## Science Blogs Physcial Sciences

Updated: 1 year 28 weeks ago

### So, you've learned that the Sun is going to explode... [Starts With A Bang]

26 April, 2012 - 06:25

"Through that last dark cloud is a dying star... And when it explodes, it will be reborn. You will bloom... and I will live." -The Fountain I want to start off by letting you all know that I, myself, do not have any children of my own. I have taught children, adolescents and adults for nearly a full generation now in varying capacities, and while each learner is different, there's one science fact that universally seems to shatter each and every one of them.

(Image credit: the bloggers at Dear Kugluktuk.)

The fact that the Sun, our Sun, the bringer of warmth, light, energy, and the sustaining force of all life on this planet, isn't going to shine forever. Quite to the contrary, someday, the Sun will die in a fiery, catastrophic explosion, one which will quite possibly obliterate our entire planet, and then eventually cease to shine at all.

Being faced with not only our own mortality, but the demise of literally everything we've ever encountered throughout the entire history of our world is a philosophical and existential challenge for even well-adjusted adults. But I was a bit taken aback when I received this question from one of my most loyal readers: I need a good explanation for a third grader, whose Mom tells me is deeply concerned, that the sun will blow up. I sympathize with parents in this position, because on the one hand, you want to tell the truth to your children. You want to expose them to our most accurate understanding of reality, to have them learn and appreciate knowledge, science, and using their minds.

But you not only want to do that with kindness, compassion, and optimism, you also don't want your kid having night terrors and years of therapy because you told them the gory details of, literally, the end of the world.

(Image credit: Brian Smallwood.)

There is, perhaps, a wrong way to go about this. As the comedian Louis C.K. once said, She started crying immediately, crying bitter tears for the death of all humanity... and now she knows all of those things: she's gonna die, everybody she knows is gonna die, they're gonna be dead for a very long time, and then the sun's gonna explode. She learned that all in 12 seconds, at the age of seven. That's one approach, but maybe not the one I would choose if I were going to put some thought into it. You see, there's a remarkable story to be told, and if I were in elementary school, it just might be the most wonderful thing I had ever heard at that point in my life. Here's what I would tell a child.

(Image credit: Hana Druckmüllerová, Úpice Observatory, and Miloslav Druckmüller.)

The Sun that you know, the brightest thing in the sky, is no more special than any other star in the sky. Even during the day, there are thousands of stars in the sky. You'd be able to see them, too, except that our star, the Sun, is so close to us that its brightness makes all the other stars invisible, except at night.

These stars, each and every one of them, live much, much longer than anything on Earth has ever lived. While some plants and animals can live for thousands of years, the stars all live, burning brightly, for millions, billions, or even trillions of years.

That's a very, very long time! But it isn't forever, and believe it or not, we're lucky that it isn't forever.

(Image credit: Oliverbeatson at wikipedia.)

Because if the stars never died, if they never exploded, and if they never blew up, we wouldn't be here, talking to each other, right now. And I'm so glad that we are, because you get to learn one of the most amazing secrets about life, and I get to teach it to you.

(Image credit: Ed Uthman.)

The secret is that practically everything that makes up you, me, and the entire planet -- the tiniest parts of everything we've ever known -- they were all made inside a star.

But it's too hot for you and me inside a star. In order to make Earth, and you, and me, all the good things that the stars make need to get out, so they can make something new. And how does that happen?

(Video credit: ESA/NASA, retrieved here.)

Why, they explode. And the insides of the star, the things that it made while it was alive, you know what they do?

(Image credit: NASA/JPL-Caltech/T. Pyle (SSC).)

The old insides from those stars make planets, like Earth, and -- because we're very lucky -- some of those insides make up us, too.

The stars of the past died so that you could be here, and someday, a long time from now, our Sun will return the favor, and help make more new planets, new worlds, and new chances for life.

(Image credit: ESA, NASA, and L. Calçada (ESO for STScI).)

So yes, the Sun will blow up, someday, but when it does, that's the greatest gift any star can ever hope to give to the Universe. After all, it took billions of stars giving that gift already in order to make you. And you know what?

It was worth it.

Categories: Education

### Historical Interdisciplinarity Examples? [Uncertain Principles]

25 April, 2012 - 14:51

For something I'm working on, I'm trying to come up with good examples of interdisciplinarity making a difference in science. Specifically, I'm looking for cases where somebody with training in one field was able to make a major advance in another field because their expertise let them look at a problem in a different way, and bring a different set of techniques to bear on it.

I can think of a decent number of examples within physics-- techniques from NMR being adopted by atomic physicists, atomic physics techniques being used to address problems in condensed matter, the whole Higgs boson business coming in part from condensed matter ideas-- but a lot of those are kind of subtle and technical. I feel like I must be missing something bigger and more obvious.

(I know about Schrödinger's turn toward biology late in life, but I'm not sure biologists find that as impressive as physicists do...)

So, help me out, here. What's the best example you know about of somebody from one field using their knowledge from that to make dramatic progress in another field? It doesn't need to involve a physicist, either (so I'll cross-list this in the life science channel at ScienceBlogs)-- chemists revolutionizing biology or geology (or vice versa) would be great, too.

Categories: Education

### The Sombrero is Two Galaxies in the Same Spot in the Universe [Greg Laden's Blog]

25 April, 2012 - 14:09

The Sombrero Galaxy's Split Personality: The infrared vision of NASA's Spitzer Space Telescope has revealed that the Sombrero galaxy -- named after its appearance in visible light to a wide-brimmed hat -- is in fact two galaxies in one. It is a large elliptical galaxy (blue-green) with a thin disk galaxy (partly seen in red) embedded within. Previous visible-light images led astronomers to believe the Sombrero was simply a regular flat disk galaxy. Spitzer's infrared view highlights the stars and dust. The starlight detected at 3.5 and 4.6 microns is represented in blue-green while the dust detected at 8.0 microns appears red. This image allowed astronomers to sample the full population of stars in the galaxy, in addition to its structure. The flat disk within the galaxy is made up of two portions. The inner disk is composed almost entirely of stars, with no dust. Beyond this is a slight gap, then an outer ring of intermingled dust and stars, seen here in red. Image credit: NASA/JPL-Caltech

From the Press Release:

Categories: Education

### Ten Years Before the Blog: 2003-2004 [Uncertain Principles]

24 April, 2012 - 20:29

The schedule called for this to appear last Friday, but as I was just back from a funeral, yeah, not so much. I had already gone through and bookmarked a whole slew of old posts, though, so here's a recap of the 2003-2004 blogademic year (starting and ending in late June).

