Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Warp wrote:
>>> Darren New <dne### [at] sanrrcom> wrote:
>>>>>   But it seems that everybody knows that it does not happen by the photon
>>>>> going through both slits?
>>>> Correct.  Or, rather, nobody has ever measured anything that would imply the 
>>>> photon goes through both slits as a wave.
>>>   The interference pattern in the detector is not a measurement?
> 
>> No. It's a bunch of individual measurements of different photons. There's no 
>> way to look at *one* photon and decide whether there was one slit or two. 
>> Because it's not a wave, it's a particle, so it always makes the same sort 
>> of single-spot quantum event in a single place.
> 
>   That's like saying that you can't measure the probability of a coin
> giving heads because you can only toss one coin at a time.

No. It's like saying a coin doesn't land half-heads-half-tails. You can 
certainly measure the *probability* of a photon hitting in a particular 
place. That doesn't mean the photon is or ever was a wave.

>   I'd say tossing 100 coins one after another is exactly as valid as if you
> had tossed one coin 100 times simultaneously (if that was physically possible).

Yes. And even tho you get about half heads and about half tails, not a 
single one of those coins wound up with half the heads showing or half the 
tails showing. They were all either 100% heads or 100% tails, when you look 
at each one individually.

Similarly, each photon is a particle, and it never goes through both slits, 
just like a coin never lands 50% heads and 50% tails.

>>>   But I thought that's the whole idea in the Copenhagen interpretation:
>>> Particles are in superpositions until they are measured, in which case
>>> they collapse into a definite state. Thus when you measure a photon, you
>>> will always find a collapsed photon.
> 
>> If every time one measures something, one gets "it isn't a wave", then why 
>> would one think it's ever a wave?
> 
>   Because of the interference pattern?

There's one set of measurements that give the same probabilities as if the 
photons were propagating as waves. But there's also other ways to explain 
the interference pattern (mathematically speaking) that has the same 
arithmetic but a different interpretation. This different interpretation is 
consistent with *all* the measurements.

It's like looking up at the sky and saying "The sun goes around the earth, 
obviously."  But yes, maybe the earth goes around the sun, and you'd get the 
same appearance as the sun, but if you look at other *planets* you can tell 
they're all going around the sun.

>   If it behaves like a wave, what can we deduce from that?

If you flip 1000 coins, and it comes up 500 heads and 500 tails, can we 
deduce that each flip landed half heads half tails?

>   It's an argument that measurement doesn't necessarily tell what was the
> state before the measurement was performed.

But *no* measurement *ever* detects waves. They only detect distributions of 
particles that match the mathematics of complex numbers. Waves also match 
the mathematics of complex numbers. But not everything that matches the 
mathematics of complex numbers is a wave.

>> Yes. But if a photon was a wave, it could interfere with *itself*. It could 
>> split up and go through two separate slits. One photon doesn't make an 
>> interference pattern, and that's how you know the photon isn't a wave.
> 
>   That just doesn't convince me. Just because the photon collapses when it
> hits the detector doesn't mean that on the way it didn't pass through both
> slits at the same time and interfered with itself.

Well, you're arguing the question that has confused nobel-prize-winning 
physicists. I can only try to explain what I understand them to say. I can't 
really convince you per se.

Nobody can figure out what would cause a "collapse", nobody has math that 
explains when the collapse happens, nobody has ever observed a particle in a 
non-collapsed state.

>   It sounds like you are arguing that particles cannot be in superimposed
> states 

No, I'm saying they aren't waves. What's superimposed isn't a "wave", but 
probabilities. Yes, particles are in superimposed states. That doesn't make 
them waves. Since the states particles can be superimposed and tangled up 
with the states of other particles, and that tangling does *not* act like a 
wave, then it's experimentally determined that superimposed states aren't 
waves either. It only looks like a wave if you look at one of them.

> and that there's no collapse phenomenon when they are measured, but
> instead they are always at single places at a time, in particle form.

That's not what I said. You only ever *measure* them in a single place at a 
single time in particle form. How would you really know what it's doing if 
you never observe it doing it?

There are theoretical reasons to believe it's impossible to observe them 
being waves. (Otherwise, they wouldn't be quantum, for example.) Indeed, the 
whole "black body radiation" question that started quantum physics falls 
down if photons are waves in flight, which is why people stopped thinking 
they were waves in the first place: it was impossible to understand 
something glowing hot if light is waves.

> other words, that the Copenhagen interpretation is wrong. (Of course, if
> I have understood correctly, nobody has proven that it's right, but you
> are seemingly claiming it's wrong. Has that been proven?)

I think people are still debating, but as far as I know, all the really 
smartest people think quantum theory comes in quantums. :-) The whole 
problem with the Copenhagen interpretation is that nobody knows why it would 
collapse, nobody has any math to explain the collapse, and it doesn't give 
you any answer better than you get with "it's never a wave", especially 
without being able to explain why it collapses.

Maybe if someone knew what caused the collapse, or under what circumstances 
it happened, you could test if Copenhagen was valid or not. But it doesn't 
make any predictions the always-a-particle theory makes.

>   (Not that I have the slightest idea what I'm talking about. The problem
> I'm having is that, seemingly, people have no idea why the interference
> pattern appears yet are completely sure it's *not* because photons are
> in wave state at any point.)

They know because when you actually put *two* photons together, they *don't* 
make an interference pattern. If photons were waves, you wouldn't get 
lasers, for example. And they wouldn't interact with electrons in the way 
they do, even when you're not "observing" them.

I may have no idea if you start out in your automobile in your driveway 
where you got to, but I'm pretty sure you didn't drive to Hawai'i. :-)

>> You 
>> don't see half the photon's energy hit here and half hit there with a blank 
>> spot in the middle.
> 
>   You don't see it because if you try to see it, the photon collapses and
> the only thing you see is a particle.

I think it's Occam's Razor here. Why postulate a quantum being a wave if (1) 
no observation is capable of ever seeing it as a wave, (2) it behaves in 
ways contrary to it being a wave when in flight, and (3) everything you *do* 
see can be explained without it ever being a wave?

-- 
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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