Another week, another deluge of BS from the White House and from the Controlled Opposition.

The Audit continues.

The collapse of the Covidschina continues.

No doubt much will be said about those today. (And I have missed a lot this past week.)

Justice Must Be Done.

The prior election must be acknowledged as fraudulent, and steps must be taken to prosecute the fraudsters and restore integrity to the system.

Nothing else matters at this point. Talking about trying again in 2022 or 2024 is hopeless otherwise. Which is not to say one must never talk about this, but rather that one must account for this in ones planning; if fixing the fraud is not part of the plan, you have no plan.

Lawyer Appeasement Section

OK now for the fine print.

This is the WQTH Daily Thread. You know the drill. There’s no Poltical correctness, but civility is a requirement. There are Important Guidelines,  here, with an addendum on 20191110.

We have a new board – called The U Tree – where people can take each other to the woodshed without fear of censorship or moderation.

And remember Wheatie’s Rules:

1. No food fights
2. No running with scissors.
3. If you bring snacks, bring enough for everyone.
4. Zeroth rule of gun safety: Don’t let the government get your guns.
5. Rule one of gun safety: The gun is always loaded.
5a. If you actually want the gun to be loaded, like because you’re checking out a bump in the night, then it’s empty.
6. Rule two of gun safety: Never point the gun at anything you’re not willing to destroy.
7. Rule three: Keep your finger off the trigger until ready to fire.
8. Rule the fourth: Be sure of your target and what is behind it.

(Hmm a few extras seem to have crept in.)

Spot Prices

Gold $1877.40
Silver $28.02
Platinum $1153.00
Palladium $2854.00
Rhodium $22,000.00

This week, 3 PM MT on Friday, markets closed for the weekend

Gold $1763.10
Silver $25.90
Platinum $1040.00
Palladium $2550.00
Rhodium $20,000.00

The metals took a major thumping this last week! Gold was at 1860 on the 15th and has fallen a hundred bucks since then.

Light
(Part VIII of a Long Series)

Introduction

The general outline of this story is to start off by putting you “in touch” with the state of physics at the beginning of 1895. Physicists were feeling pretty confident that they understood most everything. Sure there were a few loose ends, but they were just loose ends.

This week marks the end of that positioning. Next week we move into 1895.

1895 marks the year when people began tugging at the loose ends and things unraveled a bit. In the next three years, three major discoveries made it plain there was still a lot to learn at the fundamental level.

Up until now, I have been explaining what the scientific consensus was in 1895. So much of what I have to say is out of date, and I know it…but going past it would be a spoiler. So I’d appreciate not being “corrected” in the comments when I say things like “mass is conserved.” I know that that isn’t considered true any more, but the point is in 1895 we didn’t know that. I will get there in due time. (On the other hand, if I do misrepresent the state of understanding as it was in 1895, I do want to know it.)

Also, to avoid getting bogged down in Spockian numbers specified to nine decimal places, I’m going to round a lot of things off. I used 9.8 kg m/s² last time for a number that’s actually closer to 9.80665, for instance, similarly for the number 32.

Introduction

Light is our primary means of sensing the world around us (closely followed by sound, which does take top marks when talking about interacting with people specifically).

So it’s pretty important, and of course we have worked to understand it basically since…forever. Thus it might be surprising to find it was still largely an enigma as of 1895.

As is so often case, the story starts with the philosophers of ancient Greece, who engaged in all sorts of speculation, perhaps the most interesting of which is that we saw by having rays go from our eyes to the object.

Lens makers were able to gain some understanding of optics and construct the first eyeglasses about 1300 and the first telescope in the very early 1600s. (The first patent was by Hans Lippershey in the Netherlands in 1608.) These were used to observe ships coming into port, but word got to Galileo Galilei in Italy. He constructed a much-improved version, turned it skyward, and our view of the universe hasn’t been the same since. (His telescopes still exist; they are in a museum in Florence, Italy.) I’ve told parts of that story in prior posts.

Newton Splits Sunlight

But the first step in our story today was actually taken by Sir Isaac Newton, in 1666. He famously used a prism to break up a beam of white sunlight into light of many colors, in a band called a spectrum, but he also was able to use a lens and another prism to reassemble the light back into a white beam. He was also able to show that, having isolated one color nothing could change that color, not shining it on other colored objects, or the same colored object. It could be blocked or absorbed, but the color never changed to another color.

Based on this he reasoned that (say) a green object looked green because it reflected green light and absorbed the other colors.

Thus white light turned out to simply be a mixture of colors of all sorts of different bright hues.

Noting that light split into colors going through a prism, he realized that light bends going from one medium (air) to another (glass) at an angle, and that the different colors bend at slightly different angles. Going through a pane of glass the two transitions (air to glass, glass to air) cancel each other out, but with a prism the surfaces are not parallel, so the different bending angles are compounded rather than cancelling.

Newton came to the conclusion that light was made of particles (which he called “corpuscles”).

Telescopes (a digression)

A lens in a telescope also has non-parallel surfaces, so astronomers using telescopes with lenses (“refractors”) will see “chromatic aberration” where objects seen in the telescope will have rainbow fringing around them. Newton invented a different type of telescope, one that uses a parabolic mirror to gather light, avoiding a large, expensive lens there; the eyepiece is still a lens. This (“reflector”) is the dominant type of telescope today (there are many variations. That is because a lens is much more expensive than a mirror of the same size and also because a large lens will sag under its own weight, whereas a mirror can be supported from behind.

The practical limit for a refractor was reached in the late 1900s, with the Yerkes Observatory’s 40 inch diameter telescope near Chicago. However, it was possible (with some epic difficulty) to build one-piece mirrors 200 inches across (Palomar Observatory in southern California) and even larger telescopes with multiple mirrors kept in close alignment (or even shifting for adaptive optics).

The Palomar Observatory was conceived in the 1930s, and finally came on line in 1955. It is without a doubt the premier example of pre-computer precision tech on a massive scale. It weighs two hundred tons yet is finely balanced enough to be turned with a motor that could drive a washing machine. The weight of a sandwich on the right part of the mount will cause it to turn, slowly, but turn nonetheless–that’s how friction-free it is. And it is still doing work. It still stands beside Hubble, and the big multiple mirror scopes on the Big Island of Hawaii. You can take tours in the daytime, but at night it might just be imaging planets around other stars, a feat thought impossible back in the 1990s. And this was 1930s technology. But then on the other hand, it was impossible to talk about Palomar in the 1970s without some dickhead bringing up the fact that the Soviet Union was building a 236 inch telescope. It was blatantly obvious they were doing this just to beat us out. Well, guess what; it turned out to be a piece of shit, so the joke was on them. (Please stand and yell, “‘Murica!!!” now.)

The Spectrum

Where was I?

OK, so let’s take a look at Newton’s spectrum. To our eyes, it’s a long color gradient, running from deep red through red, orange, yellow, green, turquoise, blue, and violet, eventually getting to a deep violet.

If you’ve seen people make that statement before you might notice it’s a bit off from your recollection. The colors quoted are usually “red, orange, yellow, green, blue, indigo, and violet,” and there’s even a cute “Roy G. Biv” mnemonic to help people remember the order. (I never needed it, I have no trouble visualizing red shading to orange to yellow…etc.) A lot of people have opined that “indigo,” a bluish-purple, hardly seems to be worth considering to be its own color (in particular, Isaac Asimov is quoted to that effect on Wikipedia). But that’s a modern confusion. Newton was the first to list the colors, and to him “blue” meant the color of the sky, what we call today a light blue, and “indigo” meant a dark blue, like seen on the Flag of the United States. There is even a natural dark blue dye named indigo (I don’t know if the color was named after the dye or vice versa). So indigo wasn’t “bluish purple” but rather “blue” in today’s parlance. And therefore I chose to use “turquoise” where Newton was referencing (sky) blue and “blue” where he said “indigo,” more in line with present day usage.

And indeed when you look at Newton’s spectrum, or a rainbow, there are distinct light blue and dark blue bands; today we’d probably term that light blue color “cyan.” They really are distinct colors even if our language doesn’t acknowledge it. (Other languages do, Russian for instance.)

Rainbows

I mentioned rainbows in passing, and as it turns out rainbows have exactly the same cause. Sunlight enters a small water droplet (approximately spherical) in the atmosphere, and gets refracted. It strikes the far side of the droplet, and some goes on out, but some gets reflected, and leaves the front side of the droplet, getting refracted again, constructively. Down on the ground, one tiny part of the spectrum reaches your eye; perhaps you see a certain yellow-orange color from that droplet.

