A Quantum Arrow of Time

Is quantum mechanics messing with your memory? For all we know we may live in a world in which windows un-break and cold cups of coffee spontaneously heat up, we just don’t remember. The explanation is quantum entanglement.

A physicist has claimed that glass can un-break – but quantum entanglement prevents our brains from recording the event.

Imagine if a cold cup of coffee spontaneously heated up as you watched. Or a cracked pane of glass suddenly un-broke. According to physicist Lorenzo Maccone at the Massachusetts Institute of Technology, you see things like this all the time – you just don’t remember.

We have a statistical law that describes these everyday phenomena called the Second Law of Thermodynamics. This law tells us that the “entropy” or degree of disorder of a closed system never decreases. Roughly speaking, a process in which entropy increases is one where the system becomes increasingly disordered. Windows break, thereby increasing disorder, but they will not spontaneously unbreak. Gases will disperse but not spontaneously compress.

Lorenzo Maccone argues that quantum mechanics dictates that if anyone does observe an entropy-decreasing event, their memories of the event “will have been erased by necessity”.

Maccone doesn’t mean that your memories will never form in the first place. “What I’m pointing out is that memories are formed and then are subsequently erased.”

When you observe any system, according to Maccone, you enter into a “quantum entanglement” with it. That is, you and the system are entangled and cannot properly be described separately.

The entanglement, Maccone says, is between your memory and the system. When you disentangle, “the disentangling operation will erase this entanglement, namely the observer’s memory”.

But he cannot prove that entropy-decreasing events occur. Rather, he shows that if they do, we won’t remember them.

Huw Price, head of the Centre for Time at the University of Sydney, thinks Maccone is simply trading one mystery for another.

“The proposal to explain the thermodynamic arrow in terms of the [quantum] effects of observers has an obvious flaw,” he says. “It doesn’t explain why all observers have the same orientation in time … Why don’t some observers remember what we call the future, and accumulate information towards what we call the past?”

Real-world events always proceed in the direction of increasing entropy. The reason we never see events that reduce entropy is that they cannot leave behind any evidence of having happened, according to a new theory.

The mathematical laws of physics work just as well for events going forward or going backward in time. Yet in the real world, hot coffee never unmixes itself from cold milk.

When viewed in quantum terms, events that increase the entropy of the Universe leave records of themselves in their environment. The researcher proposes that events that go “backward,” reducing entropy, cannot leave any trace of having occurred, which is equivalent to not happening.

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