# Entanglement for real?

1. Nov 9, 2007

### Impulse2

Look I know Im a long way from comprehending "entanglement" but could someone help me a bit here. How can we logically say a body is in all possible states until we observe it. Dont we have to observe it to come to that conclusion? And why cant Schrodingers cat be long dead before we open up and look? Of course we can say we don`t know but how can we extend that to say "it could be alive or dead until we look"? Russ

2. Nov 9, 2007

### ZapperZ

Staff Emeritus

Zz.

3. Nov 9, 2007

### cesiumfrog

We have observed qualitative differences between mixtures of states (where we just don't know what state an element is in yet) and superpositions (where, in terms of the measurement, initially each element is not in just any single state).

We've confirmed this for fundamental particles, for molecules and for collections of many atoms. The cat question merely asks, what then do we know about whether it might also be true for bigger, classical, macroscopic objects?

4. Nov 9, 2007

### staf9

I'm not 100% sure if this is the answer you're looking for, but:

Entanglement describes quantum states of a group of objects with relation to each other. In a more direct sense, the quantum states of two objects form an entangled state, meaning their quantum states are not independent of each other.

A really common example of entanglement is in electron spin (up or down). In this example, you pair two electrons into a single quantum state in a way so that when one has spin up and the other one has to have spin down even though you can't really predict the actual set of measurements.

Another example you could probably find on google is when photons split (like when you shine a laser at a prism). When single photon splits to become two protons, their polarizations are always orthogonal to each other.

You do describe superposition there though.

5. Nov 11, 2007