The Arrow of Time in Causal Networks
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- Опубликовано: 29 июл 2024
- Sean Carroll (Caltech and Santa Fe Institute)
simons.berkeley.edu/events/ca...
Causality
Abstract:
A macroscopic arrow of time can be derived from reversible and time-symmetric fundamental laws if we assume an appropriate notion of coarse-graining and a Past Hypothesis of low entropy at early times. It is an ongoing project to show how familiar aspects of time's arrow, such as the fact that causes precede effects, can be derived from such a formalism. I will argue that the causal arrow arises naturally when we describe macroscopic systems in terms of a causal network, and make some suggestions about how to fit prediction and memory into this framework.
Sean Carroll is a Research Professor of theoretical physics at the California Institute of Technology, and Fractal Faculty at the Santa Fe Institute. He received his Ph.D. in 1993 from Harvard University. His research focuses on foundational questions in quantum mechanics, spacetime, cosmology, emergence, entropy, and complexity, occasionally touching on issues of dark matter, dark energy, symmetry, and the origin of the universe. Carroll is the author of Something Deeply Hidden, The Big Picture, The Particle at the End of the Universe, From Eternity to Here, and Spacetime and Geometry: An Introduction to General Relativity. He has been awarded prizes and fellowships by the National Science Foundation, NASA, the Sloan Foundation, the Packard Foundation, the American Physical Society, the American Institute of Physics, the American Association for the Advancement of Science, the Freedom From Religion Foundation, the Royal Society of London, and the Guggenheim Foundation. Carroll has appeared on TV shows such as The Colbert Report, PBS's NOVA, and Through the Wormhole with Morgan Freeman, and frequently serves as a science consultant for film and television. He is host of the weekly Mindscape podcast. He lives in Los Angeles with his wife, writer Jennifer Ouellette.
This talk was accompanied by a live chat that I enjoyed the most in my life (until the last minutes).
I watched this whole thing to get to slide that was used as the thumbnail. Someone realized that was the most exciting thing in the lecture.
Wonderful lecture!
I'm happy he can now fully focus on the metaphysics of physics in which I trust he can certainly make breakthroughs and expand our knowledge in interesting ways, where in teaching QM or GR specifically it would be more difficult
And I trust in the end this endeavour will tell us much more about the route where to go with QM and GR, so it will help physics directly too in the end. Because he's very good at it, and able to explain it to us
Dude, Sean is my BOY. *pounds chest* One of the most intelligent men alive. He has added so much to the world already, and will continue to until he dies at the ripe old age of 110 hopefully. Can we make him a robot by then? I say let's do it
Observations suggest that the initial gravitational entropy of our universe was very low and that certainly needs some good explanation.
Penrose's ideas like the Weyl Curvature hypothesis and his CCC cosmological model are mainly motivated by this, and there are other proposals , including S. Carroll's.
On the other hand, it's easy to imagine a highly inhomogeneous / anisotropic universe, with lots of primordial black holes , that starts with much higher initial gravitational entropy !
In that hypothetical universe , there is a forward time direction, too..
This universe will expand, probably. Also, these primordial black holes will accrete matter, merge with each other , Hawking- radiate in the far future and so on.
Entropy grows there more and more as time goes by..
So, although the low initial entropy of our universe is important and needs explanation, it does not explain, by itself, the existence of the time arrow..
There is time asymmetry at the lowest level in particle physics
because CP symmetry is violated
but CPT symmetry is assumed to hold
so T symmetry must be violated.
surprised by all the experts in these comments who can rebut all this in half a paragraph.
impressive!
08:02 Funny :-)
52:12
“When people say ‘Life is a fight against the increase of entropy’,
they have it _exactly_ wrong. The only reason life is possible is
because entropy is increasing. If entropy weren't increasing we'd
be in thermal equilibrium, there would be no life around, so life is
parasitic upon the fact that entropy increases.”
The more interesting question would be if time itself would exist without an increase in entropy. What is time in thermal equilibrium? If it exists then how can time be measured if entropy is not changing?
@@fkeyvan but entropy doesn't increase uniformly in any way. so it would be hard to find a mechanism to quantify time based on entropy increase...
and time is very much localized, while entropy is not (entropy can even decrease in macroscopic spacetime regions!)
@@deinauge7894 I think he means the increase of the entropy of the universe. That might increase more or less in some locations. ANother thought is maybe he means time emerges when entropy changes and the arrow of time emerges when entropy increases. All this doesn’t sound right because time would depend on entropy and entropy would depend on time. We need a better measure of time. We need to free time from entropy. We know that entanglement does generate space and time. Maybe it’s best to base the definition of time on entanglement or correlation.
