Is time on my side?
January 9, 2004 6:09 PM   Subscribe

Roger Ebert's review of 21 Grams (which I'm about to see) contains the following sentence: "Even though modern physics tells that time does not move from the past through the present into the future, entertaining that delusion is how we make sense of our perceptions." This kind of surprised me because I was under the impression that time DID move from the past through the present and into the future. Can someone explain how / why it doesn't?
posted by adrober to Grab Bag (21 answers total)
 
Quick-and-dirty answer: Einstein showed that there's no such thing as the past and the futureā€”it all depends on your frame of reference. Therefore the idea of time "moving" from one to the other is nonsense; there's only space-time, and any "motion" is a product of our consciousness.
posted by languagehat at 6:40 PM on January 9, 2004


There are also some more recent m-theory/superstring theory-derived notions that time itself may be an illusion, a byproduct of the interaction of fundamental substrates in eleven or more dimensions of space.
posted by adamgreenfield at 6:47 PM on January 9, 2004


You might find this Oliver Sacks article interesting/relevant.
posted by rushmc at 6:50 PM on January 9, 2004


isn't it that WE move from the past thru the present into the future all the time, and it's our consciousness of that that counts?
posted by amberglow at 6:54 PM on January 9, 2004


That's practical enough for me, amberglow. I think it is in how you define it. If time is the motion of the experience as perceived, then that's that.

But it is fun to explore the mystery, too!
posted by namespan at 7:04 PM on January 9, 2004


it is : >
posted by amberglow at 7:47 PM on January 9, 2004


I thought it was that the past, the present and the future all exist but we move through them as we move through space.
posted by CunningLinguist at 8:06 PM on January 9, 2004


sounds like psuedo-scientific wank to me. on a "deep" level, time is something of a mystery, certainly, but there's no clear, widely accepted result that i know of that says that time doesn't "move from the past through the present and into the future" (to the extent that it's sensible to say that time itself moves - what does that mean?)

special relativity makes the relative ordering of some events appear different to different observers (you might see bomb a explode before bomb b; i see bomb b explode first (where "see" means "measure" in a well defined way)). but that's only under restricted circumstances - including the two events being far enough away from each other (spatially) for them to be unable to influence each other (so it would be impossible for bomb a to trigger bomb b, or vice versa - they are independent).

it's possible for the relative flow of time to be different - some people can age much more slowly than others, for example. but it remains impossible (given what we understand, current accepted theories etc) to get younger or travel back into time. time always increases (and while you age more slowly, you don't experience a longer life - you remain "normal" and see others as if fast forwarding through a video; they remain "normal" and see you as if in slow motion - here "see" is somewhat figurative, since you'd need to be moving past them at something close to the speed of light, so you wouldn't get to actually see much at all).

special relativity unites the three dimensions of space with that of time. but the unification is not symmetric. time remains different to the other dimensions. you can walk both directions down a street, but only one way through time.

it's also possible he's referring to one of several different trendy models that seem to catch people's attention and generate silly claims (perhaps many worlds qm?), but these tend to be speculative (or have a simpler version that is more widely accepted but doesn't require/imply such fancy claims).

of course, we don't know everything, and there's still a big hole in physics - we can't get quantum mechanics and relativity to fit together properly. one of the things that keeps coming into question is causality (closely related to the flow of time) and some of what i say above may turn out to be wrong. but there's certainly not a well defined, widely accepted theory of time travel!


it may be urban legend, but a nice story anyway: there's a culture that views time as a flowing river, from the future to the past. you are stood in the river, with your back to the flow. so time flows past you and you can see it carry things into the past; the future is hidden.
posted by andrew cooke at 8:20 PM on January 9, 2004 [1 favorite]


FPP on mefi about how time flow is not linear.
posted by daver at 8:40 PM on January 9, 2004


what andrew cooke said.

Don't take Ebert's throwaway line too seriously. Physics is nowhere near telling us anything conclusive about time (other than Einstein's theory)

Time doesn't arise naturally out of most models though and so it has had to be inserted in. This has led physicists to speculate that time doesnt just behave like a dimension of space - it is space, albeit one we have a special, psychological relationship to.

Also, we have tried to decompose and recast "time" in terms of: Thermodynamics and the flow of 'order', information theory, asymmetry in basic phsyical processes (CPT violations), advanced space-time topologies and so on.

But the short answer is still - we just dont know and its unclear how much of the information we have gathered fits together. It's a deep mystery.
posted by vacapinta at 8:57 PM on January 9, 2004


The original idea (in my no doubt incomplete understanding) was that particle reactions are reversible in time -- that is, causality works properly whichever way you run the film, so two particles colliding to emit a third when moving towards the future, becomes one particle decaying into two when moving towards the past, with no real way to tell the difference. Therefore, at the fundamental physical level, there is no difference. (Google for "arrow of time" for more (such as this pdf.))

It appears to be no longer believed to be the case, however:

...it is now thought that physics does differentiate between the forward or backward movement of time. The two groups have now seen evidence for this T violation in the observed decay rates for neutral K mesons." (Whatever those are.)

So, yes, Virginia, there is a future.
posted by ook at 9:13 PM on January 9, 2004


ook, thats what I meant by asymmetry in basic phsyical processes (CPT violations) above. "T violation" means basically violation of symmetry with respect to time.

Here's a good article about it from physicsweb. I think more laypeople should understand that, no, you can't run the film backwards!
posted by vacapinta at 9:23 PM on January 9, 2004


I'm really sorry, everyone, but I still don't get it. I can't correlate the theory to my own experience of the world. Ebert says that it's a delusion we use to make sense of our perceptions. What's the non-delusional approach to time then? That the sandwich I'll eat tomorrow is something I already ate? Way confused.
posted by adrober at 9:35 PM on January 9, 2004


I think most laypeople have a very good understanding that you can't run the film backwards: easier to break a vase than to put it back together, f'rinstance.

It's just that we've gotten so used to hearing weird counterintuitive shit from the particle physicists that we're willing to believe anything they tell us at this point, as long as it sounds sufficiently improbable and has the word "quantum" in it somewhere :) So half-understood partly correct "whoah, man" factoids like this get lodged in the popular consciousness, and get used in film reviews.
posted by ook at 9:40 PM on January 9, 2004


One of my favorite zen koans starts like this: Two monks were arguing about a flag.
posted by wobh at 10:56 PM on January 9, 2004


this is not exactly in response to your question, but i think Inarritu (the film-maker) is playing with "sequence" more than "time." basically his argument for creating these non-linear films is that he is recounting events based on an emotional hierarchy rather than a scientific clock-based timeline. for instance, let us say that i knew you but hadn't seen you in a month because i went on vacation to Australia. while in Australia i got mauled by an angry kangaroo. i ended up in a hospital there, where i met a nurse who days later became my wife. when i see you, what do i tell you first? that i almost got killed by a kangaroo or that i married someone in Australia? or do i tell you about the bad airline food? most likely, i won't tell you everything in the sequence the events occured, because that is not how i feel the events. for the same reason, Inarritu doesn't tell a story that way either.

maybe if you take this argument to an extreme, you could argue that we experience events not as A to B to C to D, but more as interconnected emotional peaks and valleys that are arranged perhaps by other criteria than what clocks or calendars dictate.
posted by edlundart at 11:08 PM on January 9, 2004 [1 favorite]


But it is fun to explore the mystery, too!

That's practical enough for me, amberglow. I think it is in how you define it. If time is the motion of the experience as perceived, then that's that.
posted by namespan at 11:55 PM on January 9, 2004


hmmm. weird.
posted by namespan at 11:56 PM on January 9, 2004


thanks for the t violation stuff - that was new to me (left physics years ago). now i have some new small-talk for when i next meet my neighbour's particle physics s.o.
posted by andrew cooke at 2:47 AM on January 10, 2004


namespan: a time hiccup? : >
posted by amberglow at 6:35 AM on January 10, 2004


Time doesn't exist, except as a measurement of change. It's just a yardstick, a tape measure of sorts. If nothing changed, there would be no need for the concept of time, and no perception of the 'passing of time.'

That is all.
posted by Shane at 8:41 AM on January 10, 2004


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