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How are leaps justified in Physics?

  1. Sep 3, 2015 #1
    Often times we find a very specific theory, law or observation generalised. For instance, Heisenberg's uncertainty principle was about detecting an electron using a photon, however, it was then generalised to be a true property of particles no matter what you use to identify their positions or momenta, not just when detecting electrons with photons. How are those leaps made? What kind of evidence is enough to show that something is an inherent property of nature, such as conservation of energy or charge for instance. I know these phenomena have a ton of evidence to support them, but when they were first proposed to be inherent traits of nature, what kind of evidence does one have to produce to make such claim?
  2. jcsd
  3. Sep 3, 2015 #2
    Nothing is a "leap" as you call it. Generally, someone doesn't just come up with a general law of physics. The generalizations usually are developed from smaller ideas. For example, special relativity was proposed in 1905, and the generalization of that theory, GR, was proposed in 1915. That's 10 years of work on generalizing special relativity. The concept of electric charge was first developed (scientifically) in the 1600s. It was not completely generalized until the 1900s, and that's almose 300 years! Does this answer your question?
  4. Sep 3, 2015 #3


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    It's the writers of history who identify the 'leaps' and that's what gets taught. No one on the actual journey is convinced they made a 'leap' on any particular day, I'm sure.
  5. Sep 3, 2015 #4


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    First of all, let's correct the obvious mistake in your post. The HUP is NOT about "detecting an electron using photon". In fact, the HUP isn't that important at all, because it is merely a consequence, out of many, of the way QM describes a system and the mathematical description of an observable.

    Secondly, the arrival at an idea that something is "fundamental" or "inherent" did not come overnight. It has to come after there is (i) a huge body of physical evidence and (ii) a theoretical concept has been developed and matured. Only THEN is there an acceptance that many this is something that has a more fundamental level of validity.

    But it is also wrong to think that it stops there, because there are many examples where we think we arrive at something fundamental, and it gets superseded by something else. Physics is not about seeking "proof" that something is right. It is about finding the validity of something, and the range of which that something is valid. When we find a range in which that something is no longer valid, then we have found new physics. Physicists LIVE to find such things.

  6. Sep 4, 2015 #5

    Andy Resnick

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    Creativity and insight. And a prepared mind.
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