Today is the anniversary of the discovery, by John Tebbutt of New South Wales, Australia, of the Great Comet of 1861. Tebbutt was an astronome.
The comet was initially visible only in the southern hemisphere, but then became visible in the northern hemisphere on about June 29th. I find it interesting that word of the commet spread slowly enough that it was sen in the north before it was heard of.
It has been suggested that this comet had been previously sighted in April of 1500 (that comet is now known as C/1500 H1). The comet will return during the 23rd century.Read the comments on this post...
"I tell you, we are here on Earth to fart around, and don't let anybody tell you different." -Kurt Vonnegut Kurt Vonnegut may have it right for most of us, but not all of us spend all of our time on Earth. A select dozen of us, in fact, have made it to, as Cat Power would sing, to
(Image credit: Apollo 15, Dave Scott, NASA.)
Back in 1971, the Apollo 15 astronauts made huge strides in space exploration, making use of the first manned lunar rover and spending over 18 hours on activities outside of the spacecraft. But two (of the three) crew members experienced heartbeat irregularities on the mission, and the cause was unknown. This was the first time such irregularities were observed in Apollo astronauts, and NASA was, understandably, unhappy about this. Their biomedical research team initially concluded (incorrectly) that it was likely due to a potassium deficiency, and so some modifications were made to the astronauts' diets for the next mission.
A modification, mind you, that would change the place in history of one astronaut forever.
(Image credit: NASA, Apollo 10 official astronaut photo.)
Astronaut John Young is one of the most decorated astronauts in history. With an astronaut career spanning more than 40 years, he flew twice, each, on Gemini, Apollo, and Space Shuttle missions, including the inaugural STS-1 shuttle flight.
But John Young also was a crew member aboard Apollo 16, where he would become the ninth person to walk on the Moon. Oh, and where he was compelled to indulge in a diet very, very high in potassium. In particular, in the form of orange juice.
(Image credit: NASA / Science Source / Science Photo Library.)
Now, John Young had a history with particularities about food. He became something of an astronaut folk hero for smuggling a corned beef sandwich on board Gemini-3 in 1965, but was wholly unprepared for the ingestion of such tremendous quantities of orange juice.
Or, rather, for the effect that said orange juice would have on his body. And NASA was duly unprepared for the effect that would have on John Young's language.
(Video credit: NASA audio; YouTube user jude4021.)
While I imagine that there are few astronaut experiences worse than dutch ovening yourself inside your own spacesuit, you can also imagine that the governor of Florida was not too pleased at a mic'd up diatribe against the signature crop of his state. Words, in fact, that John Young would have to answer for in an official Apollo 16 press conference:
I don't know whatever happened to the gases released by astronaut Young (and others), but if there's any methane on the Moon, you can be sure that this is where it comes from! Read the comments on this post...
"They say 'A flat ocean is an ocean of trouble. And an ocean of waves... can also be trouble.' So, it's like, that balance. You know, it's that great Oriental way of thinking, you know, they think they've tricked you, and then, they have." -Nigel Tufnel Black holes* are some of the most perplexing objects in the entire Universe. Objects so dense, where gravitation is so strong, that nothing, not even light, can escape from it.
(Image credit: Artist's Impression from MIT.)
But there are a number of very counterintuitive things that happen as you get near a black hole's event horizon, and a very, very good reason why once you cross it, you can never get out! No matter what type of black hole you had, not even if you had a spaceship capable of accelerating in any direction at an arbitrarily large rate.
It turns out that General Relativity is a very harsh mistress, particularly when it comes to black holes. It goes even deeper than that, mind you, and it's all because of how a black hole bends spacetime.
(Image credit: Adam Apollo.)
When you're very far away from a black hole, spacetime is less curved. In fact, when you're very far away from a black hole, its gravity is indistinguishable from any other mass, whether it's a neutron star, a regular star, or just a diffuse cloud of gas.
The only difference is that instead of a gas cloud, star or neutron star, there will be a completely black sphere in the center, from which no light will be visible. (Hence the "black" in the moniker "black holes.")
(Image credit: Astronomy/Roen Kelly, retrieved from David Darling.)
This sphere, known as the event horizon, is not a physical entity, but rather a region of space -- of a certain size -- from which no light can escape. From very far away, it appears to be the size that it actually is, as you'd expect.
(Image credit: Cornell University.)
For a black hole the mass of the Earth, it'd be a sphere about 1 cm in radius, while for a black hole the mass of the Sun, the sphere would be closer to 3 km in radius, all the way up to a supermassive black hole -- like the one at our galaxy's center -- that would be more like the size of a planetary orbit!
