Science Folk Tales

by Shane L. Larson

The Cosmos is a stunning and beautiful place that inspires unabashed awe in many of us. The story of understanding the Cosmos and what makes it tick is what science is all about. But there is an extra dimension to these tales of discovery, and that dimension is the personal stories of the scientists who have wrested utterly amazing secrets from Nature.

Every discovery ever made has a human story at its core. (L to R) Galileo, Henrietta Swan Leavitt, Louis Slotin, and Emmy Noether.

Every discovery ever made has a human story at its core. (L to R) Galileo, Henrietta Swan Leavitt, Louis Slotin, and Emmy Noether.

The human stories wrapped around science stories touch each one of us on a deep level because we can identify with the uniquely human response to difficulties, to friendships and collaborations, to confusion, to success and elation, and sometimes to tragedy. Can you imagine Galileo’s astonishment when he saw craters on the Moon through his little telescope, something no one had ever seen before? Can you feel the elation Henrietta Swan Leavitt must have felt when she discovered she could measure the distance to the stars? We can sympathize with the colleagues of physicists Henry Daghlian and Louis Slotin, both of whom died from radiation exposure in accidents at Los Alamos during the Manhattan Project. We are horrified by the unexpected death of Emmy Noether, one of the greatest mathematical physicists of the early 20th Century, who died suddenly from complications after an operation.

The stories of the scientists at the heart of discovery remind us that science is an all together human endeavour; we are the only species, so far as we know, to systematically explore and understand the Cosmos. We are one of the few species that use an understanding of the Cosmos to improve our lives. Mixed in with the biographies and well documented histories of science, there is also a bit of folklore — funny tales and anecdotes that capture the endeavour in small vignettes. I think sometimes we tell these bits of folklore, whether they are true or not, because they often capture some of the ephemeral emotions that we all feel when faced with the Big Questions in the Cosmos. One of my favorite examples of this kind of folklore has to do with the realm of the atoms, quantum mechanics, and Albert Einstein.

The emission spectrum of hydrogen has a few bright lines, as well as many faint lines.

The emission spectrum of hydrogen has a few bright lines, as well as many faint lines.

In the early part of the 20th Century, physicists were trying to understand the discrete colors of light emitted and absorbed by hydrogen atoms. All atoms have a unique and discrete spectrum of light they emit — a spectral fingerprint that identifies precisely what kinds of atoms you are working with. Hydrogen, being the simplest of atoms, was the focus of everyone’s attention, in the hopes it would be the easiest to understand. There was an empirical formula for the hydrogen spectrum — a simple formula that was worked out from observations — but no one knew why the formula worked. It just did!

bohr

The first clue as to what was going on came from Danish physicist, Neils Bohr, who proposed something we now call “the Bohr Model of the Atom” in 1913; it is just the classic picture of an atom that we are all taught in grade school.  Bohr’s colleague, Ernst Rutherford had shown in 1911 that the atom was comprised of two parts — a small, hard center called “the nucleus” and an outer cloud where the electrons resided.  Bohr discovered that if the electrons are required to reside on orbits — circles of specific size — he could predict exactly the spectrum of colors emitted by hydrogen. The Bohr Model was one of the early discoveries that helped drive the emerging branch of physics called “quantum mechanics,” which was concerned primarily with how the world behaves on the smallest scales imaginable.

The classic "Bohr-Rutherford atom" with a small central nucleus being orbited by electrons on fixed orbits.

The classic “Bohr-Rutherford atom” with a small central nucleus being orbited by electrons on fixed orbits.

One of the interesting features of the Bohr-Rutherford atom is that it is mostly empty space. The nucleus is only about a femto-meter across.  That’s one-billionth-millionth of a meter, 0.000 000 000 000 001 meters. By contrast, the electron cloud is about a million times larger, about a tenth of a nano-meter across. That’s only 0.000 000 000 1 meters. That means the atom is mostly empty space. Now think about that for a minute. That sounds crazy, because if atoms are mostly empty space, then you are mostly empty space, and so is everything else!

That notion certainly doesn’t jive with your everyday experiences. When you fall off your mountain bike, you most certainly collide with the ground and stop! If you and the ground were both mostly empty space, shouldn’t you just pass right through each other? It would be a lot less painful! It turns out that electrons dislike being around one another — they are “electrically repulsive.” The reason you and the ground bounce off of one another is because the electrons in the ground repulse the electrons in you. But if the electrons are on little orbits, wouldn’t they still usually miss each other? As it turns out, the little orbits picture isn’t the right picture to carry around in your head; the sub-atomic world is much stranger than that.

The Bohr-Rutherford model of the atom was one of the central starting points in the development of quantum mechanics, the branch of study concerned with understanding the interactions and dynamics of particles on the scales of atoms. Over the course of two decades following Bohr’s model, all the major tenets of quantum mechanics were discovered. The cacophony of quantum effects that were amassed and tested in this time were triumphant revelations about the world of small things, but they all smacked of absurdity because they almost always clash with the direct sensory reality of what goes on in the macroscopic world.

The shape and direction of electron orbitals found in atoms.

The shape and direction of electron orbitals found in atoms.

One of those discoveries was that the position of tiny particles, like the electron, were not so easy to nail down. In fact, the electron was known to inhabit areas around the nucleus of an atom that we now call “orbitals” — extended regions of space where we are “most likely to find the electron” if we go looking for it.  The reality of “position” was suddenly replaced by the idea of probability and statistics. There was no definitive answer anymore to the question of “where is the electron?”  A new mathematical entity was discovered to describe this idea, called a “wavefunction.”

So what’s going on? We said Bohr’s model completely and accurately described the spectrum of hydrogen by imagining the electron was a little ball going around a fixed orbit. How can that be right, AND this electron probability cloud be right? Insights into the physical world often capture precisely the correct physics, but the picture we carry around in our head or the words we use to describe what has been captured in the mathematics are incomplete. This is the case of the Bohr atom. Bohr’s mathematics was correct, and explained the behaviour of the hydrogen atom, but the picture of an electron going around on a little orbit was not the correct picture, because it didn’t capture one important aspect of the physics, namely why only certain orbits were allowed. The reason was a discovery of one of Bohr’s contemporaries, and points the way to wave mechanics.

Louis_de_Broglie10Louis Victor deBroglie proposed in his 1924 PhD thesis that all matter behaves like waves, including electrons. This idea is known as “wave-particle duality.” The idea was so radical, his graduate committee didn’t know what to make of it. They passed the work on to Einstein, who supported it whole-heartedly, and deBroglie was awarded his PhD. Five years later, deBroglie was awarded the Nobel Prize in Physics for his discovery. How did this connect the Bohr atom to wave mechanics? deBroglie suggested that if the electron were a wave, the only Bohr orbits that were allowed were those which perfectly fit an electron wave around it. Thus the electron was not a particle located somewhere around the orbit, rather it was the entire wave that covered the entire orbit.

How deBroglie explained Bohr's restriction of orbits. (L) If an electron wave does not fit on an orbit perfectly, the orbit is now allowed. (R) The only orbits are the ones where the wave fits perfectly.

How deBroglie explained Bohr’s restriction of orbits. (L) If an electron wave does not fit on an orbit perfectly, the orbit is not allowed. (R) The only orbits are the ones where the wave fits perfectly.

The reality of the wavefunction idea was born out in experiments time and time again, forcing physicists to accept that the microscopic world was truly different than the world of Big Things like ping pong balls, Yugos, hedgehogs and popsicles. But there are certain implications of accepting the wavefunction idea that are even weirder than not knowing where the electron is. One of those things is quantum tunneling.

Imagine I have a pet electron, trapped in an aquarium. Where is the electron?

Imagine I have a pet electron, trapped in an aquarium. Where is the electron?

Imagine I caught an electron and am keeping it as a pet in an aquarium in my living room. According to quantum mechanics, if I go looking for my electron, I am most likely to find it in the aquarium. But the wavefunction extends oustside the aquarium, and that means there is a teeny-tiny probability that the electron will be found OUTSIDE the aquarium. If I do find it there (sneaky little quantum jailbreaker), we say that the electron “tunneled” through the barrier of the aquarium wall.

This really happens. If it didn’t, you wouldn’t be reading this blog post, because modern microchips work on the premise that electrons can tunnel their way through barriers; this is one of the operational principles behind transistors and diodes, which make up a significant fraction of the guts of your computer.

I don't know if Einstein had giant clown shoes, but he was well known to own and use some fuzzy slippers.

I don’t know if Einstein had giant clown shoes, but he was well known to own and use some fuzzy slippers.

