Invisibility: The History and Science of How Not to Be Seen

Today is the official publication day for my latest non-fiction popular science book, Invisibility: The History and Science of How Not to Be Seen!

As the title indicates, this is a look at the intersection of science and invisibility throughout history, ranging from the earliest attempts by science fiction authors to explain how invisibility might be possible in the 1850s right up to the present day, in which optical scientists have been attempting through theory and experiment to make invisibility cloaks.

Invisibility has a surprisingly long and subtle history in physics. The first real hints of it appeared in the early 1900s, as researchers tried to explain how electrons could be orbiting in an atom without giving off radiation, as classical physics predicted they should. This led to the strange phenomenon of “nonradiating sources,” sources of light radiation that, paradoxically, do not give off radiation. Over the next 100 years, nonradiating sources and other crude forms of invisibility kept being rediscovered, and scientists struggled to find a use for such an interesting phenomenon: it was a “solution in search of a problem!”

In the latter years of the 20th century, invisibility became associated with so-called inverse problems, in which a “cause” is deduced from measurements of an “effect.” Such problems include modern imaging techniques such as MRIs and CAT scans.

I have a personal connection to this work, which motivated the writing of this book in the first place! My own PhD research, completed in 2001, was on nonradiating sources and invisible objects. I like to describe myself as the hipster invisibility scientist — I was looking at such problems before it was “cool.” The book talks a bit about my own work, especially related to my late PhD advisor Emil Wolf, who played his own significant role in invisibility physics.

In Invisibility, I endeavor to explain in plain language how invisibility is predicted to work. In fact, the book ends up being a bit of a history of the physics of light itself, as the history of invisibility is tied closely to our understanding of light. This is a book intended to be read by everyone, and I worked hard to keep it interesting and entertaining! I should add: if you don’t completely understand some physics explanation in the book, that’s okay! Learning science is often about just picking up a little bit of new knowledge at a time. (Feel free to send me a tweet or a comment on my blog here if you want some clarification.)

The book includes quite a bit of discussion of the science fiction of invisibility, as well. Long before scientists started studying the phenomenon, a surprising number of authors attempted to give the fantastical concept a plausible scientific basis. There are so, so many science fiction stories about invisibility, almost certainly more than you’ve heard of! (I say this with confidence because a search of the internet shows that nobody has looked at invisibility in science fiction as thoroughly as I have.)

A little example of invisibility fiction: an illustration for Guy de Maupassant’s 1887 short story “The Horla.”

Throughout the month, to celebrate the release of the book, I will be blogging and reblogging about classic stories of invisibility in science fiction and horror; you can track down the archive of posts here.

The book is not all history; since 2006, invisibility has been an active field of scientific study, and researchers have predicted all sorts of strange phenomena using the tools of invisibility cloaks: optical black holes, optical wormholes, anti-cloaks, perfect illusions, and more! I talk about all of these, and discuss where invisibility physics stands today, and whether someone invisible might be standing behind you right now!

I’m very excited for folks to see this book, which has been a long time coming! It was originally going to be my first popular science book, but I ended up writing my book on Falling Felines and Fundamental Physics first!

Invisibility should be available through the bookseller of your choice (including Target — go figure). Here again is the link to the Yale University Press website, which links to a lot of the popular sellers.

I hope you enjoy it!


PS yes, the subtitle is a reference to a classic Monty Python sketch; I had to fight a little with the marketing department to get them to keep it as is!

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Optics basics: thin films

Color can have surprising origins in nature. Most of the time, the color of an object is dictated by the light it absorbs: for example, if you see an object that is blue, that means that it reflects all the blue light shining on it and absorbs all the colors that aren’t blue. But colors can arise from completely different phenomena: rainbows, for example, arise due to the phenomenon of dispersion, i.e. that different colors of light are refracted differently within a raindrop.

Then we have the not-quite-a-rainbow spectrum of colors that one sees when oil is spread out over the surface of water, such as this photo that I took a few months ago in my neighborhood:

These arise from a completely different effect: wave interference! The oil forms a thin layer on top of the water, and wave interference from the oil-air interface and the oil-water interface can produce constructive interference for colors, depending on the thickness of the oil layer.

