In 1803, Thomas Young sent a beam of light through an opaque plate with two slits in it. Instead of seeing the expected two lines on the viewing screen, he saw several lines, as if two waves of light from the two slits had been interfering (overlapping) with each other. Over the 20th and 21st centuries, it has been proven that not only light, but also individual elementary particles and even some molecules behave as waves – as if they were going through both slits at the same time.
However, if you place a sensor at the slits that observes what exactly happens to the particle at that point, and which slit it finally ends up going through, then only two lines will appear on the projection screen, as if the fact of observation (indirect influence) collapses the wave function and the experiment subject behaves as a particle.
The 10 weirdest quantum physics facts
1. Wave function collapse
2. Heisenberg uncertainty principle
3. Meissner effect
5. Quantum tunneling
6. Quantum entanglement
7. Quantum Zeno effect
8. Delayed choice quantum eraser
9. Quantum superposition
10. Quantum Cheshire Cat
The Phase. Shattering the Illusion of Reality
by Michael Raduga