Also known as the principle of indifference states, if you have a bunch of theories and don’t have a reason to prefer one of them, then they all get the same prior probability.
1) what is the probability that the trillionth digit of pi is 5? Well, until you do the calculations, the prior probability is 1 in 10.
2) Andy knows his friend Becky will arrive at the City airport between 9:00 and 10:00. Five airlines land between these timings. Airline A and B on terminal 1, C and D on terminal 2 and E on terminal 3. What should Andy do? He can eliminate terminal 3 (the lowest probability of 1/5) and then toss a coin and decide between 1 and 2 (equal prior probabilities of 2/5 each) accordingly.
