http://en.wikipedia.org/wiki/File:Guisard_-_Milky_Way.jpg

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Invisible wrote:
> I can only presume this must be due to light pollution.

You need to go out someplace like 50 miles from the nearest street light. 
It's really rather overwhelming.

> Well, photons are quantum, right?

I'm not sure you'd see a point source. You need enough surface that the 
likelihood of multiple photons reaching your eye in a short interval is 
positive.

> (Interestingly, I'm told it *is* possible to make a light source that 
> emits individual photons, one at a time, on que. And that when you do 
> this, things like the double-slit experiment still show multiple waves 
> interferring and reinforcing - despite this being obviously 
> impossible... Wave-particle duality is weird!)

It's only impossible if you think the interference is caused by waves, which 
it isn't.

-- 
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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Invisible wrote:
> But where do you have to go? Outer Mongolia?

Most national parks in the USA are big enough.

> (Also... where the hell *is* that anyway?!)

Know how China has a concave top? In there.

-- 
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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Bill Pragnell wrote:
> I'd think it was a single shot. I bet you could get away with up to a minute of
> exposure, and it's very wide angle so any movement would be less noticeable.

You can also buy telescope tripods that will use a small motor to turn the 
telescope in counterpoint so the stars appear stationary. I imagine the same 
would work for a camera, and then it would be the ground that's blury.

-- 
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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Bill Pragnell wrote:
> I'm not sure. The fact that it's a nearly-complete panorama makes it even more
> complicated - I guess it must have been unwrapped from a fisheye.
> 
> I'd think it was a single shot. I bet you could get away with up to a minute of
> exposure, and it's very wide angle so any movement would be less noticeable.
> 
> Any expert photographers here want to comment?

Servo motors work wonders, when you can gear them correctly.

There are several tripod heads designed to track correctly against the
spin of the earth, allowing for long exposures. Anything that works for
for automatic telescopes can do the same work for a camera.

Or for cheap, a really long bolt, two pieces of wood, and a hinge. They
are called equatorial mounts or, for the cheapest ones, barn door trackers.

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>> I can only presume this must be due to light pollution.
> 
> You need to go out someplace like 50 miles from the nearest street 
> light. It's really rather overwhelming.

I don't know if any such place exists in the UK. Unless maybe you sail 
50 miles out to sea...

>> Well, photons are quantum, right?
> 
> I'm not sure you'd see a point source. You need enough surface that the 
> likelihood of multiple photons reaching your eye in a short interval is 
> positive.

I doubt your eyes can see single photons anyway...

>> (Interestingly, I'm told it *is* possible to make a light source that 
>> emits individual photons, one at a time, on que. And that when you do 
>> this, things like the double-slit experiment still show multiple waves 
>> interferring and reinforcing - despite this being obviously 
>> impossible... Wave-particle duality is weird!)
> 
> It's only impossible if you think the interference is caused by waves, 
> which it isn't.

Well, the books seem to claim that it *is* caused by waves, but they 
babble some nonesense about a "quantum superposition of states" to make 
up for the fact that this explanation makes no sense at all.

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Invisible wrote:
> This is awesomer:
> 
> http://en.wikipedia.org/wiki/File:Perseid_Meteor.jpg
> 
> Here in the name of God does the night sky actually look like this?!

Dunno, but now that it is cold I may have to find a map and make a
scouting expedition to find a place. City lights are annoying here, but
that picture looks like what I grew up seeing. Even there, the lights
are brighter at night, they finally put up street lamps, and the
neighbors leave their post lamps on, now.

But here, a half hour on the road will get me clear of the city and put
me in farm land. That's always a good start, with the side of a mountain
as a back up plan.

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> You can also buy telescope tripods that will use a small motor to turn the 
> telescope in counterpoint so the stars appear stationary. I imagine the 
> same would work for a camera, and then it would be the ground that's 
> blury.

That was my point, I know how to keep the stars sharp or to keep the ground 
sharp, but how to get both in the same photo?

