2/17/16

1. Dentist appt early! Finally got my front teeth cosmetically repaired.
2. Hung out in the SPS for a while talking to people during the Regionals prep meeting time--the meeting never materialized. But what did materialize: the Theory club! This super eloquent prof Chris Talloway gave an explanation of the EPR (Einstein-Podolsky-Rosen) objections to quantum mechanics and gave us some reading material whilst we showered him with questions. The core issue, in a nutshell (go read the paper):
1. 2 entangled particles separated by large distance
2. By measuring momentum of one, can predict with certainty momentum of the other, without disturbing the other (the particles are "causally disconnected" by speed-of-light); that is, momentum of the other is an "element of physical reality", something real.
3. by measuring position of one, we can predict the position of the other, so position is also "something real" that we can predict with 100% certainty before we actually measure it.
4. However, after measuring the momentum of the "other", no experiment can give you the position of the "other" without affecting the "other"'s state, since we can't know the momentum and the position of the 'other" simultaneously in QM.
5. So QM does not allow us to predict two seemingly equally "real" physical quantities at once. 
6. Einstein objected to this, saying that QM, by failing to predict a "predictable" physical quantity, was incomplete. There must be "hidden variables" that QM was not taking into account.
7. However, and here's what takes this out of the realm of pure philosophy into crazy thought-experiment science: taking Einstein's arguments to their logical conclusions results in predictions about the correlations between different measurements, that have been tested and falsified. So there are no "local hidden variables". See Bell's Thm, Bell's Inequalities :D
8. All this led to a useful definition of a physical theory as an (implicit) giant table of correlations between all possible measurements, which has led to fruitful theoretical endeavors.
3. After Theory, went back to Haggett, talked with Xin for like half an hour while eating an apple. 
4. Then went to Swing! Again, super fun, although I got lost on the last move, the relatively complex but fundamental "swing-out"
5. Went back, worked on math
6. Ate dinner with Brandon, talked about housing. Good long discussion.
7. Filled out housing application, even though I'm thinking about dorming, sent all the applications I'd collected to Brandon. My new printer scanner works great.
8. Got to get to sleep now--one more cleaning appointment tomorrow. Cheers!