The universality of free fall
July 5, 2018 10:53 AM Subscribe
Apollo 15 astronaut David Scott showed that a hammer and feather fell at the same rate on the Moon, a modern update to an experiment that Galileo probably didn't actually perform. But if E/c^2 = m, does gravitational binding energy also fall in a gravitational field in the same way as regular mass? Replace the feather with a white dwarf, the hammer with a neutron star, the Moon with another white dwarf, and let's find out! (Cute 3:50 video.)
The video is narrated by Anne Archibald, the lead author of the paper in Nature:
Universality of free fall from the orbital motion of a pulsar in a stellar triple system, Archibald et al., 2018, Nature, 559, 73–76.
Bonus: Here's Brian Cox to show you Galileo's experiment in the world's largest vacuum chamber. (Previously.)
More: Galileo's Leaning Tower of Pisa experiment, and the Nordtvedt effect.
Disclaimer: I'm not involved in this work, but all the authors are friends of mine, and I was involved in the discovery of the triple system.
The video is narrated by Anne Archibald, the lead author of the paper in Nature:
Universality of free fall from the orbital motion of a pulsar in a stellar triple system, Archibald et al., 2018, Nature, 559, 73–76.
... PSR J0337+1715 is a hierarchical system of three stars (a stellar triple system) in which a binary consisting of a millisecond radio pulsar and a white dwarf in a 1.6-day orbit is itself in a 327-day orbit with another white dwarf. This system permits a test that compares how the gravitational pull of the outer white dwarf affects the pulsar, which has strong self-gravity, and the inner white dwarf. Here we report that the accelerations of the pulsar and its nearby white-dwarf companion differ fractionally by no more than 2.6 parts per million.News and Views Discussion by Clifford Will: General relativity verified by a triple-star system
Einstein’s theory of gravity — the general theory of relativity — is based on the principle that all objects accelerate identically in an external gravitational field. A triple-star system provides a stringent test of this principle.More coverage in the press: Discover, Forbes, etc.
Bonus: Here's Brian Cox to show you Galileo's experiment in the world's largest vacuum chamber. (Previously.)
More: Galileo's Leaning Tower of Pisa experiment, and the Nordtvedt effect.
Disclaimer: I'm not involved in this work, but all the authors are friends of mine, and I was involved in the discovery of the triple system.
For those who don't get the tags:
posted by cjorgensen at 11:16 AM on July 5, 2018 [7 favorites]
(Yeah, I should have clarified. Douglas Adams conjured up the "Someone Else's Problem" (SEP) field, which just so happens to match the initials for Strong Equivalence Principle. And the authors used the blue whale and the bowl of petunias from Hitchhiker's Guide to illustrate the linked video.)
posted by RedOrGreen at 12:06 PM on July 5, 2018 [2 favorites]
posted by RedOrGreen at 12:06 PM on July 5, 2018 [2 favorites]
This is a great post!
posted by vibrotronica at 12:16 PM on July 5, 2018 [2 favorites]
posted by vibrotronica at 12:16 PM on July 5, 2018 [2 favorites]
It’s like an FPP in equilibrium with a super-dense favorite!
posted by GenjiandProust at 12:29 PM on July 5, 2018 [3 favorites]
posted by GenjiandProust at 12:29 PM on July 5, 2018 [3 favorites]
“The Universality of Free Fall” sounds like a poem by one of those peole who want to be Wallace Stevens.
posted by thelonius at 1:25 PM on July 5, 2018 [4 favorites]
posted by thelonius at 1:25 PM on July 5, 2018 [4 favorites]
Is this is an very in-depth marketing tie-in to The Three-Body Problem novel? (I am enjoying the book, and will enjoy learning the underlying real-world physics)
posted by Diddly at 2:22 PM on July 5, 2018 [1 favorite]
posted by Diddly at 2:22 PM on July 5, 2018 [1 favorite]
> Is this is an very in-depth marketing tie-in to The Three-Body Problem novel?
Alas, no - the neutron star and inner white dwarf have a 1.6-day mutual orbit, and then they orbit the outer white dwarf in a 327-day orbit. So it's a classic hierarchical triple system, like the Moon-Earth-Sun, where we can effectively ignore the outer one while calculating the inner orbit.
If it really was a fully-interacting three-body system, the orbit would be chaotic, and we would have difficulty in even discovering such a pulsar, let alone solving the orbit with this sort of exquisite precision.
(I know you're joking, but it's an interesting question!)
posted by RedOrGreen at 2:44 PM on July 5, 2018 [8 favorites]
Alas, no - the neutron star and inner white dwarf have a 1.6-day mutual orbit, and then they orbit the outer white dwarf in a 327-day orbit. So it's a classic hierarchical triple system, like the Moon-Earth-Sun, where we can effectively ignore the outer one while calculating the inner orbit.
If it really was a fully-interacting three-body system, the orbit would be chaotic, and we would have difficulty in even discovering such a pulsar, let alone solving the orbit with this sort of exquisite precision.
(I know you're joking, but it's an interesting question!)
posted by RedOrGreen at 2:44 PM on July 5, 2018 [8 favorites]
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