Archive for the 'Physics' category

Whittaker breaks the irony meter (1910/1953)

Sep 11 2010 Published by under ... the Hell?, History of science, Physics

I'm currently working my way through E.T. Whittaker's monumental A History of the Theories of Aether and Electricity (1910), among other things.  Whittaker's book is a very comprehensive study of electricity and aether that stretches back from the seventeenth century up to the beginning of the twentieth, and it really is excellent -- I've already learned a lot, and am only 20 pages into it!  (I loved a fascinating tidbit about the first experimental measurement of magnetic field lines, demonstrating the poles of the magnet -- I'll come back to this in a future post.)

However, as I've blogged about previously, there is one glaring weakness in Whittaker's treatment.  In his second volume of the 'History, released in 1953,  he almost completely discounted Einstein's contribution to the theory of special relativity!  While discussing the "relativity theory of Poincaré and Lorentz," his primary statement regarding Einstein's work is:

In the autumn of the same year, in the same volume of the Annalen der Physik as his paper on the Brownian motion, Einstein published a paper which set forth the relativity theory of Poincaré and Lorentz with some amplifications, and which attracted much attention.

Whittaker is much more generous towards Einstein's general theory of relativity, and gives him the credit, but his dismissal of Einstein's contribution to special relativity is puzzling.  I've speculated that Whittaker was perhaps a bit miffed that his life's work on the aether was made obsolete in 1905 by Einstein before it was even published; it may also be that Whittaker genuinely didn't completely grasp the philosophical implications of Einstein's contribution.

So what is the irony in this?

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R.W. Wood's lecture demonstrations (1897-1905)

Sep 10 2010 Published by under History of science, Physics

With all the concerted efforts into popularizing science that goes on these days, it is quite easy to forget that some of the best scientists throughout history put a lot of effort into making their knowledge accessible both to students of  the arts and laypeople alike.  Physicists in particular are often viewed as "keepers of secret knowledge" who study phenomena outside the ken of mortals and who are unwilling or unable to make this knowledge accessible to others.

A perfect counterexample to this perception is the great physicist Michael Faraday (1791-1867) , who over the course of many years presented the Christmas Lectures at the Royal Institution,  targeted at nonspecialists and young people.  Two of these lectures, "The Forces of Matter" and "The Chemical History of a Candle", have been reprinted and are still available today; I will be blogging about them in detail in the near future (hopefully). Faraday in fact put much effort and thought into his public presentations; long before he was a recognized scientist and had any opportunity to speak to an audience, he observed other lecturers and took elaborate notes on the "do's" and "don't's" of lecturing.

Another example of a distinguished scientist working very hard on presentation is Robert Williams Wood (1868-1955).  Wood is best known today for his work in optics, particularly in the study of infrared and ultraviolet light.  As we have seen previously on this blog, however, Wood was also active in popularizing science: he co-authored two science fiction novels, The Man Who Rocked the Earth (1915) and The Moon Maker (1916).  He also was quite skilled at setting up simple demonstrations of optical effects; I've previously discussed his 1902 illustration of a simple form of invisibility.   Between the years 1897 and 1905, Wood in fact published a number of short articles suggesting simple lecture hall demonstrations of a variety of physical phenomena; in this post, we'll take a short look at these demonstrations.

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Alan Hirshfeld's The Electric Life of Michael Faraday

In my blogging on the history of science, I tend to focus on the details of classic experiments -- the how, why, and what of scientific history -- and don't dwell as much on "who" actually does the work.  The personalities that drive the research, however, say as much about how science gets done as the actual techniques, and I've been trying to deepen my understanding by learning a bit more about the famous figures of science.

To this end, I've started reading a number of biographies of famous physicists.  Until I started looking, I was unaware that many of these biographies existed!  The first on my list was Alan Hirshfeld's biography of my favorite scientist of all time, Michael Faraday*, titled The Electric Life of Michael Faraday (2006):

I thought I'd share a few impressions about the book, and about Faraday in general!

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Tolman goes silly for similitude! (1914)

This post is for the special "fools, failures and frauds" edition of The Giant's Shoulders.

The early 20th century was clearly an exciting time to be a physicist. In 1905, Einstein published his special theory of relativity, radically revising human concepts of space and time. In the same year, and the same issue of the Annalen der Physik, Einstein really sparked the "quantum revolution" with his explanation of the photoelectric effect, an explanation that would scramble existing preconceptions of the nature of light and matter and would eventually shake the deterministic foundations of physical theory.

