confused2Oct 23, 2025 01:39 PM (This post was last modified: Oct 23, 2025 02:00 PM by confused2.)
Our eyes are photon counters. Everything we 'see' is the result of many single photon processes .. from emission, to reflection or absorption, to detection .. all single photon processes. It is possible 'some' effects are specific to laser light but unless you live in laserworld they aren't relevant to the question.
Youtubers Looking Glass Darkly and Veritaserum have made 'interesting' videos about reflection .. I think it would be helpful to have some idea of what we expect to see before looking at what they show - and whether it is what what we (or they) think it shows.
I have yet to see a plausible explanation of reflection. This question is intended to lead on to Feynman's 'sum over paths' ..
AI on Feynman sum over paths
Quote:Feynman's sum over paths is a formulation of quantum mechanics that says a particle travels between two points by taking every possible path simultaneously, not just one. Each path is assigned a complex number called an amplitude, which is determined by the path's action (calculated from its kinetic and potential energy). The total probability amplitude for the particle to get from the start to the end is found by summing the amplitudes of all these paths. The final probability is then the square of this total amplitude.
****The really hot bit*** >>>>> https://youtu.be/qJZ1Ez28C-A?t=1567
^^^ Unfortunately Casper got a bit too excited and I lost track of what he was on about.
I was hoping for a better vid .. unfortunately LG's vid (I thought) was worse.
VIDEO INTRO: As a 42-year-old who's spent most of my life studying physics, I must admit that I had a big misconception. I believed that every object has one single trajectory through space, one single path.
But in this video, I will prove to you that this is not the case. Everything is actually exploring all possible paths all at once. So let's start with a simple thought experiment.
Say you're at a beach when all of a sudden you see your friend struggling out in the water. You want to go help them as quickly as possible. So which path should you take to get there?
The shortest path is a straight line, so you could head directly towards him. But you can run faster than you can swim, and this path requires more swimming. So alternatively, you could run down the beach to minimize the distance through the water.
But now the total distance is longer than it needs to be. So the optimal path, it turns out, is somewhere in between. To be precise, it depends on the speeds at which you can run and swim.
Now, you might recognize this mathematical relationship because it is the exact same law that governs light passing from one medium into another. So light also takes the fastest path from point A to point B.
What's weird about this is that as humans, we can see where we want to go and then figure out the fastest route. But light, I mean, how does light know how to travel to minimize its journey time? Now here is where my misconception comes in.
I shine a laser beam. The light just goes in one direction. I throw a ball. The ball just goes in one direction, you know? I would have answered, there is nothing strange about this.
Light sets off from point A in some direction. And then a little while later it encounters a new medium. And due to local interactions with that medium, it changes direction, ending up at point B.
If you later find that of all the possible paths, light took the shortest time to get from A to B, I wouldn't think it was optimizing for anything. I would just think that's what happens when light obeys local rules. But now I will prove to you that light doesn't set out in only one direction.
Instead, it really does explore all possible paths. And the same is true for electrons and protons. All quantum particles. So the fact that we see things on single, well-defined trajectories is, in a way, the most convincing illusion nature has ever devised. And the way it works all comes down to a quantity known as the action...
...sounds just a tad like this old thing from a few months ago:
KEY POINTS: Time might actually have 3 dimensions. But it also means that the space would actually be one-dimensional, instead of the three dimensions we’re familiar with. This way of looking at the cosmos could explain the quirks of quantum mechanics, like a particle being in two places at once. It would even explain hypothetical faster-than-light particles.
EXCERPT: In an effort to tackle these issues, researchers from the Universities of Warsaw and Oxford asked an altogether different kind of question. What would the universe be like if you could travel faster than light?
Now in special relativity it’s impossible to move from below the speed of light and accelerate to reach it, let alone go faster than light. But the rules of special relativity also allow the reverse situation, where objects can start off faster than light already—but then they can never slow down below that limit
.
According to the researchers, for observers who are already traveling faster than light, the connection between time and space is flipped. Instead of three spatial dimensions and one temporal dimension, faster than light observers see three dimensions of time and only a single dimension of space. This means that particles follow more than one trajectory at once. In effect, they travel into more than one future simultaneously.
From our normal slower-than-the-speed-of-light perspective, it looks like these faster-than-light objects are not behaving like particles at all. Instead, they act like waves. Think about it. If you throw a baseball, it only follows one path. But if the baseball hits a nearby pond, the water waves travel in multiple directions at once.
The researchers argue that this shift in perspective offers a possible explanation for the mysteries of quantum mechanics. Things like quantum entanglement, random probabilities, wave-particle duality, and all the other usual consequences of quantum mechanics seem to be natural outgrowths of this faster-than-light perspective. Instead of springing into existence without explanation—which is the default mode in quantum mechanics—these rules now have a potential reason.
Indeed, the researchers point out that the concept of a particle in this perspective completely breaks down. Instead you can only talk about fields, which are waves that exist throughout all of space and time. The researchers point out that many theories in physics, especially ideas concerning the fundamental physics occurring in the extremely early universe, already employ fields that have faster-than-light properties...
Wow!
What Scivillage lacks in quantity it certainly makes up for in quality.
