Education

Always Write the Introduction Last [Uncertain Principles]

Science Blogs Physcial Sciences - 31 March, 2012 - 16:14

Here are some excerpts from the introductory sections of the very first drafts of some book chapters:

[BLAH, BLAH, BLAHBITTY BLAH]

and

[Introductory blather goes here]

and

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.

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Categories: Education

Billions of Stars in the Galaxy! [Starts With A Bang]

Science Blogs Physcial Sciences - 31 March, 2012 - 02:14

"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.

skymt_payne_big.jpeg

(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.

milkywayimage.jpeg

(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.)

milkywayzoom-1.jpeg

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?

120329_tch_milky-way-star-forming-region.jpeg

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!

galactic_center.jpg

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.

gimpy_joe.jpg

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.

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Categories: Education

It Figures: The Historical Aesthetics of Scientific Publishing [Uncertain Principles]

Science Blogs Physcial Sciences - 30 March, 2012 - 17:20

Steve Hsu has a post comparing his hand-drawn diagrams to computer-generated ones that a journal asked for instead:

hsu_figure_comparison.jpg

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:

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Categories: Education

A Little Black Hole Goes A Long Way [Starts With A Bang]

Science Blogs Physcial Sciences - 29 March, 2012 - 17:37

"[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.

Morgan-Keenan_spectral_classification.png

(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.

3-Black-Hole.jpg

(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.

xray_nova_artist_impression.jpeg

(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!

312037main_cena_crop.jpg

(Image credit: X-ray: NASA/CXC/CfA/R.Kraft et al.; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; Optical: ESO/WFI.)

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.

cena-1.jpeg

(Image credit: NASA/CXC/CfA/R.Kraft et al., recommended by Peter Edmonds.)

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.

CenA-BH-BURKE.jpeg

(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!

0157blue_xray.jpeg

(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!

identified.jpg

Now, that's what I call a little black hole going a long way!

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Categories: Education

Quantum decay through the looking glass [Brookhaven Bits & Bytes]

Science Blogs Physcial Sciences - 29 March, 2012 - 15:52

This post was written by Brookhaven Lab science writer Justin Eure.

Cracked-Mirror-psd40874.pngImagine 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.

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Categories: Education

A challenge for you [Greg Laden's Blog]

Science Blogs Physcial Sciences - 28 March, 2012 - 17:10

What are we looking at here? Your answer will depend on the angle with which you approach the problem.
Tilt.jpg

hat tip: Sarah Moglia.

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Categories: Education

The Hubble Treasure Hunt [Dynamics of Cats]

Science Blogs Physcial Sciences - 28 March, 2012 - 06:55


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.

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Categories: Education

Why is there something instead of nothing? [Starts With A Bang]

Science Blogs Physcial Sciences - 28 March, 2012 - 04:30

"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.

201103_VirgoGCM_andreo.jpeg

(Image credit: Rogelio Bernal Andreo, retrieved from APOD.)

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.

2dFzcone_dots.gif

(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!

pair_production_and_annihilation.jpeg

(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.

plasmas.032-001.jpg

(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!

Abrams35c.jpeg

(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.

fig8.gif

(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.

qqbar.032-001.jpg

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.

decay.033-001.jpg

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.
In addition to being out-of-equilibrium, there's one more thing that we need.

conserve2.jpg

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!

violate.033-001.jpg

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?

leftover.034-001.jpg

More matter than anti-matter! In fact, so long as you fulfill these three famous criteria:

  1. Out-of-equilibrium conditions,
  2. Baryon-number-violating interactions, and
  3. C- and CP-violation (the differences in decays, above),
you not only can create more matter than antimatter (or vice versa), but an asymmetry is inevitable. And since something like this is required to create more matter than antimatter in the Universe, and that's the Universe we have, this is why there's something instead of nothing!

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Categories: Education

Quantum Musical Interlude [Uncertain Principles]

Science Blogs Physcial Sciences - 26 March, 2012 - 22:37

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:

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Categories: Education

Treating Big Molecules Like Electrons: "Real-time single-molecule imaging of quantum interference" [Uncertain Principles]

Science Blogs Physcial Sciences - 26 March, 2012 - 17:05

ResearchBlogging.org 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:

single_molecule_interference.jpg

(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:

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Categories: Education

Another Week of GW News, March 25, 2012 [A Few Things Ill Considered]

Science Blogs Physcial Sciences - 26 March, 2012 - 16:25

Logging the Onset of The Bottleneck Years
This weekly posting is brought to you courtesy of H. E. Taylor. Happy reading, I hope you enjoy this week's Global Warming news roundup

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Categories: Education

Fact or Friction: Slow Earthquakes [The Weizmann Wave]

Science Blogs Physcial Sciences - 26 March, 2012 - 10:05

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.

lossy-page1-536px-Hayward_fault_california.tif.jpg
Composite satellite image reveals a slow earthquake on the Hayward fault in California (Image: NASA)

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.