“But I see the whole spectrum,” you respond. True. That’s because you are also seeing light refracted through other droplets, and you just happen to be standing where some other droplet is sending red. Or blue. Or purple. Since all of the red rays coming out of all the droplets are parallel (and likewise for all the other colors) you see a nice orderly rainbow.

But you will only see it with the sun behind you; the droplets are sending light back very roughly the way it came. Therefore at noon the rainbow would be at your feet (and there’s usually not enough water droplets between your eyes and the ground for rainbows to happen, not at high noon there isn’t), so that is why rainbows always seem to happen early in the morning and late in the afternoon. And of course they follow rain showers because rain leaves innumerable microscopic water droplets in the atmosphere.

Herschel and Infrared

The next notable discovery was in 1800, by William Herschel, also of fame for discovering Uranus in 1781 (and trying to name it after King George III…yecchh). He conceived the notion that perhaps the different colors of light carried differing amounts of heat, so he put thermometers in several different locations in a solar spectrum. Like any good scientist, he set up another thermometer outside the spectrum as a control. He didn’t expect that to budge, except perhaps in response to the room itself getting warmer or colder.

He happened to set the control thermometer next to the “red” thermometer, and that was a very happy thing.

When he came back to the test area to record results, the highest temperature was on the “control” thermometer. Not one of the ones that actually had sunlight shining on it! The next highest was the red thermometer, then less and less so towards the purple end of the spectrum.

Eventually the truth became clear. There was non-visible “stuff” off the red side of the spectrum that was associated with heat, and Herschel named it “heat rays.” It ultimately became known as infrared (below red). In today’s parlance, we consider it another kind of light, and distinguish it from “visible” light (Newton’s spectrum). It’s just as “real” as visible light, and we try not to be parochial about the light we can see versus the light we cannot see.

Ritter and Ultraviolet

The very next year, Johann Wilhelm Ritter placed silver chloride soaked paper along the spectrum. Silver chloride will darken when exposed to light (the sort of phenomenon that ultimately led to photography). Presumably he was checking to see which color of light would darken it the most, and the answer turned out to be the hitherto-unknown invisible light on the far side of violet. He named these rays “deoxydizing rays” but today we call them ultraviolet.

We now know that slightly over 50 percent of the energy we get from the sun is in the form of infrared, and ten percent in the form of ultraviolet.

Ultraviolet was discovered to kill bacteria in 1878.

The Speed of Light

The first meaningful attempt to measure the speed of light was by Galileo, but he failed to detect any time delay at all; as far as he could tell light was instantaneous.

Rømer later measured light as taking 22 minutes to cross the diameter of the earth’s orbit. We didn’t know what that diameter actually was back then, but now that we do, Rømer’s measurement works out to 227,000,000 m/s.

In 1849, Fizeau set up a rotating cog wheel. He shone light through one gap, towards a mirror, and himself looked through a gap at the mirror. He could alter the speed of rotation, and thus know how fast the wheel had to rotate to let him see the light in the mirror. At the wrong rotation speed the light would be blocked by the cog, either coming or going. So he could calculate the speed of light, and got 313,000,000 m/s.

In 1862 Foucault (as in pendulum, not as in post modern bullshit) used rotating mirrors to get a speed of 298,000,000 m/s, close to today’s value.

However, it also became apparent that light moved at different speeds in different materials. It was fastest in vacuum. (In fact, these speed differences are what cause it to bend when it crosses from one material to another.)

Waves

People were arguing over whether light was made up of particles, or whether it was a wave, until the early 1800s, when Young and Euler showed beyond any reasonable doubt that it was a wave.

And now I’ve got to explain some stuff about waves. Let’s take waves on the surface of a pond as an example. Take a snapshot of these waves, and there will be two obvious things you can measure to describe the waves. First, the distance from crest to crest (or trough to trough—they are the same). This is called the wavelength, and is usually symbolized by λ, Greek letter lamba (representing the “L” sound). Logically enough, it’s measured in meters.

