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I Emergent theories in physics

  1. Jan 29, 2017 #1
    Let me write a brief intoduction to my question, just to clarify what I am not asking here, since it has been already discussed elsewhere.

    [1] intro

    Well, it is well known how the classical world of our experience can emerge from quantum mechanics in terms of decoherence. But it doesn't seem to me the only approach to generalization and emergence.
    Another well known example is how we obtain classical physics by taking the limit of Planck's constant to zero, and simlarly with relativity and other deformations (where the classical limit involves small speeds or a small mass size, etc...)

    [2] typical renormalization approach and its limits

    Unlike in systems biology, physics is dominated by effective models and theories.
    This is in large part due to the great success of continuum limit arguments and RG procedures.
    The problem is that - while renormalization group operates on field theories with a scale invariance or conformal symmetry - biochemical networks - and all what constitute the classical world - are particularly challenging due to inhomogeneity and lack of symmetries.

    [3] my question

    Machine learning methods that search for real world patterns are a growing feature of our recent research methods. In fields like ecology, systems biology, and macroeconomics, grossly simplified models capture important features of the behavior of incredibly complex interacting systems.
    In contrast to carefully and independently measure each parameter, we can instead constrain the model parameters with system-level measurements that are similar to the types of measurements we wish to predict. And somewhat counterintuitively, from the perspective of sloppy models, working to estimate precise parameter values in a model is useless while instead useful predictions of interest can be made without precisely knowing any single parameter.
    Therefore my question is how can you exclude that observed, effective laws (of chemistry, biology, etc) are - at least partially - independent from the strictly known, conventional physics (e.g standard model and general relativity) models?
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  3. Jan 29, 2017 #2


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    Unfortunately, I am still unclear on what you are NOT asking.

    For example, how is what you're asking different than what has been written by Phil Anderson and Bob Laughlin on the nature of the emergent phenomena? We don't really have to go to biological system or chemistry to seek such phenomena, since condensed matter physics is made up of nothing but emergent phenomena.

    Secondly, what exactly is meant by "... strictly known, conventional physics..."? I may not use the same elementary particles, but the physics and mathematics may look the same when I apply it to a slab of superconductor. So have I applied the same "strictly known, conventional physics"? Would a model in economics having the same form as an equation in QFT be considered as applying the same "strictly known, conventional physics"?

  4. Jan 29, 2017 #3


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    Biology is purely based on effective models.
    What do you mean by "independent"? If we modify the standard model, e.g. make the free neutron stable and the free proton unstable by changing quark masses, biology would not even exist. That looks like a strong dependency.
  5. Jan 29, 2017 #4


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    We can't - it is impossible to prove a negative of that sort.

    However, in the absence of any convincing example of a phenomenon that is not completely explained by "conventional physics" there's no reason to assume that such explanations are needed. Furthermore, the past experience with this line of thought has been discouraging - over the past few centuries physics has demonstrated ever-greater explanatory success across an ever-wider range of problems.
  6. Jan 29, 2017 #5
    I'm not asking about examples where it is easy to see that the laws of observed phenomena can be easily reduced to an appoximation of an underlying, more fundamental theory.

    As far as emergence is interpreted as opposite to reductionism, it can be that what I'm asking is somehow not different from the above quote and it could be shortened to a simple 'why not?'

    In this sentence you seem to misunderstand me maybe and it looks like contrary to the previous one: emergent phenomena meaning not reducible... so we have to go to biological system since condensed matter could be more reasonably reduced indeed.

    No, it would NOT. I'm not looking for the same math description, but for the very same physical derivation.
  7. Jan 29, 2017 #6
    I also think that this is the expected answer. I understand that there's no reason to assume that such explanations are needed, but I was asking if we can absolutely exclude they are (and I guess we can't, in line of principle ).
  8. Jan 29, 2017 #7
    But not effective with the same meaning given in physics: you can't prove they're an approximation of a more general physics law.

    The other way around. I'm asking if they are partially independent. You are proving that they are not fully independent.
  9. Jan 29, 2017 #8


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    This is unclear. What, in your opinion, is "fundamental theory"? To me, CPT symmetry is a "fundamental theory", and it applies even to emergent phenomena!

    Whoa! Really?

    Then please show me how superconductivity can be derived from the reductionist starting point. And before you do that, please read Bob Laughlin's Nobel Prize lecture first.

    I have no idea what this means.

  10. Jan 29, 2017 #9


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    We cannot exclude them as a matter of principle, but "no reason to assume such explanations are needed" is a sufficient reason to exclude them from discussion in a forum dedicated to empirical science.

    I am closing this thread. As with any such closing, PM me if you have something to add to the discussion so far.
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