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A bit of a semantic question but still

  1. Jun 17, 2006 #1
    Ok here goes:

    I had a disagreement with someone over what the word law (in physics ofcourse) stands for. Now I realise that it can refer to a prescriptive law (such as human laws passed down by an authority for example) and descriptive law (a law that describes some kind of regularity in nature that we observe in say mathematical form). However my opponent insists that (and this is the way he believes is the proper way to use the word law in the context of science and physics) that laws of nature (such as the law of gravity) do not exist before someone discovers them, all that exists is the phenomena that the law describes. Furthermore he believes that if different people come up with descriptions/laws for the same phenomenon they came up with different laws, by this he cites that the law of gravity that was discovered by Newton is a different law than the law of gravity described by Einstein's relativity. Since nature doesn't hold it's breath for Newton or Einstein to come up with a particular law it's ridiculous to claim that nature obeys these laws. His analogy would be that a law is like a drawing of something but not the actual thing. A law is not the phenomenon but is a description of the phenomenon like a drawing is a description of the thing being drawn but not the actual thing. A description that is human centric and arbitrary.

    My point of view is this: When I use the word law (referring to laws of nature) what I mean is the underlying principle in the universe that exists before humans. Otherwise why would we say that Newton discovered the law of gravity (if you discover a continent ... it was already there for you to discover... you didn't invent the continent). Then humans discover this principle and describe it mathematically in a formula. Some describe it more accurately than others but the constants remain no matter what. The principle wouldn't change if the units of measurement changed ... the outcome would still be the same (that was another point of his... that formulas would give different outcomes if they are written in different measurement units). I am not saying that these laws are prescriptive but simply that the universe operates according to these laws... we found them we didn't invent them. Anyway I hope you get my gist.... the question ultimately is which usage of the word law is the right one?

    Hopefully someone bored enough will kindly aanswer this nitpicky question :p
    Last edited: Jun 17, 2006
  2. jcsd
  3. Jun 17, 2006 #2

    Andrew Mason

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    There may be different uses and slight misuses of the term "law" when applied to physical phenomena. I would say that a law is a fundamental relationship that is always true, such as Newton's Law of Universal Gravitation; the First Law (Second Law, Third Law) of Thermodynamics; Newton's laws of motion; Planck's law; Ampere's law; Gauss' laws; Coulomb's law; Faraday's law; Lorentz force law; These are true laws, in my view.

    Kepler's laws of planetary motion, Ohm's law, Ideal Gas law; Snell's law; are examples somewhat approximate relationships that are not fundamental laws, in my view. But we are stuck with historical usage...

  4. Jun 17, 2006 #3
    ^ Except that Newton's 'Laws' of motion and gravity are also approximations which you get to high speed and gravity which were improved upon by special and general relativity.
  5. Jun 17, 2006 #4
    I would pretty much just say that the "laws" are the axioms taken in a certain physical (mathematical) theory. In this sense, the law is a human invention, while the phenomena which it attempts to describe are independent (unless you believe there was no gravity before Newton).
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