And this brings me back to our starting point: folklore. There is a story that Einstein was so uncomfortable with this idea of tunneling, that he took to wearing gigantic shoes around his house (I imagine them to be kind of like giant clown shoes), in order to inhibit his feet from tunneling through the floor while he was walking around! Now, this story about Einstein is almost certainly false; Einstein was perfectly aware of the fact that quantum effects are not important on the scales of the macroscopic, and he was certainly capable of computing the probability of his feet tunneling through his floor!

But we tell this tale tale anyhow, not because it is funny, but because quantum mechanics IS disconcerting! Quantum tunneling makes NO SENSE, especially if you are used to thinking about hacky-sacks, pomegranates, and freight trains. We use this story to tell ourselves that Einstein was uncomfortable with this idea, thus reassuring us that it is okay for us to be uncomfortable too.

And it is okay to be uncomfortable. Discomfiture over cherished ideas being challenged and overturned is the bread and butter of science. This is how our knowledge grows, and how our understanding of the Cosmos evolves to be more complete. We abandon old beliefs, no matter how cherished, if we find them to be unworkable in the face of new data and new knowledge.

A Pale Blue Glow

by Shane L. Larson

One of the great things about being a scientist is I’m exposed to amazing and awesome things. Every. Single. Day. Sometimes I am astonished by Nature itself, and other days I am amazed by our ingenuity and abilities as we come of age in the Cosmos. Today was one of those days.

The first picture of the Moon and Earth together in space, taken by Voyager 1.

The first picture of the Moon and Earth together in space, taken by Voyager 1.

This story has its origins long ago. On 5 September 1977 we hucked a 722 kg spacecraft into the sky, named Voyager 1. That was the last time any of us ever saw Voyager 1 with our own eyes. But Voyager has been on a 37-year journey to act as our eyes in the Solar System. On 18 September 1977, barely 13 days after launch, when it was 7.25 million miles from Earth, Voyager sent home the first picture ever of the Earth and Moon together in space. It went on to Jupiter, where it took pictures of clouds and storms that look for all the world like the finest paintings on Earth, and discovered the first active volcanoes beyond the Earth on the enigmatic moon Io. At Saturn, it returned the first high-resolution images of an exquisite ring system, and showed us a shattered Death Star like Moon known as Mimas, dominated by an enormous crater named Herschel. But for all the wondrous pictures, we never saw Voyager. Like your Mom taking pictures of your childhood, we have never once seen the photographer chronicling our growth.

Just a sample of the kinds of discoveries made by Voyager 1. (TopL) Exquisite cloud structure on Jupiter. (TopR) Active volcanism on Jupiter's moon, Io. (BottomL) Tremendous structure in Saturn's rings. (BottomR) Saturn's moon, Mimas.

Just a sample of the kinds of discoveries made by Voyager 1. (TopL) Exquisite cloud structure on Jupiter. (TopR) Active volcanism on Jupiter’s moon, Io. (BottomL) Tremendous structure in Saturn’s rings. (BottomR) Saturn’s moon, Mimas.

But today, I saw something that made me smile. Since it began its long outbound journey, we’ve been talking with Voyager 1 on a radio. In all, it only transmits about 20 watts of power, something typical of a larger compact-fluorescent-lightbulb. The total power received on Earth from Voyager is about a ten-billionth of a millionth of a watt. In one second, we receive less than a trillionth the energy a single snowflake delivers to your shoulder as you’re walking to work.

VLBI image of Voyager 1, diligently beaming its signal back to Earth.

VLBI image of Voyager 1, diligently beaming its signal back to Earth.

But take a look at the picture above, released by NASA last fall. See that pale blue dot right there? That is Voyager 1, seen through the eyes of the Very Long Baseline Interferometer, an array of linked radio telescopes that stretches from one side of the Earth to the other. It sees the sky in radio light. Normally it looks at quasars and distant nebulae, but this image is of Voyager 1, shining its radio back at Earth. This is the first radio signal of human origin ever to be received from outside the solar system. It is also the first picture of Voyager 1 taken since its launch. It’s a bit like seeing your friend in the dark, waving their cellphone at you from a distant mountaintop.  But it’s there, and we can see it — the pale radio beacon of Voyager 1, drifting alone in the immense dark between the stars.

Long after it runs out of power, Voyager 1 will continue to drift alone through the galaxy.

Long after it runs out of power, Voyager 1 will continue to drift alone through the galaxy.

What will happen to Voyager 1? It will continue to talk to us for a little while longer. It is powered by a small nuclear power plant, gleaning energy from the decay of plutonium. But that energy supply is dwindling, and sometime around the mid 2020’s, just more than a decade from now, Voyager 1 will fall silent. The pale blue glow will disappear forever; there will be no more pictures of our loyal emissary. Voyager 1 will continue onward however, bound for the depths of the galaxy, a dead hulk built by a race of curious lifeforms that call themselves “humans.”

But now this has me thinking. All of our knowledge of the outer solar system has been gleaned with telescopes, and with robotic emissaries.  None of the sights you have seen in pictures has ever been witnessed directly by human eyes. Not the dual-tone colors of Saturn’s enigmatic moon Iapetus; not the spider-web of canyons in Mercury’s Caloris Basin; not the misty depths of the Valles Marineris on Mars. Instead, Casinni has been twirling through the Saturn system for almost a decade, and has returned the highest resolution images of Iapetus we’ve ever seen.  Mercury MESSENGER, only the second spacecraft ever to visit Mercury, finally arrived in 2011 and sent high resolution images of the Spider Crater back to Earth. And Mars? Well, Mars has its own fleet of orbiting satellites and ranging rovers to investigate its mysteries.

(L) Saturn's moon Iapetus has a light and a dark side. (C) The Spider Crater on the floor of Mercury's Caloris Basin. (R) Fog in the Valles Marineris on Mars.

(L) Saturn’s moon Iapetus has a light and a dark side. (C) The Spider Crater on the floor of Mercury’s Caloris Basin. (R) Fog in the Valles Marineris on Mars.

What happens to all our tiny robots, sent out into the Cosmos all on their own? We’ve been tossing them into space almost non-stop since the start of the Space Age — what happens to all of them?

Only 5 will ever travel beyond the solar system. Pioneers 10 and 11 are both bound for interstellar space, now quiet and dead after their power supplies failed in 2003 and 1995. Voyager 1 and 2, having completed their Grand Tour of the outer solar system, are also outbound; we expect to lose contact with them within the next 10 to 20 years. And lastly, there is New Horizons, bound for Pluto and the Kuiper Belt beyond. It is by far the youngest of this august group of explorers. It was designed to have power for 20-25 years, but it has already spent the last eight-and-a-half years just getting to Pluto — it should last another 15 years or so.

Spacecraft that are going to escape from the solar system. (L) Pioneer (C) Voyager (R) New Horizons

Spacecraft that are going to escape from the solar system. (L) Pioneer (C) Voyager (R) New Horizons

(T) When Spirit got stuck on Mars, NASA engineers recreated the situation on Earth, trying to figure out how to free the rover. (C) Artist's imaging of what Galileo looked like as it burned up in the Jovian atmosphere. (B) The LCROSS mission before impact.

(T) When Spirit got stuck on Mars, NASA engineers recreated the situation on Earth, trying to figure out how to free the rover. (C) Artist’s imaging of what Galileo looked like as it burned up in the Jovian atmosphere. (B) The LCROSS mission before impact.

Many of our robots, like the Voyagers and Pioneers, will just die. This famously happened to the Spirit rover on Mars. It trundled around the Martian surface for 2269 days (perhaps, some say, trying to earn a trip back home) before we lost contact with it. Spirit had become stuck in a Martian sand dune and was unable to free itself. Stuck on flat ground, unable to tilt itself toward the Sun to keep warm in the cold Martian winter, we last spoke with Spirit on 22 March 2010.

The Galileo mission, which spent more than seven-and-a-half years exploring the Jovian system, was crashed into Jupiter, to prevent it from tumbling out of control when its power failed, possibly contaminating a moon like Europa, where we can imagine extraterrestrial life may exist. On 21 September 2003, it was plowed into Jupiter. We couldn’t see it take the final plunge, but we listened to it faithfully radioing us everything it could for the last few hours before its end.

Sometimes, we crash our spacecraft on purpose, for science! One of the most spectacular examples of the was LCROSS, the Lunar Crater Observation and Sensing Satellite. This goal of this mission was to look for water ice in the perpetually shadowed craters on the surface of the Moon; water on the Moon would have important implications for the sustainability of lunar colonies. LCROSS had two pieces — it’s Centaur rocket stage, and the Shepherding Spacecraft that carried the science instruments. On 9 Oct 2009, the Centaur rocket impacted the Moon at a speed of about 9000 kilometers per hour; the Shepherding Spacecraft flew through the cloud of debris and radioed the composition back to Earth. This exquisitely timed dance was a planned suicidal flight for the Shepherding Spacecraft; its unavoidable fate was to impact on the Moon about 6 minutes after the Centaur stage. The result? There is water, frozen in the lunar soil.

