seeing things in a new light

In the next month millions of students will be back in colleges and universities starting into a new term.  Some will signal their interests by what they wear.  You may have seen physics and electrical engineering students wearing a certain tee..

 

Maxwell's equations are one of the most beautiful achievements in physics, describing how electric and magnetic fields are generated by each other and by currents and charges.¹  Electromagnetism is one of the four basic forces of physics - a force fundamental to chemistry and therefore biology and one that, as we understood it more deeply, gave us much of our current technology.  

 

The precise formulation of the time-space laws was the work of Maxwell. Imagine his feelings when the differential equations he had formulated proved to him that electromagnetic fields spread in the form of polarized waves, and at the speed of light! To few men in the world has such an experience been vouchsafed ... it took physicists some decades to grasp the full significance of Maxwell's discovery, so bold was the leap that his genius forced upon the conceptions of his fellow workers.  - A. Einstein Science May 24, 1940

 

Revolutionary is perhaps not a sufficiently strong term

 

In college a physics student first encounters them as a freshman, again as a junior and then as a first year graduate student going in more deeply each time.  They are a great path to learn a bit of the language of physics - mathematics - along the way.  

 

Early on you perform a simple manipulation and get a curious result.  This turns out to be a wave equation.   It tells you that the fields involved propagate as waves at the speed of light.  My advisor noted that those who see this is beautiful go on into physics and those who don't leave fairly soon.  All of us who find passion in things hear the bits of poetry.  Perhaps this for a physicist, real poetry for a poet, and the kinesthetic manifestation of flow for an athlete.   We all have our own language of beauty.

 

The term light usually refers to what we can see with our eyes, but it is a very small part of the electromagnetic spectrum.  The wavelengths of visible light range from about four to seven tenths of a micron - with blue on the short side and red on the longer.  But the spectrum extends to enormously long wavelengths - a section we call radio as well as to very short ones that include X-rays.

 

We only sense a small part of what nature offers with our senses.  I won't dwell on that, but go to this earlier post for a bit of necessary detail.  Using our minds we have developed methods to sense what is going on in nature - we have dramatically increased the scale of what we can "see".

 

The trigger for this post was a bit of visual story telling - namely what WiFi would look like if we could see it.  The problem is it is just story telling and happens to be inaccurate - a real danger of story telling that is pretty.  You get a sense of what things would look like from the basic physics.  It is a mathematical abstraction, but turns out to be much more beautiful.  

 

Here is a note I sent to a good friend who pointed to the site:

 

The visualizations are wrong.  Pretty, but wrong.

A few points…

Let's saw our eyes were sensitive to ten centimeter electromagnetic radiation.  Probably the first problem is we don't see the photons because to have vision the photon has to strike our eye.  Vision comes when the radiation reflects, or is transmitted through something or a vacuum.  

We would see things that looked sort of the same except very blurry.  Things smaller than about ten centimeters would be completely blurry as would any feature roughly wavelength-ish.  There would be a lot of diffraction effects evident.  What is transparent and opaque would shift as some objects (like a wood wall) are fairly transparent in these bands.

So let's say this is a depiction of what the photon is doing rather than what we're seeing.  The images are still wrong.  An electric and a magnetic field strength changes with time  and this varies with position (or time as it is propagating).  

There is the issue of signal encoding.  Without information a constant frequency is just a simple tone.  The frequency, amplitude, phase or polarization can be modulated and you get schemes like frequency-shift keying for digital signaling (sort of a modified frequency modulation).  With light you detect the amplitude of the intensity which is the square of the field. Somehow our eyes would have to deal with the modulation to notice any signal (which would be at a lower rate - usually a much lower rate - than the frequency).

There are other issues, but this piece is built on incorrect physics.  What is really happening is much more complex and beautiful.  Our our eyes deal with light and forming images from it is much more beautiful and wonderful.   

Thinking about what it would really look like is a nice exercise for learning the underlying physics as well as how radio waves interact with the world around them.  It is something the radio engineers have to get right - or at least good enough.  And, when you think about them deeply you realize the current rules for spectrum allocation are more a function of receiver design - and an antiquated notion that goes back about 80 years - than physics.  Our wireless spectrum shortage turns out to be driven by arbitrary laws rather than basic physics.²

 

Ending with a bit of history...  

 

Decades of research preceded Maxwell's grand synthesis and then another twenty or so years before the commercial world began to make use of the result (Tesla and Steinmetz built their work on its foundation and later all of radio came about).  One of the great experimentalists before Maxwell was Michael Faraday.³  When William Gladstone, then Chancellor of the Exchequer, asked about the practical value of electricity in 1850, Faraday replied:

 

 One day sir, you may tax it

__________

¹ James Clerk Maxwell published an early form beginning in 1861.  Few understood them at the time as the form was so obtuse.  In about 20 years modern formulations of the equations appeared and their use began to become realized.  It turns out they are an approximation of a deeper view of electromagnetism - quantum electrodynamics.  But they work perfectly well for most of the world and technology we interact with as humans.

² This creates artificial scarcity - something exploited by those who "own" spectrum.  They complain, but it allows them to sell wireless connectivity at a very high price.

³ Faraday, in addition to being one of the great scientific minds of the 19^th century, was also the Carl Sagan and Neil deGrasse Tyson of his day - a great popularizer of science. He excelled at the art of the public lecture and his Christmas lectures for young people at the Royal Institute were famous. The six part series on the Chemical History of the Candle is brilliant and wonderful even today - you can read it courtesy of Brewster's great archive.

 

__________

 

Recipe Corner

two sketches

 

Chickpea Salad Sandwiches

More of a sketch than a recipe - use your own creativity here.  Rather than making egg salad sandwiches with eggs, use chickpeas.  The trick is to use cooked chickpeas and mash em with a fork rather than something which grinds them up finer.  I used a 15 oz can of cooked chickpeas, 1/4 cup of mayo (use vegan mayo if you like), and the goodies that make up the rest of an egg salad - I used finely chopped celery, onion and salt, pepper, a splash of lemon juice, a bit of crushed pickle, and some curry powder.  

 

I make a sandwich with a good bread, sliced tomato, lettuce and pickles, avocado or whatever you like.

_____

on someone's suggestion another sketch

 

BBQed Ice Cream Sandwiches

 

I saw a recipe and tried this variation.

 

Cut inch thick slices of brioche bread, butter lightly on each side and grill until crisply darkened.  Now put a big scoop of ice cream on a sheet and top with a fruit topping (I used a blueberry jam) and another piece of brioche.  It might even work with pound cake if you use some care.