(Roughly) Daily

Posts Tagged ‘quantum physics

“The threat of a pandemic is different from that of a nerve agent, in that a disease can spread uncontrollably, long after the first carrier has succumbed”*…

We were, of course, warned. As we do our best to digest the news of emergent new strains of the COVID-19 virus, a look back at Annie Sparrow‘s 2016 New York Review of Books essay on pandemics…

Pandemics—the uncontrolled spread of highly contagious diseases across countries and continents—are a modern phenomenon. The word itself, a neologism from Greek words for “all” and “people,” has been used only since the mid-nineteenth century. Epidemics—localized outbreaks of diseases—have always been part of human history, but pandemics require a minimum density of population and an effective means of transport. Since “Spanish” flu burst from the trenches of World War I in 1918, infecting 20 percent of the world’s population and killing upward of 50 million people, fears of a similar pandemic have preoccupied public health practitioners, politicians, and philanthropists. World War II, in which the German army deliberately caused malaria epidemics and the Japanese experimented with anthrax and plague as biological weapons, created new fears…

According to the doctor, writer, and philanthropist Larry Brilliant, “outbreaks are inevitable, pandemics are optional.”

Much of human history can be seen as a struggle for survival between humans and microbes. Pandemics are microbe offensives; public health measures are human defenses. Water purification, sanitation, and vaccination are crucial to our living longer, better, even taller lives. But these measures of mass salvation are not sexy. While we know prevention is better and considerably cheaper than cure, there is little financial reward or glory in it. Philanthropists prefer to build hospitals rather than pay community health workers. Pharmaceutical companies prefer the Western market to the distant and poor Global South where people cannot afford to buy treatments. Education is a powerful social vaccine against the ignorance that enables pathogens to flourish, but insufficient to overcome the corruption of public goods by private interests. The current enthusiasm for detecting the next panic-inducing pathogen should not divert resources and research from the perennial threats that we already have. We must resist the tendency of familiarity and past failures to encourage contempt and indifference…

An important (and in its time, sadly, prescient) read: “The Awful Diseases on the Way,” from @annie_sparrow in @nybooks.

See also “6 of the Worst Pandemics in History” (source of the image above) and “A history of pandemics.”

[TotH to MK]

Hannah Fry


As we prioritize preparation, we might recall that it was on this date in 1935 that physicist Erwin Schrödinger published his famous thought experiment– now known as “Schrödinger’s cat“– a paradox that illustrates the problem of the Copenhagen interpretation of quantum mechanics.

This image has an empty alt attribute; its file name is s-cat.jpg


“It can be argued that in trying to see behind the formal predictions of quantum theory we are just making trouble for ourselves”*…

Context, it seems, is everthing…

… What is reality? Nope. There’s no way we are going through that philosophical minefield. Let’s focus instead on scientific realism, the idea that a world of things exists independent of the minds that might perceive it and it is the world slowly revealed by progress in science. Scientific realism is the belief that the true nature of reality is the subject of scientific investigation and while we may not completely understand it at any given moment, each experiment gets us a little bit closer. This is a popular philosophical position among scientists and science enthusiasts.

A typical scientific realist might believe, for example, that fundamental particles exist even though we cannot perceive them directly with our senses. Particles are real and their properties — whatever they may be — form part of the state of the world. A slightly more extreme view is that this state of the world can be specified with mathematical quantities and these, in turn, obey equations we call physical laws. In this view, the ultimate goal of science is to discover these laws. So what are the consequences of quantum physics on these views?

As I mentioned above, quantum physics is not a realistic model of the world — that is, it does not specify quantities for states of the world. An obvious question is then can we supplement or otherwise replace quantum physics with a deeper set of laws about real states of the world? This is the question Einstein first asked with colleagues Podolski and Rosen, making headlines in 1935. The hypothetical real states of the world came to be called hidden variables since an experiment does not reveal them — at least not yet.

In the decades that followed quantum physics rapidly turned into applied science and the textbooks which became canon demonstrated only how to use the recipes of quantum physics. In textbooks that are still used today, no mention is made of the progress in the foundational aspects of quantum physics since the mathematics was cemented almost one hundred years ago. But, in the 1960s, the most important and fundamental aspect of quantum physics was discovered and it put serious restrictions on scientific realism. Some go as far as to say the entire nature of independent reality is questionable due to it. What was discovered is now called contextuality, and its inevitability is referred to as the Bell-Kochen-Specker theorem.

John Bell is the most famous of the trio Bell, Kochen, and Specker, and is credited with proving that quantum physics contained so-called nonlocal correlations, a consequence of quantum entanglement. Feel free to read about those over here.

It was Bell’s ideas and notions that stuck and eventually led to popular quantum phenomena such as teleportation. Nonlocality itself is wildly popular these days in science magazines with reported testing of the concept in delicately engineered experiments that span continents and sometimes involve research satellites. But nonlocality is just one type of contextuality, which is the real game in town.