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Categories: Education

Science Fantastic, Sales by SteelyKid [Uncertain Principles]

Science Blogs Physcial Sciences - 25 March, 2012 - 14:39

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.

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Categories: Education

Scientific Commuting: Some Answers to "How Much Faster?" [Uncertain Principles]

Science Blogs Physcial Sciences - 23 March, 2012 - 19:50

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:

commute5.png

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:

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Categories: Education

Scientific Commuting: How Much Faster? [Uncertain Principles]

Science Blogs Physcial Sciences - 23 March, 2012 - 16:17

Back in the summer, I did a post mathematically comparing two routes to campus, one with a small number of traffic lights, the other with a larger number of stop signs, and looked at which would be faster. Later on, I did the experiment, too.) Having spent a bunch of time on this, I was thinking about whether I could use this as a problem for the intro physics class. I decided against it last fall, but something else reminded me of this, and I started poking at it again.

So, I played around a bit with some numbers, and came up with the following possible framing for a question. I'll throw this out here, to see what people think, then I'll post some solutions in a few hours.

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?

Obviously, this requires some assumptions about the speed and acceleration of the car, which might make for some useful discussion. You can find the necessary math at the first link above, if you want to work it out. For a class using a clicker-type response system, I'd turn it into a poll question like so:

How much larger must the cruising speed of the second car be to finish in the same time as the first car?

So, we'll leave this up for a while, and then this afternoon, I'll post some analysis. Feel free to share your thoughts about appropriate assumptions, etc. in the comments. Or to suggest ways to re-cast the problem that might be more useful. This is classical physics, though, so you don't get to choose more than one option.

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Categories: Education

How to Teach Relativity to Your Dog On the Radio and in Vestal, NY [Uncertain Principles]

Science Blogs Physcial Sciences - 23 March, 2012 - 15:55

sidebar_relativity_cover.jpgThe quick publicity items for this weekend:

1) I will be on the Science Fantastic radio show either Saturday or Sunday, depending on when your local affiliate runs it (or when you choose to livestream it over the Internet). The interview has already been recorded, which leaves me free for:

2) I will be signing and possibly reading from the new book at the Barnes and Noble store in Vestal, NY at 2pm on Saturday. If you're fortunate enough to live in the Southern Tier, stop by and say hi.

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Categories: Education

How to Have My Dog Teach You Physics [Uncertain Principles]

Science Blogs Physcial Sciences - 22 March, 2012 - 16:52

"Hey, dude," the dog says, looking concerned. "We need to talk."

sm_talking_in_lab.jpg

"Yeah? What's up?"

"Look, it's great that you're transcribing the human puppy's stories into Twitter and all, but I'm feeling left out. I've got my own Twitter account and all, but you hardly ever type any of my tweets any more. I have to do it myself, and it's hard to be witty when you have to type with your nose."

"I'm sorry. Is there something specific you'd like to tweet about?"

"Well, yeah," she says, in a tone like I've said something stupid. "I mean, obviously, we have a new book about relativity. And look at this picture-- we're in a cool physics lab! I want to tweet about physics!"

"OK, we can do that. Anything specific you have in mind?"

"Ummmm... no. But I bet somebody else could come up with physics things for me to talk about, if you asked them..."

------

Which is how we got to here. So, here's the deal: If you're on Twitter, ask a physics question of Emmy using either her Twitter name (@queen_emmy) or the hashtag #dogphysics, and she'll answer. Ever wondered how a dog would explain general relativity? The second law of thermodynamics? Why cats land on their feet, even when you chase them off a high place really fast? Ask your question, and I'll give you her response.

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Categories: Education

This is what your Universe looks like! [Starts With A Bang]

Science Blogs Physcial Sciences - 21 March, 2012 - 22:31

"Deep into that darkness peering,
long I stood there, wondering, fearing,
doubting, dreaming dreams no mortal
ever dared to dream before." -Edgar Allen Poe When you look out into the darkness of a moonless, unpolluted night sky, you'll of course notice that it's full of stars, planets, and the occasional extended object.

MilkyWay_June8_08-1024x682.jpeg

(Image credit: Bob King at AstroBob.)

But you'll also notice that there are plenty of regions that -- other than a few stars -- don't really have very much going on. One such region, visible in the southern skies pretty much year-round, is the constellation of Sextans.

sextans.jpegsextans-t.jpeg

(Images credit: Jim Kaler.)

A region of space where there isn't very much going on -- no bright stars, no planets, no close, extended galaxies or nebulae -- is ideal for looking out, deeply, into the Universe.

You may remember, very famously, that the Hubble Space Telescope has done that a number of times, producing images such as the magnificent Hubble Ultra-Deep Field, an image which contains around 10,000 galaxies!

hudf.jpeg

(Image credit: NASA / ESA / S. Beckwith (STScI) and the HUDF team.)

