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.

Dinosaurs in the Cosmos 1: Enrico & Frank

by Shane L. Larson

shaneRockOne of the most profound consequences of the development of life on Earth is that the Cosmos has produced complex systems with the ability to question their own existence.  We are each of us a collection of atoms that the Universe has stirred together in such a way that we can contemplate the nature of the Cosmos itself. It is remarkable, really.  A rock is also a collection of atoms that the Universe has stirred together, but if a rock contemplates the Cosmos, I have no strong notion of what its rocky thoughts might be.  Humans, on the other hand, have been given a remarkable gift: we can ask questions, and then we can figure out the answers.  This game of questions and answers has a name.  We call it science.

Deep sea anglerfish (Monterey Bay Aquarium, E. Widder/ORCA).

Deep sea anglerfish (Monterey Bay Aquarium, E. Widder/ORCA).

There are many questions that we could use the atomic computing engine between our ears to consider, like: how can we grow enough food to feed 10 billion people? will a catastrophic shift in the San Andreas Fault change the geography of California? can I make a jetpack safe enough for sixth-graders to fly to school? anglerfish — what are they all about? why do some tissues develop cancer in the human body and others don’t?  Where did the Universe come from?

Questions about life and our own existence often dominate conversations in philosophy classrooms, research labs, and late nights around a campfire.  What is the origin of life?  Is there life elsewhere?  Is there intelligent life (on this planet or others)? These are BIG THOUGHTS — heady questions that have been asked for as long as we have been capable of asking them.  Some of them may have answers that can be figured out, and some of them may not.  Let’s think about one of these together — is there life elsewhere?  This is a question that could be answered by simply looking.  Except that looking for life elsewhere is difficult for two reasons: (1) Everywhere else is far away (as I’ve talked about before!) (2) We’re not even sure what life elsewhere might look like! We’re still discovering new life on Earth (like under the Antarctic ice, and even in the deep forests where humans have not tread before).

These points are hindrances to be sure, but that is the nature of this game. Our atomic computing engines are very good at facing down such adversity, and finding ways to answer our questions irrespective of the difficulties we face.  For big questions, it is often useful to make an estimate of what the answer could be before you embark on your quest for knowledge. This helps define the boundaries of your quest.  One of the defining traits of modern scientists is their ability to make quick, quantitative statements about extremely complex questions using only a few pieces of data that almost everyone agrees upon.  These kinds of problems often go by the name “back of the envelope calculations” because they are supposed to be simple enough as to fit on the back of an old bill envelope (though sometimes you may need a manila envelope).  They are often called Fermi Problems, after Enrico Fermi who was famous for this skill.

Enrico Fermi.

Enrico Fermi.

Enrico Fermi was born in 1901 in Rome; he rose to prominence in physics very quickly, completing his laurea (the equivalent of a Ph.D.) at the age of 21. He worked in Italy until 1938, when the Fascist regime passed the leggi razziali (“racial laws”), which threatened his wife Laura, who was Jewish. That same year, he was awarded the Nobel Prize in physics, and after acceptance in Stockholm, took his family to New York, where they applied to become residents of the United States. He famously worked on the world’s first nuclear reactor (“Chicago Pile-1”), and the Manhattan Project.

Fermi was, without a doubt, one of the giants of modern physics. When you first start studying physics, you are regaled with tales of the great minds of physics — their accomplishments as kids, their discoveries early in their careers, and the myriad ways they have transformed the way we view the world. As a young and aspiring physicist, it is incredibly intimidating and almost crippling; fortunately, I had many outstanding mentors. Each of them played a role in calming my doubts and fears; each of them helped me look at great scientists like Fermi and learn something about how to do science from their examples.

