If you look at the orbits of the planets adjacent to the Earth’s orbit (Venus & Mars), you’ll see that Venus’s orbit is closest to our own. That is, at its closest approach, Venus gets closer to Earth than any other planet. But what about the average distance?
According to this article in Physics Today by Tom Stockman, Gabriel Monroe, and Samuel Cordner, if you run a simulation and do a proper calculation, you’ll find that Mercury, and not Venus or Mars, is Earth’s closest neighbor on average (and spends more time as Earth’s closest neighbor than any other planet):
Although it feels intuitive that the average distance between every point on two concentric ellipses would be the difference in their radii, in reality that difference determines only the average distance of the ellipses’ closest points. Indeed, when Earth and Venus are at their closest approach, their separation is roughly 0.28 AU — no other planet gets nearer to Earth. But just as often, the two planets are at their most distant, when Venus is on the side of the Sun opposite Earth, 1.72 AU away. We can improve the flawed calculation by averaging the distances of closest and farthest approach (resulting in an average distance of 1 AU between Earth and Venus), but finding the true solution requires a bit more effort.
What the calculation also shows is that Mercury is the closest planetary neighbor to every planet, on average. Also, the authors of the paper don’t explicitly mention this, but the Sun (at 1 AU) is closer on average to the Earth than even Mercury (1.04 AU).
Ever since the Huffington Post struck SEO gold in 2011 with their post about what time the Super Bowl started, pretty much every online publication now runs a similar article in an attempt to squeeze some of Google’s juice into their revenue stream. My “attempt” from last year: What Time Isn’t the Super Bowl?
6:30 p.m. is the time the Super Bowl will start in Atlanta. Most of us are not in Atlanta. So for us, the game will start later than that. You need the time for the images to be captured by the cameras, be broadcasted to air or cable, be captured by my TV screen, leave my TV screen, get to my eyes (not to mention the time my brain needs to process and decode the images). You may say this is fast — of course this is fast. But it takes some time nevertheless, and I am a physicist, I need precision. For most of us, the game will actually start some time later than the kickoff in Atlanta.
Not only that, but time moves at different speeds for each of us:
We have discovered that clocks run at different speed depending on how fast they are moved, and depending on how high they are positioned. That’s right, it is a fact: Two equal clocks go out of time with respect each other if one is moved and the other is kept fixed. The same will happen if one is kept, say, above your head, and the other lower, say, at your feet. All this was discovered by Einstein a century ago; for a while it was just brainy stuff for nerds, but today we are sure it is true. A good lab clock can check this, and it is truly true. Your head lives a bit longer than your feet (unless you spend a lot of time upside down).
So, the clock of the guy up in the high sections of the stadium runs faster than the clock of the referee on the field. And Tom Brady’s clock (if he were to wear one) runs slower, because Tom moves fast (okay, maybe not “fast,” but faster than the people sitting and watching him).
P.S. The Super Bowl starts at approximately 6:30pm EST on Feb 3, 2019. (via laura olin)
These visualizations of the speed of light I posted last week somehow demonstrate both how fast light speed is and how slow it is compared the vastness of the galaxy & universe. Science fiction often bends the rules of physics as we currently understand them, with fictional spacecraft pushing beyond the speed of light. In Star Trek, the measure of a ship’s velocity is warp speed. Warp 1 is the speed of light, Warp 6 is 392 times the speed of light, etc. In this Warp Speed Comparison video, EC Henry compares the top speeds of various Star Trek vessels (the original Enterprise, Voyager, the Defiant), racing them from Earth to the edge of the solar system.
Once again, you get a real sense of how fast these ships would be if they actually existed but also of the vastness of space. It would take 10 seconds for the fastest ship to reach the edge of the solar system at maximum warp and just over 6 hours to get to the nearest star, Proxima Centauri. Wikipedia lists a few dozen stars that are within a day’s journey at full warp…a trip that takes light more than 16 years. The mighty speed of light is no match for the human imagination. (thx, jim)
Light is fast! In a recent series of animations, planetary scientist James O’Donoghue demonstrates just how fast light is…and also how far away even our closest celestial neighbors are. Light, moving at 186,000 mi/sec, can circle the Earth 7.5 times per second and here’s what that looks like:
It can also travel from the surface of the Earth to the surface of the Moon in ~1.3 seconds, like so:
That seems both really fast and not that fast somehow. Now check out light traveling the 34 million miles to Mars in a pokey 3 minutes:
And Mars is close! If O’Donoghue made a real-time animation of light traveling to Pluto, the video would last over 5 hours. The animation for the closest undisputed galaxy, Seque 1, would last 75,000 years and 2.5 million years for the Andromeda galaxy animation. The farthest-known objects from Earth are more than 13 billion light years away. Light is slow!
