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kottke.org posts about physics

Fly Me to the Moonmoon

posted by Jason Kottke   Oct 11, 2018

Moonmoon

In a paper called “Can Moons Have Moons?”, a pair of astronomers says that some of the solar system’s moons, including ours, are large enough and far enough away from their host planets to have their own sizable moons.

We find that 10 km-scale submoons can only survive around large (1000 km-scale) moons on wide-separation orbits. Tidal dissipation destabilizes the orbits of submoons around moons that are small or too close to their host planet; this is the case for most of the Solar System’s moons. A handful of known moons are, however, capable of hosting long-lived submoons: Saturn’s moons Titan and Iapetus, Jupiter’s moon Callisto, and Earth’s Moon.

Throughout the paper, the authors refer to these possible moons of moons as “submoons” but a much more compelling name has been put forward: “moonmoons”.

Moonmoon is an example of the linguistic process of reduplication, which is often deployed in English to make things more cute and whimsical. In the pure form of reduplication, you get words like bonbon, choo-choo, bye-bye, there there, and moonmoon but relaxing the rules a little to incorporate rhymes and near-rhymes yields hip-hop, zig-zag, fancy-shmancy, super-duper, pitter-patter, and okey-dokey. And with contrastive reduplication, in which a word repeats as a modifier to itself:

“It’s tuna salad, not salad-salad.”
“Does she like me or like-like me?”
“The party is fancy but not fancy-fancy.”
“The car isn’t mine-mine, it’s my mom’s.”

Fun! And astronomy should be fun too. Let’s definitely call them moonmoons.

Earth-Sized Telescope Aims to Snap a Photo of Our Galactic Black Hole

posted by Jason Kottke   Oct 09, 2018

Astronomers behind the Event Horizon Telescope are building a virtual telescope with a diameter of the Earth to photograph the supermassive black hole at the center of our galaxy. The idea is that different observatories from all over the surface of the Earth all look at the black hole at the same time and the resulting data is stitched together by a supercomputer into a coherent picture. Seth Fletcher wrote a great piece about the effort for the NY Times Magazine (it’s an excerpt from his new book, Einstein’s Shadow: A Black Hole, a Band of Astronomers, and the Quest to See the Unseeable):

Astronomical images have a way of putting terrestrial concerns in perspective. Headlines may portend the collapse of Western civilization, but the black hole doesn’t care. It has been there for most of cosmic history; it will witness the death of the universe. In a time of lies, a picture of our own private black hole would be something true. The effort to get that picture speaks well of our species: a bunch of people around the world defying international discord and general ascendant stupidity in unified pursuit of a gloriously esoteric goal. And in these dark days, it’s only fitting that the object of this pursuit is the darkest thing imaginable.

Avery Broderick, a theoretical astrophysicist who works with the Event Horizon Telescope, said in 2014 that the first picture of a black hole could be just as important as “Pale Blue Dot,” the 1990 photo of Earth that the space probe Voyager took from the rings of Saturn, in which our planet is an insignificant speck in a vast vacuum. A new picture, Avery thought, of one of nature’s purest embodiments of chaos and existential unease would have a different message: It would say, There are monsters out there.

A video by the EHT team says that imaging the black hole is like trying to count the dimples on a golf ball located in LA while standing in NYC.

EHT team member Katie Bouman also did a TEDx talk on the project.

P.S. There’s a cloud near the center of the galaxy that tastes like raspberries and smells like rum.

One way the universe might end

posted by Tim Carmody   Oct 05, 2018

My favorite astrophysicist Katie Mack recently reposted a Cosmos article she wrote about a relatively obscure model for the total annihilation of the universe, called “vacuum decay.”

Essentially, what vacuum decay relies on is the fact that we don’t know for sure whether space is in the lowest energy, most stable possible state (a true vacuum) or at an adjacent, slightly higher energy level (a false vacuum). Space could be only metastable, and a random quantum fluctuation or sufficiently high level energy event could push part of the universe from the false vacuum to the true one. This could cause “a bubble of true vacuum that will then expand in all directions at the speed of light. Such a bubble would be lethal.”

It’s compellingly badass, and as Mack notes, frightfully efficient. First, it’s not the slow petering out that is heat death. Also, it wouldn’t just eliminate our current universe, but all possibility of a universe anything like ours. Vacuum decay destroys space like Roman generals salting the earth at Carthage.

The walls of the true vacuum bubble would expand in all directions at the speed of light. You wouldn’t see it coming. The walls can contain a huge amount of energy, so you might be incinerated as the bubble wall ploughed through you. Different vacuum states have different constants of nature, so the basic structure of matter might also be disastrously altered. But it could be even worse: in 1980, theoretical physicists Sidney Coleman and Frank De Luccia calculated for the first time that any bubble of true vacuum would immediately suffer total gravitational collapse.

