Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Warp wrote:
>>> Darren New <dne### [at] sanrrcom> wrote:
>>>> Incidentally, it doesn't interfere with itself - I misspoke. It 
>>>> interferes with other electrons.
>>>   What other electrons?
> 
>> The other electrons in the experiment. You don't get an interference 
>> pattern from a single electron - that's exactly why people say electrons 
>> are particles. You get an interference pattern when you average the 
>> probability of many electrons.
> 
>   But the electrons are shot one at a time.

So?

> They do not interfere with each other. 

How do you know?

> (And don't start talking about the time-travelling nonsense
> again. That makes a million times less sense than the electron going
> through both slits at the same time.)

OK. So explain http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser



> 
>>>> Sure, they only go through one at a 
>>>> time. What was that about time travel?
>>>   The electron somehow magically knows that in the future more electrons
>>> will be there and act accordingly?
> 
>> I don't know. Nobody knows. Except, apparently, you. :-)
> 
>   If you don't know, why are you even suggesting it?

What do you think I'm suggesting?

> It's absolutely
> nonsensical. The electron passing through both slits (as a wave phenomenon)
> at least makes a little bit of sense if you have read even a tiny bit about
> quantum phenomena, even if it defies sense at the everyday macroscopic
> level.

OK. So explain how the electron decides, after it hits the screen, 
whether to have gone through one slit or both slits?  Certainly if 
you're sure it's going through both slits, and time travel is nonsense, 
explain how it can change its behavior based on something you change 
after it has already been detected at the counter.

>>> 1) The electron passes through both slits at the same time, interferes
>>>    with itself, and thus acts according to a logical mathematical formula.
> 
>> And yet, somehow, whenever you look, it only goes through one slit at a 
>> time. How does it know?
> 
>   How can you "look" without interfering with the electron?

http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

 > Is there any
> way of measuring the location of the electron without exerting some kind
> of force or energy on it?

http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

>   A wave which suddenly behaves like a particle when it's measured may
> make little sense, but at least it makes more sense than time-travelling
> electrons.

How about a particle that either "behaves like a wave" or "behaves like 
  a particle" depending on how you turn devices in the experiment after 
you've already measured whether it behaved like a wave or a particle?

>>>   From these two you want me to choose number 2. 
> 
>> Given the choice between a theory that has copious experimental evidence 
>> against it, and saying "we don't have a good theory", yes, picking "we 
>> don't have a good theory" is better.
> 
>   You and your mythical "copious experimental evidence". 

What makes you think it's mythical?  Do you really think physicists all 
over the world haven't thought of these questions and tried to answer 
them? That they went "Oh, it's both, depending on whether you look. Gee."

Note that it behaves as a particle if you *measure* it as a particle, 
*after* it has already gone through one slit or two.

I don't see how you can say both "time travel is impossible" and "it 
obviously has to go through both slits" and "it only goes through one 
slit if you look at it after it went thru the slits". Your combinations 
of incredulity seem contradictory.

 > The only evidence
> which you have mentioned is that when the electron is measured, it behaves
> like a particle (without even specifying how you can measure it without
> affecting its properties).

So, because I didn't spoon-feed you all the thousands of experiments 
people have done, including those easy enough to do in high school, that 
contradict your position, and you didn't bother to look at anything on 
the web to see, then all those experiments and their results must be 
mythical?

Sounds like "hey, it didn't crash for me. Must not really be a bug."

>   It's a bit like someone saying "a car can travel even faster than
> 100 km/h" and then someone going to a parking lot and saying "no, that's
> not true, look at all these dozens of cars which are not even moving!"
> He has "copious evidence" against the claim, yes.

That's not how the experiments are done, tho. You're doing a great 
disservice to scientists if you think they're too stupid to *try* to set 
up an experiment where cars go faster than 100km/h.

Did someone say "hey, I can't measure the speed of light with a 
stopwatch. Hence, it must be infinte"?

>>> but things like time travel are completely believable
>>> and understandable.
> 
>> Checked to 15 decimal places or so.
> 
>   Using hypothetical particles with no experimental evidence whatsoever
> of their existence?

No. Using electrons and photons.

News flash: Light doesn't always travel at the speed of light, either.

>>> Your reasoning doesn't make too much sense to me.
> 
>> Common sense doesn't really apply to quantum electrodynamics.
> 
>   Yet you are sure that the electron may be travelling in time, but it
> certainly does not go through both slits at the same time.

Yes, because that's the experimental evidence that actually comes out 
when you do the experiments.

>>>>  Every time you measure whether it went through both 
>>>> slits, the answer is "no, there was only one electron."
>>>   Of course there was only one electron. And yes, measuring messes up
>>> the electron. So what?
> 
>> If every time you measure whether it went through both slits, the answer 
>> is "no", why do you think it ever goes through both slits? Even if you 
>> measure after it has already passed through the slits?
> 
>   Because it's a possible explanation for the interference pattern.

But there are other possible explanations, and yours has evidence 
against. Again, fairies pushing cars could be the explanation for their 
movement. But every time you look for fairies, you fail to find them. 
How is your assertion any different?

> It may just be that when you measure it, you affect the electron and
> it stops behaving like a wave.

It doesn't *stop* behaving like a wave. It *didn't* go through both 
slits. You put the detector *after* the slits. You *never* see it go 
through both when the detector is there.

