Every other year NASA conducts a Senior Review of its astrophysics missions that have completed their nominal mission and are requesting an extension of their mission.
The 2012 review panel just reported.Read the rest of this post... | Read the comments on this post...
A Confusing Light OPERA: How Does a Loose Fiber Optic Cable Cause a Signal Delay? [Uncertain Principles]
So, the infamous OPERA result for neutrino speeds seems to be conclusively disproven, traced to a problem with a timing signal. Matt Strassler has a very nice explanation of the test that shows that the whole thing can almost certainly be traced to a timing error that cropped up in 2008. This problem is generally described as resulting from a "loose fiber optic cable," and Matthew Francis's reaction is fairly typical
The main culprit was a fiber optic cable that was slightly out of alignment. This is not quite a "loose wire", as it sometimes has been described: it's far more subtle and harder to check than that, but it's still fundamentally a simple technical problem. (My prediction that the effect was due to something really subtle turns out not to be correct!)
As a professional Optics Guy, I would beg to differ a little. Assuming that this hasn't been garbled by some sort of translation issue, this really is something subtle and surprising (albeit in a technical way, not a new physics way). You wouldn't generally expect to get a significant timing delay from a loose fiber optic connector, because of the way that fiber optics work, which is fundamentally different than the way ordinary electrical cables work.Read the rest of this post... | Read the comments on this post...
One of my favorite bloggers, Dana Hunter, who blogs with me at FTB.com, is now also blogging at Scientific American at a new blog called Rosetta Stones.I was five years old, and Mount St. Helens was busy erupting all over my teevee. I made it a get well card. It looked like it hurt. Thus began an ongoing conversation between me and objects people tend to think of as inanimate until they explode, rip apart, or fall down. Read the comments on this post...
In comments to yesterday's post, Andrew G asked:
Speaking of writing, is there an errata list somewhere for "How to teach relativity to your dog"?
No, but there probably should be. I believe there's an error in one of Maxwell's equations (an incorrect sign, though you should've seen the first typeset version...), but given the length and complexity of the book, there are almost certainly other mistakes. So, if you've spotted an error, in physics, grammar, or anything else, leave a comment here, and I'll compile a list of things to fix if we ever get the chance.Read the comments on this post...
Is poetry a driving force of Oceanography?
- Phillipe Diolé
I've written many times, although not recently, about the ocean.
When I first began Universe in 2005, it was practically a ship's log: meandering pieces on narwhal tusks, the accidental poetics of my hero, Rachel Carson, and adolescent screeds on the perils of the Mariana trench. At some point in my career, I ported my energies outward to the cosmos, reasoning, as the ancient alchemists did, that "As Above, So Below."
The movement from the deep to the distant, from sea to space, seemed like a sensible evolution. I saw parallels then, as I do now. They are both cold, forbidding, strange, contain tremulous mysteries, and do not give their secrets readily. Tales of their early exploration contain feats of unspeakable audacity, as well as tragedy. Solitary heroes stand out: Yuri Gagarin in his Vostok spacecraft, Jacques Cousteau developing the Aqua-Lung in order to push deeper underwater, the elite few men and women who have dared venture far above, far below. Listen to a veteran diver discuss the sea and an astronaut space: you'll hear the same hushed tones, the same fearful, learned respect.
After all, what experience does this planet offer us more phenomenologically similar to spacewalking than floating in a deep ocean? Water is the best environment for spacewalk training on Earth; substituting neutral buoyancy for microgravity, NASA Astronauts train at the Neutral Buoyancy Lab in Houston, a giant swimming pool. I've always been delighted by images of this place; if you squint just right, and ignore the scuba divers, it almost looks like outer space is robin's egg blue and dotted with bubbles.
In spite of our egotism, the human organism is delicate. We're only built to tromp around the accommodating portions of the Earth. The moment we're submerged in the ocean, or we ascend too high a peak—to say nothing of outer space—we're out of our league. Yet, in our incorrigible hubris, we've long used technology to wander beyond our territory. Aristotle wrote of diving bells, and (apocryphally) even Alexander the Great explored the deep ocean—in a submarine of white glass, where the fish gathered 'round to pay homage—and returned to pronounce of his experience, "the world is damned and lost." Mercury spacecraft and the early Soviet Vostok capsules may as well have been diving bells; they were so small, it's said that they were worn, not ridden.