@@fkeyvan or try to describe the world without any concept of "change" and "time". and find some emergent property that is compatible with being experienced as time.
i suspect the entenglement ansatz tries to do this - of course for spacetime as a whole, not just time
Mario ian property is the memory less one - it is fun that the memory less feature is what allows us to remember - it feels right
what is the vehicle by which Entropy "increases"?
Around 54:30 Dr Carroll argues that the most probably reason for the glass falling over is that the molecules happen to move in the same direction. The microstates must conserve momentum, so I never understood this sort of explanation - it does not conserve momentum. I don't see how integrating a lot of momentum conserving collisions in some finite time interval results in momentum beging imparted to the glass of wine as a whole at as level that could tip over the glass. I do understand Brownian motion, but we are not discussing Brownian motion as the level of the glass of wine. That depends upon fluctuations at the level of single collisions. Why would I expect the glass to topple over from 'random' fluctuations in the distribution of the molecules? Momentum is conserved for the individual particles and for a collection of any set of particles. There is still energy and momentum exchange at the surface of the wine glass and its environment. For a similar reason, I don't expect that the molecules of wine to evaporate rapidly - the liquid is in a lower energy state Aand energy is conserved at the micro level.
I was thinking about this in the lab, as I considered a jet of helium gas exiting a nozzle. To understand the ultimate Mach number of the jet (around 250-300), I needed to consider the quantum efficts between individual atoms. A millisecond or so after the atoms were treated as particles in a gas, they were being scatter from single crystal surfaces to produce a diffraction pattern. - they were treated as waves. How do 2 protons, 2 neutrons and 4 electrons form a single wave? Understanding that experiment was a real mind bender for me. Fluid dynamics, Bose condensation and wave/particle duality all in a millisecond :)
Norton’s Dome broke my notion of causality.
I wonder if there are experimental proof that microphysics is reversible? I mean from superposition to state and then back?
a superposition is also just a state... you can only call it superposition when you describe it in a fixed base. in a different base, your simple state could be a superposition and your superposition a simple state.
but i know that what you mean is the "measurement", where somehow one base is chosen (the one that matches the measured observable), and the previous state is changed to one of the base states of that observable. i don't think that this is reversible. but it is also not part of the evolution of microstates in quantum mechanics.
@@deinauge7894
Superposition makes no distinction in time.
The concept of time must be how everything relates to everything else.
Knowing that the presentation is "a foreign language" of symbols specific to the situation in which they were first used, (Dimensional Analysis was the Measurement Problem situation I was unable to process quickly enough to relate to the intended educational purpose), the Intuitive approach is to apply correspondence of what has to be default functionality intended for the Symbolic re-presentation of pure-math phenomena.
So the sequences of Quantum Computational AM-FM Logic Fields in a drawing out of a learning process, a dimensionality coordination interpretation of 0-1-2-ness GD&P line-of-sight superposition density-intensity identification of holistic integration, Fluxion-Integral Temporal Calculus, is restricted to Math-Physics analogous combinations of instantaneous trancendental orbital-orbit projection-drawing increments representing the Unit Circle at the Centre of Time Duration Timing, Spheroidal "Neutronic" Conception, and Conic-cyclonic coherence-cohesion objectives in temporal versions of the Hydrogen -> Holographic standing wave modulation in Polar-Cartesian self-defining bubble-modes of Fluxion-Integral Temporal Calculus Condensation here-now-forever, the trancendental aberration foci of self-defining Superspin Modulation Mechanism Lensing of Logarithmic Time Condensation here-now-forever continuous creation-emanation of e-Pi-i Inflation-Geometrical-Drawing-Gravitational Reciproction-recirculation Singularity positioning => pure-math relative-timing ratio-rates motion => Sublimation Zero-infinity Kelvin Freeze-frame phase-locked coherence-cohesion sync-duration shaping-shifting according to empirical laws, in time-timing metastability.
Therefore the topic of this video suggests that the perceived Arrow of Time is the directional nature of relative-timing superposition identification of fractal conic-cyclonic resonances in holographic perspectives, Reciproction-recirculation vanishing-into-no-thing ('entropic' hyper-hypo instantaneous remodulation).
