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How do you visualise particles?

  1. Nov 6, 2008 #1
    I'm struggling to keen my mind open when visualising fundamental particles. I've only been reading about quantum/particle physics for 3-4 years so I'm very much a beginner.

    (if I remember rightly) Heisenberg liked to describe things in maths and Feynman preferred visual models, I'm swinging toward the Feynman camp.

    I've read a lot of literature that particles are not dimensionless points. Why can we not think of them as such?

    Why can particles not be points of energy in space which (depending on the amount of energy in the point) cause space to fold around them? Then it's more logical to see how they give rise to fermions and bosons depending on the nature of the folding and interaction between the folds.

    How do you visualise particles and their interactions?
     
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  3. Nov 6, 2008 #2

    malawi_glenn

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    What you mean by "visualising particles" ? Define it.

    It depends on what "camp" you belong to. The answer is different depening if you are asking a high energy physicsists or a string theorist.

    Feynman approach is just that his diagram-method makes it easier to structurize your calculations in a nice way.

    You idea that they are points of energy in space etc, how can you measure why that is more logical than for instance string theory description of particles? There is a reason for why string theory has the structure it has, it tries to embrace all known physics and what we know that physical laws must obey. Your suggestion is just a "science fiction guessing" with fancy physical words.

    Sorry, but arguing in the way that "why can't particles be made out of small tiny cheese balls" does not prove that they are cheese balls, just because noone can't disprove you. Science must make positive, testable, claims.
     
  4. Nov 6, 2008 #3
    thanks for the response, its very interesting.

    I was not trying to make any scientific claims. While reading about particle physics I imagine models in my head and I want to reduce my misconceptions so I can understand things more fully. I am hoping to open a discussion to find out how the (clearly extremely learned) users of this forum think about physics.

    sorry if it came across wrong :)
     
  5. Nov 6, 2008 #4

    malawi_glenn

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    So how do define "visualise" particles?

    You can also try to search for old threads, this is one of the most frequent quetions here ; "what is a particle?"

    The most fundamental answer, as I almost alaways give - since it is very honest, is that a particle is a particle. Then particle has certain properties, which there exists coherent physical theories and models in order to describe them.

    For a high energy physicsits, an elementary particle is just a point with no extension in space, no internal structure. But for a string theorist, a particle is something like a string attached to a brane which vibrates :-p

    The difference between certain "crackpot" theories and models, is that string theory is not an "intutive game of guessing", it is a serios attempt to give a unified picture of physics-> As you might know, there are some serious "flaws" in physics, one of them is the incompatibility of Quantum mechanics and gravity.

    There was also quite recent an interesting thread about epistemology in physics, "do you sometimes have the feeling.. " or something like that was the name of it.

    Since you are quite new here, take your time to search for old threads, and perhaps take a look in our tutorial session, where some nice links to teaching material can be found.
     
  6. Nov 6, 2008 #5

    jal

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    Hi malawi_glenn!

    If I might add a comment ... Since a point has only position and location then it is not restricted by the Planck Scale (minimum length).

    As a result, different models are required when considering a "particle" or a "point".
     
  7. Nov 6, 2008 #6

    atyy

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    There is a concept of "energy bubble", but it is from high energy quantum physics. In that theory, a particle is a type of energy bubble with well defined "properties" and that is "on the mass shell". The concept of energy causing space to warp is from the classical theory of general relativity. The relationship between the two theories being currently researched.

    Veltman, Facts and Mysteris in Elementary Particle Physics, World Scientific 2003. See chapter 6:
    http://books.google.com/books?id=CNCHDIobj0IC&printsec=frontcover#PPA161,M1
     
    Last edited: Nov 7, 2008
  8. Nov 7, 2008 #7
    Thanks guys this helps a great deal.

    When I say visualise I mean to imagine as a visual model. I'm just trying to get an idea of how you guys picture particles and interactions. Surely everyone doesn't think in maths?! :)


    What does that mean?
     
    Last edited: Nov 7, 2008
  9. Nov 7, 2008 #8
    Think you mean Julian Schwinger, not Heisenberg.

