S03E10: The Gorilla Experiment

Tonight we took a 2600 year journey with Penny and Sheldon “from the ancient Greeks through Isaac Newton to Niels Bohr to Erwin Schrödinger to the Dutch researchers that Leonard is currently ripping off.”

From the Ancient Greeks: Ancient societies,  including the Greeks, watched the skies carefully.  Since they didn’t have Google Calendar, it was only by watching the positions of the stars each night could they mark the passing of the days and seasons and know the best time to plant crops.   (It must have been a nice time to be an astronomer.  If you didn’t treat your astrophysicist nicely, you might not have enough food next year.)  Most of the points of light in the sky, the stars,  appeared to stay in the same place with respect to each other, year after year for as long as anyone could remember.  But a precious few, just five, moved relative to these fixed stars.   We know them as Mercury, Venus, Mars, Jupiter and Saturn.  As Sheldon explains, our Greeks forbears called them “wanderers”, or as we have derived from their language  “planets”.

Your science consultant stands up to a UCLA astronomy professor who voted out Pluto.

When you look out the side window of your car, you can see objects fixed to the ground, bushes, trees, poles etc.  Those near the side of the road zip by.  Objects in the distance seem to barely move at all.   Although you have the same speed relative to all the fixed objects outside your car, close objects have a high angular speed and you have to turn your head fast to watch them. The far objects have a low angular speed which don’t require much tracking of your eyes.  This allows us to understand the motions in the sky of  stars versus the planets.  The change in position in the sky is determined by their angular speed.    Even though stars are moving extremely fast relative to the solar system, most faster than even the outer planets, they are so far away that changes in their position on the sky (their angular position) can only be detected with careful observation, if at all.    For example, compare the farthest planet, Neptune  (thanks, Pluto-haters) to the closest known star Proxima-Centauri, a  little red dwarf star.   Neptune is about 4,500,000,000  kilometers from Earth and moving a modest 5 kilometers per second relative to the Sun.  If you watch Neptune over the course of  a lifetime it will move halfway around the sky relative to the stars since it completes an orbit around the Sun every 164 years.    By comparison, Proxima Centauri moves even faster than Neptune relative to the Sun but its position relative to other stars barely moves; its angular speed is tiny.  The key difference is that Proxima Centauri is 40,000,000,000,000 kilometers away.  Only precise astronomical measurements can see its motions, only hundredths of a degree over a lifetime.

At the other extreme, one of the fastest lights you will see move across the night sky is likely an airplane.  They are moving at only 0.2 kilometers per second.  But since they are close, say 100 kilometers away, they move faster on the sky than planets or stars.  Galileo and Newton realized this, except for the part about airplanes. They knew that if the Earth orbited the Sun, the lack of apparent motion of the “fixed” stars meant they were extremely distant.  The Universe was much larger than imagined.  That story of the learning the Universe is larger than we thought is repeated many times throughout  the history of astronomy.  First by realizing the nearby stars are really so far away.  Then by measuring the extent of the galaxy.  When other galaxies were discovered our idea of the size of the Universe grew larger still.   Today we do not know how large the Universe is, we only know that the speed of light is not fast enough to let us see all of it.

Through Isaac Newton: Newton explained why the planets orbit the Sun much like how a child might swing a cat by its tail over his head.  If the child lets go, the cat flies off in whatever direction it was heading.  In the absence of the Sun, the planets would fly off in straight lines at constant speed in one direction.  Instead, the Sun pulls on the planets using gravity.   The inward pull causes the planets to move in orbits around the Sun rather than straight lines. The same force of gravity that pulls objects to the ground on the surface of the Earth is what causes the planets to orbit the Sun, the Moon to orbit the Earth and what causes the Earth and Moon together to orbit the Sun together, just like the planets.

But what Sheldon was trying to get Penny to say?

Notice that the Moon and Earth go around the Sun together, even though they have wildly different masses.   Objects of different masses fall at the same rate in a vacuum.  Their masses don’t matter.  The Sun causes objects at the same distance to move the same way.  So the Earth and the Moon move around the Sun at the same rate.  The Moon’s extra motion around the Earth is just a small variation in its journey around the Sun. Even the tiny International Space Station orbiting the Earth, really has its path dominated by the Sun.   Its motion around the Earth is just a tiny little wiggle in its path around the Sun.

