Craig Callender on time, QG, blackhole thermodynamics, ethics | Thing in itself w/ Ashar Khan
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- čas přidán 4. 07. 2024
- Craig Callender is professor of philosophy at UC San Diego and co-director of the Institute for Practical Ethics. His work focuses on the philosophy of science, with special emphasis on physics, time, and the environment.
0:00 intro
3:32 two times problem
7:05 going from here to there
8:47 manifest time
11:35 is manifest time universal?
15:46 can we find manifest time anywhere in physics?
22:29 cognitive science and time
35:15 objection of purifying time
42:25 philosophy of time
44:40 quantum gravity and time
49:33 interpretations of quantum mechanics
54:33 blackhole thermodynamics
1:07:01 ethics and practical ethics
1:11:26 environmental ethics
Craig Callender's Website:
www.craigcallender.com/
Craig Callender Books:
What Makes Time Special? (2007)
Introducing Time: A Graphic Guide (2001)
The Oxford Handbook of Philosophy of Time (2011)
Time, Reality and Experience (2002)
Physics Meets Philosophy at the Planck Scale: Contemporary Theories in Quantum Gravity (2001)
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Introducing the concept of 4-space, a fundamental difference between time x0 and spatial coordinates is allowed.
It supposedly consists of the fact that along the world lines corresponding to physical processes, x0 can only grow, whereas x1, x2, x3 can change as you please.
However, the unification of spatial coordinates and time into a single manifold is not formal but is a real reflection of the picture of the world, and self-closure does not take place for the 4-line.
The time coordinate pulls along with it the spatial coordinates, because if it is impossible to return to the past, then it is also impossible to return to where "there" is not with the spontaneous accumulation of space-time history.
Wow! That opening. Encapsulates pretty much my critique of the QG programs perfectly.
0D is the only necessary dimension.
space
/spās/
noun
1. a continuous area or expanse which is free, available, or unoccupied.
"a table took up much of the space"
2. the dimensions of height, depth, and width within which all things exist and move.
"the work gives the sense of a journey in space and time"
0D Monad
1D Line
2D Plane
3D Volume
4D Architecture
5D Design
4D temporal length
5D temporal length, breadth
6D temporal length, breadth, depth
Ashar, regardless of my sometimes acerbic comments below, I really enjoyed this interview, and Craig seems like a really nice guy. Thanks! I wish him well with the ethics institute. I'd recommend to him that he groks MMT - you have to understand the monetary system when you are in a monetary economy, to learn why the environmental problems are entirely surmountable. Lack of comprehension of monetary operations is what holds otherwise well-intentioned people back - they tend to think you have to tax people to get money. Well... you DO NOT! Governments are the monopoly currency issuers, they are not currency users, they issue tax liabilities to drive _demand_ for their otherwise worthless fiat currency, they are not using the tax receipts to get _supply_ of their own currency of account. The US colonies used to know this, they'd burn all the tax receipts.
The tax _revenue_ (literally "return back") is a redemption, not a supply. Once you understand this, investments by governments to address environmental problems become clearly a matter of lack of willingness to spend, not lack of capacity to spend --- because a currency issuer can always employ any idle resources, including all idle labour, without inflation bias.
That is because the private sector bid for unemployed resources is zero, and the stock of money in existence has zero inflation impact. It is the rate of flow of currency competing for already employed resources that exerts price pressure, not the stock of money. Savings accounts and bank reserves, no matter how enormous, are not inflationary; extension of bank credit into circulation from leverage of those assets (thanks to lax regulations on credit extension) is what is inflationary, but people with enormous savings are not the ones taking out bank credit.
@21:00 the "problem" of time in relativity is resolved by Einstein and pseudo-Riemannian geometry. It is a formal problem. The solution is that one can only define a time coordinate locally, infinitesimally, and only if the spacetime manifold is globally oriented (so no Planck scale gnarly topology) can you extend globally. Also, it's a Block Universe, so there is no "now" in physics, that's a problem of consciousness, not a problem of physics. (Despite George Ellis' CBU, QM doesn't add anything new or more profound to this.) Callender's advisor/mentor, Huw Price has some good stuff to say about the "arrow of time" but again that does not add anything to Einstein's answers.
