My friend and Hive Overmind co-blogger Sean Carroll is a theoretical cosmologist, which means he thinks about why the Universe is the way it is, and applies what we know about physics and mathematics to try to understand it. His particular interest is the flow of time, and why it goes from the past to the future. That may seem like a weird thing, but in fact we don’t understand why we remember the past and not the future. Space goes in all directions, but time is a one-way street. Why?
This question is so interesting, in fact, that it caught the attention of noted scientist and thinker Stephen Colbert, who discussed it (and Sean’s new book, From Eternity to Here) on his TV show last week. I highly recommend taking a look at the clip Sean has on his blog; he’s a great example of not only someone trying to pry open the secrets of everything, but also of someone who enjoys doing it, and does a great job explaining it under what must be the high-pressure gaze of Colbert. My congrats to Sean for joining the long list of my friends who have been on that TV show, and of course I’m not jealous at all. Really. Not even a little tiny bit. Seriously.
March 20th, 2010 at 8:57 am
Phil Plait:
Maybe Colbert is saving the best until last!
March 20th, 2010 at 9:31 am
A while ago I realized that when you enter a black hole, space becomes more and more like time: you can no longer choose your speed and direction. There’s only one way you can go: forward! You can’t stand still, you can’t go sideways, and you certainly can’t go back. You know what’s behind you, but you don’t know what’s in front of you. Isn’t that exactly how we experience time?
March 20th, 2010 at 10:09 am
Thanks, Phil. Hopefully you’ll appear on the show, so that all your friends can invite you to our Colbert Alumni Parties. They’re pretty amazing.
March 20th, 2010 at 10:53 am
“There’s only one way you can go: forward! ”
What about subatomic particles?
March 20th, 2010 at 10:53 am
Perhaps you should try writing a book. It worked for Carrol, and I believe Cox has one out, too. (Of course, Cox is on the telly as well.)
March 20th, 2010 at 10:58 am
Hey! While those other guys may have been on some jive TV show, *you* get mentioned on Coast-to-Coast AM all the time! You, like, a hero dude…
*sigh*
If Sean really *does* work out the whole “directionality of time” thingy, maybe you can work out a way to deal with that?
March 20th, 2010 at 12:26 pm
Not to worry, Phil. I keep sending the Colbert team reminders that I really, REALLY want to see you on the show.
Surely Sean Carroll couldn’t have more fans posting to Colbert than you? Surely not,,,
Anyway, I just sent them a reminder.
Here’s hoping they’re really just waiting for your agent to contact them. You DO have an agent, right?
GAry 7
PS. Here’s the email address to which I sent this reminder:
ccinsider@comedycentral.com
March 20th, 2010 at 1:24 pm
You’re itching to get invited, don’t you?
March 20th, 2010 at 1:27 pm
There are four fundamental forces and one, gravity, is significantly weaker than the others. There are four perceivable dimensions to space-time. We are dragged along by the expansion of all four, but we can still move about in three of the four of them. I’ve often wondered if there’s a link between the weakness of gravity and the fact that we are dragged along inexorably by time, by not by space.
March 20th, 2010 at 3:45 pm
Why should we regard the direction of time nothing more than a local convention regulated by coordinate transformation groups? The universe is just a 4-manifold, after all; ultimately choice of coordinate system is arbitrary.
March 20th, 2010 at 4:01 pm
He wrote a book?!
Seriously, I have a fresh copy waiting under some other books I have to finish first. It will be a treat!
@ Gebo: An analogy isn’t equivalence. I don’t think we have such a good handle on time that we can make much predictions here yet.
As far as experiencing time, it is exactly experienced and measured by clocks as local rates. Clocks are periodic systems, and as such they don’t go anywhere, it is more proper to say that they return (to an earlier state).
We observe that _all_ states don’t repeat though, which basically is due to increasing entropy. (This is usually, albeit IMHO erroneously, called “the arrow of time”.)
In addition to these old observations, I think the standard cosmology now puts the science of time on firm feet.
For example, the inflationary universe admits an “environmental sink” for entropy. Initial entropy is maxed out in the dense chaos, inflation holds it back relative to the rapidly increasing possible maximum, and then entropy has the rest of the lifetime of the universe to increase.
