31 Comments

Excellent post, very enjoyable as well. I think people are also under certain circumstances capable of hemispheric sleep, based on anecdotal personal evidence

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Thanks, Johnnie!

There may be something to that. The ‘first night effect’ involves an asymmetry in sleep between hemispheres in which the left side sleeps more shallowly. (https://www.cell.com/current-biology/fulltext/S0960-9822(16)30174-9)

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Such great writing! Especially because the topic isn't a main interest, yet I was fascinated. My inbox is getting cluttered with Substacks. I don't have time to read all the good essays so I leave them there until a Friday night, home with a cold, and give them the time they deserve. Bravo Gunnar!

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‘Not my main interest, yet fascinated’ is one of the finest compliments I can imagine. Thank you, Bettina! (and feel better soon)

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I mean, sharks are cool of course! But physics and the hard sciences in general need a good personal hook to keep me reading.

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Happy to have had you hooked. 😉

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This is brilliant! You made each topic so captivating. I think you’re beyond capable and smart even if things feel stagnant in life. I completely relate. Thanks for sharing!

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Thanks, McKenna! I really appreciate that.

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You’ve scooped me again! Though my idea was to play with the discovery of a reliable way to determine longitude—as opposed to sharks and swifts—as a way of navigating that overlap of time and space and feeling stuck.

Also, I’m so curious how they know how much time swifts spend in the air during migration. Do you know how they (the Royal “they,” of course) observed that?

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Like minds…

They designed a tiny backpack for the birds with an accelerometer and light sensor.

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"putting clocks in planes that fly around the world in opposite directions results in a nanosecond-but-measurable time difference" - yes but each thinks the other is slower... When they meet again how do they reconcile that?

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They were both compared to a stationary clock at the United States Naval Observatory. Also, and I admit I borrowed this from Wikipedia ;),

… a clock aboard the plane moving eastward, in the direction of the Earth's rotation, had a greater velocity (resulting in a relative time loss) than one that remained on the ground, while a clock aboard the plane moving westward, against the Earth's rotation, had a lower velocity than one on the ground.

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The one that moved westward had a slower velocity than the ground clock so you can't call the ground clock stationary.

This assumes there's such a thing as "absolutely stationary", but maybe this is a special case cos it involved rotation.

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You’re right, there is no absolutely stationary. The ground clock is called ‘stationary’ because the center of the earth provides an inertial frame of reference, unlike the moving planes.

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I've puzzled over this for years. If you take the simplest symmetrical case: two spaceships move apart and then back together. Both should see the other as older.

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I’ve wondered about this too ever since I heard about the Travelling Twins all those years ago. If you ever find the answer, can you let me know?

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The last para of the Wikipedia page offers a solution - but only by defining "stationary" ("with respect to the matter of the universe at large": is that a linear calc or inverse square law?):

In Special Relativity (1968), A. P. French wrote: "Note, though, that we are appealing to the reality of A's acceleration, and to the observability of the inertial forces associated with it. Would such effects as the twin paradox (specifically -- the time keeping differential between reunited clocks) exist if the framework of fixed stars and distant galaxies were not there? Most physicists would say no. Our ultimate definition of an inertial frame may indeed be that it is a frame having zero acceleration with respect to the matter of the universe at large."

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Wikipedia lists several supposed answers to the Twin Paradox but none of them are quite satisfying.

https://en.wikipedia.org/wiki/Twin_paradox

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The problem of measuring the speed of light in one direction looks like the extreme case of the same thing.

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This really is wonderful, Gunnar. Thank you. I love the science of time and I love the musing about all those different creatures finding their own way to fit their time into their day. But, in between the shark-time, swift-time, Albert-time and Henri-time I sensed a tiny hint of Gunnar-time that is maybe not flowing as it should.

Like the swift, I always need to be flying. I’ve lived in four countries, three states, thirteen cities and fifteen towns. I backpacked around the world in my youth. I can't stay in one place. We eventually settled in our forever home in San Jose and managed to buy a house and have children there. We were there forever, for sure. But when the west winds blew, we sold everything and came back to England to live in our final home. We’ve only been here six years but already that west wind is blowing. I’m too old to up-sticks again and change countries again — but I know we will.

I'm not so dynamic when it comes to changing jobs. I stayed roughly six years at every job but every time I moved on, I felt like I’d been there about two years too long. I'm currently in The Best Job Ever but… Man! It’s hard to ignore the call of the west wind.

I’ve no idea why I am telling you all this but your analogy with the way that animals manage their time made me hyperaware of my own time. It flows so fast. As Bergson said, the way we experience time is a personal thing and my time is running out. I’ve gotta go find some more.

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Thanks, Ragged.

Two countries and four cities here. Nearing six years at the day job as well, which means it starts to itch. Hard to ignore the call, indeed.

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“Call of the Wind”. Could make a great movie.

I hope you find the choice that's right for you.

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Loved this - elegantly done; and so interesting.

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Thanks; I appreciate that!

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even the earth, the solid, stable (read: stuck) earth is moving - these plates are floating on magma, on an object hurtling around the sun at 67,000 mph. humans are bound to earth but even then we are free ;)

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So hopeful, tracy!

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