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What does 'emergent' mean in a physics context (split from Information Paradox)


StringJunky
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40 minutes ago, Markus Hanke said:

Indeed. I think it’s important to make this really clear - it’s based on a semiclassical approach, meaning it’s standard GR with standard quantum field theory thrown in, but accounting for more quantum effects than Hawking did. It’s not about full quantum gravity, and only seeks to address the specific issue of the information paradox.

I’m personally excited that it appears to further hint at the idea of spacetime not being fundamental, but an emergent phenomenon.

What does 'emergent' mean to you in a physics context, such as spacetime?

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6 hours ago, StringJunky said:

What does 'emergent' mean to you in a physics context, such as spacetime?

This question deserves a thread all to itself.

I think any definition of emergent v fundamantal has the inherent problem/danger of becoming self referential.

This is because before (in time) anything can emerge the 'more fundamental' thing must already exist.

So how does the time bit of spacetime fit in ?

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4 hours ago, studiot said:

This question deserves a thread all to itself.

I think any definition of emergent v fundamantal has the inherent problem/danger of becoming self referential.

This is because before (in time) anything can emerge the 'more fundamental' thing must already exist.

So how does the time bit of spacetime fit in ?

Seems a good idea .There must be theories.I wonder if they are mathematics driven or physics driven.?

 

I am new to this subject and was interested to learn that both Feynman and Hawking had ideas before String theory showed up. 

 

Can their ideas still have any applicability since the jury still seems to be out?

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6 minutes ago, StringJunky said:

WTF has spacetime emergence got do with the weather. You do realise a lot of your posts are like graffiti. 

Might have been an auto spelling malfunction? (would "whether" have made any sense,even if cryptic?)

Edited by geordief
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31 minutes ago, geordief said:

Might have been an auto spelling malfunction? (would "whether" have made any sense,even if cryptic?)

If he stopped using the ellipsis so much, that might have become apparent. I don't know what he gets out of being cryptic all the time. The correct way to use ellipses is when the omitted part of a sentence is presumed to be easily understood by the context. His aren't.

Edited by StringJunky
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The way I understand it is like this: A phenomenon is emergent when it can be studied in terms of elementary parts and their relationships, while the phenomena to be explained are not present in the parts, appearing instead as a consequence of certain relationships between them.

The example par excellence is pressure, which appears as a result of miriads of molecules hitting the walls of the container in so smooth and regular a way that all we experience is a consistent and continuously-varying resistance to reduce their volume if we try to push the system into a smaller volume.

The idea that spacetime may ultimately be emergent appeared in physics in recent decades, in the form of commentary, rather than an actual proposal, I think.

There are attempts to go in this direction, like loop quantum gravity, but I don't think it's any close to come to fruition. I quite agree with @studiot in that a standing difficulty, at least for me, is: What is the more fundamental thing of which time is a derived (another word for 'emergent') concept?

Some people seem to think that considering time as made up of little chunks, discrete, is the big idea. Now, that's not how the concepts of pressure or temperature were arrived at. Pressure is not chunks of little pressure; temperature is not chunks of little temperature.

Another problem I see is that sometimes we think we've understood a concept as emergent, or derived, only to find later a version of it that seems to resist such, shall we say, reductionistic approach. Examples of this are, IMO:

1) Negative pressure of the cosmological vacuum

2) Pressure and temperature* in black holes

I don't think these can be considered just your garden-variety versions of pressure and temperature amenable to be understood in terms of 'little things doing their thing.'

But who knows. All I can say for now is that it seems to me that any concept of emergent time that emerges (pun inevitable) is bound to be essentially different from being so in the same vein of temperature and pressure, ie, as 'little things doing their thing.' Something very really bold and beautiful seems necessary.

I'm particularly interested in what @Eise and @Markus Hanke have to say about these matters.

*Temperature is not just a feature of black holes, but also of any space-time horizons; even** horizons created by just picking a coordinate system (Rindler coordinates for flat spacetime). What about that?!

