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Is matter infinitely divisible?

  1. Jan 7, 2010 #1
    First things first, so that answers will more closely approach my level of understanding; I have only completed multivariable calculus and linear algebra and haven't yet taken a "real" physics course. I am part-way through Penrose's "Road to Reality" though.

    Secondly, this question stems from an argument I was destined to lose on YouTube. I'm not looking for an argument just (hopefully) helpful answers.

    The original question (as stated in the title): Is matter infinitely divisible?

    I wrote physicists at the top 20 Google-returned sites asking just this question and of those who responded, the overwhelming answer was "No one knows" (<- Verbatim reply from UCSD). (There was also one "No" answer and one "I believe it is.")

    1) As I understand it, discounting everything else, Planck's Length is the smallest we could ever hope to zoom in on, not necessarily the smallest there is, is this correct?

    2) I have read a few articles from the mid '90's about the possibility of a substructure discovered in quarks, what came of this, was it disproven?

    3) If there is a smallest length and corresponding smallest bit of matter, can someone outline motion for me at that level? Below are my general thoughts on the matter and why I have difficulty imagining a smallest subunit.

    Assume there is a length which cannot be subdivided; Ill call it k. Take a piece of matter of size k and move it over one k unit. Since k is not divisible anything moving onto k must cover it completely instantly for if it were to at any point cover it partially, you would have subdivision of k. This implies that the movement between the two points takes no time what so ever. But instant is faster than the speed of light and so conflicts with the laws of the physics. (Obviously I really know nothing of physics, but alas I copied this from a different conversation I had in which I pretended to know something and so leave the paragraph as is for completeness sake.)

    I'm probably leaving a lot out that I wanted to ask but will stick with this for now. Thanks in advance for all who help.
  2. jcsd
  3. Jan 7, 2010 #2
    I'll try to address your questions.

    -Is matter indefinately divisible?
    The answer you'll get depends on what model you prefer, I beleive. According to the Standard Model, it stops at quarks and leptons. Someone with more expertise might elaborate more on more recent theories.

    -Smallest length
    Length is an abstract notion, invented to allow us to measure spatial distance. As it is not a physical object in itself, there is nothing stopping you from making arbitrarily short line segments.
  4. Jan 7, 2010 #3
    something not being divisible is hard to conceive.
  5. Jan 7, 2010 #4
    Yes this is true. But what he means is that lets say you take a bit of foam, you start cutting it down smaller and smaller and SMAlLER till you get an atom, then you get protons and neutrons and then you get quarks and leptons and then when you cut those? With the Standard model you wil just cut them into energy because there is no structure inside. But there might be some new studies and research sugesting that there is some sort of structure to quarks and leptons so maybe you can get something else out of them. And yes everything is divisible, once you get to the energy state its just gets infinitly smaller. As with length I also agree, there is not one length that we can reach either long or short.

  6. Jan 7, 2010 #5
    ^ that makes sense.
  7. Jan 7, 2010 #6


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    In the Standard Model, you really can't "cut up" quarks and leptons - they're assumed to be truly fundamental. You can involve them in reactions that might turn them into other particles, but the Standard Model doesn't contain any way to "divide" them into anything smaller. And there's no reason that it should, because as far as I know, there's no solid experimental evidence that these particles have any substructure.

    I'm sure there are lots of theories out there (like string theory) but that's all they are, theories.
  8. Jan 7, 2010 #7

    Physics will always have something to explore. If we ever figure it all out the MA (master architect) will probably change the rules. Even the known physics that we accept as true is very often revised as more is discovered. Infinitely small, infinitely large? How could we ever hope to know? Thankfully, our best guesses often allow us to make useful gadgets.

  9. Jan 8, 2010 #8
    I dont even know if that is even relevant to this ha ha, And what i mean by cut up is break down into its basic properties, like molecules to atoms to protons neutrons and electrons to quarks and leptons to..... something else? i havent heard of anything but people have sugested that they could have a structure. But if there isnt anything then it just breaks down to energy.