From a great distance away, geometry works just like you'd expect. But as you travel, in your perfectly equipped, indestructible spacecraft, you start noticing something strange as you approach this black hole. Unlike all the other objects you're used to, where they appear to get visually larger in proportion to the distance you are away from them, this black hole appears to grow much more quickly than you were expecting.
(Image credit: Ute Kraus, Physics education group Kraus, Universität Hildesheim.)
By time the event horizon should be the size of the full Moon on the sky, it's actually more than four times as large as that! The reason, of course, is that spacetime curves more and more severely as you get close to the black hole, and so the "lines-of-light" that you can see from the stars in the Universe that surround you are bent disastrously out of shape.
Conversely, the apparent area of the black hole appears to grow and grow dramatically; by time you're just a few (maybe 10) Schwarzschild radii away from it, the black hole has grown to such an apparent size that it blocks off nearly the entire front view of your spaceship.
As you start to come closer and closer to the event horizon, you notice that the front-view from your spaceship becomes entirely black, and that even the rear direction, which faces away from the black hole, begins to be subsumed by darkness. The entirety of the Universe that's visible to you begins to close off in a shrinking circle behind you.
Again, this is because of how the light-paths from various points travel in this highly bent spacetime. For those of you (physics buffs) who want a qualitative analogy, it begins to look very much like the lines of electric field when you bring a point charge close to a conducting sphere.
(Image credit: J. Belcher at MIT.)
At this point, having not yet crossed the event horizon, you can still get out. If you provide enough acceleration away from the event horizon, you could escape its gravity and have the Universe go back to your safely (asymptotically) flat spacetime. Your gravitational sensors can tell you that there's a definite downhill gradient towards the center of the blackness and away from the regions where you can still see starlight.
But if you continue your fall towards the event horizon, you'll eventually see the starlight compress down into a tiny dot behind you, changing color into the blue due to gravitational blueshifting. At the last moment before you cross over into the event horizon, that dot will become red, white, and then blue, as the cosmic microwave and radio backgrounds get shifted into the visible part of the spectrum for your last, final glimpse of the outside Universe.
(Image credit: ZetaPrints.com.)
And then... blackness. Nothing. From inside the event horizon, no light from the outside Universe hits your spaceship. You now think about your fabulous spaceship engines, and how to get out. You recall which direction the singularity was towards, and sure enough, there's a gravitational gradient downhill towards that direction.
But your sensors tell you something even more bizarre: there's a gravitational gradient that's downhill, towards a singularity, in all directions! The gradient even appears to go downhill towards the singularity directly behind you, in the direction that you knew is opposite to the singularity! How is this possible?
(Image credit: Cetin Bal.)
Because you're inside the event horizon, and even any light beam (which you could never catch) you now emitted would end up falling towards the singularity; you are too deep in the black hole's throat! What's worse is that any acceleration you make will take you closer to the singularity at a faster rate; the way to maximize your survival time at this point is to not even try to escape! The singularity is there in all directions, and no matter where you look, it's all downhill from here.
Like I said, General Relativity is a harsh mistress, particularly when it comes to black holes.
(* -- This is all done for a non-rotating, or Schwarzschild black hole. Other forms of black holes are similar, but slightly different, and much more complicated, quantitatively.) Read the comments on this post...
There's been a bunch of discussion recently about philosophy of science and whether it adds anything to science. Most of this was prompted by Lawrence Krauss's decision to become the Nth case study for "Why authors should never respond directly to bad reviews," with some snide comments in an interview in response to a negative review of his latest book. Sean Carroll does an admirable job of being the voice of reason, and summarizes most of the important contributions to that point. Some of the more recent entries to cross my RSS reader include two each from 13.7 blog and APS's Physics Buzz.
I haven't commented on this because I haven't read Krauss's book (and I'm not likely to), and because my interest in philosophy generally is at a low ebb at the moment (I oscillate back and forth between thinking it's kind of a fun diversion, and thinking I have better things to do with my time). I've been thinking about a new project that's kinda-sorta on the edge of philosophy-of-science type things, though, which has involved a bit of time thinking about why my regard for the subject is at a low ebb at the moment. And seeing the title of Jason Rosenhouse's "The Reason for the Ambivalence Toward the Philosophy of Science" in the "most active" sidebar widget (the post itself isn't so interesting to me, but the framing of the title made me think of something useful), combined with the second Physics Buzz post, combined with what I was writing last week made a bunch of pieces fall into place.
