NOT SPOOKY ACTION AT A DISTANCE

Quantum mechanics sometimes looks like an assorted mix of weird stuff There's wave-particle duality, superposition, the uncertainity priciple and there is entanglement. Albert Einstiens famously described this as "spooky action at a distance" , when doing something to one of a pair of entangled particles to instantly affect the properties of the other no matter how far away it is.Now,the truth is that none of these descriptions ar not quite right They're all really just efforts to use our everyday language to describe something that is fundamentally different from our everyday experience. That's especially true of entanglement, which is not a spooky action at all.

ENTANGLED PARTICLES

Entanglement is a special connection that can exist between two particles in order to understand it, let's reffer an example which we use just to understand the concept of entanglement.Lets imagine a pair of shoes, one left and one right. We put each shoe in a box and send one box to bob who is in New York and the other to Alice who is in London. Neither of them knows which shoe they have until they open their box. When Alice opens her box and sees a left shoe, she instantly knows that Bob has the right shoe, even though he is far away. This is similar to how entangled particles work. When we measure one particle, we instantly know the state of the other particle, no matter how far apart they are.

EPR

In 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen published a paper that challenged the completeness of quantum mechanics. They proposed a thought experiment, now known as the EPR paradox, to illustrate their concerns. The EPR paradox involves two particles that are entangled in such a way that measuring the state of one particle not only determines its own state but forces the other particle into opposite state instantaneously, regardless of the distance between them. Einstein referred to this phenomenon as "spooky action at a distance," expressing his discomfort with the idea that information could be transmitted faster than the speed of light. Because of this EPR responded that whole idea of properties of quantum objects remaining undetermined until one measures them,didn't make sense. They figured that there must be something-what einstien called hidden variables-that predetermined the results of measurements and fixes the orientation of the spins all along, even if we couldn't see those variables directly they must exist according to EPR.

NIELS BOHR'S RESPONSE

Niels Bohr said there is no hidden variables and that quantum mechanics is complete. He argued that the EPR paradox arises from a misunderstanding of the view of quantum mechanics. Bohr emphasized the importance of the measurement process and the role of the observer in determining the properties of quantum systems. According to Bohr, the act of measurement itself affects the system being measured, and therefore, it is not meaningful to talk about the properties of a quantum system independently of the measurement context.

JOHN STEWART BELL

In 1964, Irish physicist John Stewart Bell figure out how to set up a clever experiment to determine who was right. It involved running the experiment again and again on pairs of entangled particles.

BELL'S INEQUALITY

He conducted an experiment to test the correlations between the measurements of entangled particles. He runs the experiment again and again on pairs of entangled particles. According to Bell's theorem, if local hidden variables were responsible for the correlations observed in entangled particles, then the results of the measurements would satisfy certain statistical inequalities, known as Bell's inequalities. However, if quantum mechanics is correct and there are no hidden variables, then the results would violate these inequalities. Bell proved stronger statistical correlations in the outcomes of these measurements than any hidden variable theory possibly could.

NO EVIDENCE FOR HIDDEN VARIABLES

When Bell's experiment was first done in a lab in the 1970s by physicist John Clauser and Stuart Freedman at the university of California Berkeley, it shows there was no sign of hidden variables, and that indeed, outcomes are determined only by the act of measurement. Since then, many more sophisticated versions of Bell's experiment have been performed, all confirming the same result: there is no evidence for hidden variables, and quantum mechanics accurately describes the behavior of entangled particles.

HOW TO ENTANGLE TWO QUANTUM OBJECTS

The simmplest way to entangle two quantum objects is to create them together in a single event that conserves certain properties, such as energy, momentum, and angular momentum. For example, when a particle decays into two smaller particles, the resulting particles can be entangled. Another way to entangle particles is through interactions, such as when two particles collide or interact with each other in a specific way. Additionally, certain processes in quantum optics, such as spontaneous parametric down-conversion, can generate entangled photon pairs.