Dear Mr. Coryat,

Nice twist on the "rubber sheet" analogy of gravity. Actually this is very distinct from the usual way the rubber sheet analogy is used to present Einstein's theory of GR. A colleague of ours (Gary White) has done a fair amount of work on quantifying to what extent the rubber sheet analogy "works". This can be found in "The shape of "the Spandex" and orbits upon its surface" by G.D. White and M. Walker, American Journal of Physics 70, 48-52 (2002) and "On trajectories of rolling marbles in cones and other funnels", by G.D. White, American Journal of Physics 81, 890-898 (2013). But again this work deals mostly with the usual way the rubber sheet analogy if used, but may be of interest. By the way one of the outcomes of Gary's research was that spandex is the thing to use rather than rubber at least for this canonical version of the rubber sheet analogy.

Anyway a very good and lucid video on warping of space-time = gravity. Best of luck with the contest.

Mike, Max, Dan, Simon, Doug

    16 days later

    Karl,

    Thank you for a truly remarkable video! Your space-time stretcher fits wonderfully with the theme of this contest, "Show Me The Physics!"... better yet, "Show Me The MODERN Physics", which is, after all, what FQXi is all about! You are right when you say that the usual rubber sheet analogy is a bit of a let down, as it already requires gravity (to generate a downhill force) to explain gravity... The space-time stretcher is so much better... I want one! :)

    Your video is well produced and very pedagogical, and it is, in my opinion, one of the very best that has been submitted to this contest. I hope it makes the finals and is recognized by the jury!

    Congratulations!

    Marc

    P.S. If you have a chance to view, comment and vote on my trilogy of videos entitled "This Is Physics" --- where I try to convey the "fun of physics" by focusing on some of the greatest moments of its history --- it would be quite appreciated!

      5 days later

      Hey Karl

      as I'm a visual learner I found the space-time stretcher extremely clever and enlightening! It doesn't happen often, that one can find a simple (however not at all banal) visualization of a complex matter - like the relation between space-time. I loved the way you used the model to describe the three dimensional phenomenon. I wish you the best of luck and hope more physics teachers would come up with such creative ideas as you.

      Madeleine.

        Thank you, Doug et al. When researching for this project, one thing I didn't understand is why we should expect geodesics on a traditional rubber sheet to converge (as two falling objects converse), when the traditional rubber sheet has negative curvature, which suggests divergence. One person I talked to said that the traditional rubber sheet is really just a visualization and is not a model in any strict sense of the word. Another pointed out that the geodesics of two objects falling in the same spacetime can in fact diverge, for example when they are traveling the same path through space but at different times. The project got me to appreciate some of the subtleties of spacetime that I hadn't realized before.

        I tried to imagine taking the traditional rubber sheet demo up to the International Space Station. First, no gravity means the "sun" does not depress the rubber. Even if we were to mechanically push the "sun" against the rubber sheet, the "earth" would not follow similar paths, because the force vector from Earth's gravity, perpendicular to the (flat) surface, is taken away in zero-G. Anyway, thanks for your nice words; I wish more people would vote. I'll check out your video. -KC

        Thank you Madeleine! I had a similar flash of enlightenment when I saw the applet mentioned at the end of the video. But I really wanted to be able to see that straight geodesic get bent back into a parabola, to show a falling object's path from the perspective of the fixed observer. That's when I had the idea to make a model that would stretch and unstretch in the required way. Thanks for visiting - I look forward to watching your video on piezoelectricity ... as a musician I am very familiar with this phenomenon (as you likely know, piezoelectric pickups are commonly used for amplifying acoustic instruments). Good luck! -KC

        Joe: This contest is for presenting physics in new and interesting ways. Unlike with the essay contests, there's nothing in the guidelines that solicits original research. I therefore feel that videos like yours should not even qualify for entry. People, especially young people, have an increasingly frustrating time discerning what is part of the scientific canon and what is not, because everyone presents himself as an expert these days. When someone presents a fringe, original view under the banner of "this is real physics," it is beyond confusing for the student. In my opinion, every such video or essay should begin with a warning that the views are solely the author's and that they are not accepted by the mainstream. To not include such a disclaimer, especially in a "science outreach" effort like this contest, is irresponsible in my opinion.

        You're very welcome, Karl! We actually thought about filming a guitar session to show the piezoelectric pick-ups and underline it with music :) I hope you liked our video.

        We would greatly appreciate if you could give us your vote and feedback, since we all need at least 10 community ratings to qualify for the finals. I really hope yours will be among them, since it taught me a lot.

        I still think the Spacetime Stretcher is brilliant the way you made it work. Until then the only "model" I could find were 2-D images like this one, which do show the parabolic curvature but take a different approach to explain the phenomenon.

        Madeleine

        Piezoelectricity: A Love Story

        15 days later

        Thank you, Jonathan, that means a lot to me, especially as I am something of a fan of both your work and Cristi's (above). Best of luck in the competition!

        Karl

        Don't blow my cover Cristi! Just kidding, thank you so much for watching and commenting, and best of luck in the competition.

        Karl

        14 days later

        I Karl, your demonstration is just amazing, I was wondering if you would be kinf enough to share your construction plan with a teacher eager to use the same device in class.

        Thanks

        8 years later
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