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

[StringJunky]

15 minutes ago, joigus said:

I think there are contexts where the "weak emergence" approach is certainly useful, and I would go as far as to say that actually spectacularly so. One such example is how the equation of state for a real gas is inferred by assuming finite volume for each molecule and how molecules repelling each other at short enough distances while attracting each other at longer distances gives you a modification of the ideal-gas law that results in explaining phase transitions, the triple point of water, etc. If that's not emergence in action, I don't know what is. As Hossenfelder says, conductivity and other macroscopic parameters give you other examples.

There are other contexts where it's not at all obvious what the level from which the law is inferred might be. Example: People have suggested time could be an emergent property. What more basic level can we postulate so that time is a highly-derived, emergent property?

I do see a domain in which it's helpful, and by no means trivial.

I think you have a strong interest in biological phenomena, so you aren't disturbed by it. It is pretty normal for biological experts to invoke it, so there's that.

[wtf]

2 hours ago, joigus said:

One such example is how the equation of state for a real gas is inferred by assuming finite volume for each molecule and how molecules repelling each other at short enough distances while attracting each other at longer distances gives you a modification of the ideal-gas law that results in explaining phase transitions, the triple point of water, etc. If that's not emergence in action, I don't know what is.

Can you clarify this point? My understanding is that this is NOT an example of emergence, because in this case we CAN explain the macro behavior in terms of the constituent parts.

We only call something emergent when we CAN'T explain the behavior of the whole in terms of the parts. And that's why emergence bothers me. It seems like nothing more than a label we apply when we can't explain the qualities of the whole in terms of their parts. In which case it doesn't actually tell us anything. 

I realize I'm arguing a minority position, since everyone else seems to find the concept of emergence compelling. But can you explain your example? By showing how the macro behavior results from the properties of the parts, my understanding is that this is NOT emergence, but rather basic scientific cause and effect. When we say that "mind is emergent from brain goo," we are saying that we have no idea how the parts product the qualities of the whole, so we slap the label "emergence" on it in lieu of any better explanation.

@StringJunky, I looked back through this thread and couldn't find where I posted. I'm still not sure how I got roped into this thread yet here I am. Now THAT's emergence!

Edited June 23, 2023 by wtf

[Genady]

18 minutes ago, wtf said:

everyone else seems to find the concept of emergence compelling.

Not everyone. I don't. E.g., https://www.scienceforums.net/topic/126248-what-does-emergent-mean-in-a-physics-context-split-from-information-paradox/?do=findComment&comment=1195979

 

[StringJunky]

I'm seeing it as a limit to what one can know. It's ironic, the scepticism, when physicists embrace the uncertainty preinciple. What use  it is  it Nothing. It just says: "You can't go there." Physical limits are endemic. Emergentism, may be one of those things. Having said that: Ludditism does occur.  

Edited June 23, 2023 by StringJunky

[Genady]

55 minutes ago, StringJunky said:

I'm seeing it as a limit to what one can know. It's ironic, the scepticism, when physicists embrace the uncertainty preinciple. What use  it is  it Nothing. It just says: "You can't go there." Physical limits are endemic. Emergentism, may be one of those things. Having said that: Ludditism does occur.  

The uncertainty principle does not just say, "You can't go there." The uncertainty principle is not a first principle, not a given, but rather a theorem, a mathematical consequence derived from QM concepts of states and operators.

[StringJunky]

34 minutes ago, Genady said:

The uncertainty principle does not just say, "You can't go there." The uncertainty principle is not a first principle, not a given, but rather a theorem, a mathematical consequence derived from QM concepts of states and operators.

Position and momentum is, in principle, discoverable?

Quote

Does position and momentum follow uncertainty principle?
Roughly speaking, the uncertainty principle (for position and momentum) states that cannot assign exact simultaneous values to the position and momentum of a physical system. - Stanford U.

I interpret that as a discovery roadblock.

[Genady]

3 minutes ago, StringJunky said:

Position and momentum is, in principle, discoverable?

I interpret that as a discovery roadblock.

It is not about discovery, but about possible states of a particle:

If a particle state has a definite position, then its momentum is a superposition of different momentum states. If a particle state has a definite momentum, then its position is a superposition of different position states. If it is in superposition of both position states and momentum states, then these mixes have to have certain spreads. 

