S04E05: The Desperation Emanation

October 21, 2010

Bob on Sesame Street taught us to know the people in our neighborhood.

(Song starts at 0:50)

But Sheldon in The Big Bang Theory taught us to know the stars in our neighborhood, too.

Our stellar neighborhood is a bit larger than your own neighborhood.  As we discussed before, the nearest star to our own solar system is Proxima Centauri.   Suppose you lived in a typical suburban house with a 50 foot driveway.  If your driveway were like the distance from the Earth to the Sun, then Proxima Centauri would be about 2500 miles away.   Even survivalists can’t get this far from their neighbors.

When the writers asked me to find the names of the stars, in order of proximity to us, I figured that would be easy.  But it was a case where the internet fails.  Nearly all the lists on the web are in disagreement with each other.   And the writers needed an answer…fast.

Luckily one of my friends at  UCLA, a professor over on the Astronomy floor bailed me out.  He told me about RECONS, the Research Consortium on Nearby Stars.   They maintain a definitive list on the stars in our neighborhood.   (And for the record, Wikipedia had it right.)

These are the stars in your neighborhood. In your neighborhood. In your neighborhood.

So we heard the list from Sheldon. Special thanks to none other than “The Bad Astronomer” for helping out with the pronunciation of the star names.

(Of course the closest star to Sheldon is not Proxima Centauri at all.  It is Sol, our own Sun.   If you were thinking that during Sheldon’s song, good for you!  You may stay after class and clean the erasers.)

What about those crazy names?  These stars were discovered over thousands of years.  Some are visible to the naked eye.  “Sirius”, the brightest of the stars, was named by the Ancient Greeks after their word for scorcher.  Others are named for the constellation they are in.  “Alpha Centari A” is the brightest of the stars making up the constellation Centaurus.   “Epsilon Eridani”, named after the constellation Eridanus and the fifth greek letter, is the fifth brightest star in that constellation.  But closest need not mean the brightest.  Many of these nearby stars were not discovered until modern times and are named after their discoverers: Jérôme Lalande discovered “Lalande 21185” in 1801 and “Ross 154” was only found in 1925.

And to this day, astronomers still are finding nearby stars.  Teegarden’s star was missed until 2003.  It is so close that it moves across our sky faster than almost any other star.   Surveys find nearby stars because over the years their position on  the sky can change slightly, just thousandths of a degree per year.  But Teegarden’s star, a modest little red dwarf,  moved so fast across the sky, it was always overlooked.   It is humbling to think that the 23rd closest star closest to our own solar system was missed until this very decade.   And there may be more…

Some of the stars are close together:  Proxima Centauri and Alpha Centauri are a pair, forming a binary star system.  So are Sirius A and B.   About half the stars closest to us are pair-bonded.   Our star appears to be alone.  Or is it?  Some people have proposed we have a distant and dim partner, called Nemesis.  So-named because when its orbit brings it back close to Earth, its gravity would disrupt the comets and asteroids causing them to rain down on us.  It has been proposed to explain a possible periodicity, about 27 million years, of mass extinctions found by paleontologists.  The periodicity of these extinctions is not universally accepted.  And the explanation of periodic extinctions being induced by a companion star even less so.  Nevertheless, I named the first electronics board I build as a graduate student “Nemesis”.

If there is such a “Nemesis” star orbiting our own, a new survey will find it.  The WISE satellite, the Wide-Field Infrared Survey Explorer (led by my same friend at UCLA) is looking.  Infrared light is redder than the reddest light you can see.  Really hot objects, thousands of degrees, glow in the visible light such as a lightbulb filament or the Sun.  The reason you can see your friends’ faces it that visible light reflects off of their faces to your eyes.  But if you had infrared eyes, your friends, cooler than the Sun but still hot, would glow but in the infrared.   (Compared to absolute zero, all your friends are “hot”.  Compared to the Sun, they are “cool”.  Feel free to compliment them on this.)   So infrared is the go-to color for astronomers to find small, cool, faint stars, that might have been missed by all astronomers until now.

The human body glows with the infrared light due to the heat it generates. Astronomers look for dim, cool stars with infrared telescopes.

Such dim stars could have their own planets orbiting them, and if close enough, could sustain life, maybe even intelligent life.   There may even be one closer than Proxima Centauri.  When I mentioned that to one of the co-creators and writers of the Big Bang Theory- when he was visiting UCLA to give the Physics and Astronomy Department commencement address — he told me, “The Federation may be sooner than we think.”

Update:  Since the time this espisode aired, the measurements of the distances to the Procyon stellar system and 61 Cygni system have changed slightly, so their order according to RECONS is now different than the order in the song.   Thanks to eagle-eared viewer Åingeal S. for asking me why they were “wrong” which allowed me to locate the difference using the internet archive of the RECONS webpage.

S04E04: The Hot Troll Deviation

October 14, 2010

Sometimes you need a secret decoder ring.  We had a few shout-outs to the world of physics and chemistry tonight.

Starting with the very first line of the episode:

KOOTHRAPPALI:   (TO SHELDON) I’m telling you, if xenon emits ultraviolet light, then those dark matter discoveries must be wrong.

And now you are in on the most controversial discussions in physics today.    We’ve discussed here before that about two-thirds of the matter in the galaxy is a dark, unknown substance: the aptly named “dark matter”.   Meanwhile teams of physicists are working hard to be the first to prove dark matter exists, by capturing one of its interactions in a particle detector.  For whoever detects it first, there is no end to the fame.


Sensitive detectors look for dark matter. A dark matter particle may kick a nucleus in the detector leaving behind detectable energy, such as ultraviolet light.


The race is on.   Many detectors are running.    Each is gambling on different techniques.  But what almost all have in common is they are looking for extraordinarily weak and rare events.   So physicists build their detectors from materials with extremely low radioactivity and place them deep under ground to keep them as quiet as possible.   Two of the running experiments have a signal the authors have claimed is consistent with dark matter.  The first is called  “Dama-Libra” (the Italian group who Leonard talked about to his mother in season two) and the other is called CoGeNT (some physicists need their shift key taken away from them.)

