What is QM, for that one may refer to various sources available. In this thread I wish to discuss some interesting stuff which appear non intuitive and may provide interesting insight on the subject. To start with.. 1. Consider two objects separately, an electron and the Earth. What are the eigen states of these two quantum particles or systems? 2. What are the wave functions for these two? 3. What all information this wave function will have? 4. What is the difference between observation and measurement? Beyond the obvious, the idea is will they impact the quantum system differently? 5. What is the wave function collapse and will it happen both during observation and measurement? 6. When actually the wave function collapse happens? Say a guy is measuring some parameter of a quantum system and for that he sends a probe signal....so the collapse takes place when the signal is emitted from test device or when it hits the quantum system or when the signal is recorded back by test device after its interaction with the object? 7. How do we claim to know the prior state of system, just before measurement? 8. And if we consider our solar system as quantum system and some aliens in the far universe decide to measure our solar system, so wave function of our solar system will collapse, and assuming that this collapse has some physical impact, then what? 9. On a lighter vein, if I stare (measure) a person, the fellow starts feeling uncomfortable or may confront me or may give some weird reaction.....is it kind of his/her wave function collapse??