Tuesday, December 26, 2023

Q-Day Predicted for 2025

Reuters reports:
QD5’s executive vice president, Tilo Kunz, told officials from the Defense Information Systems Agency that possibly as soon as 2025, the world would arrive at what has been dubbed “Q-day,” the day when quantum computers make current encryption methods useless. Machines vastly more powerful than today’s fastest supercomputers would be capable of cracking the codes that protect virtually all modern communication, he told the agency, which is tasked with safeguarding the U.S. military’s communications.

In the meantime, Kunz told the panel, a global effort to plunder data is underway so that intercepted messages can be decoded after Q-day in what he described as “harvest now, decrypt later” attacks, according to a recording of the session the agency later made public.

Militaries would see their long-term plans and intelligence gathering exposed to enemies. Businesses could have their intellectual property swiped. People’s health records would be laid bare. ...

Kunz is among a growing chorus sounding this alarm. Many cyber experts believe all the major powers are collecting ahead of Q-day. The United States and China, the world’s leading military powers, are accusing each other of data harvesting on a grand scale.

Okay, I am marking the calendar. 2025 is only a year away.

I think that there is no chance of a Q-Day in my lifetime, but it is nice to have these predictions.

Sunday, December 24, 2023

Guth on Observers

Here is a short interview:
Alan Guth - What are Observers?

Why is an observer a critical part of quantum physics? What does it mean to be an observer? Does the act of observation affect what exists and what happens in the external world? Why is observation in the quantum world still a mystery?

He accepts many-worlds theory, and claims most of his colleagues do. He says it is simpler because you just accept the Schroedinger equation, and you eliminate the need for observers or for making predictions.

So a theory is simpler if you do not worry about observations.

They may sound bad, he says, but it ties in nicely with the eternal inflation cosmology theory. That has infinitely many universes being spawned for other reasons, and the infinities make probabilities hard to understand.

Guth is a big-shot MIT Physics professor. It baffles me how smart guys can recite this nonsense.

Sure, you can simplify a theory by removing the part that allows predictions to be compared with observations. But then what good is the theory?

There are no infinities in nature.

You can say that collapse of the wave function is not needed if we just better understood how wave functions can evolve into disparate pieces. Then we could focus on the piece that applies to observations in our world. But that is just another way of saying the function collapsed, with the other pieces being unreachable. Many worlds theory does not explain anything.

Thursday, December 21, 2023

Relativity was not Influenced by Philosophy

2019 article:
Last week it was revealed that Edinburgh University’s David Purdie had discovered a letter from Albert Einstein in which the great scientist notes the importance of 18th-century Scottish philosopher David Hume in developing his theory of special relativity.

Without having reading Hume’s A Treatise of Human Nature, Einstein wrote: “I cannot say that the solution would have come.”

Historians have, in fact, long known about Einstein’s debt to Hume, and indeed about that letter. They’ve known, too, about the influence on Einstein of many other philosophers, from Ernst Mach to Arthur Schopenhauer. Part of what many find intriguing about the story is the idea that scientific theories should be shaped by philosophical ideas. It has become common for scientists to dismiss philosophy as irrelevant to their work.

The flaw in this argument is that Einstein had almost nothing to do with the discovery of special relativity. He wrote a 1905 paper that is credited heavily today, but at the time it was just an exposition of Lorentz's theory, and soon superseded by papers by Poincare and Minkowski. Relativity became popular from Minkowski, not Einstein.

I have argued that a belief in causality could have led natural philosophers to the basic ideas of relativity, but it did not.

Monday, December 18, 2023

Do Black Holes have Singularities?

New paper:
There is no proof that black holes contain singularities when they are generated by real physical bodies. Roger Penrose claimed sixty years ago that trapped surfaces inevitably lead to light rays of finite affine length (FALL's). Penrose and Stephen Hawking then asserted that these must end in actual singularities. When they could not prove this they decreed it to be self evident. It is shown that there are counterexamples through every point in the Kerr metric. These are asymptotic to at least one event horizon and do not end in singularities.
It is by the same Kerr who found the general relativity solution for rotating black holes.

