Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Experimental verification of matter waves?

  1. Jul 22, 2015 #1
    I am told that even macroscopic objects like footballs obey the wave equations of quantum mechanics. Is there any experimentally based reason to believe this, or is it just said as a way of generalizing the theory?
  2. jcsd
  3. Jul 22, 2015 #2
    Google up An Interferometer for Atoms by David Keith et al.

    Matter waves are real.
  4. Jul 22, 2015 #3


    User Avatar
    Science Advisor
    Gold Member

    If atoms can behave in a wavelike fashion (and experiments do show this), there is no reason to think that macroscopic objects couldn't behave in a wave-like fashion as well.

    The problem with actually observing wavelike behavior in macroscopic objects is that the object is made up of a (relatively) gigantic jumble of atoms interacting with each other and with the outside environment (the atmosphere, sunlight, sound, etc). The Schrodinger equation only applies to a closed quantum system (large or small).

    In order to make a football behave quantum mechanically, you'd have to do two things:

    First, you'd have to cool it way way down to a miniscule fraction above absolute zero. In particular, you'll want to cool it down to the point that the football has as little internal energy as possible. As a result, the quantum state of the football will be more like one big wavefunction instead of a jumble of little ones.

    Second, you're going to want to isolate that football from any external interactions. That means no air, no sound waves, no light, and no heat (and also no gravity).

    So making a football behave like a quantum particle is within the realm of imagination, but not really achievable in the foreseeable future. we're just starting to get large molecules behaving like single quantum particles. (see for example http://www.nature.com/nature/journal/v401/n6754/abs/401680a0.html). In the future, we will be able to do better, but it's a long way between interfering objects made of dozens of atoms to interfering objects made of sextillions of atoms. It's fun to think about, though.
  5. Jul 22, 2015 #4
    So is it possible to trade the temperature constraint in the design of the experiment for span in spacetime (honestly I hate to say this, because I am become a broken record), like considering the experiment to be the presence or absence of interference in the evolution of a planetary structure surrounded by a dust cloud? A thing which has evolved over a huge spacetime interval, and may have accumulated QM effects? May have "synced"? (Ala Steven Strogatz)?
    Last edited: Jul 22, 2015
  6. Jul 23, 2015 #5


    Staff: Mentor

    I think you need to be a lot clearer what you mean here. For me the above is gibberish.

  7. Jul 23, 2015 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Who told you this?

  8. Jul 24, 2015 #7
    Fair enough, let me try to find some underlying questions I have. So I can at least learn something.

    What's the difference between cooling it to within nearly zero K and "isolating it from all interaction"?

    By isolating it from gravity, does that mean it has to be at rest in a perfectly flat spacetime? If so, at rest with respect to what frame?

    A football seems really awkward to think about because it is such a classical object. For puposes of the thought experiment, can it be set up just using an object composed of a couple few particles? I want to have a better picture of how assembling objects from the SM illuminates the problem. Are there any of those that don't have Mass? Because I don't see how you can set it up using any kind of massive particle if you are isolating it from gravity?
  9. Jul 24, 2015 #8


    Staff: Mentor

    This is way off topic - please start a new thread.

    But just as a lead into it it is impossible to isolate any system from all interaction. What is meant is isolating it well enough to investigate what's being studied.

    But please start a new thread.

  10. Jul 24, 2015 #9


    Staff: Mentor

    Look up Buckyballs.

  11. Jul 24, 2015 #10


    User Avatar
    Science Advisor
    Gold Member

    bhobba's* comment about buckyballs is intended to direct you to something like this:


    c60 has an atomic number of 720, so it is a pretty big molecule. From the article:

    "... matter wave interferometry with larger objects has remained experimentally challenging... Of particular interest is the fact that C60 is almost a classical body, because of its many excited internal degrees of freedom and their possible couplings to the environment. "

    *bhobba: my apologies for making this too easy. :)
  12. Jul 24, 2015 #11
    So that was 1999. I am assuming a lot has been done since?

    So now (after reading it) I'm confused about why jfizzix said that you would need to cool a many QM body thing down to nearly 0K to observe it acting wave-like.

    The thing that got me excited about that statement was that I thought I understood how reducing temperature is equivalent to limiting the interaction between the thing and it's environment, thereby preventing decoherence.

    This sharpened for me the question of how temperature, rate-of-coupling/interaction/observation and time relate, and whether or not the amount of interference over an object's history is inversely related to temperature?

    So, I apologize for making up some symbols, but in an effort to be more understandable - how incorrect is this gestalt?

    [itex]I\sim { \dot { O } }^{ -1 }\\ \dot { O } \sim T\\ I\sim { T }^{ -1 }[/itex]

    where [itex]I[/itex] is the amount of interference, [itex] \dot { O }[/itex] is the frequency or rate of coupling with the environment or the "rate of observation", and [itex]T[/itex] is temperature.

    So quantity of interference goes like the inverse frequency of observations or couplings
    and the frequency of observations or couplings goes like temperature, therefore
    the quantity of interference goes like the inverse of temperature

    The experiment in the paper on the other hand is moving the bucky-balls by ejecting them from an oven! But the design of the two slit (and the vaporizor-detector) is still all about preventing observation of the their passage through the two paths. So my question about temperature and rate of observation is still there.
    Last edited: Jul 24, 2015
  13. Jul 24, 2015 #12


    User Avatar
    Science Advisor
    Gold Member

    There are a lot of ways to slow things from decohering. Maintaining a low temperature is hardly the only way. A lot of interactions "net out" so there is no decoherence.

    Ultimately, you must go back and recall that any quantum object is in a superposition of states at all times. Which particular properties are in superpositions may change. So when there is an interaction with the environment, part of what changes is which basis is known and which basis is indeterminate.

    A low temperature implies electrons sitting in lower shells with fewer opportunities to drop yet lower. But a warm buckyball, during a short period of time, can have few opportunities to emit light in such a way as to cause its momentum to be precise. But still have many opportunities to interfere with itself.
  14. Jul 24, 2015 #13


    User Avatar
    Gold Member

    http://arxiv.org/abs/1410.0270 Testing the limits of quantum mechanical superpositions is an up to date reference from Nature Physics which addresses the original question.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook