omenti

about two hundred miles north of roswell, new mexico...

As Edward Teller, Emil Konopinski, Enrico Fermi and Herbert York walked to lunch one of them noticed a New Yorker cartoon taped to a door blaming trashcan thefts on aliens.  It was 1950 and the country was in something of a UFO craze.  They laughed and continued.  

 

Unidentified flying objects have been a thing in the US since the late 1880s.  As soon as flying machines captured imaginations UFO sightings were reported.  Sometimes explained as foreign war machines, more often they were from other planets in the solar system falling in line with science fiction in the penny press and dime novels.  Jules Verne and HG Wells created more sophisticated aliens and UFO sightings reported rockets and flying saucers during the Great Depression.  The movie comic book industries picked up on it and fanned the enthusiasm.  

 

After WWII the atom bomb - something right out of science fiction for most people - and conspiracy theories growing out of secret government programs gave a sense to many in the public that these events were real.  The four physicists knew everything so far had a down-to-earth explanation - and if there was something, they'd probably be among the first to know. 

 

They sat down to lunch and physics talk when Fermi, who had been uncharacteristically quiet, suddenly exclaimed "where are they?"  Everyone at the table knew what he was talking about.  He scribbled away with some guesses about life supporting planets, the probability of life and the probability of interstellar travel.

 

° there are billions of stars similar to the Sun.  Many are much older than the Sun

° Many probably have planets and some are probably Earth-like.

° Some must have developed intelligent life.  Some of these civilizations are likely to be much more advanced than us.

° even at conservative interstellar travel speed of a half of one percent of the speed of light it would be possible to spread life from one location throughout the out galaxy in under 100 million years.  Not a huge amount of time compared to the geological age of the Earth.

 

We should have been visited .. regularly, in fact.  But where are they?  Although it's not a paradox it is commonly called the Fermi Paradox.   A large number of explanations have been given.  Here's an unordered partial list of the top of my head:

 

° extraterrestrial life is very rare..  we indeed may be alone

° life might be common, but evolution to intelligent life is very rare.

° intelligent life destroys itself before it develops interstellar travel - a popular conjecture during the Cold War and one Carl Sagan warned about.

° civilizations are too far apart in space-time 

° it's too expensive to mount such expeditions.  

° AIs will replace biological intelligent life and they may be focused elsewhere.

° we don't know how to look

° they're not interested in us or they purposely are avoiding us

° they're already here .. or their sensors are

° they're too alien

° and on and on

 

Frank Drake modified a technique particle physicists use to create the first serious attempt to quantify how common life is in the Milky Way galaxy.¹  The Drake Equation differs from the Fermi Paradox in that physical contact isn't necessary.. it's a counting rather than a visit.  It's easy to criticize as many of the terms are little more than educated guesses and some of them depend on poorly defined terms like life and intelligence.  It was also conceived before the Big Bang was established and assumed a steady state universe.  Lots of issues,  nut it fires the imagination and encourages dialog to the point where some progress has been made.

 

In its original form there are seven terms that are multiplied together .. note the fractions f are between 0 and 1.0.

R_*     the rate of star formation

f_p     fraction of stars with planets

n_e     number of planets that might allow life to evolve per star

f_l     fraction of planets that could have life that have life

f_i     fraction of planets with life that evolves to intelligent life

f_c     fraction of planets with intelligent life that have the capability of interstellar communication

L     the length of time such a civilization can broadcast and listen

 

As you might imagine there's some serious guesswork involved.  The last three terms in particular give such a spread that it has been criticized as an exercise in personal bias.   But we've learned a lot since 1961.   Now we have a good estimate of the probability a star has planets .. it's very common.  Furthermore there's been a good deal of work on the signatures of life and physically where to look - so called goldilocks zones.  One of the goals of the James Webb Space Telescope - the follow-on to the Hubble Space Telescope - is probing for signs of life.   That's for one of the next posts.

 

My own view, admittedly not worth much as I don't have enough empirical evidence, is that life must be very common, but intelligent life (whatever that means) is fairly rare.  Still the Universe is so large that I think there must be many civilizations.    But I also like to think we may be very rare and that humanity is special and worth preserving.   My belief is that Elon Musk and Stephen Hawking are very wrong when they say we need to leave Earth very soon to preserve humanity.  We have a very special and amazing place that is worth saving.

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¹ The form has its roots in 19th century system efficiency calculations. If a machine or process has parts each with their own efficiency and everything connected together you simply multiply the efficiencies to get the total system efficiency.  You can use the same technique to estimate the probability of finding a potential mate:-)

 

 

 

 

the universe is a time machine

I was asked to write about extraterrestrial  life. That's an approximately big subject that I'll approach with a few posts starting off with some context.  An old friend wrote this about the Universe:

 

Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

 

Hold a finger about a foot - thirty centimeters - from your eye and focus on it.  It's part of you, but you're seeing it as it was about a billionth of a second ago.. the amount of time it takes light to travel a foot.¹  The Moon appears as it was a bit over one and a quarter seconds ago and the Sun is about five hundred seconds in the past.  