The second is the amplitude, which is the height of the waves. However, there’s a small nuance here: It’s half the trough-to-peak height, because it’s measured from where the water level would be if it were calm, to either the peak or trough. (There are rare exceptions where something different is done; this is by far the most common, followed by something called RMS [“root mean square”] which is a sort of average deviation from “flat” and is used in electrical engineering to measure, for instance, the voltage delivered to your house.) Amplitude is measured in whatever the field is measured (volts for electrical fields, meters for water waves, etc.)

The higher the amplitude, the greater the energy in the wave, generally energy goes as the square of the amplitude–twice the amplitude, four times the energy.

OK, unfreeze the action. Take a movie. Go wading out into the water, and count how many waves pass you in a second. (It’s probably less than 1 if you’re wading in water, but roll with me here.) The number of peaks (or troughs) that pass you in a second is the frequency. It’s measured in per second, 1/s, also known as hertz, but we haven’t met him yet. We will. When talking about light, the frequency is represented by ν, which looks like a v but is actually the Greek letter nu (representing the “N” sound).

[Side note: The Greek letter upsilon (which has had a bunch of different values as time has gone on, but the consensus is in ancient times it was much like German ü. Today it’s like the i in machine) looks like this: υ and they look an awful lot alike in some fonts, which takes getting used to when trying to learn Greek. Mistaking a vowel for a consonant or vice versa when trying to sound out an unfamiliar word is confusing!]

If the waves are passing by at (say) ten meters a second, and you’re measuring a frequency of five times a second, that means five waves take up ten meters. That makes the wavelength 2 meters. Or, you can go at it from another direction. If you know the wavelength, and the frequency, you can deduce the speed; in our example, a 2 meter wave passes 5 times a second, so the speed is 10 m/s.

The speed of light is invariably represented by c and we met it in an unexpected place, buried in Maxwell’s Equations. For light, we can write the following:

c = λν

(If you have trouble remembering which one is which, remember lambda and length both start with L. If you can’t remember which one of those funky symbols is lambda…well, I don’t know a good trick to remember that, so hopefully you just can remember. It’s easy if you’re looking at the capitals: Λ and Ν, because capital nu even looks like an N.)

OK, back to our story. Young was able to demonstrate that light was a wave in 1800, by measuring its wavelength.

This measurement relied on the light waves interfering with themselves. And that’s another thing about waves I’ve gotta explain.

Imagine an ocean wave approaching a breakwater head on. If there is a wide gap in the breakwater, much wider than the wavelength, the waves will simply go through the gap, remaining parallel straight lines.

But if that gap is much less than a wavelength, something else happens. The gap behaves as if were a source of waves, and on the other side of the breakwater, waves ripple out as if a stone had been dropped in the gap. This is diffraction, and it can even force a laser beam to spread out. Doing it to a ray of sunlight through a very narrow slit was strong evidence that light was a wave; particles would simply have barged through the opening without changing direction.

Even better, what if there are two gaps in the breakwater? Then you have two different “sources” of waves for the far side of the breakwater, and the waves they produce will criss-cross. You can set yourself at some fixed point and find that at some places, both wave peaks (and both wave troughs) hit that point at the same time, resulting in the wave being twice as high there, and at other points, the trough of one wave will hit you the same time the peak of the other does, and vice versa…and they cancel each other out. The water is calm where you are.

Now go to the shore, and some parts of the shore will get very high waves, and others will get calm.

Picture, instead, light passing through two slits, being projected on a screen. You should see bright and dark bands where the waves add or cancel, respectively.

And this was done by Young in 1800, also.

But it was his measuring the wavelength that is key here. He found that light’s wavelenth is less than a millionth of a meter, depending on the color. Violet light’s wavelength would be in the neighborhood of 400 nanometers (nm, a nanometer is one billionth of a meter), while red light would come in at 700 nm).

We can get the frequency (what’s the frequency, Dan?) this way:

c = λν

c/λ = ν

So let’s see; about 300,000,000 m/s divided by say 500nm (a nice yellow color) gives: 600,000,000,000,000 hertz, or 600 terahertz (Thz, tera = trillion).

600 trillion is more than the national debt…well, this week anyway; check back next week, and that many waves go past you every second when you’re out in the sun, or for that matter, basking in light from a compact fluorescent bulb.

If you get the idea that a lot of progress was made on light in 1800-1801, you are right.

Spectroscopy

On the subject of stars, all investigations which are not ultimately reducible to simple visual observations…are necessarily denied to us…We shall never by any means be able to study their chemical composition.

