Null-field radiationless sources: even more invisible than invisible?

I spend a lot of time talking about invisibility on this blog, as it is a subject near and dear to me: I did my PhD work, completed in 2001, on early historical forms of invisibility.  I like to tell people that I’m an invisibility hipster, and that I worked on invisibility “before it was cool.”

The field has progressed dramatically since I first did my work, and in recent years I’ve been playing a bit of “catch up” with my own invisibility work, trying both to build on the newest insights as well as apply knowledge from the old theories.

This past fall, my student Elisa and I used this approach to ask and answer a curious question: can something be more invisible than invisible?

Our answer was published in a paper titled “Null-field radiationless sources,” that appeared in November in Optics Letters.*  Ordinary invisible objects, including cloaking devices, are objects that don’t scatter any light outside the domain of the object; a potential null-field object will potentially not scatter light inside, as well!

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#365papers, part 1!

At the beginning of this year, my friend Jacquelyn Gill (who blogs over at The Contemplative Mammoth) suggested an interesting resolution for academics like us: read at least one scientific paper a day for the entire year.  This has been hashtagged on twitter as #365papers and, as I am always up for the latest fad, I decided to join in.  I seem to be too unfocused to actually tweet details about each paper I read, so I thought I would summarize my reading every week or so right here, with a short description of what each paper is about!

So, without further ado… here’s part 1 of 365 papers!*

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Posted in Physics | 3 Comments

John Blackburn’s Dead Man’s Handle

This post marks a minor personal milestone: with the book featured in it, I have now read all of John Blackburn‘s published works.  I put off reading this one for quite some time for a reason that I’ll explain at the end of the post.  The novel, Dead Man’s Handle (1978), was written near the end of what I might call Blackburn’s “original” writing career.


Though Blackburn would publish four more books in his lifetime, the last two — A Book of the Dead (1984) and The Bad Penny (1985) are reworkings of his earlier novels, Blue Octavo (1967) and A Sour Apple Tree (1958), respectively.  After Dead Man’s Handle, his last truly new books were Sins of the Father (1979) and A Beastly Business (1982).

I mention this because there is a bit of a decline in the quality of his work near the end of his career, and this is one reason that I was somewhat slow to read this particular book.  However, it is a rather unique mixture of mystery and horror, with a truly ghastly twist at the end.

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The Burnaby Experiments, by Stephen Gilbert

I really should be writing about novels other than those published by Valancourt Books, and I will, but they have released so many eye-catching books in recent years that I’ve had a hard time staying away.  Most recently, I read their edition of The Burnaby Experiments (1952), by Stephen Gilbert.


The goal of the titular experiments is likely familiar to those who have experienced a lot of horror and science fiction: to find out what lies beyond death.  You may have seen the movie Flatliners in 1990, for instance, or read the 1993 novel The Terminal Experiment by Robert Sawyer.  Or, like me, you may have independently written a story based on the same theme years earlier.

Gilbert’s novel offers a unique and very personal take on the concept, however.  In fact it is semi-autobiographical, and the implications of that subtext are perhaps more disturbing than the actual story at times.

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The mystery of the magnetic train

This past week, thanks to Laughing Squid and other sources, a lot of people watched and were amazed by this simple demonstration of electromagnetism in action.

It is billed as the “world’s simplest electric train,” and it is almost certainly the case.  Using only a battery, some strong magnets and some (bare) coiled copper wire, one can make the “train” travel numerous circuits through the copper “track,” until the battery is completely drained.

This caught my attention because it is a very clever twist on one of Michael Faraday’s original discoveries!  Not electromagnetic induction, as I reflexively thought, but a homopolar motor.  Below is an animation of such a motor that I whipped up in my office.

A simple homopolar motor.

A simple homopolar motor.  Just in case you don’t believe it actually works, a longer video is here.

This particular homopolar motor design is ridiculously simple: a pair of neodymium magnets are stuck (by magnetic force only) to the bottom of an AA battery. A wire loop is balanced on the top of the battery, bent so that it touches the magnets on the bottom.  When the connection is made, the wire will start to spin immediately, and will in general start spinning so fast that it will flip itself off of its perch.  More sophisticated and stable designs exist, but this one is quick and showy.

So how does the homopolar motor work, and the “magneto-electric” train shown in the video?  Both of them depend on the relationship between moving electric charges and magnetism, albeit in somewhat different ways.

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Ann Gregory, RIP (1974-2014)

One of the joys of twitter is getting to meet so many kind, interesting, and varied people from places all over the world and getting to share, at least a little, in their lives.  One of my favorite of these people was Ann Gregory, who passed away on November 26 from cancer-related complications.  Ann was one of my earliest twitter followers, and therefore one of my oldest twitter friends.

I can’t say that I knew Ann particularly well, as our interactions were unfortunately limited to twitter.  She was already a cancer survivor when I met her, but she was always unfailingly kind and fun to talk to, and chatting with her always cheered me up no matter what the situation.  We shared a love of cats, and would share photos of our cute kitties now and again.

Her cancer came back suddenly and unexpectedly, and it was a shock to me how quickly it took her life.  My thoughts and sympathies go out to her husband Chris and her family and friends.  Ann kept a long-running blog describing her life and illness, and her husband wrote a very touching post after her passing, both in memory of her and as a message to those still coping with their own difficult cancer diagnoses.  To just borrow one paragraph from it,

When Ann was diagnosed all those many years ago at 32, she would say to me, “I just want to live to my 40th birthday”.  Well, we did and could we have done anything better?  Sure.  But we didn’t live life like it was going to end on a schedule.  We lived it like everyone else does – one day at a time focused on what you need to to stay ‘normal’ when you have been touched by cancer.

The internet, and the world in general, feels somewhat empty to me with her gone.  She was a nice friend and I will miss her and remember her.

Rest in peace, Ann.


Ann’s obituary can be read at The Advocate.  As noted there, donations in her memory can be made to the M.D. Anderson Cancer Center.

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Slurstorm, and the flaws in “Shirtstorm” arguments

I hate writing posts like this.  I prefer to write about fun physics, history of science and cool horror fiction.  But some things are so appalling and disgusting that one must speak up, especially if one’s friends are attacked.

You probably already know the story.  I’m not going to directly use the names of the central victims in this post, as they’ve already been plastered all over the place, and I don’t feel like adding one more link to the pile.

In short: on the 12th of November, the Philae lander detached from the Rosetta spacecraft, landing on the surface of Comet 67P in the first ever controlled landing on a comet surface.  It was a remarkable achievement, and everyone involved was elated — everyone watching, including me, was similarly thrilled.  But the event was marred when the Project Scientist appeared on camera wearing a gaudy bowling shirt plastered with scantily clad women in a variety of poses.  He also made a comment about the mission that many felt was inappropriate: “She is sexy, but I never said she is easy.”

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Posted in ... the Hell?