As to whether the diffraction grating over the mirror should (or will) work .. I need to spend some (a long) time with the responses .. most likely I'll guess .. and so far I guess it won't work in the way intended.
Thanks guys. Deep joy.
Belatedly it occurs to me that we have been looking at what the photon does (or doesn't) do. Nothing about the mirror and how it does what it does. The 'photon absorbed and re-emitted' doesn't really work if the whole mirror is involved. Any thoughts?
(Oct 24, 2025 11:54 PM)confused2 Wrote: Belatedly it occurs to me that we have been looking at what the photon does (or doesn't) do. Nothing about the mirror and how it does what it does. The 'photon absorbed and re-emitted' doesn't really work if the whole mirror is involved. Any thoughts?
No absorption and emission. Just redirected. Well, a small amount through heat, but that's negligible.
If you're interested in this, you must have Feynman's book, right? In the book it starts on pg. 39, but in this pdf it starts on page 44.
Some (like me) might say that was a bit vague .. that's what it is .. but how?
SS Wrote:..you must have Feynman's book, right?
I did until about 30 years ago. I tried to help someone and later found they were helping themselves - to anything remotely valuable - including my copy of QED. Your link to the pdf greatly appreciated.
Some (like me) might say that was a bit vague .. that's what it is .. but how?
Here's Grok 4's explanation.
In quantum mechanics, reflection of light—such as a photon bouncing off a mirror—does not involve the photon being absorbed and then re-emitted in the classical sense. Instead, it is a coherent scattering process governed by quantum electrodynamics (QED). Here's a clear, step-by-step explanation:
1. Light as Photons Interacting with Matter
Light consists of photons, which are quanta of the electromagnetic field.
When a photon approaches a reflective surface (e.g., a silvered mirror), it interacts with the electrons in the material.
2. No Absorption/Re-emission in Ideal Reflection
In a perfect mirror, the photon is not absorbed into the material and then re-emitted.
Instead, the incoming electromagnetic wave drives oscillations in the surface electrons.
These oscillating electrons act like tiny antennas that re-radiate (scatter) the electromagnetic field in the reflected direction.
The re-radiated waves interfere constructively in the reflection direction and destructively in other directions (due to the geometry and phase relationships).
This is why reflection follows the law of reflection (angle of incidence = angle of reflection).
3. Quantum Picture: Virtual Processes (QED)
At the quantum level, the interaction is described by Feynman diagrams.
The photon interacts with electrons via virtual photon exchange.
The electron briefly absorbs the momentum and energy of the incoming photon, enters a virtual intermediate state, and then emits a new photon with the same energy but reversed momentum component perpendicular to the surface.
This is elastic scattering: the photon’s energy (frequency/color) is preserved.
Code:
Incoming photon → scatters off electron → outgoing photon (reflected)
No real energy is absorbed by the material in an ideal case.
4. Why Doesn’t the Photon Get Absorbed?
In metals (good mirrors), electrons are free or nearly free (conduction electrons).
The plasma frequency of the metal is much higher than visible light frequencies → the electrons can respond instantly and re-radiate the light without absorbing it.
In dielectrics (e.g., glass), reflection occurs at interfaces due to impedance mismatch (Fresnel equations), again via coherent scattering at the boundary.
5. Contrast with Absorption/Re-emission
Absorption/re-emission occurs in fluorescence or phosphorescence:
Photon is fully absorbed → electron jumps to excited state.
After a delay (nanoseconds to milliseconds), a new photon is emitted at possibly lower energy.
This is incoherent, loses phase information, and doesn’t produce sharp mirror-like reflection.
Reflection is coherent: phase is preserved → sharp image forms.
Key Takeaway
Quote:Reflection is not absorption and re-emission.
It is elastic, coherent scattering of the photon by the electrons at the surface, mediated by the electromagnetic interaction, with no net energy transfer to the material in ideal cases.
This is why you see a clear, instant, color-preserving image in a mirror—quantum mechanics in action!
Grok 4 Wrote:Key Takeaway
Quote:
Reflection is not absorption and re-emission.
It is elastic, coherent scattering of the photon by the electrons at the surface, mediated by the electromagnetic interaction, with no net energy transfer to the material in ideal cases.
To say the explanation for what is at the root of an electromagnetic effect 'is an electromagnetic effect' .. not very helpful. 'No net transfer of energy' .. solar sails are mirrors and use the impact of light (photons) to accelerate a thing .. maybe grok hasn't learned about conservation of momentum yet - isn't exactly rocket science [it IS it IS it is EXACTLY rocket science]. So I'm not impressed by Grok.
An aside.
Take a half silvered mirror .. if the photon goes through then no momentum transferred .. if reflected the mirror gets a kick. We don't know whether kick or no kick until we detect the photon. We can arrange to detect the photon without determining which path (effectively both) which is beyond the scope of this post. If the photon is directed towards outer space it may be years or even never before the mirror is either kicked or not. We can increase the odds of a kick by using a fully silvered mirror .. but is the kick delivered before the photon is detected?
Oct 23, 2025 01:39 PM
(This post was last modified: Oct 23, 2025 02:00 PM by confused2.)
