time

September 30, 2024 5:00 AM

Their debate began almost by accident. The meeting in April had been convened to bring together physicists and philosophers to discuss relativity theory, but Bergson came intending only to listen. When the discussion flagged, however, he was pressed to intervene. Reluctantly, he rose and presented a few ideas from his forthcoming book, Duration and Simultaneity [archive] (1922). What Bergson said in the following half an hour would set in motion a debate that reverberated through the 20th century and down into the 21st. [aeon, previously]
posted by HearHere (23 comments total)

Einstein was right of course but he was also missing something and so Bergson was right too. The gap between physical time, as a mathematical construct, and philosophical time still exists.

This topic has of course continued to evolve. For anyone who is interested in this I'd recommend the Time philosopher Craig Callender (!)'s recent book What Makes Time Special? and also the hugely influential 2004 paper by the physicist James Hartle called The Physics of Now.
posted by vacapinta at 6:55 AM on September 30 [4 favorites]

I gave this a quick skim and will return to it later, but I just want to mention that the writer of the article is Evan Thompson and he's really great. I was once embarrassed myself tremendously at a philosophy conference by cornering him at dinner and drilling him with questions when he clearly just wanted to decompress after having given his talk. My lack of decorum still haunts me to this day, but he tolerated me patiently and I learned a lot that evening.
posted by Alex404 at 7:01 AM on September 30 [6 favorites]

I've read through the introduction. I don't find the author very convincing, and so I'm reluctant to read further. Just in terms of affect I have some issues with it: the posture of "Nobody has been able to answer my very basic question" is never a good look, but later in the introduction the author admits that he's gotten such answers and simply rejects them. The quote that really bothers me, though, is this one:

"Again the question obtrudes itself: Why, if the special relativity theory is so clearly untenable, has this not been realized before? The answer, I think... is that it has become so customary in science to appeal only to experiment and not to trust reason..."

which to me reads like a complete misapprehension. Weird things are happening in our universe, things that appear to defy reason, and yet which are borne out by experiment. The incredible success of the modern scientific project has been this focus on experiment, and measurement, apropos of which another quote:

"Physics is not to be identified with science, of which it is only a part: science extends beyond the study of measurements"

I tend to reject the latter half outright; in my understanding science is necessarily empirical. I take it the argument of the introduction's author is something like: Physicists have let flawed experiments outrun reason and the whole thing is becoming a house of cards. But of course the inciting question is one on which there was no evidence satisfactory to the author at the time:

Only further experiment can tell us which of these [Einstein or Lorentz] alternatives is correct, and the most promising of such experiments would be a properly designed determination of the relation of the velocity of light to that of its source. We still await the performance of such an experiment...

and so I wonder why we ought to commit to any interpretation at all, as the author so devotedly does here. The jury is out; until it returns a verdict there's nothing more to say.

As the author rejects Morley-Michelson as bad science (a "circular argument"), I wonder if there has been experimental work in the intervening decades that might have convinced him?
posted by dbx at 8:55 AM on September 30 [6 favorites]

I started reading, and ran into unintelligible OCR like the following:

---
Therefore Bergson has
condmioT argUment ^ le *ds the relativists to their
laf^ 0 ^! by dCnyin S that ^ " time " which Peter calcu-
ates
---

Plain text is difficult to use for writing formulae, and automated methods won't be able to "guess" how to gracefully degrade italicized Greek letters with super/subscripts.
posted by rbanerjee at 9:03 AM on September 30 [1 favorite]

This pdf is better - if you don't mind the paperclip. Open Library has different formats, though I imagine they are just remixes of the text and pdf.

(Also, I feel daft. But where is the link to the article the OP is quoting? It's not the book.)
posted by bluefly at 10:07 AM on September 30 [1 favorite]

It looks like hey are arguing about things that have the same name because human language lacks adequate terminology, but time and duration are only related because of that lack. It's apples and oranges - they're both fruit, but that's about it. Physics time is a s exact as possible given a particular frame of reference as determined by certain universal rules; philosophical time is measured by the individual and is only as exact as we want it to be. Simplified, , physics is denotative, philosophy is connotative.

Note: Physics can be "connotative" of a sort, but that's not particularly useful to the results in the way that it is to philosophy and vice versa. Apples and oranges all the way down.
posted by JustSayNoDawg at 10:31 AM on September 30 [3 favorites]

bluefly, I think it's hidden in the [aeon] link in the main post for some reason.
posted by sagc at 10:39 AM on September 30 [2 favorites]

thanks sagc. my eyes conflated it with the previously link.
posted by bluefly at 10:43 AM on September 30 [1 favorite]

I may be missing something, but I don't find this convincing. Either he's arguing that another's experience can't ever be known, which is true for everything, not just duration, or I don't why the slowed clock in the train paradox isn't relevant.

Also, Einstein did address the duration issue with his quip about perceiving time differently when kissing a pretty girl vs. sitting on a hot stove. 😉
posted by CheeseDigestsAll at 11:27 AM on September 30 [1 favorite]

In response to "Only further experiment can tell us which of these alternatives is correct, and the most promising of such experiments would be a properly designed determination of the relation of the velocity of light to that of its source. " — there have been experiments on the velocity of light where the source is moving relative to the detector. See 3.3 here.

https://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#moving-source_tests
posted by kikaider01 at 11:39 AM on September 30 [2 favorites]

Thanks kikaider01! I also missed the aeon link in the original post and am reading it now. I see that my dim recollection that special relativity was experimentally confirmed was correct.

What I'm getting from the aeon article is, roughly, when we measure time we're using our consciousness to do it and shouldn't that be included in relativity? I mean, yeah, in the sense that all reality is mediated through our perception / consciousness, then sure I guess so. But that is just not a useful frame for physics, which aims to make testable predictions about that perception.

The aeon piece feels like moving the goalposts to me, in the service of bolstering Bergson's reputation. The original work which I read and responded to above was very explicitly taking issue with the physics of relativity itself, through the framing of the twin paradox, and with the possibility / reality of a fixed speed of light relative to its source. This idea that it's actually all about how we can't neglect the role of the physicist's perception of duration did not appear anywhere in the introduction to that book, as far as I could tell. That introduction really did seem to me to be misunderstanding relativity, but I'm a mathematician not a physicist and I didn't feel comfortable asserting that -- luckily the aeon article takes it as given, but seems to think that doesn't matter.

JustSayNoDawg has it as far as I'm concerned; this idea of duration just doesn't seem relevant in the context of relativity. I'm sure it's interesting philosophically but the idea that it's some great debate that Bergson could have won just feels like a category error to me. As stated in the aeon piece, it's "Immeasurable", and therefore outside the domain of science.
posted by dbx at 11:57 AM on September 30 [1 favorite]

If you're having a hard time understanding the argument, first chapter of Duration and Simultaneity is a discussion of the problems with measuring the one way speed of light. There's a great Veritasium video on this topic. Our understanding of the relativity is based on the assumption the speed of light is one half of the round trip distance.

That very much gets to the heart of the argument that it's not possible to measure a duration between places because of relativity. We can know locally how long something takes to get there and back, but comparing duration between locations is impossible.
posted by betaray at 12:11 PM on September 30 [2 favorites]

> That very much gets to the heart of the argument that it's not possible to measure a duration between places because of relativity. We can know locally how long something takes to get there and back, but comparing duration between locations is impossible.

At some level everything is subject to "we are a brain in a vat, and all of our sensory experiences and even reasoning is controlled by a demon".

So yes, we can't do anything, even compare duration between locations.

We can build what appears to be clocks that match our macroscopic experience of time passing and seem to measure it with insane precision, and we can move these clocks around and find that their frequency of ticking looks a hell of a lot like they are measuring the same thing (except insofar as something equivalent to relativity makes them tick slower), and measure time durations between locations that way.

All of this could be a trick, a facade. Light could go in one specific direction a billion times faster than the other, and all of our thoughts and experiments happen to not be able to tell.

But that is a lot of sneaking around by the universe when one that doesn't have this undetectable secret feature would look just the same.
posted by NotAYakk at 12:41 PM on September 30 [1 favorite]

A physical clock measures a succession of moments, but only experiencing duration allows us to recognise these seemingly separate moments as a succession. Clocks don’t measure time; we do.
If a clock ticks alone in a forest, is there a duration?
posted by k3ninho at 2:30 PM on September 30 [1 favorite]

> relativity makes them tick slower

Relativity says no one's clock is ticking slower, and that's also pretty important to understanding this argument.
posted by betaray at 2:33 PM on September 30 [1 favorite]

This means that Einstein’s definitions [of simultaneity as synchronised to a common reference clock] are not completely objective – they rely on the perceiver’s subjective experience of time for their meaningfulness, not just on objective procedures or tests. Only a conscious observer can establish simultaneity between an event and a clock.
Oh, now you've gone and claimed (nebulous) consciousness is needed. Plenty of animals have cause and effect, or use physical principles to hunt, survive and breed. Plus then our author is conflating an objective process that anyone might do -- even some animals predating as a pack -- with the subjective experience of actually verifying for yourself that setting a clock, walking away from it and then measuring signals from other things in sync with that clock results in simultaneous actions. Poor rhetoric, poor philosophy.

Bergson had argued that there is one universal time of duration in which all consciousness participates
I'm happy with my platonic cave and occasional ranting outside it. Aren't we sharing a moment outside each of our respective caves, but not often the same duration?
posted by k3ninho at 2:48 PM on September 30 [1 favorite]

It might just be that this guy just needed to wait for quantum mechanics to get more flushed out. So then you get to delve into this idea that time is a property that emerges from the interactions of quantum particles that are wave functions until such an interaction occurs.

I'm sure a real, modern physicist would have Bergson asking entirely different questions.