"The sea," Captain Nemo pronounces, in one of literature's more glamorous depictions of the deep, 20,000 Leagues Under The Sea, "does not belong to despots. Upon its surface men can still excercise unjust laws, fight, tear one another to pieces, and can be carried away with terrestrial horrors. But at thirty feet below its level, their reign ceases, their influence is quenched, and their power disappears. Ah! Sir, live—live in the bosom of the waters! There only is independence! There I recognise no masters! There I am free!"
This sentiment, an inverted Overview Effect, sounds familiar. Astronauts consistently speak of the irrelevance of borders, even nations, on a planet viewed from space. It's probably the most consistent revelation of spaceflight, the majestic panorama of a whole planet, seen without its despots and ideologues. The Soviet cosmonaut Gherman Titov, only the second man in space and the first to be there for more than 24 hours, described the experience of seeing the Earth from space as "a thousand times more beautiful than anything I could have imagined." After orbiting the planet over a dozen times, Titov replied a call from mission control with the elated cry: "I am Eagle! I am Eagle!"
An Eagle, of course, has no masters.
Today, in cramped cockpits and bathyspheres, astronauts and their aquatic counterparts lie contorted in the same metal cabins, surrounded by death, peering from thick windows into empty, hostile landscapes. Cloaked in metal, they transport light where there has never been any—to what James Cameron, after his much-ballyhooed recent dive to the Challenger Deep, called a "barren, desolate lunar plain," or (more viscerally) which William Beebe, passenger in the world's first bathysphere, described as "the black pit-mouth of hell itself."
This "black pit-mouth" is what interests me. Essentially every culture has a mythological history which includes primal undifferentiated formlessness. The abyss, as much topless as it is bottomless. And the abyss, figuratively speaking, is neither distinctly maritime nor interplanetary. Rather, it's a little of both: Tao, the primal ocean upon which Vishnu slumbered, amorphous being, chaos preceding time. Is this because the ancients knew on a symbolic level what our scientists empirically know now: that the abyss—in both worldly forms—is the seat of our lineage? We are, as Carl Sagan said, "made of starstuff." We're also risen from the sea. The salt in our veins is testament.
Beebe, one of the greatest American explorers, in his book Half-Mile Down, a record of his dive to 3,028 feet in 1934, wrote that it seems "a very wonderful thing, to walk about on land today, vitalized by a bit of the ancient seas swirling through our body. It is somehow of a piece with stars and time and space-something to be very quiet and thoughtful about, and proud of." Indeed, while beneath the waters lies a cruel landscape, and while the cosmos is vast and unforgiving, they are both our birthright. Our impulse to travel far below and above our limits is precisely that of children striving to return to the womb, only to discover that birth is as great a nothingness as death.
Between coral/Silent eel/Silver swordfish
I can't really feel or dream down here
Further Reading:Read the comments on this post...
Here are some excerpts from the introductory sections of the very first drafts of some book chapters:
[BLAH, BLAH, BLAHBITTY BLAH]
[Introductory blather goes here]
Blah, blah, stuff, blather.
There's a good reason for this, based on the basics of scientific writing, namely that the Introduction should give the reader a rough guide to the complete work-- exactly what you're going to say, before you go on and say it. In order to do a good job with the Introduction, you need to have a very solid idea of the shape of the finished product, and exactly what you need to mention up front for everything to hold together.
Which is why the Introduction is pretty much the last section I write. If you try to write it first, you're setting yourself up for a miserable slog, because you don't know just what you need to say in that section, and so you end up typing and retyping the same vague blather over and over, or frittering away hours on researching stuff that you may or may not actually need, because you don't know yet whether it will be relevant to the whole thing.
That's my advice for anyone setting out to write non-fiction, whether it's a term paper, a research article for a journal, a grant application (OK, that might be stretching the term "non-fiction" a bit...), or a pop-science book: Write the Introduction last.Read the rest of this post... | Read the comments on this post...
"A galaxy is composed of gas and dust and stars - billions upon billions of stars."
-Carl Sagan Perhaps the most striking feature of the night sky under truly dark conditions isn't the canopy of those thousands of points of light, but rather the expanse of the Milky Way, streaking across the entire night sky.
(Image credit: Richard Payne, retrieved from here.)
