The Police never record "Tea In the Sahara," for one thing

April 16, 2018 12:28 PM

How would the Earth's biomes be different if it rotated in the opposite direction?
posted by Chrysostom (42 comments total)

Came for the "Europe would be fucked," stayed for the delightful "Southeast US would also be fucked."
posted by medusa at 12:43 PM on April 16, 2018 [2 favorites]

Ooo... how long until there's a commercially available version of this where I can design my own planets and play god with their climates?
posted by showbiz_liz at 12:51 PM on April 16, 2018 [1 favorite]

Surprised that this has apparently not been addressed in What If. The same question was also addressed here in 2013. But all of the speculation focuses on climate effects; I wonder if continental drift/plate tectonics would be affected too, not to mention the relationship between the earth and the moon.
posted by TedW at 12:53 PM on April 16, 2018 [2 favorites]

Um... a spinning thing doesn't know what "direction" it's spinning in. If you spin a plate clockwise, it's spinning counter-clockwise if you look at it from the bottom.

Or to put it another way: you really can't have a planet where the sun rises in the west... because "east" is the direction the sun rises.

(Yes, you could define it magnetically instead... only the magnetic poles reverse every half a million years.)

So what they've done is reversed the positions of the continents north-to-south. Which is an interesting exercise! But it's weird that they never asked themselves "how do we know that para-Europe" is in the 'northern' hemisphere?"
posted by zompist at 1:01 PM on April 16, 2018 [1 favorite]

Ooo... how long until there's a commercially available version of this where I can design my own planets and play god with their climates?

SimEarth came out in 1990, if you can find a copy and a machine that can run it.
posted by penguinicity at 1:01 PM on April 16, 2018 [5 favorites]

Came for the "Europe would be fucked," stayed for the delightful "Southeast US would also be fucked."

What, no joy at para-Argentina, Brazil, and SE Asia also getting fucked?
posted by MikeKD at 1:27 PM on April 16, 2018 [1 favorite]

Australia: slightly less fucked
posted by Sys Rq at 1:32 PM on April 16, 2018 [3 favorites]

Um... a spinning thing doesn't know what "direction" it's spinning in. If you spin a plate clockwise, it's spinning counter-clockwise if you look at it from the bottom.

But there’s still a difference between something spinning one way around it’s axis and it spinning the opposite way. A car in forward gear is still going forward even if you look at its tires upside down.
posted by ejs at 1:55 PM on April 16, 2018 [3 favorites]

You can play SimEarth online.
posted by Chrysostom at 2:14 PM on April 16, 2018 [1 favorite]

Still rainy in Vancouver. Bah!
posted by helmutdog at 2:21 PM on April 16, 2018 [5 favorites]

Still rainy in Vancouver. Bah!

Shut up, you get healthcare!
posted by Abehammerb Lincoln at 2:42 PM on April 16, 2018 [7 favorites]

Um... a spinning thing doesn't know what "direction" it's spinning in.

That's not so. You could be a spinning thing. If you are asked to spin clockwise you will spin directionally toward your right hand. It's unambiguous. . That's why chirality is a thing. That's why clockwise even means anything. A clock when viewed from behind is still, by definition, clockwise.

because "east" is the direction the sun rises.

A tidally-locked planet still has east and west. But I see your point. If north is arbitrary then so is east.
posted by xigxag at 2:43 PM on April 16, 2018 [3 favorites]

So what they've done is reversed the positions of the continents north-to-south.

... Why is north any less an arbitrary label than clockwise and counterclockwise? I really don't understand what point you think you're making.
posted by PMdixon at 2:45 PM on April 16, 2018 [4 favorites]

Australia: slightly less fucked

Greenland would probably end up with all the marsupials and monotremes, though.
posted by TedW at 2:51 PM on April 16, 2018 [1 favorite]

Retrograde and prograde rotation are relative to how most of the solar system orbits -- so there's a meaningful difference with respect to how the Earth relates to the sun and moon. If the earth's rotation were retrograde, the tidal bulge would be behind the moon rather than ahead of it, and so there'd be a net angular acceleration of the rotation over time -- the day would get progressively shorter, and the moon would get progressively closer. On our prograde-rotating Earth, it's the opposite that happens.
posted by irrelephant at 2:51 PM on April 16, 2018 [5 favorites]

For the car wheel: how do you know the car is going "forward"? Because you're comparing it to the earth. That doesn't work when the object you're looking at is the earth.

