Question: what the point of pronbility (sorry about the spelling) i mean it ether is gonna happen or not :/

Tom Hartley answered on 18 Jun 2010:

That is quite a deep question (and a very good one).

I need to be careful here because I often get things wrong. But (here goes) in physics it turns out that nature doesn’t work that way. Things can both happen and not happen, or can happen two different ways at once. When something happens two ways at once, the different happenings interact with one another. Worse still, it seems to matter whether any one is looking or not. I read a lot of books about this, and I think I understand, but it’s better to get it straight from the horses mouth (i.e., a trained physicist).

Funnily, these are often pretty straightforward people who are uncomfortable with spooky things so they get uncomfortable talking about the details and implications of all this (which are very profound in my view). They even get a bit tetchy sometimes, so I’ve learned to keep my curiosity under wraps, but sometimes I lose self control (usually in the pub).

If you want to understand more, a good topics to read about are the “double slit experiment” and “Schroedinger’s Cat”.

We also need probability for more everyday situations. In psychology we use the idea of probability nearly every day to determine whether the results of an experiment are real, or just a fluke (statistics). For example, if you through a coin three times, you might get 3 heads by chance (it’s a probability of 1/8 or 12.5%) but there’s very little chance you’ll get 10 in a row (1/1024 or less than 0.09%) so if you get 10 in a row, it’s almost certainly not a fluke – there’s something wrong with the coin. You can do a similar thing to see whether your results are a fluke (or hopefully, not).

People are very bad at thinking about probability and a good example of this is the Monty Hall problem.

“Suppose you’re on a game show, and you’re given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what’s behind the doors, opens another door, say No. 3, which has a goat. He then says to you, “Do you want to pick door No. 2?” Is it to your advantage to switch your choice?” quoted from Parade magazine in 1990 (via wikipedia).

Most people prefer to keep with there original choice but (amazingly) it is better to change. You can show this mathematically, but even when you understand, it is pretty hard to believe. Read the wiki article for more information, and you might like to try it on someone who doesn’t know the trick (obviously don’t use real goats/cars).