Oil slicks are an example of what is generally known as thin film optics, in which unusual optical effects are produced by putting one or more thin layers of material, usually comparable to the wavelength of light, onto a base layer. This is not only a phenomenon seen “in the wild,” in things like oil slicks, but is practically used in optical design and engineering!

Let’s take a basic look at thin film optics and how it can produce bright colors on reflection — or suppress them entirely.

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“Invisibility” on the Colin McEnroe Show!

I get to share another interview that I did about invisibility today, this time live on the Colin McEnroe Show on WNPR in Connecticut!

It was a great conversation! It started with me talking about the science of invisibility, and then we were joined by Lisa Yaszek (Regents Professor of Science Fiction Studies in the School of Literature, Media, and Communication at Georgia Tech) to talk about invisibility in science fiction, and then we were joined by Sophia Brueckner (Futurist artist, designer and engineer, Associate Professor at the School of Art and Design, and Co-Director of the Center for Ethics, Society, and Computing at the University of Michigan) to talk about the ethics of invisibility, if it ever becomes a practical technology!

I actually learned a lot from the discussions with Professor Yaszek and Professor Brueckner, and they gave me new things to think about in the way I think about invisibility!

Anyway, please check it out, and thanks to Colin McEnroe and Lily Tyson for having me on the show!

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A short musical interlude…

I’m still working on posting something to the blog every day for a certain number of days! Tonight, I’m a little exhausted and don’t have a lot of time to finish a new optics post, so I thought I’d share a couple of videos of me practicing classical guitar. This is partly for me as well as the audience — I need a lot more practice in front of a camera, as I always play worse when I am aware of an audience or recording!

This is an Allegretto by Matteo Carcassi that I happen to like and isn’t too difficult.

(Dedicating this performance to my friend Hannah.)

More science to come! And probably more guitar, too.

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The Little Black Bag, by C.M. Kornbluth

As long as I’ve been having fun tracking down classic science fiction stories that I absolutely love, let me share at least one more! “The Little Black Bag,” by C.M. Kornbluth, first appeared in the July 1950 issue of Astounding Science Fiction. (You can read it on the Archive at this link.)

Cyril M. Kornbluth is one of my favorite science fiction authors, and largely due to three stories, that encapsulate a truly prescient view of the future and an extremely cynical one. In his story “The Silly Season” (1950), strange and nonsensical events worldwide that take up the attention of the newspapers turn out to be a distraction for an alien invasion. This story really anticipates the “noise chambers” that a lot of media companies have become, harping on nonsense issues to distract from serious ones. In his story “The Only Thing We Learn” (1949), a teacher recounts to students the heroic origins of their civilized society, whereas flashbacks show us the horror and brutality that those founders actually achieved. This story warns against the whitewashing of our history, while cynically suggesting that it will repeat itself with another conqueror.

The third story is “The Little Black Bag.” (Severe spoilers from here on out, so please read it first from the link.)

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Prisoner of the Vampires of Mars, by Gustave Le Rouge

Sometimes you just have to read a book because of its title. This was certainly the case when I decided I wanted to read Prisoner of the Vampires of Mars (1908-1909), by Gustave Le Rouge!

Like, the title has everything! Mars! Vampires! Prisoners! How could I not read it? I put the book on one of my holiday wishlists, and my roommate got it for me this past Christmas. It took me some time to read it, an admittedly my expectations were not particularly high, but I ended up enjoying the book immensely! Let’s take a look at the book, without major spoilers, below.

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So, what is “structured light?”

The fields of optical science and engineering have undergone dramatic changes over the past twenty years. Through most of its history, stretching back for hundreds of years, optics researchers have been asking the question, “what can light do?” Revolutionary discoveries have changed the question to, “how can we make light do whatever we want it to?”

One area where there has been dramatic change in recent years is in the very structure of a beam of light itself. Ever since the invention of the laser, it has been the standard source of light for experiments an applications, far superior to using natural light sources, which must be collimated and filtered to produce a directional and monochromatic beam. Most ordinary laser sources, like a laser pointer you might use to entertain your cats or give a presentation, produce a Gaussian beam, so named because they produce a brightness (intensity) spot shaped like a Gaussian function, as shown below.

