians about whether those axioms should be regarded as true. But there is not really any serious disagreement about the truth of published theorems.

Other fields, like Physics, are filled with disputes about what is true.