In 1960, the National Film Board of Canada released a short documentary called Universe. The film follows the work of astronomer Donald MacRae at an observatory in Ontario, which is accompanied a special effects-heavy tour of the solar system, galaxy, and universe: “a vast, awe-inspiring picture of the universe as it would appear to a voyager through space”. Universe was nominated for an Oscar in 1961 and also caught the eye of Stanley Kubrick, who used it as inspiration for 2001: A Space Odyssey.
“Stanley had seen the National Film Board movie Universe.” Most of the crew on 2001 were familiar with the Canadian production, made by filmmakers Colin Low and Roman Kroitor, all having seen it at the early stages of 2001’s production, it being “required watching” at the insistence of Kubrick himself, who had seen the documentary “almost 100 times”, “until the sprockets wore out,” 2001 special effects supervisor Con Pedersen remembers.
Kubrick was so taken by the depiction of the celestial objects in the film that he hired the co-director and a special effects technician from Universe to work on 2001. The narrator of Universe, Douglas Rain, also became a integral part of Kubrick’s masterpiece. After ditching the idea that 2001 would be narrated by Rain — “as more film cut together, it became apparent narration was not needed” — Kubrick chose Rain as the now-iconic voice of HAL 9000.
After finally excising the narrator altogether, he simply made Rain the voice of HAL, liking his “bland mid-Atlantic accent”. The decision was entirely Kubrick’s, who had become concerned with the character of the computer. “Kubrick was having,” Rain says, “a problem with the computer. ‘I think I made him too emotional and too human,’ he said. ‘I’m having trouble with what I’ve got in the can. Would you consider doing his voice?’ So we decided on the voice of the computer.”
But back to Universe, which is a marvelous little film (even though it asserts at one point that “it is reasonably certain” that Mars contains vegetation). I love the early sequence of the astronomer setting up his telescope — the way he walks along inside of it and then casually lifts it up into place. It’s really just a bigger version of the small reflector that I have, not any more complicated than a couple of mirrors pointed in the right direction. It’s incredible what we humans have learned about the universe simply by collecting ancient starshine with polished lenses and mirrors. (via clayton cubitt)
I love how simple questions can reveal deep truths about how the universe works. Take “why is the night sky dark?” It’s a question a small child might ask but stumped the likes of Newton, Halley, and Kepler and wasn’t really resolved until Einstein’s theory of general relativity and the Big Bang theory rolled around. Here’s the paradox: if we live in a static infinite universe, shouldn’t the sky be unbearably bright?
Distant stars look weak, and very distant stars shine too dimly for you to see with your eyes. But when space telescopes like Hubble peer deep into the darkest spots of sky, they uncover bunches of incredibly faint galaxies. And the deeper they look, the more they find. If the universe went on forever with stars sprinkled evenly throughout — as many early stargazers assumed — the night sky would be full of so many points of light that it would never look dark.
“The fact that the stars are everywhere makes up for the fact that some of the stars are far away,” says Katie Mack, an astrophysicist at North Carolina State University. No matter which way you look, in an endless universe your line of sight would always end smack on the surface of a star, and the entire sky would always blaze with the brightness of the sun.
The answer to this paradox is that the universe is both finite & unbounded (per Einstein) and the darkness we see is the Big Bang.
The mystery of the dark sky is solved by the fact that this history has a beginning — a time before stars and galaxies. Many cosmologists think the universe started out as a very small point, and then started inflating like a balloon in an event called the Big Bang. If you look deep enough, you can see so far back in time that you get close to the Big Bang. “You just run out of stars,” Kinney says. “And you run out of stars, in the grand scheme of things, relatively quickly.”