They say: “This is disheartening. The possibility that we are living in a false vacuum has never been a cheering one to contemplate. Vacuum decay is the ultimate ecological catastrophe; in a new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know it.

“However, one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some creatures capable of knowing joy. This possibility has now been eliminated.”

Dark Matter: Looking for Whispers in the Cosmic Silence

posted by Jason Kottke   Sep 12, 2018

For Motherboard’s The Most Unknown series, physicist Davide D’Angelo and geomicrobiologist Jennifer Macalady travel to Laboratori Nazionali del Gran Sasso to see one of the latest efforts to detect dark matter, the SABRE detector.

As with the search for neutrinos, looking for dark matter needs to happen under conditions of “cosmic silence” — in this case, beneath a mountain in Italy. D’Angelo, who is a collaborator on the project, likens the search to “hunting ghosts”.

Stunning high-res photo of a stellar nursery

posted by Jason Kottke   Aug 31, 2018

Carina Nebula

Astronomers using an infrared telescope at the European Southern Observatory in Chile recently released an infrared photo of the Carina Nebula that shows the inner workings of the star factory “as never before”.

This spectacular image of the Carina nebula reveals the dynamic cloud of interstellar matter and thinly spread gas and dust as never before. The massive stars in the interior of this cosmic bubble emit intense radiation that causes the surrounding gas to glow. By contrast, other regions of the nebula contain dark pillars of dust cloaking newborn stars.

This is a massive image…the original is 140 megapixels (<- that’s a 344MB download). Phil Plait notes that it may contain about 1 million stars and gives a bit of background on what we’re looking at here:

The colors you see here are not what you’d see with your eye, since it’s all infrared. What’s shown as blue is actually 0.88 microns, or a wavelength just outside what your eye can see. Green is really 1.25 microns and red is 2.15, so both are well into the near-infrared.

Even in the infrared, a lot of gas and dust still are visible. That’s because there’s a whole bunch of it here. And it’s not just randomly strewn around; patterns are there when you look for them.

For example, in this subimage you can see long, skinny triangles of dust. These are formed when very thick clots of dust are near very luminous stars. The wind and fierce blast of ultraviolet light from the stars erode away at the clump and also flow around it. They’re like sandbars in a stream! This is the same mechanism that made the Pillars of Creation in the Eagle nebula, and they’re common in star-forming nebulae.

Solving the spaghetti problem

posted by Tim Carmody   Aug 17, 2018

If you’ve ever tried to snap dried pasta in half, you know that it’s hard to get just two even pieces; what you usually get instead is macaroni shrapnel everywhere. It turns out this is due to fundamental physical forces of the universe when applied to a straight rod. The initial break creates a snap-back effect that creates additional fractures.

crack-control-1.gif

Apparently, this used to drive Richard Feynman nuts. Here’s an excerpt from No Ordinary Genius: The Illustrated Richard Feynman, where computer scientist Danny Hills describes Feynman’s obsession:

Once we were making spaghetti, which was our favorite thing to eat together. Nobody else seemed to like it. Anyway, if you get a spaghetti stick and you break it, it turns out that instead of breaking it in half, it will almost always break into three pieces. Why is this true — why does it break into three pieces? We spent the next two hours coming up with crazy theories. We thought up experiments, like breaking it underwater because we thought that might dampen the sound, the vibrations. Well, we ended up at the end of a couple of hours with broken spaghetti all over the kitchen and no real good theory about why spaghetti breaks in three. A lot of fun, but I could have blackmailed him with some of his spaghetti theories, which turned out to be dead wrong!

It turns out that controlling the vibrations does have something to do with controlling the breakage, although putting the rod underwater won’t help. Two young physicists, Ronald Heisser and Vishal Patil, found that the key to breaking spaghetti rods into two pieces is to give them a good twist:

If a 10-inch-long spaghetti stick is first twisted by about 270 degrees and then bent, it will snap in two, mainly due to two effects. The snap-back, in which the stick will spring back in the opposite direction from which it was bent, is weakened in the presence of twist. And, the twist-back, where the stick will essentially unwind to its original straightened configuration, releases energy from the rod, preventing additional fractures.

“Once it breaks, you still have a snap-back because the rod wants to be straight,” Dunkel explains. “But it also doesn’t want to be twisted.”

Just as the snap-back will create a bending wave, in which the stick will wobble back and forth, the unwinding generates a “twist wave,” where the stick essentially corkscrews back and forth until it comes to rest. The twist wave travels faster than the bending wave, dissipating energy so that additional critical stress accumulations, which might cause subsequent fractures, do not occur.

“That’s why you never get this second break when you twist hard enough,” Dunkel says.

crack-control-2.gif

It’s not exactly practical to twist spaghetti 270 degrees before you break it in half, just to end up with a shorter noodle. And linguini, fettucine, etc., have a different physics altogether, because they deviate more strongly from the cylindrical rod shape of spaghetti. But it’s cool to have one of these everyday physics problems apparently solved through a relatively simple trick.

