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Is there really such a thing as a perfect circle in nature?

  1. Aug 25, 2010 #1
    My friend and I were debating if there really could be a perfect circle in nature outside the human brain? What do you think? If you think there is, please back it up with evidence.
     
  2. jcsd
  3. Aug 25, 2010 #2

    rock.freak667

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    Well I think things like electric field lines are circular.
     
  4. Aug 25, 2010 #3
    What would you call perfect? Any circle has a radius R +- DeltaR. It's just a matter of how small is DeltaR.

    A black hole's event horizon or a lone atom surely have very well-defined radius.

    But on a regular scale, statistically, I bet could find some on oranges, raisins, eggs, pupils, and perhaps other organic systems.
     
  5. Aug 25, 2010 #4
    well, my navel looks to be a perfect circle when my body is not stretched.:wink:
     
  6. Aug 26, 2010 #5

    Danger

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    With the possible exception of a black hole circumference, as mentioned by Dr. Watts, I don't think that such exists. The Planck length limits the number of incremental steps around a point. I'm not even sure that the black hole would qualify, since its circumference is zero.
    This is a damned good question, Zeromodz, and I expect that there will be some serious discussion about it.
     
  7. Aug 26, 2010 #6
    I doubt that even a black hole would define a perfect sphere.
    Perturbation fields would for sure perturb the BH event horizon.
    Further, the BH must have a history with initital conditions that are for sure not perfectly spherical.
    Therefore I don't see why the final BH should be perfectly spherical.

    This same reasonning is applicable to any shape.
    This should imply that shapes do not exist.
     
  8. Aug 26, 2010 #7
    Human brain is nature, so yes perfect circle in nature is a go!
     
  9. Aug 26, 2010 #8
    Pi is a transcendental number. You can never build anything with a ratio of Circumference=2pi*r using a finite number of points. You can't even square a circle using a finite number of operations*.

    Maybe what you would like though is to build a circle with a finite number of objects that are perfectly sitting on on the edge, like dots around a circle. The Heisenberg uncertainty principle tells us that we can't perfectly position anything. Even an event horizon of a black hole is going to be "bubbly" according to Hawking.

    *Squaring a circle is a classical problem of geometry. Ancient geometers wondered if one could construct a square with the same area of a circle by using a compass and straight edge. It turned out to be impossible.
     
  10. Aug 26, 2010 #9
    Circle by definition means a set of all points in R^2 that are equidistant from a point called the center.

    First, there are no "points" in nature
    Second, no particle can sit still in space.
    Third, space is not continuous, as stated above (plank length is somewhere in the 1/10^36 range if i recall correctly).

    so no, its impossible.
     
  11. Aug 26, 2010 #10

    Danger

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    If your brain is a perfect circle, it is not only 2-dimensional rather than the 3-dimensional that most of us prefer... but also not human. You seem to be missing some lobes. :tongue:
     
  12. Aug 26, 2010 #11
    What about bubbles in liquids? aren't they "trying" to be a perfect circle / sphere, I guess gravity could also be squashing them slightly out of shape.
    Oil droplets in water? on the surface of water?
     
  13. Aug 26, 2010 #12

    Ranger Mike

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    rain drop is perfect circle as it handles atmospheric pressure equally around its peripheral ...
     
  14. Aug 26, 2010 #13
    Another idea is a perfectly still pond, on a perfectly still day, and something dropping down from dead vertical into the centre of the pond, then the "wave rings" around the item should be theoretically perfect right? but then I guess the item dropping into the pond would also have to be perfectly circular to create perfect "wave rings"
     
  15. Aug 26, 2010 #14

    Andy Resnick

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    A soap bubble (or any liquid drop) on board the space station is, for all practical purposes, a perfect sphere.

    Edit: I see I am not the first to think of this.
     
  16. Aug 26, 2010 #15

    He's referring to the 'concept' of a perfect circle existing inside the brain, not the shape of the brain at all. Maybe you should check your lobes.

    And I'm in the Heisenberg Uncertainty camp: If definite location does not exist in nature, then a perfect circle absolutely cannot exist in nature.
     
  17. Aug 26, 2010 #16
    All the basic geometric shapes are concepts we invent, none of them exist in nature. We use them to model phenomenon that are approximately represented by these ideal shapes.
     
  18. Aug 26, 2010 #17
    no. nothing comprised of atoms has a "perfectly smooth" circumference. even if you try to describe a perfect circle within spacetime without regard to any physical entity, you cannot acheive a perfect circle since spacetime is not perfectly smooth - it is limited to discrete fractions at the planck limit, ie the planck length.
     
  19. Aug 26, 2010 #18
    Here is something inspiring :



    But basically, because of Heisenberg's principle, a length cannot be perfectly defined, so neither can a radius. It just comes down to how small we wish the error on the circle radius DeltaR to be.
     
    Last edited by a moderator: Sep 25, 2014
  20. Aug 26, 2010 #19
    Circles aren't generally defined to have an error in their radius. The title of the thread uses the term 'perfect circle' to drive home this point.
     
  21. Aug 26, 2010 #20
    Surely it should be possible in principle to produce a perfect circle by Lissajous method, if some form of compensating circuit is employed as a filter to the scope inputs?
     
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