Chapter 1
Discoveries and Essential Quantum Physics
In This Chapter
Putting forth theories of quantization and discrete units
Experimenting with waves acting as particles
Experimenting with particles acting as waves
Embracing uncertainty and probability
According to classical physics, particles are particles and waves are waves, and never the twain shall mix. That is, particles have an energy E and a momentum vector
p, and thatâs the end of it. And waves, such as light waves, have an amplitude A and a wave vector
k (where the magnitude of
k =
, where λ is the wavelength) that points in the direction the wave is traveling. And thatâs the end of that, too, according to classical physics.
But the reality is different â particles turn out to exhibit wave-like properties, and waves exhibit particle-like properties as well. The idea that waves (like light) can act as particles (like electrons) and vice versa was the major revelation that ushered in quantum physics as such an important part of the world of physics. This chapter takes a look at the challenges facing classical physics around the turn of the 20th century â and how quantum physics gradually came to the rescue. Up to that point, the classical way of looking at physics was thought to explain just about everything. But as those pesky experimental physicists have a way of doing, they came up with a bunch of experiments that the theoretical physicists couldnât explain.
That made the theoretical physicists mad, and they got on the job. The problem here was the microscopic world â the world thatâs too tiny to see. On the larger scale, classical physics could still explain most of what was going on â but when it came to effects that depended on the micro-world, classical physics began to break down. Taking a look at how classical physics collapsed gives you an introduction to quantum physics that shows why people needed it.
Being Discrete: The Trouble with Black-Body Radiation
One of the major ideas of quantum physics is, well, quantization â measuring quantities in discrete, not continuous, units. The idea of quantized energies arose with one of the earliest challenges to classical physics: the problem of black-body radiation.
When you heat an object, it begins to glow. Even before the glow is visible, itâs radiating in the infrared spectrum. The reason it glows is that as you heat it, the electrons on the surface of the material are agitated thermally, and electrons being accelerated and decelerated radiate light.
Physics in the late 19th and early 20th centuries was concerned with the spectrum of light being emitted by black bodies. A black body is a piece of material that radiates corresponding to its temperature â but it also absorbs and reflects light from its surroundings. To make matters easier, physics postulated a black body that reflected nothing and absorbed all the light falling on it (hence the term black...