But a new type of detector started working recently.  Xenon is a gas in every breath you take, but being a noble gas just goes along for the ride, never interacting in your lungs.  But xenon can be refrigerated to below -162 degrees F where it becomes a liquid.   When a dark matter particle passes through it, it occasionally will give a single xenon atom a small kick.   That small kick causes the xenon’s atomic nucleus to move a short distance through the liquid—producing free electrons, heat, and light.   The highest frequency light your eyes can see is violet.  But energy deposited in xenon produces light with a  color a little bluer than violet, called ultra-violet light.  You can’t see it but particle detectors can.   The xenon detectors is enormous, 100 kilograms, hence its name XENON-100.  But XENON-100 doesn’t see the tell-tale ultra-violet light from dark matter collisions.   Is it because the others’ dark matter discoveries were wrong?  Or is there just not enough ultra-violet light being produced in the liquid xenon?  That’s what Sheldon and Koothrappali are arguing about.  And so. are. the physicists.

But the whiteboards today had nothing to do with this science.  Today’s whiteboards honored a special guest.  Once while talking to a Big Bang Theory writer, he recommended I watch the film Real Genius (1985).   I didn’t know what to expect but put it in my Netflix queue nevertheless.   When I saw it I was blown away….not necessarily by the story or the characters (which were fine), but by the important part: the scientific sets and dialogue.    It turns out that Real Genius had a scientific consultant,  Martin Gundersen, a professor of physics from across town, the University of Southern California (USC).    Now that I know how much goes into getting sets and stories right, I was in awe of what a great job they had done, from the sets to weaving physics right into the plot line.   So I sent Prof. Gundersen a fan letter.   He  responded and eventually was able to visit the set of The Big Bang Theory during the taping of this episode.


Prof. Martin Gundersen, the science consultant for Real Genius (1985). He recognized the whiteboard in Leonard and Sheldon's apartment during the taping of this episode.


So those of you that are whiteboard fans AND have a good memory know what was on the whiteboards.  It was identical to one of the boards used in Real Genius 25 years ago….



Chris Knight (Val Kilmer) steps out of the way so we can see the original whiteboard in Real Genius (1985).


I don’t want to spoil the plot of Real Genius by explaining how excimer lasers work.  It’s only been 25 years and not everybody has had a chance to see it yet.

Finally, we saw Sheldon make a smell of hydrogen sulfide and ammonia gas.  Hydrogen sulfide smells like putrefying eggs.  And ammonia smells like ammonia.   We were careful not to tell how hydrogen sulfide could really be made since it’s been in the news that people have been hurting themselves and others when making it with household chemicals.   We at The Big Bang Theory are nothing if not socially conscious.  So instead I imagined Sheldon made it with something only available around the lab,  an aqueous solution of hydrogen sulfide.   That immediately produces:

(NH4)2S →H2S + 2 NH3

By now I expect you are running out of the room.

S04E03: The Zazzy Substitution

October 7, 2010

In tonight’s episode we heard the names of many physicists who took part in the Manhattan Project, the U.S. program that built the first nuclear bombs.  We were  introduced first to the name of one of the most famous physicists of the twentieth century, the chief physicist in charge of building the so-called “gadgets”, Dr. J. Robert Oppenheimer.


J. Robert Oppenheimer, theoretical physicist and leader of the Manhattan Project

Unlike Sheldon (and many others),  I prefer to say “nuclear” not “atomic”.   “Atomic” tells us nothing special.  All chemical reactions use atoms, and you’d be justified in calling even T.N.T. an atomic bomb.  What is special about nuclear power is that it uses the forces in the nucleus, which are about a million times stronger than the forces holding the rest of the atom together.  It is specifically nuclear reactions, not chemical reactions, that are responsible for the extraordinary power of a nuclear bomb.

Oppenheimer was a theoretical physicist, who was reported to be extraordinary clumsy around laboratory equipment. “Oppie”, as he was called, was a fan of languages and even taught himself Sanskrit.    Those who knew him described him as somewhere between aloof and pretentious.   Either way, he had trouble dealing with people.   His brother Frank, also a physicist, reports him having said:

“I need physics more than friends.”  – J. Robert Oppenheimer

At this point I wonder, does he sounds similar to any of the fictional physicists we know?

But at the same time, Oppenheimer and our fictional hero could not be more different.  Oppenheimer had a driving ambition to be close to the political powers in Washington.  So much so, Oppenheimer even lied and falsely implicated his friend, Haakon Chevalier, as being linked to Communist espionage, ultimately causing  grave damage to his friend’s career, while furthering his own.   Like a Greek tragedy, this misstep ultimately led to Oppenheimer’s own fall from political grace, ultimately even having his security clearance revoked — a stunning blow to the man who had been the scientific leader of what was  perhaps the largest secret military project ever undertaken.

Oppenheimer also had a strong affinity toward Eastern religion, specifically Hinduism.  When the first test atomic bomb was dropped at the Trinity Site on July 16, 1945, he famously recalled pondering several phrases from the Bhagavad-Gita:

If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one.


Now I am become death, the destroyer of worlds.

I never understood the strange grammar of that second quote, since he was speaking in translation.   Perhaps a Sanskrit-reading reader of this blog could explain below if a similar construction exists in the original.  (Updated: see comments.)

As it happens, I visited the Trinity Site last weekend.   I had given a seminar last Friday nearby, at the National Radio Astronomy Observatory, home of the Very Large Array in Socorro, New Mexico.  (That’s the same array of telescopes Jodie Foster used in the movie Contact.  And yes, she really went there; they still have pictures of her visit on the walls.)  Twice per year, the Trinity is open to the public.  You can combine that with a trip to the VLA.


Your science consultant at the Trinity Site.

