I often argue that science is based on trust, while religion is based on faith. The difference is simple; trust is the positive feeling you have about something that reliably performs, while Faith is the positive feeling you have about something in spite of how it performs. But when one learns enough about the detailed underlying principles of the physical universe, things get a little fuzzy. I am not saying that science requires faith, except in that we believe that all observable effects have detectable causes, and that it is (or eventually will be) possible to mathematically model everything (within limits as we learn of them, such as Gödel, Heisenberg, etc).
But then we take a look at a photon. Most people learn in school that light is made up of particles called photons that act like waves. With a good teacher, you may learn that all exchanges of energy (except possibly for gravity) involve swapping photons. But after you have some years of calculus and a foundation in quantum theory, you can prove two mutually exclusive truths:
- Everything you can ever sense, think, or perceive is because of photons, and
- Photons don’t really exist.
Let’s start with point one: All your senses depend on photons.
To start with, everything you are and sense and think is because of chemical reactions. And all chemical reactions happen because electrons are swapping photons to move atoms from place to place. So internally, all you are depends on photons. But now to the actual proverbial Five Senses:
- Vision: Light is made up of these quanta of energy, so seeing is clearly based on detecting photons.
- Touch: This one is less obvious. All interactions between charged particles, like electrons and protons, are carried by photons. When you touch something, what you are sensing is physical contact. Physical contact is the electric field on the surface of one object repelling the electric field on the surface of another object down at the molecular scale. What feels hard on the scale of a finger is really squishy down on the atomic level, but this is such a small distance that it feels like an instant stop, a touch.
- Hearing: Sound is waves in a gas is really patterns of molecules bouncing off of each others electric fields. Photons are doing that.
- Taste: This is a chemical reaction allowing you to detect certain complex molecules by exchanging ions; charged parts of molecules. And recent research actually proved that quantum effects more subtle than those of bulk chemistry are involved in how taste buds work. But again, any interaction of charges (like chemical reactions) is carried by photons.
- Smell: See taste. Basically, smell is sensing molecules wafting in the air, as opposed to already in solution (juice) or being dissolved (crackers). In fact, smell requires your nose to dissolve the molecules before you can sense them. So smell is the same sense as taste, but in a different location in your face.
Now as to why this essential particle does not actually exist:
A photon is a convenience, a mathematical abstraction (like the square root of minus one) that has many real world repercussions, and thus really exists. But at the same time, it does not stand on its own.
A photon is a virtual particle. This squiggle below is a Feynman Diagram, invented by Nobel laureate Richard Feynman during the Manhattan Project to help understand what is going on in quantum reactions. This simple and unclear one may be illustrating two particles colliding elastically, like billiard balls (but more likely electrons or protons). Time moves downward, as the particles approach, exchange a photon, and then retreat.
Later in his career, Feynman hypothesized about (and got his Nobel Prize for) Quantum Electrodynamics (his “popular” book is actually readable by lay-people). QED (as it is abbreviated) proves that a photon (or even electron) does not actually travel in a single path, but in all possible paths. What we can measure is its most likely path. This is why they seem to act like waves; a photon spreads like ripples in water from its source, and coalesces at its destination.
So what we think of as the definition of a straight line, or the line of sight, or an Einsteinian Geodesic (for the truly pretentious), is just the most likely path (the shortest time or least energy) for a photon to take! But in reality the models that best describe all we observe show that a photon takes every possible path between here and there. Given that it is everywhere, a photon does not actually exists in any particular place in between its beginning and end.
This infinitely wide photon path is true whether the apparent distance is adjacent atoms in the crystal (less than an attosecond apart at the speed of light), or the 13.4 billion year trip from galaxy UDFj-39546284 to a telescope near you.
People wonder why I always choose not to get stoned. If you don’t occasionally have to say, “Oh, wow!” about the actual workaday world, the base, material universe that we all we live in, you just don’t know enough about it.