Exactly.
In general, no law of conservation of time is known - this circumstance is connected with the fact that space-time is a manifestation of the spontaneous evolution of the grav-inertial field. Damping takes place - vibration damping in a dynamic system by dissipation (dissipation) of the vibration energy when d
I would like to share some work on General Relativity I have done... can I drop a link here ?
Thanks for the great content, btw !
Thanks - yes, please feel free!
I have never understood what it means when physicists say that microphysics is time reversible. The way I think about it is that if the directions of velocities of particles involved in an experiment were reversed we would deduce the same laws of physics from the experiment. But the time will still run in a forward direction. In fact, it may be that talking about reverse flowing time may be a meaningless concept i.e. time has only one direction in which it can flow in and we call it forward. Just because "reverse" is the opposite of "forward" does not mean that "reverse" can be meaningfully applied to the direction of time.
You are correct in one of your observations, that there is time symmetry in physical law, which means you can't see the difference between playing the equation forwards or backwards so to say; there has not been put a non-commutative direction to time in it.
The thing about microphysics time reversibility (without having watched this video, so maybe I'm addressing the wrong thing here) can be found in Hans Reichenbachs book The Direction of Time which is actually the reasoning of Richard Feynman, namely that a positron moving forward in time is the same as an electron moving backwards in time. And if you then look at the scattering diagram instead of two seperate electrons and one position in this Feynman diagram, you have only one electron moving sideways through space so to say, by going forwards and backward in time. This is also an application of the 'single electron in the universe' idea by his PhD advisor John Wheeler.
To learn that much of Feynman's ideas have been based on such tiny single ideas is very interesting indeed, similarly he learned the path integral idea to himself by trying to solve a proof he didn't understand of Newton's Principia.
Such very simple things make him a relatable character even behind his major enigma, when you start to understand his logic
@Apsteronaldo Let me clarify what I am saying. I think the concept of reverse flowing time is meaningless. Velocity is a vector. Thus, it has magnitude and direction. The physics does not change when velocities i.e. the direction of particle motion is inverted, and the physics remains the same. In the scenario, the time is still moving from before event to after event - the only way time can flow. I think calling that "forward" has given the wrong idea that time can go "reverse".
@@SandipChitale velocity as a vector is a Newtonian concept
@23:00 tap a table, or a hot or freezing object, and you'll notice at least four lags: touch, sound, vision, heat. (Hard to discern all at once, I can only notice in pairs, sometimes a triple, with heat being the easiest to tell is lagged.) Not profound stuff really... or is it? Consciousness unifies all these events perceived at different times if we concentrate hard, so that when not concentrating they are all "One". I always feel there is hardly any better simple demonstration that consciousness is not a computation. A computational state is only ever one-off. Consciousness holds several One's in a Many, so consciousness is an entity that experiences processes (not _just_ an abstract process, as William James thought).
@11:00 we tend not to think about "carving up space into left and left" but we could. So the issue is why the past/future carving seems a lot more important than a left/right or up/down carving. The trivial part is time is uni-dimensional. The deep part is because time is correlated with conscious thought progression. A physicist is never going to understand this second deeper aspect. Because it involves consciousness it is a metaphysical question. Callender did have a good stab at it, and his eclectic approach is the way to go I feel. But he needs to be even more eclectic. You cannot ignore the metaphysics of the conscious soul. You do not have to know what the soul is in essence, but you cannot ignore the associated subjective phenomenology. (Nor should you go the continental philosophy route and tell meaningless fairy stories and string together words in mumbo-jumbo = almost every postmodernist pseudo-philosopher.)
And @34:00 spacelike directions are not 3-dimensional, they're one dimensional, and there are three of them. No event (centre of mass let's say) can move in literally 3D, it's only ever 1D + 1D. The Schrödinger equation does not spread out the quanta in space, it spreads out epistemologically (the wave-function or QFT fields are information about correlators, not the particle itself). THING IN ITSELF! = not a bad philosophical concept. ;-)
justathought.
