notes-physics-entanglement

I MADE THIS UP AND I DUNNO IF ITS RIGHT

http://en.wikipedia.org/wiki/EPR_paradox#Description_of_the_paradox

b/c of heisenberg uncertainty, making a measurement always changes a particles state

so lets say that you can measure spin in the horizontal direction, but making that measurement disturbs the spin in the vertical direction

so lets say that a particle can have spin = left or spin = right

and it can have spin=up or spin=down

if you measure horizontally, then the vertical spin gets randomized b/c the measurement disturbs it

and vice versa

so if you have 100 particles and for each of them (1) you measure the horizontal spin, and then (2) you measure the vertical spin

then even if at the beginning they all had the same vertical spin, you will measure about 50% and 50% down, because your horizontal measurement messed up the vertical

ok now: there are ways of producing "entangled" pairs of particles. in this case the entangled pair has opposite spin

so lets say you make two particles,

A and B

and theyre entangled.

so if A is up, then B is down, and if A is left, B is right

now, youre allowed to know if A is up or down, or if it is left or right, but not both at the same time, as described above

but if you measure Bs vertical spin, then you can deduce As vertical spin, because you already know they are opposite

(knowing for sure that they have opposite spins is all you need for them to be considered "entangled")

so, in order to keep you from knowing too much (<--- anthropomorphization), the universe randomizes As vertical spin if you measure Bs horizontal spin

b/c otherwise you could measure B horizontally, and then measure A vertically, and then youd be able to figure out both the verticle and horizontal spins of both

  so does this mean you can transmit information?

actually entanglement cant be used to transmit information

even though it happens faster than the speed of light

because, if Alice takes particle A, and Bob takes particle B, and they go in separate rooms,

(aside: in order for the particles to be entangled in this way, you cant know either the vertical or horizontal spins at the beginning)

then if Bob measures B horizontally, then yes it effects A, but Alice cant tell because no matter which measurement she makes, shell get 50%

you can only tell if Alice and Bob compare notes later

so an effect is transmitted, but not information

because its like if you flipped a penny and then didnt look at it, and then you had the magic power to make it flip again from any distance

the guy holding the penny couldnt tell when or if u used ur power

so you cant use it to communicate with him

but if you had another penny which initally was guaranteed to have the opposite orientation as his penny

then if you and he got together and compared notes you could see if you had used your magic power or not

and verify that you did, indeed, have a magic power