Quantum Physics questions (related to Heisenberg)

I’m reading Schrodinger’s Kittens and the search for Reality by John Gribbin. In his prologue, he speaks of a problem titled “the daughters of Schrodinger’s Cat.”

Here’s the general gist of the problem (quotes directly taken from the book with some skippage): “Imagine two kittens, each living in a space capsule linked by a narrow tube. In the middle of the tube there is a box which has an automated sliding partition across its middle which contains - you guessed! - a single electron. Each of the two space capsules contains the usual diabolical device which will kill its respective cat if an electron emerges from the tunnel into the capsul. Remember that as long as nobody looks the elctron’s probability wave fills the box uniformly. When the sliding partition in the middle of the box divides it into two halves, there is a 50 percent probability that the electron is on one side of the particion and a 50 percent probability that it is on the other side. So when the two ends of the box slide away, the probability wave will spread out into each capsule evenly.
Now, with the two capsules separated, automatic rockets can fire to propel the two craft in opposite directions through space… Eventually, one of them reaches a distant planet where there are conscious observers. Curious to find out what is inside the capsule, the intelligent observers open the hatch and take a peek. At that moment, the wave function collapses. It ‘decides’ whether or not the oridinal electron entered the capsule that is being studied. If it did, the cat dies, orrather, once the observation has been made, the cat was dead all the time. Alternatively, the aliens may open the capsule to find a live cat In which case, their act of observation has consigned the other cat to its fate.”

OK, so here’s my problem. This doesn’t to me seem to be Heisenberg’s uncertainty principle in effect. Like in the original single cat problem, we’re to believe that the act of observation creates the reality of the situation. That without observation, the cat can be both dead and alive at the same time.
But what’s being shown in both is a simple probability problem. There’s a 50% chance of the cat (or cat A) being alive and a 50% chance of the cat (or cat A) being dead. That we don’t know which is which shouldn’t influence the result.

Imagine you walk into a room and there’s a playing card facedown on the table with a note that says “guess which card.”
In a fair deck, there’s a 1/52 chance of it being any particular card. But we don’t say that it’s every card simultaenously. Picking up the card and looking at it doesn’t change its reality. Though there’s no possible way to prove it, the card it is what it was before we picked it up.

I guess this long ass OP boils down to this: We hypothesize that observing quantum particles collapses their functions down to a single reality. Also, there’s no way to observe something before it’s being observed. So how do we know? How do we prove this? Why do we say that sometihng is both X and Y simultaneously rather than that there’s a 50% of X occurring upon observation and a 50% chance of Y occuring?

The dual slit experiment is one reason.

Take a metal plate and cut two narrow slits in it. Shine a beam of light at the plate and observe the image that forms on the screen beyond. What you’ll see is a pattern of bright and dark bands. The bright bands are where a peak of the light wave from one slit coincided with a peak of the light wave from the other slit and they reinforced each other. The dark bands are where a peak met a valley and they cancelled each other out.

Now lets turn the light down so it’s very, very dim. We replace the screen with a bit of photographic film and let the experiment run for hours until the film is sufficiently exposed. Not surprisingly, when we develop the film we see the same pattern of bright and dark bands.

What if we make the light so dim that only one photon is generated at a time? Of the photons that make it to the film, 50% must have passed through the upper slit and 50% through the lower slit, right? And since each photon is passing through either one slit or the other, there’s nothing for it to interact with to produce an interference pattern. When we develop the film we shouldn’t see any bands.

But even with single photons, the banding still appears. The photons must be passing through BOTH slits simultaneously and interfering with themselves!:eek:

This is an example of quantum entanglement. We already have an active thread going on the topic; you might want to read through that and go from there. For now, though, I’ll say that the kitten example you mention isn’t a very useful way of examing the concepts involved, and that it’s much cleaner for something like electron spin or photon polarization that can be measured in multiple directions.

Every time you perform a quantum entanglement experiment, God both does and doesn’t kill a kitten at the same time.

Though I don’t quite understand that light can be both a wave and a particle simultaneously, I do accept the fact that it is. Gribbin even mentioned this type of scenario a few pages earlier than what I wrote in my OP. But what he failed to mention was the observation involved. We don’t “see” the single photon emitting from the light source, or travelling along its path, do we? We merely record its effect upon the sheet at the end.

So imagine the same scenario, but we can either slow the photon down by some means or have a suuuuuper high speed camera to capture the merry path of the photon as it jaunts along its journey. Now what happens?
Shouldn’t the very act of observing it collapse the photon into a single state of being? I can’t imagine that recording the photon as it travells along a path through one (or both) of the two slits would ruin the ultimate outcome.

Yep. If you create a situation where you can tell which slit the photon went through, then the photon only goes through one slit.

If you do this–and you can do a similar experiment with electrons–there will be no interference pattern. You will get two dots on the photographic paper, where the particle definitely went through one slit or the other.

It is entirely possible to design an experiment where one can observe the photon AFTER it has passed the slit. When it is observed, no bands, when it isn’t observed bands. Note that the observation occurred after the photon passed through the slit so the observation caused something to ‘change’ in the past. Yet another example of spookyness of QM.

I am totally unqualified to explain Quantum theory. But one thing I that helps me is to change the language a bit: instead of the phrase “concious observers”, talk about “interactions”. Often, discussions about quantum stuff get a little heavy on the use of eastern-style philosphy, using terms like “holistic” and “anthropic principle”, as if there is some great all-seeing Observer (“the mind of God”) involved.

So instead of saying that quantum rules allow for something to be in two different places at the same time until a ‘concious observer’ looks at it, you can rephrase the rule like this:
something can be in two places at the same time until it interacts with something else.
The ‘something else’ can be a human being observing, or it can be another photon that bumps into it. Once something touches the photon, the photon somehow decides to become a regular object, not a probablilty wave .

It still boggles the mind and makes no sense. But at least it helps me feel a little less weirded out :slight_smile:

For example, here’s how I try to understand the quantum computer:
So far, they have succeeded in making a computer that can contain only 4 (?) quantum bits (enough to instantaneously calculate that 5*3 equals 15. ) But they haven’t succeeded in adding more bits to produce useful larger numbers. Apparently, as you pack more bits together in a crowded space,the bits start to interact with themselves (not necessarly a conscious human observer), and the stop being quantumly weird , and just become normal objects.

(I doubt if I’m being scientifically accurate here, but I’m just trying to explain how I it helps me to use simpler language instead of relying on ‘concious observers’. I can sort of grasp the idea of weird objects that bump into each other and stop being weird. I cannot get my head around the idea of something that doesn’t exist until a human being looks at it)