can two particles be entangled without having been created together, or ever having been approximate?

sorry for the misuse of the term "approximate" as proximate is what I meant

I believe it is possible to use "quantum teleportation" to transfer the state of one particle of an entangled pair to another, remote, particle which is never in proximity to the particle it is now entangled with: https://en.wikipedia.org/wiki/Quantum_teleportation#Entanglement_swapping (but I haven't fully understood that, yet).

I think the answer is yes, but proximity makes it a lot easier. At the very least it reduces the number of steps required.

can entanglement ever be "incidental", in that with all the particles in the universe,  out of mere chance could entanglement occur between  disparate particles without human intervention ?

Edited January 21, 20205 yr by hoola

11 hours ago, hoola said:

can two particles be entangled without having been created together, or ever having been approximate?

In line with the answers already given: if 2 particles are entangled, then they:

• were entangled themselves, which means at least they were interacting directly in such a way that we only can know the wave function of the two particles together, not for the particles individually ('normal' entanglement)
• or they share a history in which the quantum state of the particles is determined by two particles that were entangled (that would be 'quantum-teleportation')

7 hours ago, hoola said:

can entanglement ever be "incidental", in that with all the particles in the universe,  out of mere chance could entanglement occur between  disparate particles without human intervention ?

See the second point above. If they 'incidentally' share a history based on an entangled pair, then yes. And thereby it does not matter how they got entangled, by human intervention, or just some 'blind physical process'. Otherwise no. 

But do not forget: locally, an observer can never find out that the particle he measures is entangled with another. The entanglement only shows up when two observers compare their measurements of the entangled particles. Then it shows that their measurements are correlated.

if there is an entanglement field (wormholes), caused by random  disparate particles "coasting" in and out of momentary entanglements all over the universe, and this field creates a  constant average scalar pressure, could this be related to or be a component of the gravitational mechanism?

Edited January 21, 20205 yr by hoola

If a pair of entangled photons is created in nature, how does an observer know that he / her is observing a actual pair of entangled photons?  I can understand how we determine that a pair of photons is entangled in the lab, but in nature /space?

If a quantum gravity theory  contains or implies a mechanism for wormhole  structures, then we might be able to ascertain wormhole behavior and how often averaged remote entanglements might occur if the effect is global,  and if the effect is local, variations in G, or rule out such possibilities.

Edited January 22, 20205 yr by hoola

9 hours ago, The Seeker said:

If a pair of entangled photons is created in nature, how does an observer know that he / her is observing a actual pair of entangled photons?  I can understand how we determine that a pair of photons is entangled in the lab, but in nature /space?

I don't know that you can. You need to be able to show correlation between the two particle states. Further, you need the statistics of many such detections to show there is this correlation exists, since e.g. two spins or polarizations are going to be aligned half the time for unpolarized systems. Simply finding two particles with aligned (or anti-aligned) spins/polarizations tells you nothing in and of itself.

 

37 minutes ago, swansont said:

Further, you need the statistics of many such detections

 

I'd like to emphasise this bit.

All to often it is forgotten that probability is defined as a limit as the number of measurement tends to infinity.

[math]{\rm{Probability}} = \mathop {\lim }\limits_{n \to \infty } \left\langle {{\rm{Description of trial}}} \right\rangle [/math]