S05E01 & S05E02: The Skank Reflex Analysis & The Infestation Hypothesis

Some of you may be wondering why two episodes of The Big Bang Theory were broadcast back-to-back tonight. Surely it cannot be a mere coincidence that this is also the first time we have a multi-episode arc on the whiteboards.

Since the beginning of the series, the executive producers have asked me to have Leonard and Sheldon working on solving a real problem on the boards over several episodes. But it wasn’t all that easy. If the boys are working on a known problem with a known solution, then anybody could answer it and spoil the surprise. But if they were working on a known problem with no known solution, there are already hundreds if not thousands of minds working on it, and how could they (meaning I) solve it by season’s end?

Axions: exciting new elementary particles, or a detergent?

We needed a fresh, tractable, problem. And over the summer I had an idea. The idea would allow physicists to make a never-before seen particle. And it could solve the dark matter problem. Perhaps our galaxy is filled with these particles. They would provide the gravitational glue that keeps the galaxy rapidly spinning, but have so weakly interacting they would usually pass through the entire Earth undetected. I thought I found a new way of making a particle that was hypothesized over three decades ago,  “The Axion”.

The Axions’ role in solving the dark matter problem is actually just a nice side effect. These particles were originally conceived in the late 1970’s to give a natural explanation of why the strong nuclear force (a.k.a., quantum chromodynamics) obeys certain symmetries so well-too well. It is a happy accident that axions could also account for all the dark matter in the galaxy. It solves two important unrelated problems at once and if elegance were a guide then theorists would likely consider the matter settled.

But physics is an experimental science and sheer elegance is not enough. The history of physics is filled with ideas that were simple, elegant, and wrong.   Physics is an experimental science and we have to find their signature experimentally.

In very dense environments at high temperature, charged particles will start to radiate axions efficiently. The core of the Sun is over 13 million kelvins (over 23 millions degrees Farenheit) and is 150 times the density of water. As shown on the whiteboards’ Feynman diagrams, electrons in this enviroment could produce a detectable number of axions. Because they are so weak they penetrate the entire Sun, leaving in all directions. A rare few strike the Earth.

So all astrophysicists have to do is find them leaving the Sun. CERN is not only home to the Large Hadron Collider, but also a clever telescope that points at the Sun. But this is no ordinary telescope.  Physicists need not only to detect these weakly interacting axions efficiently enough to find a signal, but in a way that cannot be mimicked by more mundane processes, called backgrounds. One of the funny behaviors of axions is that inside a strong, uniform magnetic field they will convert into light. Specificially, one axion will convert to one single particle of light, a photon. Because the axions are made in the heat of the core of the Sun they have an energy corresponding to 13 million kelvins. So each photon from a converted axion from the Sun will actually be an energetic X-ray.

Every morning and every evening, astrophysicists at CERN, took a prototype magnet borrowed from the Large Hadron Collider project and pointed it at the Sun. They called their device CAST, the CERN Axion Solar Telescope. If they ever see X-rays emerging from the magnetic field that would be a tell-tale sign of axions. They can check they weren’t seeing local radioactive backgrounds by pointing the telescope away from the Sun. Unfortunately to date they have seen none.

Not Galileo's optics: the CERN Axion Solar Telescope (CAST) is actually a large magnet pointed at the Sun.

Zillions of axions are wasted in this technique. The Sun would be pouring out axions in all directions, but only those entering the tiny front aperture of the magnet are detectable. That’s an efficiency of about 1 in 1025 axions. And even only a tiny fraction of these would be converted.

This summer I wondered if we could do better. The main problem is the Earth is so far from the Sun. Meanwhile physicists at Lawrence Livermore National Laboratory in California are making an artificial Sun in the laboratory. They aim 192 lasers at a small pellet of heavy water and for a short time they achieve the density and temperatures of the Sun.  Exceed it, even. But not just short, but a very short time, about a hundred billionths of a second. They do this amazing feat to copy the fusion power of the Sun, as a clean almost limitless source of energy for us on earth. It is called fusion because the core of Sun converts protons into heavier elements, mostly helium. The particles are fused together into this heavier atomic nucleus, and so is called fusion.    Because the resulting nucleus is less massive than the sum of the original protons, by Einstein’s famous formula E=mc2, the missing mass is converted to enormous amounts of energy.