The Focusing Centre of Time e-Pi-i Resonances, float in Eternity-now Actuality, pure-math motion-potential Interval, and instantaneous => Symbolic re-presentation of Dimensionality coordination sequences is composed of 3D-T abstractions-in-focus, objectives vanishing-into-no-thing, arranged in accordance with our guessed perceptions => Theoretical Calculus Analysis in specified conditions ("Define your Terms philosophically). This is the "Circle of Infinity" Conception experienced since ancient times.
The term Causality => pure-math relative-timing ratio-rates Circuitry, Reciproction-recirculation Singularity repositioning shaping - shifting Calculus = cause-effect e-Pi-i QM-TIME Completeness. Therefore General Relativistic relative-timing at Absolute, instantaneous Zero Kelvin Origin of omnidirectional-dimensional cause-effect self-defining Actuality, and so denies any connection to Big Bang Theory reasoning as a dis-located and discrete existence beyond this here-now-forever Causality, a Reciproction-recirculation instantaneous No-thing probability, and is therefore simply impossible in real-time re-evolution, ie AM-FM ONE-INFINITY hyper-hypo resonance circularity-> eternal modulation interference quantization mechanism, this landscaping Actuality floating on No-thing, trancendental condensation projection-drawing Quantum-fields Perspective.
Term definition of the concept of "therefore" is equivalent to "observation of superimposed presence in existence", ie Euler's e-Pi-i 1-0-infinity resonance, => macro-micro-loop bonding,
It is obvious that time flow is not equal, even if it seems like this due limited context. I can put and event where I state of system in the past. So I by reversing time I would be able to get to the point where I know the past = predicting the future, without calculating the interactions. This is not possible with usual arrow of time.
arrow(S) of time
In the second derivative the time t is not exactly 'sqired'.
i'm sure there's a reason for this and i get the basic equation he's talking about at the start isn't about gravity, just about forces, but every time i hear someone say "you couldn't tell if the movie of a pendulum going back and forwards was played forwards or backwards" all i can think is, if a movie of a ball being dropped was played you'd always know because gravity only goes one way.
i really wish people would say something about gravity only going one direction over time and why that doesn't give us an arrow of time. all the other forces could be positive or negative, but gravity only really goes one way. why isn't that considered time symmetry breaking?
Of course Carroll gave other examples of movies where we could tell if they were played in reverse, say of watching the cream mix or unmix in the coffee. I think his point is that (1) you can't make this distinction if the movie is just showing interactions between fundamental particles, and (2) you also can't do so for /certain/ macroscopic phenomena where entropy does not change on modestly short time-scales, e.g., a pendulum swinging (if it's large compared to the frictional force of air or on the pivot), or planets orbiting a star, where again there is essentially no friction, the system is isolated, and you only watch it for a while, not for billions of years. Actually, though, the same can be true of a ball: if it is highly elastic, and you just reverse a few seconds of a film, you may not be able to tell if you're seeing someone drop a ball to the ground, or a fragment of a larger film in which a previously-dropped ball bounced against the ground and up towards someone's hand, who then gracefully catches it. In the first case, gravity accelerates the ball toward the ground, increasing its velocity to some higher one; in the second case, the same gravitational force decelerates a ball with large initial velocity away from the ground so it is essentially motionless at the moment someone grabs it. So there's nothing special about gravity: it obeys perfectly time-reversible equations. You might be able to distinguish the two cases by looking carefully at the person's hand, or detecting speed changes due to air friction, etc. But such cases simply fall into the first category of cream and coffee mixing, where entropy increases due to the large number of ways in which motion can be microscopically distributed (e.g., when heating the air, or in the fine details of how muscles work), compared to the small number of ones which do focused work, so that it is more likely that a coherent mass of a ball will lose energy and randomly scatter some air molecules than that those fast molecules will converge to deliver their momentum in the same direction on the ball to accelerate it. So gravity, like other basic forces, doesn't work just "one way" in time: you can reverse a film of purely gravitational interactions (a perfectly elastic ball bouncing in a vacuum on a frictionless surface, planets orbiting a star) and you will see gravity operating perfectly in both cases with absolutely nothing to indicate whether the film was played forward or backward.
@@scottforschler1847 i sincerely hope they read that, because you made your points well
"Increasing entropy is the sole reason for the asymmetry of the past and the future in the macroscopic world." What about the reverse statement:
"The asymmetry of past and future in the macroscopic world is the sole reason fro the increase in entropy"?
Good point.. Scientists like Sean always stick to the more conservative and easy to digest explanations because they care more about their own PR than delving into controversial but interesting solutions
@@fkeyvan Actually, scientists love nothing more than interesting solutions, and if they are controversial then that helps the PR too! My point whether "cause precedes effects" is a consequence of "entropy increases" (as Sean proposes), or is it the other way round? Or indeed are they equivalent notions - at least for us macroscopic observers?
