# probability

##### Junior Member
but if it's not possible then how it has probability?! I mean we could have probability but in total we have zero .. ?!

#### tkhunny

##### Moderator
Staff member
but if it's not possible then how it has probability?! I mean we could have probability but in total we have zero .. ?!
I think you did nor understand my second comment.

If it isn't possible, the probability is zero and it should not be included in your distribution.

Example:

1) What is the universe of possibilities resulting from you sneezing?

2) What is the probability of a cow jumping over the moon because it is frightened by your sneeze?

3) You didn't include cows jumping over the moon in your first answer, did you?

#### Ryan\$

##### Junior Member
No you didn't understand me !
lets assume this example: the probability of people in area x is 1/2 but "sometimes" when we want to calculate how many people on that area then we would get "zero" people ! however the probability of getting people to that area is 1/2 ..so how is that logically ..the physical amount of people in that area is zero however the probability to get one of the people on that area is 1/2 ? doesn't that mean if I have probability then ofcourse I would get amount on what probability denote ?! something new to me

#### topsquark

##### Full Member
No you didn't understand me !
lets assume this example: the probability of people in area x is 1/2 but "sometimes" when we want to calculate how many people on that area then we would get "zero" people ! however the probability of getting people to that area is 1/2 ..so how is that logically ..the physical amount of people in that area is zero however the probability to get one of the people on that area is 1/2 ? doesn't that mean if I have probability then ofcourse I would get amount on what probability denote ?! something new to me
I see what you are saying but it would be best if you could give an actual problem as an example rather than explaining what's wrong with it. For example, in Quantum Mechanics a "plane wave" can be a solution to the Schrodinger equation but the probability of a particle being at any particular point is zero for this solution. There's a way to explain this one (the Heisenberg Uncertainty Principle) so it is possible to do (but very arcane as far as the Mathematics are concerned.) It may be that there is a way to explain how it could happen but we can't say that until a specific question is raised.

-Dan

#### tkhunny

##### Moderator
Staff member
* One Person
* Two Rooms
* The individual moves from one room to the other on whatever schedule allows us to assume that...
* The probability of being in either room is 1/2.

If the person is found in one room, are you truly disturbed that he/she is not in the other room?

You need a complete probability distribution. If you talk about only half of it, it never will make any sense.