Auguste Comte, 1835

This seems like a reasonable stance. How are we going to get to the stars to take a sample? However, this one wouldn’t age well. (Though oddly enough the first part of this remained true!) It was already coming undone twenty years before he wrote it.

And it almost continued into 1802. In that year, Wollaston (who would shortly discover rhodium and palladium–more chemists doing physics and vice versa) noted that there appeared to be a few gaps in the solar spectrum rather than it being a smooth continuum, but he didn’t pursue this.

In 1814, Joseph von Fraunhofer, working on improving optical glass, would invent the spectroscope for the specific purpose of obtaining spectra. He noticed a dark line in the light coming from flame, counted 576 such lines in sunlight, and noted other lines in the light coming from various stars. He was able to rule out the atmosphere as the cause because the lines were different for different stars.

There are now over half a million known of these “Fraunhofer lines”

It had long been known that different chemicals could glow differing colors when heated in flame; soon other scientists were using a spectroscope to look at what these colors were made of. They often saw that the spectrum of these glows consisted of a number of bright lines against a dark background; the exact opposite of the sun’s black lines against a bright background.

Talbot was able to tell lithium from strontium by this means. Both gave off a red light, but lithium was carmine and strontium, scarlet.

It turned out that the bright lines and dark lines were often at the same frequency; it turned out that the dark lines were due to something absorbing light, and the bright lines were that same substance emitting light.

In the mid 1850s scientists began to realize that every element had its own characteristic spectra, and by 1865 they were attributing specific bands to specific elements.

Hydrogen, it turns out, has by far the simplest spectrum. There are four lines in the visible spectrum, at 656.274 nm (red), 486.135 nm (cyan), 434.0972 nm (bluish-purple), and 410.1734 nm (very purple). There are a couple of additional lines whose wavelengths are below 400 nm, and therefore technically considered ultraviolet, but some people can see them: at 397.0075 & 388.9064 nm.

Most other elements have dozens of lines in their visible spectra.

And now we could analyze the stars chemically, though Comte did have it right in one respect: we were still using their light, because we still can’t do anything else.

In 1868, in fact, a set of totally unknown lines was noticed in the Sun, and it was eventually concluded that this was due to an unknown element. We had no idea which element it was; I imagine that after Mendeleev published the periodic table people were guessing it would fill one of the holes he left open in that table. (There was no known way of predicting what the spectrum of an element would be; you had to measure it and catalog it for future use. Today we can predict hydrogen’s, but others are difficult if not impossible.)

The element was known to be on the sun (and nowhere else), so it was named after the sun, Helios in Greek mythology, so (figuring it was a metal) they named it helium.

Other elements were discovered through the use of spectroscopes, which would tell scientists their sample contained something new. Cesium, rubidium, indium, and thallium were all discovered this way, and…every single one of them is named after the color of its spectral lines, sky blue, deep red, indigo, and sea green, respectively.

The 1860s were also the time when light was first recognized to be an electromagnetic wave, thanks to Faraday and Maxwell.

Christian Doppler

I told this story quite some time ago, and probably should not have, I should have left it for now. But it bears repeating even so.

In 1842, an Austrian scientist named Christian Doppler described what we now call the “Doppler Effect.” He was working with sound, not light, but it turns out the Doppler effect also applies to light.

Although the mechanism behind sound is very different from that of light, a source of sound still sends out waves in expanding spheres, just as a light bulb (or the sun) does. And the wavelength of sound corresponds directly to pitch: A short wavelength is a high pitch compared to a longer wavelength.

Sound travels through air (or other materials) as its medium. What happens if the source of sound is moving?

If it is moving towards you, at (say) half the speed of sound, then something curious happens. If it emits the peak of a wave at a certain time, well, by the time it emits the second peak, it has moved half a wavelength towards you. So what you will hear a sound of half the wavelength that was emitted, or twice the pitch (an octave higher for you music folks). Similarly if the same source moves away at the same speed, it will emit the second peak half a wavelength further away, so you will hear a pitch with 50% longer wavelength (a perfect fifth lower).