But the saddest fate to me, is that of Mercury MESSENGER. MESSENGER was the first spacecraft to visit Mercury since Mariner 10 flew by three times in 1974. Despite three passes, Mariner 10 only mapped out about 45% of the surface; until MESSENGER’s arrival in 2011, we had no idea what more than half of Mercury looked like.  It took MESSENGER 7 years to get to Mercury. It has been there for about three-and-a-half years at this point, and we are looking ahead to the end. Over time, the closest point of MESSENGER’s orbit has been getting lower and lower, affording us the opportunity to understand Mercury’s gravitational field and to map and  probe the surface of Mercury with exquisite resolution. But lowering the orbit, to get a closer view of the planet, is a one way ticket, eventually leading to MESSENGER’s impact on the surface of Mercury.

Mercury MESSENGER

Mercury MESSENGER

The end will come sometime in March of 2015, on the far side of Mercury from our view.  MESSENGER will die alone, cut-off from us by distance and astronomical happenstance. In the words of MESSENGER PI, Sean Solomon, “This will happen in darkness, out of view of the Earth. A lonely spacecraft will meet its fate.”

This emotional attachment and personification of machines seems disingenuine to some people; spacecraft aren’t people, they are collections of wires and circuits and nuts and bolts — they don’t have souls to become attached to.  I dunno. I think they do have souls. They are the embodiment of every one who ever imagined them, worked on them, or stared at the data and pictures they returned. These little robots, in a way, are us. They are our dreams. Dreams of adventure, of knowledge, of a better tomorrow, of understanding who and what we are in a Cosmos that is vast and daunting.

And so today I smiled at the pale blue picture of our long departed friend, Voyager 1. And on the day it falls silent, I’ll shed a tear and drink a drink to its remarkable voyage, a voyage it made for you and me.

A Thin Rain of Black Holes

by Shane L. Larson

As a scientist, I am used to being humbled by Nature. Consider how difficult it is for us to replicate physical situations that the Universe creates and maintains almost effortlessly. For instance, in the central African nation of Gabon, in the hills near the eastern border, there are vast deposits of Uranium ore in an area known as Oklo. Analysis of the Oklo ore has shown that it has been processed via nuclear fission roughly 2 billion years ago. All on it’s own, Nature created and ran a nuclear reactor.

The Oklo natural reactors are found in exposed ore deposits in central Africa. Note the person for scale!

The Oklo natural reactors are found in exposed ore deposits in central Africa. Note the person for scale!

Human beings didn’t even know of the existence of nuclear fission until 1938 when Otto Hahn and Fritz Strassman first detected it in the laboratory; it wasn’t understood until the following year when Lise Meitner explained what was going on! It would take a further 4 years and a huge team of scientists and engineers, supervised by Enrico Fermi, to create the first nuclear fission reactor under the football field at the University of Chicago. On 2 December 1942, “Chicago-Pile 1” became active, finally replicating what the Universe had figured out 2 billion years before.

(L) Strassman, Meitner and Hahn in 1956, at the dedication of the Max Planck Institute. (R) The Hahn-Meitner-Strassman experimental setup that first detected nuclear fission. Note it fits on a tabletop!

(L) Strassman, Meitner and Hahn in 1956, at the dedication of the Max Planck Institute. (R) The Hahn-Meitner-Strassman experimental setup that first detected nuclear fission. Note it fits on a tabletop!

Today, our experimental efforts in science have continued to grow, continued to allow us to peer into Nature’s great mysteries. One of the most prominent efforts is the construction of the Large Hadron Collider (LHC) outside of Geneva, on the border of France and Switzerland.  All told, more than 10,000 scientists and engineers from 100 countries contributed to the design, construction, and operation of the LHC.  It is the most powerful particle-collider in the world, smashing together hadrons (particles that are made up of quarks, bound together by the strong force).

An aerial view of the area around Geneva, with the location of the LHC indicated; the tunnel is 27 kilometers in circumference. Center left is Lake Geneva, the background are the Swiss Alps.

An aerial view of the area around Geneva, with the location of the LHC indicated; the tunnel is 27 kilometers in circumference. Center left is Lake Geneva, the background are the Swiss Alps.

The LHC is an enormous machine. The ring is 27 kilometers in circumference, and the major experiments that watch the collisions of sub-atomic particles are bigger than buildings — gigantic, complex machines designed to watch what Nature does on the tiniest scales, which we have only begun to understand over the past 100 years.

The ATLAS experiment, along the beamline of the LHC. It is difficult to comprehend exactly how huge these experiments are, but note the person in front of the experiment, lower center!

The ATLAS experiment, along the beamline of the LHC. It is difficult to comprehend exactly how huge these experiments are, but note the person in front of the experiment, lower center!

The collision energies in the LHC are so high that the protons we smash together break apart into their constituent bits: quarks, gluons, and a lot of energy. At its highest energies — as physicists say, “14 TeV” or “14 Tera-electron-Volts” — the protons we are smashing together will only be travelling about 2.7 meters per second slower than light. What does that mean? Imagine a race to the Moon, between a laser beam and a proton ejected from the LHC. The laser beam would reach the Moon in 1.282 217 0463 seconds, but the protons would only be 11.3 meters behind, arriving at 1.282 217 0578 seconds after the race started. They are moving incredibly fast, which is why they blast themselves to smithereens when they collide.

The post collision mess is a hot writhing, seething mass of energy and fundamental particles that we think is very similar to the conditions just after the Big Bang. At some point in our planning for the LHC, and as we were imagining this hot burst of quark-gluon plasma, someone asked a very interesting question.  Aren’t the collisions strong enough that all of the energy could concentrate mass and energy down to a microscopic point, creating a microscopic black hole? After all, that’s what we expect to happen after the Big Bang — we call them “primordial black holes.”

And then what you’re saying sinks in. We can MAKE black holes? What could happen? Could they sink to the core of the Earth and slowly consume the Earth? If that happened, is there anything we could do about it? This is an idea that has been explored in science fiction before, notably by my astrophysics colleague, J. Craig Wheeler, in his 1986 novel, The Krone Experiment. But what about the case of the Large Hadron Collider? Should we be worried?

There are two very simple reasons why the answer should be “No.”  First and foremost, the protons are travelling at enormous speeds, 99.999 999 1% the speed of light, and the post collision detritus will be travelling at similarly high speeds, propelled by the enormous release of energy in the collision.  Anything travelling at 11.2 kilometers per second or faster can escape the gravitational pull of the Earth.  How fast is 11.2 kilometers per second compared to lightspeed?  That is 0.0037% the speed of light. Any microscopic black holes created by the LHC will easily be travelling so fast that the Earth’s gravity could not possibly keep them stuck here.

Second is this: Nature is far better at making particle accelerators than we are. The LHC energies are paltry compared to the energetic particles that the Cosmos is bombarding the Earth with every single minute of every single day.

The Earth is constantly under the drizzle of a thin cosmic rain (that turn of phrase is the title of an excellent book by Michael Friedlander) of particles from outer space, called “cosmic rays.” These particles come from all over — the vast majority are from the Sun, but others come from highly magnetized stars, or from supernovae, or from shock fronts in vast clouds of interstellar gas and plasma, or from active galactic nuclei, or from black holes. They are constantly bombarding the planet in vast numbers; we like to tell people that TWO cosmic rays go right through your head, every second. :-)

Cosmic rays constantly bombard the Earth. Very often they collide with particles in the Earth's atmosphere, creating MORE particles (just like collisions in the LHC) when then shower down to Earth.

Cosmic rays constantly bombard the Earth. Very often they collide with particles in the Earth’s atmosphere, creating MORE particles (just like collisions in the LHC) when then shower down to Earth.

Like the particles in the LHC, every cosmic ray that hits the earth has an energy, sometimes a very large energy. Imagine grabbing some masking tape and marking out a square on the floor next to you, 1 meter by 1 meter. About 1 time per hour, every hour, a cosmic ray with the same energy as an LHC collision passes through your square.  And not just for your square — for EVERY 1 meter by 1 meter square you could make on the surface of the Earth! In the 15 minutes it takes you to read this article, roughly 10 such events will happen right in your living room. In one year, across the surface of the entire Earth, there are about 4 billion billion such events (4 x 1018).

