1 January, 1865
At least that's my take, but as usual a story lurks. With physics many stories trace back to Isaac Newton. Newtonian physics was and is an amazing triumph. While we now have a much deeper understanding of how the Universe works, it is usually accurate enough to describe how the world - how much of the solar system - works at our scale. We used it to get to the Moon. The success was so great and the math so beautiful that it created a framework for physicists and mathematicians that lasted for a few centuries. And that was a problem.
There are a few fundamental problems with Newtonian gravitation. Newton was deeply troubled by one of them In his physics space is an empty void. Gravity is an attractive force that acts on all pieces of mass in the Universe without any delay. Its force depends on the distance between two bodies and falls off as the square of distance. Just how is that force transmitted and how does it gauge the amount of empty void that separates the two bodies? The math was simple and beautiful, but conceptually the model was ugly.
Newton worked on the problem playing with several alternate conjectures. All of them failed. Many mathematicians and physicists who came immediately after saw the theory as a useful tool and, in the end, read too much into it. It was being elevated to physical law.
Michael Faraday almost shouldn't have happened. The son of a blacksmith with only a few years of schooling, he managed to get an apprenticeship with a bookbinder - a firm that printed a few science books. That was the hook. He attended some of Humphry Davy's lectures and asked enough questions to be hired as an assistant. He only had math up to trigonometry, but it was possible to do science without deep training in math then. Perhaps being clever at math would have kept him from making novel mental connections.
Like many scientists of the day Faraday was interested in electricity, magnetism and optics - three separate fields. Electric and magnetic forces appeared to share some features with gravity - after all - the strength of their force fell off with the square of distance and they appeared to act instantly. Many of the theories looked like modifications of Newtonian gravity. Faraday couldn't understand the math and turned to his wickedly powerful mind and deep physical intuition. He noticed if you spread iron filings on a piece of paper that covered a bar magnet the filings would trace arcs from one pole of the magnet to the other. These magnetic lines of force were easily explained by the Newtonian void model people. The instant forces from the magnet just act on each filing managing to orient it appropriately. It just worked. QED.
Faraday's explanation was fundamentally different and novel. He used a space filling medium - a fluid of sorts. The filings were just revealing the local state of that medium. The magnet represented a disturbance in the fluid and the filings were just reacting to the fluid's current state.
Consider the atmosphere. Imagine placing a grid of tiny weather stations - miniatured wind vane/anemometers. At each station you record the direction and speed of the wind. These instruments are measuring the field.1 Faraday had intuitively come up with field theory. His model had some problems and mathematical physicists of the day discarded it as it was far from the mainstream work in Newtonian void models. But it was a seed.
It should noted that Faraday wasn't considered a crackpot. He had enormous respect in many areas and made fundamental contributions to many areas of physics and technology. Among other things he was a phenomenal public speaker. For a treat you might want to read his six Christmas lectures on candles - a model for clear and deep public science speaking to this day. I first learned about them from a friend who referred to them as the six lessons and carols.
Not every mathematical physicist ignored Faraday's idea. He had done brilliant experimental work discovering, among other things, that moving a magnet could generate a current in a nearby wire. Not shabby as that led to the electric motor. Perhaps more importantly his idea managed to fire the imagination of one James Clerk Maxwell.
This is my favorite photo of Maxwell. He was something of a physics polymath and had a deep interest in color. Here he's holding a color wheel top created to test human color perception. Unfortunately the photo is in black and white. To see the colors you'd need color photography, but he hadn't invented that yet.
The best physicists are enormously playful and Maxwell brought that to the problem of electricity and magnetism. He flew from idea to idea with several schemes, but recognized something deep in Faraday's observation and focused for several years. By the early 1860s he managed to express several important laws of electricity and magnetism using the idea of a field (he would say fluid). The result was messy, perhaps inelegant, with something like 20 partial differential equations, but it was enough to tell him he was on the right track.
With his new model Maxwell could show how Faraday's experimental observation worked - that if you move a magnet near a wire an electric current is generated. But something else came out. If a current changes in a wire a magnetic field is generated. There were time varying magnetic fields and time varying electric fields. One could generate the other. An almost trivial, but astounding beautiful, result was that this dance of the fields propagated through space - and at precisely the speed of light! He wrote:
The velocity of transverse undulations in our hypothetical medium ... agrees so exactly with the velocity of light ... that we can scarcely avoid the inference that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena.
A necessary consequence of linking electricity and magnetism was that shaking the electromagnetic field created a disturbance that propagated at the speed of light - this disturbance was, in fact, light.