My realization was this: I'm down on philosophy of science type things at the moment because an awful lot of the conversation reminds me of interminable arguments within science fiction fandom.Read the rest of this post... | Read the comments on this post...
One final thought on the Big Science/ Space Chronicles stuff from last week. One of the things I found really frustrating about the book, and the whole argument that we ought to be sinking lots of money into manned space missions is that the terms of the argument are so nebulous. This is most obvious when Tyson or other space advocates talk about the need for "inspiring" people, but it shows up even in what ought to be relatively concrete discussions of actual science.
Take, for example, the argument over humans vs. robots. Given the success of the robotic missions to Mars and other bodies, many people ask why we should bother to send people to any of those places. Tyson himself estimates the cost of sending a human to be around fifty times the cost of sending a robot, and says that "if my only goal in space is to do science, and I'm thinking strictly in terms of the scientific return on my dollr, I can think of no justification for sending a person into space." But then, he turns around and tries to justify it on fairly standard grounds: that humans are more flexible, while a robot can only "look for what it has already been programmed to find." Having humans on the scene would enable faster and more "revolutionary" discoveries.
This is an argument that sounds fairly convincing on a surface level, but on closer inspection it breaks down in two ways: it's too generous to humans, and too hard on the robots.Read the rest of this post... | Read the comments on this post...
This post was written by Brookhaven Lab science writer Justin Eure.
With nanotechnology rapidly advancing, the sci-fi dream of a Star Trek replicator becomes increasingly less fantastic. But such radical technology would, in theory, require the kind of subatomic manipulation that far exceeds current capabilities. Scientists lack both the equipment and the fundamental knowledge of quantum mechanics (the Standard Model, for all its elegance, remains incomplete) to build items from the raw stuff of quarks, gluons, and electrons . . . but what about alchemy?
Even Isaac Newton, credited with the dawn of the Age of Reason, felt the mystical draw of alchemy, working in secret to transform one element into another. Centuries later we still can't conjure gold from lead, sure, but what if it was possible to combine a handful of elements to very closely mimic gold? What if scientists engineered a synthetic Midas Touch that tricked base metals into performing like gold, thereby conquering the hurdles of rarity and price?
Now forget the alchemist's dream of gold and consider the equally precious noble metal platinum - hovering right around $50,000 per kilogram - which may be the key to building a sustainable energy future. Now, using advanced technology and elements that cost 1000 times less, researchers at Brookhaven National Lab have created a high-performing pauper's platinum from nanoscale building blocks.Read the rest of this post... | Read the comments on this post...
"There's nothing that cleanses your soul like getting the hell kicked out of you."
-Woody Hayes There's no doubt that we lucked out when it came to the formation of our Solar System.
(Image credit: Michael Pidwirny, retrieved from here.)
Our inner Solar System, where temperatures are ideal for liquid water and life-as-we-know-it, is full of rocky planets and devoid of any gas giants for many hundreds of millions of miles. But, as we know all too well from the last twenty years of finding exoplanets, this isn't the only way it could have turned out.
In fact, of the some 2,300 planets found around other stars so far, the vast majority of them are either very, very hot, very, very large, or both.
(Image credit: Jer Thorp and John Underkoffler.)
This could just be due to the fact that those types of planets are the easiest ones to find with the technology and techniques we have available to us right now, and we may wind up finding more solar systems like ours. What seems most important, at least as far as the search for extraterrestrial life (or possibly habitable exoplanets) goes, is looking for rocky planets where the temperature is right for liquid water.
And every star has a region around it where that's possible.
But although we've found a small but important number of stars with rocky planets that live in their habitable zones, there's one type of exoplanet system that never has a rocky planet in their habitable zones.
Not only that, but they -- at least so far -- never have any other planets in their solar systems! What gives?
(Image credit: NASA / GSFC, retrieved from Softpedia.)
Over in our Solar System, we've got our rocky worlds interior to all of our gas giants, with an asteroid belt interior to the giant planets, and a kuiper belt exterior to our four Jovians. But in systems where there's a Hot Jupiter, or a gas giant very close to its parent star, we don't find any other planets anywhere near the star itself.
Why is that?
(Image credit: European Southern Observatory/L. Calcada, retrieved here.)
When you bring a large-mass planet into close quarters with a much smaller one, something's got to give. Because of the way gravitation works, you're going to have a three-body gravitational interaction, which is one of the most difficult theoretical problems in all of physics.
