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Thread: Time Travelling

  1. - Top - End - #31
    Dwarf in the Playground
    Join Date
    Aug 2019

    Default Re: Time Travelling

    I don't believe that if time travel is possible we're anywhere close. I cannot think of any technology we have access to which allows us to engage with cosmic geometry the way the solutions to Einstein's field equations admitting closed timelike curves would require us to.

    Edit. Right, a quick Google tells me that the nearest black hole is 3,000 lightyears away. Since the simplest and most natural CTC I know of appears in the Kerr metric in the neighborhood of an event horizon, the most obvious method of time travel requires traveling to said black hole. That's a distant dream at this juncture.

    Edit 2. From Landau and Lifschitz's The Classical Theory of Fields it looks like these CTCs only appear for black holes with an angular momentum greater than half the Schwarzchild radius when outside the horizon, and within the horizon supposing the Kerr metric extends inside. Landau and Lifschitz appear to be of the opinion that this means the Kerr metric should be inapplicable inside, though they take a somewhat older view that CTCs violating causality is a technically intractable issue.

    Most other CTC-admitting geometries are pathological counterexamples. A quick literature review suggests Tipler cylinders are another proposed geometry admitting CTCs, but they appear to require negative energy. Good luck finding negative energy!
    Last edited by bundlesandflows; 2020-03-30 at 04:11 PM.

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