On the matter of time, and how the past crystallises out of the future

Yes, you read the title correctly.

u block sml

In a fascinating paper written by George Ellis, of me ol’ alma mater the University of Cape Town and Tony Rothman, from Princeton University in New Jersey, they posit that the place where this crystallisation occurs is, interestingly, the present. Not as in gift (although the present is a gift, yes), but as in the now.  This moment. No, this one. Kinda (but on to that later).

But wait - this sounds a little bit like that whole ‘yes, time technically has no meaning in relative physics, but try saying that to the real world’ issue.  Or maybe that’s just me.

Apparently, cosmologists can, being the amazingly abstract people they are, think of the universe as a sort of block in which space and time are merged.  A static block in which, as the paper says:

“…Time does not ‘roll on’ in this picture. All past and future times are equally present, and the present ‘now’ is just one of an infinite number.”

Confused so far?  Excellent, so was I.  But wait, dear readers, there is more.

Up until now, this blockheaded (sorry) approach hasn’t yielded much of use, but now!  Ah! Something useful - or at least very interesting, which in this area is enough, I think - has come of it.

Our two eminent scientists have developed a new sort of block universe, one into which they’ve introduced the mind-shattering madness that is quantum mechanics.   That wonderful state in which things can be in two places at once, or pop in and out of existence, or be connected across vast distances in such a way that what affects one, affects the other, instantly.  That state.  And they’ve found something interesting.

Firstly, it tends to make the block rather less static. Time does have significance now.  And when one does this, it seems that the future is driven by quantum, and the past by relativity, with the present sitting, as expected, inbetween. For some reason, I keep having in my mind the potentiality of a good or bad cup of coffee, the present experience of a mediocre cup of coffee, and the dried grounds (wormfood) thereafter as my mental image of it.

crystallising block universeThe third graph in the paper, the block universes here take into account quantum mechanics, and show that small pockets of potentiality* can remain even when most of it has stabilised into the present (the wavy lines).  In this way, time acts something like a mixture which is crystallising - the process isn’t entirely uniform.

They also propose that this model may offer a solution for the unidirectional nature of time as we experience it - often called the ‘arrow of time’.  Apparently, it’s because the future does not, in actual fact, really exist yet (yes, yes, I know, but still)…

“One can be influenced at the present time from many causes lying in our past, as they have already taken place and their influence can thereafter be felt.  One cannot be influenced by causes coming from the future, for they have not yet come into being.”

The arxiv blog is of the opinion that the model needs a bit more work (and, of course, some testable predictions would also be super) - I’m simply of the opinion that it’s a really fun idea.

And, as usual, I’m extremely grateful to the arxiv blog for their immensely useful cribnotes.


I contacted George Ellis in early December about the paper, and here’s the quotation he kindly provided for me.  Let’s hope that the above explanation makes this a little easier to understand :) Thanks, Prof Ellis!

“Our paper looks at the idea that, contrary to what many physicists claim,  time really matters: time is not an illusion, things really do take place! But in looking at this, one has to fully take into account `quantum weirdness’ as evidenced by many experiments, and in particular by Wheeler’s delayed choice experiments.

“This leads us to the idea of a Crystallizing Block Universe: a space time which `grows’ as time evolves, but does so in such a way that one can still to a small degree influence the `past’, as in those quantum experiments.  Thus spacetime is like a Crystallizing material, where the transition from the uncertainty of the future to the certainty of the past (Quantum weirdness changes to classical certainty) takes place almost everywhere at a time we can call “the present’, but with small remnants of uncertainty remaining that crystallize out later.”

*Basically, the process isn’t completely uniform or simultaneous - apparently, say the authors:

“Quantum physics appears to allow some degree of influence of the present on the past, as indicated by such effects as Wheeler’s delayed choice experiments and Scully’s quantum eraser.”