Tuesday, June 12, 2007

Cosmic Variance's Sean Carroll on the arrow of time

I've been reading Sean Carroll's posts on Cosmic Variance, not realizing until now that he's a research associate at my alma mater. I guess blogs really are infested by amateurs destroying our culture of knowledge ...

Sean's presentation is pretty readable for the interested layperson ...

Sean Carroll: Why Is the Past Different From the Future?

... In such a universe, everything we think we "remember" ... about the past is ... a mistake.

Dinosaur skeletons arose spontaneously out of dirt.

It's been a busy road to reading material like Sean's. It started when I came across this comment in Wired  last February:

Even the best theories to explain how entanglement gets around this problem seem preposterous. One, for example, speculates that signals are shot back through time. Ultimately, the answer is bound to be unnerving: According to a famous doctrine called Bell’s Inequality, for entanglement to square with relativity, either we have no free will or reality is an illusion. Some choice.
- Lucas Graves, New York City-based writer

As near as I can tell Lucas was simplifying a bit. The complete absence of free will (aka. life in God's movie or the Tralfamadorian perspective) goes back originally to Newton (determination by mechanics) then to Einstein (determination by time slice perspectives) and returned with the transactional interpretation of QM. The good news for the non-Calvinists among us is that the evidence (as I read of it) favors the non-existence of independent reality over the kind of absolute determinism where not only dinosaurs arise from dirt, but all of space and time arise spontaneously and (seemingly) coherently.

So what does all this have to do with Carroll's talk? Well, it seems plausible that the "arrow of time" has something to do with predetermination or non-determination and that it should also have equivalences in both cosmology and quantum mechanics. Here's Carroll's conclusion about where time comes from in the view cosmology - it involves the infinite multiverse ...

...If the universe lasts forever but has no equilibrium
state, we naturally obtain an arrow of time.

It’s crucial that the way in which the multiverse
creates more entropy is to make universes like ours...

Further I cannot go! So where does the arrow of time come from in QM? I'm imagining at the moment that it comes from decoherence...*

* Ok, how did I know that "Decoherence, Quantum Measurement and the Arrow of Time" existed? I didn't, of course. I hypothesized that the arrow of time emerges as a universe of infinite possibilities collapses as the past interacts with it -- an idea that's appeared in at least one science fiction story I've read. I knew decoherence is the technical term used for the interpretation of QM most consistent with this model, so I searched on "decoherence" and "arrow of time". Easy. (The alternate explanation, of course, is that the conference didn't really exist until I thought of it, which led the quantum chaos of the past to collapse.... :-)

1 comment:

Mkhan said...

Time may be just the presence of motion and forces. Time could be due to expansion of space. Time is slow where expansion of space is slow like around large masses. If total motion and forces within a mass is a constant then as the linear motion is increased the internal motion as well forces within that object slow which is then percieved as slowing of time. If we think of two objects in orbit around each other and imagine time slowing down then we should observe motion slow down as well as forces get weaker. Forces are part of time. Forces determine the arrow of time. Without forces time will be perfectly symetrical and lack any direction.