## Illusive Time

An interesting article in New Scientist from earlier in the year summarises some interesting Quantum Physics papers, though now I look, I see they’re actually a little dated, one from 2006 and the other from 1994, with Carlo Rovelli listed as the last author of both, and quoted in the article. The problem both articles are trying to address is to reconcile the relativistic properties of time with quantum theory: we’ve already established that time behaves variably when you’re in accelerating reference frames thanks to Einstein, but quantum theory assumes time just works sensibly — which is fine and a good approximation for the places we actually use quantum theory, but we do definitively know it’s wrong.

As the article explains, getting a conceptual handle on relativity and quantum indeterminism are hard for a variety of reasons — and the usual interpretation of quantum events as “collapsing a probability wave” makes it pretty much impossible as you’re forced to choose a temporal reference frame before you start the experiment, which means you can’t get results about the time from the experiment, which was the whole point… The more recent paper addresses that, by rejigging the quantum equations to reduce multi-phase experiments into a single phase, with a bit more complicated indeterminancy. So rather than saying “at this point we know the horizontal polarisation and have collapsed the probability wave, then we randomise that again by recollapsing the probability wave of the same photon and finding the vertical polarisation”, we say “we measure a system laid out in such-n-such a manner that ends up in one state if two measurements of polarisation result in horizontally polarised and vertical polarised”. The system’s layout can then, in theory, be varied so that time goes forwards, backwards, becomes a physical dimension, or something else, without completely breaking the maths. Which is neat, because if you come up with a theory on how time and the quantum maths interact, you can feasibly plug in the numbers, and get a result that you can actually test, and either verify or refute.

The more interesting part for me is the earlier paper, which posits a framework for what time “is”, and why it looks like it does. I’m not familiar with the maths it uses so can’t check its accuracy, and it’s not really formal — it’s more a sketch of a theory that you could maybe paint over later with a real theory. But hey. The basic idea seems to be that if you take a “space” with “stuff” in it, that relates to each other in a certain sort of consistent, logical way, then essentially the randomness of the system implies a way of looking at the stuff in the space, that ends up looking like one direction is “earlier” and the other is “later”, and that the way things are “later” is something you can roughly predict from the way things were “earlier”.

The theory ends up being that time is an emergent property from the universe’s thermodynamics. And it then predicts that when you accelerate — by orbiting a black hole, or just shooting off into space in general — you’re changing what parts of the universe’s thermodynamics can actually affect you, and you’ll get a different view of “time”. The calculations of thermodynamic changes seem to match up with Hawking radiation and the Unruh effect, though as far as I can gather, that’s mostly because they’re the same calculations, derived from similar assumptions.

Presuming the two ideas actually hold up, can be filled in and put together, the maths ends up tractable, it doesn’t contradict experimental evidence, and it’s not all a pointless tautology, it seems like it provides an interesting way to get a perspective on “time” that actually lets you make useful comments. It rules out, eg, going back in time and killing your grandparents — you can’t just end up in another universe as a result, because there’s only one “space” with “stuff” in it. If the universe was created, then the universe’s creator doesn’t exist in our “time”, but looks at the entire history of the universe as a single thing, and any changes that creator desires simply changes the entire universe, past, present and future simultaneously. If the creator is interested, they really can hear every single prayer, just as a graphic artist can inspect every single pixel. But on the other hand, it’s just as easy for the creator to prevent their from being a need for prayer in the first place, as addressing it in the future. As far as multiple universes go, it’s possible the universe is being iterated through every degree of freedom it has just to see what happens, but if so, each universe exists from big bang to heat death/big crunch in its entirety, and independent as frames in a movie.

Weird, anyway. But interesting.