@@johngough2958 i am constantly thinking what are the most basic unconscious assumptions that are made about entropy, time and its arrow. I think one is that time and entropy are distinct phenomena. Like kinetic energy and distance for an object in free fall. KE increases the more an object falls is like entropy increases with time. But at the same time he states that the arrow of time or the direction time progresses is due to entropy increase. Like as if saying the direction of the object falling depends on KE increase. If that is so then entropy and time are not distinct phenomena but are manifestations of the same thing. Entropy is physical because it has to do with microstates of matter and time is abstract.
yeah that message was originally published on the internet since 2006 on hubpages in more details then later on closer to truth youtube channel:
the current mathematics and physics are not enough so it is better to focus on improving the current fuel engines by generating a synchronized continuous electromagnetic pads for thrust instead of wasting a huge amount of energy.
has been deleted too !
Unfortunately Sean doesn't say what our evidence for the Past Hypothesis is. It seems all our evidence, our observed records, are compatible with the Past Hypothesis being false, with entropy increasing in both time directions. Of course that seems intuitively absurd: Surely it is overwhelmingly likely that the Past Hypothesis is true, i.e. that there is a low entropy past. But what scientific reasons do we actually have to believe this? Is the Past Hypothesis perhaps simpler than its opposite, and therefore favoured by Ockham's razor?
Sean talks about attempts to _explain why there is a low entropy past,_ but it seems much more important to first find a solid scientific justification for the hypothesis that there is a low entropy past in the first place. It seems backwards to try to explain the truth of the Past Hypothesis before we have a solid justification for its truth.
Another puzzle is whether time without an arrow would still exist? He would probably say that time exists even if entropy does not increase. Is that really true? The only time entropy would stop increasing in the universe is at the end with all BH’s evaporated. All that would exist then would be photons and they do not experience time ( or space ). So I would think time without an arrow would NOT exist. If that is so then entropy does not increase with time, because time and entropy would be indistinguishable.
Dr. thief will need this too:
the triangles in one of my previous comments on this youtube channel is to represent particles at the quantum level, then larger to atoms, molecular, ....
the starting point of the triangle points to the beginning of the starting point of the universe, rotating the triangles is to demonstrate the concepts of constants "Pi" in this case and it is relation to Planck's and cosmological constants "space and time", .... (think about Dirac's cosmology and why he was wondering).
I cut it from one of my comments on closer to truth, I comment their since 2019, but I have noticed that they read my comments then they delete hem later purposely "probably for thievery purpose" because texts size are nothing comparing to the video content and that the interactions of the audience through comments is what gives value, why you publish videos through youtube without the public interaction?
It may be a spurious guess, but the cause-effect relationship of compounding pollutants such as Smoking to Cancer, seems to be categorised by repeated failures of Immune Systems to carry out repairs, in keeping with complex natural bio-logical temporal pulse-evolution Organic Chemistry, due to interfering imbalances of (non) "nutrients" and all that implies in zero-infinity sync-duration time-timing connectivity.
Past-future = Reciproction-recirculation Arrow of Time = Clock-work emulation of Presence in Temporal superposition Singularity-point positioning Conception=Calculus.
if you create 2 entangled particles and shoot them opposite direction and you have a detector in that direction at a distance for both, then if you measure spin of one of them on one side then it is the cause and causes the other particle's spin to be in a state. But if you are in a fast car moving parallell to this experiment you will see the other detector making the measurement and causing the other particle's spin to be determined. So cause and effect in this case depends on if you are stationery or watching this experiment from the car.
im not sure how the car part makes sense.
time has mass
the apes started to think about this too "steal":
Dr. thief will need this too:
the triangles in one of my previous comments on this youtube channel is to represent particles at the quantum level, then larger to atoms, molecular, ....
the starting point of the triangle points to the beginning of the starting point of the universe, rotating the triangles is to demonstrate the concepts of constants "Pi" in this case and it is relation to Planck's and cosmological constants "space and time", .... (think about Dirac's cosmology and why he was wondering).
I cut it from one of my comments on closer to truth, I comment their since 2019, but I have noticed that they read my comments then they delete hem later purposely "probably for thievery purpose" because texts size are nothing comparing to the video content and that the interactions of the audience through comments is what gives value, why you publish videos through youtube without the public interaction?
whatever the apes do, nothing can turn the apes into humans.
yeah the apes must think about space using patching techniques "they already have stolen time"
Apes! who can blame apes!