By the teen years of the 1900s, it must have seemed to many physicists that no idea was too crazy to possibly be true!  Furthermore, the simplicity and elegance of Einstein's relativity must have suggested to scientists that the secrets of the universe remaining to be discovered would be of the same sort of "beautifully obvious" form.

One researcher who was  seduced by this sort of thinking was Richard C. Tolman.  In 1914, he published a paper on a new physical principle that he referred to as "the principle of similitude".  In Tolman's own words, his principle represented a new form of "relativity of size", which "provides a very simple and general method for obtaining conclusions as to the form of functional relations connecting physical magnitudes."

Tolman's theory was bold, it was powerful... and it didn't really work out.  It is a great example of a failed theory, and even more fascinating because its proponent was no crackpot, and its insights turned out to have some practical use in the end.  There's even a whiff of a conspiracy surrounding similitude, which I will describe at the end of the post!

This post is closely related to the idea of dimensions in physics; if you're not familiar with this concept, check my earlier post here.

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Right-wing refutations of relativity really, really wrong!

Aug 09 2010 Published by under ... the Hell?, Relativity

Back when I first started my blog, I spent a lot more time dealing with crazy people who are convinced that Einstein's theories of relativity are wrong (see here, here and here).  More recently, I haven't spent a lot of time on the crazy train, but I have been meaning to get back to my long-neglected series of posts explaining relativity.

Enter Conservapedia, the right-wing version of Wikipedia intended to combat the liberal bias in reality!  Over the past day, Twitter has been abuzz with tweets¹ on the Conservapedia page on "Counterexamples to relativity", provides a list of 24 "points" that attempt to show the weakness of Einstein's crazy ideas!

In my mind, perhaps the most despicable sort of denialism or crankery, however, is that which is based on some sort of political or religious ideology.  This is clearly what is going on here, and the author relies on a familiar form of rhetorical trickery known as the "Gish Gallop": throw as many claims out there as possible, regardless of their validity, with the realization that most people will be swayed by the amount of "evidence", and not look too closely at the details.

Looking at the "evidence", it is clear that there isn't a single point made that isn't misleading, incoherent, or simply dishonest.  A person reading the Conservapedia post will be measurably more ignorant afterwards, and I get the distinct impression that this is what the author intended.

But never fear, dear reader!  I'm here to go through the list of some of the most entertaining assertions, and explain why they're nonsense. Why bother, you ask?  For one thing, entertainment.  For another, there's always a chance that someone may come across the Conservapedia entry and look for some sort of counterbalance... someone should write one!

One caveat: I can't guarantee that the list I present will match the list on the Conservapedia page.  I saved the tweeted list, but after all the internet attention, it was reduced to four points.  Soon afterwards,  it reverted to the original list again.  There's no guarantee that it will remain in its current form, though...

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Cerenkov sees the light (1937)

Jul 21 2010 Published by under History of science, Physics

This particular post serves a double purpose: highlighting an important event in the history of physics and highlighting an important moment of my personal interest in said history!

The event in question is the publication of a letter in the Physical Review in 1937, "Visible radiation produced by electrons moving in a medium with velocities exceeding that of light," by P.A. Cerenkov.  This was the first English paper published on the observation of what is now known as Cerenkov radiation, a discovery that has found numerous applications and made its discoverer a co-winner of the 1958 Nobel Prize in Physics.

I've talked about Cerenkov radiation before, in a previous post about "reverse" Cerenkov radiation in metamaterials.  Though I touched upon the basics of the Cerenkov effect there, it seemed worthwhile to go back and look in more detail at how it was discovered!

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Freaks & geeks: optical freak waves in the laboratory

Jul 13 2010 Published by under Optics, Physics

ResearchBlogging.orgOne of the most fruitful and intriguing avenues for developing novel scientific research is through cross-pollination with other fields of study.  This is one of the reasons I'm proud of my excessively liberal arts-focused education, as well as one of the reasons I like reading blogs on diverse subjects outside of my field: interesting ideas can often come from unexpected sources.

An example of this I found a few months ago in Physical Review Letters, in an article entitled, "Freak waves in the linear regime: a microwave study," by Höhmann, Kuhl, Stöckman, Kaplan and Heller.  Freak waves, also known as rogue waves*, are anomalously large -- and deadly -- isolated oceanic waves that can shatter and overturn ships, and they have only been acknowledged relatively recently as a genuine and unusual phenomenon, albeit one that is still not completely understood.

Hokusai's 1832 The Great Wave off Kanagawa, via Wikipedia.   Not necessarily a freak wave, but probably close to what most people would envision one to be.