To Niels Bohr: Theorists had tried many models to explain the architecture of the atom.  But it was only once the experimentalist Ernest Rutherford scattered charged particles from gold foils that it became clear that a  central positive charge, an atomic nucleus,  was surrounded by distant electrons with negative charge.   The motion of the planets around the massive central Sun served as a convenient model.  First the Japanese physicist Hantaro Nagoka (1904) proposed the electrons formed rings much like the dust surrounding Saturn.   Rutherford himself proposed a planetary model (1911), just as planets orbit the Sun under the force of gravity, Rutherford proposed electrical forces kept the electrons in orbit around an atomic nucleus.  Yet even at the time, physicists knew this could not work, since electrons moving in a circle mut radiate light, lose energy, and fall inward, crashing into the nucleus.  The Danish physicist Niels Bohr (1913) took the planetary model, but proposed that only certain distances from the nucleus were allowed, i.e. that the energy levels were quantized. Such quantization had previously served Planck and Einstein to describe the behavior of  light.  Now, Bohr gave birth to a quantum mechanical view of matter, the branch of physics necessary to explain atomic and molecular structure and upon which much of modern technology is based.

The planetary model for the atom, with which Niels Bohr started quantum mechanics, is a view of the atom still held by much of the public.

To Erwin Schrödinger: Bohr’s model was inspirational, but still didn’t work so well.  For example, all electrons in this planetary picture would carry angular momentum around the nucleus, but many do not.   The predicted intensity of radiation from atoms did not match the data.   In 1926,  Erwin Schrödinger developed a more rigorous description of quantum mechanics and the atom.  Rather than thinking of electrons like planets, it is because of Schrödinger we think of the electrons being distributed in regions around the atom.  Electrons are more or less likely to be found in any one place given by a mathematical function resembling a wave.  Schrödinger therefore called it the “wave-function” and in quantum mechanics every particle has one.

To the Dutch researchers that Leonard is currently ripping off: Wave-functions behave counter-intuitively.  Perhaps because our intuition was developed more while running across the African  Savannah than while orbiting an atomic nucleus.  One particularly counter-intuitive behavior of the wave-function is the Aharohnov-Bohm effect featured so prominently in this episode.   The effect describes what happens to the wave-function near a magnetic field.   It isn’t surprising, perhaps, that if your particle, described by its wave-function, crosses a region with a magnetic field that something about it might change.  What Yakir Aharonov and David Bohm predicted using Schrödinger’s wave-function description is that you could have an effect by just going around, but never sampling directly, a magnetic field.   Specifically, if electrons follow two different paths around a region of magnetic field and come together, they will have changed in different ways:  While one wave-function might be at the crest of its wave, another might be at its trough.   Putting the electrons together after their separate journeys, makes the “interference pattern” that Bernadette so rightly admired because they can be beautiful.   The effect was predicted and subsequently observed with magnetic fields decades ago.

The Dutch researchers Leonard was ripping off  have seen the effect now with electric, not just magnetic fields.   The Dutch researchers accomplished it using electrons naturally moving around their sample, through a process called diffusion.    Leonard was trying it even more directly by passing a beam of electrons through a sample.  You may have noticed they added a vacuum pipe carrying an electron beam into Leonard’s lab.  (The end of the pipe is covered in aluminum foil, to keep the flange clean while being built.)  The small nan0-fabricated rings would keep all their electric field inside and he would steer his electrons around either side and create an beautiful interference pattern.

An electron interference pattern. Electrons can behave like waves on the ocean, forming crests and troughs in their intensity.

I leared something new hearing Penny describe the whole thing to Leonard.   Before she said it to the live audience, I never realized the Aharonov-Bohm effect was so funny.   I bet we could have had them rolling in the aisles if we mentioned the Stern-Gerlach effect.

P.S. Easter Egg alert.  You can see your science consultant in tonight’s episode sitting across from an actual UCLA graduate student in theoretical physics, our very own Sheldon. (He is even working on one of the same problems: N=8 Supergravity.)   A gold star to the first person who identifies which scene it is. Scenes are rehearsed several times and then run through several times in front of the camera to get it right. Luckily the props department gave us an interesting little book on quadrupole moments of nuclei from the 1960s to read. Most of the books you see around the apartment and on the sets are real physics books, some very interesting, so there is always something good for us to read between takes.

