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RECENT POSTS IN THIS TOPIC

Lorraine Ford: on 8/29/19 at 22:59pm UTC, wrote When you look at the world as a system, it is obvious that there is only...

andrea gonzalez: on 8/23/19 at 15:41pm UTC, wrote Interesting stuff to read. Keep it up. If want to collect free gift card...

Steve Agnew: on 8/18/19 at 23:42pm UTC, wrote Here is a nice slide from Gu's talk that shows the superposition of...

Steve Agnew: on 8/18/19 at 22:56pm UTC, wrote You may not believe that precursors and their outcomes exist in quantum...

Georgina Woodward: on 8/11/19 at 2:01am UTC, wrote As for the quantum jump of an electron between energy levels of an atom: I...

Georgina Woodward: on 8/10/19 at 22:02pm UTC, wrote Lorraine, 1. To show a human observer is not necessary I considered other...

Vikky Corner: on 8/10/19 at 11:30am UTC, wrote As usual, great post. You keep amazing me with your content design and...

Vikky Corner: on 8/10/19 at 11:29am UTC, wrote As usual, great post. You keep amazing me with your content design and...


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FQXi BLOGS
October 17, 2019

CATEGORY: Blog [back]
TOPIC: Memory, Causality and Cats: Sean Carroll at the 6th FQXi Meeting [refresh]
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FQXi Administrator Zeeya Merali wrote on Jul. 30, 2019 @ 19:20 GMT
FQXi’s 6th International meeting is now over — and we have plenty of brilliant talks and panel discussions from the conference to now share with you.

The first session was on causality, and Caltech cosmologist Sean Carroll opened the meeting with a round-up of his search for a mathematical description of why causes happen before effects. Our reporter Kate Becker has already written a wonderful summary of his ideas in her article, “First Things First: The Physics of Causality,” so I will point you there in the first instance.

In his talk, Carroll gave a more technical discussion of the problem of the arrow of time. The underlying microscopic laws of physics have no arrow: processes are just as likely to happen forwards or backwards. Yet, on the macroscale, we clearly experience time’s arrow pointing from the past to the future. Where does this asymmetry come from?

The arrow of time is usually attributed to the law of thermodynamics that says that entropy always increases. Handily, the universe started in a low entropy state, although exactly why is a bit of a mystery.

Carroll’s strategy is to distinguish between the “microvariables” and “macrovariables” of a system, when considering thermodynamics and entropy. For the Earth, say, the microvariables would be all the particles contained within the planet, while its macrovariables — used to calculate the Earth’s motion — would be far more limited, to just the position and velocity of its centre of mass. Macrovariables, he argues, reach equilibrium slowly, while microvariables equilibriate fast. Could this somehow be the key?

Another issue that isn’t discussed as much concerns the difference between having a memory of the past versus calculating what happened by some other means. Carroll’s example is his own recollection of his cat Ariel’s hijinks, compared with his ability to work out the motion of planets long ago. He proposes that this is related to how the macrovariables themselves evolve. Sometimes the macrovariables evolve deterministically — allowing you to make calculations and predict what will happen and retrodict what has happened. But sometimes the macrovariables evolve stochastically, which means you can only assign probabilities to what will happen. It’s in the latter case, as you can hear him arguing in his talk, that you assign a memory.

Free Podcast

Causality, Memory and the Arrow of Time. Cosmologist Sean Carroll is searching for a mathematical description of why causes precede effects and asking what makes our memories of the past special. Audio of a talk from the FQXi meeting in Tuscany.



LISTEN:







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Robert H McEachern wrote on Jul. 31, 2019 @ 13:19 GMT
"why causes happen before effects... underlying microscopic laws of physics have no arrow... Where does this asymmetry come from?"

Obviously, from the initial conditions, not the laws. That is what it means to be an initial condition - something preexisting the mathematical application of any law. Cause is defined to preexist its effect, independent of any law.

Rob McEachern

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Antonio Filipe Fonseca wrote on Jul. 31, 2019 @ 15:02 GMT
I liked very much the podcast however it is difficult to understand the final part, would it be possible to post the slides of the talk? Thank you.

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Lorraine Ford wrote on Aug. 1, 2019 @ 00:55 GMT
Sorry, but “preposterous” is an appropriate word. Physicist Sean Carroll said it all in his last sentence in the podcast: “I’m optimistic that we can actually attach equations to all these things that philosophers have told us are true for quite a while now”.

Apparently, physics thinks that it can willy-nilly add new information (representable as equations, numbers and algorithmic procedures) to represent what is happening in a system (the universe). But adding these new equations, numbers and algorithmic procedures doesn’t explain why it was necessary to add them to the system.

Adding new information to a system is itself a cause of time asymmetry and increasing entropy. But physics doesn’t think it is necessary to explain where these new equations, numbers and algorithmic procedures are coming from.

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Georgina Woodward wrote on Aug. 2, 2019 @ 04:56 GMT
I'm not convinced by the argument of increasing entropy in the (material) universe. It seems that in a universe with gravity, more order is being formed by attraction of masses. A vase before it falls down is for a moment an unsupported separate object from the Earth; but when it has shattered there is no longer the vase object and the Earth but just the Earth with an extra coating of pottery- one less object. Same for an egg breaking on the ground and dust collecting on the Earth's surface. Fitting with classical mechanics, there is reduction of potential energy as action occurs. It therefore seems to me that there are regions of increasing entropy but also regions of decreasing entropy. Rather than increase of entropy throughout the universe. There are also organisms which work against entropy by growth and repair. Making larger areas of order.