This year saw a few milestones, though not quite as many as the previous year. I got a grant, passed my third-year reappointment review (the first big hurdle on the way to tenure), and we had a visiting speaker from Yale one week who mentioned in passing an idea that became central to my research program.

Probably the most significant milestone, though it didn't necessarily seem that way at the time, was when we adopted Emmy. If you've read How to Teach Physics to Your Dog, the Introduction includes a dog dialogue sitting on a bench at the Mohawk-Hudson Humane Society, which is, in fact, where I made the decision to take her home. Which has paid off far more literally than I ever would've guessed. As a bonus, this year also includes the very first conversation with Emmy on the blog, though it took a different form than the conversations that would eventually become (nerd) famous.

Other notable posts from the year include:

Categories: Education

### Physics Day Poll: Favorite Physicist? [Uncertain Principles]

24 April, 2012 - 16:17

Over in Twitter-land, there's a bunch of talk about how this is National Physics Day. I don't know how I missed that, what with all the media coverage and all.

I have too much other stuff to do to generate any detailed physics content today, so we'll settle for an informal poll to mark the occasion:

Who is your favorite physicist, other than Einstein, Newton, or Feynman?

The qualifier is just to knock out the too-obvious answers, and force a little more thought. Everybody likes Einstein and Newton and Feynman, but we hear about them all the time. For a major holiday like Physics Day, let's go a little deeper.

Other than that one restriction, it's wide open: could be living or dead, theorist or experimentalist, whatever. The definition of "favorite" is open as well-- whatever you want that to mean. Though it would be nice if you explained your reasoning in the comments.

Categories: Education

### When the fuel's all gone... [Starts With A Bang]

24 April, 2012 - 03:34

"Some painters transform the Sun into a yellow spot, others transform a yellow spot into the Sun." -Pablo Picasso But the Sun will not always be a bright spot. Though it has shone for billions of years already, and will continue to shine for billions of years more, it's currently doing this by burning its hydrogen fuel -- through the fires of nuclear fusion -- into the heavier element of helium.

But after about 10-12 billion years total, all the hydrogen that can be burned in the core will be used up! (There will still be hydrogen in the outer layers; a star our size is not fully convective.) At this point, the core's temperature will increase until the heavier elements can be burned: helium into carbon, nitrogen, and oxygen, perhaps even then into neon. The Sun's outer layers will expand, as our star becomes a red giant.

(Image credit: Oliverbeatson at wikipedia.)

To get to this point takes many billions of years, and is the fate of all stars between about 40% and 800% the mass of our Sun. But when that internal fuel is exhausted -- when the burn-able helium is used up -- what comes next? If the star were more massive, the core could collapse and we'd get a supernova, but our Sun, like most stars, is nowhere close to that.

The next step, and this only takes about 10,000 years, a blink-of-an-eye in the lifetime of a star, starts with the red giant ejecting the outer layers of the giant hydrogen envelope.

Meanwhile, on the surface of the star's core, a shell of hydrogen continues to burn, one of the last stages of fusion in a star like this. As the outer hydrogen layers continue to burn off and undergo ejection (through a process known as mass loss), the interior of the star continues to heat up.

As this process goes on, high-velocity winds are produced (like, over 100,000 miles-per-hour), shocking and shaping the gas. When it's all done, we get a planetary nebula from the outer layers, and a contracted white dwarf star at the center.

(Image credit: NASA / ESA / HEIC / Hubble Heritage / STScI / AURA.)

But I skipped the most interesting part! Before you get a white dwarf, before you get the hot, ionized planetary nebula, you go through this process of blowing off these outer layers with high-velocity winds. You wind up with dusty regions where the star is not yet hot enough to ionize the gas, collimated jets which can shine through the dust, and periodic, ring-like layers from the outward-moving gas.

With just 10,000 years, wouldn't it be something to catch one of these stars in the act?

Wouldn't. That. Be. Something.(?)

(Image credit: Raghvendra Sahai and John Trauger (JPL) / WFPC2 / NASA .)

What you're seeing is known as a preplanetary nebula! (Or, a protoplanetary nebula, for those of you who promise not to get it confused with a proto-planetary disk, which forms at the beginning of a star's life, not the end!) This was the Hubble Space Telescope's first view of the Egg Nebula, the most striking example of a pre-planetary nebula I've ever seen, and the first one ever discovered, less than 40 years ago.

The dense cocoon of dust shrouds the central star and hides it from our view: the star is not yet hot enough to ionize all that gas. However, this "cocoon" is asymmetrical, and in regions where the dust is thinner, light escapes, producing this four-beacon effect. We can learn even more about it by looking in the infrared, which measures warm gas.

(Image credit: STScI and NASA.)

While the hottest part is in blue, the most interesting part of the above image is the red signature, which indicates hydrogen gas! Because we can't see the star, we know that the hydrogen isn't fully ionized; it can block the light. But it is warm, and as the star continues to heat up towards the magic number of 30,000 K, eventually the light will be of high enough (UV) energies to ionize that gas and reveal the star inside.

One of the things that's interesting is that the light coming from the Egg Nebula is polarized, as this 2003 false-color image, sensitive to different polarizations, shows.

(Image credit: NASA and The Hubble Heritage Team (STScI/AURA).)

Different orientations of reflected starlight produce different results through a polarizing filter, and hence the difference in color shown in this image. The white areas are indicative of very dusty areas, where the light gets reflected/scattered many times, and hence doesn't come out with a single, mostly uniform polarization.

But that was then. Released earlier today is this latest, composite image taken with Hubble's WFC3 camera. The view is spectacular, and really gives you an appreciation for just how monstrous this dark, dusty disc around the dying star is.

(Image credit: ESa / Hubble and NASA.)

The two twin beacons shining out look like four floodlights in the fog, and for good reason: these are four weak spots in an extremely dusty region of space that allow the starlight to escape! The region is so obscured that we don't even know whether there's one giant star on its own, or whether it has a binary companion in there with it. Have a look at the full-scale image of the Egg Nebula, some 3,000 light years away.

But don't forget that Hubble's an amazing thing. Even though there aren't many preplanetary nebulae, you might wonder if we've ever caught one where we've had the good fortune to look down perpendicular to the dusty disk, instead of at some unfortunate angle. Well, have I unearthed a find for you. Say hello to IRAS 23166+1655 around the star LL Pegasi, and its magnificent, dusty spiral.

(Image credit: NASA / ESA and R. Sahai.)

Take a closer look in there; that's not a series of concentric spheres/circles, those are really spirals!

With an 800-year period estimated for this binary system, you can literally count the age of the preplanetary nebula by counting the rings in the spiral structure! In a few thousand years, all of this dusty structure will be gone, and all we'll be left with is a plain, ionized planetary nebula, with a white dwarf at the center. But for right now, you're looking at the last living stages of what was once a Sun-like star, ending its Red Giant phase and becoming a planetary nebula.

Welcome to your Universe, where it provides you with snapshots of the transition in action! Read the comments on this post...

Categories: Education

### Another Week of GW News, April 22, 2012 [A Few Things Ill Considered]

23 April, 2012 - 16:21

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

Categories: Education

### A Night of Celestial Excitement: Join Us April 28 at the Stargazing Party! [USA Science and Engineering Festival: The Blog]

23 April, 2012 - 15:00

Under the guidance of some of the top astronomy experts in the country, explore our amazing Universe - including up close views of the Earth's moon, Jupiter and other mysterious planetary objects - at the Stargazing Party, an exciting educational collaboration between the Festival, the Smithsonian's National Air & Space Museum (NASM), telescope manufacturer Celestron and other partners, on Saturday, April 28 at NASM in Washington, DC.

A hit with visitors at the inaugural Festival in 2010, the Stargazing Party is returning to the Festival Expo with an equally impressive lineup of evening celestial activities which include Bill Nye the Science Guy in a live recorded broadcast by Planetary Radio with host Mat Kaplan who will inspire other young astronomers to make their own unbelievable discoveries!

In addition, don't miss presentations by such prominent astronomy educators as Drs. Jeffrey Bennett and Jeff Goldstein who will give walking tours of the celebrated Voyage Scale Solar Model System located just outside the NASM and later discuss other fascinating facets of our quest to explore the universe.

Celestron will add hand-on excitement to this night with telescopes set up around NASM's Public Observatory to accommodate visitors' celestial viewing enjoyment.

Event Details:
April 28, 2012- 06:30 PM to 10:30 PM
Smithsonian Institution's National Air and Space Museum on the National Mall

6:30 pm - 7:45 pm: Walking Tours of the Voyage Scale Model Solar System (space is limited, sign up for one of the 3 thirty-minute tours at the museums info desk when you arrive)
7:30 pm: Telescopes ready for viewing around NASM's Public Observatory
7:45 pm: Doors open for Stargazing Party!
8:00 pm: Program in Moving Beyond Earth gallery, including welcome by Bill Nye the Science Guy and remarks by Celestron, and the Planetary Radio Live program
8:10 - 10:20 pm: Check out "Scale of the Universe" and "Human Exploration: the Journey Continues" in Milestones of Flight, plus "Forces of Flight" in How Things Fly, and look for hands-on Discovery Stations throughout the first floor of the Museum!

Categories: Education

### Did you hear that big giant meteor? [Greg Laden's Blog]

23 April, 2012 - 14:26

Who says that if you scream in space no one will hear you?

A rare daytime meteor was seen and heard streaking over northern Nevada and parts of California on Sunday, just after the peak of an annual meteor shower.

Observers in the Reno-Sparks area of Nevada reported seeing a fireball at about 8 a.m. local time, accompanied or followed by a thunderous clap that experts said could have been a sonic boom from the meteor or the sound of it breaking up high over the Earth.

Here's an animation:

Categories: Education

### Weekend Diversion: Happy Earth Day, No Matter Where You Are [Starts With A Bang]

22 April, 2012 - 18:25

"Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity - in all this vastness - there is no hint that help will come from elsewhere to save us from ourselves. It is up to us." -Carl Sagan Here on our planet, this is the one day that we take out of the year to stop and appreciate just how amazing the natural world really is, and how fortunate we are to have the Earth that we have. A wonderful but sad reminder of how fragile it is, and how quickly and easily we can affect it, comes through John Prine's great song,

Here on our planet, there are countless ways to celebrate what we have. But what if you weren't here on Earth; what if you were a distant space traveler, headed towards our Solar System for the first time?

(Image credit: SKY-MAP / WikiSKY.)

You'd see a rather unspectacular, whitish star. It would appear bright only because you were close to it. Even from our nearest star, Alpha Centauri, the Sun would only be the 5th brightest star in the night sky. If you knew the proper techniques, you could tell that there were gas giant planets around it, and -- if your tools were excellent -- some smaller, inner rocky worlds, too.

But unless you journeyed into the Oort Cloud, and then in past the Kuiper Belt, only at this point would it be easy for you to see Earth.

(Image credit: NASA / JPL.)

And even then, from 6 billion kilometers (4 billion miles) away, we'd appear as no more than a speck of dirt flying through the interplanetary dust.

But as you came in closer, you'd be able to see more and better details. That is, of course, if you knew to look for Earth. There are plenty of tempting distractions.

(Image credit: NASA / JPL / Space Science Institute / Cassini. Click for hi-res.)

From distant Saturn, our world is visible, seen here poking out from in between the rings. A close-up view shows that you can not only see that our planet is round in shape, but has a large moon, visible off of our upper-left limb.

If you came in all the way to the closest planet to the Sun, Mercury, your view would be different, but even more spectacular.

Our Earth, the largest disk in the photo, appears to be in either a full or nearly-full phase at all times from Mercury's vantage point, along with our Moon. Slightly more distant would be our view of Earth from Mars, which we were lucky enough to capture back in 2003 for the very first time, and in color to boot!

(Image credit: NASA / JPL-Caltech / Mars Global Surveyor.)

Seen from an outer planet, the Earth will run through all the phases, from new to crescent to gibbous to full. Our blue color, caused by our atmosphere and our oceans, surrounds patches of green and brown, where our continents poke out above the watery surface. Overlaid over all of it is the white clouds, which paint a transient covering above our world.

This is much more apparent, of course, the closer you get. When the Voyager 1 spacecraft was first leaving Earth on its journey, it snapped this far superior view than the one we can get from Mars.

(Image credit: NASA.

In fact, Voyager 1 and 2, in 1977, became the first spacecrafts to ever photograph the full Earth and Moon in the same picture.

But it's nothing compared to the first human view of the entire Earth, seen in December of 1968 by the Apollo 8 astronauts. As they emerged from behind the night side of the Moon -- the first humans ever to do so -- this was the sight that greeted them.

(Image credit: NASA / F. Borman, J. Lovell and B. Anders.)

The above photo, simply known as Earthrise, carries the following statement with it, courtesy of Anders: We came all this way to explore the moon, and the most important thing is that we discovered the Earth. Today, of course, there are thousands of satellites orbiting the Earth, taking photos of the entire planet in unprecedented detail.

(Image credit: NASA / Goddard Space Flight Center / GOES-13 / NOAA.)

This very hi-res image (click for it), taken just a few months after the BP Oil Spill, is perhaps a great example of how invisible the damage we can do to the Earth is. From even our best views from space, the Earth appears nothing if not pristine and magnificent, as this cropped section of the Gulf of Mexico shows.

So enjoy your Earth Day today in whatever way you choose. Remember that it's the only home we have, and that it's our job to take care of it, to clean up after ourselves, and to leave it in better shape than we found it. No matter where in the Universe you are, make the most of it!

Categories: Education

### Welcome Earth Day with the Greatest April Shower of All: The Lyrids! [Starts With A Bang]

21 April, 2012 - 00:45

"April is the cruellest month, breeding
Lilacs out of the dead land, mixing
Memory and desire, stirring
Dull roots with spring rain." -T. S. Eliot Of course you all know the refrain, "April showers bring May flowers," but there's one April shower that brings fireballs instead: the Lyrids!

Like all meteor showers, the Lyrids come from a comet's dust trail that forms a great ellipse with respect to our Solar System. Once per year, the Earth, in its orbit around the Sun, passes through this dusty debris. When this happens, the Earth, moving at over 10,000 miles-per-hour with respect to these dust grains, cause the dust to vaporize in a fiery plunge as they collide with our atmosphere.

Every year, right around April 22nd, this meteor shower peaks, delivering anywhere from 10 to 100 meteors per hour visible beneath dark skies.

"Why is there so much variability," you ask? Well...

These dusty debris trails that fill our Solar System all come from comets. When a comet passes close enough to the Sun, it spews off gas, dust and ions, leaving an elliptical trail in roughly the same orbit as the comet itself. But comets spend most of their time far away from the Sun, so that these big bursts of debris only get emitted at rare intervals.

Are we going to pass through one of these big bursts, or are we going to spend this year passing through a lull in the debris trail? Like every year, we never know until we get there. The Lyrid meteor shower is a particularly tough one to predict, because the comet responsible for it, Comet Thatcher (after the 19th Century astronomer, not the 20th Century Iron Lady), is not only perpendicular to the plane of our Solar System, it also has a disturbingly long period of 415 years, meaning it won't be back until 2276!

(Image credit: Astroclock 2010 blog.)

But the comet isn't the interesting thing: the dusty debris which brings us the meteor shower is! The peak of the meteor shower, which is the best time to observe it, should occur close to midnight in North America during the night of April 21st / morning of April 22nd, making it the perfect way to usher in Earth Day!

No matter where on Earth you are, here's where you want to look.

(Image credit: me, using stellarium.)

The bright star Vega, the fifth brightest star in the night sky (and #2 in the Northern Hemisphere), should be high enough in the sky by 10 PM to easily identify it. (Vega features prominently in my summer sky tutorial, here.)

There's a small (but prominent; visible even in most cities) parallelogram nearby, just slightly closer to the horizon. Combined with Vega, that's how you can easily identify the constellation Lyra. The meteor shower should originate just a few degrees away, to the upper right of the parallelogram. But don't look directly at that spot, and don't use a telescope! The meteors originate from there, but you'll see them streaking away from that point, in random directions!

(Image credit: Wally Pacholka from the 2001 Leonids, retrieved here.)

Over the course of an hour, you should see anywhere from 10 to 100 meteors, depending on how good this year's Lyrids are. You'll have the added bonus of a moonless sky; the waxing crescent will be so minuscule that it will have completely set by time the constellation Lyra is visible. The meteors themselves are worth the price of admission, but every once in a while, the Lyrids give the gift of a true fireball: a meteor so bright it outshines the entire sky combined, lasts for a few seconds, and can even cast prominent shadows.

No promises, of course, as it's impossible to predict these things, but if I've got clear skies, you can bet I won't miss the opportunity to spend some time enjoying the wonders of the night!

For those of you who want real-time updates on the Lyrid meteor shower, including reports from around the world as they come in, well, what's the point of running the best Science news service on the web if you can't make that happen? So follow the Meteor Showers & Comets trap and stay on top of it. However you do it, make sure you enjoy the show Saturday night and into Sunday morning, and know that my eyes and millions of others will be gazing upwards with you!

Categories: Education

### Euler's Solution to the Basel Problem [EvolutionBlog]

20 April, 2012 - 00:14

I'm in the mood for some math today, so here's an amusing little proof I recently showed to my History of Mathematics class. We shall derive the formula

$\frac{\pi^2}{6}=1+\frac{1}{4}+\frac{1}{9}+\frac{1}{16}+\frac{1}{25}+\dots$

Note that the denominators of the fractions on the right are all perfect squares.

The problem of evaluating the sum on the right has a pedigree going back to the 1600s, when various mathematicians, including the famed Bernoullis, tried unsuccessfully to solve it. It was Leonhard Euler who polished it off at the age of 28 in 1735, thereby announcing himself as a force to be reckoned with in mathematics.

Euler's solution is one of those exceedingly clever arguments which, if you have any taste for mathematics at all, just has to bring a smile to your face. We need two main pieces of machinery. The first is the Taylor series for the sine function. If you can think back to whenever you took calculus, you might recall that it looks like this:

$\sin x=x-\frac{x^3}{3!}+\frac{x^5}{5!}-\frac{x^7}{7!}+\frac{x^9}{9!}-\dots$

If we divide through by x we obtain:

Categories: Education

### The Whole Story on Dark Matter [Starts With A Bang]

19 April, 2012 - 21:46

"Science progresses best when observations force us to alter our preconceptions." -Vera Rubin I want you to think about the Universe. The whole thing; about everything that physically exists, both visible and invisible, about the laws of nature that they obey, and about your place in it.

It's a daunting, terrifying, and simultaneously beautiful and wondrous thing, isn't it?

(Image credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team.)

After all, we spend our entire lives on one rocky world, that's just one of many planets orbiting our Sun, which is just one star among hundreds of billions in our Milky Way galaxy, which is just one galaxy among hundreds of billions that make up our observable Universe.

Yes, we've learned an awful lot about what's out there and our place in it. As best as we can tell, we've learned what the fundamental laws are that govern everything in it, too!

As far as gravitation goes, Einstein's theory of general relativity explains everything from how matter and energy bend starlight to why clocks run slow in strong gravitational fields to how the Universe expands as it ages. It is arguably the most well-tested and vetted scientific theory of all time, and every single one of its predictions that has ever been precision-tested has been verified to be spot-on.

(Image credit: Contemporary Physics Education Project.)

On the other hand, we've got the standard model of elementary particles and interactions, which explains everything known to exist in the Universe, and all the other (nuclear and electromagnetic) forces that they experience. This, also, is arguably the most well-tested and vetted scientific theory of all time.

And you would think that if our understanding of things were perfect, if we knew all about the structure of the Universe, the matter in it, and the laws of physics that it obeyed, we'd be able to explain everything. Why? Because all you'd have to do is start out with some set of initial conditions -- immediately following the Big Bang -- for all the particles in the Universe, apply those laws of nature that we know, and see what it turns into over time! It's a hard problem, but in theory, it should be not only possible to simulate, it should give us a sample Universe that looks just like the one we have today.

(Image credit: NASA / WMAP Science Team.)

But this doesn't happen. In fact, this doesn't happen at all. This picture I painted for you above is all true, on the one hand, but we also know that it isn't the whole story. There are other things going on that we don't fully understand.

Here, as best as I can present the full history in a single blog post, is the whole story.

(Visualizations & Simulations: Ralf Kähler, Tom Abel, and Oliver Hahn (KIPAC).)

As we come forward from the event of the Big Bang, our Universe expands, cools, while the entire time experiencing the irresistible force of gravity. Over time, a number of extremely important events happen, including, in chronological order:

1. the formation of the first atomic nuclei,
2. the formation of the first neutral atoms,
3. the formation of stars, galaxies, clusters, and large-scale structure,
4. and how the Universe expands over its entire history.
If we know what's fundamentally in the Universe and the physical laws that everything obeys, we'll arrive at quantitative predictions for all of these things, including:

1. what nuclei form and when in the early Universe,
2. what the radiation from the last-scattering-surface, when the first neutral atoms are formed, looks like in great detail,
3. what the structure of the Universe, from large scales down to small scales, looks like both today and at any moment in the Universe's past,
4. and how the scale, size, and number of objects in the observable Universe have evolved over its history.
We have made observations measuring all of these things, quantitatively, extremely well. Here's what we've learned.

(Image credit: NASA / Goddard Space Flight Center / WMAP101087.)

What we consider to be normal matter, that is, stuff made up of atoms, is highly constrained by a variety of measurements. Before any stars formed, the nuclear furnace of the very early Universe fused the first protons and neutrons together in very specific ratios, depending on how much matter and how many photons there were at the time.

What our measurements tell us, and they've been verified directly, is exactly how much normal matter there is in the Universe. This number is incredibly tightly constrained to be -- in terms that might be familiar to you -- about 0.262 protons + neutrons per cubic meter. There could be 0.28, or 0.24, or some other number in that range, but there really couldn't be more or less than that; our observations are too solid.

(Image credit: Ned Wright.)

After that, the Universe continues to expand and cool, until eventually the photons in the Universe -- which outnumber the nuclei by more than a billion-to-one -- lose enough energy that neutral atoms can form without immediately being blasted apart.

When these neutral atoms finally form, the photons are free to travel, uninhibited, in whatever direction they happened to be moving last. Billions of years later, that leftover glow from the Big Bang -- those photons -- are still around, but they've continued to cool, and are now in the microwave portion of the electromagnetic spectrum. First observed in the 1960s, we've now not only measured this Cosmic Microwave Background, we've measured the tiny temperature fluctuations -- microKelvin-scale fluctuations -- that exist in it.

(Image credit: WMAP Science Team / NASA. For those of you who like your maps shown on Mercator projections, click here for that view.)

These temperature fluctuations, and the magnitudes, correlations and scales on which they appear, can give us an incredible amount of information about the Universe. In particular, one of the things they can tell us is what the ratio of total matter in the Universe is to the ratio of normal matter. We would see a very particular pattern if that number were 100%, and the pattern we do see looks nothing like that.

Here's what we find.

(Image credit: Pavel Kroupa.)

The necessary ratio is about 5:1, meaning that only about 20% of the matter in the Universe can be normal matter. This doesn't tell us anything what this other 80% is. From the Cosmic Microwave Background alone, we only know that it exerts a gravitational influence like normal matter, but it doesn't interact with electromagnetic radiation (photons) like normal matter does.

You can also imagine that we've got something wrong about the laws of gravity; that there's some modification we can make to it to mimic this effect that we can re-create by putting in dark matter. We don't know what sort of modification could do that (we haven't successfully found one, yet), but it is conceivable that we've just got the laws of gravity wrong. If a modified theory of gravity could explain the fluctuations of in the Microwave Background without any dark matter at all, that would be incredibly interesting.

But if there really is dark matter, it could be something light, like a neutrino, or something very heavy, like a theorized WIMP. It could be something fast-moving, with a lot of kinetic energy, or it could be something slow-moving, with practically none. We just know that all of the matter can't be the normal stuff we're used to, and that we've come to expect. But we can learn more about it by simulating how structure -- stars, galaxies, clusters, and large-scale structure -- forms in the Universe.

(Video credit: DEUS Consortium.)

Because the types of structures you get out -- including what types of galaxies, clusters, gas clouds, etc. -- exist at all times in the Universe's history. These differences don't show up in the Cosmic Microwave Background, but they do show up in the structures that form in the Universe.

What we do is take a look at the galaxies that form in the Universe and see how they cluster together: how far away from a galaxy do I have to look before I see a second galaxy? How early in the Universe do large galaxies and clusters form? How quickly do the first stars and galaxies form? And what can we learn about the matter in the Universe from this?

(Image credit: E.M. Huff; SDSS-III; South Pole Telescope / Zosia Rostomian.)

Because if the dark matter -- which doesn't interact with light or normal matter -- has lots of kinetic energy, it will delay the formation of stars, galaxies, and clusters. If the dark matter has some but not too much, it makes it easier to form clusters, but still hard to form stars and galaxies early on. If the dark matter has virtually none, we should form stars and galaxies early. Also, the more dark matter there is (relative to normal matter), the more smooth the correlations will be between galaxies on different scale, while the less dark matter there is means that the differences in correlations between different scales will be very stark.

The reason for this is that early on, when clouds of normal matter starts to contract beneath the force of gravity, the radiation pressure increases, causing the atoms to "bounce back" on certain scales. But dark matter, being invisible to photons, wouldn't do this. So if we see how big these "bouncing features" are, known as baryon acoustic oscillations, we can learn whether there's dark matter or not, and -- if it's there -- what its properties are. The thing we construct, if we want to see this, is just as powerful as the graph of the fluctuations in the microwave background, a couple of images above. It's the much lesser-known but equally important Matter Power Spectrum, shown below.

(Image credit: W. Percival et al. / Sloan Digital Sky Survey.)

As you can clearly see, we do see these "bouncing" features, as those are the wiggles in the curve, above. But they're small bounces, consistent with 20% of the matter being "normal" matter and the vast majority of it being smooth, "dark" matter. Again, you might wonder if there isn't some way we could modify gravity to account for this type of measurement, rather than introducing dark matter. We haven't found one yet, but if such a modification were found, it would be awfully compelling. But we'd have to find a modification that works for both the matter power spectrum and the cosmic microwave background, the way that a Universe where 80% of the matter is dark matter works for both.

This is from the structure data on large scales; we can also look on small scales, and see whether small clouds of gas, in-between us and very distant, bright objects from the early Universe, are thoroughly gravitationally collapsed or not; we look at the Lyman-alpha forest for this.

(Image credit: Bob Carswell.)

These intervening, ultra-distant clouds of hydrogen gas teach us that, if there is dark matter, it must have very little kinetic energy. So this tells us that either the dark matter was born somewhat cold, without very much kinetic energy, or it's very massive, so that the heat from the early Universe wouldn't have much of an effect on the speed it was moving millions of years later on. In other words, as much as we can define a temperature for dark matter, assuming it exists, it's on the cold side.

But we also need to explain the smaller-scale structures that we have today, and examine in gory detail. This means when we look at galaxy clusters, they, too, should be made of 80% dark matter and 20% normal matter. The dark matter should exist in a big, diffuse halo around the galaxies and the clusters. The normal matter should be in a couple of different forms: the stars, which are extremely dense, collapsed objects, and the gas, diffuse (but denser than the dark matter) and in clouds, populating the interstellar and intergalactic medium. Under normal circumstances, the matter -- normal and dark -- is all held together, gravitationally. But every once in a while, these clusters merge together, resulting in a collision and a cosmic smash-up.

The dark matter from the two clusters should pass right through one another, because dark matter doesn't collide with normal matter or photons, as should the stars within the galaxies. (The stars not colliding is because the cluster collision is like firing two guns loaded with bird-shot at one another from 30 yards away: every single pellet should miss.) But the diffuse gas should heat up when they collide, radiating energy away in the X-ray (shown in pink) and losing momentum. In the Bullet Cluster, above, that's exactly what we see.

Ditto for the Musket Ball Cluster, a slightly older collision than the Bullet Cluster, that's just recently analyzed. But others are more complicated; cluster Abell 520, for example, below, appears to have too much gravity associated with a location that ought to have only normal matter and not dark matter.

(Image credit: NASA / CXC / CFHT / UVic. / A. Mahdavi et al.)

If we look at the individual components, you can see where the galaxies are (which is also where the dark matter ought to be), as well as the X-rays, which tell us where the gas is, you'd expect the lensing data -- which is sensitive to the mass (and hence, dark matter) -- to reflect that.

(Image credit: NASA, ESA, CFHT, CXO, M.J. Jee and A. Mahdavi.)

Instead, we see evidence for the gas creating a large amount of lensing, which shouldn't be. So, perhaps something funny is going on here. Maybe this is evidence in favor of modified gravity and against dark matter, as some contend. Or, perhaps, there's an explanation consistent with dark matter, and we simply have an unusual mass distribution in this type of smash-up.

But we can go to even smaller scales, and look at individual galaxies on their own. Because around every single galaxy, there should be a huge dark matter halo, comprising approximately 80% of the mass of the galaxy, but much larger and more diffuse than the galaxy itself.

Whereas a spiral galaxy like the Milky Way might have a disc 100,000 light-years in diameter, its dark matter halo is expected to extend for a few million light-years! It's incredibly diffuse because it doesn't interact with photons or normal matter, and so has no way to lose momentum and form very dense structures like normal matter can.

What we don't yet have any information about, however, is whether dark matter interacts with itself in some way. Different simulations give very different results, for example, as to what the density of one of these halos ought to look like.

(Image credit: R. Lehoucq et al.)

If the dark matter is cold and doesn't interact with itself, it should have either an NFW or a Moore-type profile, above. But if it is allowed to thermalize with itself, it would make an isothermal profile. In other words, the density doesn't continue to increase as you get close to the core of a dark matter halo that's isothermal.

Why a dark matter halo would be isothermal isn't certain. Dark matter could be self-interacting, it could exhibit some sort of exclusion rule, it could be subject to a new, dark-matter-specific force, or something else that we haven't thought of yet. Or, of course, it could simply not exist, and the laws of gravity that we know could simply need modification. On galactic scales, this is where MOND, the theory of Modified Newtonian Dynamics, really shines.

(Image credit: University of Sheffield.)

While the NFW and Moore profiles -- the ones that come from the simplest models of Cold Dark Matter -- don't really match up with the observed rotation curves very well, MOND fits individual galaxies perfectly. The isothermal halos do a better job, but lack a compelling theoretical explanation. If we only based our understanding of the "missing mass" problem -- whether there was extra, "dark" matter, or whether there was a flaw in our theory of gravity -- on individual galaxies, I would likely side with the MOND-ian explanation.

So when you see a recent headline like Serious blow to dark matter theories?, you already have a hint that they're looking at individual galaxies. Let's see what this is about.

A paper released just two days ago took a look at stars relatively close to our solar neighborhood, and looked for evidence of this inner distribution of mass from the theoretical dark matter halo. You'll notice, looking a couple of images up, that only the simplest, completely collision-less models of Cold Dark Matter give that large effect in the cores of dark matter halos.

So let's take a look at what the survey shows.

(Image credit: C. Moni Bidin et al., 2012.)

Indeed, the simple (NFW and Moore) halo profiles are highly disfavored, as many studies before have shown. Although this is interesting, because it demonstrates their insufficiency on these small scales in a new way.

So you ask yourself, do these small-scale studies, the ones that favor modified gravity, allow us to get away with a Universe without dark matter in explaining large-scale structure, the Lyman-alpha forest, the fluctuations in the cosmic microwave background, or the matter power spectrum of the Universe? The answers, at this point, are no, no, no, and no. Definitively. Which doesn't mean that dark matter is a definite yes, and that modifying gravity is a definite no. It just means that I know exactly what the relative successes and remaining challenges are for each of these options. It's why I unequivocally state that modern cosmology overwhelmingly favors dark matter over modified gravity. But I also know -- and freely admit -- exactly what it will take to change my scientific opinion of which one is the leading theory. And you're free to believe whatever it is you like, of course, but there are very good reasons why the modifications to gravity that one can make to have gravity succeed so well without dark matter on galactic scales fail to address the other observations without also including dark matter.

And we know what it isn't: it isn't baryonic (normal matter), it isn't black holes, it isn't photons, it isn't fast-moving, hot stuff, and it probably isn't simple, standard, cold and non-interacting stuff either, like most WIMP-type theories hope for.

I think it's likely to be something more complicated than the leading theories of today. Which isn't to say that I think I know exactly what dark matter is or how to find it. I'm even sympathetic to certain degrees of skepticism expressed on that account; I don't think I would claim to be 100% certain that dark matter is right and our theories of gravity are also right until we can verify dark matter's existence more directly. But, if you want to reject dark matter, there's a whole host of things you'll need to explain some other way. Don't completely ignore large-scale structure and the need to address it; that's a surefire way to fail to earn my respect, and the respect of every cosmologist who studies it.

And that's, as best as I can express it in a single blog post, the whole story on dark matter. I'm sure there are plenty of comments; let the fireworks begin!

Categories: Education

### Tiny Visions: Capturing the Nanoscale in 3D [Brookhaven Bits & Bytes]

18 April, 2012 - 18:56

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

Let's start with a number, by chance a palindrome: 1441. Imagine taking that many photographs of a single object, a soccer ball, say - obsessively capturing it from every angle to expose all the details. Those 1441 images provide all the evidence needed to illustrate and understand the three dimensional structure of that soccer ball. Each shot reveals another curve of the sphere, another line in the checkered pattern, another scuff or scratch along the surface.

Building a 3D image gets tricky with objects billions of times smaller. (courtesy of Electric-Eye on flickr)

An adept programmer or the right piece of software can then combine those photographs to generate an accurate 3D model of that ball. More than a thousand 2D images may take time to align, but at least the structure is simple. But what if that soccer ball was itself the size of a skin cell, its patterns were smaller than airborne viruses, and you still needed over a thousand photos to know its structure?

That's the challenge that a team at Brookhaven National Laboratory overcame with a new transmission x-ray microscope (TXM), which successfully combined 1441 images of a lithium-ion battery electrode into a detailed 3D structure. The TXM, hooked up to an x-ray beamline at Brookhaven's National Synchrotron Light Source, generates unparalleled image resolutions, as demonstrated in a new paper published in Applied Physics Letters. Read the rest of this post... | Read the comments on this post...

Categories: Education

### Weird Winter, Mad March [A Few Things Ill Considered]

18 April, 2012 - 16:34

I have not watched these yet myself, but will do as soon as I download and convert them for my iPhone, but I have no doubt they are up to Peter Sinclair's usual high standards.

Embedded below are part's 1 and 2 of Weird Winter - Mad March. Enjoy, discuss!

Categories: Education

### More Physics of Sprinting [Uncertain Principles]

18 April, 2012 - 15:16

Yesterday's post on applying intro physics concepts to the question of how fast and how long football players might accelerate generated a bunch of comments, several of them claiming that the model I used didn't match real data in the form of race clips and the like. One comment in particular linked to a PDF file including 10m "splits" for two Usain Bolt races, including a complicated model showing that he was still accelerating at 70m into the race. How does this affect my argument from yesterday?

Well, that document is really a guide to fancy fitting routines on some sort of graphing calculator or something. Which is fine as far as it goes, but I think it attributes too high a degree of reality to those unofficial split times, which are obtained from some unidentified web site. They proceed to fit a bunch of complicated functions to the data, but I think they're overthinking it.

Let's look at the actual data, graphed in more or less the way you would expect to see it in an intro physics class: as a plot of position vs. time:

The black circles represent the times from a race in 2008, the white circles times from a race in 2009. They're practically right on top of each other, because in absolute terms, the difference in times is pretty tiny.

Their first step is to fit a straight line to the data, which works remarkably well, even though it can't possibly be right. Looking at the graph, though, it does look awfully linear, particularly if you threw out the first point or two. That seems pretty consistent with the "accelerate to a maximum speed and stay there" model I assumed in the previous post, especially given that we don't know anything, really, about how these numbers were obtained.

Of course, the real test is to look at the speed as a function of time:

Categories: Education

### ESA makes a big choice [Dynamics of Cats]

18 April, 2012 - 06:11

The European Space Agency has made its selection for the next Large Mission to be flown by ESA, with a launch window in about 2022

Categories: Education

### The Physics of Sprints and Kickoff Safety [Uncertain Principles]

17 April, 2012 - 14:56

Over at Grantland, Bill Barnwell offers some unorthodox suggestions for replacing the kickoff in NFL games, which has apparently been floated as a way to improve player safety. Appropriately enough, the suggestion apparently came from Giants owner John Mara, which makes perfect sense giving that the Giants haven't had a decent kick returner since Dave Meggett twenty years ago, and their kick coverage team has lost them multiple games by giving up touchdowns to the other team.

Anyway, one of Barnwell's suggestions invoked physics, in a way that struck me as puzzling:

Idea 3: The receiving team's returner is handed the ball on his own goal line. His blockers must be positioned on the 20-yard line. The "kicking" team's players are positioned on the opposition's 40-yard line. Once the whistle blows, it's a traditional kick return.

Advantages: Everyone on the field will still be colliding, but because the kick-coverage team will have been running for 20 yards as opposed to 45, there won't be anywhere near as much momentum in those collisions. That should produce fewer injuries.

Now, if you know anything about introductory physics, you know that momentum is mass times velocity (for speeds much less than the speed of light). This doesn't have any direct relationship to the distance somebody has run to get to that point, unless they're accelerating the whole time. But it seems awfully unlikely to me that any of the whack jobs covering kicks in the NFL are actually speeding up appreciably between 20 and 45 yards-- they probably hit their top speed well before that.

Ah, but is there a way to use our knowledge of introductory physics to test this idea? That is, can we estimate the distance over which an NFL player is likely to be accelerating? Well, I would hardly be posting this if I didn't have a model for this sort of thing, so let's have a run at it (heh).

Categories: Education

### The Power of Admitting "I'm Wrong" [Starts With A Bang]

17 April, 2012 - 05:50

"Truth is mighty and will prevail. There is nothing wrong with this, except that it ain't so." -Mark Twain

"It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong." -Richard Feynman Every day that you set forth in the world is a new opportunity to learn something about it. Every new observation that you make, every new test you perform, every novel encounter or piece of information you pick up is a new chance to be a scientist.

How so?

(Image credit: Alan Chen.)

You have a conception of how things work in this world. You've pieced it together as a combination of your experiences, your knowledge, and the working hypotheses that you've accepted as the best mirror of reality. And every new shred of evidence you pick up about reality interrogates these hypotheses, daring your picture of reality to hold up to this level of scrutiny.

No matter who you are, no matter how smart you are, no matter how brilliantly you've drawn the conclusions you've drawn from the evidence you've gathered, there will come an instance where the evidence you encounter will be irreconciliable with the picture of reality you presently hold. And when that moment happens, your response will mean absolutely everything.

(Image credit: Glennbeck.com.)

Because there is the possibility that your view of reality -- the way you make sense of things -- is flawed in some way. You have to open your self up to at least the possibility that you are wrong. It is a humbling admission, that you may be wrong, but it's also the most freeing thing in the world. Because if you can be wrong about something, then you can learn.

(Image credit: Dave Koerner at Northern Arizona University.)

The discovery that planets move about the Sun in ellipses required exactly that; were it not for Kepler and his ability to accept that his earlier models were flawed, and then abandon them and create new and improved ones, physics and astronomy would likely have been set back an entire generation. And if you, yourself, can do this in your own life, you can find a better explanation for the phenomena you encounter in this world. You can bring your understanding of the world more closely in line with what reality actually is. In other words, you can do what all good scientists do, and in the end, learn something amazing.

But if you can't admit that you might be wrong, if your picture of reality is unchangeable despite any evidence to the contrary, if you refuse to assimilate new information and new knowledge and re-evaluate your prior stance on an issue, then you will never learn.

Anything.

Perhaps as an adult you're entitled to that right; you are, after all, free to believe whatever you want. But if you're a student in school? Your job is to learn. If you don't do your job, particularly if you don't even try to do your job, it's your teachers duty -- and I would say responsibility -- to fail you.

At least, it should be. Recently, some incredibly appalling things have been happening in education that completely undermine this, including the banning of the words 'dinosaur' and 'evolution' from standardized tests and the passage of Tennessee's "academic freedom" bill that allows teachers to teach counterfactual scientific information to their students about biological evolution and climate science, among other topics.

(Image credit: Listverse / Mike Devlin.)

And this is unfathomable to me. See that creature above? That's a black wolf. Know what's interesting to me about it? The black wolf doesn't occur in nature! The mutation for black fur did not occur until after the domestic dog had been in existence for thousands of years. If ever you see a black wolf, that tells you that at some point in their lineal history, there was a wolf that engaged in breeding with a domestic dog that had that (dominant) black fur mutation.

Biology, of course, doesn't stop with evolution. What I just explained to you is an explanation that requires genetics to understand, which is encoded in an organism's DNA. But before you get to DNA, before you even get to genetics, at a more basic level you must have an understanding of evolution. If you want to understand disease: evolution. If you want to understand whales and dolphins: evolution. (I mean come on, they've got freakin' leg bones!)

Same deal with global warming; there are plenty of people asserting that the Earth isn't warming anymore (yes, there really are), despite all studies showing that it totally is, if you look at the data without cheating. For example, last year (2011) was "only" the 11th-warmest year on record since records began in 1880. But last year was also a La Niña year, which is characterized by cooler temperatures. It was also the hottest La Niña year of all time, since 1880.

The question I always ask people who dig in even deeper when their view on an issue is challenged by new data is the following: What evidence would it take to change your mind on this issue? For the "Is the Earth continuing to warm" question, you may very well get your wish in 2012 or 2013; one of the next two years could easily become the new warmest-year-on-record.

(Image credit: NASA / GISS global average temperature data.)

Believe it or not, it's actually harder for many of us to admit that we could be wrong about something the less we know about it! Why's that? A neat little psychological effect known as the Dunning-Kruger effect. In a nutshell, it says that people who are incompetent at something (e.g., biology, climate science, etc.) lack the very skills necessary to evaluate the fact that they are incompetent!

This results in people who know almost nothing about a particular topic who are willing to opine at length, argue with experts, and declare -- incorrectly -- that they are right and you are an idiot. Here's the original graph from the original Dunning-Kruger paper, illustrating exactly that.

(Image credit: Justin Kruger and David Dunning, 1999.)

But if we recognize that our present understanding may not be the final answer, and we can absorb that ego-bruise from possibly not being in the right when we thought we were, we can step forward. There are plenty of people working to help make it easier for us all to do exactly that. I'm not exempt from this either, even in areas where my knowledge actually is far above average. Last week, I wrote about when ultramassive stars die, and a number of people challenged some of the contentions I made. Yes, some of them may have been jerks about it, but they also had information that I didn't. Despite being a theoretical astrophysicist, I don't know all there is to know about all aspects of astrophysics, and I never will.

(Image credit: NASA / CXC / M. Weiss.)

So I went out and learned what it was that I didn't know, and now my picture of how supermassive stars die is -- while possibly still imperfect -- improved over what it was. And the next time I go to explain it, there will be at least two things that I can do a better, more accurate job of explaining, and there will be at least one misstep I won't make again.

It doesn't make me any less of a person or any less of a scientist that I didn't get everything right the first time I put it all together; on the contrary, it makes me human. I've been refining what I know and how things make sense to me my entire life, and I'll continue to do that tomorrow. There is no part of that picture of reality that I hold so dear that overwhelming evidence to the contrary couldn't change my mind. I would be surprised at a great number of things, but I wouldn't be stuck.

I know exactly what types of evidence would change my mind about the theories, hypotheses and ideas that make up my world view. Remember the words of Carl Sagan: When you make the finding yourself -- even if you're the last person on Earth to see the light -- you'll never forget it. I hope that I never reach the point where I think I'm always right; I hope I can always gather new information and knowledge, have that crisis when my preconceptions conflict with new data, and admit when I was wrong. Because I don't want to ever stop learning; no matter how much I know, there's always going to be a whole Universe out there to explore.

Categories: Education

### Another Week of GW News, April 15, 2012 [A Few Things Ill Considered]

16 April, 2012 - 15:10

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