After a short drive through the White Sands Missile Range we arrived at the site.  You might worry about the the wisdom of  walking around unprotected where a 20 kiloton nuclear weapon was detonated.  What about the radioactivity?  After the atomic bomb test, the heat of the blast melted the sand and plutonium fallout into a glass, forming a unique  mineral called trinitite.    Small bits of the green glass are underfoot nearly everywhere you walk.


During the nuclear explosion at the Trinity Site, desert sand fused with nuclear fallout to produce a new mineral, trinitite.

For the hour I walked around,  I was exposed to radiation dose of 0.5 “millirem”.   A millirem is one thousandth of a “Roentgen Equivalent Man”, an outdated but well-known unit for measuring radiation exposure.

That may sound scary but 0.5 millirem is very small compared the natural sources of radiation which are everywhere.   The average person in the U.S. receives over a 350 millirem dose every year, mostly from radon.  Even if you try to escape radon,  the potassium-40 in your bones are constantly undergoing radioactive decay.   For my trip to the Trinity site, I received by far most of my dose from the two-hour airplane flight each way from Los Angeles to Albuquerque.  In a commercial jet you are above much of the atmosphere that normally protects you from radiation due to cosmic rays, particles from space striking the earth.   (Extra for experts:  it is not just the dose, but the duration of the dose that matters.  Doses received slowly, over the course of a year, give your DNA more chance to repair itself before possibly forming tumors than if you receive it all at once.)   It takes a 100,000 millirem dose before it starts to have measurable effects on   your blood.  At twice that, you start feeling radiation sickness.

In many other cases radiation is  outright helpful.  X-rays help doctors diagnose broken bones and the positrons emitted in PET scans allow doctors to find cancer.   Gamma-ray and other beams are often used to destroy tumors once they are found.  Biologists use radioactive markers to understand all sorts of processes important to life.   Smoke detectors rely on the decays of americium  to light a phosphor.    Nuclear power reactors provide an enormous supply of electricity while producing essentially no greenhouse gases.

Now disregarding my earlier complaint about “atomic” versus “nuclear”, let us now in all seriousness consult the Doomsday Clock of the Bulletin of the Atomic Scientists:


The Doomsday Clock of the Bulletin of the Atomic Scientists

It is six minutes to midnight, folks.

S04E02: The Cruciferous Vegetable Amplification

September 30, 2010

To quote Sheldon from tonight’s episode,  “This is a photograph of the 1911 Solvay Conference on the theory of radiation and quanta:”

Members of the first Solvay Conference, in 1911. Left-to right: Standing: Robert Goldschmidt, Max Planck, Heinrich Rubens, Arnold Sommerfeld, Frederick Lindemann, Maurice de Broglie, Martin Knudsen, Fritz Hasenöhrl, Georges Hostelet, Edouard Herzen, James Hopwood Jeans, Ernest Rutherford, Heike Kamerlingh Onnes, Albert Einstein, Paul Langevin. Seated: Walther Nernst, Marcel Brillouin, Ernest Solvay, Hendrik Lorentz, Emil Warburg, Jean-Baptiste Perrin (reading), Wilhelm Wien (upright), Marie Curie, Henri Poincaré.

Unlike Sheldon, I have not Photoshopped anything onto it.   That’s not to say the above photo isn’t doctored, however.  See the fellow with the gray beard sitting at the table?   That’s Ernest Solvay, the Belgian Industrialist who sponsored the conference.  He couldn’t be present for the photo, so his head was pasted over that of a stand-in.  I heard they did it with Photoshop running on a Windows 11 laptop.

Solvay made his fortune by inventing a manufacturing process for sodium carbonate, a process used to this day.   In the Solvay method, seawater was mixed with limestone to produce soda ash,  the common name for sodium carbonate.  Among its many uses, soda ash “softens” water; it takes up the magnesium and calcium found in “hard water” that would otherwise limit the washing action of detergent.    Soda ash is used to reduce the acidity of food without using harsher chemicals,  such as lye.   In an important industrial process,  soda ash  is used to coat raw pretzels, which gives them their nice brown skin upon cooking.

Solvay dedicated much of his fortune to philanthropy, including seminal meetings among the leading luminaries of physics.   Such was the origin of the first of these, the 1911 Solvay Conference.

So what happened at the Solvay Conference?  I’ve consulted my go-to source on particle-physics history, the book Inward Bound, by Abraham Pais.  Setting the stage for the conference, Ernest Rutherford, had just completed his famous experiments indicating that an atom has a dense central nucleus surrounded by electrons located thousands of times farther away than the radius of the nucleus.   In his lab, electrically charged alpha particles scattered backwards from a gold foil target, indicating they were encountering a dense region of electric charge.

Rutherford's alpha particles could scatter backwards from a gold atom. This led him to realize there had to be an atomic nucleus.

But Rutherford didn’t say a word about it at Solvay 1911.  Meanwhile Marie Curie, also present, was headed down a different path to the same discovery.  She realized the radioactive nature of elements had nothing to do with their chemical properties such as reactivity, thermal conductivity,  etc.  She was spot on:

Radioactive phenomena form a world apart, without any connection with the preceding phenomena.  It seems therefore that radioactive phenomena originate from a deeper region of the atom, a region inaccessible to our means of influence and probably also to our means of observation, except at the moment of atomic explosions.  -Marie Curie

Rutherford was in the audience, having already realized that his alpha particle scattering experiments showed exactly this.  But he said nothing.

And yet to this day Rutherford is credited with the discovery of the atomic nucleus.  As well he should be, since he designed and interpreted the experiments that proved it true.  Of course Marie Curie did wonderful other experiments in her own right, elucidating the nature of radiactivity.  Both won their own Nobel prizes.

Tonight’s whiteboards

Here’s a little Inside-Hollywood information.  The boards Sheldon used tonight were not set dressing; they were a prop.   Most weeks, I send the material for the whiteboards to the set-dressing department.   They take care of furniture, various decorations on the set–and for our show–the white boards.  But tonight was special.  Sheldon touched a board.   Anything an actor touches automatically becomes the purview of a different department–the properties department.  So these particular boards were props.

