A curious observer’s guide to quantum mechanics, p. 3: Rose colored glasses

Yet, we have seen particles move like waves and have learned that a single particle can take multiple, broadly different paths. There are many questions that naturally arise from this behavior, one of which is, “How big is the particle?” The answer is remarkably subtle, and in the next two weeks (and articles) we will explore different aspects of this question.

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

Go long

To answer that, we need to think about a new experiment. Previously, we sent photons on two very different paths. When the paths were widely separated in that experiment, their lengths were the same: each one went on two sides of a rectangle. We can improve this setup by adding a few mirrors at the beginning, allowing us to gradually change the length of a path.

When the paths are the same length, we see stripes like in the first article. But as we make one path longer or shorter, the stripes gradually become shorter. This is the first time we have seen the stripes slowly disappear; In our previous examples, the stripes were either there or not.

We can temporarily connect this fusion of stripes as we measure the length of the path. Replace with Length The photon’s path travels down. The stripes appear only when the photon waves overlap when rearranged.

But if particles travel like waves, what do we mean by length? A useful mental image might be dropping gravel into a simple pool of water. The resulting ripples spread in all directions as a set of rings. If you draw a line from where the stone fell from the rings, you will have five to 10 of them. In other words, waves have a ring thickness.

The other way to look at it is as if we were a cork on the water; We will feel the smooth water again after a wave, the duration of the waves, then the ripple has passed. We will say that the ‘length’ of the ripple is the distance / time at which we experienced the waves.

In the same way we can think of the traveling photon as a set of ripples, a set of waves entering our experiment. The waves split naturally and take both paths, but it can only rotate when the lengths of the two paths are close enough for the ripples to make contact when they are brought back together. If the path is too different, one set of waves will pass before the other arrives.

This picture nicely explains why the stripes gradually disappear: when there is a complete overlap it is strong, but the overlap decreases, but fades. By measuring how far away the stripes are until they disappear, we have measured the wavelength of the particles.

Digging through the light bulb drawer

We can go through our common experiments and see the same features that we saw before: photon rate way down (which produces a strip paintball ball pointillism), changing color (blue color means close distance), but now we Can also. To measure how the stripes behave when adjusting the length of the path.

When we use lasers to produce light particles (it’s a great photon pea shooter), any type of light will do: a light bulb lit by a fire, LED room light, neon lamps, sodium streetlights, starlights, light passing through colored filters. The type of light we send creates stripes when the path lengths match. But the stripes range from microns to white light at a distance Hundreds of kilometers For the highest quality lasers.

Light sources with distinctive colors have the longest wave. We can send the investigation of the color properties of our light sources through its prism. In some light sources the colors are very narrow (laser light, neon lamp, sodium streetlight); Some have huge rainbows of colors (incandescent bulbs, LED room lights, starlights); While other composite colors such as sunlight sent through a color filter are intermediate in the range.

What we have noticed is that there is a relationship: the narrower the color of the light source, the longer the path difference before the stripes disappear. The color itself does not matter. If I choose a red filter and a blue filter that allow the same width of colors, they will make their stripes disappear at the same path difference. That Series Not an average color but an important color.

Which brings us to a rather surprising result: the wavelength of a particle is given by the range of those colors (and therefore powers). Length is not a set value for a particular type of particle. Just by digging into the drawer of our light source, we measured a few cm from the micron (white light). (Laser pointer) to create photons up to length.