But universally, what's going to happen is that there's going to be a transfer of momentum and angular momentum, and one of three things is going to happen. Either:
- The large planet will gravitationally capture the smaller one, turning it into a moon,
- The large planet will fling the small planet either violently into its Sun or violently out of the Solar System, or
- The large planet will collide with the small one, effectively eating it.
(Image credit: BoredofStudies.org.)
In other words, these Hot Jupiters are like the psychotic eldest child that murders its younger siblings! We see that there are no rocky planets among the gas giants in our Solar System for exactly this reason. But how does this work, and why does this prevent solar systems with Hot Jupiters from having habitable planets outside of them? This is not obvious, so let me first set up the situation for you to help you get a handle on it.
As far as we understand it, all solar systems start out the same way in the very early stages: there's a central region where a star forms, accompanied by a proto-planetary disk, which will coalesce and form into planets.
(Image credit: NASA, retrieved here.)
But over time, planets clear the space around them. They do this, believe it or not, in the same way that star clusters all eventually end up dissipating: simple gravity. Watch this simulation of a star cluster to see what I'm talking about, and pay particular attention to the first 25 seconds of the video.
(Video credit: Simon Portegies Zwart (U. of Amsterdam) and Frank Summers (STScI).)
Notice how an occasional star just sped off from the star cluster in a random direction, even early on in the simulation? That's what gravitational encounters between more than 2 bodies do, pretty much all of the time! The physical process is called violent relaxation, which is a wonderful term that (somehow) no enthusiast has created a wikipedia entry for!
Just as the structure of the star cluster changes because of these gravitational ejections, the structure of the young solar system changes because of its gravitational interactions. These large planets can migrate, depending on how they absorb or remove each tiny mass they encounter. Some encounters move them closer towards their parent star, others move them farther away. In the case of Jupiter and Saturn, they were once significantly closer to the asteroid belt than they are today; in the case of Hot Jupiters, they clear out at least the entire habitable zone!
(Image credit: NASA, ESA, and G. Bacon (STScI).)
According to research led by Eric Ford, the reason we haven't found any of these habitable, rocky planets around stars with Hot Jupiters -- even though we've found 63 of them around other stars -- is because Hot Jupiters perturb the orbits of these planetesimals in the young solar systems sufficiently so as to completely clean them out, leaving no possible rocky worlds behind!
(Image credit: NASA / JPL-Caltech.)
In our Solar System, our four gas giants completely cleared out the regions between about 4 Astronomical Units and about 30 Astronomical Units, where one of them is the distance between the Earth and the Sun. But if you put a Jupiter-sized planet anywhere in the inner Solar System, then all of the rocky planets wouldn't be here!
And that's why systems with exoplanet bullies in them -- Hot Jupiters, to be specific -- have no Earth-like planets in them, or rocky worlds with the proper temperatures for water. That's just one more example of the power of gravity!Read the comments on this post...
I go back and forth about the whole question of scientific accuracy in tv shows and movies. On the one hand, I think that complaining "Explosions don't make noise in space!" is one of the worst forms of humorless dorkitude, and I'm generally happy to let bad science slide by in the service of an enjoyable story. On the other hand, though, I am a professional physicist, and it's hard to turn that off completely.
Weirdly, one thing that tends to push me toward complaining about the science is when people start doing "The Science of ______" pieces, as both MSNBC and io9 did for The Avengers, and when movie people start patting themselves on the abck for having consulted with scientists. Because, you know, if you're going to talk up the fact that there's science behind the movie, you're asking to be held to a higher standard.
And, really, most of the recent spate of comic-book movies have had scenes of technobabble that are every bit as dumb as anything produced in the days before consulting scientists. One of the worst was an exchange in The Avengers, where the team's scientists, Bruce Banner and Tony Stark, are trying to help S.H.I.E.L.D. track down Loki and his stolen energy source:
BANNER: How many spectrometers do you have?
SHIELD GUY: We have the cooperation of every university in the country.
BANNER: Tell them to put the spectrometers on the roof, and set them to detect gamma radiation.
(That's paraphrased a bit from memory.) This is one of the stupidest science-type lines I've heard in any recent movie. To give you an idea of how stupid it is, here's an analogue in more everyday terms:Read the rest of this post... | Read the comments on this post...