  10. Jan 8, 2010 #9
    Length isn't any more abstract than the idea of measuring time, though...
  11. Jan 8, 2010 #10


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    But there's a point where what makes one form of matter unique from another stops at the molecular level.
  12. Jan 9, 2010 #11
    I think it may help to think of matter as a collection of forces as opposed to physical entities.
  13. Jan 9, 2010 #12
    Hmmm, I was under the impression that plancks length was the absolute smallest size or length recognized because anything smaller than that would be insignificant to any type of manipulation or advancement for us,kind of like an absolute minimum where anything below it we'd just ignore.
  14. Jan 10, 2010 #13
    Mathematics and numerology, to me, are the closest thing we have to science with hard fast rules, and even then only probably apply to this physical dimension. Everything else I can think of is our current best guess, and as I said earlier, thankfully allows us to make useful things. I think my best answer to the original question is that for the foreseeable future, we will continue to break matter and energy into smaller and smaller particles and sub-particles just based on what we see so far. FoxCommander, you said something about everything breaking down into energy at some level. Do we know what "energy" is?
  15. Jan 10, 2010 #14


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    Numerology?? Numerology isn't even science; it's woo-woo-ism, akin to astrology.
  16. Jan 10, 2010 #15
    Why are some musical notes when played together sound pleasant and some don't? This is a commonly accepted phenomenon, yet math cannot explain it. Our science is at a crossroads where we are going to have to start factoring in the long view, way outside the box, and accepting some obvious, real experiences we have as humans as valid parts of the equation in any given area of study. We might then be able to even resolve some of the paradoxes that plague our science. I know that this complicates our beloved scientific method, but maybe this explains why we know far more about what we don't know (for sure) than what we do. (Kind of like studying sea creatures and ignoring the ocean.)
  17. Jan 10, 2010 #16


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    It most certainly can. Why would you say such a thing?

    Read up on harmonics.

    When you say "we don't know stuff" ... maybe you should just speak for yourself... :tongue:
  18. Jan 10, 2010 #17
    I didn't think "math" had the job of "explaining" anything. Isn't math really a huge web of "if ... then" syllogisms, leading from postulates to conclusions? How could that "explain" why combinations of periodic pressure variations are "pleasant" to a given culture of some species? Why should it need to explain something like that, and why should failure to do so indicate anything?

    To DaveC... sorry, but nothing about the mathematics of harmonics has the concept of "pleasant" as a conclusion. Ever heard music you don't like?
  19. Jan 10, 2010 #18


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    It has everything to do with it. Aharmonic tones played together jar on the ear.

    Is it possible that, by "notes played together" you actually mean "notes played in sequence"? This might explain your otherwise coutnerintuitive claims.

    That is a completely different question. See above, "notes played in sequence".
  20. Jan 10, 2010 #19
    I think you've mistaken some of the text I quoted as being mine.

    Anyway, as far as the jarring of the ear, is it possible that some species are wired such that this 'jarring' stimulates their pleasure response? Or that such a pleasant response is present in some cultures? This is my only point, that such a question is not an issue of mathematics, it is physiology and culture.
  21. Jan 10, 2010 #20


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    It appears I did. I lazily duplicated the [ quote ] tag. OTOH, it seems you've picked up the ball.

    Two harmonic notes played together tend to reinforce each other. This sounds pleasant to the ear.
    Two aharmonic notes tend to do unpredictable things to each other, such as setting up unintended and unpredictable pulsing.

    (Can I give a scientific, objective definition of "pleasant" and "unpleasant"? I'm not sure.)

    There is no question that, when it comes to musicians using these to achieve a desired emotional effect, aharmonic tones can make for enjoyable music. Angst and stress are often important elements of deep music. But that is because the unpleasant qualities of aharmonic tones are known and taken advantage of.
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