If you take a closer look at these props, you will see he has Bayes’ theorem up there.  Perhaps that’s because since he is studying the meaning of some genetic tests.  Here’s a question about medical tests, showing you must know Bayes’ theorem to understand what yours mean.  Suppose you take a blood test for a disease that only has a small chance of error:  Say  99% of the time the test identifies the disease when one is present.  But also rarely, say 5% of the time, it will say you have the disease when you don’t.  Question:  Your test comes back positive; what is the probability that you have the disease?

Answer: Not enough information.

You still need to know the probability that the disease occurs in your population and apply Bayes’ theorem, the theorem on the board.  It is straightforward to see.  If we test you for smallpox with such a test, a disease nobody on Earth has, then 1 time in twenty (5%)  you will be positive for smallpox, even though we know you don’t have the disease.   Now if only 0.5% of the population has the disease and you test positive, then there is still over a 90% chance you don’t have the disease.  This is  why your doctor does not give you the tests that would have found problems early…it would cost too much in all those who were identified as false positives.   From your insurance company’s point of view, you aren’t worth it.

As for the family tree on the board, that is official genetic counselor notation.   My sister Linda just graduated with a master’s degree in genetic counseling and she gave me all the symbols to use, including that Sheldon has a fraternal (“dizygotic”) twin, Missy.   So for this episode , your consultant consulted  a consultant.

(Tonight’s blog edited by my friend Karen Joyce, USAP)

S04E01: The Robotic Manipulation

September 23, 2010

The Big Bang Theory, gives us not just toilet humor, but a contemporary physics controversy, too.   Tonight Raj worries about how Aquaman uses his toilet.  How can he flush it underwater?

Water sticks to itself, as shuttle astronaut Leland Melvin can see.  Blobs of water float around the space station, without diffusing into a mist, but remain cohesive.   Is this cohesion at work in a toilet flush?

The most common toilet in North America is a spectacle of physics, the “siphoning toilet”.   Using a design honed for over two thousand years, here’s how the toilet works:   Water sits in the bowl of the toilet just below the level of the top of an  S-shaped curve in the drain pipe behind the bowl.   This water does a nice job of sealing off the toilet from the noxious gases in the sewer pipe as well as keeping the bowl tidy.

When you push the tank handle, water rushes into the bowl rapidly, pushing a column of water through the entire S-shaped curve.   The modern explanation is that gravity and the cohesive properties of water do the rest.  Once there is a continuous column of water through the S curve, the water farthest along is falling down to the sewer.  It is sticking to the water behind it and pulls it along, making the familiar whoosh sound.  This flow continues until there is a break in the contiguous column of water.  That break happens when the tank empties and the water in the bowl is low enough to allow air in and separate the water from itself.    That is why the whoosh is followed by the gurgle.   It’s the air breaking up the column of water in the S-shaped pipe.  The process finishes with the water in the bowl just below the level of the top of the S-shaped pipe, ready to serve another day.

Gravity pulls the water (and what’s in it) down to the sewer.

“Wait,” some might object.  None of this explanation used the effect of atmospheric pressure to explain the siphon.  Many of us learned that it is atmospheric pressure pushing the water over the obstacle–not cohesion pulling it along.    If the cohesion argument were correct, why is the maximum height of an obstacle the siphon can pass equal to 34 feet of water, the typical atmospheric pressure?   Even the ancient Greeks knew they could not siphon water out of a mine farther than 34 feet vertically.   You can even calculate the maximum height of a siphon using Bernoulli’s equation and atmospheric pressure.  These sure makes it look like atmospheric pressure is a key player in the operation of a siphon.

Here’s what I suspect the cohesion camp would say is happening: as the water gets higher and higher, its pressure decreases until it actually boils at room temperature.  The presence of water vapor breaks the cohesion of the column of water.  The argument that it is the cohesive properties of water, and not atmospheric pressure, seems to rest on a discussion of siphons in vacuum.  It’s been claimed that a siphon will work even in a vacuum which would certainly remove atmospheric pressure from the explanation.    So unlike Aquaman, Vacuum-man would have no problem using his toilet. (Take that, DC Comics!)   But I am skeptical of this  particular claim.  Since water has no liquid state in vacuum, I don’t see how a vacuum siphon can even exist.   The experiments the proponents of cohesion point to only put the water in the tube under vacuum, not the reservoirs.  So this is not the proof that is claimed.

A physicist in Sydney shows us a pretty convincing experiment that atmospheric pressure pushes the water over the obstacle.  I have not yet finished thinking about if his experiment could be explained with a cohesion argument.

At the moment, I don’t think either claim is proven…whether atmospheric pressure pushes the water up to the height of the obstacle, or whether the cohesion to water already past the obstacle pulls it along.  To be a meaningful question, it must be possible to answer experimentally, at least in principle.  Perhaps by studying under what conditions fluids of different cohesiveness (“tensile strength” to experts)  and boiling points break the siphon the answer will be revealed.  If no experiment can distinguish the two cases, even in principle, it may turn out to be just semantics.  I suspect the latter. On a molecular scale, the cohesion force (created by an imbalance of electrical forces on water molecules) and the pressure force (created by an imbalance of electrical forces on water molecules) seem to me to look the same.

Regardless of whether you adhere to the cohesion or atmospheric pressure argument for driving the water over an obstacle, there is no question that is is gravity that drives the siphon.  This year it was noted that even the entry for siphon was wrong in the Oxford English Dictionary (OED).  The error was pointed out this summer by Australian physicist Dr. Stephen Hughes who noted:

“An extensive check of online and offline dictionaries did not reveal a single dictionary that correctly referred to gravity being the operative force in a siphon.”

New Scientist magazine combed through the history of Wikipedia entries, and they never had that wrong.  (Take that, OED!)

