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Theory vs law

  1. Sep 27, 2011 #1
    I was just wondering what the difference between law and theory is?

    My teacher said that there is no difference and both can be disproved?
    But I think he is wrong and that a theory evolves to law after series of experiments; reaching to a conclusion that a law is "impossible" to disprove.??

    So give me a guidance!
  2. jcsd
  3. Sep 27, 2011 #2


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    A law is simply a mathematical model. It is not related to a theory and a theory cannot become a law. There is no higher title to give an idea in science than "theory".
  4. Sep 27, 2011 #3
    I second what russ said. What most people think of as a theory is to scientists merely a hypothesis. A theory expresses the best understanding scientists have of an issue. As russ says, a law is a mathematical model or a relationship of one quantity to another. Laws are not impossible to disprove. Einstein revised Newton's Law of Gravitation.
  5. Sep 27, 2011 #4
    Oh. my mistake then.

    So, a law is just a mathematical model.
    What does principle mean?

    Thx. This site is greatly helpful
  6. Sep 27, 2011 #5


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    Maybe these two articles will help.

    I suggest you read all of both articles, but this seems to expand on what russ was saying about mathematics.



  7. Sep 27, 2011 #6


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    A mathematical law can be proven to be true mathematically. A scientific theory can not be proven, though a theory can be dis-proven, and strong scientific theories usually have withstood vigorous attempts at disproving them.
  8. Sep 27, 2011 #7
    Whilst I acknowledge the previous posts, things may seem a little bit more complex, take for instance the [URL [Broken] Ballot law[/url]:

    No math model whatsoever and it will be pretty difficult to falsify that, which is possible with a theory.

    here are some possible definitions

    Last edited by a moderator: May 5, 2017
  9. Sep 28, 2011 #8
    I think I understand their difference. Greatly explained Andre. Thank You

    So what is a principle?
    what is a postulate?
  10. Sep 28, 2011 #9


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    one theory is that nature is governed by laws
  11. Sep 28, 2011 #10
    Neither laws nor theories are provable - that's why it's called science. If something was "proven" then nothing could come along later to change it. They can, however, be disproven.

    Andre put it well: Laws are generalized patterns we have noticed that have never deviated from their foundation nor do we expect them to ever deviate, such as the Law of Gravity, Law of Natural Selection, etc. However, they don't explain these patterns, and that's where theory comes in. Theories are processes. That's why theories are so powerful - they predict other things. However, both laws and theories are models of how nature works.

    http://ncse.com/evolution/education/definitions-fact-theory-law-scientific-work" [Broken] site is especially useful.
    Last edited by a moderator: May 5, 2017
  12. Sep 28, 2011 #11


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    I think to some extent the confusion over the terms is because there has been a shift in meaning over the last 100 or more years. At the time of Newton, it was believed that his "law" of gravity was absolute and final. No one could image it ever changing.

    Physicists now don't use "law" that way because they KNOW that even things that SEEM they will never be falsified may well be, so "law" has an aura of finality that is no longer considered acceptable.

    I like Russ's statement that "There is no higher title to give an idea in science than 'theory'" and I think idiots like Rick Perry who say "oh, well, Evolution is just a theory" should be severly beaten about the head and shoulders and then made to take a science course or two.
  13. Sep 28, 2011 #12

    Ivan Seeking

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    Yes. It only takes one counter example of either.
  14. Sep 28, 2011 #13
    I don't have the article on my work computer, but when I was going through my MEd courses, this was found to be a myth (which didn;t surprise me). It actually takes a good number of independent counterexamples before these counterexamples are accepted as contradictions to accepted theory or law. Take the whole idea of FTL neutrinos right now - no one is accepting them outright, and it will take several independent measurements for the scientific community to accept it as true (assuming it is, of course).
  15. Sep 28, 2011 #14