When the process is successful, we can think of “burning” hydrogen into helium to release energy, in analogy with how a burning of a log releases energy as heat. The major difference is rather than a chemical reaction which drives fire, this is a nuclear reaction. Nuclear reactions typically release a million times more energy than chemical reactions for a given supply of fuel. The physicists at Lawrence Livermore call the successful implosions “ignition” and built the National Ignition Facility with its 192 powerful lasers to do it.

The National Ignition Facility focuses 192 lasers onto a small pellet, briefly creating an artificial Sun on Earth.

The National Ignition Facility is the prototype for what its physicists think will be a power plant as powerful as the big coal plants or nuclear power plants.  Even a 1000 gigawatt plant is still a lot less power than the Sun’s 1017 gigawatts, but we can put the magnet much closer:  We could put an axion telescope 10 meters away instead of 150 billion meters away, our distance from the Earth. Since the rate improves as the square of the distance drops, that is a whopping improvement of 1020, more than making up for the lower power.

The numbers looked really good. I was excited. Accounting for distance and power, I reckoned I could do about 1000 times better than the CERN Axion Solar Telescope. That didn’t even account for the fact that the background would be lower since the artificial Sun is only on for 100 billionths of a second, not all day. And since the magnets don’t have to follow the Sun in the sky we could make them much larger. The emission mechanism even looked more efficient than the Sun.

But that’s not the whole story. This was actually a three-episode whiteboard arc. I suppose CBS wanted to create some suspense and the third episode will not be aired until next week. That next episode contains the result of my summer’s worth of calculations. If you think you know the answer, comment below. Otherwise, tune in next week to find out if we are on the verge of creating and detecting axions on Earth.

To be continued…

26 Responses to “S05E01 & S05E02: The Skank Reflex Analysis & The Infestation Hypothesis”

  1. Chris Says:

    Is there some missing energy from the sun? We can calculate the energy the sun should be producing, is there is theoretical-experimental which would allow for the number and energies of axions you are talking about?

    • David Saltzberg Says:

      Yes, axions would take energy away from the core of the Sun and make it cooler than it would otherwise be. So some parameters of axions were ruled out from the beginning just because our star, Sol, works the way it does. An even stronger constraint came from the fact that “red giant” stars were not cooling too fast. This often happens in physics: Astrophysics constrains the parameters of a theory even before you do a single experiment in the lab.

  2. phil Says:

    I always thought the solution to the dark matter problem was simple. There’s a giant green battery at the center of the galaxy which produces massive amounts of energy controlled by the thoughts of the person who wears the ring. The energy produces the additional gravity necessary to solve the “missing mass” problem.

    There’s even clues in several BBT episodes where Leonard wears the uniform of one of the ring bearers.

    (Chuck Lorre – if you’re reading this I’ve got a script outline to show you.)

  3. feldfrei Says:

    That’s an interesting story 🙂 I’m wondering about in what near or far future fusion power plants of this type would be available. A plant of 1 TW (average power) would be huge – a typical fission-based plant has the order of 1 GW and the world’s energy consumption is in the order of 15 TW).

    A big obstacle is the duty cycle which is usually horribly small for a laser system. At NIF it’s currently about one trillionth. For a net energy-producing plant repetition rates in the order of a few Hz would be required. Given a released fusion energy per shot in the order of tens of MJ one would bring the plant into the few 100 MW, possibly GW class. But that’s still three orders of magnitude off your estimate given above.

    I’m looking forward to further comments here and your next blog 🙂

  4. Jonathan Mizrahi Says:

    Very interesting idea. Why not use tokamak style fusion? If all that is required is extremely high temperature and pressure, tokamaks are already around and working (albeit producing less power than is put into them). The NIF is still a work in progress.

    On a side note, you are essentially the only reason I still watch this show. Thank you for all your work! Please tell the writers that fewer sex jokes and more science jokes would be greatly appreciated.

    • David Saltzberg Says:

      Thanks for the nice comments. The problem with the tokamak for this use is that there is much less density. Just not enough electrons around to radiate the axions.

      • Marco de Baar Says:

        Dear Dave,

        sorry to reply so late to this thread. I only discovered your blog now.

        It turns out that there is an interesting link between tokamaks and axion research: It is suggested to exploit the vacuum chamber and magnetic field of the French tokamak Tore Supra (TS) for this purpose: http://www.fusenet.eu/node/282
        Note that TS had a significant power supply problem, and went into shut-down some time ago, so I don’t know what came of these plans.