 

Generally we don't think about these things unless we have to synchronize events or consider the historical context of an event.   It comes into play exploring the Solar System, but also when measurements are made of events recorded in more than one place.  In experimental physics you worry about it all of the time, but it's important in high frequency market trading. 

 

When you look at the closest star - Centauri Proxima - you're seeing something that took place about four and a quarter years in the past.  A few years ago some of us studied weather patterns on a type of star known as a brown dwarf.  One could make predications and we issued a weather report.  The problem was we were looking at something that happened about sixteen years in the past and if some being near that star could read our report, they'd be looking at our history making the total out-of-dateness of the report about thirty two years.   When I know when someone was born I sometimes send them a birthday greeting naming the star from which starlight that originated when they were born is just making it to Earth.

 

The farthest in the past you can usually see with your naked eye is the Andromeda Galaxy .. about two and a half million years ago.  Telescopes take us farther back to about thirteen billion years ago when gravity was beginning to pull the primordial elements of hydrogen and helium into stars and organizing the earliest galaxies. Thi distant past is bizarre and quite foreign to anything more recent, but it's there for the looking if you have enhanced your senses properly.  Getting that far back is difficult and many more recent histories exist, so most Astronomers work in different time periods.,

 

We're not at the center of the Universe.  Rather we're at the center of our own perception.  Our finger is a bit in the past and our friend on the other side of the room a bit father back.  We look out into concentric layers of the past marking different epochs.   The history of the Universe that is written in light and now even in sound in these layers until we get to the last layer.. the fire of creation.  

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¹ Assuming your perception is instant, which it isn't..  it adds 250 to 300 thousands of a second, but that muddies the point.

We also live in neurological and acoustic pasts.  Those signals travel much more slowly than light, but over short distances so we tend not to think about them except during thunderstorms.

 

 

 

 

hope for nature and humanity

In grad school I came across The Limits to Growth - a book by the Club of Rome. Basically a report on computer simulations of exponential population growth and limits of the carrying capacity of the planet for a number of resources.  It struck me as bleak and depressing suggesting zero population growth was our only path out. I was curious about their model and found issues with the underlying data set and models. It wasn’t possible to describe population growth trends with simple exponentials. Something else was going on. They admitted some issues, but swept it under the rug sort of claiming “correct” data would fit their model. It began to slowly eat at me.

 

A few years later  I found myself traveling to Princeton regularly as part of a collaboration. It’s a great place to run into people and ask questions.  Eventually I found some demographers and learned at their feet. They weren’t terribly impressed by the book. They freely admitted there were serious issues, some of which may be existential threats.  At the same time there were some extremely positive trends.. Instead of simple exponential models there are periods of development with different population dynamics.  At first I had a my doubts, but their models fit the available data and fit some emerging trends much better than the CoR report.  There are a  variety of models, but they mostly boil down to three main stages.

 

The first is a period where the death rate is very close to the birth rate - sometimes exceeding it, sometimes falling short. Humanity was scattered around the globe and regions would fade in and out.  Eventually with trading centers becoming stable with very low population growth. The death rates were enormous.. for a family to continue to the next generation you generally needed more than six children.

 

The second stage is marked by the introduction of sanitation and successful disease prevention. Death rates drop dramatically, but people still maintained extremely high fertility rates.   The sanitation and medical knowledge is quickly communicated to populations at a similar stage. This results in enormous population spikes.  In the US the core part of this stage was from about 1920 to 1970.

 

The third stage sees women gaining education, opportunity and control over their bodies and fertility. Incomes are rising and families begin to focus putting more into fewer children. The fertility rate drops .. often dramatically.  Think Japan and parts of Europe. 

 

Different regions of the world go through these at different times and rates. One of the huge drivers for the second and third stages is urbanization. At first it  seemed counterintuitive, but when you talk to demographers and read their papers it becomes clear the growth of cities is the rocket fuel that enables the rest.

 

About fifteen years ago I organized a small conference on this at Aspen. I left with great hope and enthusiasm believing that lowering some of the other potentially existential threats would only make this process easier. In my mind the immediate low hanging fruit was working on global warming. It could have been, but I didn’t understand the inertia and control of the fossil fuel industry.

 

I could go on and on about these demographic trends and had intended to, but it would be book length and others are more expert in the area. I may talk about it in the future. The next stage is cloudy I can argue for at least four very different paths .. some of them pretty awful. But I recently came across a nice discussion of the saving nature piece..

 

Now for the good part.  Sean Carroll of Caltech interviews Joe Walston - the senior VP of Field Conservation at the Wildlife Conservation Society.  Joe offers a better summary of these issues than I could in an hour of writing  It's a bit over an hour long, but worth it if you have any interest in demographic trends, why they happen and where they could go.

 

Finally it's interesting these trends appear to be society independent.  We like to think how different we are, but in many ways, for good and bad, we're the same.  I find that comforting.