I will have to read this. It is hard to believe that everyone exaggerated the Penrose Hawking singularity theorems.

Thursday, December 14, 2023

Why we use the Lebesgue Integral

Non-mathematicians are often baffled at why mathematicians seek generalizations and abstractions, and often think that the abstractions can have no practical purpose.

Here is an example. The Riemann integral appears to suffice for any function of practical interest, and yet mathematicians insist on defining a Lebesgue integral to handle a wider variety of cases.

Andrew D. Lewis writes:

Should we fly in the Lebesgue-designed airplane? -- The correct defence of the Lebesgue integral

It is well-known that the Lebesgue integral generalises the Riemann integral. However, as is also well-known but less frequently well-explained, this generalisation alone is not the reason why the Lebesgue integral is important and needs to be a part of the arsenal of any mathematician, pure or applied. ...

The title of this paper is a reference to the well-known quote of the applied mathematician and engineer Richard W. Hamming (1915–1998):

Does anyone believe that the difference between the Lebesgue and Riemann integrals can have physical significance, and that whether say, an airplane would or would not fly could depend on this difference? If such were claimed, I should not care to fly in that plane.
The paper goes on to explain this very well. In particular, it shows why the Riemann integral is not good enough. In short, the Lebesgue integral makes Lp(R) complete normed vector spaces. If a sequence appears to converge, then it really does converge to a function in the space. This allows the use of limits in Fourier analysis, differential equations, and other areas of analysis.

Monday, December 11, 2023

Deriving Lorentz Metric from Electromagnetism

New paper:
Chen, Lu and Read, James (2023) Is the metric signature really electromagnetic in origin?
The paper is interesting, but the 4-metric signature +++- is mainly a consequence of causality, be it electromagnetic or anything else.

Causality requires that events only affect nearby events. If spacetime were Euclidean, with metric signature ++++, then an event could be close to an event outside its light cone. Affecting that nearby event would mean going faster than light. Action at a distance.

Electromagnetic effects do not go faster than light. You need the non-euclidean geometry of a +++- signature metric. Once you accept all that, Maxwell's electromagnetism is one of the simplest possible field theories, compatible with the geometry.

Friday, December 8, 2023

Harvard/MIT claims Quantum Error Correction

Scott Aaronson announces:
The biggest talk at Q2B this year was yesterday’s announcement, by a Harvard/MIT/QuEra team led by Misha Lukin and Vlad Vuletic, to have demonstrated “useful” quantum error-correction, for some definition of “useful,” in neutral atoms (see here for the Nature paper). To drill down a bit into what they did:

They ran experiments with up to 280 physical qubits, which simulated up to 48 logical qubits. ...

They don’t claim to have demonstrated quantum supremacy with their logical qubits—i.e., nothing that’s too hard to simulate using a classical computer.

Assuming the result stands, I think it’s plausibly the top experimental quantum computing advance of 2023 (coming in just under the deadline!). We clearly still have a long way to go until “actually useful” fault-tolerant QC, which might require thousands of logical qubits and millions of logical gates. But this is already beyond what I expected to be done this year, and (to use the AI doomers’ lingo) it “moves my timelines forward” for quantum fault-tolerance. It should now be possible, among other milestones, to perform the first demonstrations of Shor’s factoring algorithm with logically encoded qubits (though still to factor tiny numbers, of course). I’m slightly curious to see how Gil Kalai and the other quantum computing skeptics wiggle their way out now, though I’m absolutely certain they’ll find a way! Anyway, huge congratulations to the Harvard/MIT/QuEra team for their achievement.

What, is it my job to critique these experiments? He says "assuming the result stands", so he is not so sure himself. This is all I know.

Thursday, December 7, 2023

IBM may soon have one Logical Qubit

SciAm reports:
IBM has unveiled the first quantum computer with more than 1,000 qubits — the equivalent of the digital bits in an ordinary computer. But the company says it will now shift gears and focus on making its machines more error-resistant rather than larger.

For years, IBM has been following a quantum-computing road map that roughly doubled the number of qubits every year. The chip unveiled on 4 December, called Condor, has 1,121 superconducting qubits arranged in a honeycomb pattern. ...