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    The thing I find most interesting about the political discourse around law/theory is that politicians would likely not THINK of questioning Newtons law of gravity, even thought it is known to be totally wrong (even though it gives the right answer to numerous decimal places under limited conditinos) but they readily question the theory of evolution which has not had even a single counter-example.
  16. Sep 28, 2011 #15
    But now you add subjective elements indicated with "accepted". The question should be objective though. A theory/law can be true as long as there is not a single exception, regardless if it's accepted or not. If the theory is that all swans are white, then any single black swan falsifies it. That's Poppers philosophy. If we have to discuss if the beautiful theory is really slain by an ugly fact, then we get into the range of Thomas Kuhn. Ah well, maybe most swans are white. Maybe not everything is exactly true, and maybe that is not true either.
  17. Sep 28, 2011 #16
    Yeah, we looked at those two folks (as well as a few others such as Bacon, Hume, etc.) in the Philosophy of Science Education class (it was kinda cool, too!), so I agree with your subjective/accepted point.
  18. Sep 28, 2011 #17

    Ivan Seeking

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    However, the truth of the FTL neutrinos hasn't been determined. Obviously the example doesn't apply technically until it has been accepted, but it still only takes one example.

    If the orbit of the moon were violating Newton's "Laws", we wouldn't need more examples to know it's true.

    I think you meant more than one observation, but it only takes one example to overturn a "law".
    Last edited: Sep 28, 2011
  19. Sep 28, 2011 #18
    Yes, that's what I meant (and what I thought you meant...my bad).
  20. Sep 28, 2011 #19


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    "The label 'law' ... is not a technical term defined in any empirical science, and it is often used, especially in common discourse, with a strong honorific intent but without a precise import.... scientists disagree about the eligibility of many statements for the title 'law of nature' and the opinion of even one individual will often fluctuate on whether a given statement is to count as a law.....
    The term 'law of nature is undoubtedly vague. In consequence, any explication of its meaning which proposes a sharp demarcation between lawlike and unlawlike statements is bound to be arbitrary. ...

    ...not only is the term 'law' vague in its current usage, but its historical meaning has undergone many changes."

    So you should be chary of anyone overconfidently laying down of the, er, law about this.

    Still according to the same author (Ernest Nagel: 'The Structure of Science') it is not total anarchy and, er, lawlessness, for "members of the scientific community agree fairly well on the applicability of the term for a considerable though vaguely delimited class of universal statements"

    He goes on to list about eight logically/epistemologically different types of statement which have got the name 'law' attached to them.

    Not consciously following him but probably agreeing I think in Physics we have particular concern with these types

    1. Fundamental Physical Laws. These are thought essentially universal as far as we know. Include Maxwell's, Newton's, Coulomb's, QM postulates. Whole lot can be written on a single sheet of paper.

    Have not been proved or derived from anything else, though it is hoped they can be.

    I might include a related category

    1a Essentially universal laws or Fundamental Laws that hold to a great and well understood degree of approximation within well understood limits, I guess laws like Newton's law of gravitation which is not always quite right but we know when and how much, is in this category.

    2 Derived Laws: which are derived from the above or other very general principles, any limits to their applicability well understood. Examples 2nd law of thermodynamics, Kirchoff's laws, Lenz's laws, Dalton's Laws, Faraday's Law of electrolysis, Boyle's Law. Would often need a delimiter to clarify what set-up and material they apply to, contingent to that extent. Not many pages.

    3 Phenomenological or empirical laws. Almost always of limited range of applicability and approximate, not universal. Examples: Hooke's Law for certain materials, Ohm's Law, Dulong and Petit's,... More pages.

    The collocation is not fixed, for instance some were in class 3, were discovered empirically, but later promoted to class 2 when they found their explanation.

    It is helpful to science learning to understand these categorisations: I think pre University in my Science learning there were just all these laws you had to learn with scarcely a distinction of logical category, admittedly their boundaries are debatable but even that I only leaned later. (So please no niggles about my examples :biggrin:).
  21. Oct 1, 2011 #20
    Could somebody explain to me what a "principle" is? I think I have understood the difference between law and theory.
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