 

 

 

coming november 26th - seven minutes of terror and planetary farts

minipost

 

Great science communication takes a variety of forms.  Recently I've been impressed by some great blogs and YouTube videos, but traditional story telling and the illustrated comic format can be equally amazing

On the 26^th of November InSight will land on Mars.  For understanding the solar system robotic spacecraft win hands down over manned flights.  The exploration of Mars has been an incredible story and it could take a huge leap forward starting Monday.  The Oatmeal put together a wonderful science explainer. Learn about the mole, martian farts and the number.

 

great stuff!  read the full piece.

Manned spaceflight is still cool and possibly even justifiable, but it generally isn't science.  In my mind some of the most impressive work has been the inspiration Chris Hadfield has given to million of children.  That may be enough to justify the price.  I'm not a fan of flying Teslas, but that's another story.

 

 

 

 

 

 

 

 

 

pop go the bubbles

The wooden crate arrived via air freight from Geneva.  Fifteen bottles of champagne and a simple handwritten note with the words "I concede" and the name of the sender.  

 

A few branches of physics have a curious way of dealing with a class of disputes. People make conjectures that are impossible to test at the time.  When strongly held disagreements flare.  The tradition, dating back at least to 19^th century Cambridge is the gentleman's wager.  A statement is made by one of the conjecture holders in writing and witnessed.  Often these are of the nature "in ten years such-and-thus will have been found."  In this case it was fifteen years and was the sort of thing Paul would be committing the next ten or so years of his life chasing.  Paul's hunch was right.  In this case the quality of the champaign wasn't specified.  I'm told two of the bottles were excellent and the rest average.

 

There were four of us from the old group and we couldn't let the booty go to waste.  We wanted to learn something about the physics of popping the cork and immediately began asking questions.  Where does the pressure that pops the cork come from, how strong is it, how fast does the cork fly, what happens in the liquid when the cork comes off, what happens to the gas above the liquid and so on... The only thing we had to make  was the mechanical cork popper.  

 

We read what was available - literature on champagne told us about ten grams of carbon dioxide is produced by yeast fermentation in the standard 750ml sized bottle.  Outside the bottle it would occupy about six liters, so the pressure inside the bottle was fairly high - nearly 90psi (or over 600 kPa) , or roughly what you have in a bicycle tire.  It jus sits in equilibrium waiting...

 

When the cork is released the pressure gives it a fine sendoff.  Our fastest cork cocked in at a shade over 11 meters per second - about 25 miles per hour.  Our release mechanism wasn't that good and one high speed photograph showed a hand released cork moving a bit faster.   The speed depends on the temperature of the liquid.  CO₂ is less soluble at high temperatures, so warm champagne will give you a faster cork.  This, of course, is offensive to the French, so we tried to stay below 10° C. 

 There's an immediate drop of pressure in the neck of the bottle with the temperature falling to about -60°C for a few milliseconds.  Water and alcohol vapor condense in a short lived cloud that your eye might catch.  (We used photography and scattered laser light to get a sense of droplet size)

 

Inside the liquid a fizz starts as the carbon dioxide comes out of solution.   There is some disagreement on how to properly pour the liquid and what kind of glass should be used.  These questions and others are addressed by a number of papers that came about a decade after our little investigation.  The dynamics of the bubbles near and above the surface of the liquid are very important.  Ideally the fizz throws bits of wine into a diffuse cloud that hangs over the surface.  People say this greatly enhances the drinking experience.  The bottom line is a flute shaped glass does the best job of concentrating the cloud, but high carbon dioxide concentrations are acidic in the nose and mouth.  The trick, apparently, is a tulip shaped glass.    The trick for pouring is to tilt the glass at an angle and pour down the side.  Anything else leads to turbulence that liberates too much carbon dioxide.

 

 

Bubbles are historically important in particle physics. You've probably see photographs of particle decays.  From the mid 1950s up until about 1970 most of those images really were photographs. A high speed particle would collide with a particle in a target  and the collision products would head towards a bubble chamber.  These were tanks fulled with a clear liquid (usually liquid hydrogen) under pressure and a dissolved gas (hydrogen in this case).  Just before the collision the pressure in the chamber was lowered by quickly pulling a piston out a bit.  This sensitized the  liquid  just before particles from the collision flew through at a fraction of the speed of light.  They were long gone when the exposure was made, but they disturbed the liquid enough to form tiny strings of bubbles along their paths. At just the right time a flash went off and three exposures - one for each axis - were made.  Timing and lighting were issues and the optics were mind boggling, but miles and miles of special film was exposed in the day. An The results were measured by hand by "girls" (sexism of the day) on digitizing screens and then sent to a computer for pattern recognition.  Later computer programs digitized the images directly from the film eliminating a very tedious job.  To my knowledge this was the first use of a computer to make sense of an image and possibly the first example of big data.  Certainly one of the most exotic types of camera every made and they led to over a dozen Nobel Prizes.

 

(cork popping image by Niels Noordhoek [CC BY-SA 3.0], from Wikimedia Commons