Sabrina Kilian wrote:
> Invisible wrote:
>> I doubt your eyes can see single photons anyway...
> 
> If the photon hits a rod cell in the eye, then yes. Whether the brain
> would process this over the photon flux of your surroundings would be up
> for question. In total darkness, I think you would see it.

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?

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

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Orchid XP v8 wrote:
>>> babble some nonesense about a "quantum superposition of states" to
>>> make up for the fact that this explanation makes no sense at all.
>>
>> It's only nonsense if you don't know what it means.
> 
> "And the waves interact to generate these interference patterns."
> 
> "OK, so why do I still get the exact same patterns if there's only one
> photon there?"

You don't get the interference pattern with only one photon. You get it
if you sum a lot of photons emitted one at a time. A single photon will
still hit only one place*, but that place is more likely to be in one of
the locations that you would expect from a wave.

Many-Worlds Interpretation not withstanding.

> "Um... right, OK... that's because there are these extra versions of the
> photon, that all exist at the same time. They generate the interference
> pattern. Oh, but you can't measure them, see? Because as soon as you
> look at them, they stop existing, right?"
> 
> "Dude... WTF?"
> 

Not quite the same, but how can a 4D object interact with it self in 3D
space?

Photons are not waves, but their position is governed by a waveform that
represents the probability that the particle will be at any given point.

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Orchid XP v8 wrote:
>>> babble some nonesense about a "quantum superposition of states" to 
>>> make up for the fact that this explanation makes no sense at all.
>>
>> It's only nonsense if you don't know what it means.
> 
> "And the waves interact to generate these interference patterns."

That's mistaken. There are no waves.

> "OK, so why do I still get the exact same patterns if there's only one 
> photon there?"

Because there are no waves.

> "Um... right, OK... that's because there are these extra versions of the 
> photon, that all exist at the same time.

That's an attempt to explain the interference patterns *assuming* photons 
are waves to start with. But they're not, so it's mistaken.

http://www.youtube.com/watch?v=_7OEzyEfzgg

Note that "amplitude" is the 2-D complex probability.  It's not that two 
photons get to the same place at the same time and cancel out.  It's that 
the photon just doesn't go there. Hence, no need for multiple photons to 
cancel.

What he's talking about at the end is things like, you know they're not 
waves because you only have two electrons in the innermost shell and you get 
lasers with bosons but not fermions.  I.e., you can't make an electron 
laser, only a photon laser. Hence, electrons aren't waves.

-- 
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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Sabrina Kilian <ski### [at] vtedu> wrote:
> You don't get the interference pattern with only one photon. You get it
> if you sum a lot of photons emitted one at a time. A single photon will
> still hit only one place*, but that place is more likely to be in one of
> the locations that you would expect from a wave.

  To put it more clearly:

  You don't need to send all the photons at the same time in order to get
the interference pattern. You can send photons one by one, with a significant
time interval between sending the photons, and you *still* get the exact
same interference pattern as if you had sent them all at the same time.
This means that a photon does not need other photons to interfere with in
order for the interference pattern to appear. A lonely photon traversing
through the double-slit will still present the same interference.

  I think that the vernacular interpretation is that the single photon
traverses as a wavefront and interferes with itself when it passes through
both slits at the same time.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> Orchid XP v8 wrote:
> >>> babble some nonesense about a "quantum superposition of states" to 
> >>> make up for the fact that this explanation makes no sense at all.
> >>
> >> It's only nonsense if you don't know what it means.
> > 
> > "And the waves interact to generate these interference patterns."

> 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.

> > "OK, so why do I still get the exact same patterns if there's only one 
> > photon there?"

> Because there are no waves.

  You get a wave interference pattern *because* (not "even though") there's
no wave. That makes sense.

  I wonder if the same principle could be applied to all non-intuitive
phenomena: The phenomenon happens *because* of what makes it non-intuitive,
not *regardless* of what makes it non-intuitive. Of course that claim is
quite non-intuitive all in itself.

-- 
                                                          - Warp

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On Mon, 30 Nov 2009 11:45:53 +0000, Invisible wrote:

>> There is nothing like spending a couple of hours on your back in a
>> field with a truly dark sky - it feels like there are far more than
>> mere thousands visible!
>> 
>> :o
> 
> But where do you have to go? Outer Mongolia?

You could probably see a fair bit from Stonehenge....For me, I'd probably 
have to travel about 30 miles up into the mountains (have done, actually, 
the night sky is quite cool to see from up on the eastern side of the 
mountains to the east of where I live).

As for where Outer Mongolia is, GIYF. ;-)

Jim

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On Mon, 30 Nov 2009 23:20:44 +0100, Orchid XP v8 <voi### [at] devnull> wrote:
>
> 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



-- 
FE

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Warp wrote:
>   I think that the vernacular interpretation is that the single photon
> traverses as a wavefront and interferes with itself when it passes through
> both slits at the same time.

Well, not really. The basic problem is people calling it an "interference 
pattern" to start with. It's not really "interference" as such, since 
there's only one particle. Calling it "interference" just encourages people 
to go looking for what wave is causing the interference.

-- 
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.

No, it doesn't. It has the same math as a wave, *if* there's only one. If 
there's more than one, the behavior isn't like waves.

What function of waves produces lasing? Polarization?

>>> "OK, so why do I still get the exact same patterns if there's only one 
>>> photon there?"
> 
>> Because there are no waves.
> 
>   You get a wave interference pattern *because* (not "even though") there's
> no wave. That makes sense.

No, you get the exact same patterns when there's only one photon there, 
because it's not caused by interference between photons.

-- 
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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Darren New wrote:
> No, you get the exact same patterns when there's only one photon there, 
> because it's not caused by interference between photons.

Actually, if you really want to push it, you could say the pattern is caused 
by interference between the two slits, not between multiple photons. That's 
why it changes based on whether you measure what goes thru the slits or not.

-- 
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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