One of those things is Fermi problems. Fermi was famous for his ability to quickly estimate the answers to complicated problems. When his answers were checked against precise calculations, his results were amazingly close to the “real” answer! One of the most famous examples was Fermi’s estimate of the strength of the atomic explosion at the Trinity test. Fermi dropped handfuls of paper from a height of 6 feet before, during, and after the blast wave washed over the observation post. Based on the distance the paper spread as it fell, Fermi estimated the explosion to be the equivalent of 10,000 tons of TNT; the strength reported after the test had been fully analyzed was 20,000 tons of TNT.

The Trinity fireball, 16 milliseconds after the first human-made atomic explosion. Fermi was the first person to estimate the energy in the explosion.

The Trinity fireball, 16 milliseconds after the first human-made atomic explosion. Fermi was the first person to estimate the energy in the explosion.

Calculating the yield of an atomic bomb is definitely a big physics problem; it’s not the kind of thing most of us have to do in our lives. But all of us do Fermi problems every day. Every one of us. Things like: you’re going to watch curling with 4 other friends; how many pizzas should you order? how many bikes can fit in your garage with everything else? what time do you need to leave home to make it to work on time?

The classic problem that Fermi used to introduce this estimation concept is “how many piano tuners are there in your city?”  With Google, or the yellow pages (if you are a caveman), this question could easily be answered definitively.  But it can also be calculated by using some things you know or can estimate from your own personal experience.  Let’s try this together — I’ll do it for Logan, Utah, and you do it for wherever you happen to be right now.

The number of piano tuners in a given city is not general knowledge that most of us carry around. Despite its seemingly esoteric nature, it is a number that can easily be estimate to high accuracy using Fermi estimation methods!

The number of piano tuners in a given city is not general knowledge that most of us carry around. Despite its seemingly esoteric nature, it is a number that can easily be estimate to high accuracy using Fermi estimation methods!

The method is to ask a series of questions upon which the answer must depend, and that you may know the answers to. Questions like: how many people live in your city? how many households are there? how many households have pianos? How often do they tune pianos?  if you are a piano tuner, how many days a year do you work? how many tunings can you do in one day?  The answers to these questions don’t need to be 100% correct, nor do all of them have to be the same as someone else would guess.  All in all, the guessing and errors average out to give about the same answer for everyone.  This is a beautiful and elegant method of trying to understand the nature of the world by relying on the fact that your knowledge sometimes does better and sometimes does worse than reality, but overall combines to give something close to the truth.  In the figure below, I show the calculation for Logan, Utah. If I check the answer in my phone book, I find that I was pretty close!

Estimating the number of piano tuners in a city. Starting at the top, there is a simple series of numbers you need to estimate, most of which you probably know or can guess.

Estimating the number of piano tuners in a city. Starting at the top, there is a simple series of numbers you need to estimate, most of which you probably know or can guess. (Click to embiggenate)

The key methods to bear in mind in your quest to become a good Fermi problem estimator are:

  • Most problems seem unanswerable when posited, but usually can be broken down into simpler bits which you do know the answer to.
  • Rely on numbers you know the value of, or can estimate a reasonable value for.
  • Don’t worry about being precise!
  • Round relentlessly (“7 is about 10”)
  • Combine numbers sloppily (“15 x 6 is about 100”)
  • Use everyday experience as averages (“a human masses about 70 kg”)

This is a powerful and robust technique for answering questions. More to the point, you do this every day when you figure out how many cupcakes to make when the cousins are visiting, or when you buy rope to make a new tire swing, or when decide how long before the football game to start mowing the lawn to make sure you are done on time.  You could do it for all kinds of other things that may be important in your life and business, like: estimating how much pizza is consumed on a nearby college campus every day, or how many ball point pens are sold in your city each year, or how many car crashes there are in town each month.

Frank Drake.

Frank Drake.

For our purposes here, we are going to use this powerful technique to figure out how much life there might be elsewhere in the Cosmos.  One of the first people to think about this was astronomer Frank Drake. Drake was a radio astronomer, and made important discoveries regarding the nature of Jupiter’s magnetosphere, and in pulsar astrophysics. In the 1960’s he also began to think about how radio astronomy could be used to search for transmissions from extraterrestrial civilizations, initiating Project Ozma in 1960 to search for possibly intelligent transmissions from the nearby Sun-like stars, Tau Ceti and Epsilon Eridani.

When thinking about life in the Cosmos, and whether we are alone or members of a vast chorus of civilizations spanning the galaxy, Drake asked a specific (but plausibly unanswerable) question: how many civilizations might exist in the galaxy that we could communicate with?  The Fermi problem solution to this question is known as The Drake Equation.  We’ll examine the Drake equation and its implications next time.

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This is the first of two parts. The second part can be read here.

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

Chasing Starlight 2: Recipes for Discovery

by Shane L. Larson

When you and I were in elementary school, we were taught “The Scientific Method” (which we’ve talked about before) and told that it was how scientists do science. In a similar vein, I was once told that cooking is just stirring stuff together and heating it up. I’m sure that is how chefs do cheffing. But as any chef knows, the art of cooking is not so easily distilled to a pithy soundbite easily told to 4th graders.  So it is with science. Astronomy in particular often defies the rigid, black and white portrayal of science given by The Scientific Method.

Cooking is like science. (L) Sometimes it works perfectly! (R) Sometimes disasters happen.

Cooking is like science. (L) Sometimes it works perfectly! (R) Sometimes disasters happen.

For the most part, astronomy is not a bench science. Astronomers do not have controlled experiments that can be repeated and studied. Instead, astronomy is a spectator science — all we can do is look at the Cosmos, and see what it has thrown up on the vast canvas we call the sky. Some things persist, and can be looked at over and over and over again. Other things happen only rarely, and if we aren’t looking or aren’t prepared to look closely, the information washes across our small planet then vanishes forever.  Because of the unpredictability of Nature and because of the paucity of many astronomical events, one of the most important aspects of astronomy is squeezing every possible bit of information out of the signals we receive, so that we may best understand what created those signals. Our primary partner in this endeavour has for most of the history of modern science, been light.

This is what typical "bench science" looks like in physics: experiments that have been carefully designed to probe a physical effect, and are run over and over again until we understand the outcome. Astronomy is not usually like this.

This is what typical “bench science” looks like in physics: experiments that have been carefully designed to probe a physical effect, and are run over and over again until we understand the outcome. Astronomy is not usually like this.

It’s not surprising that light provides one of our main connections to the Cosmos. We are creatures that have evolved to depend on our sight as one of our primary senses. In addition, light is readily generated by atoms, which make up all the stuff that the stars and planets and interstellar gas are made of. There are both obvious and subtle ways that information is encoded in and carried by light, most of which are useful in astronomy.

The constellation of Orion is covered by a large cloud known as the Orion Molecular Complex. The large circular structure is known as "Barnard's Loop"; if you look closely in the center left, you'll see the Flame Nebula and the Horsehead Nebula, both part of the complex. The red star at upper left is Betelgeuse; the right star at lower right is Rigel. In the middle of Barnard's Loop, below the three belt stars, you can see the famous Orion Nebula.

The constellation of Orion is covered by a large cloud known as the Orion Molecular Complex. The large circular structure is known as “Barnard’s Loop”; if you look closely in the center left, you’ll see the Flame Nebula and the Horsehead Nebula, both part of the complex. The red star at upper left is Betelgeuse; the right star at lower right is Rigel. In the middle of Barnard’s Loop, below the three belt stars, you can see the famous Orion Nebula.

