A photon emitter was set to aim through two rectangular slits in a screen, onto photographic paper; a regular interference pattern emerged.
Wanting to know how the light interacted though it, sensors were put to measure how the light went through, but this time the pattern did not emerge, and it was just a nebulous cloud, as if there was no screen at all.
When they turned off the sensors, the pattern emerged again- but the sensors were still physically there.
So, they eventually got the experiment to this: The emitter would only shoot ONE photon at a time, the sensors would measure the light, *then* be recorded by computer, *then* the computer would go through a 50/50 program to decide whether to *erase the data or not*, well after the photons (which traveled at the speed of light, and thus, at the highest limit any information in the universe can travel) were initially measured.
If the data was saved, there was a cloud. IF not, the pattern emerged.
This hints at the strangeness of what must be Quantum Mechanics:
1) A photon can *interfere with ITSELF* to cause a pattern
2) Information in the present can *change the past*
If you want the messy math of this look here
-Schrödinger's Cat: A cat, along with a flask containing a poison and a radioactive source, is placed in a sealed box shielded against environmentally induced quantum decoherence. If an internal Geiger counter detects radiation, the flask is shattered, releasing the poison that kills the cat. The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Yet, when we look in the box, we see the cat either alive or dead, not both alive and dead.
ARRR!
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