Researchers have generally said that state-of-the-art error-correction techniques will require more than 1,000 physical qubits for each logical qubit. A machine that can do useful computations would then need to have millions of physical qubits. ...

A new IBM road map on the its quantum research unveiled today sees it reaching useful computations — such as simulating the workings of catalyst molecules — by decade’s end.

Okay, one logical qubit, as soon as IBM gets that error correction figured out. And something useful by the year 2029.

Monday, December 4, 2023

Philosophy of Quantum Mechanics

David Wallace writes Philosophy of Quantum Mechanics:
This is a general introduction to and review of the philosophy of quantum mechanics, aimed at readers with a physics background and assuming no prior exposure to philosophy. It is a draft version of an article to appear in the Oxford Research Encyclopedia of Physics.
He summarizes the interpretations, and concludes:
Among physicists, the (more operationalist versions of the) probability-based approach, and the Everett interpretation, are roughly as popular as one another, with different sub-communities having different preferences. (The modificatory strategies are much less popular among physicists, although they are probably the most common choice among philosophers of physics.) But more popular than either is the ‘shut-up-and-calculate’ approach [167]: the view that we should not worry about these issues and should get on with applying quantum mechanics to concrete problems.

In its place, there is much to be said for ‘shut up and calculate’. Not everyone needs to be interested in the interpretation of quantum mechanics; insofar as a physicist working on, say, solar neutrinos or superfluidity can apply the quantum formalism without caring about its interpretation, they should go right ahead — just as a biochemist may be able to ignore quantum mechanics entirely, or a behavioral ecologist may be able to ignore biochemistry.

There is some overlap here. The theory described in textbooks could be called probability-based, or shut up and calculate.

Wallace has sympathies to Everett many-worlds, but admits:

More productive criticisms4 of the Everett interpretation have mostly fallen into two classes, known collectively as the ‘preferred basis problem’ and the ‘probability problem’. ...

It is fairly widely accepted that decoherence provides a solution to the preferred-basis problem. ...

The probability problem remains largely intact when decoherence is considered, and has been the main locus of controversy about the Everett in- terpretation in 21st-century discussions.

I am coming around to the view that there are really just two interpretations: QM with and without the probabilities. With the probabilities, you can make predictions and do experiments. Without, you get many-worlds, and a lot of philosophers and physicists love it, but I don't see what it has to do with the real world.

Friday, December 1, 2023

Carroll has new course on Many Worlds

Physicist Sean M. Carroll announces a new course:
The Many Hidden Worlds of Quantum Mechanics

One universe is not enough. Learn about the Many-Worlds Interpretation of quantum mechanics in this exciting course taught by a renowned expert. ...

Professor Carroll explains how quantum mechanics predicts the existence of a large number of universes parallel to our own. ...

Use the concepts developed in the course so far to learn how physicist Hugh Everett arrived at a bold new approach to quantum mechanics. Called the Many-Worlds Interpretation, it holds that the wave function represents reality and evolves smoothly into multiple distinct worlds when a quantum measurement takes place. Contrast Everett’s straightforward idea with the opaque Copenhagen Interpretation. ...

Many-Worlds theorist David Deutsch helped pioneer quantum computing, which he argues is an outgrowth on the Many-Worlds Interpretation. ...

By contrast, Many-Worlds is deterministic. We can derive an understanding of probability by thinking about where we are in the quantum wave function. ...

Many-Worlds and competing theories on the foundations of quantum mechanics may seem essential for our understanding of reality, but they were long ignored by no-nonsense practicing physicists. Close the course by witnessing how the tide is turning, as it becomes increasingly clear that the foundational issues are likely the key to unlocking the outstanding mysteries of the cosmos.

This is all nonsense. There is no practical value to Many-Worlds, or to the other "competing theories" he presents. They do not even make sense has scientific theories. This course is crackpot stuff.

I have posted many times with details on why Many-worlds is nonsense. Carroll giving a course on this is like giving a course on Astrology. The students should be warned that they will not learn anything worthwhile.

His Thanksgiving post was a plug for his latest book, saying that he is thankful for quanta.