On the nature of wormholes

posted by Jason Kottke   Aug 13, 2018

Are wormholes science or just science fiction? As this video by Kurzgesagt shows, they’re actually a little bit of both. Einstein and string theory both posit that these “short cuts” through spacetime could exist, but finding or building a stable wormhole, a la Star Trek, is another matter altogether.

In the description of the video, they link to a pair of papers published by Michael Morris and Kip Thorne in the late 80s: Wormholes, Time Machines, and the Weak Energy Condition and Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity. For a high school physics class, I gave a presentation on wormholes & time travel and I’m pretty sure I used at least one of those papers as a reference. The presentation also included a clip of Bill & Ted’s Excellent Adventure. The teacher gave me a B+ — he felt the presentation was excellent (*guitar riff*) but that I had, in spite of the movie clip, “lost most of the other students” and should have chosen a more suitable topic.

A 20-year time lapse of stars orbiting a massive black hole

posted by Jason Kottke   Jul 31, 2018

The European Southern Observatory’s Very Large Telescope in Chile has been watching the supermassive black hole in the center of our galaxy and the stars that orbit it. Using observations from the past 20 years, the ESO made this time lapse video of the stars orbiting the black hole, which has the mass of four million suns. I’ve watched this video like 20 times today, my mind blown at being able to observe the motion of these massive objects from such a distance.

The VLT was also able to track the motion of one of these stars and confirm for the first time a prediction made by Einstein’s theory of general relativity.

New infrared observations from the exquisitely sensitive GRAVITY, SINFONI and NACO instruments on ESO’s Very Large Telescope (VLT) have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometres from the black hole and moving at a speed in excess of 25 million kilometres per hour — almost three percent of the speed of light.

S2 has the mass of about 15 suns. That’s 6.6 × 10^31 pounds moving at 3% of the speed of light. Wowowow.

An explainer video from 1923 about Einstein’s theory of relativity

posted by Jason Kottke   May 29, 2018

In 1923, Inkwell Studios1 released a 20-minute animated explanation of Albert Einstein’s theory of relativity, perhaps one of the very first scientific explainer videos ever made. Films were still silent in those days and the public’s scientific understanding limited (the discovery of Pluto was 7 years in the future, and penicillin 5 years) so the film is almost excruciatingly slow by today’s standards, but if you squint hard enough, you can see the great-grandparent to YouTube channels like Kurzgesagt, Nerdwriter, TED Ed, minutephysics, and the 119,000+ videos on YouTube returned for a “einstein relativity explained” search. (via open culture)

  1. Inkwell later became Fleischer Studios, which made cartoons like Betty Boop, Popeye, and the first animated Superman series. They also introduced the bouncing ball as a technique for singing along to on-screen lyrics.

Cities flowing like liquids or organized like crystals

posted by Patrick Tanguay   Apr 30, 2018

File this story at Citylab adjacent to concepts like complexity, scale, and fractals. It turns out—according to this research paper anyway—that cities’ heat islands function differently depending on the “texture” of the city itself.

[S]cientists know that the density of buildings, the absorption of light by those buildings, and the relative lack of vegetation in cities are major contributors to the urban heat island effect. It’s why cities like Chicago are hoping to find relief through green roofs and reflective construction materials, or through planting more trees and banning cars. In a more radical move, Los Angeles even began painting their roads white as part of Mayor Eric Garcetti’s effort to bring down the city’s temperature by just under 2 degrees over the next 20 years. […]

The difference is even starker at night: even as the temperature cools, the release of heat absorbed during the day by asphalt and densely packed buildings can make the downtown area some 20 degrees warmer in some cities.

Street Grids May Make Cities Hotter

Roland Pellenq, a senior research scientist at MIT’s Concrete Sustainability Hub, looked at city grids and the relative positions of buildings, to see if patterns emerge.

Indeed, the fingerprints of cities like Boston and Los Angeles mirror the disorderly atomic structure of liquids and glass, while the likes of Chicago and New York City, with their streets and avenues perpendicular to one another, exhibit a more orderly configuration found in crystals.

Using formulas borrowed from physics, originally developed to measure atomic interaction in condensed materials, they found that more tightly packed cities have more intense heat island effects but also:

[T]hat cities with more rigid grid-like street patterns (that is, a higher local order) tended to display a higher temperature difference between their urban and rural areas. This has to do with air flow, said Pellenq. In disorganized cities, the air tends to flow uniformly with little or no interruption. But the perpendicular streets of Chicago and the like often trap heat by disrupting that airflow.

Fascinating.

How to harvest nearly infinite energy from a spinning black hole

posted by Jason Kottke   Apr 23, 2018

Well, this is a thing I didn’t know about black holes before watching this video. Because some black holes spin, it’s possible to harvest massive amounts of energy from them, even when all other energy sources in the far far future are gone. This process was first proposed by Roger Penrose in a 1971 paper.

