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Why are some things darker when wet?

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Re: Why are some things darker when wet?

#161

Post by izietto »

zamadatix wrote: post #147
dandelany wrote: post #138

Earlier quoted context omitted.

The point is, if A) photons carry no individual identity, and B) the interaction happens instantaneously, then there is no meaningful difference between saying "the photon bounced off like a ball" and "the photon was absorbed and a new one was instantly re-emitted". It's literally a distinction without a difference. As humans living in the classical world, we hear that and think "oh, that just means we don't know wha…

I'll try again in another way and if this doesn't work I may need to come back to trying to communicate what I mean. When you encounter an XY problem question/statement only stating "this doesn't make any sense. Computers are very complicated and don't work like that in the first place" is useless to everyone except maybe a comment or that wants to boost their ego. Taking the XY question, explaining why it's wrong, a…

I understand that my previous comment lacks of explanation, but I'm not a native English speaker so it's really hard for me to dig into details. I beg your pardon

Re: Why are some things darker when wet?

#162

Post by tigershark »

improv32 wrote: post #101
tigershark wrote: post #30

Earlier quoted context omitted.

That doesn’t look right at all to me. Why the photon is then re-emitted in exactly the same direction that it would have if it was reflected rather than a random direction?

The photon has some amplitude for reflecting in all possible directions, it happens that for certain directions these amplitudes are very close to the same value and so reinforce and become more probable, and at wider angles tend to cancel out and become less probable. When this is not the case and wider angles instead reinforce you can observe this directly in for instance a diffraction grating.

Yes, I agree. But what this has anything to do with the probability of emitting a photon in a specific direction? The parent was speaking about absorption and re-emission, not reflection.

Re: Why are some things darker when wet?

#163

Post by MrPatan »

izietto wrote: post #127
zamadatix wrote: post #110

Earlier quoted context omitted.

A photon doesn't need to carry a UUID for people to conceptualize a difference between a photon going through free space and being absorbed and re emitted. The parent comment asks the right question, what is being meant by "the same" is required to know before being able to say the discussion makes no sense. Taking your first literal interpretation as the only way the discussion could have value is no more helpful th…

> "I'm going to the store, do you want the same hot dogs we have in the fridge?" "That doesn't make sense, the store can't have the same hot dogs we have in the fridge" Yeah but hot dogs belong to classical mechanics, while photons to quantum mechanics, and in quantum mechanics you can actually have the same hot dogs in different places, until you observe them

There is no classical mechanics, only quantum mechanics. Or are you suggesting it's an optimization of the simulation or something?

Re: Why are some things darker when wet?

#164

Post by yesenadam »

yesenadam wrote: post #124
cameldrv wrote: post #109

Earlier quoted context omitted.

You can also watch the original lecture. This is one of my very favorite explanations of anything: http://www.vega.org.uk/video/programme/46 This explanation starts at about 30 minutes, but I highly recommend watching from the beginning.

Thanks! I hadn't seen these. There are 4 Feynman lectures on this page[0], the Douglas Robb Memorial Lectures, of which you linked to the second. http://www.vega.org.uk/video/subseries/8 1. A gentle lead-in to the subject, Feynman starts by discussing photons and their properties. 2. What are reflection and transmission, and how do they work? 3. Feynman diagrams and the intricacies of particle interaction. 4. What do…

Update: have now watched 3 of the 4 videos. Can see why you loved it so much! I've watched a lot of Feynman talks and lectures, and read most of his books. ..but this has particularly good explanations of the material, distinctly clearer than a couple of talks of his I'd seen before. Plus a few priceless references to NZ and the NZ national character! (filmed Auckland 1979)

Re: Why are some things darker when wet?

#165

Post by izietto »

MrPatan wrote: post #163
izietto wrote: post #127

Earlier quoted context omitted.

> "I'm going to the store, do you want the same hot dogs we have in the fridge?" "That doesn't make sense, the store can't have the same hot dogs we have in the fridge" Yeah but hot dogs belong to classical mechanics, while photons to quantum mechanics, and in quantum mechanics you can actually have the same hot dogs in different places, until you observe them

There is no classical mechanics, only quantum mechanics. Or are you suggesting it's an optimization of the simulation or something?

What do you mean there is no classical mechanics? I was referring to this: https://en.wikipedia.org/wiki/Classical_mechanics

Re: Why are some things darker when wet?

#166

Post by hutzlibu »

fennecfoxen wrote: post #154
hutzlibu wrote: post #82

Earlier quoted context omitted.

This debate is very old. Newton and Huygens fought long over it .. and eventually it was solved by: it is both or rather neither. It is a quant. https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality#...

A "quant" is someone who studies quantitative finance, typically found in investment fields. The word for this wave-packet with particle properties is "quantum". It is a singular noun; its plural is "quanta".

Thx. Not a english native speaker. In german it would be just "quant".

Re: Why are some things darker when wet?

#167

Post by whatshisface »

ggggtez wrote: post #134
whatshisface wrote: post #49

Earlier quoted context omitted.

Having thought about it, I'm not sure if I agree. Light can reflect off of transparent crystals, which do not have the right electron energy levels for absorption (that's why they're transparent.) It's possible that the Feynman diagram of a reflection might involve the photon "going away and another one replacing it" (I don't know what the diagram looks like), but Feynman diagrams cannot be interpreted as sequences o…

I think this is called, "knowing enough to be dangerous". You clearly have some understanding of light, but you are missing some key facts that would lead you to the correct understanding. >Light can reflect off of transparent crystals No, the point of the above post is that a photon is not "reflected", but captured and re-transmitted by photo-electric effect. Light travels at maximum speed C, only when in a vacuum.…

Absorption and emission are not the only two processes by which light can interact with matter, reflection is another. The argument is that if the material can't store the energy then you can't really call the event an absorption. Feynman diagrams aren't sequences of events so just because you see the photon coming to, disappearing, and then departing an electron doesn't mean it happens in that order.

Re: Why are some things darker when wet?

#168

Post by wizzwizz4 »

hn3333 wrote: post #100
wizzwizz4 wrote: post #68

Earlier quoted context omitted.

WikiBooks really does have everything: https://en.wikibooks.org/wiki/A-level_Physics_%28Advancing_P... This example is wrong , but useful, and it's (probably) less wrong than what you've been talking about so far. At the very least, it's more useful.

Thanks for correcting me and thanks for the link. But what have I been talking about so far? I don't understand. Also I just watched this video I'd recommend that explains the idea: https://www.youtube.com/watch?v=NumSE2LvSmQ

Sorry, by “you” I meant the people way up thread.

Re: Why are some things darker when wet?

#169

Post by kyberias »

matt-attack wrote: post #125
kyberias wrote: post #98

Earlier quoted context omitted.

Well, we may well be able to simulate it perfectly, but it might not fit into Frozen 2's limited budget for rendering.

I thought I'd read up, and googled "cgi wet fabric". For me the number one result was my own comment above!

For me, when I google "cgi wet fabric" the top result is your comment here referring to the top result that you found in Google when googling "cgi wet fabric"!

Re: Why are some things darker when wet?

#170

Post by socceroos »

aphextron wrote: post #18

This is a bit hand-wavey in its' description of light reflecting. One of the most mind blowing bits of physics I've ever learned is that photons do not actually "bounce" off of a surface like little balls. They are always absorbed and re-emitted. The actual photons that hit an object are not the same ones that eventually enter your eyes. The atoms in an object are stimulated by photons hitting them to then emit a new…

Dumb question: why do these ejected photons mirror the incoming photon's trajectory if they're a new particle?
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