I froze mid-chew on that line. It's one of those self evident in your face the entire time thing that I never saw.
That's not really accurate. Photons like everything else are time dependent. Particles, photons and otherwise including those with mass, exist as probability densities. While a portion of the wavefunction (equation describing the probability, also synonymous and indistinguishable from the particle; the wavefunction
isthe particle) and thus the particle itself exists at all points, it does not behave that way in the real universe. As individual particle's wavefunctions interact with one another they constantly evolve, in time, into new wavefunctions that describe the system as a whole. This essentially sets boundary conditions to particles that are dependent on these sequential interactions and restricting on their probabilities. In an isolated system, photons would behave more independently of time but nothing to our knowledge can be a truly isolated system. So in a sense, if they could rationalize a thought, photons would not have a "sense" of time the same way we don't have a "sense" of anything but our observable spacetime dimensions, even though they are still passing through and interacting with it.
As I mentioned, all particles behave this way including those with mass. In general chemistry, shells and then orbitals are introduced. The orbitals have bubbly, cloud shapes and the introductory explanation is that Heisenberg's Uncertainty Principle doesn't let us know exactly where in the cloud it is, so we just draw it as a cloud. This explanation is just a glossing over of quantum mechanics, in which the electron isn't just unfindable exactly in the cloud, it exists at every point in the cloud with different probabilities. We call this "electron density" and is a major factor in atomic and molecular interactions. A large portion of introductory quantum chemistry courses goes in to the wavefunctions that result from the combination of individual electron interactions with one another in covalent bonding. While electrons move pretty fast on our time scale, they aren't that fast to the atomic world. If the electron were actually just moving back and forth around both atoms, all molecules would show a much higher fluctuation in energy depending on the electron's current location and also exhibit higher reactivities across the board. Thus, the bonding we observe can only exist if the electron's wavefunctions (and thus the electron itself!) are around both atoms at the same time.
Disclaimer: I'm pretty good with chemistry but am only 3 months into my first quantum mechanics course. The introductory course glosses over the time dependent Schrodinger equations as the math goes another major step up but we do talk about them qualitatively. Time dependency isn't until next year. So basically I may not know exactly what I'm talking about but the good news is that it's quantum mechanics, so no one does!