When astronomers talk about cosmic rays, they often think about something called FLUX -- how many particles go through a known area in a known time. The cosmic ray flux at LHC energies is about 1 particle in a square meter (the blue square in this image) every hour.

When astronomers talk about cosmic rays, they often think about something called FLUX — how many particles go through a known area in a known time. The cosmic ray flux at LHC energies is about 1 particle in a square meter (the blue square in this image) every hour.

But that’s not the whole story either. Because at higher energy, it should be easier to make black holes, right? If I smash harder, I can compress more, and get into that black hole state much more easily. Imagine making a square 1 kilometer by 1 kilometer.  About 1 time every year, a cosmic ray particle will hit that square with an energy that has 1 MILLION times the energy of the LHC. That means every square kilometer on Earth (0.4 square miles) will get hit about 1x per year by a particle that has about 1 MILLION times the energy of the LHC. Over the entire surface of the Earth then, there are about 500 million events every year that have 1 million times the energy of the LHC.

And this has been going on for the entire 4.5 billion year history of the solar system!

Because of this, most scientists aren’t worried by the idea that the LHC could make black holes or transform the quantum state of the Universe, because Nature is already doing its best to do the same thing, and doing it at energies we could only imagine in our wildest experimental dreams.

I’m not worried about the LHC making microscopic black holes. You should not be worried about the LHC making microscopic black holes. Because there is probably already a thin rain of them showering over us every moment of every day. Thanks, Universe!

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This post is based on a short “Expert Show” talk I gave at the iO Improv Theatre in Chicago; I talked for about 10 minutes about the LHC and black holes, and then the improv troop took over. :-)

Stand in the Shadow of the Moon

By Shane L. Larson

Imagine a late August morning on the Oregon seashore. Around 10 AM the morning breezes whip your hair around your face. You can hear the crying call of gulls over the relentless crash of waves on the packed sand of the beach. Rocky hills and cliffs rise up to the north and south, giving way to green forests that race eastward toward the seaside town of Lincoln Beach, Oregon.  The water is cold here — the currents flow south along the Oregon coast after skirting the shores of Alaska far to the north; you’re thankful for the warm Sun on your back, drying you off after a brave leap into the chilly water.

Photograph of the 1919 eclipse captured by Sir Arthur Stanley Eddington on an expedition to test general relativity. With the face of the Sun occulted, the outer corona is visible to the naked eye.

Photograph of the 1919 eclipse captured by Sir Arthur Stanley Eddington on an expedition to test general relativity. With the face of the Sun occulted, the outer corona is visible to the naked eye.

But the warm respite provided by the Sun on this morning is soon interrupted, because to the west, beyond the distant horizon, a vast darkness is racing across the Pacific toward you. Around 10:15am, you will experience the darkness  yourself — it will race inland across the Pacific coast, and for 1 minute and 58 seconds, the Sun will vanish, its once brilliant disk replaced by an inky black orb surrounded by ghostly streamers, silently dancing in the sky where moments before you had seen blue skies and that seemingly eternal friend that has warmed and comforted you since childhood. The skies will darken as if night had fallen, the temperature will noticeably drop, and nighttime birds and insects will suddenly become active.  You will be experiencing one of the great spectacles of Nature: a total solar eclipse. But your two minutes of darkness will pass quicker than you can imagine, and the Sun will suddenly appear, as the darkness that you once stood in races eastward toward inland North America.

You will be able to experience this, almost exactly as I’ve described it, on 21 August 2017, when a total solar eclipse crosses the United States from Oregon to South Carolina. It will be the first total solar eclipse visible in the United States since 1979. This is your chance to see what I’ve described, with one notable exception: you will probably be surrounded by thousands of others who have traveled to the centerline to witness this spectacle and stand in the darkness. Never-the-less, it is well worth the experience, and I suggest you start making travel plans now!

What is a total solar eclipse? A total solar eclipse happens when the Moon passes between the Earth and the Sun. When that happens, along a thin path on the Earth, you can see the Sun completely covered by the Moon. For a couple of minutes along the eclipse line, day becomes night — the bright face of the Sun is hidden, making a halo of blazing streamers known as the corona.

A total solar eclipse occurs when the Moon passes between the Earth and Sun. The Moon's shadow races across the surface of the Earth, blotting out the Sun for those who stand under the racing shadow. [Illustration by S. Larson]

A total solar eclipse occurs when the Moon passes between the Earth and Sun. The Moon’s shadow races across the surface of the Earth, blotting out the Sun for those who stand under the racing shadow. [Illustration by S. Larson]

Because the Earth is spinning and the Moon is moving in its orbit, the shadow is moving along, just like your shadow does when you are moving. The combined motion of the Moon in its orbit with the spin of the Earth means the shadow will rocket across the North American continent at 1200 miles per hour. From the moment total shadow first occurs on the Oregon coast (10:15:58am MDT) to the last moment of total darkness on the South Carolina coast (2:49:01pm EDT), only 1 hour 33 minutes and 3 seconds will have elapsed. After that, the event will be all over for those of us rooted to the land.

Track of the 21 Aug 2017 total solar eclipse across North America. The red line is the centerline; anyone standing between the blue lines at the right time will witness the entire Sun being hidden by the Moon.

Track of the 21 Aug 2017 total solar eclipse across North America. The red line is the centerline; anyone standing between the blue lines at the right time will witness the entire Sun being hidden by the Moon. Map from NASA’s eclipse page.

Can you imagine what it was like, hundreds or thousands of years ago, before we had blogs and newspapers and radios to tell us all of upcoming astronomical marvels? The astronomical know-how to predict (and explain!) eclipses has been around for sometime, understood in the Middle Ages by priests and astrologers and in more recent eras by scientists and astronomers. But there was no way (or reason?) to tell anyone what was going to occur. If you and I were peasants in medieval times, we should have been dumbstruck with terror to witness the Sun being eclipsed, yet today we know it is a great marvel and wonder to behold.

The fact that we have such beautiful eclipses on Earth is a matter of complete, cosmic happenstance. It just so happens that the Moon and the Sun appear to be about the same size in the sky, so the Moon can almost perfectly cover the Sun. But this will not always be the case. At some point in the distant future, there will be one last, perfect total solar eclipse, and then none ever again.  There will come a day when there are no more eclipses on planet Earth.

The reason is that the Earth and the Moon are locked together in an inexorable gravitational dance. These two worlds have been locked together almost since the beginning of the solar system. You can see evidence of their sensuous cosmic tango every day. The relatively large size of both bodies, and their proximity, means that each has a profound effect on the other, largely through tides.

Most of us are familiar with the notion of ocean tides — the daily rise and fall of the seas on the Earth’s coasts. These cycles of high and low tides are caused by the effect of the Moon’s gravity on the Earth. The Moon’s gravity pulls on the parts of the oceans that are closest to it, causing a “rise” in the sea, a “tidal bulge” that points toward the Moon. There is a second bulge, on the far side of the Earth, caused by the fact that the strength of the Moon’s gravity grows weaker the farther you are from the Moon. The oceans on the far side of the Earth from the Moon get “left behind” as the Earth and near side oceans are pulled more strongly toward the Moon.

(A) The Moon's gravity raises ocean tides on the Earth. (B) The rotation of the Earth pulls the tides out of alignment with the Moon. (C) The Moon tries to pull the tides back into a line, slowing the rotation of the Earth.

(A) The Moon’s gravity raises ocean tides on the Earth. (B) The rotation of the Earth pulls the tides out of alignment with the Moon. (C) The Moon tries to pull the tides back into a line, slowing the rotation of the Earth.

The Earth is constantly rotating, so the interaction of the Earth’s crust with the bulged oceans drags the bulge in the direction the Earth spins, so the bulges don’t point directly at the Moon, rather they point in a direction off to one side of the Moon.

The gravity of the Moon is still pulling on the bulges, so the Moon tries to pull the bulges back in line. Since the Earth is simultaneously trying to move the bulge ahead, the net effect of this gravitational tug-o-war is to slow the spin of the Earth down, ever so slowly (between 15 and 25 millionths of a second every year).

Despite this diminutive change in the Earth’s spin speed, it represents a substantial amount of energy. Where does all that energy go? The only place it can — into the Moon’s orbit. When you dump energy into an orbit, the orbit gets larger. In the case of the Moon, it is getting farther and farther from the Earth every year, at a rate of about 22 mm/yr.

As the Moon gets farther from the Earth, it appears smaller in our sky. Eventually, it will be so small in the sky that it will not be able to cover the Sun, and we will see no more total solar eclipses. At the current rate of 22 mm/yr, the last solar eclipse will happen in about 733,200,000 years.