With an estimated 200-400 billion stars contained within our island Universe, the Milky Way is just a regular, run-of-the-mill spiral galaxy compared to the rest of what's out there.
But it's our home. And, despite the tremendous difficulty associated with resolving the individual stars within it, we've been trying to do exactly that since the first modern astronomers took to the skies with their telescopes.
For the first time ever, we've finally gotten up to over one billion stars identified, and stitched together into a single image.
(Image credit: Mike Read (WFAU), UKIDSS/GPS and VVV, as are all images below.)
The European Southern Observatory's VISTA telescope, combined with the UK's Infrared Telescope in Hawaii, have combined forces to create the VISTA Data Flow System project, where the telescopes have been recording up to -- get this -- 1.4 Terabytes of data, per night, which they plan to do for a total of ten years.
This release comes just a fraction of the way into that time, but there have been over a billion stars identified in the space measured, above. Let's zoom into that white box, in the region on the left of the image above, to get a closer, higher-resolution look. (As always, click for the larger version.)
This small fraction of the galaxy contains more than we could possibly count, or even show at this resolution, so let's go in even deeper, to the tiny region indicated by the box above. What do we find, looking at one of the Milky Way's tiny, active star-forming regions?
Over 10,000 stars, in a region far away in the outskirts of the galaxy. For comparison, we could have taken a look towards the galactic center. The dense chaos should provide you with a stark contrast to the image of the outskirts, and should truly help you understand how we get to a billion so quickly!
The incredibly brave (and patient) among you can attempt to download the stitched-together giant TIFF file (which is what I used -- with a lot of patience -- to create the images above and below), but even this huge 150 Megapixel image can't possibly contain all of the data taken by VISTA Data Flow System.
After ten years, we should have somewhere -- depending on clouds -- around a 5 Petabyte image archive of the Milky Way, a literal treasure trove for astronomers. In the meantime, I've flipped the Milky Way on its side, and created one image, viewable below, where you can view nearly the entire stretch of our home galaxy in one convenient scroll. Take your time and enjoy it.
As you look at this magnificent image, as you marvel that we've passed the milestone of counting up one billion stars in our galaxy, keep in mind that this is still less than 1% of the stars in just one galaxy out of hundreds of billions in the Universe.
And all the same, this is home.Read the comments on this post...
Steve Hsu has a post comparing his hand-drawn diagrams to computer-generated ones that a journal asked for instead:
He's got a pretty decent case that the hand-drawn versions are better. Though a bit more work with the graphics software could make the computer ones better.
This reminded me, though, of something I've always found interesting about scientific publishing, namely the evolution in the use of figures through the years. Whenever I need to do literature searching, I always suspect you could guess the approximate date of a paper's publication by looking at the figures.
If you go back far enough, reproducing figures was a very difficult process, so there tend to be relatively few of them. What figures you do get, though, are exquisite:Read the rest of this post... | Read the comments on this post...
"[The black hole] teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as 'sacred,' as immutable, are anything but."
-John A. Wheeler To an astronomer on any other world, the most important object in our Solar System wouldn't be the Earth, but rather our Sun. Just one example of the hundreds of billions of stars in our galaxy, our Sun is a G-type star, burning at around 6,000 Kelvin and with a lifetime of around 10 billion years.
But stars come in a great variety of masses, sizes, temperatures and lifetimes.
(Image credit: user Kieff, retrieved from wikipedia.)
Although they are the rarest type of stars, the bright blue O and B stars are perhaps the most spectacular in all of existence. With masses reaching, twenty, fifty, or even hundreds of times the mass of our Sun, these stars burn hotter and faster than our Sun ever could. Emitting energy often at rates in excess of 100,000 times our Sun's, and frequently living for less than even one million years, these stars build up massive cores through nuclear fusion, and then have no choice but to collapse under the irresistible force of gravity.
Not, mind you, to contract into a white dwarf star, like our Sun will, but to destroy the individual atoms making up the star itself. In the most extreme cases, the stellar corpse will collapse into a black hole: an object so dense not even light itself can escape from it.
(Image credit: NASA / CXC / M. Weiss, retrieved from Discover.)
On its own, you'd probably never even know a black hole like this existed, given the fact that it's likely going to be thousands of light years away. But every once in a while, we get lucky.