Continuing the blog recap series, we come to the "split year" of 2005-2006. The blog was initially launched in late June, so that's when I'm starting the years for purposes of these recaps, but ScienceBlogs launched in January 2006, so this year was half Steelypips and half ScienceBlogs. This post will cover the Steelypips half, June-January; I'll do the ScienceBlogs stuff in a second post, once I figure out the best way to go through those posts (the ScienceBlogs archives aren't set up well for reading straight through).
In reading through this, I was amused to discover this pan of Seed's relaunch, in which I call the magazine "Maxim for science geeks." Not quite three months later, they were paying me to write a blog... I remembered writing that, but didn't remember how close it was to the launch of ScienceBlogs.
So, what was on the blog in the second half of 2005?Read the rest of this post... | Read the comments on this post...
Some time back, I reviewed a cool book about Fermi problems by Aaron Santos, then a post-doc at Michigan. In the interim, he's taken a faculty job at Oberlin, written a second book on sports-related Fermi problems, and started a blog, none of which I had noticed until he emailed me. Shame on me.
Anyway, his new book is just out, and he's running an estimation contest with a signed copy as the prize. So, if you're the sort of person who enjoys Fermi problems, read his post then grab a convenient envelope and start estimating on the back. You have until June 1.Read the comments on this post...
"Without a wish, without a will,
I stood upon that silent hill
And stared into the sky until
My eyes were blind with stars and still
I stared into the sky." -Ralph Hodgson The next month -- from May 5th to June 5th -- brings three of the most spectacular astronomy sights possible on Earth back-to-back-to-back for skywatchers of all types, without telescopes, binoculars, or any special equipment. Tonight, May 5th, marks what's come to be known as a Supermoon, or the largest, brightest full Moon of the year.
(Image credit: Chris Kotsiopoulos at Earth Science Picture of the Day.)
Not that you'll notice, mind you, unless you've got both an incredible eye and an incredible memory. The full Moon is, by far, the brightest thing in the night sky, outshining the brightest star in the sky by a factor of around 40,000.
A supermoon, on the other hand, is only about 30% brighter than a normal full Moon.
(Image credit: science @ NASA, retrieved from Tara Hastings at WDTN.)
The Moon, of course, orbits the Earth in an ellipse, rather than in a perfect circle. When the Moon is farther away from Earth in its orbit -- or closer to apogee -- it appears smaller in the sky, while when it's closer to Earth -- near perigee -- it appears larger. The supermoon is the one full Moon out of the year that occurs when the Moon is at its minimum distance from the Earth, and hence appears the brightest.
(Image credit: Essay Web's astronomy site.)
These differences, however, are relatively small. The full Moon at apogee is only 20% smaller than the full Moon at perigee, a difference completely un-noticeable to even a trained observer, unless you put these two images right next to one another.
(Image credit: Marco Langbroek, the Netherlands, retrieved here.)
Having the closest, brightest full Moon of the year is a great excuse to go out and look at it, attempt to photograph it, or if you're far away enough from streetlights, enjoy the shadows cast by the moonlight.
There's nothing you can't do with a supermoon that you couldn't do with any, ordinary full Moon, but it is fun to think about why this happens.
(Image credit: Ryan, footnote #3 on Carrie Fitzgerald's site.)
The Moon makes an ellipse around the Earth, which in turn makes an ellipse around the Sun. Right now, the Moon's perigee is in the opposite direction of the Earth from the Sun, so full Moons appear as large as they're ever going to. New Moons and crescents, on the other hand, will appear somewhat smaller, as they occur closer to apogee.
But six months from now, the Earth (and Moon) will be on the other side of the Sun, so the Moon's apogee will occur close to the full phase, resulting in somewhat smaller full Moons, while new Moons and crescents will be larger. You can see NASA's apogee and perigee calculator for more information, but I think the diagram below illustrates things pretty clearly.
(Image credit: NASA, Fred Espenak and Jean Meeus.)
Right now, we're extremely close to position "C" in the diagram above, where the Moon's apogee (farthest from Earth) occurs close to the Sun, and the Moon's perigee (closest to Earth) occurs away from the Sun. This gives us the supermoon that you can see tonight, but fifteen days from now, it's going to give us something far more rare and special.
The Moon's apogee occurs on May 19th, and the very next day, at nearly its most distant from Earth, the Moon, Earth, and Sun will all line up, producing the spectacular and rare sight of an annular Solar Eclipse!
(Image credit: Kopernik Observatory and Science Center.)
On the evening of May 20th in North America, close to Sunset, the Moon will pass in front of the Sun. But because the Moon is so close to apogee, it will actually appear ever so slightly smaller than the Sun in the sky, and thus will not be sufficiently large to block it completely!