Both position and momentum are not simultaneously discoverable, because there does not exist such a state where they both are definite, i.e., not superpositions.

[StringJunky]

20 minutes ago, Genady said:

It is not about discovery, but about possible states of a particle:

If a particle state has a definite position, then its momentum is a superposition of different momentum states. If a particle state has a definite momentum, then its position is a superposition of different position states. If it is in superposition of both position states and momentum states, then these mixes have to have certain spreads. 

Both position and momentum are not simultaneously discoverable, because there does not exist such a state where they both are definite, i.e., not superpositions.

But you understand why it's not discoverable. I think it's early days for emergentism discovery. 

[Genady]

Just now, StringJunky said:

But you understand why it's not discoverable. I think it's early days for emergentism discovery. 

We understand why no state exists with definite position and definite momentum. It is shown via basic calculus.

[joigus]

16 hours ago, wtf said:

Can you clarify this point? My understanding is that this is NOT an example of emergence, because in this case we CAN explain the macro behavior in terms of the constituent parts.

We only call something emergent when we CAN'T explain the behavior of the whole in terms of the parts. And that's why emergence bothers me. It seems like nothing more than a label we apply when we can't explain the qualities of the whole in terms of their parts. In which case it doesn't actually tell us anything. 

As far as my understanding goes, emergence --at least in the weak sense S.H. was talking about-- is not about whether or not we can explain something in terms of its parts/constituents, etc. After all, how can we be sure that we can't instead of we haven't been able to just yet?

It's rather about whether the properties in question make sense at all for said 'constituents' or 'parts' or 'more elementary' elements.

Phase transitions only make complete sense in what's called the thermodynamic limit, ie, infinite number of particles; or, if you will, all extensive --additive-- properties being infinitely large, and therefore scale-independent. A phase transition does not make sense at all for, say 17 molecules. It's not that it becomes fuzzy, so to speak. I wouldn't even know how to start talking about that. It's like trying to talk about a 'shiny atom' or an 'uninhabitable photon'. What would that even mean? It's a property of the collectivity, not of its parts.

[StringJunky]

I don't think it's that hard, but I'm used to it. Quite simply, one person can't do a Mexican wave, or any other wave because it's a collective property. 

Does the Mexican Wave exist in the absence of an observer, is what gets me thinking.

[studiot]

On 12/10/2021 at 2:33 AM, StringJunky said:

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

Emergent is a very slippery concept, especially in a diswcipline that tries to 'nail things down'.

 

I would offer the idea that emergence is a way of selecting one particular response of system to input/stimulus/configuration or whatever.

That response nedds to be special, perhaps unique, in some way when counted amongst the many possible responses.

So In a physics sense think the calculus of variations, the shakedown theorem, plasticity, 

This definitely does not make it some sort of mystic woo.

But it does not necessarily make it predictable either.

Sorry for rambling, ask again about anything that is not clear.

 

 

[StringJunky]

11 minutes ago, studiot said:

Emergent is a very slippery concept, especially in a diswcipline that tries to 'nail things down'.

 

I would offer the idea that emergence is a way of selecting one particular response of system to input/stimulus/configuration or whatever.

That response nedds to be special, perhaps unique, in some way when counted amongst the many possible responses.

So In a physics sense think the calculus of variations, the shakedown theorem, plasticity, 

This definitely does not make it some sort of mystic woo.

But it does not necessarily make it predictable either.

Sorry for rambling, ask again about anything that is not clear.

 

 

I appreciate your input. As you say, it is slippery. Would you say Emergence was conceived to fix a problem?

[studiot]

30 minutes ago, StringJunky said:

I appreciate your input. As you say, it is slippery. Would you say Emergence was conceived to fix a problem?

Definitely not.

You mentioned 'spacetime.

I had meant to point out that one particular quadratic expression is preferred over other (emerges).

When you look at it is seems very reasonable and is what we would prefer it to be since it is easier than most.

But we have no theoretical basis for saying that it must be this way.

 

Most emergences seem to be beneficial as for instance in the shakedown theorem.

Some are just interesting ad pretty vas in the B-Z reaction.