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Intro Physics Which book written: only measurable quantity - length?

  1. Dec 27, 2015 #1
    In which book is it written that the only measurable physical quantity is the length?

    In any book I've seen thoughts and images that very clearly illustrate the sequence of actions and implicit assumptions when measuring something.
    The result has been that in any measurement key was the length measurement.
    For example, in the book Fundamentals of Physics Extended, Halliday&Walker correctly begins the description of start a physics - measurement is the basis of physics. The following describes what is the length. Then time and so on.
    But! Is not described that the measurement of time in a mechanical watch arrow implicitly counts the length of the circumference by minute and hour-markers.
    I don't remember in which book these thoughts are clearly documented.
    Please tell me this book.
    Thank you.
  2. jcsd
  3. Dec 27, 2015 #2
    Is it? If I want to measure the pH of something, and a put a pH indicator in the substance. The color changes, and the end color will tell me the pH. In the pH indicator I have, red would mean a very low pH. How is this measuring length?
  4. Dec 27, 2015 #3


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    Good example, but I think the OP could claim that you are using the wavelength of the light to make the measurement... :smile:
  5. Dec 27, 2015 #4


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    Staff: Mentor

    I would think a good counterexample would be a measurement of mass...
  6. Dec 27, 2015 #5
    Yeah, I would be expecting that answer. But then the discussion is over. Why? Because everything we measure is done by our eyes. And our eyes basically take in waves/particles/whatever of light. So everything we see can be expressed by properties of light, and those properties can be expressed by lengths of the waves. So it's not really a very useful thing to think about, I feel.
  7. Dec 27, 2015 #6
    I guess it depends how you measure mass. If you take a scale and you put in a certain mass, then you will measure the length of the needle. So you measure length.

    I mean, all measurements we do are all real numbers. And a real number can be seen as a length.
  8. Dec 27, 2015 #7


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    Gold Member

    The claim you've seen is probably about position, not length. It's a bit of an oversimplification, but I wouldn't say that it's wrong. For example, a momentum measurement is done by detecting the particle at two different locations. A detection is an approximate position measurement, because the particle can only be detected if it's interacting with the detector, and once that interaction is complete, the wavefunction is close to zero outside of the region where the interaction took place. So we can argue that momentum can't be measured directly; we make position measurements and then calculate the momentum.

    Similar comments apply to all observables in quantum mechanics. The thing to understand here is that every measurement involves an interaction between the specimen and the measuring device, so the position of the specimen can always be inferred from the position of the relevant parts of the measuring device. In this sense, every measurement is a position measurement. Not necessarily a good one, but at least an approximate one.

    I like to take this one step further, and say that what a measuring device really does is to produce signals that indicate that an interaction has taken place. Everything else, including position, is inferred from such signals.

    I don't know if there's a book that explains this any better. I would be surprised if there is.
  9. Dec 28, 2015 #8
  10. Dec 28, 2015 #9
    https://en.wikipedia.org/wiki/Mass : Mass is not the same as weight, even though we often calculate an object's mass by measuring its weight with a spring scale instead of comparing it to known masses.
    The measurement of mass is equivalently the measurement of weight and it is like the measurement of time in a mechanical watch: arrow implicitly counts the length of the scale by units of weight.
  11. Dec 28, 2015 #10
    I thank you for the reply! :)
    Now I won't waste time searching for books.
    Tomorrow I can make some comments slightly, clarifying your opinion.
    Today I'm busy. :(
  12. Jan 8, 2016 #11
    Firstly, I'm sorry for what I've not given the promised comments.
    The New Year is to blame!
    With which all the Congrats!

    Secondly, I thank all answered my question.

    Now a few words about the causes that have created my question on this forum.

    Never have I had the need to reduce all measurements to the length.
    But the discussions more relevant to philosophy than in physics, I was having some experience. In some elementary textbooks on physics necessarily it should have been written that all measurements are reduced to information written on the scale with divisions.

    If the measured time, are marked on the scale of minutes and hours. If the measured thermodynamic temperature scale are marked on the degrees. If the measured weight on the scale are marked kilograms (not Newton, although we measure weight). Electric current - Amps. And so on. Thus we see our world through a length, if we get through it information on the status of the world. All this was not interested until fate led me to work in metrology.

    Due to some peculiarities of metrology, I would like to clarify how the information is obtained for any measurement.

    Considerations on the measurement of base physical quantities, from International System of Quantities ISQ, I have stated and tried to publish an article on http://arxiv.org/: arxiv.org_submit_1396781.pdf. Some time later I received a note from the refusal of publication. The refusal of the publication has been written:

    > [moderation #155592] arXiv: submit/1396781 removed
    > From:
    > arXiv Moderation <moderation@arxiv.org>
    > olem2k@i.ua
    > Date:
    > 16 nov, 18:30
    > Your submission has been removed. Our volunteer moderators determined that your article does not contain sufficient original or substantive research to merit inclusion within arXiv. Please note that our moderators are not referees and provide no reviews with such decisions. For in-depth reviews of your work you would have to seek feedback from another forum.
    > Please do not resubmit this paper without contacting arXiv moderation and obtaining a positive response. Resubmission of removed papers may result in the loss of your submission privileges.
    > For more information on our moderation policies see:
    > http://arxiv.org/help/moderation
    > --
    > arXiv moderation

    I drew attention to the phrase "your article does not contain sufficient original or substantive research to merit inclusion within arXiv” and followed the advice of a moderator. Once again run through The Feynman Lectures on Physics, Berkeley Physics Course, Fundamentals of Physics, etc. and I did not find an explicit description of the issue. Then I turned to this forum, to find such a textbook. After receiving answers from the comments I understood that this feature in the measurements is generally not covered in textbooks.

    Could it be that if the material does not describe even in textbooks, it may not contain sufficient original or substantive research to merit inclusion within arXiv?
    I don't know which tasks would be changed, if you are know what decision the only measurable physical quantity is the length. So I'm not sure whether such publication. But I know for sure that the absence of any part of knowledge necessarily lead to substantial losses.

    So again I'll try again at arXiv to moderating with a request to republish. Or try to publish an article elsewhere.

    PS: I will be grateful if someone tell me where can I publish this article.

    PS: special thanks to
    Last edited: Jan 8, 2016
  13. Jan 8, 2016 #12
    It really is more philosophy than science. So you probably won't find any science journal that publishes this. Perhaps you can look for philosophy journals.
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