I suppose it is appropriate that the post ending my nearly three-month-long hiatus is about the nature of time. I just recently returned from the absolutely fantastic FQXi conference Setting Time Aright that took place first onboard the *National Geographic Explorer* sailing the coasts of Norway and Sweden starting in Bergen, and then in Copenhagen. It was eight days of intellectual bliss – interdisciplinary, cutting edge, and small enough that we could really all interact in some way. I met and/or hung out with some amazing people including Jaan Tallinn, Nick Pritzker, David Eagleman, Jesse Dylan, and Julian Barbour, among many others (see the conference website for a complete list). At some point soon the full conference will be available to watch on the Net. For now you’ll have to contend yourself with my pithy comments.

On the surface, it would seem that there was little agreement about the nature of time, i.e. what it is. Certainly the neuroscientists and psychologists have a very different take on it than the physicists. But I don’t think anyone would deny that what physics tells us time ‘is’ must be what time really *is*. The question is, then, does physics tell us specifically what time actually is?

Yes and no. Anyone who really studies physics will (or at least should) know that relativity has quite a bit to say about time (I recommend, by the way, the superb book *Six Ideas That Shaped Physics, Unit R: The Laws of Physics Are Frame-Independent* by Tom Moore for learning basic, non-tensor special relativity). In fact there are several kinds of time: coordinate time, proper time, and the spacetime interval (which is the kind of “time” measured by a photon).

That’s all very well and good for someone who doesn’t care about the fundamental nature of time and who only needs an operational definition. But physics didn’t get where it is today by remaining content with operational solutions to problems. Physics is, ideally, like a child that doesn’t stop asking *why?* So physics should ask where time comes from to begin with. Is it something that is fundamental to the universe or does it arise from something else? If it arises from something else we should seek to know how and why. One never knows the interesting doors this might open for further research (or even technology).

While there seemed to be a great deal of disagreement about the nature of time at this conference (e.g. Julian Barbour is convinced it doesn’t even exist), there very clearly was an underlying commonality to all of the views – even those of the psychologists and neuroscientists.

First let me say that one of the most striking things I found was that everyone’s work – absolutely every last one including the psychologists’ – involved either quantum mechanics or probability & statistics (including statistical mechanics and information theory, i.e. anything Edwin Jaynes would have written about – actually he wrote a bit about quantum stuff too). Ironically these are not the topics we emphasize in basic science and mathematics education (surprisingly few people have a good understanding of probability and statistics and most people are never even *exposed* to quantum mechanics!).

So given that commonality that seemed to cross disciplines, it is no surprise that pretty much everyone agreed that time has something to do with entropy. In fact many of the presenters and attendees probably think this is simply a trivial truth. So perhaps we should have been debating entropy, which is something that is still not entirely well understood as a concept. What *is* clear, however, is that it is some kind of statistical phenomenon. This is true for every single definition of entropy in every field (including instances in which the word is completely abused). Thus it would seem that there’s an underlying consensus – whether it is realized or not – that time must be some sort of statistical phenomenon.

This is actually quite remarkable. First, it points to the likelihood that time is *not* fundamental in the universe and so, in some sense, Julian Barbour is correct in that it doesn’t exist as a fundamental entity. In other words it would seem to be an emergent phenomenon. Second, if it is emergent, then due to the fact that it is at the heart of relativity, perhaps relativity is an emergent phenomenon as well (actually it is not difficult to argue this on a philosophical level). Following this line of reasoning would suggest that gravity would then have to be an emergent phenomenon (which actually makes some sense).

Now before everyone starts talking about these observations as being indicative of what was discussed at the conference, please know they represent my extrapolation from the commonalities I saw in all of the talks. Precisely how much of this any given attendee would agree with would likely vary greatly. Nevertheless, it is an intriguing line of reasoning to take and it certainly not unique (gravity has been proposed as being an emergent and/or thermodynamic phenomenon before).

What all of this means for your daily life is … well, nothing really. However, there were a number of talks that had some very interesting and useful insights into certain aspects of daily life. Keep an eye peeled for the conference videos (and a possible documentary). Nevertheless, they are fascinating and intriguing ideas to contemplate. Perhaps this sign from Bergen was a bit of a foreshadowing of the rest of the conference…

It’s kinda funny that you write that time, relativity, entropy, gravity, etc. are probably emergent rather than fundamental. It has occurred to me that all physical processes/objects/phenomena are emergent, since they all “emerged” from the cosmological singularity! What then is fundamental? I suppose anything that is both necessary and sufficient for the singularity to become the universe we know today, i.e. the conservation laws, the singular condition (and whatever that entails), cosmological expansion into a background hyperspace, and mathematics. I don’t quite agree with Max Tegmark that the cosmos * is * a mathematical structure, yet IMO mathematics are indeed necessary for the universe to exist. How can even the most basic physical geometry exist without its pre-existing mathematical counterpart? IOW, how does the actual exist without the potential?

Actually I just had a conversation with someone about that today. Indeed, to some extent, everything

isemergent. But I think that relativity and gravity are emergent in another respect – they have little or no meaning for isolated point particles.