If a black hole happens to have a binary companion -- particularly a large-sized binary companion -- it can steal some of the mass from this much less dense star. When it does so, it not only forms an accretion disk around the black hole, but the matter can get accelerated by the black hole's powerful magnetic fields, and shot out in a pair of jets, perpendicular to the disk, moving in opposite directions.
(Image credit: European Space Agency, retrieved from here.)
This acceleration, like all charged particles accelerated by magnetic fields, will cause the emission of light. Not visible light, mind you, but in the case of black holes, powerful X-ray light.
In our own galaxy and very nearby, we've detected a few black holes like this, where the mass of the black hole is only a few times the mass of our Sun. For example, GRO J0422+32, for which an artist's impression is shown, above, has a black hole maybe 10 times the mass of the Sun, and is located about 8,000 light-years away.
One characteristic of these little black holes is that these powerful X-ray sources emit their energy in great bursts, which die down after a few years to become incredibly quiet. The other types of black hole -- the supermassive ones at the centers of galaxies -- do not do this at all!
Centaurus A, located about 11 million light years away, is a giant elliptical galaxy with an unusual dust lane in it. It's also one of the closest active galaxies to us, with two radio jets extending for about a million light years in space, moving at speeds of about half the speed of light in the innermost regions. Needless to say, with this kind of power behind it and a supermassive black hole that's many millions of times the mass of our Sun, these X-ray emissions aren't going anywhere for quite some time.
But a much smaller black hole -- even though it would be much less luminous to X-ray eyes -- can have its intensity drop by a factor of hundreds or even thousands within just a single year, if you happen to be watching at the right time. So far, we've found many stellar-mass-scale black holes this way, but nearly all of them have been within our own galaxy, and none of them have been as far away as Centaurus A.
But let's take a look at Centaurus A itself, in the X-ray.
Yes, the central, supermassive black hole and its jets are easily the most prominent feature in this image, but there are other bright X-ray sources, too. So you don't just look at it once, you look at it many times, separated by long periods of time! What did we find when we did exactly that? The team used the orbiting Chandra X-ray observatory to make six 100,000-second long exposures of Centaurus A, detecting an object with 50,000 times the X-ray brightness of our Sun. A month later, it had dimmed by more than a factor of 10 and then later by a factor of more than 100, so became undetectable.
(Image credit: NASA/Chandra, retrieved from here.)
That would be this object, above. It makes you wonder, of course, what all of these other bright X-ray sources are! Are they also small-ish black holes, ready to drop off in brightness as soon as their fuel is spent? Or are they more robust, long-lasting objects?
But make no mistake, this object just became the most distant, stellar-mass black hole ever discovered! Want some more proof? Take a look at this 2001 X-ray image of Centaurus A, and notice a very suspiciously missing point of light!
(Image credit: NASA/SAO/R.Kraft et al.)
So, if you want to know where the first stellar-mass black hole located more than 10 million light-years from Earth is, it's right here!
Now, that's what I call a little black hole going a long way!Read the comments on this post...
This post was written by Brookhaven Lab science writer Justin Eure.
Imagine looking in the mirror and finding your familiar face reflected back as you've always known it. But as you look more closely, as you precisely examine that mirror image, subtle distortions emerge. The glass itself remains flawless, but real and fundamental differences exist between you and the face that lives on the other side of the looking glass.
Something similar happens in the quantum world when matter is examined against its exotic reflection: antimatter. The analogy is admittedly fanciful, but it's no more dramatic than the dynamics of these almost-twins, which annihilate one another on contact.
Elegance and simplicity suggest that during the Big Bang there were equal numbers of particles and antiparticles - a kind of balanced pure energy. But in reality, we live in a curiously lopsided universe, one in which matter reigns supreme. So what happened? Understanding the mechanism behind that cosmic preference remains one of the great puzzles in science, and physicists are closer than ever to tunneling through the looking glass to seek out the answers.
A new landmark calculation executed by an international team of physicists employed unparalleled experimental results and advanced supercomputers to reveal more about just how and why some fundamental symmetry breaks.Read the rest of this post... | Read the comments on this post...
What are we looking at here? Your answer will depend on the angle with which you approach the problem.
hat tip: Sarah Moglia.Read the comments on this post...
Read the rest of this post... | Read the comments on this post...
Many of the Hubble Space Telescope images have never been looked at.
You can now browse the archives and win valuable prizes for finding cool new pics.