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> City lights are annoying here, but
> that picture looks like what I grew up seeing.

I have never, ever, in my entire life, seen anything that remotely 
approximates this, except on TV and in posters. Every time I see 
something like this in films it looks like over the top CG, because real 
skies never, ever look like this.

It's quite impressive driving home, actually. By the time you reach 
Weedon, you can already tell where MK is because one entire side of the 
sky is bright orange. (I have no idea how far it is from Weedon to MK, 
but it's surely more than 10 miles.)

If you approach from the south, there's high ground that way. As you 
come down the hill, you can see the entire city laid out before you. It 
looks utterly huge. It seems to extend from one horizon to the other. 
(Obviously an effect of the terrain and it's slope.) And the entire 
thing is glowing.

I don't know about you, but when I look up at the orange horizon when 
I'm more than 10 miles away, I wonder what the HELL the council's 
electricity bill must be, and how much of the light we're paying for is 
leaking uselessly into the sky rather than illuminating the streets... 
Surely there's some more-efficient way to do this?

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scott wrote:
>> You can also buy telescope tripods that will use a small motor to turn 
>> the telescope in counterpoint so the stars appear stationary. I 
>> imagine the same would work for a camera, and then it would be the 
>> ground that's blury.
> 
> That was my point, I know how to keep the stars sharp or to keep the 
> ground sharp, but how to get both in the same photo?

Really, really friggin' BIG lenses, as a guess...

Apparently bigger lenses capture more light and generate better images. 
Seen any telescopes recently? Big, aren't they? ;-)

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> I'm not sure you'd see a point source. You need enough surface that the 
> likelihood of multiple photons reaching your eye in a short interval is 
> positive.

If the point source was emitting photons at the same rate as a star though, 
I don't think you'd be able to tell the difference between the star and such 
a point source.

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Invisible wrote:
> I have never, ever, in my entire life, seen anything that remotely 
> approximates this, except on TV and in posters. 

Like that line in Madagascar, when they're still in the New York Zoo.

"Oh, look, the star is out!"
"Whoops, nope, just a helicopter."

-- 
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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Invisible wrote:
> I doubt your eyes can see single photons anyway...

Somewhere between 5 and 10 over the course of 100 ms, for humans.

> Well, the books seem to claim that it *is* caused by waves, 

Those books are wrong. It's the same *math* as waves, but it isn't waves.

> 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.

-- 
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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>> 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?"

"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?"

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

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Invisible <voi### [at] devnull> wrote:
> > City lights are annoying here, but
> > that picture looks like what I grew up seeing.
>
> I have never, ever, in my entire life, seen anything that remotely
> approximates this, except on TV and in posters. Every time I see
> something like this in films it looks like over the top CG, because real
> skies never, ever look like this.

Skies look like this in most places in the world (clouds and moon permitting, of
course!), considering how relatively sparse human population centres are. Just
think of all that ocean, too!

You can definitely see skies like this in many locations in the UK. You'll see
good skies within 50 miles of MK. But you do need to make the trip!

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Sabrina Kilian <ski### [at] vtedu> wrote:
> Bill Pragnell wrote:
> > Any expert photographers here want to comment?
>
> Servo motors work wonders, when you can gear them correctly.
>
> There are several tripod heads designed to track correctly against the
> spin of the earth, allowing for long exposures. Anything that works for
> for automatic telescopes can do the same work for a camera.

Yah... as Scott said, if it was done with a tracking mount then it must be a
composite, because both sky and ground are in focus.

I must try some sky photography sometime, though. :)

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scott wrote:
>> You can also buy telescope tripods that will use a small motor to turn
>> the telescope in counterpoint so the stars appear stationary. I
>> imagine the same would work for a camera, and then it would be the
>> ground that's blury.
> 
> That was my point, I know how to keep the stars sharp or to keep the
> ground sharp, but how to get both in the same photo?
> 
> 

With a camera, the trees are going to move relatively little if you are
tracking stars relatively high in the sky. And that little bit they move
will be hidden by the stars that take up the field of view where the
tree was before.

