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Hypothesis, theory, model, and law definitions

  1. Jan 20, 2009 #1
    I think this merits its own discussion so I am creating a new thread for it. This was broken off from the Completeness of Quantum Mechanics thread.

    -MIH

    If it is labeled as a theory then whatever it is describing has been tested hundreds of times, generally finding the same result each time, with the exception of the occasional outlier. I assume that it is because of these outliers that those experiments cannot be predicted. What is a "complete theory"? To me it just seems like an ironic term. If a theory were truly complete there would be no outliers, and then, just maybe, it would be termed a scientific law.
     
    Last edited by a moderator: Jan 23, 2009
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  3. Jan 21, 2009 #2

    turbo

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    Re: Completeness of Quantum Mechanics

    It is common for people to ask that quantum theory be held to the same standards as a classical theory, and this is a problem. On small scales, indeterminancy becomes a dominant player. We do not understand the nature of sub-atomic particles well enough to be able to describe them in terms that are understandable to us as if they were physical entities. This doesn't mean that quantum theory is wrong, or even incomplete.
     
  4. Jan 21, 2009 #3

    Hurkyl

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    Re: Completeness of Quantum Mechanics

    Outliers are mostly unrelated to the notion of completeness. They happen when unusual events occur (e.g. a random tremor in the Earth, or a cosmic ray strikes your experiment), mistakes happen (e.g. an experiment is allowed to run too long, or a solution isn't mixed well), or even for no other reason than statistics (e.g. 5% of results should lie outside of a 95% confidence interval). If there were no outliers at all, that would actually be reason to be suspicious of tampering with the data....
     
  5. Jan 21, 2009 #4
    Re: Completeness of Quantum Mechanics

    Thank you for those statistics, I guess I can see your point. But what about scientific laws? With gravity for example, where are the outliers? Gravity is directly proportional o mass and density, I have heard of no outliers with scientific laws, which is how they become laws in the first place.
     
  6. Jan 22, 2009 #5

    ZapperZ

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    Re: Completeness of Quantum Mechanics

    In physics, "theory", "law", "model", etc. are interchangeable. These are only labels. They do not evolve into one another as they become more verified. This is a common fallacy that many hold, especially those who are questioning the "Theory" of evolution by saying that it is "only a theory". A theory doesn't graduate into a law as it becomes more verified. And a law doesn't imply it is more valid than a theory.

    These are all meaningless English labels and should not be used as a measure of the validity of something.

    Zz.
     
  7. Jan 22, 2009 #6
    Re: Completeness of Quantum Mechanics

    Well thank you for that, even though it was contradictory to the terminology I learned in my science classes.
     
  8. Jan 22, 2009 #7

    ZapperZ

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    Re: Completeness of Quantum Mechanics

    You had a science class that spent time teaching you about the labels we call "theory", "model", and "law"?

    You can check this out yourself. If you think a "law" is more complete or more well-verified than a "theory", then how come Newton's Laws are more of an approximation to the Special THEORY of Relativity? Or why is the classical law of gravitation has, as its foundation, the General THEORY of relativity? Or why is the Landau's Fermi Liquid THEORY really is the explanation for Ohm's Law?

    Zz.
     
  9. Jan 22, 2009 #8
    Re: Completeness of Quantum Mechanics

    No, but I swear in 4th grade they said, "a theory is a hypothesis that has been tested many times, with generally the same result each time. A law is a scientific fact, and has been proven many times beyond dispute." I have no idea why I still remember that.
     
  10. Jan 22, 2009 #9

    George Jones

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    Re: Completeness of Quantum Mechanics

    In which theory of gravity?

    In Einstein's theory of gravity, which is more widely applicable than Newton's, mass density is just a part of the source of gravity, i.e, just a part of the second rank energy-momentum tensor.
    Robert Geroch, a particularly careful and deep thinker about math and physics, and at one time a professor in both the departments of mathematics and physics at the university of Chicago, wrote some interesting stuff about the nature of theories.

    Read the last paragraph that starts on on page 182, and that ends with "I wouldn't recognize the "proof of a physical theory" if I saw one."

    http://books.google.com/books?id=Uk...:geroch&lr=&as_brr=0&as_pt=ALLTYPES#PPA182,M1
     
  11. Jan 22, 2009 #10
    Re: Completeness of Quantum Mechanics

    A "theory" is different from "a law", even though these terms have been used confusingly, probably because the difference is subtle.

    A "theory" is focused on mechanism, while a law is focused on intention. A "theory" provides a mechanism, to describe and explain observable natural phenomena. A law on the other hand describes the intention in nature that produces observable natural phenomena.
     