This effect was coming to people’s attention because they could hear it in train whistles as the train passed by. Of course the train might only be moving at 10-20 percent of the speed of sound, but that’s more than enough. At first people thought the train engineers were doing something to cause the phenomenon, just trolling the people outside the train, but that would have required multiple whistles at different pitches, and besides as far as we know none of them were ancestors of Donald Trump (though who knows about Melania’s family tree).

If you can determine the frequency emitted, and the frequency heard, you can calculate the speed of the source, but only along a radial line. It’s no good for transverse motion. (Likewise if you want to work with wavelengths.)

The Doppler effect also works on things that sound (or light) bounces off of. In fact this is how the local constabulary’s radar gun works; it knows the frequency of emission (since it is doing the emitting); it just senses the frequency of the returning signal and does the calculation and informs the officer whether or not he’s one step closer to meeting the quota he denies having to meet.

As I said, light is subject to the Doppler effect, and it’s possible to use that effect to determine how fast a star is moving in the radial direction. (Painstaking, detailed observations over time will reveal how fast it’s moving in the transverse direction, at least assuming other stars in the photographs are much farther away, and provided we know how far away the star is.)

Simply take the star’s spectrum and see how much it is shifted. If it is shifted towards shorter wavelenths (becomes bluer) it’s moving towards us, if shifted towards longer wavelenths (becomes redder) it’s moving away.

But wait…a star puts out all frequencies. If some blue wavelength gets shortened by 10 nm, won’t some slightly less blue wavelength get shifted into the position as it gets shifted 10 nm as well?

Aaah, but you see, a star’s light doesn’t contain all frequencies. The Fraunhofer lines are darkk! And we know what their frequencies are “supposed” to be, so when we see them shift, we can measure the red- or blue-shift of the star and get its velocity.

(Typical radial velocities are in the tens of kilometers per second, relative to the Sun which is also moving along with the herd. The true speed with respect to the center of the galaxy is a couple of hundred kilometers per second.)

Sometimes we can even tell how fast a star is rotating! Consider, the side that is moving towards you will look slightly blue-shifted, and the side rotating away from you will be slightly red-shifted. This will cause the Fraunhofer lines to get thicker as they are shifted in both directions at once, though they will also not appear as dark.

Neill de Grasse Tyson (yeah, I know, but here he’s talking about stuff he knows quite a bit about) considers the discovery of the Fraunhofer lines the birth of astrophysics, because it opened the door to knowing the composition and motion of the stars.

Black-body Radiation

Hot objects glow. You know this from watching embers in a fire or perhaps you’ve seen molten metal glowing either in person or in a video.

It’s also what makes an incandescent light bulb work. The filament gets hot; as much as 3000 K. Because it is hot, it emits light over a spread of frequencies. That would be enough to cool it off, because light carries off the energy, but of course there’s an electric current going through it and the filament is a resistor which means there’s a voltage across it and, well, power = current x voltage, and power is just a rate of energy, so more energy is coming into the filament as it is radiating away. (Radiating like this is one of three major ways to transfer heat, the other two are direct contact and convection.)

If you’ve ever seen an unfrosted incandescent light burning, that dinky little filament is bright. How bright it is, per surface area, is a direct consequence of its temperature. Imagine looking at a molten blob of metal at that temperature; it’d be very bright, every square millimeter of it putting out as much light as a square millimeter of the filament (which might not even have one square millimeter of surface area).

As it turns out a perfectly black object will behave in an ideal manner, so this is called black-body radiation.

Another thing that turns out to depend directly on the temperature is where the “peak” of the curve is. For some reason, the glow isn’t just done at any old frequency, there’s a distinct distribution, which is why objects that are glowing from the heat can be colored from red (relatively cool) to orange to white, and even blue. (That requires a temperature so high that you’ve probably never seen anything glowing blue hot…other, that is, than many stars in the night sky.)

Scientists were unable to explain why the curve didn’t just go higher and higher into the ultraviolet, rather than displaying the distinct hump you see here.

But one thing that should be plain, is that a 5000 K “white hot” body emits far, far more radiation than a 3000 K “red hot” body. At every single wavelength, even the red ones, the white hot object far outshines the red hot one. In fact, it turns out that the total emission goes up as the fourth power of the temperature: Double the temperature, increase the emission by 2x2x2x2 = 16 times!