Tracking a star at the horizon would be more difficult. I would have to
think of a good trick there that doesn't involve just cropping or
zooming in on only stars.

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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.

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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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Darren New <dne### [at] sanrrcom> wrote:
> 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.

  I see a pattern here (pun semi-intended). Shooting individual photons one
at a time results in a pattern which is identical to the interference pattern
which results from shooting huge bunches of photons at the same time, a
pattern which is what one expects from a wave. But since a photon is not a
wave, it's not an interference pattern. It's just a pattern which happens
to look exactly like an interference pattern, but without being one.

  And if I follow your earlier logic, the pattern looks like an interference
pattern *because* it's not an interference pattern.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> 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?

  Your logic seems to be that since photons do *more* than waves do, in
other words, photons seems to be a superset of pure waves, then they are
not waves at all.

  Why not apply the same logic in reverse? Since photons seem to do more
than pure particles would be expected to do, then they are not particles
either.

  It feels a bit like saying that a seaplane is not a plane because normal
planes can't land on water but a seaplane can.

> >>> "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.

  I find it rather amusing that QM doesn't seem to have any problem in
accepting phenomena which feel completely supernatural and counterintuitive,
such as the state of one particle instantly determining the state of another
particle which is light-years away, when the state of the particle is
"observed" (whatever that might mean), but the idea of a photon passing
through two slits at the same time and interfering with itself seems too
hard to swallow.

  (I'm not saying that's what's happening. I'm saying that the way you write
makes it sound like that.)

-- 
                                                          - Warp

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Warp wrote:
> It's just a pattern which happens
> to look exactly like an interference pattern, but without being one.

Right!  The math works out to be the same, in some limited cases.

Did you watch the youtube video I linked to? Or are you trying to apply 
common sense to a field which even nobel prize winners in that field agree 
it doesn't make common sense?

>   And if I follow your earlier logic, the pattern looks like an interference
> pattern *because* it's not an interference pattern.

No, you misread that. I said you know it's not an interference pattern 
because it happens with only one photon at a time.

Look, don't argue with me. Argue with Feynman if you want.

-- 
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:
>   Your logic seems to be that since photons do *more* than waves do, in
> other words, photons seems to be a superset of pure waves, then they are
> not waves at all.

No, that isn't my logic. Did you watch the video I linked to, where Feynman 
talks about a few of the things that show why photons aren't waves? Do you 
realize that Einstein got his nobel prize for showing that photons can't be 
waves?

The point is that they aren't waves when you look at more than one at a 
time, because they don't even cause interference patterns like you would 
expect. (Otherwise, lasers wouldn't work.) They aren't waves when you use 
electrons, even though you get "interference" patterns as long as you *only* 
shoot one at a time. One photon traveling through vacuum (or otherwise not 
interacting) follows the same math as a wave. Two photons don't. Two 
electrons don't. A photon interacting with an electron 100 feet down the 
road doesn't act like a wave *here*.

I'll agree it isn't intuitive that the motion of particles obeys some 
unobvious rules. That doesn't make them waves.

>   (I'm not saying that's what's happening. I'm saying that the way you write
> makes it sound like that.)

It's not "too hard to swallow". It's simply counter to experimental 
evidence. The interference has nothing to do with how many slits the photon 
passes through. Indeed, that's the *point* of the two-slit experiment. You 
*only* get "interference" patterns if you *don't look*.  If the 
"interference" patterns were caused by the photon passing through both 
slits, then they would persist if you did something to the photon *after* it 
passed through both slits. But it doesn't.

Indeed, if it was caused by the photon passing through two slits at once, 
you'd expect to get the interference pattern if you closed the slits only 
after you'd measured where the photon landed. But you don't. If you can 
explain that in terms of waves, there's a nobel prize waiting for you.

