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Why do we need particles in our theories?

  1. Nov 30, 2009 #1
    One thing I don't understand is that most of our theories include particles...the oversimplified analogy is, of course, balls on a billiard table. Even the "theory of everything" or String Theory/M-theory tries to explain everything with one particle and one force. My question is this...why do we need particles anyhow...they seem to get in the way of everything. Can't we just be a universe of forces and no particles per se?
  2. jcsd
  3. Nov 30, 2009 #2
    For a while in the early 20th century, scientists believed that the atom was like plum pudding, a plumb of one charge surrounded by pudding of opposite charge. In 1909, Rutherford scattered alpha particles off of thin gold foil, and discovered something very small and very "hard", meaning a "particle" called a nucleus. In the 1950's, Hofstadter cataloged nuclear sizes by electron scattering. So how can we have forces that don't ever represent finite size objects like nuclei, protons, neutrons. etc.?
    Bob S
  4. Nov 30, 2009 #3
    At the end of the day we don't actually measure a particle. We measure a force applied to the particle. I don't see the need for "building blocks" in our physical universe.
  5. Nov 30, 2009 #4
    At the end of the day we don't actually measure a particle. We have no idea that it exists...it's a garbage pail variable incorporating a number of concepts that we don't understand. What is the physical basis for it's existence other than empirical observation. Does it make sense that the entire contents of a galaxy can be squished down to an infinitely small volume...those ain't building blocks, in my opinion. We measure a force applied to the particle. I don't see the need for "building blocks" in our physical universe. I guess, what I am asking is the fundamental question what are the data that says mass is a true entity. How do we know that we didn't make it up simply defining subconsciously as M=F/A (though it is taught as F=M*A)...I don't see the need for M...can't we just get rid of it and in it's place have F'/A'=F/A?
  6. Nov 30, 2009 #5


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    What about luminosity? M^3.5 how can that be used when mass is taken away.
    I think particles help people visualize the universe and how it works. Take quarks for example, they help us understand protons and neutrons with up, down, etc. In turn, protons and neutrons help us understand atoms, and atoms help us understand elements and so on. How easy would it be to teach highschoolers chemistry using only the weak nuclear force and other extremely complicated forces?
  7. Nov 30, 2009 #6
    Definitely, for teaching purposes, billiard balls are definitely convenient. But for explaining black holes and quantum mechanics the whole thing breaks down. I will, however, take some time to read about your other suggestions in the physics world where "mass" may be necessary.
  8. Nov 30, 2009 #7
    Depends on what you mean by "particles," if I can oversimplify things significantly. It seems to me like you're suggesting that the mathematical constructs themselves -- things like tensors or wavefunctions -- become the fundamental aspects of scientific theories....as opposed to the actual objects that occur in reality, which are described by those constructs. But again, I'm not sure if I'm interpreting you correctly since a lot of this conversation depends on that one word "particle."
  9. Dec 1, 2009 #8

    Vanadium 50

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    Isn't that enough?
  10. Dec 1, 2009 #9
    I felt your pain, years ago. Then I did a lot of schooling on the subject...
    A sub-atomic particle really isn't a particle per se; it's (take your pick of 'particle') actually both a particle and a wave--I mean, all of them! Protons, nutrinos, electrons, and yes, even photons are both particle in nature and wavelike in nature. This is called, 'particle/wave duality'.
    Why must we have this particle/wave duality? Because of a very thorny aspect of the quantum world called, 'uncertainty', that's why. To elaborate, when we try to measure an electron, for example, we may know the electron's momentum, but are uncertain about its position in space. Conversely, we may know by observation the electron's position, but are uncertain about its momentum. This is because our measuring of the electron has the effect of disturbing the observation. In fact, a Physicist (Werner Heisenberg) came up with an equation to describe this uncertainty, and called it the 'uncertainty principle'. The uncertainty principle:

    As for mass, it can simply be defined as, "A resistance to a change in motion," thus it's a dimensionless unit. The wavefunction for mass is called the Higgs Boson and is a sub-atomic particle/wave.
  11. Dec 1, 2009 #10
    Thanks for your reply. I'll have to ponder the concept of mass being defined as anything that resists change...interesting concept...I like the fact that it is unitless. Never could understand "kilogram" - what the heck is that metaphysically speaking. Let me take that and do a layman review of quantum mechanics and so if that makes more sense. Appreciate it.
  12. Dec 1, 2009 #11
    In reference to empirically derived formulas.

    I get nauseated when I see an empirically derived formula...they tell us very little. The ideal gas law PV=nRT, does a decent job at cranking out accurate numbers...doesn't do a thing for telling us how gases behave at the atomic level. Well, that is until you start to compare it to the real gas law which has a physical basis for derivation and starts to tell you something about atomic particle behaviour.
  13. Dec 1, 2009 #12


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    In the end, all equations are empirical when you get down low enough. For example, we do not know why Pauli's Exclusion Principle is true, but we know from experimental evidence that it holds for fermions (well, that's a bit by definition but) to the best of our knowledge. The very basics of physics are defined and supported empirically. We use particles because that explains practically everything from non-relativistic quantum mechanics and beyond. It is only in relativistic quantum mechanics, like quantum field theory that we start to really diverge from the particle idea. But then, we replace "particles" with "quanta" and still retain some of the basic ideas about particles. All matter and substance in the Universe are fields, but their interaction is done by quantization of fields. These quanta interact in the form of particles in the classical system.
  14. Dec 1, 2009 #13
    :smile: I think that is why I majored in chemistry...less empirically derived formulas...but the questions physics seeks to answer are definitely funner to think about. Point well made. Though, string theory is not empirically derived which is probably why, in my opinion, it has attracted a lot of attention.
  15. Dec 1, 2009 #14