**Not a typo for 'event'

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43 minutes ago, joigus said:

What is the more fundamental thing of which time is a derived (another word for 'emergent') concept?

Obviously I don’t have definite answers on offer, since no one knows if macroscopic spacetime really is emergent, and if so, emergent from what.

The only more ‘fundamental’ concept I can think of, which is in accord with known physics, and which might be able to give rise to spacetime somehow, are correlations. So we are talking information theory. And alas, a quick search on arXiv reveals that there is indeed work going on in that direction:

https://arxiv.org/abs/2110.08278

51 minutes ago, joigus said:

A phenomenon is emergent when it can be studied in terms of elementary parts and their relationships, while the phenomena to be explained are not present in the parts, appearing instead as a consequence of certain relationships between them.

Sounds good to me!

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2 hours ago, joigus said:

The way I understand it is like this: A phenomenon is emergent when it can be studied in terms of elementary parts and their relationships, while the phenomena to be explained are not present in the parts, appearing instead as a consequence of certain relationships between them.

Do we call things 'emergent' because we don't know all the steps or processes that leads to a particular phenomenon;  a placeholder word for things that seem to suddenly manifest by magic. :)

Edited by StringJunky
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Quote

I wonder if everything we observe is a function of pareolalia, that allows us to turn the scene around us into discrete things that we can give names to and communicate them. I am considering the idea of emergence as an observer-dependent phenomenon, and that's why it's so hard for me to put my finger on. No thing is actually discrete per se, since everything is connected. Discreteness of things is perhaps just a mental construct that's not reflected in reality, like these murmurations.

--StringJunky

From:

 

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7 hours ago, StringJunky said:

Do we call things 'emergent' because we don't know all the steps or processes that leads to a particular phenomenon;  a placeholder word for things that seem to suddenly manifest by magic. :)

Far from it.  Temperature is often quoted as an example of an emergent phenomenon, yet we know exactly how it arises. As I understand it, it is meaningless to speak of the temperature of an individual molecule, because temperature applies to an assembly of molecules, statistically large enough to form a Boltzmann distribution, in which the probabilities of each state the molecules can occupy is proportional to exp(-e/kT), T being the temperature.  

Other bulk properties of matter that arise from statistical distributions of atomic-scale entities - and there are lots of them - would be similar.

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6 hours ago, StringJunky said:

Do we call things 'emergent' because we don't know all the steps or processes that leads to a particular phenomenon;  a placeholder word for things that seem to suddenly manifest by magic. :)

Magic ?

You 'started'  this thead by introducing a difficult to define concept. Please don't introduce another one.

:)

 

I am glad to see folks working together in this knotty question here are some of my thoughts.

Althought the thread is specifically aimed at Physics it is worth noting the meaning of emergence in other sciences and comparing.

Also the age old technique of taking simple examples and seeing how they stack up against proposed definitions is valuable.

So.

1)

Emergence has long (centuries) been used to describe radical change or transformation in the biological sciences.
For example the emergence of a butterfly from the pupa.
Characteristics are that you cannot have a butterfly without a pupa, but once you have a butterfly you no longer have a pupa.
The change is not reversible.
You cannot resolve a butterfly into a pupa as you can with sinusoidal functions in my third example below.

Note this example does not conform to Joigus' definition (which I like) so that definition is is not complete.

OK back to applied maths (sorry physics)

2)

1+1 = 2,  3+5 = 8  in fact take any two or even lots of numbers and add themtogether and you will get another number.
That is the result is contained within the set of all numbers.
You do not move outside the set.

But add all numbers in that set and you get infinity, which is not a number.
So you have something that is not in the set ie outside the set.

This example does conform to Joigus and the relationship is the additive property of individual numbers.

3)

A more complicated example comes from the set of all continuous functions  - commonly called C∞ -
All sinusoids belong to this category.
Like with the numbers above, adding any two or a large number get you another member of the set C∞.
But adding an infinite number can get you you a function that is not continuous ie is discontinuous, notably a square wave.
So once again takes you outside the set.