Is it really that hard to believe that there are multiple ways to come up 
with the same numbers that waves give you?

-- 
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 <dne### [at] sanrrcom> wrote:
> Or are you trying to apply 
> common sense to a field which even nobel prize winners in that field agree 
> it doesn't make common sense?

  That is contradictory with:

> I said you know it's not an interference pattern 
> because it happens with only one photon at a time.

-- 
                                                          - Warp

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Or are you trying to apply 
>> common sense to a field which even nobel prize winners in that field agree 
>> it doesn't make common sense?
> 
>   That is contradictory with:
> 
>> I said you know it's not an interference pattern 
>> because it happens with only one photon at a time.

I don't see that as contradictory, unless you mean that if it doesn't make 
common sense, you can't talk about it with common words at all. I'm down 
with that. The math doesn't work out the same either.  :-)

But seriously, for there to be an interference pattern, something has to 
interfere with something else, right?  As soon as you interfere with the 
photon, the pattern goes away.  Indeed, the pattern is *only* there exactly 
to the extent that there is *no* 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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Darren New <dne### [at] sanrrcom> wrote:
> But seriously, for there to be an interference pattern, something has to 
> interfere with something else, right?

  If the photon is a wavefront which traverses from the emitter to the
detector, passing throug the slits splits it into two wavefronts, which
interfere with each other. When the wavefront collides with the detector,
it collapses back into a particle.

  I'm not saying that is what happens. I'm just saying it's exactly as
plausible as eg. a particle being in many places at the same time or
affecting another particle instantly.

>  As soon as you interfere with the 
> photon, the pattern goes away.  Indeed, the pattern is *only* there exactly 
> to the extent that there is *no* interference.

  So why does the interference pattern appear? Is nature trying to confuse
us to make it look exactly like it was a wave, without it being so?

-- 
                                                          - Warp

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> But seriously, for there to be an interference pattern, something has to 
>> interfere with something else, right?
> 
>   If the photon is a wavefront which traverses from the emitter to the
> detector, passing throug the slits splits it into two wavefronts, which
> interfere with each other. When the wavefront collides with the detector,
> it collapses back into a particle.

But it doesn't work that way. If you look to see which slit the particle 
passed through, you find out that it only went through one. You never, ever 
see it go through both slits. You basically never see a wave or measure a 
wave. You always measure a particle, even as the whatever goes through the 
slits, even *after* the whatever goes through the slits.

>   I'm not saying that is what happens. I'm just saying it's exactly as
> plausible as eg. a particle being in many places at the same time or
> affecting another particle instantly.

Plausible? Yes. Confirmed by experimental evidence? No. Contradicted by 
experimental evidence? Yes.

I'm just stating what the guys who study this say. You're trying to tell me 
it sounds absurd. Sure, maybe it does. Maybe the world *might* work a 
different way than it does. Maybe if the only experiment you did was the 
two-slit experiment, you'd think photons are sometimes waves. But they're not.

>   So why does the interference pattern appear? 

You know when you do something with macro-sized objects, you get 
one-dimensional probabilities, right?  If you say "flip a coin, twice", 
you'll have the probability of getting two heads being the probability of 
getting one head *times* the probability of getting one head, right? (I'll 
leave it as an exercise for you to decide *why* that is the case, beyond 
"common sense.")  The probability of getting heads either time is the 
probability of getting heads the first time *plus* the probability of 
getting heads the second time *minus* the probability of getting both (just 
so you don't count the same event twice).

It's the same way with quantum particles, except the probabilities are 
complex numbers, hence "amplitudes". The probability of it hitting the 
screen at a given position is the amplitude of it going from the emitter to 
the left slit to that point on the screen *plus* the probability of it going 
from the emitter to the right slit to that point on the screen. But those 
probabilities change based on the distance the particle travels, and when 
you do all the adding and multiplying, the imaginary components wind up 
canceling out some of the "real" components in a way that looks like waves.
Because the probability of a quantum particle going in any given direction 
is a function of its amplitude.  "Amplitude" is a technical term meaning 
"two-dimensional probability." You get the probability of finding a particle 
at a particular place by adding together all the amplitudes of it getting 
there, then taking the absolute value (i.e., the length of the result).