An annular solar eclipse happens when the Moon is too far away, so it does not appear big enough to cover the entire Sun. [Illustration by S. Larson]

An annular solar eclipse happens when the Moon is too far away, so it does not appear big enough to cover the entire Sun. [Illustration by S. Larson]

Filtered image of the annular eclipse on 20 May 2012 as seen from Cedar City, Utah. [Image by S. Larson]

Filtered image of the annular eclipse on 20 May 2012 as seen from Cedar City, Utah. [Image by S. Larson]

While those days are in the very far future, we sometimes get a hint for what they will be like, because the Moon’s orbit is not perfectly circular, so sometimes it is a bit too far away to completely cover the Sun, and we see an “annular eclipse.”  When this happens, the entire Sun is not covered, and the daylight does not fade. To the unaided eye, the Sun appears much like the Sun always does, but through a filtered telescope you can see that The Moon has clearly occulted the Sun — 733 million years in the future, that is all our descendants will ever see.

But that is not your fate — you live in a time when you CAN witness the spectacle of the eclipsed Sun, and you should.  Take a look at NASA’s eclipse page, and start planning where you might go.  But be quick; before too long, hotels are going to start filling up. Look at that — another one just got sucked up in Casper, Wyoming. :-)

PS: If you for some reason miss this one, you’ll only have another 7 years to wait. There will be another North American solar eclipse on 8 April 2024, running from Texas to Maine. It may not be as easy to get to for most people, but it will be worth the effort. My advice: see the eclipse in 2017, because after your first eclipse you immediately ask, “When is the next one?! :-)  Here is NASA’s page for the April 2024 eclipse.

An #IceBucketChallenge

by Shane L. Larson

Nasa_blue_marbleThe planet Earth, like many planets I suppose, is a planet of wonders. Its landscapes are carved and wrought over aeons of geologic time by titanic forces that are almost beyond our comprehension. Mountains soar to altitudes so high a human can barely breathe; the ocean hides dark depths that have never seen the light of the Sun and never will. Entire continents move, shifting slow and steady, a few inches per year, until the world has utterly changed its face.

One of the greatest wonders of our small blue world, and so far as we know a unique one, is life. Life appears on this planet in myriad forms, and new forms are constantly being discovered and categorized. Over the last several centuries, we have slowly assembled our understanding of the machinery of life — how it works, how it survives, how it perishes.

At the frontiers of our investigations about the workings of life are our attempts to understand the nature of disease. For many diseases, we understand their symptoms, and in some cases what causes a particular disease. We do not in all cases know how to deal with — or how to cure — diseases.

Lou Gehrig in the dugout at Briggs Stadium (now Tigers Stadium) in Detroit, on 2 May 1939. The game marked the end of his 2,130 consecutive game playing streak.

Lou Gehrig in the dugout at Briggs Stadium (now Tigers Stadium) in Detroit, on 2 May 1939. The game marked the end of his 2,130 consecutive game playing streak.

One example is amyotrophic lateral sclerosis (ALS) disease. It is the most common of several degenerative motor neuron disorders. These diseases affect the cells in your nervous system (motor neurons) that control voluntary muscle activity (walking, speaking, breathing, etc.).  In the United States, ALS is commonly known as “Lou Gehrig’s disease,” named after the famed first baseman who played for the New York Yankees from 1923 to 1939. Gehrig was a powerhouse hitter in his day, holding the career grand-slam record (23) for 74 years until it was broken by Alex Rodriguez in 2013, and also the record for most consecutive games played (2130), a record that stood for 56 years until it was broken by Cal Ripken, Jr. in 1995.  Gehrig’s performance and health decreased rapidly in the 1938-39 seasons. He voluntarily benched himself on 2 May 1939 in a game against the Detroit Tigers, ending his consecutive game streak. The Detroit Tigers fans honored him with a standing ovation. In June of 1939, he visited the Mayo Clinic in Rochester, Minnesota, where he was diagnosed with ALS. He passed away two years later, on 2 June 1941.

1024px-Stephen_Hawking_050506In the gravitational physics community, we are at least sub-conciously aware of ALS because it affects one of our own colleagues — Stephen Hawking. Hawking was diagnosed with ALS at a very young age, in 1963 when he was only 21. The life expectancy of those afflicted with ALS is, on average, just a few years; Hawking was told he had about two years to live. Against all odds, he has survived well beyond that prognosis, now made 51 years ago. Hawking is one of a rare few who have survived for so long. It doesn’t happen often, but it does happen. In the time he has had, he has contributed immeasurably to our knowledge of gravitational physics. In 1970, working in classical cosmology he proved a singularity theorem that showed there was a point of infinite density associated with the Big Bang. In 1974 he discovered that black holes over time evaporate, fading away into nothing; we still don’t know what happens during their last moments. In 1988, he published “A Brief History of Time,” one of the best selling public science books of all time, with more than 10 million copies in print.

Few with ALS live as long has Hawking has. Most, like Lou Gehrig, die after only a few years, typically when they lose the ability to trigger the muscles that control breathing or swallowing. There is no known cure for ALS, but in the last few years medical research has begun to reveal what some of the causes are.

Diseases are a part of life. Some diseases are caused by one kind of lifeform infecting another; AIDS is a classic example, caused by a virus that infects the human body. Other diseases, like ALS, appear to be a result of a lifeform’s own machinery malfunctioning or breaking down in some fashion. In ancient times, before science and modern medicine, diseases were poorly understood. Sickness, particularly devastating and debilitating illnesses, killed quickly and were viewed with fear and superstition.  The advent of scientific research began to shed light into the dark corners of our biology, allowing us to understand, at least in part, how to avoid and combat some diseases.  The development of scientific research over the past four centuries has evolved our perceptions of diseases from superstition to knowledge.

motor_neuron2So what do we know about ALS?  It was first identified as a distinct disorder in 1869 by French neurologist Jean-Martin Charcot, who was also the first person to identify multiple sclerosis. However, after its initial identification, very little progress was made in understanding the disease. It wasn’t until 1991 that any kind of genetic connection was made.  Since then, it has also be found that abnormal proteins and neurotransmitters seem to be related to the disease, but our understanding is still evolving. In about 10% of cases, genetics are a contributing factor to the development of ALS. In the remaining cases, where there is no known family history, the causes of ALS are virtually unknown.

Like all scientific investigations, medical research takes time and resources, and progresses slowly. We cannot know what investigations will lead to a breakthrough, so work progresses on many fronts — genetic investigations, studies of degenerating nerve cells,  looking for correlations in environment or lifestyles, searches for therapies and drugs that ameliorate symptoms and prolong life, and more. Eventually, these avenues of investigation lead to treatments and perhaps, someday, cures.

ALS, like other motor neuron diseases, is incredibly difficult to understand and fight. In the United States there is only a single drug approved to use in the fight against ALS, but its efficacy is limited, extending life by only a few months at most. More research is needed; research requires resources.

The ALS Association (http://www.alsa.org/) is an organization dedicated to fighting ALS. It helps fund research internationally, aids patients and families who are living with ALS every day, and works to educate the public about this disease. As a non-profit organization, they are reliant on donations to fund their battle. This year, a viral donation campaign has started to support the fight against ALS, known as the ALS Ice Bucket Challenge. It’s the reason you are reading this post right now.

It goes something like this: I dump a bucket of ice on my head and challenge three other people to do the same within 24 hours or make a donation to ALS research.  Click the donate button the upper right of the ALSA homepage.

I have made two ALS Ice Bucket Videos for the different social media milieus where I post most often — Facebook, and Twitter.  On Facebook, I have challenged several of my friends: they are Trae Winter, Jackie Anderson, and David Zartman.

On Twitter, I have challenged some other folks whom I have not yet found have participated in the challenge. They are: Phil Plait (@BadAstronomer), Scirens (@Scirens), and Lucianne Walcowicz (@shaka_lulu). I also put out a special 4th challenge to another acquaintance of mine: the President and CEO of the Adler Planetarium, Michelle Larson (@AdlerPrez).

In addition to making my challenges, I have also made a monetary donation to the ALSA, and written this blog. Perhaps I’m sentimental because Hawking is a colleague in my scientific field. Perhaps I wonder where physics would be if Hawking had succumbed to ALS in his youth, and by simple extrapolation wonder how much the world has lost because of those that this disease — that any disease — has taken from us. And perhaps I’m just hearing my mother’s voice, telling me that everyone who can help, should help. I can help with this.

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I don’t have any personal friends that I know of who are fighting against ALS. I do however have many friends who are battling or have battled severe and life threatening illnesses — cancer, multiple sclerosis, diabetes, leukemia. This post is dedicated to them all, with much love, admiration, and hope.