Scary.

4)

I potential energy an emergent phenomenon ?
Particles, by themselves, do not possess PE.
By configure two or a bunch of them and they suddenly possess PE by virtue of their configuration and their interaction relationship.
The number of configured particles for this example of emergence does not have to be infinite.
Indeed we can only determine what happens in some specific cases if they are infinite in number.

5)

Take a pile of bricks.
In most configurations the pile is unstable.
But configure them into an arch and the configuration becomes very strong and stable.
Again only  finite number of participants is necessary.
But in this case we also have extremal principles to apply.


 

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1 hour ago, studiot said:

By configure two or a bunch of them and they suddenly possess PE by virtue of their configuration and their interaction relationship

So ,when  system goes into less than 3 components does any related phenomenon go into "reverse emergence"

 

And by the way(or an elephant in the room?) ,is life itself a prime  example  of emergence ?

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10 minutes ago, geordief said:

So ,when  system goes into less than 3 components does any related phenomenon go into "reverse emergence"

 

And by the way(or an elephant in the room?) ,is life itself a prime  example  of emergence ?

Thank you for reading my long post.
I tried to make it short but needed to get a lot in.

Life  -  I don't know. Good question.

One thing about life as an emergent phenomenon is that Physics expects reproducability.
So every time you perform a particular procedure you get the same result.
Is that an essential characteristic of emergence ?
All my examples have this characteristic, but life doesn't.

Not not less than 3, less than 2, ie a single component.

Take electric charge or gravity.

A single mass or a single charge has no potential energy.

PE only arises (emerges) when you introduce a second mass or charge called a test mass or a test charge.
But there is very little configuration you can do with only two participants.

Edited by studiot
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36 minutes ago, geordief said:

Is entanglement the only one?

 

@studiot"All my examples have this characteristic, but life doesn't."

Can you say that?

Neither of the particle pairs are entangled in my gravity or electrostatic examples.

Ther is only one line between their centres and the relationship obeys the inverse square law along that.
The PE is found by considering the work done in bringing one of the particles from infinity to its distance from the other one.

 

"Can you say that?"

Why not ?

We don't know what sequence of events lead to life, but would life occur every time ?

There have certainly been attempts to mix molecules thought to have mixed at random and they equally certainly haven't resulted in life.

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14 minutes ago, studiot said:

but would life occur every time?

Maybe if the right circumstances applied.It could be entirely reproducible (my preference) and there would be a formal connection between the preceding and the subsequent arrangement. 

 

Obviously I am imagining.

 

Wonder what your particle pairs are. How fundamental?(I mean what happens when they are more fundamental?)

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20 hours ago, StringJunky said:

If he stopped using the ellipsis so much, that might have become apparent. I don't know what he gets out of being cryptic all the time. The correct way to use ellipses is when the omitted part of a sentence is presumed to be easily understood by the context. His aren't.

Maybe, one day, a meaning will emerge...

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7 minutes ago, geordief said:

Maybe if the right circumstances applied.It could be entirely reproducible (my preference) and there would be a formal connection between the preceding and the subsequent arrangement. 

 

Obviously I am imagining.

That is why I said I don't know.

We are in the best guess situation for life.

And yours is as good as mine.

 

8 minutes ago, geordief said:

Wonder what your particle pairs are. How fundamental?

Well I don't know of any charged particles that have no mass, so take your pick.

A further thought about 3 particles and Markus Hanke's definition.

An eclipse is a particular phenomenon concerning one particle blocking the light of the second from being received by the third.
But this only occurs momentarily in a particular configuration.

Can this be considered emergent ?

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3 hours ago, studiot said:

Magic ?

You 'started'  this thead by introducing a difficult to define concept. Please don't introduce another one.

:)

 

I am glad to see folks working together in this knotty question here are some of my thoughts.

Althought the thread is specifically aimed at Physics it is worth noting the meaning of emergence in other sciences and comparing.

Also the age old technique of taking simple examples and seeing how they stack up against proposed definitions is valuable.