The Penrose process (also called Penrose mechanism) is a process theorised by Roger Penrose wherein energy can be extracted from a rotating black hole. That extraction is made possible because the rotational energy of the black hole is located not inside the event horizon of the black hole, but on the outside of it in a region of the Kerr spacetime called the ergosphere, a region in which a particle is necessarily propelled in locomotive concurrence with the rotating spacetime. All objects in the ergosphere become dragged by a rotating spacetime. In the process, a lump of matter enters into the ergosphere of the black hole, and once it enters the ergosphere, it is forcibly split into two parts. For example, the matter might be made of two parts that separate by firing an explosive or rocket which pushes its halves apart. The momentum of the two pieces of matter when they separate can be arranged so that one piece escapes from the black hole (it “escapes to infinity”), whilst the other falls past the event horizon into the black hole. With careful arrangement, the escaping piece of matter can be made to have greater mass-energy than the original piece of matter, and the infalling piece has negative mass-energy.

This same effect can also be used in conjunction with a massive mirror to superradiate electromagnetic energy: you shoot light into a spinning black hole surrounded by mirrors, the light is repeatedly sped up by the ergosphere as it bounces off the mirror, and then you harvest the super-energetic light. After the significant startup costs, it’s basically an infinite source of free energy.

Physics giant Stephen Hawking dead at age 76

posted by Jason Kottke   Mar 14, 2018

Lego Stephen Hawking

Stephen Hawking, who uncovered the mysteries of black holes and with A Brief History of Time did more than anyone to popularize science since the late Carl Sagan, has died at his home in Cambridge at age 76. From an obituary in The Guardian:

Hawking once estimated he worked only 1,000 hours during his three undergraduate years at Oxford. In his finals, he came borderline between a first- and second-class degree. Convinced that he was seen as a difficult student, he told his viva examiners that if they gave him a first he would move to Cambridge to pursue his PhD. Award a second and he threatened to stay. They opted for a first.

Those who live in the shadow of death are often those who live most. For Hawking, the early diagnosis of his terminal disease, and witnessing the death from leukaemia of a boy he knew in hospital, ignited a fresh sense of purpose. “Although there was a cloud hanging over my future, I found, to my surprise, that I was enjoying life in the present more than before. I began to make progress with my research,” he once said. Embarking on his career in earnest, he declared: “My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all.”

From Dennis Overbye’s obit in the NY Times:

He went on to become his generation’s leader in exploring gravity and the properties of black holes, the bottomless gravitational pits so deep and dense that not even light can escape them.

That work led to a turning point in modern physics, playing itself out in the closing months of 1973 on the walls of his brain when Dr. Hawking set out to apply quantum theory, the weird laws that govern subatomic reality, to black holes. In a long and daunting calculation, Dr. Hawking discovered to his befuddlement that black holes — those mythological avatars of cosmic doom — were not really black at all. In fact, he found, they would eventually fizzle, leaking radiation and particles, and finally explode and disappear over the eons.

Nobody, including Dr. Hawking, believed it at first — that particles could be coming out of a black hole. “I wasn’t looking for them at all,” he recalled in an interview in 1978. “I merely tripped over them. I was rather annoyed.”

That calculation, in a thesis published in 1974 in the journal Nature under the title “Black Hole Explosions?,” is hailed by scientists as the first great landmark in the struggle to find a single theory of nature — to connect gravity and quantum mechanics, those warring descriptions of the large and the small, to explain a universe that seems stranger than anybody had thought.

The discovery of Hawking radiation, as it is known, turned black holes upside down. It transformed them from destroyers to creators — or at least to recyclers — and wrenched the dream of a final theory in a strange, new direction.

“You can ask what will happen to someone who jumps into a black hole,” Dr. Hawking said in an interview in 1978. “I certainly don’t think he will survive it.

“On the other hand,” he added, “if we send someone off to jump into a black hole, neither he nor his constituent atoms will come back, but his mass energy will come back. Maybe that applies to the whole universe.”

Dennis W. Sciama, a cosmologist and Dr. Hawking’s thesis adviser at Cambridge, called Hawking’s thesis in Nature “the most beautiful paper in the history of physics.”

Roger Penrose, the eminent mathematician and physicist who collaborated with Hawking on discoveries related to black holes and the genesis of the universe, wrote a lengthy scientific obituary for Hawking in The Guardian.

Following his work in this area, Hawking established a number of important results about black holes, such as an argument for its event horizon (its bounding surface) having to have the topology of a sphere. In collaboration with Carter and James Bardeen, in work published in 1973, he established some remarkable analogies between the behaviour of black holes and the basic laws of thermodynamics, where the horizon’s surface area and its surface gravity were shown to be analogous, respectively, to the thermodynamic quantities of entropy and temperature. It would be fair to say that in his highly active period leading up to this work, Hawking’s research in classical general relativity was the best anywhere in the world at that time.

