After giving up on T.V.
as it just got so bad as to be a waste of time even turning the thing
on, I cancelled my T.V. licence and was forced to resort to reading
books instead.....
I have been reading lots of popular science books and
have found the world of physics really is a fascinating one.
After reading all about quantum physics and of
course all about the classic double slit experiment I decided I needed
to see it for myself.
- for more info see THIS
video or THIS wikipedia page.
Double
slit experiment
BTW - If you want to learn more about this subject, I highly recommend
having a look at
THIS book by Brian Greene - it is by far he best
beginners type book I know of and contains a staggering amount of
information.
I had already tried a couple of times before to do this experiment
but failed
to see any interference
pattern, my problem it turned out was that I had not realised you
need to project it several meters rather than the 30cm or so I had been
doing - Doh! - Once I figured this out it is very easy and I
think it something everyone should give a try as the implications of
this simple experiment are mind blowing......
What to do:
Firstly you need a laser, any laser pointer should do
(you
can get them for a couple of pounds on eBay or even some times from a
local pound shop), put this on
some kind of mount to hold it (a big blob of Blue tack is
good enough), you need to keep it switched on, some
tape over the button will do this.
In front of this you need to place the
slits. To
make the slits place a small piece of tin foil onto a paper pad and with
a ruler and craft knife cut a couple of parallel small slots approx 1mm
apart (they only need to be a few mm long). BTW - Instead of
using slots you can just make a couple of pin pricks if you prefer.
You now need to place this slit in the laser's beam, again some blue
tack or a clothes peg will do the job fine.
Now you need to project the image across the room (if you
try to view it any closer you will not see anything of interest, as I
discovered).
Here are a couple of examples of the sort of image you should see:
The different images are from varying the gap between the 2
slots
Quantum
Eraser
Experiment
The next thing I
wanted to try for my self was a Quantum Eraser Experiment (more info
here). This gets even weirder - you can make a change to the light
after it has left the slits and it still changes the lights mind as
to if it will be a particle or a wave today.
The simple home
experiment I tried involves putting a polarizing filter in front of
the two slots so that light from one slot is horizontally polarised
and the other vertically. Because the photons can now be identified
as to which slot they went through (depending on how they are
polarised) it no longer produces an interference pattern. but, if
you now put a polarizing filter between the slots and projection
screen which is at 45 degrees this has the effect of twisting the
polarization of the light from the slots putting them both to the
same, now that you can no longer identify which photon came from
which slot it returns to producing an interference pattern.
It is a bit fiddly
getting the polarizing filters in front of the two slits. I cut a
small square of filter, cut this into triangles so they could be
rotated relative to each other and blue tacked onto the tin foil
behind the slits.
You then just see a
solid bar instead of an interference pattern (because the information
exists to identify which slit each photon went through) but if you
put a polarizing filter anywhere along the beam it changes to an
interference pattern (because you have destroyed the which slit
information in the photons of light)
Just think about
this though!!! Each photon of light must have left a slot heading
for a certain point on the screen, so this event/decision is now in
the past but by removing the which slit information this has changed
???
THIS
video explains more about this experiment
(although I have not
managed to get it to work myself using a pin)
There are lots of experiments which have been done on this and it gets
even weirder - take a look at
THIS.