But Aquaman is not from North America, where siphoning toilets are ubiquitous.  He is from the sunken continent Atlantis, which must have evolved their own toilet technology.  If a siphoning water toilet were flushed where would the water go?  It would not work if the water went back directly into the same ocean.  If sent elsewhere, then the toilet would continuously flush forever.   But that would eventually drain the ocean.  Another possibility would be to make the toilet operate with a denser fluid, such as glycol, or sulphuric acid (don’t splash).    But this would only work if Aquaman somehow voided himself with fluids and other material denser than sea water, so it would not float away before flushing.  Alas, some important questions are beyond the scope of even physics.

S03E23: The Lunar Excitation

May 24, 2010

The Moon is being pulled into the Earth.   Both are being pulled into the Sun.

But don’t duck and cover. That’s what orbits are all about.    I find a common misconception among students about why astronauts float around the Space Station.   They sometimes think that this is because the astronauts are out the reach of Earth’s gravity.  That, or because they drink Tang.

Scale drawing shows that the Space Station astronauts are not far enough from Earth to ignore its gravitational pull.

Neither is true.   Orbiting astronauts,  Space Stations and satellites  are being pulled by gravity toward the center of the Earth just as we are.   At the Space Station’s altitude, about 185 miles  above the Earth’s surface, the astronauts experience a pull of gravity that is still about 90% as strong as down here.   The astronauts you see floating still have nearly their entire weight.

The astronauts are falling, but so is the floor of the station.  Just like when you go on the free fall ride at an amusement park you experience weightlessness, not because you have no weight, but because the floor falls away from you at the same rate you are falling.  You weigh the same.  On Earth, the ride can can last only a couple of seconds.  The astronauts and the Space Station fall for years and years.    The astronauts still have 90% of their weight, but you just can’t tell by putting a bathroom scale on the floor, since the floor is falling away.   The astronauts don’t drink Tang any more either.

The reason the astronauts don’t hit the ground is that they are moving fast, over 17,000 miles per hour, at a right angle to the downward direction.    In the absence of any other force, they would move in  a straight line forever,  disappearing from our solar system.  The pull of the Earth changes their direction, not enough to pull them to the ground, but to keep the astronauts and the station in a  circular orbit that takes them around the earth every hour and a half.   (Physicist nitpickers would probably want to comment that the orbit is not perfectly circular, so in the spirit of full disclosure:  the orbits can be ellipses rather than circles.)  It is just as if you were to swing a cat over your head by its tail.  You pull inward but the body of the cat stays at the same distance from you, moving perpendicularly to the direction you are pulling.  When the speed and distance are just right, the astronauts and station stay forever at the same altitude above the Earth.

The same thing happens for the Earth orbiting the Sun.   It is why we haven’t yet fallen into the Sun even though the Earth feels a large gravitational force towards it.  The Moon orbits the Sun too.  If  it didn’t we’d have lost  it by now.

So the Earth and Moon are falling into the Sun.   Like Galileo dropping one-pound and ten-pound objects from the Tower of Pisa we can ask, “Do they fall at the same rate?”  This is where a “lunar ranging” experiment such as performed by the boys comes into play.   They can bounce a laser off of mirrors left by the Apollo astronauts on the Moon.  The mirrors are the corner of a cube and any light ray that hits them bounces of all three mirrors at just the right angles so that it returns from the direction it came.

Retroreflectors left by the Apollo 11 astronauts on the Moon will reflect lasers back in the direction from which they came.

It takes about 2.5 seconds for the light to travel to the Moon and back.  By measuring the exact timing to better than a hundred billionth of a second, these laser lunar ranging experiments have measured the distance to the Moon to better than a millimeter.   Now astrophysicists can check that the Moon is behaving exactly as it should.

The central principle of Einstein’s theory of general relativity is the “equivalence principle”, that objects should fall at the same rate regardless of their mass or chemical composition.   This gives a testable prediction.  The Moon are Earth are significantly different materials and size.  Yet the lunar ranging experiments show the Moon and the Earth fall together towards the Sun.   Actually this is only just the “weak” version of the equivalence principle.   There is more to mass than just the composition of the objects.  Since the energy of assembling the Earth and Moon is so much different, according to Einstein’s  famous m = E/c2 , they have a different amount of  this source of mass as well.    Yet still, lunar rangers measure that we and the Moon fall at the same rate.  The best test of this “strong equivalence principle” comes from this lunar ranging.

The lunar ranging experiments are the best tests of  many other aspects of Einstein’s theory of relativity.  In addition their close monitoring of the Moon have told us that it actually has a liquid core.  The lunar ranging experiment is one of the longest running experiments in physics.  In its 35 year history it has marked that not only is the Moon not in danger of actually hitting the Earth, but it is moving away from us at about 1.5 inches per year, due to energy lost as it creates high and low tides for surfers.   In about five hundred million years the Moon will be so far away, there will never again be a total eclipse of the Sun.   So go out and enjoy one while you still can.

Laser ranging to the Moon. (From the Apache Point Observatory Lunar Laser-Ranging Operation). The Moon is overexposed to take the photo.

Last (and certainly least), as Leonard explained to Zack, the presence of reflections from the retro-reflectors  often are used to rebut claims that humans did not really go to the Moon.   Actually Leonard’s argument is specious.   After all, unmanned missions could have left the reflectors, just as the Russians did.    I’m still waiting for the producers to invite me to see NASA’s soundstage on the backlot.

While preparing the set, a few BBT crew members asked a question I never thought of.  Two and a half  seconds later, the apartment, and detecting apparatus has moved since the Earth is rotating.   So why doesn’t the laser spot miss their detector?   The experiment still works because the laser’s spot  spreads out as it travels.  The spot size when it returns to Earth is over 10km, much bigger than a laser pointer, and smaller than the distance Pasadena moves in 2.5 seconds due to the Earth’s rotation.

Tonight was the season three finale.  Thanks to those who followed this blog after each show this year.  Tune in next season, when  ***SPOILER ALERT*** the Moon will be about an inch farther away.