So.

1)

Emergence has long (centuries) been used to describe radical change or transformation in the biological sciences.
For example the emergence of a butterfly from the pupa.
Characteristics are that you cannot have a butterfly without a pupa, but once you have a butterfly you no longer have a pupa.
The change is not reversible.
You cannot resolve a butterfly into a pupa as you can with sinusoidal functions in my third example below.

Note this example does not conform to Joigus' definition (which I like) so that definition is is not complete.

OK back to applied maths (sorry physics)

2)

1+1 = 2,  3+5 = 8  in fact take any two or even lots of numbers and add themtogether and you will get another number.
That is the result is contained within the set of all numbers.
You do not move outside the set.

But add all numbers in that set and you get infinity, which is not a number.
So you have something that is not in the set ie outside the set.

This example does conform to Joigus and the relationship is the additive property of individual numbers.

3)

A more complicated example comes from the set of all continuous functions  - commonly called C∞ -
All sinusoids belong to this category.
Like with the numbers above, adding any two or a large number get you another member of the set C∞.
But adding an infinite number can get you you a function that is not continuous ie is discontinuous, notably a square wave.
So once again takes you outside the set.

Scary.

4)

I potential energy an emergent phenomenon ?
Particles, by themselves, do not possess PE.
By configure two or a bunch of them and they suddenly possess PE by virtue of their configuration and their interaction relationship.
The number of configured particles for this example of emergence does not have to be infinite.
Indeed we can only determine what happens in some specific cases if they are infinite in number.

5)

Take a pile of bricks.
In most configurations the pile is unstable.
But configure them into an arch and the configuration becomes very strong and stable.
Again only  finite number of participants is necessary.
But in this case we also have extremal principles to apply.


 

Very good points.

Your point No. 2) and 3) Let me add another example from topology: An infinite instersection of open set doesn't necessarily give you an open set.

Example (for those mathematically-minded):

infinite_intersection_open_sets.png.e075808daba2380cdcae5e139205ffff.png

So by making so-called transcendent operations (performed in infinitely many elementary steps) you can lose even the most common-sense properties that you would think should be preserved.

Intermediate case between your points 2)/3) and your points 4)/5) (kind of what @exchemist is talking about:

The key, IMO: You don't need infinitely many elements to have emergent behaviour. A large enough number could be enough.

E.g. In statistical mechanics we know that when your system has a finite number of entities, but big enough that the Stirling approximation holds:

 

lnn!nlnnn

Then the Maxwell-Boltzmann distribution, and describing the system in terms of thermodynamic equilibrium is on safe grounds. So you can describe the system with far fewer variables than it fundamentally has.

Your points 4) and 5) are very similar in that:

In some cases, you don't need the number of variables to be especially large in any sense. Your examples of potential energy, and the bricks necessary to make an arch, or a corbelled roof, don't really require big numbers. Another example similar to your potential-energy one is entanglement of two particles.

As to your point 1)

I don't think we're talking about the same concept of emergence there. Although the words are the same, that's more like what I would call*, morphing, mutation. A right choice of word would be needed to distinguish them, but it's not the same. The one you propose is more about causal emergence, IMO.

*'Evolution' would be another possibility, but liable to be confused with 'evolution by natural selection' which is another kind of emergence. 

EDIT: I didn't see you were already talking about entanglement.

Edited by joigus
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1 hour ago, studiot said:

An eclipse is a particular phenomenon concerning one particle blocking the light of the second from being received by the third.
But this only occurs momentarily in a particular configuration.

Can this be considered emergent ?

Would the light find a way round ?(I have listened to a fair few Al Khalili  documentaries so I know my stuff)

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39 minutes ago, geordief said:

Would the light find a way round ?(I have listened to a fair few Al Khalili  documentaries so I know my stuff)

Not if the blocvking object was big enough.

 

There is a strong link between emergence, complexity and catastrophe theory.

You should read up on Rene Thom

https://mathshistory.st-andrews.ac.uk/TimesObituaries/Thom.html

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