        My wife and I love the show: I think that my colleagues are portrayed very well. My wife has a slightly different angle on this 😉 !

      • Marco de Baar Says:

        and this link: http://www.iter.org/newsline/227/1196

      • David Saltzberg Says:

        Ah, but that is axion-photon conversion in a magnetic field. I was considering direct axion production as in the core of the Sun.

        On Mon, May 13, 2013 at 9:29 AM, The Big Blog Theory

      • Marco de Baar Says:

        Oh…Sorry for the con-fusion (pun intended). Cheers, M.

  5. lurker Says:

    In case the show’s execs read this board… how about less crude comments?

  6. Aitor Says:

    I like this blog so much but I support Jonathan’s point: It have passed so much time since there were plenty of intelligent and funny science jokes, that were what in first place gave the point to the program. Now all jokes are about sex or how freaky/trekkies the characters are, but I have seen nothing scientifically interesing since the moon laser ( I mean in the series, the blog is still as great as ever). Please tell the writters and producers that we want the science jokes again!!!

  7. Francois Says:

    Nice to see the new season of TBBT starting.

    Was looking for it as much for the show itself than to have the pleasure to read your blog! A gold mine of general public outreach material! 😉 Thanks for that.

    Pity the first episodes came a bit too early. Would have been nice to propose Leonard and Sheldon to solve the apparent mystery spotted by an experiment linked to CERN the very same day the new season was out: have neutrinos travelled faster than light between CERN and Gran Sasso? See: http://press.web.cern.ch/press/PressReleases/Releases2011/PR19.11E.html
    Still to be confirmed though!

    Have a nice season David!


  8. Pomita Says:

    It’s wonderful to see this great blog back! That certainly sounds exciting.

    To add a request to Francois’ comment above, as a neutrino physicist myself and a devoted fan of this show.. can we please, please have a later episode in which the BBT guys at least talk about the OPERA result? If possible, a whole episode dedicated to it? It’s such a thrilling possibility.

    • David Saltzberg Says:

      Thanks for the nice comment! I don’t have any say over what goes in the episodes, but pay attention to the whiteboards and you might see something about FTL neutrinos.

  9. Pomita Says:

    Thanks so much for the FTL reply. That would be great. Though I suspect that they might themselves want a little dialogue in, regarding this, at some point.. it’s all over. The day the OPERA paper appeared, ‘neutrinos’ trended for the first time on Twitter. And I find myself having to answer questions about this to all kinds of people on BBT fan forums. 🙂

    • David Saltzberg Says:

      There is about a month delay between when a script is mostly settled and when it airs. That fluctuates though throughout the season. So you may have to be a little patient.

  10. Pomita Says:

    Sure. Thanks!

  11. Ryan Boudreaux Says:

    Im so happy BBT is back. Love the show, Pearson has made this Houstonian proud. I just can never find the equations you create for the show. You wouldnt have an archive if them do ya?

  12. Howard Wallace Says:

    “One of the funny behaviors of axions is that inside a strong, uniform magnetic field they will convert into light. Specificially, one axion will convert to one single particle of light, a photon.”

    This appears to violate conservation of momentum. In the rest frame of the particle, pre-conversion momentum is zero. Afterwards, there is a single photon with non-zero momentum.

    • David Saltzberg Says:

      There actually is a momentum recoil by the magnetic field (and hence, the magnet). It corresponds to a very small velocity and would be essentially undetectable, but you are right it must be there.

  13. Pomita Says:

    Thank you so much for the mention of FTL neutrinos in the dialogue this time, by none other than Sheldon himself! It made my day. And what a wonderful analogy that was, about the Swiss cheese. 🙂

  14. Our Bodies Create More Energy than the Sun « Thus Spoke Jon Says:

    […] Last week we saw two episodes where upon our heroes’ whiteboards unfolded about making an exciting new particle, “the axion” on Earth. Could axions be made inside an artificial Sun made by the National Ignition Facility?  This summer, I was excited about this, but as you already know by now from reading tonight’s whiteboards, I made a terrible, terrible mistake. […]

  15. Lubos Motl Says:

    Dear Prof Saltzberg, I just needed a picture of axions for a BICEP2/N-flation blog post


    and guess which picture on the Internet won the contest! I hope it’s OK to hot link the picture directly. 😉

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