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Steve Agnew replied on Aug. 2, 2019 @ 20:13 GMT
Very good!

You are correct to state the gravity seems to lead to increasing and not decreasing order. Increasing entropy, you see, is a macro effect of microscopic charge and not really an effect of gravity at all. Classical action is not a reduction of potential energy, but rather a path of minimum energy. The sum of potential and kinetic is minimized and so potential energy can both increase and decrease in an action.

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Georgina Woodward replied on Aug. 2, 2019 @ 21:47 GMT
Steve, I stand corrected. I was thinking about falling things. As I have understood 'action', the path of least resistance is taken i.e. requiring the least energy. (As you said "path of minimum energy") I can think of siphoning water as an example where increase in potential energy is involved.

Another example of increasing order is flocculation. If a flocculant chemical is added to water containing suspended algae, the algae will clump together and fall out of suspension. Making a layer of algae at the bottom of the container and clear water above.

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Georgina Woodward replied on Aug. 4, 2019 @ 03:44 GMT
Erosion and deposition along a river's course, and along a coastline are processes whereby entropy is increasing and is decreasing respectively. Both can and do happen simultaneously at different locations. That is over the same sequence of configurations of the material universe. Foundational passage of time, the sequence of configurations of the material universe is the same for both processes. There is no going backwards in time. Reversal of a process is still change in the material universe's configuration and so passage of time as normal. It is the same for increasing entropy, decreasing entropy and change that maintains entropy as the same. Each material universe configuration is a time. A change to that configuration is a different time. Type of change does not dictate direction of time

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Lorraine Ford wrote on Aug. 4, 2019 @ 00:55 GMT
The so called “causality”, and arrow of time, that physicist Sean Carroll is talking about is all smoke and mirrors:

1) He is not actually talking about causality in the sense of X causes number N1 (representing e.g. the position of a particle) to jump/change to number N2 , within a system of law of nature relationships . He is merely saying what macro outcome is more likely given underlying micro events: micro events are where the actual causal events are occurring. The macro variables don’t have a life of their own: entropy, like temperature and pressure, are macro-level statistical quantifications of micro events, which don’t explain the cause of change occurring in micro events at all.

2) Seemingly physics has given up on the attempt to explain genuine causality at the micro level. Note that the life of Schrödinger’s cat is a macro event that is dependent on a single micro event. Only if such micro events are genuine ratchets in the system (i.e. the universe) is time irreversible: Carroll’s appeal to entropy, i.e. statistics, to explain the arrow of time is absurd.

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Lorraine Ford replied on Aug. 4, 2019 @ 00:57 GMT
Also, physics fails to analyse itself: what physics is doing is part of the picture. Statistical measures require algorithmic procedures. But physics is blind to what it is doing; physics does not recognise that it is performing algorithmic transformations of information; physics does not recognise that algorithms are necessary to describe what happens in the world.

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Lorraine Ford replied on Aug. 6, 2019 @ 01:01 GMT
Physicist Sean Carroll hypothesises that time is unidirectional because some possible events are more likely than other possible events, which is complete and utter nonsense, if only because it assumes that “possible events” have a weight and a real existence.

However, I think that he is correct in his unspoken assumption that time is unidirectional because of events, not because of some special property of time.

If you want to have unidirectional time, you have to have events that are ratchets in the system (the universe). Quantum events, like the above-mentioned Schrödinger’s cat event, are the only type of event that are genuine ratchets in the system, the only known genuine unidirectional events. Quantum events are a different type of event.

I.e. If you want to have unidirectional time, you have to have quantum events or the equivalent of quantum events in the system.

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Georgina Woodward replied on Aug. 6, 2019 @ 03:59 GMT
Lorraine, while possible events are not materially real, the conditions, (part of the configuration of materially reality) that makes those possibilities possible are materially real.

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Georgina Woodward wrote on Aug. 5, 2019 @ 02:38 GMT
we clearly experience time’s arrow pointing from the past to the future. Where does this asymmetry come from? Zeeya Merali

An observer generates observation products (Vision /Image reality) using received electromagnetic radiation. For any seen object the order of transmission of the Emr from the material object is the same order as received by the observer. For a reversal of order appearing as time reversal it would be necessary to outrun an already transmitted signal, I.e. travelling faster than the speed of light; The EMr being received in the opposite to usual order. That is not seen as there aren't faster than light speed observers. 'Underlying' what is seen is the changing material configuration of all that exists. The order of its reconfiguration being the same as the order of transmission of the EMr from material things.

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Lorraine Ford wrote on Aug. 29, 2019 @ 22:59 GMT
When you look at the world as a system, it is obvious that there is only one natural time-direction ratchet in the system, and that is quantum events.

When you look at the world as a system, it is obvious that the algorithmic cause of number change in quantum events is the driver of all other number change in the system via law of nature relationships.

But physics makes the mistake of thinking that a set of equations and numbers, without algorithmic drivers, constitutes a system. It doesn’t.

This is why physics continues to look for ever more weird statistical and probabilistic solutions to the issue of causality.

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