Today was one of those Spring days had managed to wander in from the Summer and I found myself a bit bored as I sat near a busy swimming pool in the heat, humidity and noise. My mind wandered as I considered the wild motions of waves as they spread around the pool. The surface of the water was an amazing complex surface - a basically two dimensional membrane moving up and down all over its surface as it occupied a bit of a third dimension in space and a forth if you count time.
I wondered what it would be like for an insect to be on that surface of the water - perhaps near the edge of the pool holding onto the side somehow. Perhaps it would have a couple of feelers probing the water surface. Now imagine what was making the surface of the pool jiggle so much. Sally dog paddling in the deep end, the twins happily splashing each other with their hands, George in a determined crawl as he did laps, and Kevin's rather nasty belly flop a second ago. What would it take for our insect to visualize what was going on? Could it reconstruct the locations of the events and a bit about them in real time as it felt the surface of the water jiggle back and forth with that terribly complex interaction? What would its sensors have to do and what kind of computation would be required?
As I considered this I was watching these events transpire with my own two small arrays of receptors - nerves that are sensitive to a different sort of wave. These arrays - my retinas - are about 3 centimeters in diameter and are located on the backs of my eyes. The light they detect is really a just electromagnetic radiation. The space around me is filled with an incredibly complex jiggling field of electromagnetic waves. Some pass through these two little black holes on the front of my eyes. These pupils are probably only about two or three millimeters (maybe a tenth of an inch) in diameter on this bright day as they allow bits of this mass of complex vibration to makes its way back to my retinas where they are converted into electrical signals that send information to my brain where an image representing the scene is formed in three dimensions and color.
This three dimensional space that we sit in is filled with electromagnetic waves that come in a wide range of sizes. The AM radio wave that corresponds to a frequency of 650 kHz has a wavelength nearly half a kilometer long while some of the ultraviolet light that is threatening to penetrate my melting sunscreen has a wavelength of about three tenths of a micron. These differ by more than a billion in wavelength and don't begin to describe the range of wavelengths found in this complex jiggling mess.
Some of this electromagnetic field is absorbed as it strikes an object, some reflected, some is absorbed and then retransmitted. I can see the scene from my vantage point and Sukie who is sitting about 90° to my right can see her own version with the waves that end up impacting my eyes passing cleanly through those that impact hers. And without thinking we manage to assemble an image of what is taking place with only a short delay.
the mind wobbles
It turns out our eyes are sensitive to only a tiny portion of what is really around us. Our vision is extremely limited in its scope, but is still wonderful.1
We tend to label the different wavelengths with colors that correspond to them. So 0.45 micron light might be called blue, 0.63 red .. When we break up sunlight with a prism we see a spectrum in seven bands of color - red, orange, yellow, green, blue, indigo and violet ...
But it turns out color is really something done in our head that we assign.
Take a red light and shine it onto a white piece of paper. You see a red splotch. Now shine a green light onto the paper so the two splotches partially overlap. What your eye is picking up is electromagnetic radiation corresponding to two distinct wavelengths, yet where they overlap we see yellow even though there is no radiation with the wavelength of yellow.
It turns out we have three types of color receptors in our retinas - the cones. They come in three varieties each with its own response and cleverly labeled as s (short), m (medium) and l (long) cones. They are not sensitive to narrow ranges of wavelength, but rather have sort of gaussian shaped response curves that overlap a bit. Electric signals are produced by the cones and the rods (which are sensitive to non color specific brightness across the visible light range) that travel to the brain. There colors are assembled.
A color TV generally has three colors of pixels that produce a subset of the color range our eyes can perceive. Some new TVs have a forth color - yellow - to produce a more accurate color range. But to date all attempts have been approximations as some tough engineering compromises are made. Some research indicates that five color tvs would be remarkably close to our color vision.
We can rapidly get off into perception, what other animals can see (your dog sees a rather limited piece of a rainbow and other animals, even butterflies, leave us with what would seem like very poor color discrimination.
A recent Radiolab has an excellent feature exploring color. I struggle with explaining it in an interesting and even exciting voice. Jad Abumrad and Robert Krulwich do a masterful job connecting the dots - and finding an exciting story telling voice. Robert, by the way, did one of the best commencement addresses I've ever heard and the best for science majors at Caltech in 2008. (note: both of these Radiolab segments will fail on iOS devices - the Radiolab player is antiquated and requires Flash)
All of this has been a lead-up to something quite remarkable from Jad and Robert - a recent show on color that touches history, science, poetry and beyond. This is required listening. find something delicious to snack on and perhaps someone you love and listen - and I will listen again in the next few days.
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1 Red light has a wavelength on the order of seven tenths of a micron and blue light, about four tenths. Radio waves tend to be fractions of a kilometer for AM broadcast radio, to about the width of your palm for the waves in your microwave oven. Many of us have a bias to refer to visible electromagnetic radiation and perhaps bits that are close to it in size - infrared and near ultraviolet - as "light" ... when we really mean visible light.
Also note there is a wave-particle duality for light that we're not mentioning in order to keep things simple. Talking in terms of photons makes more sense for other aspects - but they are just two different views of the same thing.
Our understanding of nature has been dramatically altered as we learned how to probe it at wavelengths shorter and longer than those available to just our eyes. The same is true to signals weaker than we can detect. And in a way that went far beyond our imaginations. Building new instruments to extend our vision has been a fundamentally important piece of science.
important point!
There is a subtle, but critically important point to make. Receiver sophistication is extremely important when it comes to how much of the signal can be pulled out of this jiggling mess of waves. When radio was first developed we had very primative receivers that weren't very sensitive (they required strong signals) or selective (signals close in frequency could confuse the receiver). Technologies rapidly improved through the 1920s, but then the concept of receiver design became somewhat fixed - at least in policy.
Since the late 20s receiver technology has greatly improved and slight modifications to policy have been made, but mostly receivers are considered to be primitive. Now computers make so-called agile radios and some other exotic techniques possible that hugely expand the amount information density we can transmit into a volume and decode in a receiver. The so-called spectrum shortage is not a physical limit, but rather only a policy limit! It is very possible that your mobile device bill could be dramatically lower if we moved to some of these newer technologies and the concept of data caps would be just silly.
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And now the recipe for the day - very easy to make. It is very important to use very fresh ingredients, but this is terrific on a hot Summer day. Note that the eggs are not cooked - it just tastes much better than way. You need to use pasteurized eggs for safety!!
Chocolate Chip Ice Cream and just six ingredients!
Ingredients
° 2 large pasteurized eggs
° 3/4 cup white sugar
° 2 cups whipping cream
° 1 cup whole milk
° 2 tsp of a high quality vanilla extract (I make my own from vanilla beans and rum)
° 2 bars (100g each) of a good chocolate chopped into chunks. I like a mixture of a roughly 60% and a 80 or even 85% chocolate. Some people like some or all milk chocolate. I usually use Lindt or Scharffenberger.
Technique
° Whisk the eggs in a mixing bowl until light and fluffy - about 1 or 2 minutes depending on your style. Then mix in the sugar a bit at a time and completely blend - another minute or so.
° Add the cream, milk and vanilla and continue to whisk until blended.
° Transfer to an ice cream maker and churn freeze to the manufacturer's instructions. Just before the ice cream sets (when the motor or your arm begin to labor depending on your ice cream maker), add the chopped chocolate and let it distribute.
° You can put it in a freezer to allow it to ripen - or, if you are like me, just be a barbarian and eat it directly.
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