Deeper Into Jeopardy! XVII: A Brief History of Time – $2000

Jeopardy! category: A BRIEF HISTORY OF TIME (05-05-2014)

$2000 clue: Clocks flown around the earth in 1971 diverged from stationary ones, confirming the relativity concept “time” this

Correct response

The gist: It’s the classic twin paradox: a set of twins; one gets in a spaceship and travels near the speed of light; when she returns on his birthday, finds a cake for herself with thirty candles and one for her twin brother with 31.The “paradox” (which is not a paradox at all, it turns out), is an illustrative example of time dilation. The subjective experience of time, which, as we learned yesterday, is not a separate entity but bundled up with space in space-time, depends on one’s velocity relative to an observer. A less-than-satisfactory understanding of special relativity implies that both twins should see the other as having aged faster, since both are traveling from the other’s frame of reference – the twin on Earth sees the spaceship leave, while the twin in the spaceship, looking back at Earth, sees the planet rapidly flying away from him. This would result in a real paradox when the twins met up again and each saw the other as being a year older than they were.

However, the paradox is resolved when it’s realized that the twin in the spaceship has accelerated to near the speed of light, which is an absolute value (that is, its inertial frame changes). This solution was first proposed by Paul Langevine in 1911. As the clue says, time dilation has been proven experimentally by physicists Hafele and Keating, who put atomic clocks on airplanes, flew them around the world, and compared them against Earth-bound ones. Since then, many more experiments have confirmed the concept, including the entire Global Positioning System, which runs on satellites whose internal clocks are corrected for their orbital speed and their slight difference in gravity due to their distance from the Earth.

A pleasant .gif demonstrating the relative speeds of a stationary and moving clock.

The clue: A toughie. There’s not much to go on here without knowing about the experiments themselves, I think. Clocks on planes could be testing any number of things, couldn’t they? The writers do give “time” in quotes, which clears it up a bit, but I suspect that’s just to constrain the possible answers.

In Jeopardy!: Welcome to the J!Archive, time dilation! This is the very first time those two words appear in a clue together, save for one presented by Dr. Oz, where migraines are triggered by dilation of brain arteries, and are “sometimes accompanied by nausea.”

One thought on “Deeper Into Jeopardy! XVII: A Brief History of Time – $2000

  1. Time dilation is a pretty basic example of relativistic effects (others would be length contraction, relativistic mass increase, speed-of-light-as-maximum-speed and mass-energy equivalence). Anyone* who has taken any intermediate-level physics should certainly be familiar with it and I think most interested lay-people who read Scientific American or the like should be aware of its existence as an important consequence of Einstein’s theory, even if they don’t understand the nuts and bolts of how it works.

    I suppose clocks on planes could be testing other effects, but describing the divergence of the measured time as the key finding and the fact that “time” is indicated to be part of the response should focus your mind on the time dilation concept. It is a $2000 clue, don’t forget, so it can’t be too obvious/easy. Sure it could be other things, but this is by far the most likely and worth taking a guess at for $2000, I think.

    **I realize that this likely does not include the majority of people, or even a majority of the trivially-inclined.

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