Warp wrote:
>   So why does it interfere with itself when there are two slits but not
> when there is only one?

I don't know, offhand.  That's actually one of the burning questions of 
quantum physics.  Are you saying you've figured it out? :-)

Incidentally, it doesn't interfere with itself - I misspoke. It 
interferes with other electrons. Sure, they only go through one at a 
time. What was that about time travel?

>   However, when there are two slits, the electron passes through and starts
> interfering with itself, as if it has passed through both and changed
> direction in different ways.

How do you know?  Every time you measure whether it went through both 
slits, the answer is "no, there was only one electron." You keep 
asserting this, with no evidence other than "I can't think of any other 
explanation", along with rejecting both evidence and other explanations.

>   How else can this be explained? How does the electron "know" that there's
> another slit so that it "knows" to start interfering with itself, other than
> actually going through the other slit as well?

Your intuition is confusing you. How does it "know" there's a back 
surface to the glass and therefore needs to reflect differently? How 
does it "know" there's another electron already "on the way" to where 
it's going and hence that position needs to be avoided?

Why is it a wave going through both slits but a particle by the time it 
gets to the detector?

>   (I believe this has something to do with wave-particle duality: In the
> double-slit experiment the wave nature of the electron shows up: The wave
> goes through both slits and starts interfering with itself.)

That's the older explanation from when physicists thought like you're 
thinking, yes. The math works like a wave function, so people thought it 
was a wave. It's not.

>>>   So you are saying that, even though the only possible explanation for
>>> interference patterns is that the electron passed through both slits,
>>> there's still no evidence of that?
> 
>> Yes. What makes you think that the only *possible* explanation is that 
>> the electron passed through both slits?
> 
>   What is the other explanation?

I don't know, and as far as I understand, nobody else does either. But 
all of the evidence so far suggests your interpretation is incorrect.

For example, if you do the same thing with photons, wait for them to go 
thru the slits, and after they've already passed through, you either 
turn on or off the detector that says which slit they went through, you 
always see them only go through one slit when the detector is on, and 
always generate interference probabilities when the detector is off. How 
do you explain that?

>   The interference can be explained with the electron passing through both
> slits at the same time.

Yes. But that's also at odds with many other experiments. If the 
electron goes through both slits, why is it that you never see it go 
through both slits when you put a detector behind each slit? It's one 
possible explanation with reams of experimental evidence against it.

The sun rising can be explained by angels pushing it along, as well, but 
that too is at odds with many other experiments. "I can't think of a 
better explanation" isn't the same as "the one I thought of must be 
true", *particularly* when evidence from other measurements is 
consistently at odds with one's explanation. (True regardless who "I" is 
in there.)

-- 
   Darren New / San Diego, CA, USA (PST)
     "That's pretty. Where's that?"
          "It's the Age of Channelwood."
     "We should go there on vacation some time."

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