S03E22: The Staircase Implementation

May 17, 2010

Fans will no doubt complain about a scientific inaccuracy tonight.  The production crew wouldn’t let me bring real rocket fuel for the episode and instead used water. Apparently Warner Brothers has some rule against bringing hydrazine and nitrogen-5 onto their sets.

Hydrazine has a long history in the rocket world as a propellant.  Its first use was for the German rocket-propelled military aircraft, the Messerschmitt Me 163 Komet.  To date, the only such aircraft ever in regular operation.

A hydrazine-fueled aircraft in WWII

When mixing the hydrazine with solvents, the Germans called the fuel “B-Stoff”.   Today hydrazine is used for more peaceful purposes, such as adjusting the orbits of satellites and as auxiliary power for the International Space Station.

The hydrazine reaction was on tonight’s boards so it was a kind of spoiler for those paying attention.

The boards in an early scene show how hydrazine works as a rocket fuel... and foreshadows what happens next.

The concept the writers explained to me was that Leonard’s mistake was that something didn’t scale.   They wanted that what would work for a real rocket, would not scale to the small amount of fuel he brought.   The hydrazine reactions happen faster by exposure to the element iridium.   The word chemists would use, is to say the reaction is “catalyzed” by iridium.  A catalyst accelerates a reaction but is not used up.   This is what the platinum does in a car’s catalytic converter and was the reason for the ‘iridium flask’.

By what is now the season’s third application of  the square-cube law, the full amount of hydrazine would be exposed to a relatively small surface area of iridium.  In Leonard’s small container, a far greater fraction of hydrazine is exposed to iridium, and as Sheldon realizes, becomes highly explosive as shown on the boards above.

We added some “Nitrogen-5”, or pentanitrogen, to sweeten the mixture.  That was a fuel that was being developed in 2003, and would likely have some secret aspects Leonard should not discuss.

Not everything on the boards relates to rocket fuel.  Recall it is 2003.   Drs. Abrikosov, Ginzburg and Leggett had just received the Nobel Prize in physics

for pioneering contributions to the theory of superconductors and superfluids.

Their theoretical work is laid out on the boards as well, as something Sheldon would have been thinking about.

The whiteboards star the show once again.   I don’t know why the director keeps letting the actors walk around and upstage them.

S03E21: The Plimpton Situation

May 10, 2010

In the music world, the death of a star is  precipitated by sex, drugs and rock-n-roll.  In the Universe, the death of a star is precipitated by extinguishing the nuclear fusion reactions in its stellar furnace.  The end result is often one of the most fascinating objects in the universe,  a pulsating neutron star,  “pulsar” for short.

Shortly after discovering pulsars (while still a graduate student in 1967) Jocelyn Bell was told "Miss Bell, you have made the greatest astronomical discovery of the twentieth century".

Neutron stars hold the key to what Dr. Elizabeth Plimpton had written on her hand in this episode.

Dr. Plimpton has the coordinates to what?

The life of a star is a constant tug-of-war.  The force of gravity never ceases pulling all the star’s material inward, attempting to make it smaller and denser.  But a denser star would accelerate the nuclear fusion reactions, raising the star’s temperature.  Like heating a pan of jiffy-pop, the heat causes an outward pressure, trying to making the star larger.   For much of a star’s life the forces strike a balance and stars such as our own stay pretty much the same size for billions of years.

But gravity always wins.  Fo now,our own Sun shines largely by turning hydrogen into helium.  By making a more tightly bound nucleus in this reaction, energy is left over and produces the light and heat of the Sun.   About 5 billion years from now, after its hydrogen is used up, our Sun will turn to alternative energy, fusing  helium into carbon and oxygen, becoming much larger and growing briefly into a Red Giant star (while engulfing Mercury and Venus, and incinerating the Earth) in the process.   But that’s all folks.   Our  Sun will finally run out of energy, and puff off all the excess material.  The Sun’s now naked core will quietly cool.   Gravity will pull it tighter and tighter until the electrons in the Sun resist being pushed any closer together.  The remaining ember of carbon and oxygen is incredibly dense.  A white dwarf  with the mass of the Sun will be the size of only the Earth.  It really isn’t even much of  star any more since it is no longer producing its own energy.  It only glows by  radiating the energy from its former life, a cosmic Zsa Zsa Gabor.

But a star more massive than our Sun face a different fate.    A larger star does not go quietly but often blows off material in a dramatic supernova explosion followed by a gravitational collapse of the remaining core.  The inward pressure due to gravity is so great that the electrons that hold up a White Dwarf are “pushed into” the remaining protons to form neutrons.   The stellar material now moves even further inward under the force of gravity to make an object as dense as an atomic nucleus.  Since it is mostly made of neutrons, it is called a neutron star.   A neutron star 3 times the mass of Sun is so small and dense, it is smaller than Los Angeles.

A typical neutron star is smaller than Los Angeles and more massive than the Sun.

It is so dense, that one teaspoonful of neutron star material here on Earth would weigh as much as a mountain.   As Dr. Plimpton says in the episode, if you went even close to its surface you’d be crushed by its strong gravity.   That is if not first ripped limb-from-limb first by the differences in its strong force of gravity on different sides of your body.

But a neutron star’s useful life is far from over.  While a graduate student Jocelyn Bell and her thesis advisor Anthony Hewish discovered regular bursts, from seconds to fractions of a second, of radio static from specific points in the galaxy.  These turned out to be the fast spinning remnant neutron stars.  Just as when a slowly rotating Olympic skater pulls his or her arms inward to speed up, the small neutron star remnant of a star that probably rotated about once per few weeks, now  rotates every few seconds or even faster.   When the poles of the neutron star point at us on Earth we see a burst of radio and other light.   Just as the spinning lamp in a lighthouse produces a flash of light to those at sea, we on Earth see a bursts of energy from the pulsar as it rotates.  For this and her career’s work, Dr. Bell-Burnell was awarded the highest rank an British citizen can attain, Dame of the Britsh Empire.