Days of Summer

by Shane L. Larson

As a father, I watch my daughter scoot off to summer camp with a vaguely unsettled sense of longing for those by-gone days of my youth. As grown-ups, we don’t go to “summer camp” any more. Instead, we sometimes have “vacation,” but vacation never has quite the same care-free, no-holds barred, reckless sense of fun, adventure and freedom that summer camp always had. There’s just too much of the trappings of being a grown-up tied up in “vacation.”  Too much “enjoying the morning paper by the pool” instead of “dodge-ball.”  Too much “eating a salad with this fancy dinner” instead of “let’s blow every last penny I have in this candy store.”  Too much “looking for the Museum of Historical Art” instead of “standing on our heads to find the Zowie Rock so our cabin wins the giant popsicle tonight!

kayak

But sometimes I find myself in a kayak on a still mountain lake, my phone forgotten (or dropped overboard), and nothing on my mind except that serene fugue state of thought that whispers, “if you keep paddling, there is no telling what’s on the other shore…

As a scientist, I have the immense good fortune of doing something I love every day — probing the mysteries of the Cosmos, mentoring young (and old!) minds on their own voyages of self-discovery, and adding to the collective knowledge of our species. But a job as a scientist is still just like every job, and it has its share of interruptions and stresses. There is always another telecon to be on; there is always another deadline for book orders and class website requests; there is always a student who needs some career advice; there is always another midterm exam to write or grade; there is always another grant you should write a proposal for to support your next student on their path to knowledge. Like every job, there are good days and bad days, and many days that make you long for those by-gone days of summer camp!

aspenPhysics

This year I was able to spend three weeks in a workshop at the Aspen Center for Physics. Founded in 1962 by George Stranahan and Michael Cohen, the Aspen Center for Physics is located on a small, 3 building campus in Aspen, Colorado. It shares this idyllic setting with two other world-renowned intellectual organizations: the Aspen Institute, and the Aspen Music Festival and School. The idea of the Aspen Center for Physics is simple — bring scientists together, away from the demands of every day life, and give them freedom and opportunity to think and interact. Isolation combined with creative intellectual colleagues can and will spawn remarkable and ingenious moments of progress at the forefronts of science.

Let me tell you some tales about my few, short weeks at the Aspen Center for Physics.  If my third grade teacher (Mimi Martin) is out there reading this, you might call this my “What I Did This Summer” essay!

My office at the Aspen Center for Physics

My office at the Aspen Center for Physics

The Setting: The Aspen Center for Physics is set on a small campus with three buildings that are, for the most part, comprised entirely of offices for scientists, and small meeting “alcoves” where groups of us can gather to hash out mysteries and plot to win Nobel Prizes.  We share offices, kind of like when we were students, usually with a complete stranger, and often with someone who is not in our same discipline. This mixing of minds is an essential part of the Aspen Center for Physics’ recipe for success — exposure to new ideas and learning new things about other subjects always generates new and interesting approaches to science (I’ve written about that before).

The campus itself is pastoral and idyllic, replete with gathering spaces and benches conducive to quiet contemplation and speculation about the inner workings of the Cosmos. Again, the setting is purposeful — intended to produce an isolated and minimally distracting environment, free of the normal trappings of everyday life, in an effort to allow the mind the freedom to explore new ideas and discover new approaches to science.  All things being equal, it is a model that has succeeded admirably — over 10,000 physicists have visited the Aspen Center for Physics since its founding, including 52 Nobel Laureates. Over the years, more than 10,000 scientific publications have emerged as a result of time spent at the Center.

Campus of the Aspen Center for Physics.

Campus of the Aspen Center for Physics.

The Workshop: The workshop I came to the Center for was about “ultra-compact binary star systems.” That’s a mouthful — the kind of thing you like to tell your mother you work on because it sounds important. Whatever does it mean? Most stars you see in the sky, possibly as many as 50%, have a companion star that orbits them, like the planets orbit our Sun. We call these systems “binary stars.”

binarySystem

When stars reach the ends of their lives, they typically evolve into one of three different kinds of skeletons that mass as much as the Sun or more. These three stellar skeletons are called white dwarfs (something about the size of the Earth, made by low mass stars), neutron stars (something the size of a small city, made by medium mass stars), or a black hole (also about the size of a city, but made by much more massive stars).  Given the menu of stellar skeletons, you can imagine that long after binary stars are born, you can (and do!) end up with a binary made up of TWO stellar skeletons!

Evolutionary pathways from stellar life into the graveyard after stellar death. The three end states are white dwarfs, neutron stars, or white dwarfs, depending on the mass of the star in its life. [Image by NASA/CXC/M.Weiss]

Evolutionary pathways from stellar life into the graveyard after stellar death. The three end states are white dwarfs, neutron stars, or black holes, depending on the mass of the star in its life. [Image by NASA/CXC/M.Weiss]

Over time, the orbits of these skeletal star systems shrink smaller and smaller and smaller, until the stars are so close together they orbit at phenomenal speeds. For a pair of white dwarfs that orbit once every 15 minutes, they are separated by about half the Earth-Moon distance, and are travelling at a speed of 1 million meters per second (about 2.4 million miles per hour)!  These are “ultra-compact binary star systems.”

Ultra-compact binary systems have stellar mass objects, like two white dwarfs, orbiting in extremely small, short period orbits at extreme speeds.

Ultra-compact binary systems have stellar mass objects, like two white dwarfs, orbiting in extremely small, short period orbits at extreme speeds.

My office chalkboard after just a couple of days at the Aspen Center for Physics.

My office chalkboard after just a couple of days at the Aspen Center for Physics.

What Happens: We talk. A LOT. There are chalkboards all over the Center — in the offices, in the hallways, and outside on the patios.  There are always clusters of physicists around them — debating, deriving, teaching, learning. I know it sounds funny, but this is where a lot of science is born.

For instance, my graduate student and I have been working on a project where we need to know something about the number of neutron stars in the galaxy.  We need to know how many there might be, because we are thinking about an interesting way to observe them. If there aren’t very many neutron stars, we should abandon the idea, but if there are a lot of neutron stars, it could be important. I promised her that I would ask around at the workshop to see if anyone knew anything that could help us out.

(L to R) Me with my colleagues, Matt Benacquista and Melvyn Davies.

(L to R) Me with my colleagues, Matt Benacquista and Melvyn Davies.

So one day I was talking about this to my colleagues, Melvyn Davies (Lund University, Sweden) and Matt Benacquista (University of Texas-Brownsville) — they’re both experts in this sort of thing. They told me some very useful stuff, which I’ve passed on to my student. But at one point Melvyn asked me from how far away we could detect the gravitational waves from systems with a neutron star and a white dwarf together. I sketched out a quick calculation that suggested this was a very interesting idea to think about, and soon the three of us will publish a paper about how to study these systems with gravity, not light. It’s perhaps surprising that no one has thought about this before, but it’s a big Cosmos — there is a lot to think about! This is what the Aspen Center for Physics was designed to do — put scientists together, and let their brains roam free to make new discoveries.

And it’s not just at the Center that this stuff goes on. We are together all the time, which means we are always thinking and talking about science, usually intermixed with other enjoyable life activities.  We segue in and out of science and life the way you often segue in and out of sports and life or weather and life.  For instance, on any given evening if you are in Aspen, hanging out, eating dinner at the famous Hickory House, you might find us sitting next to you. You might be engaged in pleasant conversation about a nice hike you took earlier that day; we of course were hiking earlier that day too, but are still debating the question that occupied us on that hike, namely whether or not star systems with highly elliptical (oval shaped) orbits can be detected farther away in the Universe by LIGO than star systems with circular orbits.

When two stars orbit one another, the orbits can be perfect circles, or they can be elongated ellipses; we say these orbits are "eccentric."

When two stars orbit one another, the orbits can be perfect circles, or they can be elongated ellipses as shown above. When they are elongated, we say the orbits are “eccentric.”

Fun and Games. While it is all science all the time, it’s not all high-brow esoteric research. Physicists, as a rule, love to talk about what they do, as most of you who have a physicist neighbor or relative know. The Aspen Center for Physics hosts a regular public lecture series, intended to explain for a popular audience what physics is all about, and why and how we do physics. This summer I had the good fortune to hear K.C. Huang from Stanford talk about the evolutionary life cycles of bacterial cells and colonies, and also a talk about the dark energy in the Universe from my colleague, Bob Kirshner of Harvard (Bob has written a very nice book on this topic).

Bob Kirshner (Harvard) during his 2014 Heinz Pagels Public Lecture about Dark Energy and the Accelerating Universe.

Bob Kirshner (Harvard) during his 2014 Heinz Pagels Public Lecture about Dark Energy and the Accelerating Universe.

