My talk on “Forgotten milestones in the history of optics”

I just got finished giving a talk to the graduate students of my department on “Forgotten milestones in the history of optics”.  The talk seemed to be very well-received, and I’ve already had faculty suggesting that I should give it again in the engineering department.

The talk was scheduled at 1 hour, and I prepared 45 slides.  My only miscalculation was that I didn’t take into account how long-winded I get when I’m talking about a subject I’m really passionate about — I ended up speaking for 1h10m!

Here is the presentation:  2010_historyofoptics

Three of the four topics are essentially adapted from history of science posts I’ve put on this blog before, though the first one — on Ibn al-Haytham — is new.

If any departments are interested, I could be coaxed into coming to give a presentation… 🙂

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15 Responses to My talk on “Forgotten milestones in the history of optics”

  1. Aydin says:

    Thanks for providing your slides. I am enjoying reading them.

  2. Melf_Himself says:

    Very interesting presentation.

    I recall you linking previously to some work ( showing that full coherence is obtained at particular positions of a Young interference screen even if the light illuminating each pinhole comes from two different sources.

    How does this reconcile with Dirac’s statement that “a photon only interferes with itself, not with other photons” statement?

    • That’s a very good question, and I don’t have an immediate answer — let me think about it for a while and hopefully get back to you. (I thought I’d comment to let you know I’m thinking about it, and not ignoring you.) 🙂

    • Melf_Himself says:

      No problems, thanks 🙂 I’m not sure if there’s a definite answer, so I won’t blame you if you wax philosophical on that one…

      • Melf_Himself says:

        Refreshing my head on coherence basics almost a year later and I stumbled across this earlier post of yours:

        I see that you had actually addressed this specific quote of Dirac’s previously! Although, one of the commenters on that post pointed out that the authors of one of the references you had cited (Phys Rev 159, 1967 p1084) actually claimed that their results support Dirac’s statement.

        With some hindsight are you able to clarify this issue at all? It is just amazing that the basic double slit experiment is still being understood all this time later…

      • My apologies on the late reply; I’ve been quite crazy busy with travel. My thought is more or less what I said at the end of that post, though I can state my objections more clearly now, I think.

        The real problem with Dirac’s statement is that it wouldn’t have predicted either experiment done by Mandel. Dirac’s statement would seem to imply that the 1963 experiment shouldn’t show any interference at all, because it seems to require two photon interference. The 1967 experiment isn’t predicted for a different reason — up until that test, one would have interpreted a photon as coming from a single, definite, source, and in such a case a single photon shouldn’t have been subject to interference at all. Nevertheless, we see interference, evidently because it is unclear which source the photon came from!

        This is way weirder than Dirac’s statement can imagine. Picture the laser sources each being 10 light-years away from the central part of the experiment. In principle, we should still see interference, but does it seem reasonable to assume that some aspect of the single photon came from both sources at once? I certainly don’t know, but this is what much of Mandel’s later work entailed — using these unusual results to illuminate the foundations of quantum mechanics.

        In short, one can semantically twist Dirac’s statement to explain all of the results described, but quantum mechanics has shown itself to be far weirder than Dirac envisioned.

      • Melf_Himself says:

        I found this more complete quote from Dirac in Wikipedia:

        “Some time before the discovery of quantum mechanics people realized that the connection between light waves and photons must be of a statistical character. What they did not clearly realize, however, was that the wave function gives information about the probability of one photon being in a particular place and not the probable number of photons in that place. The importance of the distinction can be made clear in the following way. Suppose we have a beam of light consisting of a large number of photons split up into two components of equal intensity. On the assumption that the beam is connected with the probable number of photons in it, we should have half the total number going into each component. If the two components are now made to interfere, we should require a photon in one component to be able to interfere with one in the other. Sometimes these two photons would have to annihilate one another and other times they would have to produce four photons. This would contradict the conservation of energy. The new theory, which connects the wave function with probabilities for one photon gets over the difficulty by making each photon go partly into each of the two components. Each photon then interferes only with itself. Interference between two different photons never occurs.”
        —Paul Dirac, The Principles of Quantum Mechanics, Fourth Edition, Chapter 1

        So Dirac’s statement was aimed at making a distinction between a) QM predicting the total number of photons being observed, and b) QM predicting the probability of a single photon being observed. Whether he meant to or not, I think his statement nicely avoids commenting on what would happen if you could interfere light from two different sources altogether. I wouldn’t say that his statement can be used to predict or to refute Mandel’s later results (i.e. I agree with you that it is not really a relevant statement as far as that goes).

