[adonovan]

Feynmann is very clear that the photons bouncing off a mirror are not the same ones that hit it. They are absorbed by electric oscillators (free electrons in the material) and destroyed; then new ones are created and emitted.

He's also careful enough to point out that electrons don't really have an identity that would allow you to meaningfully define "not the same". :)

[AgentME]

Electrons aren't unique in not having identities. Photons of the same wavelength are similarly fungible if I remember right, though it's a little more defensible to call the reflected light not the same photons since the original photons are transformed to something we don't call photons before photons are produced again.

[doodlebugging]

But at a reflection event you aren't producing a new photon, you are only reflecting a portion of the original determined by the refractive indices of the reflection interface. At that interface, part of the original photon is reflected and the rest is transmitted across the interface as a new photon and both have a modified bandwidth relative to the parent photon. So the one you see reflected is the same photon after modification by the medium it traversed and the transmitted components escape your view unless you are monitoring the other side of the medium.

[mmmBacon]

A photon is indivisible that’s the quantum nature of light. You aren’t reflecting a part of it. To do so is a classical wave interpretation of light. The photon after reflection is not the same photon.

[wizzwizz4]

That would imply a frequency shift, which clearly doesn't happen (mirrors don't redshift the light that hits them).

[ASalazarMX]

I balked at that too, because infinite mirrors and mirror houses also don't show any wavelenght shift no matter how many reflections they do. They do change perceived amplitude, as no mirror is perfectly reflective.

[Jerrrry]

Blue, but it's more to do with manufacturing defects and the minerals used for the mirrors.

[adonovan]

Yeah, I meant to say "photon" in my last sentence; but the point is equally true for electrons.

[dylan604]

Electrons? We were just told that there is only one single electron in yesterday's posts. It's almost like they don't know what an electron is

[doodlebugging]

I believe they're right about there being only one single electron. I tried to start my Pathfinder yesterday and it was dead as a doornail. None of the dash lights lit and there was not even a click from the starter. Someone else must've been using that electron though since I tried again a few minutes later and it cranked right up. I had my turn with it so I'm not mad at all.

[westmeal]

Um maybe check your battery terminals for corrosion :)

[doodlebugging]

I covered all those bases. I'm not 100% sure what happened but when I initially tried to start the vehicle I had it connected to a solar battery maintainer in full sunlight. It should've had bazillions of photons sacrificing part of themselves to be stored electrons but instead I got nothing. After disconnecting that from the battery and testing all the fuses I made another attempt to start it up and it worked fine. It's possible that the voltage output of the panel swamped the voltage expected by the ECU and it refused to energize to save the system from electrical damage by overvoltage.

Or maybe that single electron hadn't quite made it to my battery on my first attempt. That's one busy e.

[westmeal]

I find pouring electrons into a funnel usually helps by avoiding an electron spill all over your battery. Glad it works tho!

[doodlebugging]

So sorry for the delayed reply. I had to hit several O'Reilly stores to find someone who had any idea what I was looking for. I finally found one with a college-looking kid behind the counter instead of all those old farts like me and after I explained what I wanted he knew just which aisle it was on.

Turns out that an electron funnel isn't a fancy new tool. Instead, I already have several of them in my shop but just didn't make the connection. It became clear though when he handed me the plastic funnel after rubbing it through his hair vigorously for a few seconds and I got shocked by the crackling electrons streaming from the funnel to my fingers.

If this power thing ever happens to my battery again I'm just gonna get the big funnel from the set, rub it through the remnants of my hair and pour some electrons at it till it charges enough to start the engine.

Thanks for this suggestion about a new way to use an old tool.

[dylan604]

I wonder if that's how they get electrons into the particle accelerators too?

[mmmBacon]

It’s a true statement that they don’t know what the electron is. In the standard model the electron is a point particle with no volume.