Astute skywatchers who plan their trip right and are blessed with clear skies will get to observe the elusive "Ring of Fire" shown above. I've already written my eclipse guide for those of you preparing to join me in watching this, but there is one cheap piece of equipment I'll recommend that everyone pick up for looking at the Sun: a pair of Welder's Goggles.
For around $10 (tops), you can get a piece of equipment that will allow you to look at the Sun, whenever you want, for short periods of time. Make sure the density of the goggles is 14 or greater, and never use a telescope or binoculars with them, just your naked eye. But this is an inexpensive, easy way to allow yourself to view partial or annular eclipses (or perhaps even sunspots) whenever it strikes your fancy. (I've got my pair already.)
But there's another reason to get welder's goggles that's even more rare and spectacular than the upcoming solar eclipse. Those of you who've had clear skies in the west for the past month or two may have noticed an extremely bright object there just after sunset.
(Image made with stellarium.)
This is what the night sky will look like at 9 PM at 45 degrees latitude (where I live) tonight. That bright object, fifteen times brighter than Sirius, is the planet Venus, which just achieved its greatest apparent brightness in the sky. (And appears as a gorgeous crescent with binoculars if you can focus properly!)
Venus, being an interior planet to Earth, appears brightest not when it is closest to us, nor when it's in its full phase, but rather when it's a crescent, where the combination of proximity to us and the amount it's illuminated is maximized.
(Image credit: Torquay Boy's Grammar School's Observatory.)
Over the coming month, Venus will descend in the sky, with progressively less and less of the planet becoming illuminated to our eyes, percentage-wise. However, Venus' angular size will increase, as the apparent diameter of the planet will increase in the sky due to it physically getting closer and closer to us.
(Image credit: Shamefully retrieved from this website.)
Eight years ago, Venus didn't just pass interior to Earth, missing the Sun by just a degree or two; in 2004, Venus actually transited across the disc of the Sun, blocking a small fraction of the Sun's light. These transits are incredibly rare; you and I will get two in our lifetimes.
The last Venus transit before the 2004 one took place in 1882, and the next one won't be until 2117. Unless, that is, you're ready on June 5th of this year.
(Image credit: Tonk at CloudyNights.)
It is perfectly safe to look directly at the Sun for brief periods of time with a good pair of Welder's goggles, and I've already got mine.
Where should you be to see it? That depends on where you live.
(Image credit: Fred Espenak / NASA, retrieved here.)
Where I am in North America, the Venus transit will start at about 3:00 PM on June 5th and will continue through sunset. The entire transit won't be visible in North America, as it takes many hours to complete, but this is your one chance to witness an event like this with your own eyes.
In Europe, parts of Africa, and most of Asia, of course, you'll be able to see the transit in the morning of June 6th instead. But those of you living in Iceland get the most special treat of all: a transit that spans both sunset and sunrise!
(Video credit: user transitvenus on YouTube.)
Three major astronomical events -- the supermoon, tonight, the annular solar eclipse, on May 20th/21st, and the transit of Venus, on June 5th/6th -- all occurring within a month of one another! There's never been a better time to purchase a pair of welder's goggles, that's for sure!Read the comments on this post...
Enough slagging of beloved popularizers-- how about some hard-core physics. The second of three extremely cool papers published last week is this Nature Physics paper from the Zeilinger group in Vienna, producers of many awesome papers about quantum mechanics. Ordinarily, this would be a hard paper to write up, becase Nature Physics are utter bastards, but happily, it's freely available on the arxiv, and all comments and figures are based on that version.
You're just obsessed with Zeilinger, aren't you? All right, what have they done this time? The title is "Experimental delayed-choice entanglement swapping," and it's pretty much what it sounds like. They've demonstrated the ability to "swap" entanglement so as to create quantum correlations between two photons that have never been close to one another. And they've done this in a "delayed-choice" fashion, where the decision about whether to entangle them or not is made well after the two photons they're entangling have been detected.
Oh, OK, that sounds-- Wait, what? They entangled them after detecting them? Yep. The basic scheme is illustrated by this quasi-spacetime-diagram from the supplementary material:
The vertical axis represents time, moving into the future as you go up. They start with two pairs of entangled photons, which are sent into optical fibers. Two of these (one from each pair) go directly to detectors that record their polarizations roughly 35 ns after they were produced. The other two go into very long fibers, and are sent to a detector that either records the two original polarzations, or makes a joint measurement of the two together. If they measure the individual polarizations, the original pairs remain independent of one another, but if they make a joint measurement of the two, that entangles their states, meaning that the polarizations of the other two photons are now entangled with each other, and should be correlated.