On the left: a simulation of the brightness of a Gaussian spot, as if you would see if you looked directly in the beam (don’t do that). On the right: the cross-section of the spot, showing its Gaussian shape.

A Gaussian beam is great for most uses: it is very directional, and propagates long distances without significant spreading, it is very close to being a single frequency wave, which also means it is coherent (more on this momentarily). However, researchers have gradually realized that beams with properties different than a Gaussian beam could show unusual, beneficial, and even seemingly impossible behaviors! These beams are created by modifying, or “structuring,” the properties of the beam spot.

There are a number of properties that can be structured in the transverse cross-section of the beam. The shape of the intensity spot can be changed, the phase of the light wave can be modified, the polarization properties of the light can be manipulated, and the spatial coherence can be adjusted. Let’s look at examples of each of these “structured” light beams, and see what weird things can be done!

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Relook at “Giants From Eternity,” by Manly Wade Wellman

In my investigations of classic pulp magazines over the past year, I’ve come across some classic stories and real gems that I had forgotten about. One of these guilty pleasures is “Giants From Eternity,” by Manly Wade Wellman, published in the July 1939 issue of Startling Stories.

The cover image, incidentally, doesn’t represent Wellman’s story in the magazine.

I’m a big fan of Manly Wade Wellman’s work; his Silver John series of stories and novels, about a wandering Appalachian minstrel who fights evil with wit and a song, are absolutely delightful. With his son, he wrote a story about Sherlock Holmes squaring off against H.G. Wells’ invaders from The War of the Worlds! I’ve also written about Giants From Eternity before, when I read it in a modern edition, though I read it and blogged about it over a decade ago!

Digging up the story in magazine form gives me an excuse to take another look at the story, and share the original images from the magazine! (And once you know what the story is about, you’ll see why.) If you want to read it in advance, the issue is available on the Internet Archive, or you can buy a modern edition.

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A Subway Named Mobius, by A.J. Deutsch

I’ve spent a lot of time talking about short stories about invisibility, but my searches have occasionally reminded me of some of my other favorite, non-invisibility-related, science fiction stories. Today I thought I’d take a short look at “A Subway Named Mobius,” written by Armin Joseph Deutsch and which appeared in the December 1950 issue of Astounding Science Fiction.

This story is one of the true classics of science fiction, all the more remarkable because I believe it is the only story that Deutsch ever published! It is a semi-humorous story based on one of the more challenging subjects in mathematics, topology: the study of those properties of sets or objects that are invariant under continuous deformations of the object. A classic example of this line of thinking is the topological similarity of a coffee cup and a donut; both of them have a single hole, and if we imagine them made out of clay, one could be molded into the other, as long as we obey the rule that we can stretch and compress and warp the clay, but not tear it.

Another classic structure from topology is the Möbius strip, a one-sided surface, that gives the story its name. It is created by taking a ribbon of paper, giving one end a half-twist, and then taping the ends together. It is distinct from a cylinder, which could be created by taping the ends of the paper together without the half-twist.

A paper Mobius strip.

So let’s take a look at “A Subway Named Mobius!” You can read the entire story from its original source at this link.

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Rogue Moon, by Algis Budrys

Oh, what the heck — as long as I’m thinking of Algis Budrys’ work, and I’m still on a blogging roll, let me say a few words about his most famous novel Rogue Moon (1960). I read it on a Kindle on a trip a few years ago, which is why I suppose I never got around to blogging it — by the time I returned from the trip, I was already reading other things.

But Rogue Moon is a classic of science fiction, and well worth exploring. However, readers may find that the novel is not exactly about what it seems to be about at first glance!

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Me on the “6 Degrees of Cats” podcast!

Hey folks! I’ve appeared on yet another podcast! Fortunately, for those who are tired of me talking about invisibility, this one is about cats, and related to my previous book on Falling Felines and Fundamental Physics.

I’m part of an episode discussing the righting reflex. Click on the image above to go to the episode, or this link here. Thanks again to Amanda for having me on the show!

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