There are few observations in science at that level. I doubt there are more than a handful of times when such a brilliant discovery presented itself. There were some issues to work out. Maxwell had expressed the electric Gauss's Law, the magnetic Gauss's Law, Faraday's Law, and Ampere's Law. These were almost enough, but there was a sticky point which was fixed with something called Maxwell's law. Five laws that ultimately were expressed as four partial differential equations. He presented the result in December of 1864 and published A Dynamical Theory of the Electrodynamic Field on 1 January, 1865.
It needed to be verified by experiment or it was just another piece of beauty that didn't represent Nature. Verification came in 1886 when Heinrich Hertz was able to generate and detect a radio wave starting with a spark neatly inventing radio in the process.
The math was too much for most physicists and mathematicians of the day. Around the time of Hertz's discovery a simple version with just four equationswas proven to be identical to Maxwell's original equations. The simple version of the equations was taught in engineering and physics classes directly impacting the last, and possibly most important, part of the Industrial Revolution - which became the a revolution in communication.
Electric power and radio - and now understood deeply. There was great and unexpected predictive power that continues to this day. Perhaps as important, he gave credence to the idea of fields. It took a generation or two for that to really since in, but most physicists now describe the fundamental Nature in terms of fields.
Let's go back and pick up on Maxwell and color. We see an array of colors when sunlight is broken into a spectrum, but some are missing - pink for example. Artists have long known that pigments can be mixed to obtain any number of colors and some rules and ideas had been floated, but none were robust.
Maxwell approached the problem playfully. He noticed that patterns smear out when you spin a child's top. Our minds assemble a model of the world from very sketchy input - in the case of vision roughly twenty fives images per second are assembled into something that appears to have continuous motion. Spin a top fast enough...
Yellow is a simple example. It exists in the spectrum of of sunlight and yellow pigments reflect it. But if you blur two other spectral colors - red and green - by spinning them on a top, the mind perceives the result as yellow even though no yellow light is directly reflected. Maxwell painted a yellow reference ring on the top and added concentric arcs of red and green. He added non-reflective black to control the apparent brightness.2 By choosing just the right amount of certain shades of red and green his mind created a yellow that appeared identical.
Most colors required three primary colors. Maxwell carefully built a color triangle showing just how much of each of the primary colors were required to form nearly anything you wanted. The work was extended to transmitted light and he was able to show that if you want to use just three colors, they need to be a bit artificial.
Around 1855 it occurred to him that by taking three exposures with either filters or colored illumination and a photographic film that responded to the those colors that color photography was possible. A few years later, working with a photographer, the first color photo was made.3
Maxwell's equations had shown that light was just an electromagnetic wave traveling at the speed of light. Visible light had a tiny wavelengths - four tenths of a micron for blue growing to seven tenths of a micron for red. Hertz's radio waves were the same thing, but impossibly longer - many meters long. In fact there is a continuous spectrum of light ranging from incredibly gamma rays produced by very energetic events to radio waves of enormous wavelengths. Our eyes only detect the tiniest silver - but a silver that coincides with much of the Sun's output that makes it to Earth. Evolution selected the light we see based on solar physics and the nature of our atmosphere.
There are so many jumping points from here - the hallmark of a rich result and one that marks the beginning of modern physics and with that probably the most important point in the development of modern technology. Deep beauty lies here.
1 For the physics types note that the word field is used to describe two things. One is the force divided by charge in the electric field - it is somewhat analogous as the wind velocity at the point of measurement. The other field is the underlying 'fluid' -- an electric fluid of sorts. In one case it is a description of the measurement, in the other it is the medium itself. Using the wind analogy it is like one is the wind, the other the air.
2 poorly drawn on an iPad in about two minutes:-) The iPad is a poor drawing tool for my purposes - perhaps that will improve some day.
3 There were some technical issues, but the concept was sound and others ran with the idea. That's a Tartan ribbon ...
Tomatos are finally great. I love to roast them to pull out even more flavor
° 3 pounds large tomatoes sliced into 3/4" thick rounds
° 2 garlic cloves, peeled and smashed
° 1/4 teaspoon dried oregano
° kosher salt and freshly ground pepper
° at least a half cup extra-virgin olive oil (I probably use half again as much)
° oven rack in the middle and oven to 425°F
° line a baking pan with foil and spread the slices .. smaller ones in the center. put garlic cloves between the tomatoes and sprinkle with oregano and salt (maybe 1/4 tsp to start) and pepper to taste. drizzle with oil
° Bake for a half hour rotating the sheet halfway through if your oven is uneven like mine.
° remove sheet and flip tomatoes. Reduce heat to 300°F and hold door open to let it cool to temperature (I use an oven thermometer, but final temperature isn't too critical)
° cook until skins are blistered and spots of brown appear. I go for a final thickness 1/2" or less .. maybe 90 minutes, maybe a bit more.
° pull the sheet, cool, discard the garlic and move the tomatoes and oil to an airtight container.