I also got to put my public game on, when I was asked if I could do a half-hour chat at the “Physics for Kids” picnic, hosted by the Aspen Science Center at the Center for Physics. This was a crowd of about 20 or 30 9-10 year olds and their parents, so I decided to talk to them about energy, which is and will continue to be a crucial topic of conversation during their lives.  So we talked a bit about how scientists think about energy, and then I did three demonstrations. First, we made craters in a tray of flour, showing how the size of the crater depends on the energy of the impactor — the biggest crater was made with a hollow shell shot from a paint-ball gun.

Impact crater made by a paintball shell from a distance of about 1.5 meters. Typical speed for a paintball shell is about 90 m/s (~200 mph!). Crater size is about 7 cm across.

Impact crater made by a paintball shell from a distance of about 1.5 meters. Typical speed for a paintball shell is about 90 m/s (~200 mph!). Crater size is about 7 cm across. (Click to enlarge!)

Second, we showed how energy is stored and converted using the famous “Bowling Ball of Doom” demo. You mount a bowling ball to a long cable, then hold it against your chin. When you release it, the bowling ball swings out across the room, then comes right back at your head but stops at the precise point you released it! It really looks like it is going to smash you in your face, but that is an impossibility because that would require it to obtain some energy from nowhere.

First person views of the Bowling Ball of Doom Demo. (L) The bowling ball is initially held touching your chin. (C) After release, the bowling ball swings away, then right back at you! (R) If you tie a camera to the bowling ball, you see it is moving pretty fast (about 3.5 m/s, or 8 mph!).

First person views of the Bowling Ball of Doom Demo. (L) The bowling ball is initially held touching your chin. (C) After release, the bowling ball swings away, then right back at you! (R) If you tie a camera to the bowling ball, you see it is moving pretty fast (about 3.5 m/s, or 8 mph!). (Click to enlarge!)

The last demo, as any of my students can tell you, is the Number One Physics Demo of All Time: the Bed of Nails. I lay on a bed of nails. A second bed of nails is laid on my chest. A cinder block is placed on top of that. A volunteer (in this case, my colleague, Stephan Rosswog, from Stockholm University) takes a 10 pound sledgehammer and smashes the cinder block. Obviously I survive (otherwise I wouldn’t be writing this blog!). How? The cinder block dissipates the energy of the hammer by breaking, thus sparing my life. You can see some videos of this demo: slow motion view; low, ground level view; first person head-mounted GoPro view.

(L) My Bed of Nails hammer weilder, Stephan "Thor" Rosswog (C) Matt Benacquista makes sure the GoPro is ready to capture the action! (R) Stephan works out some of the day's frustrations... :-)

(L) My Bed of Nails hammer weilder, Stephan “Thor” Rosswog (C) Matt Benacquista makes sure the GoPro is ready to capture the action! (R) Stephan works out some of the day’s frustrations… :-) (Click to enlarge!)

Me and J. Craig Wheeler. He's one of the reasons you're reading this blog right now!

Me and J. Craig Wheeler. He’s one of the reasons you’re reading this blog right now!

But probably the most important thing that happened this summer at Aspen, was I closed a loop in my career. When I was a young man, just starting out in college at Oregon State University, I was a mechanical engineering major. The reason for this was I was going to be an astronaut, and the way to become an astronaut (during the shuttle era) was to become a mission specialist, and one way to become a mission specialist was to design experiments that flew on the shuttle. At Oregon State during this time, there was a general science class taught called “Rocks and Stars,” and during my first year there they brought to campus a guest speaker: Dr. J. Craig Wheeler, from the University of Texas at Austin. Wheeler gave a great public lecture about black holes, which made me start seriously thinking about this whole astronomy business. This, of course, ultimately culminated in me becoming a physicist (a story I have written about before). As it turns out, he was at the Aspen Center for Physics this summer. We got to chat and hang out, I got to tell him the story that I just told you, and got a selfie of the two of us. :-)

My colleague, Enrico Ramirez-Ruiz, a professor in the Department of Astronomy and Astrophysics at the University of California – Santa Cruz, summarized a sojourn at the Aspen Center for Physics very succinctly: “It’s like summer camp for physicists.

And so it is. It clears the mind, it rejuvenates the soul, it connects you with people of like mind and like spirit. We argue, we debate, we eat, we laugh, we play, and we try to push science a little bit farther forward.  And like those summer camps from our youth, it is over far too soon. But you go home with new friends, with new ambitions, and a burning desire to come back again soon.

sunsetACP

 

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This post was written during, and after, a summer residency at the Aspen Center for Physics.

Dinosaurs in the Cosmos 2: Dinos without Radios

by Shane L. Larson

One of the things physicists and astronomers do very well is make simple estimates about the physical nature of the world around us. Part of this skill is (simple) math, and another part is knowing what physical quantities are important.  The most astonishing fact about this skill is that you and I do it every day, we just don’t realize it! Scientists have honed the skill — the place where science comes out is when those unconscious habits are used purposefully!  So how does it work? How is it that you and I are perfectly capable of describing complex physical phenomena, without necessarily resorting to equations we memorized in some long forgotten science class? To demonstrate, let’s consider sticking your hand (or your dog’s head) out the window of your car.

There is some serious physics behind dog ears in the wind, or flying your hand like an airplane. Despite that fact, you have some well defined and excellent intuition about what is important for this problem!

There is some serious physics behind dog ears in the wind, or flying your hand like an airplane. Despite that fact, you have some well defined and excellent intuition about what is important for this problem!

What affects how much force the wind presses on your hand (or your dog’s face) with?  With a little experimentation (something you probably did a lot as a kid, and have committed to memory but forgotten) you find there are three things:

  • how fast the car is driving. If the car is going faster, the force is stronger.
  • how you hold your hand (or, how big your hand is). If you hold your hand palm out, there is a bigger force than if you hold your hand finger tips out. The force is stronger if there is a bigger area being hit by the wind.
  • how thick the air is. Most of us don’t experience thick and thin air too often, at least not that we can tell the difference. But air is a fluid, like water, and water is much thicker than air. When you run your hand through water (a thick fluid) there is a much greater resistance than through air (a thin fluid).

That’s it — those are the three physical quantities that affect how much force you experience when you hold your hand/dog head out the window of your car. And you knew them, at least intuitively, whether you could explain it out loud or not! In a very similar way, the genesis of thinking about extraterrestrial life began with a few intuitive numbers that astronomer Frank Drake wrote down.

Frank Drake, circa 1962.

Frank Drake, circa 1962.

The serious scientific consideration of searching for extraterrestrial intelligences had started with a paper in the scientific journal Nature in 1959, by physicists Giuseppe Cocconi and Philip Morrison. This paper sparked Drake’s interest, leading up to his Project Ozma in 1960, the first human search for radio signals from an extraterrestrial civilization. By 1961, Drake decided to host a small scientific conference at the National Radio Astronomy Observatory, in Green Bank, West Virginia, where the Project Ozma search was carried out. Drake made a list of topics that should be discussed at the conference, dutifully writing down all the things that could affect how many communicative extraterrestrial civilizations there might be. When he was done, he realized he had created a Fermi problem estimate of the number of alien civilizations in the galaxy that we might communicate with — his list of topics were seven numbers that could be multiplied together.

A plaque showing the Drake Equation, hanging on the wall of the conference room where the equation was first presented. [NRAO].

A plaque showing the Drake Equation, hanging on the wall of the conference room where the equation was first presented. [NRAO].

He presented his seven number equation at the conference. It was promptly dubbed “The Drake Equation,” and has been used ever since as a baseline estimate for the kinds of discussions we are having now. A plaque of it now resides on the wall in the conference room where the meeting was held.

So what was Frank’s famous equation? Simply put, it is seven numbers — you multiply those seven numbers together, and you get the number of civilizations in the galaxy that could be communicated with, a number we denote as “N.”  It is written as:

          N = (R* x fp x ne) x FL x Fi x Fc x L

Of those numbers, the first three are matters of observational astronomy that can be verified and estimated from what we see of the Cosmos through our telescopes.  The last four numbers are quantities for which answers certainly exist, but whose values we are still uncertain about; it is playing with plausible values of these four numbers that illustrates our uncertainty about the Cosmos.

The stellar nursery, RCW 108, near the new emergent cluster of young stars (on the left), NGC 6193.

The stellar nursery, RCW 108, near the new emergent cluster of young stars (on the left), NGC 6193.

Let’s look at the first three numbers.  The first is R*, the rate at which stars are born in the galaxy.  The star formation rate is a simple way to start thinking about issues related to planets and life, because the number of planets must necessarily depend on the number of stars in the galaxy — you can’t have planets without parent stars for them to orbit!  For this number, astronomers think R* ~ 6/yr.