"Think binary. When matter meets antimatter, both vanish, into pure energy. But both existed; I mean, there was a condition we'll call 'existence.' Think of one and minus one. Together they add up to zero, nothing, nada, niente, right? Picture them together, then picture them separating--peeling apart. ... Now you have something, you have two somethings, where once you had nothing." -John Updike Looking out at our Universe, at the myriad of stars, galaxies, and, well, "stuff" in our Universe, it's hard not to ask yourself where it all came from.
When we look out at the Universe, each point of light that's out there, whether a planet, star, galaxy, cluster of galaxies or something even bigger, contains the entire history of the Universe as part of its story.
There's a great cosmic spider-web of structure that's traced out by the galaxies in the Universe, with each pixel of light representing the location of a single galaxy.
(Image credit: 2dF Galaxy Redshift Survey.)
When we consider our Universe, sure, it's full of dark matter and dark energy; that's how you make the structure we observe today. Even if we allowed ourselves to modify the laws of General Relativity, there's simply no other way to reproduce/recreate the Universe we have today.
Looking at the matchup between simulations and observations, the cosmic web of great clusters, filaments and empty voids fills the entire modern Universe.
(Video credit: V. Springel et al. (2005), Millenium Simulation.)
How did they get there? It took the billions of years the Universe has been around, the irresistible force of gravity, and the runaway growth of structure in the expanding Universe to bring it all together.
The beautiful simulation below, by Ralf Kähler, scales out the expansion of the Universe so that we can visualize just how matter -- both normal and dark -- collapses over time into galaxies, filaments and clusters.
(Visualization: Ralf Kähler and Tom Abel; Simulation: Oliver Hahn and Tom Abel (KIPAC).)
But it's the normal matter -- the protons, neutrons, and electrons -- that produce the visible light we pick up with our telescopes. The stars and galaxies that we see are all, as best as we can tell, made out of normal matter. And yet, this, itself, is a puzzle.
Because the laws of physics don't allow you to create or destroy matter without also creating or destroying an equal amount of antimatter!
(Image credit: Addison-Wesley, retrieved from J. Imamura / U. of Oregon.)
At least, this is true experimentally and observationally. But it couldn't always have been true, otherwise the Universe would have an equal amount of antimatter in it to the matter that's present.
And it doesn't. In fact, if there were an equal amount of antimatter created to the amount of matter we presently have in the Universe, the Universe would be so sparsely populated that there'd only be about one subatomic particle per cubic kilometer.
It would be less than one-billionth as dense as the Universe we have today.
So let's go back to the very early stages of the Universe, when it was filled with a hot, dense plasma, with equal amounts of matter and antimatter, and see if we can't make the Universe we have today.
(Image credit: me, background by Christoph Schaefer.)
Against the background of this hot, dense, fully ionized plasma, an equal quantity of particles and antiparticle flit back-and-forth. They collide with one another, annihilating, while other particles, like photons, interact with one another, producing equal amounts of matter and antimatter when they do.
If the Universe were of a constant size, a constant temperature, and all the particles and antiparticles in it were stable, it would be impossible to create more matter than antimatter, or vice versa. But in our Universe, none of those things are true!
(Image credit: Ben Moore, retrieved from N. Abrams and J. Primack.)
The Universe is expanding and cooling, and what this means is that -- when the temperature drops below a certain point -- you can no longer create matter/antimatter pairs as quickly as you destroy them! Why's that? Because E = mc2, and once the energy of your Universe drops below the mass necessary to create the particles/antiparticles you're looking to make, the ones that already exist simply go away.
How do they go away? They annihilate away, as only matter and antimatter can. But as they do, it gets more and more difficult for the matter and antimatter particles to find one another. Because the Universe is expanding, the density is dropping, and these particles/antiparticles are disappearing, you reach a point where they can no longer find one another. This "leftover" stuff you get, after all the annihilation the Universe can muster, is called freeze-out.
(Image credit: Ned Wright's Cosmology Tutorial.)
Getting this "frozen out" stuff is a consequence of the Universe being out of thermal equilibrium. For example, for example, at some point, you're going to be left with a Universe that contains a bunch of muons and anti-muons. Like most particles we know how to make, these are unstable, and will decay. For most particles/antiparticles, like muons/antimuons, this isn't a big deal. Whatever the particle decays into, the antiparticle will decay into the anti-counterpart, giving you a net gain of nothing.