And then there was that time Hawking threw a party for time travellers but didn’t advertise it until after the party was over (to ensure only visitors from the future would show up).

Tonight is perhaps a good night to watch Errol Morris’ superb documentary on Hawking (with a wonderful Philip Glass soundtrack) or build a version of Hawking out of Lego.

Why speeding is so dangerous

posted by Jason Kottke   Feb 13, 2018

Let’s say you’re doing 100 mph in a car and suddenly a downed tree, stopped car, or person appears in the road up ahead and you need to slam on the brakes. How much more dangerous is that situation than when you’re doing 70 mph? Your intuition might tell you that 70 mph is only 30% less than 100 mph. But as this video shows, the important factor in stopping a car (or what happens to the car when it collides with something else) is not speed but energy, which increases at the square of speed. In other words, going from 70 mph to 100 mph more than doubles your energy…and going from 55 to 100 more than triples it. (thx, david)

Physics lessons using simple homemade marble tracks

posted by Jason Kottke   Nov 15, 2017

Bruce Yeany teaches physical science to 8th graders in Annville, PA and he is very enthusiastic about it. On his popular Homemade Science YouTube channel, Yeany highlights all sorts of physics experiments and demonstrations without using any special equipment. In one of his latest videos, he shares a bunch of marble tracks that he’s built to demonstrate motion and momentum.

The “identical track race” starting at 1:43 might blow your noodle a little bit unless you’re familiar with Galileo’s pendulum research. (via digg)

How to make an Extremely Large Telescope

posted by Jason Kottke   Nov 09, 2017

The Giant Magellan Telescope, currently under construction at the University of Arizona’s Mirror Lab, will be one of the first of a new class of telescopes called Extremely Large Telescopes. The process involved in fashioning the telescope’s seven massive mirrors is fascinating. This is one of those articles littered with mind-boggling statements at every turn. Such as:

“We want the telescope to be limited by fundamental physics — the wavelength of light and the diameter of the mirror — not the irregularities on the mirror’s surface,” says optical scientist Buddy Martin, who oversees the lab’s grinding and polishing operations. By “irregularities,” he’s talking about defects bigger than 20 nanometers — about the size of a small virus. But when the mirror comes out of the mold, its imperfections can measure a millimeter or more.

Precision of 20 nanometers on something more than 27 feet in diameter and weighing 17 tons? That’s almost unbelievable. In this video, Dr. Wendy Freedman, former chair of the board of directors for the GMT project, puts it this way:

The surface of this mirror is so smooth that if we took this 27-foot mirror and then spread it out, from coast-to-coast in the United States, east to west coast, the height of the tallest mountain on that mirror would be about 1/2 an inch. That’s how smooth this mirror is.

You need that level of smoothness if you’re going to achieve better vision than the Hubble:

With a resolving power 10 times that of the Hubble Space Telescope, the GMT is designed to capture and focus photons emanating from galaxies and black holes at the fringes of the universe, study the formation of stars and the worlds that orbit them, and search for traces of life in the atmospheres of habitable-zone planets.

The telescope has a price tag of $1 billion and should be operational within the the next five years in Chile.

A scientific simulation of Seveneves’ Moon disaster

posted by Jason Kottke   Oct 06, 2017

In the first line of Seveneves, Neal Stephenson lays out the event that the entire book’s action revolves around:

The moon blew up without warning and for no apparent reason.

Mild spoilers, but fairly quickly, scientists in the book figure out that this is a very bad thing that will cause humanity to become extinct unless drastic action is taken.

In the novel, one day the moon breaks up into 7 roughly equal-sized pieces. These pieces continue peacefully orbiting the Earth for a while, and eventually two pieces collide. This collision causes a piece to fragment, making future collisions more likely. The process repeats, at what Stephenson says is an exponential rate, until the Earth is under near-constant bombardment from meteorites, wiping out (nearly) all life on Earth.

Jason Cole wondered how plausible that scenario is and created a simulation to model it. Turns out Stephenson had his figures right.

If you blow air through sand, it behaves like a liquid

posted by Jason Kottke   Sep 21, 2017

If you take a bin full of sand and blow air up through the bottom of it, the sand behaves like a liquid. The bubbles were freaky enough when I watched this for the first time, but when the guy reached in to submerge the ball and it buoyantly popped right to the surface, my brain broke a little bit. This video from The Royal Institution explains what’s going on:

Note that this is a different effect than non-Newtonian liquids (which are also very cool).

Update: Mark Rober made a hot tub-sized fluidized air bed:

Black holes could delete the Universe

posted by Jason Kottke   Aug 25, 2017

In their latest video, Kurzgesagt takes a look at black holes, specifically how they deal with information. According to the currently accepted theories, one of the fundamental laws of the Universe is that information can never be lost, but black holes destroy information. This is the information paradox…so one or both of our theories must be wrong.