In the most succinct sentence possible, contextuality is the name for the fact that any real states of the world giving rise to the rules of quantum physics must depend on contexts that no experiment can distinguish. That’s a lot to unpack. Remember that there are lots of ways to prepare the same experiment — and by the same experiment, I mean many different experiments with completely indistinguishable results. Doing the exact same thing as yesterday in the lab, but having had a different breakfast, will give the same experimental results. But there are things in the lab and very close to the system under investigation that don’t seem to affect the results either. An example might be mixing laser light in two different ways.

There are different types of laser light that, once mixed together, are completely indistinguishable from one another no matter what experiments are performed on the mixtures. You could spend a trillion dollars on scientific equipment and never be able to tell the two mixtures apart. Moreover, knowing only the resultant mixture — and not the way it was mixed — is sufficient to accurately predict the outcomes of any experiment performed with the light. So, in quantum physics, the mathematical theory has a variable that refers to the mixture and not the way the mixture was made — it’s Occam’s razor in practice.

Now let’s try to invent a deeper theory of reality underpinning quantum physics. Surely, if we are going to respect Occam’s razor, the states in our model should only depend on contexts with observable consequences, right? If there is no possible experiment that can distinguish how the laser light is mixed, then the underlying state of reality should only depend on the mixture and not the context in which it was made, which, remember, might include my breakfast choices. Alas, this is just not possible in quantum physics — it’s a mathematical impossibility in the theory and has been confirmed by many experiments.

So, does this mean the universe cares about what I have for breakfast? Not necessarily. But, to believe the universe doesn’t care what I had for breakfast means you must also give up reality. You may be inclined to believe that when you observe something in the world, you are passively looking at it just the way it would have been had you not been there. But quantum contextuality rules this out. There is no way to define a reality that is independent of the way we choose to look at it…

Why is no one taught the one concept in quantum physics which denies reality?” It’s called contextuality and it is the essence of quantum physics. From Chris Ferrie (@csferrie).

* “It can be argued that in trying to see behind the formal predictions of quantum theory we are just making trouble for ourselves. Was not precisely this the lesson that had to be learned before quantum mechanics could be constructed, that it is futile to try to see behind the observed phenomena?” – John Stewart Bell


As still we try, we might relatively hearty birthday greetings to Sir Marcus Laurence Elwin “Mark” Oliphant; he was born on this date in 1901. An Australian physicist who trained and did much of his work in England (where he studied under Sir Ernest Rutherford at the University of Cambridge’s Cavendish Laboratory), Oliphant was deeply involved in the Allied war effort during World War II. He helped develop microwave radar, and– by helping to start the Manhattan Project and then working with his friend Ernest Lawrence at the Radiation Laboratory in Berkeley, California, helped develop the atomic bomb.

After the war, Oliphant returned to Australia as the first director of the Research School of Physical Sciences and Engineering at the new Australian National University (ANU); on his retirement, he became Governor of South Australia and helped found the Australian Democrats political party.


“The ‘paradox’ is only a conflict between reality and your feeling of what reality ‘ought to be’”*…

One of the most bizarre aspects of quantum physics is that the fundamental entities that make up the Universe, what we know as the indivisible quanta of reality, behave as both a wave and a particle. We can do certain experiments, like firing photons at a sheet of metal, where they act like particles, interacting with the electrons and kicking them off only if they individually have enough energy. Other experiments, like firing photons at small thin objects — whether slits, hairs, holes, spheres, or even DVDs — give patterned results that show exclusively wave-like behavior. What we observe appears to depend on which observations we make, which is frustrating, to say the least. Is there some way to tell, fundamentally, what the nature of a quanta is, and whether it’s wave-like or particle-like at its core?

That’s what Sandra Marin wants to know, asking:

“I wonder if you could help me to understand John Wheeler – the delayed choice experiment and write an article about this.”

John Wheeler was one of the most brilliant minds in physics in the 20th century, responsible for enormous advances in quantum field theory, General Relativity, black holes, and even quantum computing. Yet the idea about the delayed choice experiment hearkens all the way back to perhaps our first experience with the wave-particle duality of quantum physics: the double-slit experiment…

Although Einstein definitively wanted us to have a completely comprehensible reality, where everything that occurred obeyed our notions of cause-and-effect without any retrocausality, it was his great rival Bohr who turned out to be correct on this point. In Bohr’s own words:

“…it…can make no difference, as regards observable effects obtainable by a definite experimental arrangement, whether our plans for constructing or handling the instruments are fixed beforehand or whether we prefer to postpone the completion of our planning until a later moment when the particle is already on its way from one instrument to another.”

As far as we can tell, there is no one true objective, deterministic reality that exists independently of observers or interactions. In this Universe, you really to have to observe in order to find out what you get.

