Some technical revolutions enter with drama and thunder, others enter our daily lives unnoticed. And one of the quietest revolutions of our century is the entry of quantum mechanics into our everyday technologies. Previously, quantum effects were limited to physical laboratories and delicate experiments. But modern technology is increasingly relying on quantum mechanics for its core work, and the importance of quantum effects will only grow in the coming decades.
As such, the time has come to explain quantum mechanics ̵
My goal in this series of seven (!) Parts is to present the strange beautiful effects of quantum mechanics and explain how they came to affect our daily world. Each edition will include a guided tour of the quantum mechanical forests, where we will admire a new – and often surprising – effect. Once we return to the center of the visitor, we will talk about how this effect is used in technology and where to look for it.
Starting a series of articles on quantum mechanics can be daunting. Few things cause more fear than a “simple introduction to physics.” But I will make a few promises to the fearless and brave before we begin:
- Without math. While the language of quantum mechanics is written with quite advanced mathematics, I don’t believe that one has to read Japanese before you can appreciate Japanese art. Our journey will focus on the beauty of the quantum world.
- There is no philosophy. There was a fascination with the “meaning” of quantum mechanics, but we will leave this discussion about pints in the pub. Here we will focus on what we see.
- Everything we encounter will be tested experimentally. While some of the results may be surprising, nothing we encounter will be speculative.
If you decide to follow me through this series of articles, we will see quantum phenomena on a galactic scale, we will observe how particles mix and blend, and we will see how these effects give rise to both our current technology and the progress that is on the verge of finding it. of the laboratory.
So put on your mental hiking boots, get your binoculars and follow me as we set out to explore the quantum world.
What is quantum mechanics?
My mother once asked me, “What is quantum mechanics?” This question has been bothering me for some time. My best answer so far is that quantum mechanics is the study of how small particles move and interact. But this is an incomplete answer, as quantum effects can also be important for galactic scales. And this is doubly unsatisfactory, because many effects such as superconductivity are caused by mixing and mixing multiple particles.
In many respects, the role of quantum mechanics can be understood by analogy with Newton’s gravity and Einstein’s general theory of relativity. Both describe gravity, but the general theory of relativity is more correct – it describes how the universe works in every situation we have been able to test. But in 99.99% of cases Newton’s gravity and the general theory of relativity give the same answer, and Newton’s gravity is a lot easier to use. So unless we’re close to a black hole or making accurate time measurements with an optical clock, Newtonian gravity is good enough.
Similarly, classical mechanics and quantum mechanics describe motions and interactions. Quantum mechanics is more correct, but most of the time classical mechanics is good enough.
What I find fascinating is that “good enough” is increasingly not the case. Much of the technology developed in this century is beginning to rely on quantum mechanics – classical mechanics is no longer accurate enough to understand how these inventions work.
So let’s start today’s march with a deceptively simple question, “How do particles move?”
Kitchen quantum mechanics
Some of the experiments we will see require specialized equipment, but let’s start with an experiment that you can do at home. Like a culinary show, I will explain how to do it, but you are encouraged to continue and do the experiment for yourself. (Share your photos in the discussion below. Bonus points for setting up the experiment in your booth / workplace / other creative setting.)
To study how particles move, we need a good pea shooter to make a lot of particles to play with. It turns out that the laser pointer, in addition to entertaining the cat, is also great particle source. It creates abundant amounts of photons, all moving in almost the same direction and with almost the same energy (as shown by their color).
If we look at the light from a laser pointer, it comes out of the end of the laser pointer and moves in a straight line until it hits an obstacle and scatters (or hits a mirror and bounces). At this point, it is tempting to assume that we know how the particles move: they protrude from the end of the laser like small ball bearings and move in a straight line until they hit something. But as good observers, let’s make sure.
Let’s challenge the particles with an obstacle by cutting thin slits in aluminum foil with razor blades. I made several different cuts in the aluminum foil. The first is a single slit a few millimeters long. For the second, I arranged two razors together and used them to cut two parallel slits a few tenths of a millimeter apart.
In a darkened room, I adjust my laser pointer to shoot across the room and hit an empty wall. As expected, I see a place (provided the cat is not around). Then I place the single slit in the aluminum foil in the path of the laser and look at the pattern on the wall. When we send light through a single slit, we see that the beam expands dramatically in the direction perpendicular to the gap – not along the gap.
Interesting. But let’s move on.
Now let’s place the tightly spaced slits in the laser beam. The light is spreading again, but now there is a striped pattern.
Congratulations! You just noticed the quantum mechanical effect! (whoo hoo animated emoticons) This is the classic double-slit experiment. The striped pattern is called interference and is a telltale signature of quantum mechanics. We will see many stripes like these.
You’ve probably seen similar disturbances before, as water and sound waves show just that kind of streak.
In the photo above, each ball creates waves that move in a circle. But a wave has both a peak and a trough. In some places, the peak of the wave from one ball always coincides with the trough from the other (and vice versa). In these areas the waves always give way and the water is calm. Elsewhere, the wave tips of the two balls always arrive together and come together to produce a wave that is extremely high. In these places the troughs also gather to be extremely deep.
So does the fact that we see streaks when our laser pointer passes through two slits mean that the particles are waves? To answer this question, we will have to look more closely.