“Time is out of joint.”
I’ve long puzzled over the idea that physics is reversible. That its laws, with some caveats, work the same if time runs forwards or backwards. It’s even been suggested that, except for entropy, time could run backwards just as easily as forwards.
But this seems contrary to our everyday experience. With some exceptions, we can tell if a film or video clip is shown in reverse. Objects that fall, break, or grow (such as plants or crystals), look different seen in reverse.
I think there is more going on there than just entropy.
Last year I kicked off the new year with a post about open and challenging questions in physics. Those remain open and challenging and probably will for some time. Some of them are very old (and very unresolved) questions; others were from modern scientific efforts and understandings. It’s possible we may never find answers for some.
At some point, for some reason, about a month ago I started making a list of things I thought were probably true; things I believe in. I say “probably” because, as with those open science questions, we don’t know the truth of these things; many are vigorously debated.
Some of what follows pertains to those science questions, some of it is more social observation on my part.
I skipped Friday Notes last month, and almost skipped it this month. To some extent that’s due to the note pile getting smaller, but the larger share of it is the exhaustion and ennui I’ve been feeling all year. My posts-per-month count has been noticeably down since April.
Over the 110 months of this blog (which doesn’t count 2017, the year I took off), the average is 10 posts per month, but in the previous two years it’s 14, so I do seem off my feed lately. OTOH, only 74 posts in 2018 (my lowest year), and I’m at 96 now, so there’s that.
In any event, here’s another edition of FN.
I’ve been reading science texts almost as long as I’ve been reading anything. Over those years, many scientists and science writers have taught me much of what I know about science. (Except for a Computer Science minor, and general science classes, most of my formal education was in the Liberal Arts.)
Recently I read Time Reborn (2013), by Lee Smolin, a theoretical physicist whose personality and books I’ve enjoyed. I don’t always agree with his ideas, but I’ve found I do tend to agree with his approaches to, and overall sense of, physics.
However in this case I almost feel Smolin, after long and due consideration, has come around to my way of thinking!
My serious effort lately to reduce my pile of notes has resulted in picking the low-hanging fruit and leaving the ones that demand more effort. (One reason those notes have been notes all this time is not feeling the effort needed to develop them into something.)
The good news is that I’ve dug through most of the new layer — the one that formed when I started blogging again after taking a break all through 2017 (being in shock from 2016). Now I’m tapping into the older much larger — and in many cases now outdated — pile from before 2017. (Notes about politics in 2016 I can now just toss.)
Three of today’s notes are from that old pile. Three obviously aren’t.
particles & their momenta
Over the decades I’ve seen various thinkers assert that entropy causes something — usually it’s said that entropy causes time. Alternately that entropy causes time to only run in one direction. I think this is flat-out wrong and puts the trailer before the tractor. (Perhaps due to a jack-knife in logic.)
The problem I have is that I don’t understand how entropy can be viewed as anything but a consequence of the dynamical properties of a system evolving over time according to the laws of physics. Entropy is the result of physical law plus time.
It’s a “law” only in virtue of the laws of physics.
As people age, especially later in life, most report that time seems to pass faster. That is certainly true in my case — Mondays I often find myself surprised that it’s already laundry day again. Friends my age report the same thing; the weeks, months, and years, seem to pass at an ever faster rate.
My theory was it’s mainly due to percentages. At ten years old a year is 10% of a lifetime, but at 60 years old it’s just 1.666%.
Recently, a friend of mine floated an interesting alternate theory.
I just finished Time Travel: A History (2016) by science historian and author James Gleick. The New York Times Book Review, Anthony Doerr described it as, “A fascinating mash-up of philosophy, literary criticism, physics and cultural observation.” I agree with that description minus the word fascinating. I would have said tedious.
This is not the book’s fault. I’m not saying it’s bad. There was nothing I disagreed with. There were even a few parts I got into. The problem is I found it ambling, rambling, and meandering. It wasn’t incoherent, but it seemed disconnected to me.
Overall I found it easy to put down and hard to pick back up.
I’ve been chiseling away at Cycles of Time (2010), by Roger Penrose. I say “chiseling away,” because Penrose’s books are dense and not for the fainthearted. It took me three years to fully absorb his The Emperor’s New Mind (1986). Penrose isn’t afraid to throw tensors or Weyl curvatures at readers.
This is a library book, so I’m a little time constrained. I won’t get into Penrose’s main thesis, something he calls conformal cyclic cosmology (CCC). As the name suggests, it’s a theory about a repeating universe.
What caught my attention was his exploration of entropy and the perception our universe must have started with extremely low entropy.
There is something about the articles that Ethan Siegel writes for Forbes that don’t grab me. It might be that I’m not in the target demographic — he often writes about stuff I explored long ago. I keep an eye on him, though, because sometimes he comes up with a taste treat for me.
Such as his article today, No, Thermodynamics Does Not Explain Our Perceived Arrow Of Time. I jumped on it because the title declares something I think many have backwards: the idea that time arises from entropy or change. Quite to the contrary, I think entropy and change are consequences of time (plus physics).
Siegel makes an interesting argument I hadn’t considered before.