Since these photons went into much longer fibers (104m vs. 7m), though, the entangling measurement is made after the two photons whose states are being entangled have had their polarizations measured-- about 520 ns after they were produced.
In keeping with the silly jargon of the field, the two photons that are detected immediately (Photons 1 and 4) go to detectors that are imagined to be held by people named "Alice" and "Bob." The two that are measured together to determine the entanglement (Photons 2 and 3) go to a third imaginary person named "Victor," and it's Victor's measurement that determines everything.Read the rest of this post... | Read the comments on this post...
I was tremendously disappointed and frustrated by this book.
This is largely my own fault, because I went into it expecting it to be something it's not. Had I read the description more carefully, I might not have had such a strong negative reaction (which was exacerbated by some outside stress when I first started reading it, so I put it aside for a few weeks, until I was less mad in general, and more likely to give it a fair reading). I'm actually somewhat hesitant to write this up at all, for a number of reasons, but after thinking it over a bit, I think I have sensible reasons for being disappointed in the book, and it's probably worth airing them.
As mentioned in yesterday's post about "Big Science", this is a book whose central message is that we ought to be spending more money than we are on space exploration in order to boost science as a whole. And when I saw Tyson promoting this on either the Daily Show or the Colbert Report, I was excited by the idea. As anybody who's been reading the blog for any length of time knows, I'm all in favor of bringing science to a broader audience (which is why I write books where I discuss physics with my dog). While I'm skeptical the space is the most effective tool for getting the job done, I'm prepared to hear a good argument for that, and Tyson seemed like just the guy to do that: to provide a clear and coherent vision of what space exploration ought to be in order to serve as a driver of science in general.
But this is not that book. Instead, it's a collection of... stuff. Some essays, some speeches, some interview transcripts, a whole bunch of Twitter posts. Collectively, they're all about space exploration as a general matter, and many of the individual pieces are as good as you would expect. But it's not a sustained and coherent argument. And that's a missed opportunity.Read the rest of this post... | Read the comments on this post...
- Andrew Johnston has a review of the UK edition, praising it because "it's bang up to date, and goes beyond the basic quantum concepts into more complex areas like decoherence, entanglement and quantum teleportation," which I like to see because that's one of the things I especially wanted to do.
- Natasha Zaleski, a grad student, has a review of How to Teach Relativity to Your Dog, which is good but not great, because it hit the usual failure mode: the talking-to-the-dog thing wore thin for her. Which is, of course, the danger of the whole talking-to-the-dog conceit.
- The Polish edition is out-- I got my author copies, which are very nice. This has led to a review in a pop-culture magazine, between Steig Larsson and Terry Pratchett. Google Translate makes hash of it, in part because it does a literal translation of my surname, leading to sentences like "Even so, Eagle shows the world a lot of physics accessible, than does the bulk of textbooks for physics."
- The vanity search also turned up a mention of the books in the Raised Indoors podcast-- one of the hosts bought both from Amazon in Canada (thanks!), but hasn't yet read them. Hope you like them. The podcast itself is a general-interest pop-culture thing, and the Clive Cussler rant is pretty amusing.
And that's the latest from the vanity search.Read the comments on this post...
"This is the way I wanna die. Torn apart by angry fans who want me to play a different song." -Regina Spektor You're familiar with the classic picture of a black hole: a dark, dense region at the center from which no light can escape, surrounded by an accretion disk of matter that constantly feeds it, shooting off relativistic jets in either direction.
(Image credit: University of Warwick, retrieved from here.)
This is a pretty accurate picture of active black holes. But most black holes aren't active, and of the ones that are, they aren't active most of the time!
Most people think of black holes as marauders, gobbling up whatever poor stars happen to get in their way. You very likely have a picture of a black hole as though it behaves like a great cosmic vacuum cleaner, sucking up anything that dares get too close to it.
I can't fault you for thinking that; this is a genuine NASA video, and the picture that some very smart people have been painting for you for a long time. But that isn't quite how the Universe works.
So, how does it work? When any object falls in close to a black hole, it experiences different forces on different parts of the object. We call these forces tidal forces, because they're the same types of gravitational forces that cause the tides we experience here on Earth!
(Image credit: Barger and Olsson.)
Only, in the vicinity of a black hole, the tidal forces are much stronger than we experience on Earth. They are, in fact, much stronger than Jupiter's innermost moon, Io, experiences, and those forces are powerful enough to constantly tear Io apart, making it the only volcanically active moon in the Solar System!