The paradox arose after Hawking showed, in 1974-1975, that black holes surrounded by quantum fields actually will radiate particles (“Hawking radiation”) and shrink in size (Figure 4), eventually evaporating completely. Compare with Figure 2, where the information about the two shells gets stuck inside the black hole. In Figure 4, the black hole is gone. Where did the information go? If it disappeared along with the black hole, that violates quantum theory.

Maybe the information came back out with the Hawking radiation? The problem is that the information in the black hole can’t get out. So the only way it can be in the Hawking radiation (naively) is if what is inside is copied. Having two copies of the information, one inside, one outside, also violates quantum theory.

So maybe black holes holographically encode their information on the surface?

How to predict total solar eclipses

posted by Jason Kottke   Aug 18, 2017

The Exploratorium in San Francisco has produced a great explainer video about the science of predicting total solar eclipses. Each eclipse belongs to a repeating series of eclipses called a Saros cycle that repeats every 18 years 11 days and 8 hours.

Saros 145

There are now 40 active Saros cycles and the August 2017 eclipse belongs to Saros 145, which produced its first total eclipse in June 1909 and will produce its last total eclipse in September 2648.

A tour of our solar system’s eclipses

posted by Jason Kottke   Aug 16, 2017

In a meditative video for the NY Times, Dennis Overbye takes us on a tour of eclipses that happen in our solar system and beyond.

On the 21st day of August, 2017, the moon will slide between the Earth and the sun, painting a swath of darkness across North America. The Great American Solar Eclipse. An exercise in cosmic geometry. A reminder that we live on one sphere among many, all moving to the laws of Kepler, Newton and Einstein.

Humans have many more vantage points from which to observe solar eclipses than when the last solar eclipse occurred in the US in 1979. I had no idea that the Mars rovers had caught partial solar eclipses on Mars…so cool. (via @jossfong)

A visual explanation of quantum mechanics

posted by Jason Kottke   Jul 27, 2017

From the ViaScience YouTube channel comes this 31-part video explainer of quantum mechanics. As the introduction video notes, there is a fair bit of math in these videos presented at a quick pace, but if you took calculus in high school or college and remember the notation, that (and the pause button) should get you through this pretty well. (via @jsonpaul, who calls the series “fantastic”)

Quantum entanglement effects observed over 100s of miles

posted by Jason Kottke   Jun 19, 2017

A group of Chinese scientists say they have demonstrated the effects of quantum entanglement over a distance of 1200 km (745 miles).

Entanglement involves putting objects in the peculiar limbo of quantum superposition, in which an object’s quantum properties occupy multiple states at once: like Schrodinger’s cat, dead and alive at the same time. Then those quantum states are shared among multiple objects. Physicists have entangled particles such as electrons and photons, as well as larger objects such as superconducting electric circuits.

Theoretically, even if entangled objects are separated, their precarious quantum states should remain linked until one of them is measured or disturbed. That measurement instantly determines the state of the other object, no matter how far away. The idea is so counterintuitive that Albert Einstein mocked it as “spooky action at a distance.”

What’s weird to me is that all the articles I read about this touted that this happened in space, that an ultra-secure communications network was possible, or that we could build a quantum computer in space. Instantaneous communication over a distance of hundreds of miles is barely mentioned. Right now, it takes about 42 minutes for a round-trip communication between the Earth and Mars (and ~84 minutes for Jupiter). What if, when humans decide to settle on Mars, we could send a trillion trillion quantum entangled particles along with the homesteaders that could then be used to communicate in real time with people on Earth? I mean, how amazing would that be?

Update: Well, the simple reason why these articles don’t mention instantaneous communication at distance is that you can’t do it, even with quantum entanglement.

This is one of the most confusing things about quantum physics: entanglement can be used to gain information about a component of a system when you know the full state and make a measurement of the other component(s), but not to create-and-send information from one part of an entangled system to the other. As clever of an idea as this is, Olivier, there’s still no faster-than-light communication.

(thx, everyone)

If you can’t explain something in simple terms, you don’t understand it

posted by Jason Kottke   Jun 15, 2017

Feynman Blackboard

In the early 1960s, Richard Feynman gave a series of undergraduate lectures that were collected into a book called the Feynman Lectures on Physics. Absent from the book was a lecture Feynman gave on planetary motion, but a later finding of the notes enabled David Goodstein, a colleague of Feynman’s, to write a book about it: Feynman’s Lost Lecture. From an excerpt of the book published in a 1996 issue of Caltech’s Engineering & Science magazine:

Feynman was a truly great teacher. He prided himself on being able to devise ways to explain even the most profound ideas to beginning students. Once, I said to him, “Dick, explain to me, so that I can understand it, why spin one-half particles obey Fermi-Dirac statistics.” Sizing up his audience perfectly, Feynman said, “I’ll prepare a freshman lecture on it.” But he came back a few days later to say, “I couldn’t do it. I couldn’t reduce it to the freshman level. That means we don’t really understand it.”