And just as the spinning lamps in a lighthouse  produce a regular flash of light for ships, cosmic voyagers would see these pulsars, spinning neutron stars,  as regular and bright beacons from afar.   The Pioneer spacecrafts launched in the 1970s are now leaving the solar system.  With them they take our calling card on a gold-plated plaque.    To instruct whoever or whatever discovers them how to find us, we show them the Earth relative to pulsars, cosmic beacons that will be visible throughout our portion of the Milky Way.

The plaques carried on the Pioneer spacecrafts out of our solar system shows our location relative to 14 neutron stars (pulsars)

I’m told Carl Sagan caught hell for putting naked pictures in space.  So for the subsequent Voyager spacecrafts, now the farthest spaceprobe from Earth, we instead  sent “the golden record”…

The "Golden Record" (click to hear) riding on the Voyager spacecrafts includes "The Sounds of Earth". The cover still includes the location of Earth relative to nearby pulsars...but without the naughty pictures.

…which sends our regards with more puritanical messages.  The record is our ultimate mix tape to our alien friends.   If we humans were to launch such a space probe now, I fear it would only have a golden MP3.  Voyager 1 has left the Solar System and is about 110 times further than the Earth is from the Sun and is our most distant space probe.  It will leave our solar system around 2015 and carry out message into interstellar space.

But as Steven Hawking points out, this might not have been such a good idea.  Just ask the ancient Aztecs how much they benefited from the visits of the Spanish explorers.   Even if we are visited by a species that is not violent, visitors  may inadvertently bring microbes we’ve never been exposed to before that wipe us out.    This may even be an inevitable by-product of all such contacts.   If you haven’t read it, I highly recommend the masterpiece Guns Germs & Steel written by Jared Diamond (also at UCLA) who gives a scientific basis to the unfolding of such historical events.   But the sword cuts both ways…  In H.G. Wells’s War of the Worlds, it is our own microbes that ultimately killed the Martian visitors.

So it was the location of a new pulsar, a new neutron star, that Elizabeth Plimpton had written on her hand for tonight’s episode.  A brand-new one  (a “Soft Gamma-ray Repeater” at RA 4h40m, Dec 55035′, which is effectively its longitude and latitude on the sky) was announced on the  The Astronomer’s Telegram before the episode was taped.   In another easter-egg to the High-Def enabled,  note the shout-out to Brian Greene’s excellent popular science book, in the title of Dr. Plimpton’s book:  The Effervescent Universe.

No matter how much we hide, our radio and television transmissions are already giving us away, at the speed of light.   Even tonight’s episode is already beyond Mars.   The extra-terrestrials can easily find us, and may already be on their way.

S03E20: The Spaghetti Catalyst

May 3, 2010

The weather tonight (May 3, 2010)  is a cool 10,000 degrees Fahrenheit.  In some regions temperatures may increase over the next few days to over 15,0000,000 degrees.    Wind-speeds will be in excess of one million miles per hour.  That’s the actual forecast.  If you live on the surface of the Sun.

Keeping the science correct  for an episode typically involves just a little research and maybe a few notes on a napkin.  But  tonight’s episode involved serious prognostication and luck.    Tonight Raj says there are no solar flares.  All I needed to know, back in early March when the writers sent me that line, was that Raj would be right, i.e. that tonight, when the episode would air, that there would be no particles arriving at Earth produced by solar flares.

(Click to activate.) Image of the Sun with a solar flare by NASA's SOHO satellite with ultraviolet light

So I’ve been anxiously reading the space weather every day for the last few weeks and hoping for the best:

April 15:

“Solar activity is very low. No significant flare events are expected.”

Whew.  April 16, the same!  And so on every day April 17 and onward.   Right down for the rest of the month:

“Solar activity is very low. No significant flare events are expected.”

But then, with a small addition on April 30:

“There is a small active region in the NE disk.”

Uh oh.  Then I saw this for May 1:

Two C-class flares were observed yesterday….Unnumbered region, N24 E68 (X=-800,Y= 400). Alpha region. C-class flare possible. Position approximate.

My luck had run out.

What am I worrying about?  The weather report at the top of this entry really does describe the active Sun.    Lines of magnetic field on the Sun can burst open releasing enormous amounts of energy, comparable to millions of atomic bombs within minutes.  Light of all types reach Earth: from radio waves to gamma-rays.  ( My undergraduate senior thesis work was a cyclotron experiment to predict the rate of gamma from solar flares.)   Worse still, trapped charged particles such as electrons protons and atomic nuclei, previously tied to the Sun by magnetic fields, pour out of the opening and some make their way to Earth.   It is as if the Sun produced a giant fart.

X-ray image of the Sun from the Japanese satellite Yohkoh. Unlike X-ray pictures from your dentist, this image is not made by absorbing X-rays. Rather million-degree hot gas in solar flares directly emits the pattern of X-rays that are photographed.

Yohkoh webpage

Ejected particles arrive at Earth a day or so later and can wreak havoc.  Usually we are protected from charged particle radiation by the Earth’s magnetic field which deflects them.  But these can stream into openings in our own Earth’s magnetic field near the poles, releasing bursts of energy that at their worst can disrupt all sorts of radio communications and the power grid.   The largest storms can eject matter and magnetic fields together.  Those magnetic fields can cancel that at the Earth and create an opening for the energetic, and damaging, ionizing particles deep into the Earth’s atmosphere, even reaching the ground.

One among many famous solar events, on Halloween 2003, such a solar storm interrupted satellite communications and even destroyed a research satellite.  Astronauts on the Space Station hid as best they could deep in the station but still saw flashing lights in their closed eyes, due to cosmic rays crossing and ionizing their eyeballs’ vitreous fluid.  In March 1989, a solar storm disrupted power transmission and knocked out power to 6 million Québécois.  In 1958,  radio communication from  the U.S.  to Europe was cut off.   But perhaps the most tragic event was the complete interruption of a critical four minutes of the 1941 radio broadcast of the  baseball playoffs of the Pittsburgh Pirates against the Brooklyn Dodgers.