34 Responses to “S03E10: The Gorilla Experiment”

  1. J Reilly Says:

    The scene you refer to is the cafe scene where Howard is introducing his girlfriend Bernadette to anyone and everyone….

  2. Paul Holt Says:

    Amazingly, it was Ptolemy in the Almaghest who made the first accurate estimate of the distance to the stars.

    “The Earth, in relation to the distance of the fixed stars, has no appreciable size and must be treated as a mathematical point.”

    His proof was around the simple observation that as star A sets, another star B can be found which rises at the same time on the opposite horizon, and when star B sets, star A immediately rises.

    • David Saltzberg Says:

      From what I can see Ptolemy had a limit on the distance to the stars as greater than 20000 times the Earth’s diameter, or about 250 million kilometers. That is smaller than the size of the solar system, and far less than the distance to the closest star. (Since it was “greater than” he was not wrong.) At the time the lack of angular motion of the stars was an argument that could be taken for the geocentric model of the solar system if you could not fathom the stars being so far away. If you disagree, I would like to see a reference.

  3. Anonymous Says:

    The name is Niels Bohr, btw.

  4. JC Says:

    Wonderful wonderful I like how you combined with pop culture helps me get friends and family interested in science. I’ve often sent the link and a parsed quote to tell friends “DUDE!”

    One thing that irked me though that’s more a character thing than your field. I’d assume Sheldon would have said BCE rather than BC.

  5. BigBongTheory Says:

    If I remember my college physics correctly, Niels Bohr didn’t give birth to quantum mechanics. It was Einstein who first conceived of quantized energy as property of radiation itself, not as property of the process of emission and absorption, which was Planck’s understanding.

    • David Saltzberg Says:

      OK, I’ll buy that. I was thinking more along the lines that Bohr’s model was the necessary step that brought us to the wavefunction. I’ll fix it up somehow.

    • PG Says:

      Ah, but it was Bohr that conceived of the idea that the electrons must be limited to orbits of certain energies (and no energies in between them), and the spectrum of the hydrogen atom was due to electron transitions between these orbits. He thereby quantizing the energies of atoms, although it was an ad hoc theory.

      Einstein showed that the photoelectic effect could be explained if light came in quantized packets of energy and not as waves.

  6. Calin Says:

    I assumed Sheldon used BC rather than BCE just from habit. He’s not that concerned with history, and he grew up in Texas. I’m sure he heard and read BC up until he went to college and it was an irrelevant distinction. It’s like Sheldon saying “Good Heavens” when it’s pretty apparent he doesn’t believe in heaven at all. It’s a phrase from his upbringing.

  7. Patricio Says:

    I just came here to ask you if you were the one in the cafe scene. Congrats for that.

    By the way, nice post. I had basic physic in my career and I remembered only the Ancient Greek part.

    Great ep!

  8. Uncle Al Says:

    Split an electron beam, run it on either side of an isolated electric field, recombine, get a diffraction pattern for the spooky phase shift. Kewl! Split an electron beam, run it on either side of an isolated magnetic field, recombine, get a diffraction pattern for the spooky phase shift. Kewl!

    Split an electron beam, run it on either side of an isolated relativistic uncharged mass current, recombine… and get a diffraction pattern for the spooky phase shift? Gravitoelectric Aharonov-Bohm effect? The Relativistic Heavy Ion Collider has a taut beam of 100 GeV/nucleon fully stripped gold, 3×10^26/cm^2-sec. Add 79 parallel fast electrons/nucleon and Leonard need not be derivative with his perpendicular probe.


    BTW, it’s “Aharonov” not “Aharanov” or “Aharahnov.”

  9. paloma Says:

    Hi!! It was great meeting you a while ago after the show! Just found this blog, it’s amazing!!!! I won’t spoil anything about next episodes ;)

    Didn’t know (maybe just didn’t remember) about Nagoka’s model for the atom’s structure. Neither was I familiar with the Aharonov-Bohm effect, your explanation is a very good insight, thank you. I missed the vacuum pipe’s presence in the scene, I’ll pay more attention if I watch it again.

    Will you have more episodes featuring robotics soon to come? I guess you can’t tell.