John Gruber writes the simple explanations are the goal at Apple as well:

Engineers are expected to be able to explain a complex technology or product in simple, easily-understood terms not because the executive needs it explained simply to understand it, but as proof that the engineer understands it completely.

Feynman was well known for simple explanations of scientific concepts that result a in deeper understanding of the subject matter: e.g. see Feynman explaining how fire is stored sunshine, rubber bands, how trains go around curves, and magnets. Critically, he’s also not shy about admitting when he doesn’t understand something…or, alternately, when scientists as a group don’t understand something. There’s the spin anecdote above and of his explanation of magnets, he says:

I really can’t do a good job, any job, of explaining magnetic force in terms of something else you’re more familiar with, because I don’t understand it in terms of anything else you’re more familiar with.

Feynman was also quoted as saying:

I think I can safely say that nobody understands quantum mechanics.

Pretty interesting thing to hear from a guy who won a Nobel Prize for explaining quantum mechanics better than anyone ever had before. Even when he died in 1988 at the end of a long and fruitful careeer, a note at the top of his blackboard read:

What I cannot create, I do not understand.

The absurd precision involved in detecting gravitational waves

posted by Jason Kottke   Apr 27, 2017

Back in September 2015, the LIGO experiment detected gravitational waves formed 1.3 billion years ago when two black holes merged into one. The physics is pretty straightforward but to get the measurement, scientists had to build one of the most sensitive machines ever built. How sensitive? To get an accurate result, they needed to measure a distance of 4km with an accuracy of 1/10000th the width of a proton. This video from Veritasium looks at how the scientists and engineers accomplished such an amazing feat.

What will the night sky look like in 5 million years?

posted by Jason Kottke   Apr 13, 2017

Based on the motions of the 2 million stars observed by ESA’s Gaia mission over the past two years, scientists created this simulated animation of how the view of the Milky Way in the night sky will evolve over the next 5 million years.

The shape of the Orion constellation can be spotted towards the right edge of the frame, just below the Galactic Plane, at the beginning of the video. As the sequence proceeds, the familiar shape of this constellation (and others) evolves into a new pattern. Two stellar clusters — groups of stars that were born together and consequently move together — can be seen towards the left edge of the frame: these are the alpha Persei (Per OB3) and Pleiades open clusters.

Stars seem to move with a wide range of velocities in this video, with stars in the Galactic Plane moving quite slow and faster ones appearing over the entire frame. This is a perspective effect: most of the stars we see in the plane are much farther from us, and thus seem to be moving slower than the nearby stars, which are visible across the entire sky.

Well, how’s that for some perspective? (via blastr)

The Orion Nebula, our friendly neighborhood star factory

posted by Jason Kottke   Apr 03, 2017

Orion Nebula

Rolf Olsen recently took this amazing photo of the Orion Nebula using a home-built telescope.

The Orion Nebula is one of the most studied objects in the sky and also has a significant place in the history of astrophotography. In 1880 it was the first ever nebula to be photographed; Henry Draper used the newly invented dry plate process to acquire a 51-minute exposure of the nebula with an 11 inch telescope. Subsequently, in 1883, amateur astronomer Andrew Ainslie Common recorded several exposures up to 60 minutes long with a much larger 36-inch telescope, and showed for the first time that photography could reveal stars and details fainter than those visible to the human eye.

Thanks to Phil Plait for the link…he’s got much more to say about the image and the nebula here.

Also called M42 (the 42nd object in a catalog kept by comet hunter Charles Messier in the late 18th century), it is a sprawling star factory, a gas cloud where stars are born. It’s a couple of dozen light-years across, and sits well over a thousand light-years from Earth. That’s 10,000 trillion kilometers, and you can see it with your naked eye! It’s so bright because of a handful of extremely massive hot stars sit in its center. They blast out ultraviolet light that energizes the gas in the nebula, causing it to glow.

It’s actually a small section of a much larger dark cloud, what’s called a molecular cloud, that we cannot see directly. Stars were born near the edge of that cloud, not too deeply inside it, and when they switched on their fierce light and stellar winds blew a hole in the cloud, popping it like a bubble. The Orion Nebula is a cavity in the side of that cloud, carved by the newborn stars.

A full rotation of the Moon

posted by Jason Kottke   Mar 31, 2017

All but a few humans have seen no more than half of the Moon with their own eyes. For the rest of us stuck on Earth, we only get to see the side that always faces the Earth because the Earth & Moon are tidally locked; the Moon’s rotation about its axis and its orbit around the Earth take the same amount of time. But NASA’s LRO probe has taken high-resolution photos of all but 2% of the Moon’s surface, which have been stitched together into this video of the Moon’s full 360-degree rotation.