It was probably inevitable that researchers in optics would become interested in freak waves: broadly speaking, a wave is a wave, and an effect that appears in water waves is likely reproducible in electromagnetic waves.  Experts on oceanic freak waves have even been invited to speak at optics meetings; a session at the 2009 Optical Society of America's Frontiers in Optics meeting was opened with the invited talk, "Freak Ocean Waves in One and Two Dimensions," by Peter Janssen and Jean-Raymond Bidlot of the European Center for Medium-Range Weather Forecasts.

In this post I thought I would take a look at the phenomenon of freak waves, the physical origins of said waves, and methods that physicists have used to create electromagnetic versions of them in the laboratory.

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Invisibility physics: Kerker's "invisible bodies"

Jul 02 2010 Published by under Invisibility, Optics

(This is a continuation of my “history of invisibility physics” series of posts.  The earlier posts are: Part I, Part II, Part III, Part IV, Part V, Part VI)

The history of invisibility physics truly began with the concept of radiationless motions of charged particles, as described by Ehrenfest in 1910 and Schott in 1933.  There are many more discoveries associated with these and related phenomena, which would eventually be referred to as nonradiating sources.

I would like to jump ahead in the history a little bit, however, and discuss a paper published in the Journal of the Optical Society of America in 1975 by Milton Kerker, entitled, "Invisible bodies".  The article, relatively unknown today, is the first article to describe an object which is invisible in the true sense of the word -- although the object itself is microscopic!

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Shocking: Michael Faraday does biology! (1839)

May 15 2010 Published by under History of science, Physics

(This is my entry to the first "special edition" of The Giant's Shoulders, dubbed "The Leviathan's Shoulders", with an emphasis on oceans and ocean life.  The post is actually about a river creature, but, hey, it's still aquatic!)

I've spent a lot of time talking about Michael Faraday (1791-1867) and his scientific accomplishments on this blog.  His thorough investigations into the nature of electricity and magnetism paved the way for all of modern electromagnetics as well as optics, and he is rightly viewed as one of the greatest experimentalists of all time.  Among his monumental works are the observation that changing magnetic fields induce electric fields (electromagnetic induction) and the observation that light polarization can be affected by an applied magnetic field (Faraday rotation).

Though it is natural to think of Faraday as a researcher of electricity alone, in his era the study of electricity connected to almost every aspect of the natural sciences.  In the late 1700s Luigi Galvani had shown that an amputated frog's leg could be made to move by electrical stimulation, demonstrating a connection between biological function and electricity.   By 1800 it was known that chemical reactions can be induced by electricity, in a process known as electrolysis; Faraday himself published fundamental results on electrolysis in 1834.  Electricity could be connected to thermodynamics through the observation that an electrical current heats the wire it passes through (Joule heating); this process was rather mysterious because neither the origins of heat (atomic motion) nor electricity (electrons) were established in Faraday's time.

Electricity could be generated through atmospheric, chemical, and mechanical means, and it was by no means obvious that these different sources were manifestations of the same fundamental electrical phenomenon.  (In fact, Faraday himself did a significant amount of research to demonstrate that all forms of electricity are in fact the same. )

A researcher of electricity could therefore be expected to make forays into quite diverse areas of study.  In 1839, Faraday published the scientific results of one of his forays, "Notice of the character and direction of the electric force of the Gymnotus," in the Philosophical Transactions of the Royal Society (pp. 1-12).

What is the "Gymnotus"?  The taxonomy of the species seems to have been changed over the years, but at this time seems to be referring to what used to be known as Gymnotus electricus, or the electric eel (image source):

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Wave interference: where does the energy go?

Apr 07 2010 Published by under Optics, Physics

Last week was a relatively lousy one for me, but it was made up in part by getting a good question from a student on waves and interference after class.  It's really nice to get a question that indicates a genuine interest in the science (as opposed to just wanting an answer to homework), and I thought I'd discuss the question and its answer as a post.

The situation in question is as follows: suppose you have a harmonic wave on a string traveling to the right such that in a snapshot of time, the string looks as follows:

This wave carries energy, and there is a net flow of energy to the right.  Now suppose we excite the string with an additional wave of the same frequency and amplitude, but completely out of phase.  The sum of the two waves then vanishes:

The two waves cancel each other out, leaving a completely unmoving string due to destructive interference.  My student asked me: what happens to the energy?  As posed, it seems that we started with two waves carrying energy, but they canceled each other out, leaving no energy!  This interpretation cannot possibly be correct, so where is the flaw in our description?

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