How, without time travel, does the electron know it's going to hit a 
detector after it has been through both slits? How does it know this, 
even when the device that decides whether or not to turn on the detector 
does so after the electron has gone through the slits?

> Why? I don't know. But it sounds less
> nonsensical than time-travelling electrons.

Explain delayed-choice quantum erasure, then, without sounding nonsensical.

>> Quantum physics isn't intuitive. But you don't get to throw out 
>> experimental evidence just because you can't figure out *why* you get 
>> those results.
> 
>   Who is throwing out experimental evidence?

You.

>   I'm just saying that having a million cars that don't move doesn't
> necessarily mean that cars can't move.

And having a million cars without fairies in the back seat doesn't mean 
there aren't any. Yet, absence of evidence *is* evidence of absence. 
That's fundamental probability theory.

>> How do you explain electrons going through both slits if, after it goes 
>> through the slits, you measure which slit it went through, and you 
>> always get the answer "only one"?
> 
>   How many times do I have to repeat this?

Until you actually answer the question I'm asking. The fact that 
measuring which slit the electron went through *after* it has passed the 
slits shouldn't affect whether it goes through one slit or both slits, 
unless you're also willing to accept time travel, which you aren't.

I'm trying to get you to explain *why* the electron "goes through two 
slits" when you don't look for it and "goes through one slit" when you 
do look for it. The fact the interference disappears when you *see* it 
only went through one slit is irrelevant to that question. It's a 
result, not a cause.

>>>> 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?
>>>   What another electron? I don't understand.
> 
>> Electrons don't interfere with or cancel themselves out.
> 
>   You act inconsistently. Sometimes you are all like "nobody knows,
> quantum mechanics defies all sense, how can you be so sure?", and other
> times you write absolutes as if you had perfect knowledge on the subject.

I didn't say it defies all sense. I said it defies common sense, which 
is what you're trying to apply. I know electrons don't interfere with 
themselves because I can do experiments showing interference patterns 
without losing electrons.

The electrons go different places based on whether you know where 
they've been or not. That doesn't make them waves.

>>>> Why is it a wave going through both slits but a particle by the time it 
>>>> gets to the detector?
>>>   Why do quanta behave both like waves and particles? I don't know.
>>> It just seems they do.
> 
>> Then why is it so hard to believe that's true even without it going thru 
>> both slits?
> 
>   The wave going through both slits explains the interference pattern.
> The wave going through one slit doesn't.

But it *does*. That's what you're missing.

OK, so what's an electron waving, if it's a wave? You use the term 
"wave" like it's well-defined.

>> How do you know it went thru both slits? Every time you ask, it only 
>> goes through one slit. You're saying "the only way you can have an 
>> interference pattern is for every electron to go through both slits." 
>> That's an invalid inference.
> 
>   And you are saying "every time you measure the electron, it's going
> through only one of the slits, and the interference disappears, thus
> the only explanation for this is that the interference pattern is not
> caused by the electron going through both slits". I don't see that as
> any more valid of an inference.

You're conflating cause and effect.

>   On the contrary, the fact that the interference pattern *disappears*
> when you mess up with the electron (in other words, when you *make* it
> go through one slit,

How am I making it go through one slit? I'm measuring it *after* it goes 
through the slit.

> it starts behaving like it's going through only
> one slit) seems like a stronger evidence that it indeed is going through
> both slits when it's not messed up with.

How does something on the far side of the slit, in the future, affect 
whether the electron went through one slit or both?  How does measuring 
a second electron *after* the first has already been detected at the 
screen affect whether the first electron went through one slit or both?

>   I have never said it's the only *possible* explanation. I have said that
> it's the only *existing* explanation. There's a categorical difference.

Except that it doesn't explain anything, because you've added in time 
travel.

>>>   I don't know why measuring quanta messes up with their behavior.
> 
>> So do you believe in time travel or not? Because clearly the decision as 
>> to whether the electron went thru one slit or both is traveling back in 
>> time in this experiment, *if* that's what's happening.
> 
>   Yeah, that's the only *possible* explanation, sure.

http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

Explain this otherwise.

>>>>>   The interference can be explained with the electron passing through both
>>>>> slits at the same time.
>>>> Yes.
>>>   First you say that *all* evidence suggests that the claim is incorrect,
>>> and now you admit that at least one piece of evidence doesn't.
> 
>> No. The interference can also be "explained" by God screwing with our 
>> heads, by intelligent electrons trying to confuse you, or by magic fairy 
>> dust. None of those are correct either.
> 
>   Please don't start making straw mans. You are trying to make the
> explanation sound ridiculous by comparing it to other ridiculous
> "explanations".

"The particle knows when it gets to the screen whether in the future 
you're going to measure whether it went through both slits or only one, 
and if you're going to measure, decides to only go through one."

Not sure how to make that sound less ridiculous. Help me out?

>>>> 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?
>>>   I don't know why measuring quanta messes up with their behavior.
> 
>> But you *do* know that they go through both slits. Interesting.
> 
>   And you *do* know that they don't. Interesting.

Yeah, cool, isn't it?

>> How come it's reasonable that time isn't comparable everywhere, but that 
>> subatomic particles can't travel in time?
> 
>   Time going at different speeds at different locations is not the same
> thing as time-travelling.

http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

And Event A happens before Event B *and* Event B happens before Event A, 
depending on where you happen to be standing? That "reasonable" and 
"common sense"?

-- 
   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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