[yencabulator]

I feel like this applies: https://www.youtube.com/watch?v=MO0r930Sn_8 (Feynman on how certain questions can be very hard to answer)

[out_of_protocol]

> only one single electron

> an electron

THE electron? /s

[doodlebugging]

I wonder about the all the photons lost in fiber optic installations. What happens to them in their short lives? There must be a creation and an extinction event.

A photon jumps into the glass fiber and travels until it encounters an opto-electric coupler where the photon craps out and is converted to an energized stream of electrons, or maybe it borrows the only real electron in the universe for an instant as it flips across the coupler to the next glass fiber where a new photon is born, only to flare out at the next junction.

[lolc]

My understanding is that photons don't have a life the way we do. They move at the speed of light and thus time does not advance for them. They cannot change between emission and absorption, no matter the distance. Always bends my mind to think about it.

[Kranar]

Almost everything you said is correct. Photons do not have a reference frame, so time does not advance because for a photon there is no time coordinate system in the first place. It's not simply that photons don't experience time, it's that time and space don't exist for photons.

>They cannot change between emission and absorption, no matter the distance.

From the point of view of a photon, neither time or space exist. They have no reference frame at all. However, from an outside frame of reference that is travelling less than the speed of light, photons do change for example they get red shifted as they move through stronger gravitational fields.

[lolc]

Not to quibble about definitions of what "change" means, but I thought the red shift depended entirely on the relative speed of the emitting and receiving body? A laser beam for example could not be analyzed for its red shift, unless we knew the original frequency, because there would be no spectral absorption pattern to determine the shift. So we cannot tell how far laser light traveled before it reached our sensor.

[Kranar]

Not a quibble at all. The redshift I'm referring to is the kind of redshift due to gravity, as opposed what you're describing which is redshift due to the Doppler effect.

[lolc]

I'm trying to come up with a scenario to understand the difference: Say I have a triangle of emitter, receiver, and a large body, all at a fixed distance. And the receiver would see emitted light both directly and bent around the body. The bent light would be red shifted?

[rvbissell]

> They move at the speed of light and thus time does not advance for them.

Isn't it more accurate to say that photons move at the speed of causality, when the medium is a pure vacuum? Because in some other medium like glass, the speed of light is slower than the speed of causality.

So my follow-up question is: do slower photons (such as those propagating through a fiber-optic strand, or water) then experience the advancement of time?

[Kranar]

There is no such thing as slow photons, photons always travel at the speed of light.

When light enters a medium there are two mostly (but not entirely) equal ways to think about what happens, one is to view light as a purely electromagnetic wave that interacts with atoms and causes the atoms to oscillate. This oscillation produces its own electromagnetic wave that interferes with the original wave. The result of this interference will be an electromagnetic wave with the same frequency, same amplitude, and travelling in the same direction as the incoming light but shifted backwards and it's that shift backwards that gives the appearance of light slowing down.

That explanation is pretty good and accounts for almost everything except for the latency of light through a medium.

If that's what you want to model, then it's better to think of light as made up of photons instead of being a wave, and then when photons enter a material they no longer exist as independent particles but through a process of absorption and reemission by electrons in the material become particles called polaritons. Polaritons do have mass and hence travel slower than the speed of light.

Neither of these explanations are perfect, but the full explanation is ridiculously complicated and there's no suitable metaphor for it. If you are interested in knowing the edge latency of light through a medium, then the polariton explanation is appropriate. If you want to know the "bandwidth" explanation of light through a medium, then the wave explanation is appropriate.

[nullserver]

It could be the same electron after all. Although probably not.

One electron theory. https://youtu.be/9dqtW9MslFk?si=qdWGUyJnDRCOns9F

[credit_guy]

Does Feynman say that? If an electron absorbs a photon, why would it create another one of the same frequency, and with polarization perfectly rotated by 90°?

[candiodari]

Because of the layout of the electron orbitals.

[credit_guy]

Feynman certainly didn’t say anything like that, or only the photons with certain frequencies would reflect, those corresponding to the energy differences between various orbitals.