    Andy Resnick

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    There are several branches of physics that do not deal with discrete particles: thermodynamics, continuum mechanics, general relativity. They work just fine.
  16. Dec 1, 2009 #15
    There is such a thing as non empirical chem.I only took the intro chem and intro organic courses but i can't think of a concept in chemistry that is not completely empirically derived.In physics some of the concepts and equations may be derived from axioms just like mathematical theorems but in the end they must agree with the observations. As for the existence of particle I think the problem is that you try to apply the regular meaning of the word particle to atomic particles.We only use the word because it is convenient. In truth a physical particles is a thing in itself with a set of properties that we can clearly observe and define therefore we can say that it exist.
  17. Dec 1, 2009 #16
    For the very small things what would be better then a particle to explain it? Its basically just a very tiny unit of matter. If the very tiny things do have matter it may turn out they are not very point like at all but the difference from where we are standing between a point particle and what actually exists could be fairly small.
  18. Dec 2, 2009 #17
    Generally speaking, the intro chem courses are based on empirical data. It's not until you get into the later courses where they basically tell you that the stuff you learned in the first year isn't quite accurate. The subsequent chem courses try to use basic concepts to derive formulas that match the data. Whereas empirically driven formulas, there is less derivation and more focus on the formula matching the data.
  19. Dec 2, 2009 #18
    I think you are answering your own question...we have the concept of mass because it is convenient and works real well in the Newtonian world...it does not tell you anything about the universe...granted that is a very tall order to come up with a formula that actually gives us insight. What is a kilogram? You can't break it down any further...it's not like acceleration which can be defined as deltaV/deltaT...and thenvelocity can be further defined as d/time...well we know what distance is and we know what time is. There's no mystery behind acceleration. You can't do the same thing with a kilogram. And I would argue that since we perceive or universe through forces, that you don't need mass, just forces.
  20. Dec 2, 2009 #19
    How would you define particle/mass...someone on this thread suggested anything that resists change and that seems reasonable...perhaps a little too inclusive, but it's the best thing that I can digest conceptually.
  21. Dec 2, 2009 #20

    Andy Resnick

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    It seems like you are asking about the conceptual foundations of empirical science (which includes all of science except for mathematics). It is true that 'mass' has no axiomatic foundation (as opposed to, for example, length, which can be defined axiomatically from purely mathematical objects) and that the standard kilogram is one a very few remaining standards still defined by a physical object (I think the Ohm, Candle, and Kelvin are as well). That does not support a claim that we therefore know nothing about the universe.
  22. Dec 2, 2009 #21
    Thanks for putting the real scientific terms behind a lot of questions I am asking...it is making it easier to look things up. Before I go any further, I am not trying question the very foundations of science...I fully recognize that I need to reading in many areas. Having said that, the other standards that are defined by a physical object that you mentioned do have working models behind them. Kelvin - Model says that a Kelvin is a measure of how fast atoms vibrates. Ohm - well there are electrons around a nucleus and resistance is a measure of how tightly bound the outermost electrons are (I believe that is correct). Now, whether these models are correct or not, who really knows and it would take decades of study to answer that question. But they are accurate enough that they tell us about our universe. Now, what is the model of a kilogram mass - without trying to be fascetious, in my textbooks, it's usually a filled in circle...not a very complex, active and working model...it looks more like a garbage pail of a multitude of concepts that we don't know about. That is my rationale for saying the concept of mass doesn't tell us anything about our universe.

    Also, I want to clarify what I consider to be empirical vs non-empirical science. A mathematially driven formula arising from a simple model that matches our observations is not what I consider empircal. However, a formula that does not have a simple model behind it but matches data is an empirically driven formula. I am not sure if I have it entirely correct or not.
  23. Dec 3, 2009 #22

    Andy Resnick

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    I'm not sure I understand you. The reason there is a standard Ohm is the same reason there is a standard kilogram: if I wanted to make a 1-ohm resistor in my lab, I would have to compare it to another physical object. This is *very* different than if I wanted to make a 1-meter ruler, which I can do without recourse to comparison with another physical object. In fact, NIST is trying to come up with better physical standards of mass and resistance (I don't know about temperature and radiance) that do not depend on comparison with other physical objects.

    Having a model that consists of abstracted properties of real objects is how empirical science works- verifying the models, extending and refining the models, is the true aim of science. Models can't be 'really correct or not', there is a limited domain of applicability. Enunciating that domain is essential. Curve-fitting is not science- it's phenomenology.
  24. Dec 4, 2009 #23
    I'm new to the forum so this might sound stupid:
    Can you not define mass by the curvature of space-time it creates ?
    I don't know GR very well but I think the curvature can be viewed only as a mathematical entity and it depends only on the mass that created it.
  25. Dec 4, 2009 #24

    Andy Resnick

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    It's not a stupid question. The curvature is a measure of the local *energy* density, tho.
  26. Dec 4, 2009 #25


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    What about the conservation of energy? Isn't that empirically derived? And yet it says so much.
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