# Is this a good definition of entanglement

1. Feb 18, 2013

### g.lemaitre

I don't like the way Wiki describes entanglement. Here is my own definition. Tell me if it is in essence correct. If I have left out an important detail please let me know

objects are entangled if and only if by changing the property of one object one instantaneously changes the property of another object. Objects need not be next to each other in space.

Last edited: Feb 18, 2013
2. Feb 18, 2013

### g.lemaitre

I guess I should add that by observing something you become entangled with it.

3. Feb 18, 2013

### Staff: Mentor

"Changing the property of an object" is just asking for trouble; that wording implies that the property had a pre-existing value that was changed by the act of measurement.

"By changing... one instantaneously changes..." suggests that there's some causality at work, and that's also going to get you in trouble in a number of ways.

But with that said, I have to admit that I share your distaste for the wikipedia non-definition. How about:
That's still not right, because it suggests that we have separate objects that we've somehow tied together, instead of a single quantum system that happens to be measured at different locations.... But this defect may be inherent in the "entanglement" metaphor; you can't speak of entangling A and B without suggesting that they're "really" independent entities, and the entanglement is something that happened to them, like fish swimming into a net.

4. Feb 18, 2013

### g.lemaitre

How about this definition. You seem to think that object A and B are the same object if they are entangled. For the moment, we'll stick with just the objects electrons. We know what it means when we say two electrons.

Two electrons are entangled iff by setting the properties of one you set the properties of the other. By measuring an electron you become entangled with it.

Also, how accurate is it to say that everything in the universe is entangled. After all, the properties of the objects in the universe are affected by temperature and temperature is set by a collection of objects, their mean kinetic energy. An object can only be affected by another object if it is entangled with it.