Only a Matter of Time

Einstein transformed the way we look at gravity, the force Newton apocryphally comprehended when an apple fell upon his head, proposing a radical shift in our paradigm for describing the Universe. His big breakthrough? Essentially an “the Earth is curved, not flat!” moment, but for time: instead of time being something that is rigid, inexorable, and the same for everyone, Einstein proposed that it was a fluid, relative quantity, which flows differently depending where you are and how fast you happen to be moving. Clearly, Einstein was no stranger to radical and extremely strange revolutions in physics! However, quantum mechanics, the ‘quantum leap’ that succeeded Einstein’s theory of relativity, was far too weird even for a revolutionary mind like Einstein’s. He famously dismissed as implausible two of the sacred tenets of quantum theory, responding to Heisenberg’s Uncertainty Principle by scoffing, “God does not play dice,” and calling quantum entanglement impossible, “spooky action at a distance.” He formulated his objections in a paper that essentially said, “quantum mechanics cannot be true because it would imply X, and how crazy would that be!?” Unfortunately for Einstein, ‘X’ was experimentally demonstrated in the 1960’s, and quantum mechanics has been established as the most accurate (albeit crazy) theory we humans have ever devised. Despite Einstein’s thorny history with the concept, recent progress in entanglement research actually continues the work Einstein began, in a way, by further dethroning our intuition of Time as something absolute and separate from ourselves.

Einstein in 1921.

Entanglement is like marriage, in a way. After two people are married, they become in many senses one unit – a single, cohesive whole. In some ways, it makes more sense to speak about the couple instead of the individual members. We can be more certain about the trajectory of the couple than we can about either member. For example, we can say with a fair degree of certainty that a married couple will live in the same city ten years from now, while we might not be able to predict with certainty specifics of either individual’s trajectory, such as where he/she is employed. Entangled entities are like that. They have a bond between them so strong that it makes more sense to describe them mathematically as a whole rather than two (or more) parts.

In quantum mechanics, we can never know the state of things with absolute certainty. Think of the famous example of Schrodinger’s cat: until we actually look at it, the cat is both alive and dead. It’s only when we check inside the box – or ‘measure’ the cat – that the cat ‘makes a decision.’ Now, if we had two cats that shared this special property of entanglement, measuring one would allow us to know for certain whether the other one was alive or dead, too. For example, if we look inside box #1 and cat #1 is alive, cat #2 will also be found alive when we look in box #2. Similarly, if we look inside box #1 and find cat #1 dead, we will also find cat #2 to be dead when we check. There is no quantum uncertainty left in the second cat – once we’ve checked box #1, we don’t even need to check box #2 to know what will happen when we do. So now, like the married couple, we know more about the behaviour of the two cats combined (we can say for certain they are both in the same state) than we do about either one (we’re still not sure if an individual measurement of cat #1 will yield alive or dead). The entangled cats behave in a beautifully symmetric way even if they are at opposite ends of the universe and have no possible way of communicating with one another. This is why Einstein thought entanglement was ‘spooky’ – it seems as though entangled particles have a bond that lies deeper than reality itself.

If this confuses you, you’re in good company: entanglement is a notoriously difficult concept to explain and comprehend, and physicist Richard Feynman purportedly said, “anyone who claims to understand quantum mechanics is lying.” The difficulty lies in how paradoxical the implications are in light of the intuition humans naturally have about how the Universe works, specifically, notions of cause and effect. The alive/dead outcome of cat #1 in the Milky Way should not be able to affect the alive/dead outcome for cat #2 in Andromeda…but somehow, it does. Things get even weirder when you consider the experiments that have demonstrated that entanglement bonds can allow the cats to communicate with one another backwards in time…but that’s a matter for another post!

So much for entanglement. Now, what does all this have to do with Time and Einstein? Basically, entanglement invites a new view of time that inverts our conventional notions arguably as drastically as Einstein’s theory of Relativity did. Recent research [1-3] has linked evolution in time with entanglement. In some sense, it proposes that what we humans perceive as time is simply an increasing number of entanglement bonds being formed between us and the rest of the Universe.  Once we get “in on” the bond, or “married to” the rest of the Universe, we’ve experienced it as part of the flow of time. The experience of the present moment is distinct from our relationship with the future because we are acquiring the intimate, special links of entanglement with everything that is in the present, but we are not yet linked to the future. So what we call time is merely the accumulation of entanglement. A pretty nifty spin on a concept that is Einstein’s old stomping ground. I hope he wouldn’t be too upset.

References

[1] Linden, N., Popescu, S., Short, A. J., and Winter, A. (2009). Phys. Rev. E. 79:061103

[2] Short, A. J., and Farrelly, T. C. (2012). New J. Phys 14:013063

[3] Goldstein, S., Hara, T., and Tasaki, H. (2014). arXiv:1402.0324