    -Spoon
     
  10. Nov 7, 2008 #9

    malawi_glenn

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    Well then we use feynman diagrams, if you are asking a high energy physicsist. Particles are lines in space and times and interaction between particles are described as "virtual particle" exchange. This tool was invented by Feynman, in order to help one to structurize the calculations -> at each point where lines meet (called vertex) certain things must be conserved and so on.

    http://en.wikipedia.org/wiki/Feynman_diagram

    Mathematical formalism is the only way we can describe particles (well everything that is governed and dominated by quantum mechanics) is by using the language of physics -> Math. Same thing for strings, they exists in 10spatial dimension, now how do you draw that on a sheet of paper? ;-)

    "Off mass shell"

    Is another way of saying that the particle does not obey the "rule":
    [tex] E^2 = (pc)^2 +(mc^2)^2 [/tex], i.e the general formula for [tex] E = mc^2 [/tex].
    They can do that during a small time interval, so that this uncertanty rule is not violated:
    [tex] \Delta E \Delta t \sim \hbar/2 [/tex].
    Particles can thus violate the rule E^2 = p^2 + m^2, but only during a short time that [itex] \Delta E \Delta t \sim \hbar/2 [/itex] is fullfilled.
     
  11. Nov 7, 2008 #10

    malawi_glenn

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    Jal, there are many different interpretations on what the planck lenght resembles.
     
  12. Nov 7, 2008 #11
    One of many issues is that "particles" sometimes appear as "particles" and sometimes appear as fields/waves... think of the double slit experience. Quantum field theory and the Schrodinger wave equation give two different perspectives from a field/wave viewpoint, quantum mechanics sees discrete particles,but bigger than planck length, and string theory as, well, strings..maybe membranes.

    So you get to pick, then haggle which is "best" !!!!...until you realize it's rather imprecise in many respects "down there" no matter what ...maybe a result of quantum uncertainty and anamolies like wave particle duality, Heisenberg uncertainty over position/memontum as well as energy/time...I'm getting a headache thinking about all the confusion...

    Lee Smolin says in THE FABRIC OF THE COSMOS: "The overarching lesson that has emerged from scientific inquiry over the last century is that human experience is often a misleading guide to the true natrue of reality."

    "we know much, we understand little"
     
  13. Nov 7, 2008 #12

    malawi_glenn

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    particles as in "tiny billiard balls". For a particle physicsists, a particle is a particle - it has the properties of a classical tiny billiard ball, and the properties of a wave such as light. Just as light both as wave and "billiard"-particle properties.
     
  14. Nov 8, 2008 #13
    I always thought they were ball-like or spherical shapes.. somehow that's what education has gotten that into us.
     
  15. Nov 8, 2008 #14

    malawi_glenn

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  16. Nov 8, 2008 #15
    The quantum particles are excited states of the quantum field so I imagine them as some kind of soliton ripples propagating on the surface of a lake (which visualizes the quantum field). The ripple is a parcel of specific energy and momentum.
     
  17. Nov 8, 2008 #16
    Seriously, nobody here has answered the question adequately. If you can't explain it to your grandmother, you don't understand it!

    Without leaving the domain of conventional physics, we should consider the wave-particle duality, the Heisenberg uncertainty principle, and de Broglie wavelength concept.

    A point-like particle, in reality, has a certain amount of room to move - within the planck scale - as shown by Heisenberg. This means we don't actually have a point, but a radius.

    Now, since there is such a thing as the de Broglie wavelength of any particle, insisting that every particle can be mapped as a thing of a specific wavelength and interacting as such under the correct type of observation, we can in fact model a fundamental particle as follows (now we're talking quarks, leptons, and gauge bosons, and everything else is built up from this in a complex way):

    A particle should be seen as a "wavicle"; that is, we have a wave that is confined within a given radius. To model a reaction in one plane, we *could* treat it as a circle with a squiggle inside it, or it might be seen as a squiggly loop. Those aren't quite billiard balls, as they allow wave interactions *as well*. Either is good for the purpose of this question.

    For first and second order interactions, we can even use this to try and predict scattering patterns and use mathematical perturbation to correct anomalies as we go.

    Smallphi, that kind of talk is why we're not able to sell string theory to the rest of the physics world.

    Those of you who referred to Feynmann diagrams are certainly on the correct path, but the actual diagrams can be tailored to whatever particle description you're using.

