A definition of infinity?

The problem isn`t the observer per se, but the means for observing. in order to observe the electron, you would have to shine some light on it. The act of shining that light changes the behaviour of the electron and distroys the interference pattern. That turns out to be a general principle. No matter what you do, you cannot at the same time know which slit the electron went through, and still get the interference pattern. It`s just not possible.But note that the interference pattern will still be distroyed even if you turn off the observing device but keep the lights on. You don`t really need to have a concious observer taking notes of which slit the electrons went through.

I'll quote myself

quote:

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No matter what you do, you cannot at the same time know which slit the electron went through, and still get the interference pattern. It`s just not possible.

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It's a consequence of the uncertainty principle. In the first experiment, (Without the observer) the position of the electron is uncertain (We don't know which slit the electron went through). that allows for a less uncertain momentum which is the same as a more shaply defined wave-length (By the de Broglie's relation p=h/lambda). This shaply defined wave-length leads to the observed interference pattern.In the second experiment the position of the electron becomes more determined and, by the uncertainty principle, its wave-length becomes blured (more uncertain) destroying the interference pattern. I don't think so. the validity of quantum mechanics (QM for short) has been confirmed by a huge range of experiments to the point that it is not unreasonable to consider it incontrovertable.