But some particles are fundamentally different from their antiparticles, and this difference can create more matter than antimatter in the Universe! Here's how.
Let's imagine the Universe is filled with a new kind of unstable particle, the positively-charged Q+, and its antiparticle, the negatively-charged Q-. Because of certain conservation laws, they have to have the same mass, the opposite charge, and the same total lifetime.
But they don't have to be the same in every way. Let's say the Q+ can decay into either a proton and a neutrino, or into an anti-neutron and a positron. That means the Q- must be allowed to decay into an anti-proton and an anti-neutrino, or into a neutron and an electron.
Although this looks weird, because you sometimes have matter decaying into antimatter and antimatter decaying into matter, there are three important things about this type of decay:
- it allows you to violate the conservation of baryon number. (That is, the number of protons + neutrons combined.)
- This is allowed by the standard model, so long as the number of baryons minus leptons is conserved, and
- it can, if things work out correctly, create more matter than antimatter.
If the percentage of the Q+'s that become protons and neutrinos is the same as the percentage of Q-'s that become anti-protons and anti-neutrinos, this won't help you at all. The protons and anti-protons will be equal in number, and you won't create any more matter than antimatter.
Same deal with the anti-neutrons/positrons and the neutrons/electrons. But although it's possible that these individual percentages are equal, it isn't mandatory. The other possibility is -- and this happens in nature -- that particles will prefer one type of decay, while antiparticles will prefer a different type!
If this happens, then the Q+'s would make more protons and neutrinos than the Q-'s would make anti-protons and anti-neutrinos, while the Q-'s would make more neutrons and electrons than the Q+'s would make anti-neutrons and positrons.
Looking solely at the protons/neutrons/anti-protons/anti-neutrons that result from this decay, what would we wind up with?
More matter than anti-matter! In fact, so long as you fulfill these three famous criteria:
- Out-of-equilibrium conditions,
- Baryon-number-violating interactions, and
- C- and CP-violation (the differences in decays, above),
The title says it all: an animated video of Heisenberg singing about the Uncertainty Principle:
So, you know, there's that. It's pretty good, but he's no Feynman:Read the rest of this post... | Read the comments on this post...
Treating Big Molecules Like Electrons: "Real-time single-molecule imaging of quantum interference" [Uncertain Principles]
Richard Feyman famously once said that the double-slit experiment done with electrons contains everything that's "'at the heart of quantum physics." It shows both particle and wave character very clearly: the individual electrons are detected one at a time, like particles, but the result of a huge number of detections clearly traces out an interference pattern, which is unambiguously a wave phenomenon. The experiment has been done lots of times, but a particularly nice realization of it comes from Hitachi's R&D department, where you can see both still images and video of their experiment, with arriving electrons making little dots on a fluorescent screen.
Of course, an interesting question in all this is just how big you can make some material object and still see interference. I've research-blogged before about experiments in Austria using big floppy organic molecules with up to 430 atoms. Those didn't have the "arrive one at a time" feature of the best electron interference experiment, though. But now, the same group in Austria has a new paper in Nature Nanotechnology doing just that. The paper is at least temporarily free to access, making it a good target for a new ResearchBlogging post.
OK, so what's interesting about this again? If people already did interference with large molecules, and already did interference with electrons, how is this in a Nature journal? Well, the previous interference experiments using molecules used slow detectors that had to collect signal for a long time. They couldn't see an individual molecule showing up at a particular spot at a particular time. This leaves open the possibility that what they see is some collective effect of lots of molecules going through their apparatus at the same time. What they did here detects the individual molecules, one at a time, closing that notional loophole, and making this experiment essentially equivalent to the double-slit experiments with electrons. You can see the buildup of the pattern in this image:
(Figure 3 in the paper, also used in their press release)
Each individual dot in the figure represents a single molecule detected at the end of their apparatus. Images a)-d) show the slow buildup of the pattern from many individual detections, and part e) is the end result. You can compare this to the corresponding figure from Hitachi's electron experiment:Read the rest of this post... | Read the comments on this post...
Earthquakes are once again in the news, this time in Mexico. Although it is only the biggest quakes that make international headlines, we might take a minute to contemplate other quakes - the ones you'll never feel. So-called "slow" or "silent" earthquakes slip so softly they don't even show up on regular seismographic equipment.