The foremost and most obvious role light plays in astronomy is that of signal beacon — light is shed from an object, and makes its way across the Cosmos to say to the astronomers of Earth, “I’m here! Look at me!” In the case of stars, that light is rather pointlike and fixed in space; often it is steady and unchanging, at least over timescales that are readily noticed. Many stars have color.  Consider the constellation of Orion, one of the most recognized constellations the world over.  This deep sky image shows both unincorporated gas as well as stars. The three belt stars lie in an almost perfect line, and are roughly the same brightness, shining with a blue-white light. They are called (from east to west): Alnitak, Alnilan, and Mintaka. Orion’s eastern shoulder is a baleful red star known as Betelgeuse; the right knee is a brilliant blue star called Rigel. These names have been passed to us down through the ages, from a time before we knew what the stars were, what they were made of, or what their colors meant. But today, we know far more than those who first named these beacons in the sky. Both Rigel and Betelgeuse are supergiant stars, and both are about 10-20 times the mass of our Sun, but their similarities end there. Their colors were different — one blue, one red — and it was later discovered their sizes were different: Betelgeuse is about 1000x the diameter of the Sun, whereas Rigel is about 74x the diameter of the Sun.

We’ve talked before about how the fingerprints of atoms impress themselves in light (read that post here) by making spectral lines, and how the color of a star is a direct measure of its temperature (read that post here). Together these two properties allow us to say much about the stars without ever visiting them up close — this is one of the most important discoveries about light that has ever been made. In the case of Rigel and Betelgeuse, it has allowed us to know that Rigel is blue because it is far hotter than red Betelgeuse. Why the color discrepancy? Because Rigel is young, and Betelgeuse is elderly.

If all we ever learned about the Cosmos was the temperature and composition of the stars, we would consider those discoveries triumphs of the human intellect.  But is there more that light can tell us? Of course there is! But all observations of Nature require us to be careful observers. Light is a tempestuous partner in the game of astronomy. Like messages on the internet (how science propagates on the Internet was famously described here), the news carried by light might be very interesting, but is subject to distortion and confusion because during the long journey to Earth, light is easily influenced. Any matter the light encounters during transit has the potential to change the light, to corrupt and distort the news it carries from the distant corners of the Cosmos.  There are many such effects that distort the stories told by light, but let me tell you two of them.

One example is called gravitational lensing. Einstein taught us that mass and energy are equivalent. What does that mean? There are many consequences, but the important thing for this conversation is this: energy feels the pull of gravity, just like mass does. That means light, a form of energy, should feel the pull of gravity as it is speeding along through the Universe. This is exactly what would happen to you or me. Suppose we are drifting along in our starship, and pass a large object to our left, say a galaxy. The gravity from the galaxy would tug on us, and pull our course inexorably to the left.  Once we were past the galaxy, the gravitational pull would fade with distance, and we’d continue to travel on a straight line, but it would be a different straight line than the one we started on!

(L) If a starship (that looks mysteriously like a Lego version of NdGT's Ship of the Imagination) were coasting on a straight line, a massive object will deflect its course. (R) Objects with strong gravity can also deflect the course of light; the effect on astronomy is to project the location of the source somewhere else on the sky from the perspective of observers on Earth.

(L) If a starship (that looks mysteriously like a Lego version of NdGT’s Ship of the Imagination) were coasting on a straight line, a massive object will deflect its course. (R) Objects with strong gravity can also deflect the course of light; the effect on astronomy is to project the location of the source somewhere else on the sky from the perspective of observers on Earth.

This is exactly the same thing that happens to light! Suppose light is speeding through the Cosmos, and passes a large object on its right, say a galaxy. The gravity from the galaxy tugs on the light, and pulls its course inexorably to the right. Once it is past the galaxy, the gravitational pull fades with distance, and the light continues to travel along a straight line, though it is now travelling a different direction than it started out in — this has important consequences for astronomy? Why? Because as astronomers, we often make the default assumption that when I see a light ray from the Cosmos, it came directly from its origin — we like to think that if we simply extend the direction all the way back through the Universe, we can determine where the light came from! But the deflection of light by gravity has made that extended line point somewhere else!

