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Thought Experiment: Portals, Magnets, and Power

  1. Jul 27, 2010 #1
    I was surfing digg yesterday, and saw the following post:

    http://images.wildammo.com/2010/07/24/world-energy-problems-solved/ [Broken]

    For those who don't recognize it, it's based off a video game called 'portal'. In the picture, the water falls towards the floor where it falls through the blue ring, and is then teleported out of the orange one above. This forms a semi-closed loop in which the water constantly accelerates, and this can be harvested by a water wheel. Here's an example of how portals work:


    Now this got me thinking; let's assume that such a connected pair of portals existed, and that they did not require any external form of energy to operate (or perhaps they do, but there is ample energy available from some undefined source). Now say that they are placed one above the other as above, but this time in a magnetically-shielded vacuum chamber. If we were to drop an object down the hole, it would gradually accelerate to relativistic speeds; this much I know.

    Now the tricky bit. Say that instead of just dropping some generic object, we were to drop a very large fixed-magnet down the hole, such as a 2 foot by 5 foot neodymium cylinder. Surrounding the magnets 'flight' path is a toroidal induction coil designed to harvest electrical energy from the alternating magnetic field. Would such a setup work? Or would there be a cancellation effect from the bisected magnet? Another line of thought comes from whether or not portals can propogate magnetic fields or not. They can transmit light, so I imagine that the field strength would behave like an infinitely long string of such magnets falling through an infinitely long stack of rooms. The magnet would also experience a substantial amount of drag from interactions with the coil. I'm also wondering if the magnetic field would increase as it accelerated, or if it would remain constant. Any thoughts? I've posted a (laboriously created) image of my setup here:


    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jul 28, 2010 #2
    Let me get this straight, you want us to speculate on the possible behaviour of an imaginary device in an imaginary universe on the basis that you've drawn a picture of it?
  4. Jul 28, 2010 #3
    Though it's operation is imaginary, it can still be modeled mathematically. Just as 'frictionless surfaces' and 'perfectly elastic collisions' don't really exist, you can still model them and determine how they might behave if they were real. Sure nobody has an infinitely large hockey arena with a frictionless surface and a perfect vacuum free of light or other interactive fields, but if you were to slide a hockey puck across it, it would move in a straight line for all eternity, never slowing or speeding up. The setup may be imaginary, but you can still speculate based on known physics laws/etc. It's called a http://en.wikipedia.org/wiki/Thought_experiment" [Broken]. You can even draw a picture if it helps describe the setup you want to explore!

    p.s. The basis isn't that I drew a picture of it, it's that I drew a picture and accompanied it with a 3 paragraph description that includes all of the details necessary to draw conclusions.
    Last edited by a moderator: May 4, 2017
  5. Jul 28, 2010 #4
    A thought experiment is a proposal for an experiment that would test or illuminate a hypothesis.

    The hypothesis in question is in the form of a prediction of the behaviour of the proposed experiment in accordance with the laws of physics.

    Since the laws of physics in your imaginary world are entirely at your discretion, the behaviour of your proposed 'experiment' is entirely subject to your own imagination.

    You should be aware that speculative posts are outlawed on this forum. Read the rules.
  6. Jul 28, 2010 #5
    Sorry. I didn't know speculative posts were https://www.physicsforums.com/search.php?searchid=2225649" [Broken]...
    Last edited by a moderator: May 4, 2017
  7. Jul 28, 2010 #6


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    For any self-consistent physics, potentials will remain conservative, and forces will be proportional to gradients of these potentials.

    For example, if your portals "glued" together two surfaces in space, like in Portal, and the potential on the two sides is unequal, there would be a force field proportional in strength to the difference in potential at the boundary.

    So if you have two portals at different heights, for example, you'd loose the amount of kinetic energy going in equal to the difference in potential energy at two heights due to the force field at the portal boundary. If you aren't going fast enough for that, you aren't going to make it through. And the odds are, even if you do make it through, it will not be pleasant. You are going to hit that force field like a brick wall.

    Wormholes in general relativity, which is the closest known approximation of portals in real world, do behave that way.

    Portals in Portal, of course, don't follow these laws, hence their ability to violate energy conservation.
  8. Jul 30, 2010 #7
    Due to the contention over the use of portals, I've mocked up a version of the problem without them. It's still the same basic problem, but without the ambiguity of a fictional device. The revised version of the problem goes like this:

    "If a sufficiently large number of cylindrical fixed magnets are dropped at high speed through the center of a suitably-constructed toroidal induction coil, would it produce a current?"

    The two main sticking points I can't figure out are whether or not the local magnetic field of the magnets would increase in proportion to their speed, as well as whether or not the moving field could even be harnessed (or would the field of an 'approaching' magnet be canceled-out by a 'receding' one). The original portals are irrelevant to the problem; they were simply there to facilitate having a continuous supply of moving magnets. You could also just link the magnets together into a big loop that passes through the inductor if you wanted to make it 'realistic'.

    Attached Files:

    Last edited: Jul 30, 2010
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