Recreating the Asteroids arcade game with a laser

posted by Jason Kottke   Mar 22, 2017

Watch as digital artist Seb Lee-Delisle recreates the old school video game Asteroids with a laser. But why use a laser? There’s actually a good explanation for this. In the olden days of arcade video games, the screens on most games were like Pac-Man or Donkey Kong…a typical CRT refreshed the entire screen line-by-line many times a second to form a pixelized scene. But with vector games like Tempest, Star Wars, and Asteroids, the electron beam was manipulated magnetically to draw the ships and rocks and enemies directly…and you get all these cool effects like phosphor trails and brighter objects where the beam lingers. When you play Asteroids on a contemporary computer or gaming system, all those artifacts are lost. But with a laser, you can emulate the original feel of the game much more closely.

You’re not going to want to because it’s 17 minutes long, but you should watch the whole video…it’s super nerdy and the explanations of how the various technologies work is worth your while (unless you’re already a laser expert). I loved the bit near the end where they slowed down the rate of the laser so you could see it drawing the game and then slowly sped it back up again, passing through the transition from seeing the individual movements of the laser to observing an entire seamless scene that our mind has stitched together. In his recent book Wonderland, Steven Johnson talks about this remarkable trick of the mind:

On some basic level, this property of the human eye is a defect. When we watch movies, our eyes are empirically failing to give an accurate report of what is happening in front of them. They are seeing something that isn’t there. Many technological innovations exploit the strengths that evolution has granted us: tools and utensils harness our manual dexterity and opposable thumbs; graphic interfaces draw on our powerful visual memory to navigate information space. But moving pictures take the opposite approach: they succeed precisely because our eyes fail.

This flaw was not inevitable. Human eyesight might have just as easily evolved to perceive a succession of still images as exactly that: the world’s fastest slide show. Or the eye might have just perceived them as a confusing blur. There is no evolutionary reason why the eye should create the illusion of movement at twelve frames per second; the ancestral environment where our visual systems evolved had no film projectors or LCD screens or thaumatropes. Persistence of vision is what Stephen Jay Gould famously called a spandrel — an accidental property that emerged as a consequence of other more direct adaptations. It is interesting to contemplate how the past two centuries would have played out had the human eye not possessed this strange defect. We might be living in a world with jet airplanes, atomic bombs, radio, satellites, and cell phones — but without television and movies. (Computers and computer networks would likely exist, but without some of the animated subtleties of modern graphical interfaces.) Imagine the twentieth century without propaganda films, Hollywood, sitcoms, the televised Nixon-Kennedy debate, the footage of civil rights protesters being fire-hosed, Citizen Kane, the Macintosh, James Dean, Happy Days, and The Sopranos. All those defining experiences exist, in part, because natural selection didn’t find it necessary to perceive still images accurately at rates above twelve frames a second — and because hundreds of inventors, tinkering with the prototypes of cinema over the centuries, were smart enough to take that imperfection and turn it into art.

A fictional flight above real Mars

posted by Jason Kottke   Mar 15, 2017

Using real images of Mars taken by the HiRISE camera on the Mars Reconnaissance Orbiter, Jan Fröjdman created a 3D-rendered flyover of several areas of the planet’s surface.

In this film I have chosen some locations and processed the images into panning video clips. There is a feeling that you are flying above Mars looking down watching interesting locations on the planet. And there are really great places on Mars! I would love to see images taken by a landscape photographer on Mars, especially from the polar regions. But I’m afraid I won’t see that kind of images during my lifetime.

It has really been time-consuming making these panning clips. In my 3D-process I have manually hand-picked reference points on the anaglyph image pairs. For this film I have chosen more than 33.000 reference points! It took me 3 months of calendar time working with the project every now and then.

Watch this in the highest def you can muster…gorgeous.

The time crystals concept is now reality

posted by Jason Kottke   Feb 07, 2017

Time Crystals

In 2012, physicist Frank Wilczek speculated that it would be possible to make a crystal whose lattice repeats in four dimensions, not just three.

Wilczek thought it might be possible to create a similar crystal-like structure in time, which is treated as a fourth dimension under relativity. Instead of regularly repeating rows of atoms, a time crystal would exhibit regularly repeating motion.

Many physicists were sceptical, arguing that a time crystal whose atoms could loop forever, with no need for extra energy, would be tantamount to a perpetual motion machine — forbidden by the laws of physics.

Now, a team at Berkeley have succeeded in making time crystals, publishing a method that two other teams have already successfully followed.

For Yao’s time crystal, an external force — like the pulse of a laser — flips the magnetic spin of one ion in a crystal, which then flips the spin of the next, and so forth, setting the system into a repeating pattern of periodic motion.

There are two critical factors. First, after the initial driver, it must be a closed system, unable to interact with and lose energy to the environment. Second, interactions between quantum particles are the driving force behind the time crystal’s stability. “It’s an emergent phenomenon,” says Yao. “It requires many particles and many spins to talk to each other and collectively synchronise.”