  12. Jan 22, 2009 #11
    Re: Completeness of Quantum Mechanics

    I was talking about the Newtonian theory of gravity.
     
  13. Jan 23, 2009 #12
    While its true these words are used in different ways both in relation to science and more generally. One could make the following distinctions.

    A hypothesis is most generally a prediction, either based on evidence or some form of reasoning.

    A theory is an explanation, ie string theory, theory of evolution, etc... which explain facts.

    A law is more basic than a theory, as it describes a certain pattern of observed phenomena. Newtons law of gravity didn't explain gravity, it just described what it did. Einstein's theory of relativity is more an explanation of gravity.

    A model is a representation of a complex system. It may, be used to test a hypothesis, or support a theory, and will utilize known laws.

    Bear in mind, there is of course much disagreement in the philosophy of science with regards to these terms, but they *can* be used distinctly.
     
    Last edited: Jan 23, 2009
  14. Jan 23, 2009 #13
    Re: Completeness of Quantum Mechanics

    Dear Piscuit,

    You are right. There were four distinct categories of scientific thought: thesis (thought to be defended by PhD aspirants), hypotheses (peer reviewed thesis supported by independent observations), theory (generally accepted hypothesis supported by independent observations) and law (theory supported by independent observations all the time).

    These categories fell into disarray as our measurements grew more precise and as we tried to specify “laws” more precisely. For example, the second “law” of thermodynamics. (Some are here still thinking about it as law.) Maxwell gave us his little demon to think about it. (Still unresolved puzzle.) Max Planck also abandoned the second “law” as absolute law of nature when he was working on his law now known as Planck’s radiation law. He had to embrace Ludwig Boltzmann's interpretation, that the second law was a statistical law.

    Nowadays, scientists are very reluctant to proclaim anything as absolute law of nature.

    I would also add that all four categories of scientific thought are attempts to predict what will occur in future under similar circumstances. Depending on past observations we are trying to predict what we will observe in future.

    Up to now, we were not able to articulate anything that could predict what we will observe in future 100%. There is always that little devil, called chance, that spoils otherwise “perfectly predictable” outcome. I also doubt that we will have anything like law even in distant future. (This may hurt feelings of some who would like to have something like absolute truth to judge others.)

    Kind regards,
     
  15. Jan 24, 2009 #14
    I can see now why new experiments won't always coincide with previous results.
     
  16. Jan 25, 2009 #15
    Piscuit,

    You make an interesting point, but you miss a key aspect of the "Scientific Process" and "Science " itself. Science by its very nature is evolutionary, meaning that our understanding of phenomenon evolves with time and technology. As more and more experiments are done, and new technology allows us the ability to collect more and more relevant data, more precisesly and with greater understanding and discrimenation, these "outliers" act as our stimulus or catalyst for going to the next level of understanding. Scince by its very nature is "dyanmic" and not "static". As you are well aware, when a scientifc concept becomes static, it becomes in danger of becoming a "dogma" and is no longer sound science.

    Therefore, finally getting around to your main point. It may be that there is no such thing as a "complete theory" That would be oxymoronic with the definition of science itself. To be "complete" is ethnocentric (assumes as humans we understand every aspect and everything there is to know about anything) and begins us down the road toward stagnation and dogma.

    I don't know if this helps or is what you meant. i look forward to your response and input.

    Terry
     
  17. Jan 25, 2009 #16
    Zapper,

    It's possible that the term "Scientific law" is no longer relevant. The concept of "Law" may fall into that archaic set of ideas that pass down to us through tradition (yes, even we in Science have traditions), but no longer carry the weight or relevancy that it once held. It comes from a time when Science was still in its infancy and a term was needed to discrimenate the differing levels of idea development and reliability. I feel that the term "Law" should be dropped altogether from the scientific lexicon. Law is now synonymous with "theory". It is my contention, that when we think "Law", we should just replace it with the word theory. "Theory" is more relavant to modern thinking and better reflects the dynamic nature of the field of science itself.

    As we look at the new challenges to Newton's laws, and the new insights being discovered about gravity, we find that the term "Scientific law" takes on less and less significance.

    Terry
     
  18. Jan 25, 2009 #17
    Science itself evolves, hm, I never thought about it quite like that before; but I can see what you mean.
     
  19. Jan 25, 2009 #18
    I do think their should be a distinction between hypothesis and theory, but then I'm not a String Theorist so I would say that. :wink:

    I don't think we should be handing out the term theory for any speculation with no evidence or seemingly currently no means of verification or falsification. Probably just me. :smile:
     
  20. Jan 25, 2009 #19
    No, its not just you.
     
  21. Feb 3, 2009 #20
    Yeah, I can see what you mean.
     
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