The history and the results of John Wheeler‘s famous “delayed choice” experiments: “Is Light Fundamentally A Wave Or A Particle?

* Richard Feynman


As we reconsider categories, we might recall that it was on this date in 1404 that King Henry IV signed the “Act Against Multipliers,” stipulating that “None from hereafter shall use to multiply gold or silver, or use the craft of multiplication; and if any the same do, they incur the pain of felony.” Great alarm was felt at that time lest any alchemist should succeed in “transmutation” (the conversion of a base metal into gold or silver), thus undermining the sanctity of the Royal currency and/or possibly financing rebellious uprisings. Alchemy, which had flourished since the time of Bacon, effectively became illegal.

The Act was repealed in 1689, when Robert Boyle, the father of modern chemistry, and other members of the vanguard of the scientific revolution lobbied for its repeal.


Written by (Roughly) Daily

January 13, 2021 at 1:01 am

“Oh how wrong we were to think immortality meant never dying”*…



Quantum simulation (Verresen et al., Nature Physics, 2019)


Further (in a fashion) to yesterday’s post…

Nothing lasts forever. Humans, planets, stars, galaxies, maybe even the Universe itself, everything has an expiration date. But things in the quantum realm don’t always follow the rules. Scientists have found that quasiparticles in quantum systems could be effectively immortal.

That doesn’t mean they don’t decay, which is reassuring. But once these quasiparticles have decayed, they are able to reorganise themselves back into existence, possibly ad infinitum.

This seemingly flies right in the face of the second law of thermodynamics, which asserts that entropy in an isolated system can only move in an increasing direction: things can only break down, not build back up again.

Of course, quantum physics can get weird with the rules; but even quantum scientists didn’t know quasiparticles were weird in this particular manner…

Maybe some things are forever.  More at “Scientists Find Evidence a Strange Group of Quantum Particles Are Basically Immortal.”

Read the underlying Nature Physics article, by physicist Ruben Verresen and his team at the Technical University of Munich and the Max Planck Institute for the Physics of Complex Systems, here.

* Gerard Way


As we ponder perpetuity, we might send carefully-deduced birthday greetings to Richard Bevan Braithwaite; he was born on this date in 1900.  A Cambridge don who specialized in the philosophy of science, he focused on the logical features common to all sciences.  Braithwaite was concerned with the impact of science on our beliefs about the world and the appropriate responses to that impact.  He was especially interested in probability (and its applications in decision theory and games theory) and in the statistical sciences.  He was president of the Aristotelian Society from 1946 to 1947, and was a Fellow of the British Academy.

It was Braithwaite’s poker that Ludwig Wittgenstein reportedly brandished at Karl Popper during their confrontation at a Moral Sciences Club meeting in Braithwaite’s rooms in King’s College. The implement subsequently disappeared. (See here.)



Written by (Roughly) Daily

January 15, 2020 at 1:01 am

“Aside from velcro, time is the most mysterious substance in the universe”*…



Detail from Salvador Dali’s Persistence of Memory


In normal life, you open the car door before getting into the car. Operation A happens before operation B. That’s the causal order of things. But a new quantum switch weirdly enables two operations to happen simultaneously. From Science News:

The device, known as a quantum switch, works by putting particles of light through a series of two operations — labeled A and B — that alter the shape of the light. These photons can travel along two separate paths to A and B. Along one path, A happens before B, and on the other, B happens before A.

Which path the photon takes is determined by its polarization, the direction in which its electromagnetic waves wiggle — up and down or side to side. Photons that have horizontal polarization experience operation A first, and those with vertical polarization experience B first.

But, thanks to the counterintuitive quantum property of superposition, the photon can be both horizontally and vertically polarized at once. In that case, the light experiences both A before B, and B before A, Romero and colleagues report.

While this is deeply weird and amazing, it unfortunately doesn’t occur at the human scale but rather in the quantum realm where measurements are in the nanometers. Still, quantum switches do have clear applications in future communications and computation systems.

Indefinite Causal Order in a Quantum Switch” (Physical Review Letters)

From the ever-illuminating David Pescovitz at Boing Boing: “Weird time-jumbling quantum device defies ‘before’ and ‘after’.”

* Dave Barry


As we check our watches, we might send timely birthday greetings to Louis Essen; he was born on this date in 1908.  A physicist, he drew on his World War II work on radar to develop the first generally-accepted scientific measurement of the speed of light (one that has held up well as measurement techniques have advanced.).

But Essen is probably better remembered as the father of the atomic clock: in 1955, in collaboration with Jack Parry, he developed the first practical atomic clock by integrating the caesium atomic standard with conventional quartz crystal oscillators to allow calibration of existing time-keeping.


Louis Essen (right) and Jack Parry (left) standing next to the world’s first caesium-133 atomic clock


Written by (Roughly) Daily

September 6, 2018 at 1:01 am

%d bloggers like this: