Pluto’s Day of Reckoning

by Shane L. Larson

NB: I originally wrote this post to outline my TEDx NorthwesternU talk in 2014.  Watch the video here.  Please enjoy both!

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As an astronomer, I get to talk to people about all kinds of things. Some people want to talk about black holes, or about asteroids killing the dinosaurs, or about life on other worlds. But the one subject everyone always wants to talk about is Pluto!

How many people feel about Pluto's demotion. [Image by Mathias Pedersen, used with permission]

How many people feel about Pluto’s demotion. [Image by Mathias Pedersen, used with permission]

That’s because people have this uneasy feeling that Pluto has been treated unfairly by scientists.  We have this queasy feeling down in the pit of our stomachs because as children we were told Pluto was a planet, and now scientists have flip-flopped and are telling us it isn’t!  And we feel bad for Pluto!

The truth is astronomers are engaged in a very serious (and good-natured) debate about what it means to be a planet. It’s the kind of debate scientists have every day about all kinds of things that don’t catch the attention of the public or garner headlines. The difference is people seem to care about Pluto!

The reason you and I are even talking about this is because in 2006 the International Astronomical Union reclassified Pluto as a “dwarf planet.” To use more common vernacular, Pluto was DEMOTED.  Now that’s a word that carries a certain amount of emotional baggage with it!  That visceral response we have to describing Pluto’s demise was captured by the American Dialect Society who made their 2006 word of the year,

plutoed (PLUE-toed): to demote or devalue
something, as happened to the former
planet Pluto...

The changing of Pluto’s status clearly struck a chord with people.  But why?

Suppose I show you a picture of a “Pluto protest.”  This image doesn’t phase any of you! That’s because in the back of everyone’s mind, there is a little voice telling you which side of the street you’d be standing on and what your sign would say!  I’m right there with you. I’ve picked my side of the street, and I know exactly what my sign would say!

(L) A "Pluto Protest" staged in Seattle [Image: Wikimedia Commons] (R) My own sign, expressing solidarity with Pluto; my daughter is more vehement in her support.

(L) A “Pluto Protest” staged in Seattle [Image: Wikimedia Commons] (R) My own sign, expressing solidarity with Pluto; my daughter is more vehement in her support.

So the world has divided itself into two camps — the Pluto Apologists, and the Demoters (they sound like rock-n-roll band names, don’t they?).  Pluto inspires deep emotions in everyone, whether they are scientists or members of the public.  Even today, nearly 8 years after the reclassification, discussion of Pluto sparks vehement debate, but the debate is nuanced and subtle, even among the cognoscenti.  In one corner, there are people who are avid Pluto-philes and just would like Pluto to be back in the club. In another corner, there are people who think Pluto is clearly just a small rock, like many other small rocks, and not classifiable by the word “planet.” And in another corner there is a third group of people who think we really don’t know what the hell we mean when we say “planet,” and that our understanding of the Cosmos and what it means to be a “planet” must constantly evolve. This is the group I stand with.

The story of Pluto’s demotion and the ensuing arguments and exasperations about its status are an excellent backdrop to understand how science works and responds to ever changing knowledge about the Cosmos. The fact that people exhibit deep emotions about the entire affair is simply a very human dimension to the story, a manifestation of the fact that we long to be deeply connected to the Cosmos, that we want our perceptions and thoughts about the Universe to matter.  That emotional connection is a foothold for us to explore this tale.

For kids, and short people like me, Pluto always had a certain allure because it was the smallest planet — the runt of the Solar system.  I’ll freely admit that my love affair with Pluto started at a very young age, when I was even shorter than I am now! I got started looking at the sky because my Mom was a birder.  She had an old beat up spotting scope that she would use to watch birds at our house, but at night I would grab it and look at the sky.

(L) My mom's spotting scope, that I first used to look at the sky. (C) My friend Hazel and her telescope at a star party, circa 2000. (R) My own big scope, named Cosmos Mariner.

(L) My mom’s spotting scope, that I first used to look at the sky. (C) My friend Hazel and her telescope at a star party, circa 2000. (R) My own big scope, named Cosmos Mariner.

I saw the Moon and all the big planets — Mars and Jupiter and Saturn — but I always wanted to see Pluto. But it was impossible; that little spotting scope, for all the wonders it showed me, was just too small.  It took many years, but eventually a 70-year old friend of mine named Hazel showed me Pluto through her 20” telescope. I got to see Pluto with my own eyes, and it only validated all that long held wonder and ardor I held for this small world. One thing led to another and eventually I built my own big telescope and now I show other people Pluto!  My wife figures there are worse things I could be doing with my life.

But not all of us have had the chance to see Pluto with our own eyes. Even so, people all over the world love Pluto just the same.  Part of the reason is that people recognize the story of Pluto’s discovery as a kind of modern fairy tale that could have happened to any of us.

(L) Clyde Tombaugh and his homebuilt reflecting telescope. (R) The Lowell Observatory 13-inch astrograph, used to discover Pluto. [Images: Wikimedia Commons]

(L) Clyde Tombaugh and his homebuilt reflecting telescope. (R) The Lowell Observatory 13-inch astrograph, used to discover Pluto. [Images: Wikimedia Commons]

Pluto was discovered by a farmboy from Kansas named Clyde Tombaugh, who couldn’t go to college because hail had destroyed his family’s crops. But he loved astronomy, and in his early 20’s he built a telescope, and started sketching Mars and Jupiter from his family’s farm in Kansas.  In 1929 he sent some of those sketches to Lowell Observatory in Flagstaff, Arizona, and they were so impressed they hired him to come run one of their new photographic telescopes.  The job was only supposed to only last for three months, but he ended up working at Lowell for more than 14 years.

During his first year he was taking pictures of the night sky looking for Planet X, a proposed new world somewhere out in the dark beyond Neptune.  Very soon after he arrived, on the nights of January 23 and January 29, 1930, he captured two images that would change the world, though he didn’t know it at the time. Astronomers lead rugged lives — we’re in the observatory all the time, we stay up late, we sleep very little, and sometimes we don’t get to our data right away.  It took Clyde almost a month to go back to those images, but on February 18, he was looking at the images on a blink comparator, a machine that rapidly flashes back and forth between two astrophotos while you are looking at them. Stars stay put because they appear in both images, but things that move become very obvious.

The Pluto discovery images, blinked back and forth as they might appear in a blink comparator.   Click to animate. [Animation: S. Larson, from Lowell Observatory archive images]

The Pluto discovery images, blinked back and forth as they might appear in a blink comparator. Click to animate. [Animation: S. Larson, from Lowell Observatory archive images]

That night Clyde saw the tell-tale dot jumping back and forth across the center of these images and knew he had found a new world.  The discovery was announced on March 13, 1930 and made headlines around the world.

Headline announcing Pluto's discovery on 14 March 1930; the world had yet to be named. [Image: Chicago Tribune]

Headline announcing Pluto’s discovery on 14 March 1930; the world had yet to be named. [Image: Chicago Tribune]

At the time, the Lowell Observatory had the right to name the new planet and they were flooded by suggestions.  I’m sure if Stephen Colbert had been alive then, the Colbert Nation would have petitioned to name it after him.  But in the end, the name Pluto was suggested by an 11-year old English girl named Venetia Burney.

Venetia Burney [Image: Wikimedia Commons]

Venetia Burney [Image: Wikimedia Commons]

She was very interested in classical mythology, and suggested the name Pluto to her grandfather (Falconer Madan) who was a former librarian at Oxford. The name was passed through his professional colleagues until it arrived at Lowell, and on March 24, 1930 every employee at Lowell Observatory voted by secret ballot on the name for Tombaugh’s new world.  “Pluto” received every single vote, and the name was fixed!

The name was almost instantly embraced in our popular culture. Walt Disney is famously rumored to have named Mickey Mouse’s dog companion Pluto after the planet, and in 1941 Glenn Seaborg continued a tradition of naming new elements after planets when he named a newly discovered chemical element “plutonium.”

Today, it’s almost exactly 84 years since the discovery of Pluto. What do we know about it? And why did it take 76 years for us to start arguing about whether it is a planet or not?

solarSystemZones

We can think of the Solar System in zones.  Down near the Sun, the worlds are small and rocky.  In this zone, we call the planets “terrestrial,” the domain of Mercury, Venus, Earth and Mars.   A bit farther out, the planets get large, notable for their vast gaseous atmospheres and lack of solid surfaces. In this zone, we call the planets “jovian,” — Jupiter, Saturn, Uranus and Neptune.  Beyond Neptune is the Third Zone.  This is out where Pluto lives, and all the worlds out here are small, made up mostly of rock and ice, and are on weird orbits that don’t always line up with the solar system’s inner two zones.  These worldlets are the detritus, the flotsam and jetsam, left over from the formation of the Solar System.

We’ve always known that Pluto lived out here in this Third Zone, and that it was a bit weird. It lives on a strange orbit that is highly tilted and sometimes is closer to the Sun than Neptune.  In addition, it is smaller than other planets — it’s smaller even than the Earth’s Moon.  One of the arguments that’s made for Pluto’s reclassification is that it is more like worlds in the Third Zone, than is it is like the terrestrial or Jovian worlds. Those of us who object to Pluto’s reclassification don’t disagree with this.  What we don’t like, is the definition that is being used to define “planet.”

Here is the current definition:

  1. A planet must orbit the Sun
  2. A planet must have enough gravity to be round
  3. A planet must have cleared its orbit

Pluto fails only on this last point — it lives in a part of the solar system where there are lots of things floating around and there just hasn’t been enough time in all the 4.5 billion year history of the solar system to knock things out of the way.  So why should this definition bother anyone?

The difficulty with this definition is the first and the last points — they are dynamical qualities that depend on the interaction of the object in question with other things, not on the physical properties of the planet itself. The definition was created this way because we all knew Pluto needed reclassified, but we didn’t know enough about Pluto itself to know how to do it any other way. We made up this definition, but now we have to use it for everything. As a way of defining the world, it represents a very narrow and provincial view of the Cosmos.

So why does a definition like this matter? Can it really cause us trouble in the future?  Of course!  You see, all of us organize our thoughts about the world by sorting.  We do it every day — we decide what goes in our garden sheds, we decide where to put groceries in our kitchens, and we decide how to make different piles on our desks.

Scientists do exactly the same thing. We take things that we can see around us — rocks, flowers, slime molds, stars, galaxies — and we organize them based on what they look like. Everything you see gets sorted into a bucket, which is really useful when we’re learning about something for the first time — we quickly sort things based on how they look.  We call this TAXONOMY, and this is the game astronomers are engaged in right now when we talk about planets.

Pluto is just one of many worlds that have been discovered in the dark past Neptune. How do we classify these "trans-Neptunian objects"? [Image: Wikimedia Commons]

Pluto is just one of many worlds that have been discovered in the dark past Neptune. How do we classify these “trans-Neptunian objects”? [Image: Wikimedia Commons]

In today’s day and age, the rules for planetary taxonomy are being changed by technology. Telescopes are getting bigger, cameras are going digital and getting more sensitive, and roboticized telescopes are controlling those telescopes and cameras 24 hours a day, continuously searching the sky for things that go bump in the night. The result is a veritable bonanza of new objects being discovered, many in the dark beyond Neptune, in the Third Zone with Pluto, all of which have to get sorted into our planetary taxonomy.

Technology is also pressing us on other fronts.  Today, after spending centuries speculating on the matter, we’ve discovered that there are indeed worlds around other stars (not just the Sun!).  We know of almost 2000 planets orbiting other suns!  As of the time of this writing (19 April 2014), there are 1783 “planets” in our catalogs (the air quotes are necessary because they aren’t planets — they don’t orbit the Sun!). We’re going to have to put all of them into sorting buckets — into our taxonomy — and it is going to challenge us to think about what we mean when we say the word planet.

Let me tell you about two of those many thousands of planets.

Hot Jupiters are large, gas giant worlds that orbit far closer to their parent star than any worlds we have ever seen in our own solar system. [Image: ESA/NASA/STScI [M. Komesser]  (STScI-PRC2008-41) ]

Hot Jupiters are large, gas giant worlds that orbit far closer to their parent star than any worlds we have ever seen in our own solar system. [Image: ESA/NASA/STScI [M. Komesser] (STScI-PRC2008-41) ]

One of the first “planets” we found outside the solar system is orbiting a dim, naked eye star in the constellation Pegasus, called 51 Pegasi, a star much like our Sun about 50 lightyears away from Earth.  The planet is affectionately called “Bellerophon” after the Greek hero who tamed Pegasus, but astronomers call this planet “51 Pegasi b.”  This planet is about half the mass of Jupiter — if it were here in our solar system we’d consider this a serious planet!  But there is something odd about Bellerophon — it orbits 10 times closer to its parent star than Mecury does to the Sun!  We call planets like this “hot Jupiters” or “roasters”, and we have no idea how they get to be so close to their parent stars!

Rogue planets drift along among the stars, without orbiting a parent star. [Image: NASA/JPL-Caltech (PIA14093)]

Rogue planets drift along among the stars, without orbiting a parent star. [Image: NASA/JPL-Caltech (PIA14093)]

Here’s another “planet” we discovered only just last year.  Astronomers call this world PSO J318.5-22.  It is about six and half times the mass of Jupiter. If it were in our solar system, not only would it be “a serious planet,” it would be the most serious planet!  It would be larger than any other world in our home system.  So what’s special about this world?  It’s what we call a ROGUE PLANET.  It has no parent star it orbits. At some point early in its life, it was ejected from its home in some unimaginable gravitational battle.  Now, it will drift forever between the stars.

BOTH of these worlds, and many like them, challenge our definition of planet. Looking around the Cosmos, we have found something new, some new worlds that we have to sort into our buckets, like the hot Jupiters and the rogue planets. Maybe it will make us think about Pluto once again too.

New Horizons will fly past Pluto in July of 2015. This is the first spacecraft ever to visit Pluto and will return the first, up-close pictures of this far away world. [Image: NASA/JHU-APL]

New Horizons will fly past Pluto in July of 2015. This is the first spacecraft ever to visit Pluto and will return the first, up-close pictures of this far away world. [Image: NASA/JHU-APL]

There is one last part of Pluto’s story, still to come, and it also involves technology. In the summer of 2015, for the first time in history, a spacecraft from planet Earth will visit Pluto. It’s called New Horizons, and was launched in 2006. When it arrives at Pluto, after almost a decade of flying through the dark of space, it will blaze through the Pluto system in a single pass, measuring everything it can, and snapping every picture it can get. That data, those pictures, are precious commodities that will be sent back to Earth on the faint whisper of a radio link, and will, without fail, once again make us ask some deep questions about Pluto. For the first time, we’ll see Pluto up close, and we’ll start up this whole planet debate one more time — after the champagne is done, of course.

An artist's impression of the surface of Pluto. [Image: European Southern Observatory (L. Calcada)]

An artist’s impression of the surface of Pluto. [Image: European Southern Observatory (L. Calcada)]

The great truth in this story is this: Pluto doesn’t care what we call it. It is, more or less, the same today as it was when Clyde Tombaugh discovered it.  For that matter, it is more or less the same as it was it formed more than 4 billion years ago.  The notion that things can be sorted into “planets” and “not planets” is a human construct, something we made up to try and organize our imperfect understanding of the Cosmos. The debate gives me and you and all our astronomer friends an opportunity to chat and have fun and take a serious look at how we view the Cosmos and our place in it.

But I’m willing to make a promise: Someday, we’re going to come back to this question of “what is a planet.”  I don’t know if we’ll change Pluto’s status — I hope we do! — but what I do know is this.  We WILL change our definition of planet.

It doesn’t mean we were wrong, it doesn’t mean we were dumb, it doesn’t mean we were ignorant of the facts.  It just means that we are wiser than we once were. And that’s what the entire game of science is all about — to become wiser when faced with Nature’s awesome spectacle.

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This post is derived from a talk I gave at TEDx NorthwesternU 2014. You can see the video of that talk (17 min) here: TEDx – Pluto’s Day of Reckoning

For those of you interested in this debate, there are many great resources out there that you can take a look at. First, Mike Brown from Caltech has an excellent talk online at the Keck Institute:

  • How I killed Pluto & Why It Had It Coming, Mike Brown (Caltech) — 15 September 2011 (Video link)

There are also several books that I would recommend.

  • * “How I killed Pluto & Why It Had It Coming”, Mike Brown (Amazon link)
  •  “The Pluto Files”, Neil deGrasse Tyson (Amazon link)
  • “The Case for Pluto”, Alan Boyle (Amazon link)

Behind the Curtains of the Cosmos 3: Keys to the Cosmos

by Shane L. Larson

The fact that the curtain of the Cosmic Microwave Background exists is a huge boon to astronomers, giving us confidence in our understanding of Big Bang cosmology. But is that all? We have all this microwave light coming at us from every direction in the Cosmos — what can we do with it?  Is there anything else we can learn?

As it turns out, there is more to the light than meets the eye. Astronomers excel at taking information from the Cosmos and digging deeper, to tease out secrets and information that at first glance are not easy to see.  If you look closely at the Cosmic Microwave Background you discover some Very Important Things. One thing is that it is not absolutely, perfectly smooth. Imagine picking up a ball off a pool table — it looks and feels very smooth; that is analogous to the uniform temperature of the Cosmic Microwave Background looking the same no matter where we look on the sky.  But if you take that same pool ball and look at the surface closely with a magnifying glass, you find that it has some scratches and roughness to it — they are so small as to not be detectable by your fingertips, nor to your naked eye.

(L) A billiard ball looks and feels smooth to your eye and your finger tips. (R) But if you can look at it very carefully under a microscope, you find there are minuscule imperfections that are only detectable with excellent technology.

(L) A billiard ball looks and feels smooth to your eye and your finger tips. (R) But if you can look at it very carefully under a microscope, you find there are minuscule imperfections that are only detectable with excellent technology.

The Cosmic Microwave Background is very similar. If we use a highly accurate microwave telescope to look, we find that there is a small scale  “roughness” to the sky; astronomers think this roughness is an indicator of clumpiness at the time atoms formed, ultimately leading to what you and I see today — galaxies and clusters of galaxies in the Universe. This roughness was first detected by the COBE satellite in 1992. It was later mapped at even finer precision by the WMAP mission, and by the Planck mission.The spots on this map can be thought of as hot and cold spots on the sky. The red spots are the hottest, at only about 2.7 Kelvin (1 Kelvin is 1 degree Celsius) above absolute zero. The blue spots are the coolest, about 0.00001 Kelvin cooler than 2.7 Kelvin — a difference almost so small as to be undetectable except with the most exquisite astronomical instruments! Before the microwave background broke free from matter, the small variations in the density of matter were spread across the Cosmos. When the matter condensed to form neutral atoms, these variations imprinted themselves in the Cosmic Microwave Background. The spotted map of the Cosmos seen by COBE, WMAP and Planck is a message from the other side of the curtain!

The Planck All-Sky Map of the Cosmic Microwave Background variations. [Planck Collaboration]

The Planck All-Sky Map of the Cosmic Microwave Background variations. [Planck Collaboration]

Is there any other property of the Cosmic Microwave Background that might be measured? Is there any other physical imprint that might tell us something about the early days of the Cosmos?  Of course there is!  It is called polarization. Light is known to scientists by its proper name, “electromagnetic radiation.” As the name suggests, it has an electric part and a magnetic part, called “fields.” The way we visualize light is as a wave of electric fields and magnetic fields travelling together, at right angles to each other. For any light you receive, the direction the electric field is waving defines the polarization of the wave.

Light is a propagating "electromagnetic field," a waving electric field travelling together with a waving magnetic field. The direction the electric field waves defines the polarization of the light.

Light is a propagating “electromagnetic field,” a waving electric field travelling together with a waving magnetic field. The direction the electric field waves defines the polarization of the light.

Polarization encodes many kinds of information, related to how light and matter interact with one another. The most common way you encounter this every day is with sunglasses. Reflected light is polarized, so we build sunglasses that block polarized light, cutting down glare off of reflected surfaces. You might have noticed that the display of your smartphone is polarized too — you can’t see it in certain orientations through your polarized sunglasses.

Light reflected off of surfaces is polarized, like these mud flats. (L) The waves and the sand look bright when polarized light is seen. (R) When polarized light is blocked, as with polarized sunglasses, the appearance changes dramatically. [Image from Wikimedia Commons]

Light reflected off of surfaces is polarized, like these mud flats. (L) The waves and the sand look bright when polarized light is seen. (R) When polarized light is blocked, as with polarized sunglasses, the appearance changes dramatically. [Image from Wikimedia Commons]

Light from the Cosmic Microwave Background is expected to be polarized, imprinted with patterns because during decoupling (the time when electrons were binding to nuclei to form atoms) the light bounced off of the free electrons (in physics-speak: it “scattered”) giving it a definite polarization. Astronomers call these polarization patterns “E-modes” and they are recognizable because they make symmetric patterns in the sky — the polarization pattern looks exactly like itself if you look at a reflection of the pattern in a mirror. This kind of pattern was discovered by the DASI experiment in 2002.

Polarization of the Cosmic Microwave Background detected in 2002 by the DASI Collaboration. These are "E-mode" polarizations, caused by scattering.

Polarization of the Cosmic Microwave Background detected in 2002 by the DASI Collaboration. These are “E-mode” polarizations, caused by scattering.

So what does this all have to do with inflation? Inflation happened shortly after the Big Bang, before anything that you and I might recognize as a particle had formed. The forces of Nature spontaneously appear as the Universe cools, enabling different kinds of physical interactions to appear. Gravity had appeared sometime before inflation, during a time cosmologists call the “Planck epoch.” Inflation was the sudden, rapid expansion of everything — the energy soup, and spacetime itself — from the incredibly tiny point that expanded to become the Observable Universe. Think of spacetime like a balled up bundle of wrapping paper being unfolded, flattened and smoothed out by inflation.  On the smallest scales, spacetime is changing — expanding, stretching, flexing of the folds in our bundle of paper. Physicists call these happenings “quantum fluctuations.” The stretching and unfolding of spacetime means the gravitational field is changing. But that’s exactly what we said causes gravitational waves! As the Universe inflates, the quantum fluctuations in spacetime itself generate gravitational waves. This has physicists really excited, because detecting these gravitational waves would be the first hint of the quantum nature of gravity itself.

As we noted last time, gravitational waves interact with matter very weakly, so they propagate through the slowly evolving soup of the Cosmos, pushing matter here and their until the formation of the Cosmic Microwave Background.  What is the net result? The net result is that gravitational waves leave a polarization imprint in the microwave light. Just as with the expected polarization from electron scattering, there is a pattern to the polarization made by the gravitational waves. Astronomers call this pattern “B-modes” — they have a twist to them.  You can recognize a B-mode pattern, a twist, because in a mirror the pattern appears reversed.

(L) E-mode polarization patterns look identical if viewed in a mirror.  (R) B-mode polarization has a "twist." If the twist is clockwise, then when viewed in a mirror the twist is counter-clockwise, and vice versa.

(L) E-mode polarization patterns look identical if viewed in a mirror. (R) B-mode polarization has a “twist.” If the twist is clockwise, then when viewed in a mirror the twist is counter-clockwise, and vice versa.

Which brings us back to the story of BICEP2. Astronomers have been looking for the tell-tale twist of polarization in the Cosmic Microwave Background for some time. Major experiments have been slowly gearing up to look for and characterize the unique, gravitational-wave signature of inflation. The science team at BICEP2 won the race. What has all of us so excited is the measured value is larger than we anticipated, indicating the relative importance of the gravitational waves is large.  This has provided sudden and unexpected guidance for theoretical physicists trying to model inflation, and for future experimenters attempting to build new experiments to probe the early Universe.

The BICEP2 polarization map, showing B-mode ("twist") patterns.

The BICEP2 polarization map, showing B-mode (“twist”) patterns.

So what now?  Astronomy is a spectator sport — we keep looking!  Now that our colleagues at BICEP2 have made the initial detection, we are gearing up to look more closely at the result, and to dissect it for clues that confirm we are on the right track to understanding the Cosmos.  New papers are appearing rapidly (I counted about 100 at the time of this writing). The result doesn’t precisely agree with other results we already have (there is “tension” between the results, in physics-speak), and some of us still have reserved skepticsm.  The field has been thrown into a big mess, and now we have to figure out what happened. It’s a bit like coming home to find your living room in a disastrous state, and trying to figure out if it was the kids, the cat, the dog, or some combination thereof that made the mess! But astronomers don’t mind — it’s the figuring out of the mess that is so rewarding. But make no mistake — it was an outstanding achievement, a triumph of the human intellect and human ingenuity. And onward we go.

The BICEP2 Telescope at the South Pole. [Image: National Science Foundation]

The BICEP2 Telescope at the South Pole. [Image: National Science Foundation]

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This is the last installment in a 3-part series about the March 2014 BICEP2 announcement about the detection of a putative signal from inflation in the Cosmic Microwave Background.  Part 1 can be found here.

Behind the Curtains of the Cosmos 2: Gravitational Waves

by Shane L. Larson

Nearly every picture you have ever seen of galaxies and nebulae and stars, and virtually everything that we know about the Cosmos, has been obtained with light.  Light is plentiful and easily created, so it is natural to use it as a probe of the Universe. Vision is, for most of us, the primary sense by which we interact with the world, so again light is an obvious probe for us to lean on.

Three dimensional gravitational wave emission from colliding black holes (NASA-Goddard).

Three dimensional gravitational wave emission from colliding black holes (NASA-Goddard).

But there are other physical phenomena in Nature, and technology enables us to probe those phenomena, whether we can personally sense them or not. One such phenomena, first predicted by Albert Einstein in 1916, are gravitational waves. Gravitational waves are propagating disturbances of gravity — in the modern language of gravity, they are ripples in the fabric of space and time.  If a massive object moves, it takes time for the gravitational field to respond because nothing can travel faster than light.  Heuristically then, gravitational waves are the shifting of gravitational fields, in response to dynamical motion of mass.

When two massive objects (like stars or black holes) orbit one another, the information about how the gravitational field is changing moves outward at the speed of light. These ripples spiraling outward are gravitational waves, and carry detailed information about the source. [Image by S. Larson]

When two massive objects (like stars or black holes) orbit one another, the information about how the gravitational field is changing moves outward at the speed of light. These ripples spiraling outward are gravitational waves, and carry detailed information about the source. Click to animate. [Image by S. Larson]

Most of us are familiar with the idea of a spectrum from light, produced by a prism or seen as a rainbow after a storm passes. The “electromagnetic spectrum” encompasses more than just those few colors we can see with our eyes; it also includes kinds of light our eyes can’t see, like gamma rays, ultra-violet light, radio waves, and microwaves.

The electromagnetic spectrum --- light in all its varieties, illustrated in the many different ways that scientists describe the properties of a specific kind (or "color") of light.

The electromagnetic spectrum — light in all its varieties, illustrated in the many different ways that scientists describe the properties of a specific kind (or “color”) of light.

Gravitational waves also form a complete spectrum, independent of the electromagnetic spectrum. Since we can’t sense gravitational waves with our bodies, we have no sensory experience to describe them, and have no names for the different parts of the spectrum, so we simply identify the waves by their wavelength (the distance between peaks of the wave) or alternatively their frequency (how often a peak passes by you, if you just stand still and let the waves wash by). As astrophysicists, we have thought hard about the Universe, and can easily imagine Nature creating “high frequency waves” (short wavelength), where thousands of wave peaks pass by you every second, all the way down to “very low frequency waves” (long wavelength), where a wave peak may only pass by once every 30 million years.

There are many different sources of gravitational waves that we expect to see. These include (clockwise from upper left): Colliding neutron stars, merging supermassive black holes, white dwarf binaries, supernova explosions, the Big Bang, and the capture of compact stars by supermassive black holes.

There are many different sources of gravitational waves that we expect to see. These include (clockwise from upper left): Colliding neutron stars, merging supermassive black holes, white dwarf binaries, supernova explosions, the Big Bang, and the capture of compact stars by supermassive black holes.

Gravitational waves are generated by all kinds of different astrophysical systems, and as such the waves themselves are as varied as the phenomena that created them. From the simplest viewpoint, the astrophysical system making the waves defines how big they are. Systems that have large spatial extent and large masses tend to make much longer wavelength waves than small, super-compact systems. To develop some intuition about this, consider one of the bread-and-butter source for modern gravitational wave observatories, a binary black hole — two black holes, locked in a mutual gravitational dance, orbiting one another the way the planets orbit the Sun. When the black holes are far apart (larger orbit) they complete their orbits more slowly. As a result the gravitational waves emitted have low frequencies. Suppose the orbit shrinks. What happens? The black holes orbit each other more quickly, so the frequency of the gravitational waves increases.  What we see here is that the size of the orbit influences the size of the gravitational waves. Similar arguments can be made for other physical properties that influence the shape and form of the gravitational waves, which makes them useful for doing astronomy.

A simple example of how the properties of the source change the structure of the gravitational waves. If we can detect and measure the waves, that will tell us something about the sources. [Image by S. Larson]

A simple example of how the properties of the source change the structure of the gravitational waves. If we can detect and measure the waves, that will tell us something about the sources. [Image by S. Larson]

Astronomy is a game of detection — as I like to say, “astronomy, unlike life, IS a spectator sport!”  Our job as astronomers is to watch the Cosmos and record what we see. We build instruments to help us accomplish that mission, instruments with cool names that you can use to impress your mother or a date: telescope, observatory, detector, bolometer, radiometer, and so on. If you want to build an instrument to look for some form of putative radiation, then you need to know how it interacts with your detector. The basic behaviour we exploit with light is that it bounces off of appropriately designed surfaces, whether the light is radio waves, optical light, or x-rays, it bounces off of surfaces, a fact that humans have exploited to gather light for more in depth experiments.

The effect of a PLUS (+) polarized gravitational wave on a grid of particles. [S. Larson]

The effect of a PLUS (+) polarized gravitational wave on a grid of particles. Click to animate. [S. Larson]

The effect of a CROSS (X) polarized gravitational wave on a grid of particles. [S. Larson]

The effect of a CROSS (X) polarized gravitational wave on a grid of particles. Click to animate. [S. Larson]

So what do gravitational waves do? Gravitational waves change the proper distance between particles. There is a very nice way to visualize this. Imagine a grid of particles — little marbles or marshmallows, arranged on this screen.  Now imagine a gravitational wave shooting straight through the screen: from your eyes, through the middle of your grid, and out the back.  What happens? The distances between all the marshmallows changes in a very specific way, illustrated in the animated images here.  At the start, in one direction all the marshmallows are stretched farther away from each other, while at the same time marshmallows in the perpendicular direction are pulled closer together. If you wait a while, the gravitational waves move a bit farther on in its cycle and it returns the grid to its original appearance. But it doesn’t stop there! On the “downside” of the wave cycle, the stretching and pulling swap directions!  This pattern repeats itself for as long as the gravitational wave is flying through the grid of marshmallows. There are two different “flavors” of gravitational waves (what astronomers call “polarizations”) that both distort our grid of marshmallows, just in different directions.  One flavor is called “PLUS” because the pattern of deformation looks like a + sign.  The other flavor is called “CROSS” because the pattern of deformation looks like a X sign.

So if we want to detect gravitational waves, we need a way to see this distortion. Like other radiation we encounter in astronomy (particularly electromagnetic radiation — light), gravitational waves carry energy which can affect other objects in the Cosmos. A “detector” is a device which extracts some of that energy to let us know the wave is passing by. But gravitational waves have one big problem —- they interact very WEAKLY with matter! That means it is hard to get them to deposit energy in a detector, and that means they are hard to detect.  This is a fact that Einstein appreciated full-well — he knew if we were ever going to see gravitational waves, technology was going to have to get better — much better. It would not be until the 1960s that any serious effort to detect gravitational waves would begin.

The gravitational wave interferometer concept is to measure the changing proper distance between points using lasers.

The gravitational wave interferometer concept is to measure the changing proper distance between points using lasers.

If you look at our particle grids, you see the effect is more pronounced for particles that are farther apart, so the bigger the instrument is the better.  Today, the premiere technology for gravitational wave searches is a classic physics instrument called a “laser interferometer” —  a device that times how long it takes a laser to fly in two different directions and very precisely compares the results to tell you if the two directions have different lengths! This is perfect for gravitational wave detection! Laser interferometers are easy to build in the lab (or at home, if you can acquire a few parts — try these instructions), but it is easier to detect gravitational waves over larger distances, because the stretching effect is larger.  So we’ve built HUGE laser interferometers, that stretch 4 kilometers (2.5 miles) from one end to the other! We’ve built two of them here in the United States — they are called LIGO.  The Pictionary style picture of LIGO is three mirrors — one at a corner, and two at the far ends of two long arms. Think of any three marshmallows in our grid — those are the functional locations of the mirrors in LIGO that the lasers are measuring distances between. When gravitational waves change the distances between the mirrors, we can measure those changes with our lasers.

(L) Aerial view of LIGO-Hanford Observatory [top] and in Google Maps [Bottom].  (R) Aerial view of LIGO-Livingston Observatory [top] and in Google Maps [Bottom].

(L) Aerial view of LIGO-Hanford Observatory [top] and in Google Maps [Bottom]. (R) Aerial view of LIGO-Livingston Observatory [top] and in Google Maps [Bottom].

Just as in traditional photon astronomy, we have to build different kinds of detectors to detect different kinds of gravitational waves. As a general rule, when the wavelengths of the gravitational waves we want to see are longer, we have to build bigger detectors. A laser interferometer could be built in space by imagining the mirror locations being free-flying spacecraft. Such a concept exists, known as LISA, where the spacecraft are 5 million kilometers apart (that’s 13 times the distance from the Earth to the Moon; it will take the lasers 16.6 seconds to fly between the spacecraft!).

Spacecraft concept for a gravitational wave detector in space [eLISA Consortium]

Spacecraft concept for a gravitational wave detector in space [eLISA Consortium]

Eventually it becomes impractical to imagine building bigger and bigger interferometers. Does that mean there are parts of the gravitational wave spectrum that we simply will never be able to observe? No; astronomers are clever folks and have devised ways to use astrophysical systems as gravitational wave detectors by measuring the imprints the gravitational waves leave behind them.

There are two primary ways we monitor astrophysical systems to detect gravitational waves. One way is we watch pulsars — the spinning dead hulks of massive stars that died in supernova explosions, and now spin relentlessly, periodically flashing the Earth with a bright beam of electromagnetic radiation.  Many pulsars spin in a very stable manner, shining their spinning light on us at very precise intervals, which we can time and write down.  If a gravitational wave passes between us and a pulsar, then it stretches the space between us, and it takes the pulses longer or shorter amounts of time to reach us! We can detect gravitational waves by watching for changes in the arrival time of pulsar pulses!  This is called pulsar timing.

We can detect gravitational waves by monitoring the arrival times of pulses from many pulsars in different directions on the sky.

We can detect gravitational waves by monitoring the arrival times of pulses from many pulsars in different directions on the sky.

The second astrophysical method for gravitational wave detection is to look very closely at the Cosmic Microwave Background, and see if gravitational waves left very tiny distortions in the microwaves. There are many different distortions that can and do appear in the Microwave Background radiation, but the signature of gravitational waves is unlike just about every other kind of known distortion. They are of intense interest because if that signature could be detected, it would mean the gravitational waves came from the other side of the Curtain! This is exactly what the BICEP2 experiment was all about, and will be the theme of our discussion in the next and final post of this series.

————————————————–

This is the second installment in a 3-part series about the March 2014 BICEP2 announcement about the detection of a putative signal from inflation in the Cosmic Microwave Background.  Part 1 can be found here.

Behind the Curtains of the Cosmos 1: Inflation and the Microwave Background

by Shane L. Larson

The world was all atwitter last week (on twitter and otherwise) with the announcement from our friends at the BICEP2 collaboration that they had detected the echo of the Universe from the earliest moments after the Big Bang. (links to press releases and videos discussing the result can be found here).

The BICEP2 Telescope at the South Pole. [Image: National Science Foundation]

The BICEP2 Telescope at the South Pole. [Image: National Science Foundation]

Have no doubt — this achievement is remarkable, a testament to our ability to probe and understand the secrets of the Cosmos that Nature has left for us to find. Nobel Laureate Stephen Weinberg once waxed poetic in his book The First Three Minutes, claiming, “The effort to understand the universe is one of the very few things which lifts human life a little above the level of farce and gives it some of the grace of tragedy.”  This is one of those moments; an instant in time when every member of our species should raise up their head, stand a little taller with pride and know that despite all the trials and tribulations that face our race and our planet, we are capable of great things.

But what does it all mean? What is the hub-bub all about?  There are two elements of this that you will hear people talking about.  One is about inflation and one is about gravitational waves.  Today, let’s talk about inflation.

What is inflation all about?  In order to understand inflation, let’s first talk about The Big Bang.  Most of us have heard about The Big Bang, a model for the Cosmos that arises naturally from the notion of taking what we can see today (the expansion of the Universe) and running the movie backward in time.  The development of Big Bang cosmology evolved as many ideas in science do — a few fundamental observations inspire someone to imagine what the underlying Laws of Nature might be. Those ideas are written down, and everyone begins to think of all the possible consequences — what kinds of things must be true, and how could we observe them? Big Bang cosmology is a result of imagining “running the movie backward” from the current, expanding state we see when we look out from the Earth.  If you shrink the current Observable Universe into the distant past, then it should have been smaller, and as a consequence much denser and hotter.

So what was it like, the tiniest fraction of a second after the Big Bang?  It was hot. Our understanding of the densities and temperatures then suggest it was 1032 ºC = 100,000,000,000,000,000,000,000,000,000,000 ºC. What does that even mean? A temperature like that is so far outside our common, everyday experiences with coffeepots and campfires as to seem quite ridiculous.  But to an astrophysicist, high temperatures are synonymous with great speeds.  If the Universe was this hot, then that means everything in the Universe was flying around at tremendous speeds. Since the Universe was much denser, everything was tightly packed together, increasing the number of collisions.  What happens when you have collisions at high speeds? You break things apart!

PrimordialSoup_croppedAt this time, things are crashing together so hard that atoms can’t exist. In fact, things are crashing together so hard that the nuclei of atoms can’t exist.  The entire Universe is filled by a Primordial Soup of protons, neutrons, electrons, and photons (light) — energy, and the building blocks of atoms.

As the Universe expands, it cools. By 100 seconds after the Big Bang, the Universe has cooled to a mere 10 billion ºC.  At that temperature, protons and neutrons can stick together to form the cores of the first atoms. At these temperatures, when they crash together, the strong nuclear force is strong enough to keep them together. This moment of creation of the nuclei is called nucleosynthesis.

Nucleosynthesis was the formation of the cores (the nuclei) of atoms. Most were hydrogen nuclei (single protons) with a little bit of helium, and an even smaller amount of lithium. Observations of these proportions is one of the strongest pieces of data supporting Big Bang cosmology.

Nucleosynthesis was the formation of the cores (the nuclei) of atoms. Most were hydrogen nuclei (single protons) with a little bit of helium, and an even smaller amount of lithium. Observations of these proportions is one of the strongest pieces of data supporting Big Bang cosmology.

Now, 10 billion ºC is still too hot for electrons to bind to these newly formed nuclei; each time they try, a collision knocks them loose, so no proper atoms can form at this time.  The result is that the early Universe is a swirling maelstrom of charged particles. The consequence of that fact is that light is effectively trapped. Photons (light) are easily deflected (astronomers use the term “scattered”) by charged particles. If a photon is flying along minding its own business and happens upon a charged particle, it gets bumped off its path in a new direction. Since the early Universe is very dense, it soon encounters another charged particle and it gets scattered again! The result is that a photon’s path through the early Universe is a bit like a drunken sailor’s walk, and has little chance of ever looking like anything else.

The Universe continues in this state for about 400,000 years, continuing to expand and continuing to cool. Around 400,000 years the temperature has fallen to a balmy 3000 ºC. At that temperature, electrons can stick strongly enough to nuclei that collisions don’t knock them free.  Suddenly, neutral atoms form!  This event is called “recombination,” which always struck me as a funny term because this is the first time particles combined to form atoms! Almost all of the atoms that form are hydrogen, mixed with a good amount of helium, and a little bit of lithium. These amounts have been measured by astronomers and agree exquisitely with the amounts predicted by Big Bang Cosmology; this is one of the strongest pillars of evidence convincing us that the Big Bang is the correct model for the Universe.

(L) Before atoms form, the Universe is filled with a vast soup of charged nuclei and electrons, and photons cannot travel very far without scattering off of them.  (R) When the electrons bind to nuclei ("recombination") to form neutral atoms, the photons no longer scatter so easily, and they fly free --- the Universe has become transparent.

(L) Before atoms form, the Universe is filled with a vast soup of charged nuclei and electrons, and photons cannot travel very far without scattering off of them. (R) When the electrons bind to nuclei (“recombination”) to form neutral atoms, the photons no longer scatter so easily, and they fly free — the Universe has become transparent.

The most important consequence of recombination is that all the charged particles are bound together into neutral atoms. As far as the photons are concerned, the Universe is suddenly devoid of any charged particles to scatter off of, and they burst free and start travelling on long, unscattered paths. This is called “decoupling” — the photons no longer strongly interact with the “stuff” that became atoms. Free to stream through a suddenly transparent Universe, the photons begin their long 14 billion year journey to us.  We see them here on Earth as microwaves, coming from every direction on the sky.  We call these microwaves the Cosmic Microwave Background, and it is the relic light from the moment that atoms formed.

Arno Penzias (L) and Robert Wilson (R) in front of the Bell Labs microwave antenna that first detected the Cosmic Microwave Background. They were awarded the 1978 Nobel Prize in Physics for their discovery.

Arno Penzias (L) and Robert Wilson (R) in front of the Bell Labs microwave antenna that first detected the Cosmic Microwave Background. They were awarded the 1978 Nobel Prize in Physics for their discovery.

The Cosmic Microwave Background was discovered in 1965 by Penzias and Wilson at Bell Labs. As expected, it was coming from every direction on the sky, and exceedingly uniform — it looks exactly the same, to our ability to measure it, no matter which direction we looked. The Cosmic Microwave Background is relic radiation that is a precise probe of the temperature at the time atoms form. The fact that we see the same microwaves in every direction means atoms formed at the same time in the same amounts at the same temperature in every direction.

A recreation of the 1965 Cosmic Microwave Background map, covering the entire sky (Penzias and Wilson could not see the entire sky from Bell Labs). The band of stronger microwave light is the signature of the Milky Way Galaxy.

A recreation of the 1965 Cosmic Microwave Background map, covering the entire sky (Penzias and Wilson could not see the entire sky from Bell Labs). The band of stronger microwave light is the signature of the Milky Way Galaxy.

Despite the fact that this is exactly what was predicted, it poses a certain problem for us to understand. The uniformity is confusing because the way things get to be the same temperature is through thermal contact — they talk to each other, and trade bits of energy (heat) until they are at the same temperature. This is why Popsicles melt if you leave them on your counter — heat from the counter flows into the Popsicle, melting it until the puddle of goo is the same temperature as the counter. This is why your cup of coffee cools down — heat from the coffee flows into the air, warming the air in the room until the coffee and the air are at the same temperature.  So why should that bother us with the Cosmic Microwave Background? Because there is an ultimate speed limit in the Universe — the speed of light.

To understand this, look up in the sky to your left. The microwave background in that direction is so far away it has taken the entire age of the Universe for the light to reach Earth!  Now look up in the sky to your right — the microwave background is just as far away in the other direction! In the entire age of the Universe, these two patches of the sky have only had time to send light to the Earth, NOT to each other.  But that means we have a great mystery! The two patches are at EXACTLY the same temperature as each other. How did they know to be the same temperature if they aren’t in thermal contact, if they can’t talk to each other and trade heat in less than twice the age of the Universe?   This is called “The Horizon Problem” — pieces of the sky are too far away from each other to collude to have the same appearance and physical properties.

The page from Alan Guth's research notebook where he had the first idea for inflation (box at the top).  [[On display at the Adler Planetarium; the notebook is part of the collection curated by the Adler's Webster Institute for the History of Astronomy.]]

The page from Alan Guth’s research notebook where he had the first idea for inflation (box at the top). [[On display at the Adler Planetarium; the notebook is part of the collection curated by the Adler's Webster Institute for the History of Astronomy.]]

The solution to the problem was initially discovered by Alan Guth in 1979.  Guth imagined a moment very early in the Universe. How early? About 10–35 seconds after the Big Bang (about a hundred-billionth of a trillionth of a trillionth of a second!). At that time, the Universe was very small, and as a result very hot and very dense. The fact that it was very small means than the entire Universe was in thermal contact — it could all trade heat until it all had the same temperature.  So how to you grow a very tiny, uniform temperature Universe into a gigantic huge Universe that still looks like it is in thermal equilibrium?  Guth realized the way to do this was to grow the Universe very large, very fast.  This sudden, rapid expansion is called inflation, and it occurred very shortly after the Big Bang, from about 10–36 seconds to 10–34 seconds! During that time, the Universe inflated, like a balloon, by a factor of about 1026 in size.  Now 1026 is clearly a big number (100 trillion trillion), but what does it mean to expand by that factor?  Imagine an atom.  An atom is about 10–10 meters across (1 angstrom).  By contrast, a lightyear is nearly 1016 meters, or a factor 1026 bigger than an atom. If you grew an atom to be a lightyear across, it would have increased in size by a factor of 1026.

Cosmologists put this all together in a chain of reasoning that can be hard to keep in your head. Here are the salient points:

  1. Early on, everything was extremely close together and the Universe was in thermal equilibrium — all the parts of it were in contact and reached the same temperature.
  2. Inflation suddenly occurs — the Universe is stretched and pushed apart, so that different parts of it are so far away they are no longer in thermal contact.
  3. The now distant parts have the same thermal properties because they were in equilibrium before the expansion!
  4. Now, after inflation, the different parts of the Universe continue to cool, but they all cool in exactly the same way, so they look as if they are at the same temperature.

Voila! Horizon problem explained!  :-)

At this point, you might think we’re done because the idea of inflation neatly explains some of the observational questions we have about Big Bang cosmology. But we’re scientists, so we’re always pushing hard on our ideas to make sure they are right, to understand all that they imply.  So what else does inflation do that we can measure?  Is there anything we can observe that continues to confirm the basic principle of inflation? Are there measurements that can be made that might explain more about how inflation started, how it stopped, or whether is is something more complicated than plain old simple inflation?

Observing the Universe at the time of inflation is hard.  Why? We know inflation happened right after the Big Bang, almost 400,000 years before the creation of the Cosmic Microwave Background.  The Cosmic Microwave Background is like a curtain — it is the oldest light we can see, because it was released at the first moment when light could travel freely.  Before that moment, light was inhibited from travelling very far at all — it scattered and bounced around and could never make a beeline for Earth and our telescopes.  As a consequence, we can’t see beyond the Cosmic Microwave Background. If we have any hope of probing our ideas about inflation, we’re going to have to find a way to see beyond the Curtain, or discover some unique signature that inflation left in its wake that imprinted itself in the Cosmic Microwave Background.  Fortunately for us, these are not idle wishes.  One thing inflation should have done is generate an echoing background of gravitational waves that should have left their imprint on the Cosmic Microwave Background.  This will be our focus next time.

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This is the first in a three-part series to explore physics and astronomy behind what the BICEP2 observation of the Cosmic Microwave Background is all about. The other two parts are:

2: Gravitational Waves (5 April 2014)

3: Keys to the Cosmos (11 April 2014)

Days of Pi and Wonder

by Shane L. Larson

My watch on Pi-day, 2012. The time makes the 4th through 8th digits of Pi: 3.14 15926!

My watch on Pi-day, 2012. The time makes the 4th through 8th digits of Pi: 3.14 15926!

Each year when Pi Day (March 14, or 3-14) rolls around, geeks around the world rejoice. Everyone seems to get their geek on, and that makes me walk around with a grin on my face.  People do all kinds of things, like make pies shaped like the Greek letter Pi, or making square pies because they are punny (“pie are square,” which is a pun for Pi*r2, the area of a circle). Or they take pictures of their watches at exactly a moment to write out the digits of Pi.

What is all this Pi business? Fundamentally, it is the number you get by dividing the distance around the outside of a circle by its diameter.  Not just any circle — every circle. It is one of the great wonders of the fabric of the Cosmos that it works for every circle. It’s the kind of thing that keeps me up late at night!

Pi is a natural number that appears from Nature. It is the ratio of the circumference around a circle to the diameter.  It is the same for EVERY circle!

Pi is a number that appears from Nature. It is the ratio of the circumference around a circle to the diameter. It is the same for EVERY circle!

Pi is an irrational number, meaning it cannot be written as a fraction. It has an infinite number of digits that go on and on and on and on.  The first 200 digits are: 

3.14159265358979323846264338327950288419716939937
5105820974944592307816406286208998628034825342117
0679821480865132823066470938446095505822317253594
0812848111745028410270193852110555964462294895493
038196...

You can see a million digits here, and here. There are even more digits (in case you want to memorize them in an effort to attract a date :-) ).

Wikipedia lists a LOT of things that happened on Pi Day in history, but I want to focus on a warm spring day in 1879, in the city of Ulm on the banks of the River Danube. On that day Hermann and Pauline Einstein welcomed their son, Albert, into the world.

Albert Einstein is one of the most easily recognized figures in our culture, so much so that he is recognized in imaginary fantasies, like this one of Albert being a master of the electric guitar in my band ("MC Squared and the Relatives"). In reality, his colleague Robert Oppenheimer noted that Einstein was "almost wholly without sophistication and wholly without worldliness ... There was always with him a wonderful purity at once childlike and profoundly stubborn."

Albert Einstein is one of the most easily recognized figures in our culture, so much so that he is recognized in imaginary fantasies, like this one of Albert being a master of the electric guitar in my band (“MC Squared and the Relatives”). In reality, his colleague Robert Oppenheimer noted that Einstein was “almost wholly without sophistication and wholly without worldliness … There was always with him a wonderful purity at once childlike and profoundly stubborn.”

There is perhaps no figure in the world, historical or otherwise, more recognizable than Albert Einstein. His Facebook page has 8.7 million likes (!), even though he died in 1955 (Einstein passed from this Cosmos on April 18, 1955, almost exactly 34 years before the birth of Facebook’s founder, Mark Zuckerberg).  He is widely regarded as one of the towering geniuses of the human race, and was named the Person of the Century in the 20th Century for the impact his scientific findings had on our modern lives. While most of us know about Big Al, do you know how his work filters into your every day life?  Let me tell you a few stories of how it does.

Einstein in 1905 in his famous "patent clerk" jacket. I always imagined it to be green!

Einstein in 1905 in his famous “patent clerk” jacket. I always imagined it to be green!

Let’s go back to 1905. Einstein had finished his doctorate at the University of Zurich, but unable to find an academic position had taken up work as a patent clerk in Bern. Now in those days, there was no evening reality television, no new episodes of Cosmos, so Einstein continued to work on physics “in his spare time.” This is the sort of thing scientists do when we’re between jobs, with the hope that by still being productive we will become attractive candidates for an academic position in the future. As it turns out, Einstein was very productive in 1905. The Latin phrase “annus mirabilis” (“year of wonders”) has in modern science become synonymous with Einstein’s published works in 1905. There were four seminal papers: (1) a paper explaining the molecular origin of Brownian motion; (2) a paper explaining the photoelectric effect by revitalizing the photon theory of light; (3) a paper describing special relativity, and proposing the ultimate speed limit in the Universe; (4) a paper describing the equivalence of mass and energy, captured by the famous formula E = mc2.  These four papers laid the foundations for our understanding of much of what we call “modern physics,” fundamentally altering the way we think about energy, space, and time.  What are these concepts, and what do they have to do with your life?

Brownian motion was named after botanist Robert Brown, who in the early 1800s was using a microscope to observe pollen grains suspended in water. Inexplicably, the grains appeared to move around at random, with no discernible cause. Brown tried in vain to discover the cause of the motion, but could not explain it. He then dutifully did what scientists do, he reported his observations to his peers and the phenomena passed into the scientific memory. Nearly a hundred years later, Einstein showed that the observed motion could be explained by the constant buffeting of the large grains by the motion of the much smaller particles of water that it was suspended in, what we today call molecules. There are many applications for the use of Brownian motion once you understand it. For instance, in modern pharmaceutical manufacturing, medicines delivered through pills are created from a suspension of the active drugs with inactive ingredients that comprise the entire pill; this controls the delivery of the drug on ingestion. Brownian motion is used to control the suspension in the mixing stages, to insure the proper distribution of the active drug throughout the pill.

Mixing pharmaceutical molecules is like mixing marbles. The active ingredients (white marbles) need to be mixed evenly with the inactive ingredients (green marbles). Brownian motion can be exploited for this mixing.

Mixing pharmaceutical molecules is like mixing marbles. The active ingredients (white marbles) need to be mixed evenly with the inactive ingredients (green marbles). Brownian motion can be exploited for this mixing.

The nature of light has always been a matter of intense scrutiny for physicists. In the early 1700’s, Newton famously championed the “particle theory” of light, but these ideas fell into disfavor when a particle approach could not explain effects like diffraction and interference; this gave way to the “wave theory” of light. In 1900, Max Planck proposed his “quantum hypothesis” to explain how objects like red-hot pokers and lightbulb filaments emit energy — in discrete packets called “quanta.” Einstein adopted the quantum hypothesis, and revitalized the particle  idea to explain how some materials eject electrons when you shine light on them: electric particles (electrons) are ejected when illuminated with light (photons) — the “photoelectric effect.”  The number of applications of this effect in modern technology are numerous, including solar cells, the imaging sensors in the digital camera in your smartphone, and remote controls.

Your TV remote emits infrared light (which you eye cannot see). When the sensor on your TV is hit by the light, the photoelectric effect generates an electrical signal that activates the control circuit in the TV.  The image on the right was taken by pulling the infrared filter off of an ordinary digital camera (most digital cameras can see infrared, but that light is blocked so your pictures don't look weird).

Your TV remote emits infrared light (which your eye cannot see). When the sensor on your TV is hit by the light, the photoelectric effect generates an electrical signal that activates the control circuit in the TV. The image on the right was taken by pulling the infrared filter off of an ordinary digital camera (most digital cameras can see infrared, but that light is blocked so your pictures don’t look weird).

Special relativity is one of the most profound and important discoveries about Nature that humans have ever made, and its veracity has been borne out, literally, by billions of experiments since its inception in 1905. Einstein’s insight that there is an Ultimate Speed Limit in the Universe (the speed of light) has profound consequences for how we think about motion and dynamics at high speeds, and challenges our old-fashioned notions about the distinguishability of space from time. Most of us have heard all kinds of special relativity stories about how it changes the nature of measurements of distances and times, and the resulting perception of paradoxes — length contraction, time dilation, old and young twins. It blows your mind and is vaguely unsettling because it seems far from our everyday lives, and as a result our everyday intuition built around watching baseballs, Volkswagens and chipmunks doesn’t seem to apply.

Calvin's father doesn't quite understand relativity. [From Calivn & Hobbes, by Bill Watterson]

Calvin’s father doesn’t quite understand relativity. [From Calivn & Hobbes, by Bill Watterson]

But special relativity explains why we see cosmic ray muons from space when they should have decayed before they hit ground; it is demonstrated by every one of the 115 billion protons the LHC bashed together at a time; and we have discovered that if our engineering is up to it, we can use special relativity to travel to the stars.  Mass-energy equivalence (E = mc2) is usually mixed into our thinking about relativity, and most prominently impacts the world through its application ot nuclear weapons and nuclear energy.  Deep in the heart of the Sun, the nuclear fusion of hydrogen into helium converts some of the mass of hydrogen into energy, which you and I eventually feel as the warm dapple of sunlight during a lazy afternoon picnic.

The Disintegration of the Persistence of Memory, by Salvador Dali. We have a vague and unsettled feeling, especially when confronted by relativity, that we do not understand the fabric of space and time.

The Disintegration of the Persistence of Memory, by Salvador Dali. We have a vague and unsettled feeling, especially when confronted by relativity, that we do not understand the fabric of space and time.

Perhaps the most important way that special relativity changed our lives is that it made us realize that all the laws of physics had to obey special relativity, which led Einstein to think about gravity. It took about 10 years, but he was the first person to understand how gravity and special relativity worked together, and the result was called “general relativity.” Today, general relativity has transformed the world because the Global Positioning System (GPS) would be impossible without it. General relativity (and special relativity) tells us that if you have two clocks that are moving differently, and experiencing gravity differently, then you will think they are ticking at different speeds when you compare them.  What does that have to do with GPS?  

Fundamentally, GPS works by broadcasting a clock signal from satellites. On the ground, your smartphone receives those signals and triangulates your position from the clock signals.  Suppose there are two GPS satellites, one is 100 km away from you, and the other is 200 km away from you. At the same moment, they broadcast their current time, say 2:00pm.  The 2pm clock signal from the satellite closest to you arrives first; the 2pm signal from the distant satellite arrives later. By comparing the arrival times of those two signals, you know exactly where you stand between the two satellites.  Where does relativity fit into this picture?  If you don’t include relativity, the clock signals from the satellites, compared to clocks on the ground (in your smartphone) are different by 38 microseconds — 38 millionths of a second!  That is so tiny!  Does it matter?  Sure it does, because the radio signal from the satellite is a kind of light, which travels 11.4 kilometers (7 miles!) in 38 microseconds!  If you didn’t have a little bit of relativity working inside your phone, your GPS would not be useful for navigation!  11.4 km is a HUGE distance when you’re trying to find a Dairy Queen, the Lego store, a hospital, or your kids’ baseball game.

GPS triangulates your location by comparing the received time from multiple satellites.

GPS triangulates your location by comparing the received time from multiple satellites.

Of course, Einstein’s work did not end with the annus mirabilis. In fact, he had a long and influential career after that, as most scientists do.  Let’s end with a story about a little paper he wrote in 1917. That year, Einstein explained the idea of stimulated emission –– light can cause an atom to emit an identical particle of light, and the two photons can travel along together exactly in synch. Okay, that sounds cool, but so what? You may shrug your shoulders, but what this leads to is the LASER. In fact, “laser” is an acronym built from Einstein’s idea — “Light Amplification by Stimulated Emission of Radiation.”  Einstein was the person who predicted the possibility of building a LASER, though it took until the 1950s for us to develop enough technology that one could actually be built. Today our world is literally filled with lasers — CD and Blu-Ray players, laser pointers, lasers for cutting industrial materials, lasers used to resculpt the lens of your eyes, and a whole host of medical applications.

Einstein is just one example of one scientist who changed our lives with his passion for uncovering Nature’s secrets. There are many examples of other scientists who have had similar influence on us, in ways that you and I don’t often think about nor quite possibly even know. But it is all there in our every day lives, from our trucks and carburetors, to our antibiotics and heart stents, to our smartphones and MP3 players, to our aerobees and yoga tights. It all comes from clever insights, accidental observations, random musings, and delight in something as simple as a round shape called a circle. Enjoy your Pi Day, and enjoy your pie!

Cosmos 14: A Personal Voyage

by Shane L. Larson

As I write this, I’m heading home from the PhD defense of a new young mind in Physics, where we argued about how Nature might have created time from gravity. I’m typing this on an iPad, a glossy piece of imagination made of glass and aluminum that instantly connects me to all the collected knowledge of the human race.  I’m sipping a cup of coffee, water infused with flavor and essences of a plant, extracted with one of the oldest human discoveries, fire.  Most impressively, I’m sitting in an airplane as I write this, blazing along at 520 mph.  To quote the comedian, Louis C.K., I’m sitting in a chair in the sky! I’m like a Greek myth right now.

The CRJ700 I flew today; one small bit of a modern Greek myth.

The CRJ700 I flew today; one small bit of a modern Greek myth.

All these things are a result of the human proclivity to know the world around them. Each one is an evocative realization of imagination and creativity. Someone once imagined that we could do what birds do, and fly through the sky — an ancient dream told in the myth of Icarus, unrequited in the notebooks and imaginings of Leonardo da Vinci, realized at last barely more than a century ago. Someone imagined that I should be able to more or less instantly find out when the Slinky was invented, or hear Johann Sebastian Bach’s Brandenburg Concerti  on demand (No. 2 in F major is included on the Voyager Golden Record). Someone imagined that we could understand how Nature created time itself, and suggested ways that we could test those ideas. And perhaps most importantly, someone imagined that you should throw an innocuous bean into the fire, pull it out before it is completely destroyed, mash it up, mix it with boiling water and drink it — a stunning tour de force of imagination, perseverance and creativity!

iPad and coffee -- two important and remarkable outcomes of science!

iPad and coffee — two important and remarkable outcomes of science!

These are the kinds of things I think about every day — the trappings of every day life, which we often take for granted.  We overlook how truly remarkable every one of them is. Everything around you in your life we discovered by studying the world and figuring out how it works. That game of curiosity, exploration, discovery and application is what we mean when we say SCIENCE, and it is one of the most important things humans have figured out how to do.  Not just important because we know how to make smartphones and pharmaceuticals and band saws and rubber duckies, but important because in all the vastness of the Cosmos, we are the only form of life that we know of (with certainty) that has figured out how to do science. The methods of science are a natural and inevitable consequence of applying our curiosity to the world, and with it we can improve our lives.  This was one of the central themes of Cosmos.

The frontpiece to my Ph.D. thesis.

The frontpiece to my Ph.D. thesis.

For the past two and a half months, I’ve revisted Cosmos each week, once again walking along the shores of the Cosmic Ocean, turning over interesting shells and poking at bits of cosmic flotsam and jetsam that have washed up on our shores.  I’ve listened to the tales of adventure and discovery; I sailed along side our robotic emissaries once again as they made the first grand voyages to the other planets in our solar system; and I once again learned a little bit of the history of how we came to start thinking about the wonder and mystery of the Cosmos.  And woven throughout it all, I once again soaked in the unshakable belief in our ability to learn, adapt, and make a better tomorrow.

I’ve enjoyed revisiting Cosmos one more time; I’m sure I will do it again, many times in the future.  On this particular visit, I did something I hadn’t done before — I tried to add to the stories, as many of you reading along know (my series started here).  All told, this game produced 31,000 words posted to the blog (not including this post).  I learned some new things along the way, and enjoyed myself immensely. For now, this is the last bit that I’ll write about Cosmos directly, though I’m sure we’ll return to it now and again in the future.

For the moment then, my Personal Voyage has come to a resting point.  In a few short hours, we will all return once again to a broken cliff on the shores of the Pacific Ocean, a place where more than thirty years ago we set off on a journey with Carl Sagan to explore the Cosmos.  Tonight, we’ll start the journey anew, with a new guide.  Like that first personal voyage, this one promises to be full of wonder, mystery, introspection, and discovery.  It’s time to get going again.

Carl Sagan, on the Pacific Coast, where the Cosmos journey began.

Carl Sagan, on the Pacific Coast, where the Cosmos journey began.

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This post is the last in a series celebrating the forthcoming science series, Cosmos: A Spacetime Odyssey by revisiting the themes of Carl Sagan’s classic series, Cosmos: A Personal Voyage.  The introductory post of the series, with links to all other posts may be found here:  http://wp.me/p19G0g-dE

Cosmos 13: Who Speaks for Earth?

by Shane L. Larson

Let me tell you a story about me that many people don’t know. When I was in junior high school, I was a small, exceptionally nerdy child who loved Star Trek, science, games of all sorts (provided they didn’t involve “teams” or “athletics”), and learning. My very best friend of the day was a similarly minded young gentleman, who introduced me to computer gaming (“Colossal Cave”, which we played on the mainframe at Ball Aerospace, where his father worked), World War II aircraft, and car mechanicing. He also had epilepsy. It was frightening when he would have seizures, because he would go blank and suddenly it was like he didn’t know me or anything about the world around him. I don’t recall how long these episodes would last, but what I do remember is his father would swoop in, and sit with him for time, and eventually my friend would be back, and we’d be off to explore the world again.

A scar on the orbit of my left eye; stitches in my 7th grade year. The scar has faded slowly over the years, but is still obviously there if you know to look for it.

A scar on the orbit of my left eye; stitches in my 7th grade year. The scar has faded slowly over the years, but is still obviously there if you know to look for it.

Now, as was often the case in the cruel world of middle-school aged children, we were the target of bullies. My locker neighbors reveled in shutting my locker each time I opened it, or knocking all my books on the ground so I was tardy to next period. Once they took my prized possession of the day, the Collected Novels of H.G. Wells; when I decided that day to fight back, I was bodily thrown across the room into a metal chair, gouging myself on the orbit of my left eye, requiring 7 stitches and leaving a scar I still have today. My best friend was a similar target, with more serious consequences because the physical bullying would often trigger a seizure. The school administration took an all too common viewpoint on these matters: no one saw it, so it is your word against theirs. An odd viewpoint in light of the amount of blood streaming down my face (I don’t know what the bully had told them, but to be fair I had bit him when he had me in a headlock).

Me and my family, in my high school years. My mom and dad instilled in all three of us boys a robust sense of justice.

Me and my family, in my high school years. My mom and dad instilled in all three of us boys a robust sense of justice.

Now my parents are the most moral, upstanding people I know, and taught me a deep personal philosophy about justice. Now, in the wisdom of my adulthood, I like to hang quotes from Gahndi on it, like “It is better to be violent, if there is violence in our hearts, than to put on the cloak of nonviolence to cover impotence.”  But really, what I remember are words from my Pa: “Bullies are really just cowards, so knock them down. And make sure the bastards don’t get back up.”  The matter all came to a head on a late winter day during my 7th grade year. My best friend had his head bashed against a locker, which triggered a bad seizure. No teacher saw it happen, but I resolved it was going to stop.  At the end of lunch period that day, I bought an extra milk, and opened the carton on both sides. I remember one of my other nerdy-friends standing next to me saying, “Aw, how are you going to drink that now?” I didn’t answer; I was standing behind the locker-basher, who was sitting at a table. I upended the carton of milk over his head, and beat the tar out of him. The event instigated one of the largest food fights the junior high school had ever seen, and I was awarded a 2-week suspension, which I took without argument.

