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What is the point of particle accelerators?

  1. Nov 3, 2009 #1
    A.) Slamming particles together at high energy to see what they are made of and how matter is formed is like taking a clock and smashing it off the wall, then looking at all the broken pieces flying around in a hope to figure out how clock works, or so it would seem?

    B.) Beside that, is anyone seriously hoping to find a real "atom" as in "the smallest indivisible particles" from which everything is composed? Isn't that just like looking for the edge of the universe? Why would universe be infinitely large, but not infinitely divisible? Infinity that goes only one way? Is that logically possible?
  2. jcsd
  3. Nov 3, 2009 #2
    Looking at an atom from "far distances" gives an image of a neutral atom. But we know that we can decompose it. So it is a compound system. To look "inside" we need a short-wave probes - photons, X-rays, neutrons, and fast charged particles. The accelerators are made for the latter.

    By the way, with help of X-rays we can build a 3D image of your clock.
    Last edited: Nov 3, 2009
  4. Nov 3, 2009 #3


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    Why? No one knows why the laws of physics are as they are.

    (Logically) possible? Well it certainly appears that way. I don't think we know about infinity on the large side. But things appear finite on the small side.

    Now, does that mean that a distance smaller than the planck length is possible? This is more of a metaphysical issue as we can't really answer that via experiment. How many angels fit on the head of a pin?
  5. Nov 3, 2009 #4
    In about 1910, Rutherford used alpha particle scattering to determine that the atomic nucleus was only about 10-13 cm in size, and most of the atom's size was "empty" space. In the late 1940's, accelerators started producing mesons, p'is mu's etc. altho later the mu meson was determined not to be a meson. In the 1950's electron scattering accurately determined the nuclear sizes. About 1970, high energy electron scattering determined that the proton was made up of 3 quarks (partons). I left a lot out, but you see the pattern.
    [added] Recent collider experiments, like planned for LHC, produce zillions of particles in each collision, using 1000's of physicists from 100's of institutions with detectors that have masses exceeding 1 million Kg's. How much is the discovery of the Higgs worth?
    Bob S
    Last edited: Nov 3, 2009
  6. Nov 3, 2009 #5
    Smash a clock 100 times and you'll only find the same constituent parts. Smash atoms together and you will get products which were not in the initial particles, and which may differ each time. You learn about the processes that happen by smashing particles.
  7. Nov 3, 2009 #6
    The point of them is that, the day humankind stops looking deeper and deeper into the structure of matter, or stops peering further and further into the depths of the universe is the day that we stop being humans and start the backward slide into being hairless apes.
    Maybe one day we won't need atom smashers any more because we will have discovered the mechanics of matter and the cosmos, but I'm certain that we will have found other questions that need new answers, and hopefully new machines as awesome as the LHC.
  8. Nov 3, 2009 #7
    I'll take this as a good answer.

    But, it will still not tell you how clock works, just what the parts are... and even then you can't be sure if you are looking at completely functional parts or just some broken pieces.
  9. Nov 3, 2009 #8
    In 1969, Robert Wilson, the developer of Fermilab, testified before Congress on the usefulness of high energy accelerators. Here is what Robert Wilson said:

    Senator Pastore: “Is there anything connected with the hopes of this accelerator
    that in any way involves the security of the country?”

    Robert Wilson: “No sir, I don’t believe so.”

    Pastore: “Nothing at all?”

    Wilson: “Nothing at all.

    Pastore: “It has no value in that respect?
    Wilson: “It has only to do with the respect with which we regard one another,
    the dignity of men, our love of culture. It has to do with are we good
    painters, good sculptures, great poets? I mean all the things we really venerate
    in our country and are patriotic about. It has nothing to do directly
    with defending our country except to make it worth defending.”

    Bob S
  10. Nov 3, 2009 #9
    I also agree with this, but what do we do in 100 years with 100 more of new particles? What do we do with all that? What do we really want to know as a human race as a sentient beings? -- I think it's much more important to figure out how quantum interaction works on a much larger scale, such as protons and electrons, atoms and molecules, so we can actually uncover the secret of chemical bonding and intermolecular interaction that produces self-replicating molecules, the secret of the brain and neurons, the mystery of human mind and what does it really mean to be self-conscious.

    We do not need to go further than that to discover the secret of life itself, or so it would seem.
  11. Nov 3, 2009 #10
    I am not sure you understood my point- you will not get the parts of the atom when you smash it, you will get all kinds of things that weren't there before. The energy of the collision opens up the possibility of heavy particles to exist, such as resonances, for short periods of time. The particles annihilate and, given enough kinetic energy, produce huge particle jets and showers which are statistically analysed to make deductions about what can and can't form.

    The information gained from the detectors surrounding the collision point is not so much to do with finding what was inside the particles, not at all in the case of electron/positron collisions at SLAC since they are fundamental, or the proton antiprotons at LHC, but more to explore the governing rules of interactions (EM/weak/strong) which throw up all the showers and processes that happen.
  12. Nov 3, 2009 #11


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    The point is that how the clocks "responds" to provocation, perturbation or stress is exactly what characterizes "how a clock works".

    I think one of the lessons of modern physics is that the the purest ways of defining what something is, is operationally in terms of how it appears to react upon disturbances and measurement. The operational ideal is one of the satisfactory traits of a theory of measurement, rather than the old style realist theories.

    The response pattern of a system, is inferred from experience with acually interacting with it.

    Without an interaction history, you have no relation with the system in question. Thus there is no way of finding out how something works, without disturbing it. All forms of communication and interaction is a form of disturbance.

    When you decode the response patter you don't go from small interaction to full power blast with total destruction in one step. We've gradually found out about the response properties of matter by gradually increasing the energy scales. Some response pattern are simply not visible util the energy is large enough.