In other words, the probability of something going from A to B is the sum of 
all the amplitudes of the ways it can get from A to B, then you take the 
resulting size. Just like if you want to get a heads on the first flip or a 
heads on the second flip, you add the probabilities.

The probability of two things happening is the multiplication of the two 
*probabilities*, because you know the things happened.

If you measure the likelihood of the particle going from the emitter to the 
screen without checking which slit it went through, the probability is the 
absolute value of the sum of all the ways it could get there.

If you check which slit it went through, it's the probability that it got 
there by going through the first slit plus the probability that it got there 
by going thru the second slit. (Since it never goes through both, you don't 
have to subtract out that possibility like you do with flipping coins.) The 
probability of it going from the emitter to either one of the slits, or from 
the slit to any point on the screen, you still measure by adding up complex 
amplitudes for each possible path, and not just using probabilities.

Note that when you don't check which slit, you add up a bunch of complex 
numbers, then take the absolute value. When you check which slit, you add up 
a bunch of *real* numbers (one for each possible measurement), each of which 
is the result of adding up a bunch of complex numbers.

That's why doing things in the *future* can affect what you measure *now*, 
which isn't how waves work.

> Is nature trying to confuse
> us to make it look exactly like it was a wave, without it being so?

Not every addition of complex numbers is a wave. Just so, not every 
collection of converging lines is caused by perspective. Having converging 
lines in nature that don't converge to the horizon isn't any more 
"confusion" than complex numbers not caused by waves.  In much the same way, 
I can show you that *those* lines are *not* perspective, because if you 
shift your point of view, they don't converge at the horizon. But if you 
only look at exactly one experiment, namely the two slits with no other 
measurements made, it *look* like perspective/waves, but as soon as you do 
another experiment, it stops looking like that.

-- 
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 <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > Darren New <dne### [at] sanrrcom> wrote:
> >> But seriously, for there to be an interference pattern, something has to 
> >> interfere with something else, right?
> > 
> >   If the photon is a wavefront which traverses from the emitter to the
> > detector, passing throug the slits splits it into two wavefronts, which
> > interfere with each other. When the wavefront collides with the detector,
> > it collapses back into a particle.

> But it doesn't work that way. If you look to see which slit the particle 
> passed through, you find out that it only went through one. You never, ever 
> see it go through both slits.

  But if you observe it going only through one of the slits, the interference
pattern doesn't appear, IIRC.

  Wouldn't that be kind of evidence that when the interference pattern appears,
it did to through both slits? When someone forces it to go through only one of
the slits (by observing it) the interference pattern disappears.

> You basically never see a wave or measure a 
> wave. You always measure a particle, even as the whatever goes through the 
> slits, even *after* the whatever goes through the slits.

  But does the interference pattern remain if the particle is measured?
If it does, then *that* would be indicative that the pattern is not
appearing because the photon behaved like a wave.

> >   I'm not saying that is what happens. I'm just saying it's exactly as
> > plausible as eg. a particle being in many places at the same time or
> > affecting another particle instantly.

> Plausible? Yes. Confirmed by experimental evidence? No. Contradicted by 
> experimental evidence? Yes.

  Contradicted how? "We forced the photon to pass through only one of the
slits and what do you know, the interference pattern disappeared." That
would be confirming evidence, not contradicting one.

> I'm just stating what the guys who study this say. You're trying to tell me 
> it sounds absurd.

  I'm not saying it sounds absurd. I'm saying that the argument of "it's
only one photon, it cannot interfere with itself" all by itself doesn't
convince *me*. I need more.

  Explaining the reason why the interference pattern appears even though
the photon does not behave like a wave would help.