This is much the same for quantum mechanics, where decoherence takes observation into observables. It is the inflationary universe expansion that results in an always guaranteed “environmental sink” for decoherence by entangling quantum states with the environment, and by ensuring decoherence admit that classical states can appear.
So here at long last we now have two predictions out of observing time, properties of entropy predicts an inflationary universe and so does decoherence.
Conversely, universes that are too short-lived and rather just fluctuates in and out of existence will not have much of an emergent time (and space) as we understand it. But we knew that.
March 20th, 2010 at 4:34 pm
Oh come on. If time ran backwards, I’d be having breakfast for dinner. And that’d just be silly.
March 20th, 2010 at 6:00 pm
Sean Carroll needs to talk to Merlin, who apparently lived backward in time.
March 20th, 2010 at 9:32 pm
@9. wildride Says:
There are four fundamental forces and one, gravity, is significantly weaker than the others. There are four perceivable dimensions to space-time. We are dragged along by the expansion of all four, but we can still move about in three of the four of them. I’ve often wondered if there’s a link between the weakness of gravity and the fact that we are dragged along inexorably by time, by not by space.
Gravity can drag pretty badly too. Just ask anyone who’s struggled to cycle up a steep hill, climb a mountain or fallen out of a tree!
March 20th, 2010 at 9:36 pm
Perhaps the initial assumption that space can move in all directions is incorrect. I am not a physicist, but I seem to recall reading that the universe has been observed as expanding at an accelerated pace instead of the expected slowing, or reversing direction due to gravity, dark matter/energy, whatever.
If space itself is still expanding, perhaps it can only move in one direction, meaning it can only move away from the location of the big bang. I thought perhaps the fact that space can move in all six degrees would be irrelevant when talking about space itself; each “segment” of space is still moving in only one direction relative to the big bang. And since time and space are the same thing, then time moving in only one direction would make more sense.
Of course this would also mean that time itself is accelerating…
Has there ever been any data showing that space itself has moved in any direction except away from the big bang?
I would really appreciate any answers I could get to my complete novice physics statements as I am seriously interested in pursuing cosmology or some other type of astronomical science as a profession. Thanks.
March 21st, 2010 at 6:51 am
“and of course I’m not jealous at all. Really. Not even a little tiny bit. Seriously.”
Dr Phil,
You don’t have to say that. I think you have pure white heart, geek and people who have high sense of humor always enjoy having that kind of hearts:)
March 21st, 2010 at 9:19 am
““There’s only one way you can go: forward! ”
What about subatomic particles?”
What about tachyons?
March 21st, 2010 at 10:11 am
“(from Sean) Thanks, Phil. Hopefully you’ll appear on the show, so that all your friends can invite you to our Colbert Alumni Parties. They’re pretty amazing.”
Hahaha! Zing!!!!
March 21st, 2010 at 11:10 am
Someone needs to start a “Get Phil Plait on Colbert” FB page. It recently worked to get Betty White on SNL! I am NOT volunteering.
March 21st, 2010 at 8:06 pm
@2. Gebo,
I read somewhere that space and time trade attributes inside the event horizon. Your path through space becomes unidirectional. However, and bizarrely enough, you can time travel with complete freedom!
However no matter what, you’re going in the singularity.
March 21st, 2010 at 8:37 pm
Loved the book, but it was heavy…heavy stuff. Not just theoretically heavy, but fast and heavy. I am a science teacher (biology/astronomy/earth sci) who dabbles in the ‘amateur physics” world, and I had to re-read sections, google ideas that were mentioned, etc. It was a tough, though illuminating, slog.
That said, it was a wodnerful book. Just not a light read!
Awsome selection for a book club, I would say!
March 22nd, 2010 at 11:14 am
Maybe it’s time to give up on Colbert and start courting Oprah.
July 7th, 2010 at 1:28 am
Professor,I am a student of China.I love physics and I want to study in Caltech.
Could you help me with my question: Statement in accordance with special relativity, high-speed movement in the earth, the spacecraft, the spacecraft will shrink, I understand this principle, but I am not sure how this contraction is measured? Can you help me to answer this question, thank you.