If you’re anything like me, you just had a Little Bang go off in your brain. (via laura olin)
I’ve always had a hard time wrapping my head around the idea that the universe could be both finite and infinite at the same time (or something like that *takes bong rip*), but this passage from Coming of Age in the Milky Way by Timothy Ferris succinctly explains what’s going on:
General relativity resolved the matter by establishing that the universe could be both finite — i.e., could contain a finite number of stars in a finite volume of space — and unbounded. The key to this realization lay in Einstein’s demonstration that, since matter warps space, the sum total of the mass in all the galaxies might be sufficient to wrap space around themselves. The result would be a closed, four-dimensionally spherical cosmos, in which any observer, anywhere in the universe, would see galaxies stretching deep into space in every direction, and would conclude, correctly, that there is no end to space. Yet the amount of space in a closed universe would nonetheless be finite: An adventurer with time to spare could eventually visit every galaxy, yet would never reach an edge of space. Just as the surface of the earth is finite but unbounded in two dimensions (we can wander wherever we like, and will not fall off the edge of the earth) so a closed four-dimensional universe is finite but unbounded to us who observe it in three dimensions.
In the terms of Edwin Abbott Abbott’s Flatland: A Romance of Many Dimensions, we are Flatlanders living in a Lineland world who, with the aid of mathematics, have been able to peer into Spaceland.
Equipped with only a magnifying glass and the light of the Sun, it’s pretty easy to start a fire.1 So, with a much bigger glass, could you start a fire with moonlight?
First, here’s a general rule of thumb: You can’t use lenses and mirrors to make something hotter than the surface of the light source itself. In other words, you can’t use sunlight to make something hotter than the surface of the Sun.
There are lots of ways to show why this is true using optics, but a simpler — if perhaps less satisfying — argument comes from thermodynamics:
Lenses and mirrors work for free; they don’t take any energy to operate.[2] If you could use lenses and mirrors to make heat flow from the Sun to a spot on the ground that’s hotter than the Sun, you’d be making heat flow from a colder place to a hotter place without expending energy. The second law of thermodynamics says you can’t do that. If you could, you could make a perpetual motion machine.
In a better world, Randall Munroe would be writing middle school science textbooks.
A few summers ago when I was showing my kids how to do this, I started futzing with the small pile of tissue paper and pine needles we’d assembled and forgot about the magnifying glass I was holding…until I felt a searing pain in my leg and looked down to see a bit of smoke curling up from my slightly toasted thigh. Kids, do as dad says, not as he does.↩
Perhaps the most fundamental way to think about the Universe is in terms of energy. Even when you get away from physics and chemistry (where energy is obviously central) and into a topic like human history or economics, following how and where energy flows can be enlightening. In 1964, Soviet astronomer Nikolai Kardashev proposed thinking about the progress of human civilization in terms of how much energy we were capable of harnessing. On the Kardashev scale, a Type I civilization would be capable of using all of the energy available on their planet, a Type II civilization could use all the energy from their local star, and a Type III civilization could harness all the energy in a galaxy.
According to an equation suggested by Carl Sagan, humans are currently sitting at ~73% of a Type I civilization. But once we reach that milestone in perhaps a few hundred years (assuming we don’t blow ourselves up in the process), the construction of a Dyson sphere or, more likely, a Dyson swarm around the Sun is probably the key to eventually hitting Type II. In the video above, Kurzgesagt explores what would go into building some type of Dyson structure capable of harvesting most of the Sun’s energy. For starters, we’d probably have to completely dismantle the planet Mercury in order to have enough raw materials to build the swarm.
As of December 1, 2018, the LIGO experiment has detected gravitational waves from 10 black hole merger events. In the computer simulations shown in this video, you can see what each of the mergers looked like along with the corresponding gravitational waves generated and subsequently observed by the LIGO detectors.
Stephen Hawking passed away back in March, but left us with a final book that just came out this week: Brief Answers to the Big Questions. There are 10 questions asked and answered in the book:
Is there a God?
How did it all begin?
Can we predict the future?
What is inside a black hole?
Is there other intelligent life in the universe?
Will artificial intelligence outsmart us?
How do we shape the future?
Will we survive on Earth?
Should we colonize space?
Is time travel possible?
Take the chapter on “Can we predict the future?”. Starting with regular astronomical events, it swiftly moves on to scientific determinism, quantum physics, hidden variables and Heisenberg’s uncertainty principle. Under the guise of a simple question, Hawking has managed to take the reader on a whistle-stop tour of the quantum world (bottom line: no we can’t predict everything). It’s a clever ruse. Ask a simple question and you’ll draw in readers who might otherwise not know they’d be interested in complex science.
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.
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.
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.
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.”
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”.
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.
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.
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.
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.
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.
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.
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.
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)
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.↩
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.
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.
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.
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.”
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.”
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.
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)
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)
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.
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 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:
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?
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.
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.
Stay Connected