> The probability of it hitting the 
> screen at a given position is the amplitude of it going from the emitter to 
> the left slit to that point on the screen *plus* the probability of it going 
> from the emitter to the right slit to that point on the screen.

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

-- 
                                                          - Warp

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Warp wrote:
>   But if you observe it going only through one of the slits, the interference
> pattern doesn't appear, IIRC.

Correct.

>   Wouldn't that be kind of evidence that when the interference pattern appears,
> it did to through both slits? 

Not really, no.

> When someone forces it to go through only one of
> the slits (by observing it) the interference pattern disappears.

That would only be true if the observation occurs before the particle goes 
through the slits. If it *really* goes through both slits, wouldn't it have 
to do so *before* it gets to the detectors on the screen side of the slits?

The whole "quantum eraser" thing is designed to prove you can measure which 
slit it went through after it has already hit the screen, and you still 
erase the interference pattern.  If the interference pattern was based on 
the particle turning into a wave and going through both slits, that wouldn't 
work.

>> You basically never see a wave or measure a 
>> wave. You always measure a particle, even as the whatever goes through the 
>> slits, even *after* the whatever goes through the slits.
> 
>   But does the interference pattern remain if the particle is measured?

No. The "interference" is caused not by the particle, but by the slits.

> If it does, then *that* would be indicative that the pattern is not
> appearing because the photon behaved like a wave.

Correct. But the pattern goes away even if you measure the path of some 
*other* particle *after* the particle that went thru the slits has already 
been measured. Hence, it's not a property of the particle/wave by itself.

>   Contradicted how? "We forced the photon to pass through only one of the
> slits and what do you know, the interference pattern disappeared." That
> would be confirming evidence, not contradicting one.

Contradicted by the fact that the pattern also disappears if you measure 
which slit some other particle went through *after* the original particle 
has already been measured. In other words, it also disappears if you decide 
whether or not to look which slit it went through *after* it has already 
been detected.

You have your choice of the particle looking at your experimental setup and 
telling itself backwards in time whether to go thru one slit or both, or 
just accepting that the particle never goes through both slits.

What you're doing is saying that the medical screening procedure *causes* 
cancer, because every time you do the blood test and it comes up positive, 
the person has a higher chance of being sick.

>   Explaining the reason why the interference pattern appears even though
> the photon does not behave like a wave would help.

http://vega.org.uk/video/subseries/8

http://www.amazon.com/QED-Strange-Theory-Light-Matter/dp/0691024170

I'm trying to. You get an interference pattern because the probability for a 
particle to go somewhere is based on 2D numbers that when you multiply them 
wind up "interfering" with each other. But there's no wave there.

Watch this, which is Feynman answering exactly your question:

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

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

As I said, "amplitude" is a technical term that means a two-dimensional 
probability. It's not talking about the distance from the trough to the 
crest of a wave. You can replace it with any word you want, but you won't 
understand what quantum mechanics are talking about if you don't know what 
the word means.

-- 
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:
> when the state of the particle is "observed" (whatever that might mean)

Merely that you have done something to it which changes its unknown 
state, usually causing it to make contact with another particle(s), such 
as a detector. In effect, if the particle is on its own, and hasn't hit 
anything, it can be in a lot of places at once. In the case of light, 
"hitting" requires that the thing it hits have optical properties that 
have a high chance of making such a change, which things like air don't. 
But, don't ask me why in that case, other than it maybe involves optical 
properties and perhaps how often it "will" hit the other particles in 
the air itself. lol

-- 
void main () {
   If Schrödingers_cat is alive or version > 98 {
     if version = "Vista" {
       call slow_by_half();
       call DRM_everything();
     }
     call functional_code();
   }
   else
     call crash_windows();
}

<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models, 
3D Content, and 3D Software at DAZ3D!</A>

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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?

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

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

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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.

Post a reply to this message

> 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.

Post a reply to this message

>> 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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