  13. Nov 3, 2009 #12


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    The following is is my personal opinon, others may disagree:

    It's worth noting that any inference of smallest possible distinguishable scale, or largest possible distinguishable scale, are always dependent on another scale, namely your own scale. OR generally the scale that defines the measurement system. A given system can not produce an interaction of arbitrary strength, this naturally constrains what two systems can learn about each other, and hence also the way they respond to each other.

    So there is more at stake here than the analogy of smashing a watch, since the process of system-system interaction in general, seems to be almost the essence of matter itself.

  14. Nov 3, 2009 #13
    I am not sure... the scale of measurement are fixed on one side by quantum mechanics and on the other by cosmic expansion, giving us absolute bounds on measurements on either side..
  15. Nov 4, 2009 #14


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    Can you define the things you mention, operationally, without choosing an observer?

    Even the notion of cosmological horizons are relative to the observer. And usually the pure operational meaning isn't respected since when one observer talks about the horizon of another observer that it strictly speaking a part an inferred image, that IS operationally defined.

    Of course I was trying to make a subtle point, that have little relevance to normal QM, but I think there is a point when you try to merge QM with gravity.

    Usually the default observer scale is probably the earth based scale in terms of cosmology, since we humans more or less control earth, and a laboratory frame in terms of particle experiments.

    From a human-human perspectve, the lab fram is effective human-observer indepedent, but this must not fool ourselves to think that measurements in general is that. IMHO there is always a defining context where the operational prescriptions "live", either implicit or explicit.

  16. Nov 5, 2009 #15
    I agree with pretty much everything Fredrik said.

    We are limited in what we can grasp with our thick fingers, we can pick up some salt, maybe even a single grain of sand, but to grasp a single atom we need something appropriately smaller. And if can not make our fingers any smaller, that that is as far as we can go. At that point we may conclude there is nothing smaller than that, but we would only be talking about the resolution we are able to experience, not the real nature of things. I believe the universe is very mathematical, which I call logical, and in mathematics numbers are infinitely divisible.

    This kind of brings us to "Achilles and the tortoise", Zeno's paradox and what is the real nature of motion and moving bodies. Is there such thing as continuous trajectory, or do we actually need something like the Planck constant to make this work. If we were simulated entities inside some matrix, some computer, this Planck size would correspond to the pixel size of the computer screen.

    If we were simulated entities inside some matrix, some computer, then how much we could actually learn about our universe? We could find about algorithms aka physics that makes things behave as they behave, we could figure out this pixel size with which our universe is being drawn, but we would hardly have any chance to find out if our universe is being simulated on PC or Mac, what are the pixels made of and what is the structure and functionality of the CPU, memory and graphic card. We would hardly ever be able to realize where is this computer really located, and then we could wonder if we should actually care. I'm sorry if this sounds pessimistic.
    Last edited: Nov 5, 2009
  17. Nov 5, 2009 #16
    I am not an expert on this, but a rephrased question would be: "Why should one build HUGE particle accelerators, with most of the cost being things like the plumbing, instead of laser accelerators"? In any event the point is to accelerate the beam to huge speeds or energies. But if the electric field can be made larger, that energy can be acquired over a much shorter distance. Essentially, starting from rest V_final=(F/m)t. If the force can be made stronger, as with laser accelerators, then less time of flight is needed. I suppose the reason for still building BIG accelerators is that laser accelerators either don't work or are not yet ready for prime time.
  18. Nov 5, 2009 #17


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    I need to make sure I correct the overriding myth here that should be stopped.

    What you should ask is the need for particle colliders, not accelerators. There is a difference. There's a good chance that you used a particle accelerator when you had your x-ray taken. All the synchrotron centers around the world used particle accelerators for YOUR benefit.

    Read this article:


    So do not lump "particle colliders" and "particle accelerators" to be one of the same. They are not! And I'm guessing that after reading this, you will not be asking anymore for the point of particle accelerators in general.

  19. Nov 6, 2009 #18


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    Even if things were infinitely divisible, it would be logical to continue looking for the next division of particles below what is currently known.

    There is research going on looking at all of this: elementary particle physics, the biology of replication, and the biology of the brain and nervous system. Why do you assume we, as a society, can only do one of these things at a time?

    And who says that "to discover the secret of life" is the only valid justification for funding science?
  20. Nov 7, 2009 #19
    Agreed. I just wanted to point out we should not hope too much to reach some "bottom" of infinity, just like we do not expect to find the edge of the universe.

    Agreed. I just think that quantum physicists might have actually a better chance than neurological biologist in unlocking the secret of human mind. The point is that there is no real boundary where quantum mechanics turns into chemistry and where chemistry turns into biology, so they should all be working together or they should all be trained in all three disciplines to get the full and better picture of the nature of things.

    I think that should be the primary goal of all the science and I am afraid the funding is not divided appropriately. The main point is that they all should be working together, because it all really connects at some point, one way or the other.
  21. Nov 8, 2009 #20
    What sort of observer are you talking about? In the context of your post that I originally quoted I'd expect you to be talking about observers of different scale. But I don't see the difference between an ant looking at an object and a human, though there is a 10^3 difference in length scale.

    On large distances our measurements are restricted by finite light speed, very slow compared to cosmological phenomenon. We can't measure the topology of the universe because of this- it is immeasurable.

    re: funding: The more sources of funding there are, the more money to build machines, the more people you can hire to work on an idea, and the further science progresses. The more sources of funding also means more collaboration with industry, new ideas, new insight, and access to technology. My opinion is that science has a duty to society to provide value to the civilisation, which may mean to further understanding, but also means to improve people's lives through new technologies and discoveries.
    Last edited: Nov 8, 2009
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