    I’d be extremely grateful if you get me that autograph :)

    BTW, can anyone tell me what the E in BCE stands for? I’m Spanish and I think I haven’t come across that acronym before. Why should Sheldon use it instead of BC?

    David, thank you for your awesome work and for this blog. I’ll stay tuned, what a great discovery!

    • Calin Says:

      BCE stands for “Before Common Era”, which is more acceptable in most scientific circles than the original “Before Christ”.

    • David Saltzberg Says:

      BCE = “Before the Common Era” or similar variants which is a way of referring to the enumeration of years without a religious context. Similarly “AD” becomes “CE”.

  10. Impres Says:

    Neptune’s actually around 4.5 _billion_ km from Earth, not _million_.

  11. Nomæd Says:

    I noticed that Sheldon said “supernovas” in the episode. If I did hear that correctly, isn’t that something that couldn’t have ever happened? I mean, there’s no way Sheldon Cooper would say Supernovas instead of Supernovae…

    • David Saltzberg Says:

      Personally I say supernovas. I am so done with Latin.

      • PG Says:

        I believe that both forms of the plural are acceptable in modern English, although I agree that Sheldon would say “supernovae” (the purist that he is).

      • Nomæd Says:

        Of course Supernovas is acceptable in English, but as PG above here said, Sheldon would probably use Supernovae :)

  12. David Miller Says:

    I didn’t notice you in the cafeteria scene on the first viewing, but after reading your post, I re-watched it, and there you are! That’s really great, a bit of time in front of the camera (OK, as an extra, but still, cool.) Except for that argyle sweater vest. That’s from Wardrobe, right? :-)

    About Leonard’s lab: good job. The set design people made it look like a real laboratory. I like the aluminum foil over the hole in the pipe – nice realistic touch!

    That optical table with all the mounts and components – they looked real. Those things are not cheap, were they borrowed from a real laboratory or does the prop department have their own?

    • David Saltzberg Says:

      Thanks! Melles Griot and Newport lent real tables and optics hardware to the sets department. All real stuff. Sad to say, I don’t own a brown argyle vest. My light-gray shirt was to bright for the cameras. The cinematographer said I “popped” too much. Some quick chatter on their radios and a vest magically appeared from wardrobe 30 seconds later. Too bad there is no Emmy for extras.

  13. jg Says:

    “most faster than even the outer planets”? The solar system isn’t a record player, as you well know. Mercury’s the fastest!

    • David Saltzberg Says:

      That’s right. It would be a stonger statement if I had said “than the inner planets” but I don’t think that would be true.

  14. CB Says:

    You had me at “Dutch” :)
    (I live in the province of Drenthe).

  15. Simon Says:

    Wow! Congrats for that you was in the cafe scene. :)

    I was almost crying like Penny when I was taking introductory of quantum mechanic class. sigh.

  16. Mr. Jody Bowie Says:

    I showed a clip of Sheldon and Penny’s conversation to my classes. I told them I hoped they didn’t ever feel the way Penny with Sheldon in my class. I did, however, tell them they look at me often the same way Penny looks at Sheldon in this scene. Its such a great insight into the teacher/learner relationship. Not to mention funny!

  17. TJ WILLIams Says:

    I’m 57 and I love the show. My daughter was a science geek (she LIVED on “robotics row” at JPL) I was so worried she would be socially ostracized.
    She ended up writing science fiction. The show constantly reminds me of her awkward college years and my struggle to help her thru them.

    It is one sitcom I do not miss. Thanks for all the effort by the staff to keep if funny, fresh and interesting. Sheldon and Penny send me to the floor rolling with laughter. Also…pure genius the southern fried football background Sheldon has taking up space in his brilliant brain.

  18. cegger Says:

    This is my favorite episode. I’d love to watch a one-man physics show with Jim Parsons as Sheldon.

  19. Tradução: “S03E10: The Gorilla Experiment (O Experimento do Gorila)” « The Big Blog Theory (em Português!) Says:

    [...] feita a partir de texto extraído de The Big Blog Theory, de autoria de David Saltzberg, originalmente publicado em 7 de Dezembro de [...]

  20. Anonymous Says:

    You are very good at explaining complex scientific ideas in a very simple manner. If you are not a professor/teacher you would be very good at it.

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