No, when you get close to a black hole, you get stretched at either end so severely, and compressed in the middle so thinly, we call the process spaghettification, one of the greatest astrophysics words ever invented!
(Image credit: John Norton at Pittsburgh.)
But "falling in" to a black hole, like illustrated above, practically never happens! Space is simply too big, and even for supermassive black holes -- like the multi-million-solar-mass behemoth at the Milky Way's center -- the event horizon is too small. Most stars and objects that pass nearby to a black hole simply do what all other objects in the Universe do.
Gravitate! (Ha ha ha ha haaaaa!)
Remember that space is huge, and that getting within a paltry 0.001 light years of our galaxy's supermassive black hole won't even disrupt the passing star, much less "vacuum it up," as you might have thought.
"But what if the star does get close enough," you ask, "then what happens?"
(Video credit: NASA, S. Gezari (Johns Hopkins), and J. Guillochon (UCSC).)
Note how, first, the star gets completely ripped apart by these intense tidal forces! But rather than acting like a vacuum cleaner and sucking it all up, most of the mass from this star doesn't get devoured at all; quite to the contrary, most of it gets ejected back out into the space around the black hole! It's only a small fraction of the original that gets swallowed, but that's totally sufficient to take a quiet, supermassive black hole, and bring it back to life!
And we know this, because we just observed a super distant galaxy -- more than 2 billion light years distant -- just become ultra bright thanks to its supermassive black hole sneaking a bite out of an unlucky passerby! Let's take a before-and-after look.
(Image credit: NASA, S. Gezari, A. Rest, and R. Chornock, as are the next two.)
The above images, from GALEX (in the Ultraviolet) and Pan-STARRS (in the visible/IR), show this distant galaxy shortly before it started snacking on its newly accreted material. The images are low-resolution because GALEX and Pan-STARRS focus on grabbing very wide fields-of-view; when you're looking for very rare occurrences like this, you need to grab as much of the deep sky as possible!
So, that was 2009. But the next year...
The galaxy has brightened by a factor of around 350 in the Ultraviolet, and the visible/IR image has turned much bluer, an indication of the extraordinarily high energies being belched out by this suddenly noisy galaxy!
Taking a look at the before-and-after images together, you can really see the difference.
But don't be fooled by the vacuum cleaner description; it's not eating the entire thing that ran into it! This is, in fact, something that we may see happening for much smaller black holes that are much closer to us; the nearby galaxy Messier 83 just had a very similar outburst from a much smaller black hole!
Black holes aren't giant leviathans, devouring anything that comes nearby, but nor are they dainty, steady nibblers on objects that orbit. Rather, black holes are wild, violent and inevitable, tearing anything that dares approach too closely into shreds, but coming away with a snack-sized meal whose first bite makes quite an impression!
Now, if you'll excuse me, all this black hole talk has made me hungry! Where did I put the spaghetti...Read the comments on this post...
A week or so ago, lots of people were linking to this New York Review of Books article by Steven Weinberg on "The Crisis of Big Science," looking back over the last few decades of, well, big science. It's somewhat dejected survey of whopping huge experiments, and the increasing difficulty of getting them funded, including a good deal of bitterness over the cancellation of the Superconducting Supercollider almost twenty years ago. This isn't particularly new for Weinberg-- back at the APS's Centennial Meeting in Atlanta in 1999, he gave a big lecture where he spent a bunch of time fulminating about what idiots politicians were for cancelling the project. If anything, the last decade and a bit has mellowed him somewhat.
Sort of in parallel with this, I've also been reading Neil deGrasse Tyson's latest book, Space Chronicles (I say "sort of" because I actually stopped reading it for a couple of weeks, because I found it maddening for reasons that I may go into in another post). This is a collection of things from other sources that collectively sort of advances the argument that we need to spend flipping great wodges of cash on space exploration, for the good of science and society as a whole.
While these aren't directly related to each other-- and, indeed, are somewhat in conflict, as Weinberg has no use for manned space flight-- they're both making a similar argument: that we should be spending money on Big Science projects, because they're important for science as a whole. Which is fine, to a point-- I'm all in favor of increasing the amount of money we spend on scientific research-- but I can't help thinking that it's awfully easy to make this argument when the Big Science projects just happen to fall very close to your area of interest.Read the rest of this post... | Read the comments on this post...
Check out the image below from NASA's Earth Observatory: