So, Ive been doing a bunch of talking in terms of decades in the last couple of posts, about the physics defining eras in the 20th century and the physics defining the last couple of decades. Ill most likely do another decadal post in the near future, this one looking ahead to the 2020s, but the end of a decade by definition falls at the end of a year, so its worth taking a look at physics stories on a shorter time scale, as well.

New year 2019 change to 2020 concept, hand change wooden cubes

You can, as always, find a good list of important physics stories in Physics Worlds Breakthrough of the Year shortlist, and there are plenty of other top science stories of 2019 lists out there. Speaking for myself, this is kind of an unusual year, and its tough to make a call as to the top story. Most of the time, these end-of-year things are either stupidly obvious because one story towers above all the others, or totally subjective because there are a whole bunch of stories of roughly equal importance, and the choice of a single one comes down to personal taste.

In 2019, though, I think there were two stories that are head-and-shoulders above everything else, but roughly equal to each other. Both are the culmination of many years of work, and both can also claim to be kicking off a new era for their respective subfields. And Im really not sure how to choose between them.

US computer scientist Katherine Bouman speaks during a House Committee on Science, Space and ... [+] Technology hearing on the "Event Horizon Telescope: The Black hole seen Round the World" in the Rayburn House office building in Washington, DC on May 16, 2019. (Photo by Andrew CABALLERO-REYNOLDS / AFP) (Photo credit should read ANDREW CABALLERO-REYNOLDS/AFP via Getty Images)

The first of these is the more photogenic of the two, namely the release of the first image of a black hole by the Event Horizon Telescope collaboration back in April. This one made major news all over, and was one of the experiments that led me to call the 2010s the decade of black holes.

As I wrote around the time of the release, this was very much of a piece with the preceding hundred years of tests of general relativity: while many stories referred to the image as a shadow of the black hole, really its a ring produced by light bending around the event horizon. This is the same basic phenomenon that Eddington measured in 1919 looking at the shift in the apparent position of stars near the Sun, providing confirmation of Einsteins prediction that gravity bends light. Its just that scaling up the mass a few million times produces a far more dramatic bending of spacetime (and thus light) than the gentle curve produced by our Sun.

This Feb. 27, 2018, photo shows electronics for use in a quantum computer in the quantum computing ... [+] lab at the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y. Describing the inner workings of a quantum computer isnt easy, even for top scholars. Thats because the machines process information at the scale of elementary particles such as electrons and photons, where different laws of physics apply. (AP Photo/Seth Wenig)

The other story, in very 2019 fashion, first emerged via a leak: someone at NASA accidentally posted a draft of the paper in which Googles team claimed to have achieved quantum supremacy. They demonstrated reasonably convincingly that their machine took about three and a half minutes to generate a solution to a particular problem that would take vastly longer to solve with a classical computer.

The problem they were working with was very much in the quantum simulation mode that I talked about a year earlier, when I did a high-level overview of quantum computing in general, though a singularly useless version of that. Basically, they took a set of 50-odd qubits and performed a random series of operations on them to put them in a complicated state in which each qubit was in a superposition of multiple states and also entangled with other qubits in the system. Then they measured the probability of finding specific output states.

Qubit, or quantum bit, illustration. The qubit is a unit of quantum information. As a two-state ... [+] system with superposition of both states at the same time, it is fundamental to quantum computing. The illustration shows the Bloch sphere. The north pole is equivalent to one, the south pole to zero. The other locations, anywhere on the surface of the sphere, are quantum superpositions of 0 and 1. When the qubit is measured, the quantum wave function collapses, resulting in an ordinary bit - a one or a zero - which effectively depends on the qubit's 'latitude'. The illustration shows the qubit 'emitting' a stream of wave functions (the Greek letter psi), representing the collapse of the wave function when measured.

Finding the exact distribution of possible outcomes for such a large and entangled system is extremely computationally intensive if youre using a classical computer to do the job, but it happens very naturally in the quantum computer. So they could get a good approximation of the distribution within minutes, while the classical version would take a lot more time, where a lot more time ranges from thousands of years (Googles claim) down to a few days (the claim by a rival group at IBM using a different supercomputer algorithm to run the computation). If youd like a lot more technical detail about what this did and didnt do, see Scott Aaronson.

As with the EHT paper, this is the culmination of years of work by a large team of people. Its also very much of a piece with past work quantum computing as a distinct field is a recent development, but really, the fundamental equations used to do the calculations were pretty well set by 1935.

Glowing new technology in deep space, computer generated abstract background, 3D rendering

Both of these projects also have a solid claim to be at the forefront of something new. The EHT image is the first to be produced, but wont be the last theyre crunching numbers on the Sag A* black hole at the center of the Milky Way, and theres room to improve their imaging in the future. Along with the LIGO discovery from a few years ago, this is the start of a new era of looking directly at black holes, rather than just using them as a playground for theory.

Googles demonstration of quantum supremacy, meanwhile, is the first such result in a highly competitive field: IBM and Microsoft are also invested in similar machines, and there are smaller companies and academic labs exploring other technologies. The random-sampling problem they used is convenient for this sort of demonstration, but not really useful for anything else, but lots of people are hard at work on techniques to make a next generation of machines that will be able to do calculations where people care about the answer. Theres a good long way to go, yet, but a lot of activity in the field driving things forward.

So, in the head-to-head matchup for Top Physics Story of 2019, these two are remarkably evenly matched, and it could really go either way. The EHT result has a slightly deeper history, the Google quantum computer arguably has a brighter future. My inclination would be to split the award between them; if you put a gun to my head and made me pick one, Id go with quantum supremacy, but Id seriously question the life choices that led you to this place, because theyre both awesome accomplishments that deserve to be celebrated.

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What Was The Most Important Physics Of 2019? - Forbes