Something that still blows my mind is how a photon is a wave function until it interacts with something and then it's actual position is determined. Until then it's position is a bundle probabilities. So a when a photon goes from point A and arrives at point B it really arrives at some position around point B as defined by it's wave function and may appear slightly ahead or behind of the actual point. Which means the photon may have arrived slightly before or slightly after the most probably position. In which case the speed of light was slightly slower or slightly faster than...well...the speed of light. I'm sure I'm not fully understanding how wave functions work in this case but all that quantum stuff is weird.
posted by VTX at 3:15 PM on September 30 [1 favorite]

when you think of how mathematics has transformed in the 20c, i don't have any trouble thinking that this is as far as we will get until we come up with better mathematics; & it's only lack of imagination to suppose that we can't.
posted by graywyvern at 5:06 PM on September 30 [1 favorite]

roughly, when we measure time we're using our consciousness to do it and shouldn't that be included in relativity?
philosophically?

> a stopped clock’s right twice a day [tiktok]

> ☀️
posted by HearHere at 5:24 PM on September 30

I haven't delved into Bergson in detail but besides his dismissal of special relativity--and both special and general relativity have exquisitely passed all tests, see Is Einstein Still Right?--he seems to put way too much faith in his intuition and has closed himself from embracing something more complex if it fits detailed experiments better.

I don't think the problem in measuring a "one-way speed of light" is a barrier to relativity. One derives relativity from the assumption that c is the same for all, and that makes it a tightly constructed theory. It's not just arbitrary formulas put together. And then you find you're describing Minkowski spacetime. And the speed of light becomes kind of a conversion factor between space distances and time distances, like 100 is the conversion factor between centimeters and meters. If you wanted to use different conversion factors in different situations you could do that. In GR you have "general covariance", meaning you can shift around coordinates but as long as you adjust your spacetime distance formula, everyone's in agreement on the laws of physics. But you need a SPACETIME distance, not just separate space and time intervals.

Quantum theories have to strictly obey the Lorentz invariance that's at the heart of special relativity. However, quantum weirdness can lead to effects that SEEM to conflict with the spirit of "nothing moves faster than light." The Feynman propagator, which tells you about the effects of the presence of a particle here on other places and times, has a term that goes beyond where the particle can travel by speeds less than c, but this mathematical construction doesn't allow any communication faster than light.

Physicists and philosophers can both be guided by intuition but thinking is fallible. For a while physicist Lee Smolin was on about how our modern theories of physics don't have room for there being something meaningful corresponding to NOW. But ideas about our world have to be put to the test.
posted by Schmucko at 12:37 AM on October 1 [2 favorites]

Bergson's focus on needing a concept of absolute rest in order to describe time as it's experienced has a mathematical counterpart in relativity as the "proper time", which is relative to a world line; one can be "at rest" relative to that world line. And it is an important quantity in the theory, it is something that is a real part of nature, whereas the time used in a coordinate system for a frame of reference is a convention. But still the proper time needs to be related to a state of motion.

But in physics we're trying not just to describe the experience of an observer but to patch together different observers' views as as reality. That you always have the same subjective time isn't the final word on the universe, because the universe isn't just your own experiences.
posted by Schmucko at 12:06 PM on October 1 [2 favorites]

Our understanding of the relativity is based on the assumption the speed of light is one half of the round trip distance.

That's actually not an assumption, it's a result derived from the decision to define simultaneity with respect to a given inertial reference frame as that collection of events from which light would take an equal amount of time to propagate to points at an equal spatial distance if everything in between were a vacuum.

The key insight prompting the need for this definition was that simultaneity doesn't actually work as an absolute property of events in and of themselves, but must also take the observer's state of motion into account. The speed of light is actually more fundamental than simultaneity, because it just falls out of Maxwell's equations that describe the relationship between dynamic electric and magnetic fields. That speed is absolute given only a system of units to describe those fields, and fiddling about with it in an attempt to preserve absolute simultaneity yields results inconsistent with those well-confirmed equations. So Maxwell wins, and simultaneity loses, and to remain at all useful it needs to be redefined on Maxwell's terms instead of the other way around.

Two observers whose relative velocity is nonzero will not, in general, experience the same sets of distant events as precisely simultaneous because they will not, in general, measure the same positions for those events (assuming that the reference frames within which those measurements have meaning put the observer's own velocity at zero). For inertial reference frames (i.e. those within which acceleration is also zero) they can use the Lorentz transformation to reconcile their disparate measurements; more complicated transformations can be used to achieve the same thing for non-inertial reference frames.

However, those transformations all transform both timing and distance measurements in ways that do not preserve simultaneity across reference frames. And as it turns out, there is no transformation that does preserve simultaneity across reference frames while remaining consistent with Maxwell.

And none of these considerations have anything whatsoever to say about events that are co-located with an observer (i.e. occurring at distance zero within that observer's reference frame), so none of them are in any way inconsistent with the passing of time being a thing that any given observer is capable of experiencing. Which means Bergson is mostly talking out his arse here, as respectable philosophers are wont to do.
posted by flabdablet at 2:48 AM on October 2 [3 favorites]

then it's actual position is determined

Correct me if I'm totally blowing this but the "correct" understanding is that it's determined only as much as it needs to be determined for the particular physical interactions that actually occur. Otherwise, those remain "unspecified".
posted by DeepSeaHaggis at 11:12 PM on October 3 [1 favorite]