Warp wrote:
>   I don't think you can talk about amplitudes after claiming so firmly that
> photons are not waves.

Here's another analogy that might help.

You're flipping coins. You notice that coins come up 50% heads and 50% 
tails.  You say "How can that be, if every coin has to come up either heads 
or tails? How do you get a coin coming up only 50% heads?"

Well, in spite of that, every *other* measurement tells you a coin comes up 
heads or tails, never 50% of each.

Same thing with photons. There doesn't have to be waves to get an 
interference pattern, just interference. But what's interfering is the 
possibilities, not the electrons. Just like the thing that's 1/2 in the 
coins is that each possibility is only half likely, when any given 
individual coin flip always comes up 100% heads or 100% tails.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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>> It's true that in very low light conditions, vision takes on a 
>> "speckley" character, presumably due to some combination of small 
>> numbers of photons or small numbers of individual nerve impulses 
>> generating a fairly noisey signal. I'm not sure whether one single 
>> photon is enough to generate a nerve action potential though; maybe it 
>> takes 10 or so?
> 
> Not a bad guess.
> 
> http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html

Well, I have a book - a truly awful book written by a guy who thinks 
that molecular biology *proves* that Darwin is wrong. The book spends 
most of its time with broken analogies and flawed logic, but inbetween 
is some really quite interesting stuff about various chemical processes 
of the cell - including the cascade for either retinol or rhodopsin, I 
forget which.

Essentially, when a single molecule of this protein absorbs a single 
photon, it undergoes a structural change which causes it to react with 
another protein, which causes one of the ion pumps on the cell wall to 
shut off, thereby macroscopically altering the ion concentration inside 
the cell, generating a minute but measurable net charge for the entire 
cell, which leads to a nerve impulse being fired... or something like 
that. It's *complicated*!

But anyway, I don't recall the exact pathway off the top of my head, but 
it would seem that you'd need a few photons for one of them to actually 
hit a rod (rather than a cone or some other random cell), in the right 
place to collide with a rhodopsin molecule (instead of some other 
protein floating around in the cytol), and it seems reasonable that 
you'd need to switch off a few ion pumps at once to make an action 
potential big enough to "fire" the neuron... so it seems reasonable that 
some smallish number of photons is required. Biological systems can 
become ludicrously efficient where there's some advantage to it, so it's 
not going to be thousands of photons either...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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On Tue, 01 Dec 2009 21:42:56 +0000, Orchid XP v8 wrote:

> Jim Henderson wrote:
> 
>> You could probably see a fair bit from Stonehenge....
> 
> With Salisbury 11 miles to the south, and Amesbury 4 miles to the east?

That's not that far, really.

> Unrelated but... I gather they don't let you go near Stonehenge any
> more.

Depends on your definition of "near" - when we visited, they had the 
stones themselves roped off, but you could still walk around them.  
Problems with vandalism apparently led them to cordon them off except for 
during special events (like the Solstice).

Jim

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> That's mistaken. There are no waves.
> 
>   It looks like a wave, it behaves like a wave, it produces all the
>   effects
> that a wave would produce, but it's not a wave.

Conclusion: quantum physics doesn't have duck typing :)

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Nicolas Alvarez wrote:
> Warp wrote:
>> Darren New <dne### [at] sanrrcom> wrote:
>>> That's mistaken. There are no waves.
>>   It looks like a wave, it behaves like a wave, it produces all the
>>   effects
>> that a wave would produce, but it's not a wave.
> 
> Conclusion: quantum physics doesn't have duck typing :)

Heh.  More precisely, there's one situation in which it behaves like a wave 
in one aspect.  So it's kind of like a java interface.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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Warp wrote:
>   It looks like a wave, it behaves like a wave, it produces all the effects
> that a wave would produce, but it's not a wave.

By the way, just so you know, this sort of statement comes across to me as 
sarcastic, as if you're ridiculing my statements. I don't know if that's 
your intention here, but that's why after a number of exchanges I sometimes 
get ruder than I need to be. I don't know if it's a communication issue or 
you getting frustrated at my inability to explain quantum mechanics in a 
2-paragraph post ;-) but sometimes when you don't agree, your expressions of 
that lack of agreement (not necessarily disagreement, mind) sound sarcastic.

-- 
Darren New, San Diego CA, USA (PST)
   Human nature dictates that toothpaste tubes spend
   much longer being almost empty than almost full.

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> Essentially, when a single molecule of this protein absorbs a single 
> photon, it undergoes a structural change which causes it to react with 
> another protein, which causes one of the ion pumps on the cell wall to 
> shut off, thereby macroscopically altering the ion concentration inside 
> the cell, generating a minute but measurable net charge for the entire 
> cell, which leads to a nerve impulse being fired... or something like 
> that. It's *complicated*!

With some quick calculations and rather dubious assumptions I estimate that 
from a star like Betelgeuse approximately 10^6 photons are going into your 
eye per second.  This is about the same as a 100 W light bulb 10 km away.

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>> Essentially, when a single molecule of this protein absorbs a single 
>> photon, it undergoes a structural change which causes it to react with 
>> another protein, which causes one of the ion pumps on the cell wall to 
>> shut off, thereby macroscopically altering the ion concentration 
>> inside the cell, generating a minute but measurable net charge for the 
>> entire cell, which leads to a nerve impulse being fired... or 
>> something like that. It's *complicated*!
> 
> With some quick calculations and rather dubious assumptions I estimate 
> that from a star like Betelgeuse approximately 10^6 photons are going 
> into your eye per second.  This is about the same as a 100 W light bulb 
> 10 km away.

Dubious assumptions FTW! :-D

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"scott" <sco### [at] scottcom> wrote:
> With some quick calculations and rather dubious assumptions I estimate that
> from a star like Betelgeuse approximately 10^6 photons are going into your
> eye per second.  This is about the same as a 100 W light bulb 10 km away.

Interesting. Perhaps bizarrely, I know exactly what Betelgeuse looks like to the
naked eye, but not a lightbulb 10km distant!

What are your dubious assumptions? This is just the sort of 'sensible
guesstimation' calculation I used to enjoy at university. :)

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> What are your dubious assumptions?

That all the energy from the star/light bulb comes out equally in all 
directions in the form of 550 nm photons, and your eye has an opening of 2mm 
x 2mm.

Obviously all the energy doesn't come out as visible photons, and you could 
probably do something clever with the spectrum to get a more accurate 
figure.

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