Title: Q & A: Observer Effect? | Department of Physics | University of Illinois at Urbana-Champaign
Headings: 
Q & A: Observer Effect?
Follow-Up #1: quantum
Follow-Up #2: observation and light
Follow-Up #3: measurement and consciousness?
Follow-Up #4: free-will?
Follow-Up #5: confusion between the uncertainty principle and the observer effect
Follow-Up #6: Quantum for the non-scientist
Follow-Up #7: Unconscious observers
Follow-Up #8: Bell's Inequalities and free will
Follow-Up #9: free will and quantum mechanics
Follow-Up #10: what collapses wavefunction?
Follow-Up #11: What causes quantum interference loss

Content: Observer Effect? Learn more physics! Most recent answer: 04/12/2019
Q: the theory of observing changing the observed
- Anonymous (age 55)
seward, mpls
A: In quantum mechanics we learn that the behavior of the very smallest objects (like electrons, for example) is very unlike the behavior of everyday things like baseballs. When we throw a baseball at a wall, we can predict where it will be during its flight, where it will hit the wall, how it will bounce, and what it will do afterward. When we fire an electron at a plate with two closely spaced slits in it, and detect the electron on a screen behind these slits, the behavior of the electron is the same as that of a wave in that it can actually go though both holes at once. This may seem odd, but its true. If we repeat this experiment lots of times with lots of electrons, we see that some positions on the screen will have been hit by many electrons and some will have been hit by none.