Try reading his book "What makes time special", he goes all on about the psychology as well
Check 5-min video "Time = Quantum Fluctuations. Gravity = Time Dilation. Strong Force = Gravity."
It is said that in the block universe or the growing-block universe it is said that the past (events) exists. I do not understand that. I think that is basically changing the definition of the word "exist". Only if the traces of the effects of a past event can be accessed in the present, only then it can be remembered. If all the traces are lost effectively those events might as well have not happened. For example, if someone walked on the beach last night and the waves erased the footprints, then we cannot claim the event that someone walked on the beach last night happened. Also, note that the footprints were erased because of increasing entropy. And that increasing entropy was the cause of erasing the traces. This puts a hole in the past hypothesis which claims that we remember the past because the entropy was low in the past, yet in the example the increasing entropy erased the past event of someone walking on the beach in the example above.
Time emerges from change. If there is no change the concept of time is rendered meaningless. The order of events provides the direction to the time. Subparts of the universe that have cyclic configurations (which we can abstractly think of as clocks) open the possibility of the concept of the "rate of flow" of time. If there are no subparts of the universe that are cyclic in configuration, the meaning of the "rate of flow" of time disappears.
The block universe, growing-block universe and Presenting are not about manifest time. It is my understanding that they are about the time of physics.
it seems has something at 20 minutes
@41:00 zooming i on the screen to read your bookshelf Ashar,... I have to say I really object to you having _Gray's Anatomy_ only a book apart from Strangs' _Linear Algebra._ I mean, what the hell man? Book subjects and titles have a well-ordering,
Honestly, you’re totally right and I’ll never fully live this down.
@@Thinginitselfpodcast 🙏
@1:04:00 this was interesting. I agree the "informatization of physics" is a lot of bullshyte (it is meaningless nonsense to locate all physics in information theory, just as it is nonsense to say a sentence describing a cow _is_ a cow). However, once again Craig seems a bit naïve. The issue is not really "information loss" per se, I mean who cares if Richard Nixon got thrown into a black hole together with your old laundry? The issue is _unitary time evolution_ in quantum mechanics. Because it recks physical probability entirely if time evolution is non-unitary. It would mean probabilities do not always sum to unity. That is what is at issue. "Information loss" is a rubric term for this, and is not quite the right phrase, it's slightly misleading, because Craig is right: subjectively accessible information can be lost all the time, but that does not change the probability sums in the (now inaccessible) objective reality. No matter how inaccessible the states inside a black hole are, they should obey unitarity, otherwise the entire universe literally would make no sense!
In starker terms, if I could make probabilities sum to 1.2 (or 0.9, or anything non-unit) then I would have the power of a god (or at least something like Thanos).
His manhole gap in spacetime metaphor is only slightly apropo. That metaphor _does_ describe true information loss AND loss of unitarity. But that is precisely why the BHIL puzzle is important. One could call this the "No Callender manholes conjecture" or something, but what that restates is just the principle of unitary time evolution.
@1:00:00 not sure what Craig's beef with BHT is, even after reading the paper with Dougherty. If a BH can radiate away mass, then it's a heat engine, it can perform work, and that's independent of the statistical mechanics details. So it _is_ a thermodynamical system. But that's not _all_ a black hole is! (Like that's not all a locomotive engine is.) So sure, it is not an identity. I could not figure out what identity he is talking about (even though he strings words together in his paper to state what he thinks the identity is!) Thermodynamics is an abstraction, it is not "real physics". So there is not even an identity worth talking about. So when he claims thermodynamics is "only an analogy" used to study black holes, that is all anyone really says. Those who claim BHT is some "identity" to SM thermodynamics probably do not really think hard about what they mean. The way we count accessible states differs for _every_ SM system. It is done one way for an ideal gas, differently for a real gas, different for a fluid, different for an Ising model, different for a black hole. So methinks Craig constructed a strawman in order to write a journal paper (though I am sure he honestly did not see it as a straw-man.)