One of the most often reproduced Apollo images; Jim Irwin on the plain at Hadley, in front of the Lunar Module Falcon and Lunar Rover. [NASA Image AS15-88-11866]

One of the most often reproduced Apollo images; Jim Irwin on the plain at Hadley, in front of the Lunar Module Falcon and Lunar Rover. [NASA Image AS15-88-11866]

The aftermath was the most important. My friend and I were never the target of these particular bullies again; nor were we the target of a somewhat wider group of bullies who had always circled on the fringes of our lives. This kind of mayhem was far outside the boundaries of what was expected from me. The event somehow incited some people to ask what really happened, and to pay attention. After a long discussion with the faculty advisor about the event and the reasons behind it, my National Junior Honor Society membership was maintained. My suspension was lifted a week early, so my friend and I both could attend a school assembly featuring Apollo 15 astronaut Jim Irwin, whom we met and talked with! But most importantly, my science teacher docked my term project about the anatomy and life cycles of frogs from a 100% to an 80%, dropping me a letter grade in the class. It blemished an otherwise admirable middle-school academic record. She never said a word, and just kept right on treating me like the scientist she seemed to know I was going to become. She reinforced a lesson my parents had already touted — there are always consequences, even when you are doing the right thing, but it shouldn’t stop you from doing the right thing.

Now, in my adulthood, I still carry that same overbearing, black and white opinion about justice, and an unfailing opinion that people who can stand up should stand up for those who can’t. It is something that I often think about as I push my way blindly forward in my career.  What do I do everyday, when I’m not writing this blog for you to read?  I’m a scientist; an astronomer. What does that have to do with bullies and childhood scraps? Everything in the modern world.

A white dwarf is the skeleton of a star like the Sun, long after it has died. It has about the mass of the Sun, but is the size of the Earth. [Image by STScI]

A white dwarf is the skeleton of a star like the Sun, long after it has died. It has about the mass of the Sun, but is the size of the Earth. [Image by STScI]

In my everyday life as a professional scientist, I spend my time thinking about astrophysics, exploring our understanding of how gravity influences the evolution and life of white dwarf stars, the ancient cooling skeletons of stars that lived their lives like the Sun. Some days, I teach intro science classes to young women and men bound for careers in business, medicine, law and management; people who may never take another science class in their lives, nor think all that much about science ever again. Every now and then, one of them asks me, “What is understanding white dwarfs good for?” There are a whole host of reasons related to how stars act as astrophysical laboratories, simulating conditions that are difficult and expensive to replicate on Earth, and how the knowledge has applications to technology, energy, and medicine.  But the real reasons, the important reasons are these:

(1) Astronomy, unlike bench science in a laboratory, in an exercise in looking, thinking, and understanding Nature from afar. The practice of astronomy teaches us how to think deeply about the Cosmos, how to unravel the secrets of Nature, and not fool ourselves into thinking something false. More than any other science, astronomy teaches us to be harshly critical of our reasoning, to be brutally honest about what we know and don’t know, and to be quite certain of our conclusions when we say them out loud.

secretCancer(2) Every person has a deep seated sense of wonder, waiting to be ignited and tapped. We cannot know who or what will inspire those who see the future for us, but we know it will happen, just as it has happened in the past to people named Steve Jobs, Temple Grandin, Dean Kamen, Rachel Carson, and a thousand others. We explore, learn, and teach the wonder of the Cosmos with the certainty that it can and will inspire someone someday to consider a life in science and technology, a life in service to our species and our planet. The consequences of not teaching people about the wonders of astronomy are almost too awful to contemplate. What if the next Newton never discovers science? What if the cure to cancer is hidden inside someone who is never inspired to continue their education?

(3) Lastly, in a world increasingly dependent on science and technology, science has become a weapon.  Not a a tangible device of destruction (though there are certainly plenty of examples of those), but a psychological bludgeon used to prey on those who have weakness or uncertainty in the realms of science and evidence based reasoning. The Earth faces an uncertain future in terms of its long term evolution, and the survivability and impact of our species on this planet. Special interests, driven by economics, politics, or ideology, have become the bullies of the modern world. Their tactic of choice is the subversion of knowledge and evidence-based wisdom, using modern media to sow uncertainty and discontent, holding the world hostage in a constant state of confusion and embittered debate. The weapon against those with shallow vision and self-serving interests is critical thinking, and common cause.  For the first time in all the history of the Earth, we have both. The practice of science is the human species’ profound realization of the process of critical thinking; it’s only goal, is to seek the truth with unflinching respect for the evidence and facts. Technology has given us the ability to communicate, directly and personally, with every person on the planet.

In a 1990 essay for the Committee for Skeptical Inquiry Carl Sagan wrote, “We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology.”  This is a trend that has not changed in the two decades since; if anything, it has become exacerbated as technology and mobile technology has interlinked our world and become enmeshed with our daily lives.

Smartphones and carburetors, two of the great mysteries of the modern world. Making sure everyone can explain their inner workings is not the goal of science literacy.

Smartphones and carburetors, two of the great mysteries of the modern world. Making sure everyone can explain their inner workings is not the goal of science literacy.

The danger is not that people don’t understand the workings of a smartphone touchscreen or the purpose of a carburetor.  No, the true danger lies with people being told what they should think about a complex and interconnected world, instead of being able to think critically about how trustworthy the information being passed to them is. The best way for the citizenry of the Earth to protect themselves from charlatans is to know how science works. The second best way is for scientists to put some more skin in the game.

Science cannot be limited to those who practice it; it cannot be an esoteric playground of wonder and imagination for the privilege of a few.  What scientists know must be explained and popularized for the citizens of the world; people must understand that the purpose of science is to improve their lives, and it has.  Modern medicine has erased crippling diseases, satellites girdle the world providing a never-ending stream of data about the weather and evolving state of the planet, and telecommunications technology has deprovincialized knowledge to build a global community. The world-spanning internet has made communications instantaneous and egalitarian, exposing a vast fraction of the world to the wisdom and art of our species, but also connecting all of us instantaneously to the abject horrors our race is capable of, and showing the implacable forces of Nature casually destroying human constructs. Science is all around us.  It is not perfect, but it has repeatedly demonstrated an unfailing ability to change the world.

There are plenty of vocal scientists and active science communicators.  Phil Plait (twitter: @BadAstronomer) is a robust opponent (among many other things) of the anti-vaccination lobby. James Hansen and Michael Mann (twitter: @MichaelEMann) are prominent faces in the battle against climate denialism. Jennifer Ouellette (twitter: @JenLucPiquant) writes and blogs tirelessly about science and mathematics.  But there need to be more — many more. It is estimated that only 5% of the labor force in the United States are practicing scientists or engineers. That is an extraordinarily tiny fraction, so there is a challenge for everyone.

Richard Feynman

Richard Feynman

On the part of the scientists, the challenge is to talk with your neighbors, talk with your friends, talk with anyone who will listen. There has been a slow and steady decline in the public percpetion of the value of scientists and academics in general.  This has been widely discussed recently in light of an excellent OpEd by Nicholas Kristof. Many academics have taken great affront to this article, but as I tell my 7-year old: how you act is up to you, but how people think you act is up to them. If you want people to change how they think of you, then you have to change how you act (especially when they are watching). In this case, many many decades of unremitting dedication to the urbane life of an academic, steeped in our own traditions and mindsets, have burned bridges that should never have been severed. Scientists are particularly bad at this, and we see the results — charlatans are slowly eroding public confidence in science to the point where despite overwhelming evidence, people don’t know what to think about the future of our planet or species. Richard Feynman always said, “Science is what we do to keep from lying to ourselves.”  Our job is to help people understand that.

George Bernard Shaw.

George Bernard Shaw.

On the part of everyone else, the challenge is learn to think critically, just as you do with everything else in your lives — you are the ones who are going to decide the future of our civilization, with your money, your actions, and your votes. Talk with your neighbors, talk with your friends, talk with your children.  Honor the wisdom of George Bernard Shaw, who admonished us to “Beware of false knowledge; it is more dangerous than ignorance.” We are being bullied, scarred for life, and we don’t even know it.  Forces within our society think they can play on our fears, for their own benefit, by encouraging us to doubt and deny our hard-fought ability to reason.  It’s time to fight back against these nebulous and callous forces, with the most powerful weapon we have: science. Denial of science is a denial of our birthright, an abandonment of a legacy of 40,000 generations of human beings who have walked before us.

With all the long future days of our planet and our race in front of us, there is but one task before us: preserving the lives of the citizens of the Earth, be they human or not, and ensuring the future habitability of this planet, the only place in the Cosmos we know, with certainty, where any form of life can and does survive.

We speak for Earth, you and I.  Our loyalties are to the species, and the planet. We speak for Earth. Our obligation to survive and fluorish is owed not just to us, but to the Cosmos, ancient and vast, from which we spring.

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Final Note: This closing quote, is the closing quote from Cosmos as well. Thank you, Carl, for a journey that defines much of what I think, say, and do every day of my life. From the stars we came, and to the stars we shall return, now and for all eternity.

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This post is part of an ongoing series, celebrating the forthcoming science series, Cosmos: A Spacetime Odyssey by revisiting the themes of Carl Sagan’s classic series, Cosmos: A Personal Voyage.  The introductory post of the series, with links to all other posts may be found here:  http://wp.me/p19G0g-dE