Michelson and Morley

Albert Michelson was fascinated by light and experimented on it a lot. He pioneered the use of the interferometer…and I’m not going to try to explain how it works in brief, other than it splits a beam of light and sends one half at a ninety degree angle to the first. Both parts of the beam reflect off mirrors and meet at a detector. Do the waves constructively or destructively interfere? If destructive, you can shift one of the mirrors slightly to get constructive interference, and the distance you shifted is half a wavelength (so one can measure the wavelength of light by this means).

Link here: https://en.wikipedia.org/wiki/Michelson_interferometer

If you get the thing set up so the two beams constructively interfere, you can rotate the entire apparatus 45 degrees to see if that changes due to, say, the light travelling at a different speed in that direction, because we (riding along on planet Earth) are moving through the medium through which the waves propagate.

If you were to try a similar experiment with sound on a moving platform, it would appear to move slower when measured in the direction you’re traveling, faster when measured backwards in the direction you’re getting farther from, and in the middle somewhere, just about at the rest velocity, to the sides. That’s because you are moving through the air that sound propagates through.

In 1887 Michelson and Morley built a very accurate interferometer, isolated it from vibration as best they could, and decided to try to detect our velocity through the medium it was presumed to move through, known as the aether.

And got nothing. We weren’t moving through the medium, and that was true no matter when we took the measurement, or where. At different times of the year the earth ought to be moving in different directions, so we should see something sometime even if the aether were moving along with the earth at one time of the year.

But nothing. Apparently the speed of light didn’t depend on how much the observer was moving; it was dead constant (in a vacuum).

Hertz and Radio

There is just one more story, before we assume the runner’s crouch in preparation for dashing across the 1895 line next week.

Heinrich Hertz (1857-1894, yes he didn’t even live to see 40) was looking for a topic for his doctoral thesis and noted the claim made by Maxwell in 1864 that light was an electromagnetic wave.

He reasoned that he ought to be able to create electromagnetic waves of much lower frequency by setting up a couple of long straight wires in line, with a tiny gap between them. By getting a spark to jump the gap he could set up a standing wave in the wires, which would presumably cause EM waves to radiate away from the wires.

So how would he detect the waves? He’d set up another circuit with a gap some distance away, and see if sparks jumped the gap in response to an electric field–the electric field of his propagating wave.

And indeed it was so! It was 1886 and Hertz had just discovered radio. He was transmitting, rather fitfully, at about 50 MHz, a frequency now used by television. Ironically, he thought it would be of absolutely no use whatsoever.

Hertz also noticed something rather peculiar. It was hard to see the spark at the receiver, so he’d put it in a dark box. But when he did that, he had to bring the two terminals closer together to get the spark to happen. Something in the light, apparently, made it easier for a spark to jump the gap. He put a window in the box, made of glass, and the spark jumping distance remained the same, no matter how bright the light was.

When he use quartz, instead of glass, he could move the terminals further apart again.

What was the difference? Glass blocks ultraviolet light. Quartz does not.

So there is something about ultraviolet waves that gives the electrical fluid in the receiver a bit of an extra kick. But not visible light, and certainly not infrared.

No matter how bright you make visible light, it doesn’t help. If light is a wave, the brightness corresponds to the amplitude, and the energy depends on the amplitude. But ultraviolet had an effect, even ultraviolet of much lower amplitude.

This is known as the “photoelectric effect” and, since this didn’t make any sense, it’s our 1895 mystery of the week.

Hertz, alas, passed in 1894…so he wouldn’t ever know the answer, nor how very useful radio turned out to be.

Obligatory PSAs and Reminders

China is Lower than Whale Shit

To conclude: My standard Public Service Announcement. We don’t want to forget this!!!

Remember Hong Kong!!!

中国是个混蛋 !!!
Zhōngguò shì gè hùndàn !!!
China is asshoe !!!

China is in the White House

Since Wednesday, January 20 at Noon EST, the bought-and-paid for Joseph Biden has been in the White House. It’s as good as having China in the Oval Office.

Joe Biden is Asshoe

China is in the White House, because Joe Biden is in the White House, and Joe Biden is identically equal to China. China is Asshoe. Therefore, Joe Biden is Asshoe.

But of course the much more important thing to realize:

Joe Biden Didn’t Win

乔*拜登没赢 !!!
Qiáo Bài dēng méi yíng !!!
Joe Biden didn’t win !!!