        Yet in Mandel’s 1967 paper he states that his results support Dirac’s view. I think Mandel said this because he wanted to uphold that QM does only predict the probable states for a single photon. Mandel points out that a photon is a detection event, he does not think about it “taking a path” through the system. The probability of detection occurring due to multiple sources adds up at each point in space, creating an interference pattern.

        The only nagging issue I have is that we do not seem allowed, in Mandel’s experiment, to know when one of the sources has emitted a photon. Because if we did, and if the other source had not emitted one around that time frame, we would know where the photon on our screen came from (which would destroy the interference pattern). Usually “quantum censorship” in this regard is about not knowing, say, the momentum of the photon to a certain precision. Here it seems that we can not even know that a photon was emitted at all.

  3. agm says:

    Thanks for the slides. Took me a bit to visualize the rationale and the geometry in Barkla’s setup. Then I realized the polarization works the same as Sh and Sv seismic. Much easier to see when you can tie it to something you’ve been dealing with for work…

    BTW, when’s the book out?

    • There’s a bit more explanation about the experiment and polarization in my original post, here; since I was speaking to a (presumably) optics-heavy audience, I left that out of the talk. (But I still ran over the allotted time.)

      I’m not entirely sure when the book comes out; the publisher received the draft this week, and presumably they’ll take a month or so to go through it and send me proofs to go through, etc. I’m guessing that it may be out in early fall, though that’s still just a guess — I have to ask my editor what she thinks, once she’s back from vacation!

      • agm says:

        Yes, I recall that post.

        I’ve been thinking about this. No conclusions yet, but it’s lovely to realize that the momentum transferred into an oscillator via the field and then recoupled out is a general principle, no matter how simple or complex the math.

  4. IronMonkey says:

    The statement “How can we make light behave how we want it to?” to describe the modern era of research in optics is pretty bold but quite accurate I believe. Thanks to our predecessors and technological progress, our “control” over light is better than ever.

    Moreover, while the visible, near-infrared, microwave and radio-frequency parts of the spectrum have been studied/used extensively during the last centuries, another hot topic these days it seems is the (re)discovery of other useful spectral bands: terahertz, deep-UV, middle-infrared, etc. Again helped by technological advances in optical sources, devices and detectors.

    The slides on Indian and Arabic influence before the Western renaissance and later, were very interesting (and enlightening ;-))

    • The statement “How can we make light behave how we want it to?” to describe the modern era of research in optics is pretty bold but quite accurate I believe.

      I guess it is a little bold, isn’t it? I think the statement is accurate as it stands, but the question is whether the science will live up to the hype building around it. As it stands, we’re still not terribly good at making 3-D metamaterials, or photonic crystals, for that matter, and most of the proposed applications depend on being able to reliably tailor 3-D structures. It may turn out that the metamaterial revolution ends up like phase conjugation before it: useful, but not nearly as transformative as originally thought.

      The slides on Indian and Arabic influence before the Western renaissance and later, were very interesting

      Thanks! The pre-Renaissance era is something I’m going to be looking into in much more detail, as I know relatively little about it. Embarrassingly, most of the questions during my talk were about that period!

  5. Joe Howard says:

    Nice presentation… a little “light” on the geometrical optics side, but hey, I’m biased! Let me know if you’re ever in the DC area, and we’ll get you on the local OSA section docket, or even a lunch presentation here at Goddard if you’re up to it.

    • Joe: Thanks! No plans to be in the DC area in the near future, but I’ll let you know if things change!

      I do need to study more the era between Newton and Young; I’m sure there’s lots of interesting research in that era, but haven’t come across too much of it.

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