Quantum Enstranglement

[cooperdxx]

Hi, I ran into a problem with understanding some strange quantum physics stuff I know someone will know. When dealing with entanglement, if system A is spinning up then system B approaches 100% probability of spinning down without nessecarily being observed, and that contradicts my understanding of shroedingers observable reality in that system B does not have deterministic properties unless it is being observed, right? Therefore, how can it have any probability of spinning down if it has no deterministic properties in its unobserved state but is ultimately entangled? In addition, how would we know that it's entangled if we don't observe it? And doesn't this kind of smack of ethos physics if the entire universe is entangled on a level beyond the speed of light appearently or maybe? I'm so lost please help smart people.

 

[f95toli]

Do you have a link?

I am not sure I understand what you are asking but there are obviously cases when you know that system b has spin up with probability 1, but then can only happen if you have already measured system A and measured spin down (conservation of spin, the total spin must to be zero if e.g. a spin 0 particle decays).
However, this does not work if you have an entangled system because a measurment will always destroy entanglement
I.e. once you know the state of system A or B the total system is not entangled anymore and loses its "quantum properties" (interference etc)

This is MUCH easier to understand once you know bra-ket algebra.

 

[AdamNuhfer]

Theres a couple links in the other thread about quantum physics you might like.

f95toli: would it destroy it if we were to observe it at absolute zero? Since we can't achieve absolute zero, yet. {they have come very close} I don't believe anyone has factored this in as another realm of what if. Help me out if you would, I can't think of the guys name that put the theory forth about how matter will/would behave at absolute zero. That's what happens as you get older, your mind starts to go.

 

[f95toli]

Yes, it would.
In most cases these experiments are done in situations where temperature does not play any role (quantum optics). You can include temperature in the theory but it is pretty tricky and does not really change situation much (it is much easier to calculate things assuming 0K then to actually take temperature into account).