Young planetary systems form early on during the growth of a young star. [ESO image]

Young planetary systems form early on during the growth of a young star. [ESO image]

The second is fp, the fraction of stars that develop planetary systems. For a long time, we had no idea what this number was. For most of recorded history, no star other than the Sun was known to shepherd planets.  Then, in 1995 astronomers discovered planets around the star 51 Pegasi, a star very similar to the Sun about 51 lightyears away.  Today, we think planets may very well be common around most stars, and we are regularly discovering planets. As of the time of this writing (23 June 2014) there are 1797 planets known around other stars (visit the exoplanet catalogue here). To be conservative, let’s assume that not every star develops planets (though astronomers are beginning to think that a star without planets may be the exception, not the rule). We’ll take fp = 0.5.

Are there worlds like the Earth, orbiting other suns?

Are there worlds like the Earth, orbiting other suns?

The third number, ne, is the number of planets that could support life in a planetary system. Here, we don’t have a definitive value for this number, but any value we do use has some of our personal prejudices built into it since we have not had the opportunity to study an alien biology! One prejudice we have is that water plays an important role in the chemistry of life. Looking around the Sun, we find Venus, Earth and Mars are all at a distance from the Sun where liquid water could exist under the right conditions (this generic concept, the distance from a star where liquid water can exist on a planetary surface, is called “the habitable zone“). Venus has no liquid water, but Mars may harbor subsurface water. Based on what we know about our own planetary system then, let’s take ne = 2.

These numbers could change as we see more and more of the Cosmos, but probably not much.  So let’s multiply them all together and leave that number alone:

 R* x fp x ne = 6 x 0.5 x 2 = 6

For convenience, we now write the Drake Equation as:

N = (R* x fp x ne) x FL x Fi x Fc x L = 6FL x Fi x Fc x L

Now what about the last four numbers? These are numbers which have more uncertainty, and more speculation in them. They are absolutely numbers of importance when trying to figure out the number of civilizations in the galaxy, we just don’t have good ways to reliably estimate their values.

Prokaryotic cellular organisms were among the first forms of recognizable life to develop on the Earth.

Prokaryotic cellular organisms were among the first forms of recognizable life to develop on the Earth.

The first two are FL, the fraction of planets that develop life, and Fi, the fraction of planets with life that develop intelligent life.  These are complete unknowns; Earth is the only planet we know of with life!  Is it common for life to arise on other worlds? We know from the fossil record on Earth that simple life arose on Earth soon after its formation, in the form of single celled organisms — prokaryotic bacteria (cellular organisms with genetic material free floating in the cell, and not contained in a central nucleus), algae and the like. Given the simplicity of making the organic building blocks of life (chemical combinations called amino acids, used to build proteins), and given that self-replicating molecular systems are not uncommon, the early origin of life suggests that maybe life, in its simplest forms, may arise on planets quite often.  I’m an eternal optimist, so let’s assume FL = 1.  We’re just multiplying numbers together, so I can always go and change this number later.

If life arises, how often does that life become “intelligent?”  This is a harder question to answer, but again we can make an educated guess based on what we see on Earth. It is a fuzzy concept because you have to decide what you mean by “intelligent,” but there are many species on Earth we might consider intelligent — monkeys, dolphins, cats, even humans.  But there are many species that aren’t — oak trees, slime molds, or sea cucumbers.  How common is “intelligence?” Let’s assume Fi = 0.01 — a 1 in 100 chance.

What might life on other worlds look like? How do we define whether or not life is "intelligent?" In the Drake Equation context, we mean life capable of understanding and using science. [Image by David Aguilar]

What might life on other worlds look like? How do we define whether or not life is “intelligent?” In the Drake Equation context, we mean life capable of understanding and using science. [Image by David Aguilar]

The next number is Fc, the fraction of civilizations that can or want to communicate.  Here also, there are several extremes.  Consider humans — since the early 20th Century, we’ve been willy-nilly broadcasting our radio and television signals all over the place, blasting music videos of Eric Clapton and Chuck Berry out into the Cosmos (which I’ve written about before here).  We’ve even sent a few organized messages out, specifically with the intent of communicating with extraterrestrials; these have included radio signals, as well as physical messages.  On the another extreme, one could imagine a completely xenophobic civilization. Maybe they don’t want anyone to know of their existence, lest aliens invade and use them for food.  One could also imagine that a civilization never develops the technology to communicate. If Europe had not emerged from the Middle Ages in the Age of Enlightenment, perhaps we would have never had an Industrial Revolution; we’d all still be peasants, living off mushrooms and earthy root vegetables and not burdened by technology like smartphones or microwave ovens. Certainly the dinosaurs never developed radio communications, despite the intelligence we’d like to associate with marauding bands of velociraptors.  Let’s make a guess at this number (which we can always change) of Fc = 0.01.

We have no idea how easily civilizations rise, or how long they survive. All we can do is look at examples from Earth's history, such as the Indus Valley Civilization, which lasted for several millenia, then utterly vanished.

We have no idea how easily civilizations rise, or how long they survive. All we can do is look at examples from Earth’s history, such as the Indus Valley Civilization, which lasted for several millenia, then utterly vanished.

Now for the last number: the lifetime L of the civilization. There is enormous latitude in possible values for this number because we know absolutely nothing about it, and that is where this discussion gets interesting.  Suppose we take L to be the length of time modern humans have been on the planet.  We don’t know exactly how long that is, but our written history goes back only to about 3000 BCE, so we could take L to be the length of recorded human history, L = 5000 years.  By contrast, the dinosaurs lived on the planet for 170 million years before an asteroid obliterated them, so you could take L = 170 million.  Considering both of these cases we get:

 N = 6 x 1 x 0.01 x 0.01 x 5000 = 3

N = 6 x 1 x 0.01 x 0.01 x 170,000,000 = 102,000

That is quite a range in numbers — there could be more than 100,000 civilizations broadcasting radio; or there could be 3, with a very strong possibility that we are the only ones. The consequences of this calculation could be elating, or very depressing. Whatever the result is, the answer to this question will have profound consequences for our understanding of the Cosmos.

Which brings me back to where we started: dinosaurs and Fermi problems.  In many ways, the Drake equation is a Fermi problem.  What is different from many Fermi problems is that we don’t have a good handle on the last four numbers. But what if we didn’t care about all of these numbers?

What if all I wanted to know was "are there dinosaurs elsewhere?" [Images by S. Larson, at Eccles Dinosaur Park, Ogden, UT]

What if all I wanted to know was “are there dinosaurs elsewhere?” [Images by S. Larson, at Eccles Dinosaur Park, Ogden, UT]

What I love about the Drake equation is that it allows you to answer many related questions, by simply deciding what you think is important.  Let’s take the radical viewpoint that we don’t care about communicative civilizations; instead let’s simply ask how much life (of any sort) might there be in the galaxy?  Is the galaxy teeming with life, or is it a barren wasteland populated only by the descendants of some monkeys on a backwater forgotten world?

Suppose we don’t care about communication.  What if we only wanted to know if there were, say, dinosaurs?  We don’t keep the intelligent number or the communication number. That makes a modified Drake Equation that looks like this:

N = (R* x fp x ne) x FL x L = 6 x FL x L

Let’s keep our optimistic estimate of life developing on every planet possible, FL = 1. I’m interested in dinosaurs, and the dinos lived on the Earth for 170 million years before an asteroid whacked the Earth, erasing them utterly from the Cosmos; so I take L = 170 million years.  Multiplying this all together, I find

N = 6 x 1 x 170,000,000 = 1,020,000,000

There could be 1 BILLION worlds with advanced, but non-intelligent, lifeforms.  If you imagine those lifeforms to be something as complex as a dinosaur, then you might say it this way: there could a BILLION WORLDS with dinosaurs on them in the Milky Way!

That makes the little kid inside of me very happy. :-)

PS: As an even more interesting exercise, suppose we treat L not as the lifetime of a civilization, but simply the length of time for which life exists on a planet, and again ignore the issue of intelligent and technologically able lifeforms.  Taking Earth as the role model, life on Earth arose soon after the planet formed, and while there have been MANY extinction events, life has never been eradicated on Earth, making L ~ 3.5 billion years. If I replace the 170 million years we used with the dinosaurs with 3.5 billion years, we get N ~ 21 BILLION worlds with life.  Go stare at the stars tonight, and think about that for a little while.

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This is the second of two parts; the first part, about Fermi problems, can be read here.

This particular piece was completed while in residence at the Aspen Center for Physics.