On a positive note, these charged particles produce beautiful displays of light as they ionize the air in the upper atmosphere creating Auroras, curtains of shimmering light typically only seen near the polar regions, but on the night of Feb 11, 1958 could be seen as far south as Los Angeles.

Aurora ("Northern Lights") produced by charged particles from the Sun hitting the Earth.

(From Astronomy Picture of the Day)

Radiation damage caused by the particles in storms is one of the major hazards to astronauts in space.  Personally I worry more for them about memory leaks from C++ programs.

Raj’s report of no solar flares had been a pretty good bet.  Astrophysicists worldwide have marveled at the lack of solar activity over the last few years.  NASA reports the Sun has not been this quiet in nearly a century.  Fear not though.  The solar activity follows a reliable 11 year cycle.  Every 11 years the orientation of the Sun’s magnetic field changes direction completely.  During the flip, the magnetic field becomes unstable and the number of solar storms increases dramatically.  In 2012 and 2013 solar astrophysicists predict a large number of storms that will disrupt GPS service and perhaps even broadcast of the 2012 Olympics.  Dish Network subscribers may as well order seasons 5 and 6 of The Big Bang Theory (TBBT) on DVD now.

Time to check the latest report for solar activity on May 2, which would let us know if Raj will be  right tonight:

An unstable nest of magnetic fields emerged over the sun’s northeastern horizon yesterday, and it is crackling with C-class solar flares.

Image taken on May 1 this year of the current active region on the Sun that I am worrying about.

Image by P. Lawrence at Spaceweather.com

Sounds grim. But C-class are among the weakest solar flares we have.  They are fun for amateur astronomers to look at, but shouldn’t disrupt Sheldon’s GPS nor, more importantly, your reception of tonight’s episode of TBBT.

S03E19: The Wheaton Recurrence

April 12, 2010
Giant ants were the terror of the movie Them! (1954).  Tonight Rajesh and Howard realize giant ants would be a cool new method of transportation.  But Sheldon Cooper is right:  unfortunately physics determines that giant ants cannot exist on our planet as we know it.

Giant ants in the film Them! (1954) violate the square-cube law.

The evolutionary biologist, J.B.S. Haldane, won this argument already in his 1926 essay On Being the Right Size“.  In his essay, Handane did more than observe elephants are larger than mice but explained, using physics, how changes in size demand changes in form.

A typical ant we know and love is about 5mm long and has a mass of about 5 milligrams.   The giant ants you might like to have around would be 1000 times longer.   Not just longer, but 1000 times wider.  Not just wider, but 1000 times taller.  To calculate the new mass of the giant ant we have to multiply these all togher–a billion times the volume.   At the same density, a giant ant would weigh about 5 tons.   But its legs would only be wider in two dimensions.  They are a million times stronger, but that is not enough–for a creature a billion times heavier.   Before taking their first step they would break all their legs, leaving them immoblile and harmless.   While mass increases as the cube of size, the function of its structure improves only as the square, hence the name “square-cube law”.

Note to bug spray companies:  Just make a chemical that grows ants 1000-fold in every dimension.  That will stop ants in their tracks.   That’s sure to be a best-selling item.

Elephants have no problem being 5 tons.  But they don’t support themselves with just the flimsy exoskeleton that suffices for ants.  We and other animals our size have internal bones to support us.   This is just one example of how physics determines that animals must fundamentally change their form if they are to be much larger or smaller.

So there is no need to watch Honey, I Shrunk the Kids (1989).   If our bodies shrunk to the size of an ant, we would be just as hopeless as the giant ant.   As warm-blooded creatures, we humans lose body heat with our surface area, which goes as the square of our linear size.  Meanwhile our total body mass decreases much faster, as the cube.   Even at such a miniscule size, you would never be able to eat enough to stay warm.    Whales, warm-blooded mammals of the sea, benefit from growing so large in keeping warm, especially since water conducts heat away faster than air.  But they have no legs to stand on, being able to rely on their buoyancy in water.  So physicists could have predicted the largest mammals would live in the sea.  

The square-cube law explains why there are no mice in Spitsbergen.

Worse still for the giant ants, they bring oxygen into their system directly through their exoskeleton.  It is as if you could breathe directly through your skin.   That’s a lot less effort than growing lungs, but that won’t work at our size….the volume needing to be sustained by air diffusing through the surface is just too large.  Animals had to develop lungs in order to grow to larger.   For life,  form follows not function, but rather systems serve size.

Physics constrains the nature of life.  So fear not elephant-sized eagles:   Wind speed must increase as the square of length to keep a body aloft, limiting the size of winged creatures.  Some physicists, such as Carl Sagan and E.E. Salpeter, have even gone so far as to predict the properties of life on Jupiter  in its large gaseous “oceans” of ammonia possibly inhabited by their so-called “sinkers”, “floaters” and “hunters”.  If not found on Jupiter, surely somewhere among the billions of Jupiter’s cousins in our galaxy there might be some such life.

I went into physics because I didn’t like biology.  (Too smelly and squishy.)  After teaching physics to life-science majors, I suspect the reverse is also often true.   Unfortunately for the biologists though, physics is everywhere, right down to explaining the basic structures of life.   Physics cannot determine exactly which life forms we will encounter, the details being largely accidents of history.  But whatever path successful lifeforms go down, they are constrained to obey the laws of physics.

Now we can think back to Sheldon’s dream last episode.  He had a dream that he was a giant but didn’t know it because everything else was increased by the same scale.   Sheldon said the reason he knew, was because he was wearing size 1,000,000 pants.   But at that point, he must have also realized it was a dream.  I don’t think Sheldon would be fooled.  After all, TBBT will not be found on the long list of TV shows,  movies and comics that have violated the square-cube  law.

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