Haroon Averroes
3 weeks ago
59:00 give your clown this:
time strongly related to space, humans need space as arena to calculate time, time travel to the past is not possible, why it is a long story, basically if that is possible humans in future would come to me directly ! unfair!
your brain makes continuous calculations for dimensions and change thus "time", the cerebellum plays main role in that process, but you are unaware of that, that is why speed, acceleration, velocity,... are strongly related to space and time and how we measure them.
reference, memory, ..... it is a long story! the clock and hour, minute hands are the reference and memory, ticking is the measurement, ....
the story is in space itself, they have misunderstanding, there is a process of space creation and there are two cycles not only one cycle, still too early for that.
that does not mean that time does not exist or just an illusion, it only means: there is no time without space.
they can use thievery as patching techniques as usual "it is an old habit".
doesn't that seems familiar? I mean what the irrational thieves have discovered later (time!)
by the way I have wrote that many years ago, the apes couldn't comprehend, but later was clearer to the apes.
Sean says the arrow of time exists because entropy of a closed system increases with time. This seems to me a circular argument. Anyone?
It does seem circular. You can't say something is increasing without already presupposing a direction of time. That same thing would be decreasing if you presupposed the opposite direction of time.
@@brianfreeborn2965 thank you. You made it clearer. Any further ideas?
@@golagaz we’re talking about the arrow of time, not time itself. Sean says the arrow of time exists because entropy increases with time. Nothing to do with energy- momentum
How I understood it, from the slide at 23:24, entropy doesn't increase in one direction of time, but in general increases in both directions.
Aka, if you observe a system at some point in time with non-maximum entropy, without knowing anything else, you're best guess for how both past and future look like, is higher entropy.
Take for example billiard balls that have been bouncing around for eternity. If at some point you observe them to be all in a triangle (= a low entropy state), then the best guess is that just before and just after they were something random.
So what breaks the asymmetry is the assumption that in one of the two time directions (which we happen to call the past), there happens to be a very low entropy state (the big bang).
I disagree, if you have to invent probability states for your analysis then you don't understand entanglement which is the reason to analyze a complex system in the first place. Hence, some of your concepts are OK but your theory is not, proper handling of the probability distribution should always lead to entanglement equations of a complex system.
Dr. thief wants to steal this: it is a comment on Dr. Brian Keating youtube channel:
please give Jimi this to do his homework:
time strongly related to space, humans need space as arena to calculate time, time travel to the past is not possible, why it is a long story, basically if that is possible humans in future would come to me directly ! unfair!
your brain makes continuous calculations for dimensions and change thus "time", the cerebellum plays main role in that process, but you are unaware of that, that is why speed, acceleration, velocity,... are strongly related to space and time and how we measure them.
reference, memory, ..... it is a long story! the clock and hour, minute hands are the reference and memory, ticking is the measurement, ....
the story is in space itself, they have misunderstanding, there is a process of space creation and there are two cycles not only one cycle, still too early for that.
that does not mean that time does not exist or just an illusion, it only means: there is no time without space.
they can use thievery as patching techniques as usual "it is an old habit". they steal gradually so no one can notice.
The universe began in a perfect state. Then Adam & Eve caused God to pronounce a curse against Satan.
This was when entropy began. 😊
Entropy is a word, like Love, that we use out of convenience, but that hardly describe the reality. IMHO.
Entropy is a word but it is also a representation of states of a system.
Just like love, entropy has a very clear and simple definition. It's just that most people choose to ignore those definitions and make up their own magical ones...
wow, I bet you write great Valentine's Day cards.
@Maloxi please define entropy with words. also i would like to see your definition of "love" seeing as how you carelessly bring an abstract concept like love into a scientific argument.
Your egg analogie is garbage, because energy is being added to the system in the scracking, scrambling and cooking, and no one scrambled the shell. Plus, it is becoming more homogenous, so is that more order or less than a separate egg and white.
He is a thief 100% steals gradually (thievery as patching techniques"
He is a thief, very clear
A whole lot of talk to define entropy and the arrow of time. Light always travels away from it's source. It's that simple. So these con men get paid by the word???
it's very funny you should use massless particles to make whatever your point is
@@WeeWeeJumbo The point is these scammers take something very simple and fill it full of lies and then they make the government force their gibberish bs onto us. All for profit. The definition of entropy is light always travels away from it's source. One simple sentence.