As the name implies, slow quakes release the energy built up along the fault over hours or even days, as opposed to mere seconds for a fast, shaking quake. So why should we care about what happens in earthquakes that even scientists have barely noticed? For one thing, says the Institute's Dr. Eran Bouchbinder, slow quakes are likely to be a part of the larger seismic picture, possibly releasing stresses from one part of a fault by adding to the stress on another. There is some evidence that certain slow earthquakes might precede the big, fast ones.
Are slow earthquakes really different from fast ones? Bouchbinder thinks that the answer may possibly be: yes. He and his team have developed a new model for sliding friction - friction between two moving plates, for instance - that suggests an explanation for the physics of slow quakes.
Here it is in a tiny nutshell: Earthquakes - of any type - occur when the shear forces pushing the tectonic plates past each other surmount the force of friction that is holding them in place. In a big quake, the frictional interface fails very quickly, releasing huge amounts of energy in a short period of time. The speed of failure is limited by the speed of sound - the very same speed at which waves propagate through the earth's crust, shaking everything above. But the slow quakes seem to be different - the speed of sound may not influence them, says Bouchbinder. The model he and his team propose for movement at frictional interfaces might explain the underlying mechanics without sound wave physics. Instead, it implies that friction and sliding speed have a more complex relationship than previously thought, so that friction might increase at speeds where it was thought to decrease. For more on the model, go to our online article or check out the paper in Geophysical Research Letters.
The new model, by the way, might also help explain the dynamics of other frictional interfaces, e.g. between car tires and roads, or lend insight into nano-mechanics, among other things.
I had a signing yesterday at the Barnes & Noble in Vestal, NY, which drew a smallish crowd mostly of friends and family. SteelyKid came, of course, and while she spent most of her time bopping about other parts of the store, she came over to the signing area while I was signing books for people after reading a bit. They had a big stack of copies of How to Teach Relativity to Your Dog, and she started picking them up and handing them to me.
"No, honey," I said, "Those are for other people. Give them to somebody else." So she happily ran one over to my mother. And then to one of my aunts. And then I stopped paying attention.
Until my mother came over to return a copy to the pile, and told me that SteelyKid had been running up to total strangers and trying to give them copies of my book.... Which was really a brilliant marketing strategy, on reflection. I should've tried that earlier...
Also yesterday, I was on the Science Fantastic radio show with Michio Kaku. The interview was taped this past Monday, and appears in the second hour of the three-hour show (the first hour had Ian Stewart talking about his new book, the third hour was questions from callers). If you didn't hear it, but would like to, there are a whole bunch of stations carrying it that run it today, many of them offering audio streams over the Internet (which is how I listened to it, and recorded my bit...). I think it went pretty well, but I'd be happy to hear from somebody else.
And that's your How to Teach Relativity to Your Dog publicity update for today.Read the comments on this post...
So, the previous post poses a physics question based on some previous fooling around with modeling my commute:
A car starts from rest at the beginning of a straight 1km course, accelerates up to some speed, cruises at constant speed for a while, then decelerates to a stop at the end of the course. A second, identical car does the same course, but decelerates to a stop at the halfway point. It then immediately accelerates back to its cruising speed, and then decelerates to a stop at the end of the course.
How much faster does the second car have to go in order to complete the course in the same time as the first car?
This is deliberately somewhat vague, because I want to leave room for some discussion of what are reasonable values for cruising speed and acceleration, and so on. For the purposes of attempting to answer this, I used values that were moderately realistic and also mathematically convenient: A cruising speed for the first car of 16 m/s, and an acceleration (both speeding up and slowing down) of 4 m/s/s.
So, how do you work this out mathematically? Well, if you look back at the first post I did modeling this, you find that the time required to make the trip in N stages is:
Here you see the reason why I didn't end up doing anything with this last fall: this is an equation that's a little tricky for intro physics students, whose level of math preparation isn't always what we would like it to be. To get an algebraic solution, you would need to take this equation with N=1 and set it equal to the equation for N=2 but a different final speed, and solve for that final speed. That's more math than I really want to wrestle with, and I guarantee it would be a disaster for most of our intro students.
However, this is an easy enough equation to plug into a computer and generate solutions, which you can plot as nice graphs. So here are a few graphs giving the answer for the situations I looked at:Read the rest of this post... | Read the comments on this post...