Is a Photon a Particle?
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A Caution
I start this section with a caution sign. It is one typically used for lasers, which at this point you might wonder about. Are laser beams streams of particles or a wave? Are those photons, the description of which earned Einstein his Nobel prize, particles of light?
We are going to discuss quantum field theory (QFT), and I should caution you on a few things here. While quantum field theory (QFT) is the most successful and elegant theory of reality that mankind has formed, some still fight against it. That is not to say that we are not in good company. It was Einstein's quest to find a set of such equations along with many of the great minds of the early quantum era. Richard Feynman eventually moved over to the field camp. There are also a host of recent Nobel laureates that have their hand in it.
So why don't all modern physics texts start off with discussions about QFT? First off, education has made it so. Nobody seems to mention much about QFT even to physics majors since it is so mathematically challenging. Instead they tend to teach mostly early 20th century quantum mechanics. I should hope that this has changed since the decade or so since I left school, but old habits die hard.
Second, and sadly, lots of people - even physics people - just want to get to the right answer for any given problem rather than considering the implications of the road taken to that solution. In that case, they often prefer the easiest math even if it involves philosophical paradoxes. It is often easier to swallow a paradox than to resolve one.
Lastly, I see waves and interference and phase everywhere I look, when I look with my mind. But my eyes see differently. With the exception of the interference phenomena that we described in the last chapter, experience of life somehow lends itself to believing in hard, delineated, concrete things rather than wavy fields. So maybe this could be called experiential bias, or bias acquired through life experience.
So why I am confident in teaching you with a leaning toward QFT? Because it is the most elegant solution to the rules and structure of nature that we have. And just about every famous physics theoretician of the past has marveled at the relative elegance of the rules of nature when we find them. I also have an innate dislike for paradoxes into which the standard description of quantum physics tends to run too often.
So is a Photon a Particle?
No. Nothing in nature is. Every "particle" and wave in our universe is simply a quantized excitation on the quantum field that is itself a property of space and time. This is the view of QFT. I know it sounds troubling. Especially in light of the discussions earlier. What about the photoelectric effect? What about blackbody radiation?
In order to make sense of all that and to understand the foundations of QFT, we need to look more closely at what these excitations or quanta that we mistake for particles really are.