In the summer of 1935, the physicists Albert Einstein and Erwin Schrödinger engaged in a rich, multifaceted and sometimes fretful correspondence about the implications of the new theory of quantum mechanics.
The focus of their worry was what Schrödinger later dubbed
entanglement: the inability to describe two quantum systems or particles
independently, after they have interacted.
Until his death,
Einstein remained convinced that entanglement showed how quantum
mechanics was incomplete. Schrödinger thought that entanglement was the
defining feature of the new physics, but this didn't mean that he
accepted it lightly. 'I know of course how the hocus pocus works
mathematically,' he wrote to Einstein on 13 July 1935. 'But I do not
like such a theory.' Schrödinger's famous cat, suspended between life
and death, first appeared in these letters, a byproduct of the struggle
to articulate what bothered the pair.
The problem is that
entanglement violates how the world ought to work. Information can't
travel faster than the speed of light, for one. But in a 1935 paper,
Einstein and his co-authors showed how entanglement leads to what's now
called quantum nonlocality, the eerie link that appears to exist
between entangled particles. If two quantum systems meet and then
separate, even across a distance of thousands of lightyears, it becomes
impossible to measure the features of one system (such as its position,
momentum and polarity) without instantly steering the other into a
corresponding state.
Up to today, most experiments have tested
entanglement over spatial gaps. The assumption is that the 'nonlocal'
part of quantum nonlocality refers to the entanglement of properties
across space. But what if entanglement also occurs across time? Is there such a thing as temporal nonlocality?...<<<Read More>>>....