    If you want to learn something properly, TEACH it. You will have to answer questions you ought to know, clarify models, and argue against other ideas - and maybe you'll even have to admit sometimes, that you don't know.
     
  18. Nov 9, 2008 #17

    malawi_glenn

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    What it the wave composed of "TimeDependent"? The wave is "what"? According to mainstream QM the wave is a wave of probability density.

    A wave confined within a given radius, is that testable? Is that what current knowledge from a experimental point of view tells us?

    It would be very kind of you, prove the theorem above: "A point like particle can move within the planck scale".

    The use of feyman diagram is a beutiful way to "illustrate" a reaction, so that it can be printed within a popular science book with the feeling that "this is what physicsists really are using", but physicsits are using the diagram in another sence - to structureize their calculations, which is contains the physics.


    i) Why don't you understand something if you can't explain it to your grandmother? There is no such criterion in the mainstream philosophies of epistemology. The problem of understanding might lay within my grandmother, who don't have enough background knowledge to understand the things I am talking about. Then of course I can always, as popular science books do, start to describe things in a non-mathematical sense and compare with daily life observations.

    But what if it is impossible to explain things which are described by mathematics and counter-intuitive in a non mathematichal and intuitive way? Classical and ordinary day life experience explanations on quantum physics will always fail to give the same description as the language of physics - math - will do.

    By swiching language I immediately loose information. It's like going from CD to MP3...

    ii) Having the idea that one KNOWS what a particle REALLY is, is like giving a statement that one have 100% correct description of god or anything else which is beyond of our ordinary day life experiences. What a particle "is" depends on who you ask, which then of course, needs to have a coherent use of his/her particle concept.
     
  19. Nov 9, 2008 #18
    Don't use quotation marks on a name, malawi glenn. You sound like you're getting rather too personal about the argument.

    The wave, the 'squiggle' as i refer to it, is normally seen as a wave of probability density, indeed, but this is not fundamentally proven, depending on the interpretation of quantum mechanics used. It could, in fact, be a string, if one wished to consider it thus.

    By within the Planck scale, i mean that dt*dE=h/2pi. This gives us a maximum radius for the probability density under measurement of any type.

    By switching language, i *may* lose information if i'm not careful, but the point is to try and explain something -without losing the basic point- in simple language. The idea of teaching one's grandmother is based on a quote from Einstein anyway, and no doubt his grandmother *did not* have any physics background. This is actually the point - you have to explain it as simply as possible, but no more so.

    Wave-particle duality is the commonly accepted (Standard Model) theory, and whilst modified under string theory is not outright rejected by it.

    The interactions, however, often are not intuitive, but there are specific examples which one can mentally examine in a non-mathematical way.

    At any rate, particles are not quite billiard balls.
     
  20. Nov 9, 2008 #19

    malawi_glenn

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    I do it all the time, its a nice way to show that "TimeDependent" is your name.

    Now "dt*dE=h/2pi" is not Heisenberg.. calling it heisenberg uncertainty relation is a bit wrong.
    https://www.physicsforums.com/showthread.php?t=230693&highlight=demystifier

    Now do a full calculation to obtain the planck scale, should be a trivial calculation.

    Some things require advanced fancy math, that is my point. And just because he is Einstein, doesn't mean that we should take his word as standard. Physics have no prophets. Einstein beleived in locally hidden variables, "God Dont Play Dice", should we abandon the probibalistical description of nature just because that quotation? Einstein also lived in a world which is quite different then ours, we are dealing with quantum mechanics severel times each day - transistors etc. For Eistein, these things where quite new and spooky.

    Thus describing a particle as a "wave confined within a radius" you leave the particle concept open to many different interpretations; "what is the wave?" - and how do you tell what interpretation which is plausible?

    I can give you a quote from Bohr: "If you think you have understood quantum mechanics, you have not understood Quantum mechanics"

    Now try to examine a QED interaction mentally, NO mathematics at all, I am waiting.
     
  21. Nov 9, 2008 #20
    I dont think the OP was asking whether particles ARE waves or classical particles. I think the OP simply wished to know, when you think about particles whilst problem solving does it help at all to THINK of them as a wave or a classical particle or something else all together?

    The OP was not after a scientific answer, simply a point of view.


    Also i believe that was R. Feynman.

    -Spoon
     
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