A Curious Observer’s Handbook of Quantum Mechanics, pt. 3: Pink colored glasses

Getty Images / Urich Lawson

One of the quietest revolutions From our current century, quantum mechanics has entered our everyday technology. Quantum effects used to be confined to the laboratories of physics and microscopic experiments. But modern technology increasingly relies on quantum mechanics for its fundamental processes, and quantum effects will only increase in importance in the coming decades. As such, physicist Miguel F. Morales took on the arduous task of explaining quantum mechanics to the rest of us normal people in this seven-part series (without the mathematics, we promise). Below is the third story in the series, but you can always find it The story starts here.

So far, we’ve seen particles moving as waves and we’ve learned that a single particle can take multiple, widely spaced paths. There are a number of questions that arise naturally from this behavior – one of which is, „How big is the particle?“ The answer is remarkably accurate, and over the next two weeks (and articles) we’ll explore various aspects of this question.

Today, we’ll start with a seemingly simple question: How Long Is it particle? „

Going for a long time

To answer that, we need to consider a new experience. Earlier, we sent a photon on two completely different paths. While the tracks were broadly separated in that experiment, their lengths were identical: each revolving around two sides of the rectangle. We can improve this setting by adding two mirrors, which allows us to gradually change the length of one of the paths.

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An improved two-track experience where we can adjust the length of a path.
Zoom in / An improved two-track experience where we can adjust the length of a path.

Miguel Morales‘ photo

When the paths are the same length, we see lines just like we did in the first article. But when we make a path longer or shorter, the lines slowly fade. This is the first time we’ve seen slowly disappearing streaks; In our previous examples, the lines were either present or not.

We can initially associate this fade with lines while changing the path length to Length The Photon goes down the track. The lines only appear if the photon waves overlap when re-assembled.

But if particles travel in waves, what do we mean by length? A useful mindset might be to throw a pebble into a soft pool of water. The resulting ripples are spread out in all directions as a set of loops. If you draw a line from where the rock fell through the loops, there are five to 10 of them. In other words, there is a thickening of the wave ring.

Another way to look at it is as if we were cork on water; We won’t feel any waves, a period of waves, then the smooth water again after the ripple has passed. We can say that the „length“ of the wave is the distance / time that we have passed the waves.

Ripples on the pond.  Note the thickness of the wave ring.
Zoom in / Ripples on the pond. Note the thickness of the wave ring.

Roberto Machado Noa / Getty Images

Likewise, we can think of a traveling photon as a set of ripples, a mass of waves entering our experience. The waves naturally separate and take on both paths, but they can only be reunited if the lengths of the two paths are close enough for the ripples to interact when brought together. If the paths were very different, one set of ripples would have already crossed before the other arrived.

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This image nicely explains why the lines disappear slowly: they are powerful when there is perfect interference, but they fade as the interference decreases. By measuring the distance until the lines disappear, we measured the wavelength of the particle’s ripples.

Drill through a light bulb tray

We can go through our usual experiences and see the same features that we saw before: lowering the photon rate (which results in paintballs dotting the lines), changing color (blue colors mean closer spacing), etc.But we can now also measure the behavior of the lines while adjusting Path length.

While we often use lasers to generate particles of light (they are cool photon launchers), any kind of light will do the job: incandescent lamp, LED room lamp, neon lamp, sodium street lights, starlight, light passes through color filters . Whatever type of light we send through, it creates lines when the path lengths match. But the lines fade at distances from microns to white light Hundreds of kilometers For the highest quality laser.

Light sources with distinct colors tend to have the longest ripples. We can investigate the color properties of our light sources by sending their light through a prism. Some light sources have a very narrow range of colors (laser light, neon lamp, sodium street lamp); Some of them have a wide rainbow of colors (incandescent lamp, LED room lamp, starlight); Others, such as sunlight transmitted through a colored filter, are intermediate in the composite color range.

What we notice is that there is a correlation: the narrower the spectrum of color for the light source, the longer the path difference will be before the streaks disappear. The color itself does not matter. If you choose a red filter and a blue filter that allow the same color rendering through it, their streaks will disappear when the same path differs. It Domain From the color that matters, not the average color.

Which brings us to a somewhat surprising result: the wavelength of a particle is determined by the range of colors (and thus energies) that they possess. Length is not a specific value for a specific type of particle. Just by drilling into the light sources tray, we made photons in lengths ranging from microns (white light) to a few centimeters (laser pointer).

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