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Searching for understanding

  1. Feb 25, 2010 #1
    Long ago and far away I had a chemistry teacher who told the class that there is no macroscopic analog for an electron in our experienced world. Because be have no referent for comparison we can never conceptualize the particle(wave) - nothing to end the statement: “It’s like a...” He added that the study of quantum particles focused on mathematical characterization and prediction rather than conceptual envisioning.

    Frequently I grasp for a conceptual understanding of four dimensional space-time and the role gravity plays in distorting it. I am always insulted by non-fiction-television’s gravity analogy to a rubber plane with a brick on it. “See,” they say. The ball falls towards the brick.” (Of course it does dummy...gravity (the thing your trying to explain) is pulling it. Try doing it in interstellar space.) When we make the statement: “because we are moving through time, we are compelled to move through space when local space-time is distorted by mass” we are using the term compelled and compelled sounds a lot like gravity to me. What's the compulsion? Our equations simply (and concisely) characterize the effect but can we conceptualize or intuitively understand its nature - or why it happens - from our limited reality.

    In analytic geometry we deliberately avoid defining the terms point, line, and plane because of the circular reasoning their definition invokes. Our intuitive, conceptual understanding substitutes for rigorous definition. Can we conceptually “know” four dimensional space-time and why gravity does what it does or... can we only characterize it? Is conceptual understanding beyond the observation limits of our 3D-experienced world and therefore a subject for philosophers?
    Last edited: Feb 25, 2010
  2. jcsd
  3. Feb 25, 2010 #2


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    The rubber sheet analogy is as good as any when trying to get you to conceptualize GR. I mean, in essence GR says that objects, in the absence of forces, travel in geodesics. The metric can be found using the Einstein Field equations, and the geodesics for these metrics can be found using the geodesic equations.

    I don't know how you would visualize that since space-time is 4 dimensional, and therefore the geodesics are the geodesics of a 4 dimensional surface.
  4. Feb 25, 2010 #3
    One thing about quantum is that you can show weird things happening with just a laser. It's pretty easy to perform some experiments that let you see "weird stuff" happening before your eyes.

    Curiously enough that's a very good analogy for the underlying mathematics. What's happening is not that the ball is falling toward brick, but the brick changes the geometry of the region around the brick so that the ball starts curving.

    Yes. What you works for me is to find some phenomenon that I'm familiar with that is described by similar equations. As with all analogies, you have to realize that they have limits, but moving from things that you do know to things that you don't is part of the exercise.

    And if you are doing math, you want rigorous definitions. The trouble is that this often gets in the way of physics where a lot of things works through non-rigorous analogy. It's also really, really hard to *teach* a mathematical concept without using induction from things that the student is familiar with.

    Science doesn't deal too much with "why" Coming up with a *description* of gravity is hard enough.

    One thing is that just because you are familiar with something doesn't mean that you really understand it. 3D-space is weird in some interesting ways. Also, all science is based on observation. We happen to be in a world that looks like its 3+1 when you are at low speeds, but it's not hard to observe things in which that view of the world breaks down.
  5. Feb 25, 2010 #4


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    Right. mathematical description and prediction. Goes for gravity as well. Beyond the everyday description and testing predictions, there are some (mostly tacit) standards of taste, about what mathematical descriptions are more elegant, more economical, deeper, more pregnant with new understanding, wider reaching in their predictions. But it all comes down describing how the world goes, finding mathematical expressions of regularity.

    Sounds like a straw man. We do not say compelled. We say that freely moving bodies simply do follow geodesics. It is descriptive. In the context of Gen Rel we do not say that something MAKES them. We simply say that they DO. In essence things still follow straight lines, only the geometry is more up-to-date than Euclid. The straight lines are still the shortestdistance paths, and light still follows them, but it's not quite Greek any more. :biggrin: Nothing in spacetime is straighter than a geodesic.

    Then there is the research that the TV program does not tell you about, trying to figure out what underlies Gen Rel. That is quantum gravity research. It is work in progress. They don't have complete explanations, they have pieces of the puzzle, they have conjectures, approaches to explaining that need to be explored.

    You sound like you have metaphysical questions in mind. Like you would like to talk philosophy---the philosophy of science, and epistemology, foundations etc.

    You need to find the right forum for that kind of discussion. This forum is for learning cosmology. It's a mathematical science based on observation---fitting the standard mathematical model to the data as it comes in. If you want to learn and ask questions about that, the ongoing science, this would be the place.

    There are different kinds of "understanding". If you only want metaphysical "understanding" then it probably won't work out here. There is a philosophy forum though.
    Last edited: Feb 25, 2010
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