Also, their paper gets some things plain wrong, they write: "A key assumption throughout BHT is that the entropy of a body that has fallen into a black hole is lost." But that is not true . No one serious in BHSM research ever writes "entropy gets lost." They'd say information is lost. That's not the same as entropy. Entropy is a count of the microstates accessible to the system, given a set of constraints. When matter falls in the number of accessible states goes up, so entropy increases. This is not the same as Shannon entropy which concerns probabilities. It is related to Shannon entropy only when one coarse grains the information, so losing information in the subjective sense, not the objective sense. It is not the Shannon entropy that's the problem for the BHL paradox. (And, if you ask me, ER=EPR has resolved the paradox for good.)
Also, there is nothing weird about the BH area being proportional to the BH entropy. That's just ordinary general relativity. Susskind says it is a new principle, the holographic or black hole complementarity principle, but that's a bit grandiose. All the observable infalling matter is stuck at the horizon as measured (as "seen") by an external observer. So the information is never lost to the rest of the universe, it can be "read off" in principle. ER=EPR tells you the information is still there after full evaporation too. So it is just general relativity that makes the BH entropy a bit weird. That's hardly shocking, given it is already "weird" (read: not so intuitive to us slightly non-dumb apes) that time dilates near a strong gravity gradient or with inertial acceleration (via Principle of Equivalence.).
Also, the dimensionality of a geometry has nothing directly to do with entropy. Like I said above, entropy is a measure of accessible states. So on a smooth geometry some sort of discrete coarse graining is needed just to get an entropy - so one is already engaged with a (very useful) fictional abstraction. If the Area is how to best compute the number of states, then you have Area in the entropy formula. There is nothing bizarre about that. The entropy of an ensemble of very thin soap bubble films would have the film thickness mostly factored out (or only a small higher order correction term). And btw, higher order field corrections to black hole entropy also will have volume terms - we just do not need to compute them, because no one depends upon such terms for current theoretical applications. Black hole complexity (which does involve bulk volume) is the far more important thing, the entropy puzzle is largely passé.
@40:00 Yes, it is a fools game to try to contrive a theory of language in such terms. But Craig seems to be ignoring or avoiding the phenomenology of metal qualae here. Yes: You cannot talk about time without using tense. You cannot talk about other subjects without using indexicals. There is no bootstrapping of language from language in these cases. This, to my mind, is strong evidence language or linguistics is not the core of human thought.
Besides this, it just seems prima facie more plausible that mental qualae arise first, and language faculties later. Language needs a mental realm with which to create references, and not just indexical references! All sorts of references. The concept of quantity and hence abstraction to numbers for instance. Craig mentions also the concept of space, hence abstraction to geometry. The abstractions are always mental, not physical. They are not computations or physical states, they are subjective qualia.
Even the great linguist, Noam Chomsky, admits he has non-linguistic thoughts all the time (as do I freely admit I do), some that are even barely conscious. It's these almost unconscious mental qualae that again strongly suggest language is post mentality, not pre-mentality.
@1:01:00 again Craig comes across as very naïve (despite his undoubted broad knowledge). The black hole horizon (there are several varieties) is an observable. You can detect lensing and gravity and just compute where the horizon will be. A horizon does not just "float past us". We'd in principle feel an acceleration of the BH, however feeble it is, it is only a witless non-astronomer without a gravity detector who would "not notice." OK, so that means most people on Earth would "not notice". But those who do notice would fast be in the world wide press, I can assure you.
I think what Craig must mean is that the horizon is "not visible" or is "intangible". But so what? Not all observables are visible or tangible. Heck, mass-energy itself is intangible, because it depends upon interaction to become observable. You cannot "see a mass" there is no such notion. You can only ever "see" light scattering off a mass.
Geodesics don't measure gravity my friend. It is called freefall. You would need a normal force to "measure the gravity"
'The observations are done by people ...' - in regard to phenomenology. But to get past 'the everyday', people equipped with devices that greatly augment their senses! Bergson could (and did) get nowhere compared wit say Einstein whose thought experiments, later backed up by actual ones, were able to pick up a far more extensive understanding than Bergson ever could - or did.