There is a remarkable consequence of this gravitational deflection that was predicted by Russian physicist Orest Chwolson in 1924: an “Einstein Ring.” Light from a distant source doesn’t just fly to one side of a deflecting galaxy — it flies on every side. If you are sitting in the right place, the gravitating galaxy that is bending the light will act like a cosmic magnifying glass, making a ring out of light that goes around every side of the galaxy!

The basic geometry of an Einstein Ring. Light that goes to the left is deflected to Earth, as is light that goes over the top, under the bottom, and to the right. From the perspective of an observer on Earth, they see bits of light in all of those directions, which appears as a ring on the sky.

The basic geometry of an Einstein Ring. Light that goes to the left is deflected to Earth, as is light that goes over the top, under the bottom, and to the right. From the perspective of an observer on Earth, they see bits of light in all of those directions, which appears as a ring on the sky.

In 1936, Einstein famously panned the idea of seeing a ring, thinking the chances of a perfect alignment would be small, and even if an alignment occurred, our telescopes would not be up to the task of seeing the small ring. But as is often the case, technology outstrips our most pessimistic predictions. In 1988 radio astronomers discovered the first Einstein Ring; many more have been found, like the one shown below, LRG 3-757.

A nearly complete Einstein Ring observed by the Hubble Space Telescope, a galaxy known as LRG 3-757 (read the Hubble page here).

A nearly complete Einstein Ring observed by the Hubble Space Telescope, a galaxy known as LRG 3-757 (read the Hubble page here).

For our second tale, remember where this conversation started last time — with Feynman diagrams. A Feynman diagram shows us how light and matter (specifically electrons and positrons) interact. One of the things we learned by drawing Feynman diagrams is that you can predict new effects, then go look for them. A classic example is called “pair production” where two photons collide and create an electron and a positron. This effect was first seen in  the lab in 1997 (read a NY Times article about the result here), and scientists are currently working on the design of a “photon collider” that will make pair creation a regular event in the laboratory.

But this begs an obvious question: could we use this effect to do astronomy? Is there some way we could observe this effect, and use it to answer some deep question about the Cosmos?  The answer of course is yes!

Consider a blazar — an active galaxy, billions of lightyears away. A blazar is characterized by the emission of extremely high energy light, created by the jet of a super-massive black hole that is pointing almost directly at the Earth. The light from blazars must travel through most of the known Universe to reach us here on Earth. During that time, it will pass through ever increasing amounts of starlight generated by the generations of stars that have come into being, evolved, and perished over the ages of time. Gamma ray astronomers call this “the Cosmic Fog” because it acts just like real fog on Earth.  If you shine your flashlight out into a fog bank, you can only see it from a certain distance away, and that distance depends on how thick the fog is.  Starlight is the same way — the more starlight the gamma rays have to pass through, the more likely it is that they will encounter a photon of light from a star.  And what can happen when two photons meet? They produce an electron-positron pair, and the photons vanish (their energy was used to make the particles)! The net result is that when viewed from Earth, the blazars don’t have as much high-energy gamma ray light as we expected — the gamma rays are absorbed by the Cosmic Fog of Starlight.

A map of the "extra-galactic background light" that comes from all the stars in the Universe, as seen by the Fermi Gamma-ray Observatory. The dots are 150 blazars whose gamma ray deficiency was measured.

A map of the “extra-galactic background light” that comes from all the stars in the Universe, as seen by the Fermi Gamma-ray Observatory. The dots are 150 blazars whose gamma ray deficiency was measured.

The most important thing about this is: scientists can measure how much of the gamma ray light has gone missing. That tells us how much starlight was encountered. Since we know something about how much starlight a star puts out (based on its temperature and size), this allows us to estimate the number of stars in the Universe whether we can see them directly in the telescope or not!

That is an astounding feat, and one that should impress upon you one thing: that we are an exceedingly clever species, and with science as a tool, we can figure out just about anything.

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This post is the second and final part in a sequence talking about clever ways to use starlight to understand the Cosmos. The first part was here.