And that, well, that's a lot. But is that the record?

If it was, it certainly isn't anymore! Because that region of space I showed you, above, in the constellation of Sextans? The European Southern Observatory has -- with their VISTA telescope -- created the deepest wide-field image of all-time, containing over 200,000 galaxies!

eso1213a.jpg

(Image credit: ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU.)

The ESO has released a couple of videos, where you can see exactly where on the sky this region is, and zoom in a bit on some of these 200,000+ galaxies. In the video below, the full region of the survey -- known as UltraVISTA, of the COSMOS field -- is visible at about 0:31 into the clip.

(Video credit: ESO/A. Fujii/Digitized Sky Survey 2/UltraVISTA teamESO; music by John Dyson.)

Zooming even deeper into the field and panning around, the video below showcases some of the highlights of this survey.

(Video credit: ESO/A. Fujii/Digitized Sky Survey 2/UltraVISTA teamESO; music by John Dyson.)

Of course, they've also created an interactive, zoomable version of this survey. I've taken the liberty of creating for you a sample of what it's like to zoom in, by a factor of 4, on a given region of the original, full wide-field survey.

To remind you, here's the original image.

eso1213a.jpg

Now, let's zoom in to the upper-left quarter of this field.

eso1213a_4th.jpg

Now, let's take another quarter (lower right) of that, for 1/16th of the original image.

eso1213a_16th.jpg

And another quarter (lower right) of that, giving us just 1/64th of the original field-of-view...

eso1213a_64th.jpg

And another quarter, bringing us to 1/256th the original...

eso1213a_256th.jpg

And finally, down to the maximum resolution, just 1/1,024th of the original image!

eso1213a_1024th.jpg

Remember, as we did this, that the only remarkable thing about this patch of space is how unremarkable it was! With the exception of two or three faint stars, every dot of light in this image is a galaxy, containing hundreds of billions (or more) of stars! And by doing this to the entire image, we can determine that there are more than 200,000 galaxies in this space.

And that's what your Universe looks like! I'll be away at MidSouthCon until next week; hope you have a great one until then!

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Categories: Education

Shedding Light on Quantum Gravity: "Probing Planck-scale physics with quantum optics" [Uncertain Principles]

Science Blogs Physcial Sciences - 21 March, 2012 - 17:05

ResearchBlogging.orgIt's been a while since I did any ResearchBlogging posts, because it turns out that having an infant and a toddler really cuts into your blogging time. Who knew? I keep meaning to get back to it, though, and there was a flurry of excitement the other day about a Nature Physics paper proposing a way to search for quantum gravity not with a billion-dollar accelerator, but with a tabletop experiment. There's a write-up at Ars Technica, but that comes at it mostly from the quantum gravity side, which leaves room for a little Q&A from the quantum optics side.

Wait a minute, you said this is in Nature Physics? I don't have access to that. You're in fine company, because neither do I. Thanks to the arxiv, though, you can read a preprint for free, and that's what I'll be working from.

OK, so what's the deal with this quantum gravity stuff? Are you telling me they can make a black hole with lasers, now? No, there aren't any black holes involved, even though black holes are the canonical example of a system where you need quantum gravity to understand what's going on. Black holes are rather difficult to work with, though, so people who want to look for a quantum theory of gravity try to find other ways to see its effects.

In this case, they make use of the fact that most theories of quantum gravity involve a minimum length scale. That is, there's a minimum length below which you can't talk about distances in any sensible way.

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Categories: Education

Max Kurzweil Describes the Science Behind the Potato Chips [USA Science and Engineering Festival: The Blog]

Science Blogs Physcial Sciences - 21 March, 2012 - 16:00

By Max Kurzweil

allen kurzweil.jpgWhen we're at a baseball game or on a picnic we call 'em chips. But when we're cooking up experiments at the Chip Science Institute we maintain in our basement, or at the USA Science and Engineering Festival in Washington D.C., we call the world's most beloved munchie "research material."

For the last five years my dad and I have been using potato chips as a portal into the world of biology, chemistry, earth science, and physics. Who knew thin-sliced, deep-fried tubers could teach us about buoyancy, electrostatics, surface tension, acoustics, forensics, Bernoulli's principle, and more. When we tell you that investigating the material properties of the potato chip can be a BLAST, we mean it. (We'll be giving away a few dozen potato propulsion pipes to prove the point!) So for folks who like snacking on science high in saturated facts, you can't go wrong analyzing the material properties of chips, bags, lids, spuds, and tubes. Hope to see in D.C. -Max Kurzweil, co-inventor of Potato Chip Science (the bright blue bag of experimental swag).

You can meet Max Kurzweil and Featured Author Allen Kurzweil at the Festival Sunday, April 29th at 12:45 PM on the Family/Hands On Science Stage.

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Categories: Education

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