Is it wrong to ask what happens from the perspective of the photon?
Not wrong, but is it particularly useful? Not really, because it’s not a reference frame that is (or ever can be) shared by the material universe.
From the perspective of the photon, the universe of only has two spatial dimensions, being infinitely contracted in its direction of travel. The photon takes no time to travel because it’s origin and destination are the same point.
Which I think answers the OP. There is literally no time to accelerate or decelerate. The photon arrives the instant it is produced.
in Re: the You Tube explanation. Why does the second way generated by the electrons accelerated by the original way move slower than c? It’s an electromagnetic wave as well. And the answer can’t be because it’s moving in the glass because that’s what’s being explained in the first place.
It’s not slowed, it’s delayed.
Not what the video said or illustrated but OK.
Off the top of my head it’s because the electrons are heavier than photons so the electron-sourced wave is going to be slower.
Can’t be. The electrons create electromagnetic waves which always travel at c in a vacuum. Chronos has already they don’t travel slower but are “delayed”.
Only in the photon’s own reference frame. From any observer’s reference frame it takes a finite amount of time.
This brings up the question of how to calculate from a photon’s reference frame. I assume that the answer must be the same, since that’s the core of relativity, but that’s beyond my math.
BTW, at one time there was a convention to use C for “Einstein’s Constant” or what we also call “the speed of light,” and c for the actual speed of particles in a medium. Using this would avoid a lot of confusion in threads like these.
Strictly speaking, “the photon’s own reference frame” is not a meaningfully-defined concept. For some things, you can just take a bunch of well-defined reference frames at ever-increasing speeds and take a limit, but for others, that doesn’t work.
My brain slow today. I was going to quote somebody but I had to look up who it was.
It’s Kenneth W. Ford, one of the grand old men of physics, who was in his 80s when he wrote 101 Quantum Questions: What You Need to Know About the World You Can’t See. He starts with simple questions and then builds and builds. It’s aimed at the general reader, and has few equations, and I found his explanations to be more illuminating and understandable than in many longer books.
Anyway, he said that the way to think about atomics is that photons and everything else are particles when they are formed and when they are absorbed and waves at all times in between.
You are talking about the “index of refraction”.
The index of refraction is a dimensionless construct and stated as n = c/v. In it “c” is equal to C and “v” is equal to “c”, as I defined it earlier. So it’s not the same, and it’s an excellent example of why the two speeds need to be distinguished.
I guess that’s why I was having trouble with the concept.
Indeed.
If we took the photon’s perspective then being made and flying 100 feet across a laboratory would be the same as being made at the Big Bang and flying across the universe. No time would pass, no distance would be traversed (AIUI).
Then consider this is true for all photons ever created including the ones you are seeing at this moment from your computer screen.
Sorry if I got weird there…but not seeing a way around that if you consider the photon’s perspective.
As a number of people have already pointed out, a massless particle, such as a photon, cannot experience time. That is how they know a neutrino must have mass. There are three kinds of neutrinos: electron neutrinos, muon neutrinos, and tau neutrinos. Once it was discovered that the electron neutrinos emitted actually oscillate between these three “flavors” between their emission from the sun and detection on earth, it follows that neutrinos must experience time and therefore must have some mass. Before that discovery, physicists worried about the solar neutrino unit (SNU). Earlier detectors detected only electron neutrinos and there were only a third as many as their computations predicted. Newer detectors solved that problem. It’s stories like that that give me confidence that those guys really know what they’re doing.
Or, equivalently, a timeless particle, such as a photon, cannot experience mass. ?