Re: Youngs double slit experiment

gil heron wrote:

>Does that mean the wavefunction determines what the photon can do when
>it reaches the double slit ?

certainly

>Does it mean possibly that the photon wave function is interfering with
>itself at the double slit ?

certainly

>What happens in the double slit experiment when the slits are 20 or 30
>metres apart ?

When the light (presuming it was spatially coherent over the 30 metres)
diffracts at the exit side of the slits, it will need to travel quite a
way before the two diffractions significantly interfere with eachother,
thus the intensity will be very low. This can be remedied by having a
high power beam on the impinging side, and waiting a long time with
single-photon detectors on the far side to collect a good quality
signal.

Secondly, the interference fringes will wash out at some stage. With
wider separation, the fringes get closer together, and when the spacing
is of the order of the slit width or the wavelength, then you will lose
the "visibility" of the fringe. If you had really really narrow slits,
really very close to monochromatic light, really high power beam, and
removed the detecting screen way back, then I don't know of any
priniciple that says the fringes should not be seen. But due to the
finite slit widths, non-monochromatic light, etc, the fringes wash out
at some stage.

I don't know which thread you are quoting, but there is no upper limit
to the "width" of a photon, a photon with wavelength 500 nm could in
principle have a "width" tens of metres across.

br

.

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