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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