For your right hand: sure, you can define rotations depending on, in effect, a local landmark. What's the earth's right hand?

irrelephant: You can certainly define directions relative to the sun. How do you define the sun's direction of rotation? (If your answer is "by reference to the galaxy", then the question applies to the galaxy instead.)

(Also, for historical reasons, we defined "east" long before we understood solar system motions. If we'd evolved on Venus, which has "retrograde" motion, would we have redefined "east/west" once we realized that the sun's rotation was in a different direction?)

This isn't even Einsteinian relativity, folks, it's Galilean.

(If astronomical bodies routinely changed their axes of rotation, directions would be even more arbitrary!)
posted by zompist at 3:13 PM on April 16, 2018 [1 favorite]

At last we have an answer to Amy's (rhetorical) question "So?" at the end of "That Darn Katz!"
posted by drdanger at 3:20 PM on April 16, 2018 [1 favorite]

Still rainy in Vancouver. Bah! -- Shut up, you get healthcare!

Nope. On reverse Earth Canadians are rude anarchocapitalists.
posted by justsomebodythatyouusedtoknow at 3:38 PM on April 16, 2018 [2 favorites]

You mean Albertans?
posted by Sys Rq at 3:41 PM on April 16, 2018 [9 favorites]

Now I have even more reason to be skeptical of the accuracy of the ending of Superman: The Movie (and the sequel, for that matter)
posted by RobotVoodooPower at 3:51 PM on April 16, 2018 [3 favorites]

What about plate tectonics? Would we have different continents? And in the retrograde version of Earth, would Sting have a goatee?
posted by Napoleonic Terrier at 6:45 PM on April 16, 2018 [1 favorite]

I'm down for visiting Nidnol.
posted by maxwelton at 6:55 PM on April 16, 2018 [1 favorite]

The Police never record "Tea In the Sahara," for one thing

Or, rather, Paul Bowles never writes The Sheltering Sky.
posted by fuse theorem at 7:49 PM on April 16, 2018 [2 favorites]

For the car wheel: how do you know the car is going "forward"? Because you're comparing it to the earth. That doesn't work when the object you're looking at is the earth.

Oh boy. Mods, please delete this if this is too much of a derail. But let’s say there is no Earth, you’re driving your car on a giant scrith highway leading into the Sun. “Forward” is what advances you toward your objective (the Sun). For you to go “forward” the wheels on your car have to turn a certain way around their axes. If they turn the opposite way, you get farther from the Sun. This is true no matter your frame of reference or invocation of semantics. Turning one way around an axis is different from turning the other way around that same axis, even if you’re talking about the Earth, which is certainly not the only nail every frame of reference is hung upon.
posted by ejs at 8:47 PM on April 16, 2018

“Forward” is what advances you toward your objective (the Sun).

Yes, directions are defined relative to something.

One more try. You come to a star with one planet. Both are rotating in the same direction. What direction on that planet do you label "east"?
posted by zompist at 9:32 PM on April 16, 2018

Doesn’t matter. You could label the direction in which the planet is rotating as “kitten puke.” What matters is that rotating in the kitten puke direction is observably and materially different from rotating in the counter-kitten-puke direction.
posted by ejs at 10:05 PM on April 16, 2018 [2 favorites]

You're not taking into account the fact that the earth's orbit isn't circular. At present, perihelion — the earth's closest approach to the sun — is a few weeks after what those in the Northern Hemisphere call the winter solstice, and aphelion, the farthest point, is a few weeks after the Northern summer solstice. It has a small but non-zero impact on climate.

Reversing the direction of the earth's rotation preserves this association; perihelion near the European winter solstice. Reversing the north and south poles reverses the association, so that perihelion occurs near the European summer solstice. Ergo, the two are not equivalent.

(And yes, the axis precesses over time, but with a 26000 year cycle, and we're only looking at a 7000 year simulation here.)
posted by DevilsAdvocate at 10:11 PM on April 16, 2018 [2 favorites]

Why is it that mirrors reverse west to east, but not north to south?
posted by Segundus at 10:13 PM on April 16, 2018

Mirrors don't reverse left and right and they don't reverse up and down.
posted by Pendragon at 11:14 PM on April 16, 2018 [2 favorites]

Why do mirrors flip horizontally (but not vertically)?
posted by Pendragon at 11:22 PM on April 16, 2018 [5 favorites]

Yes, directions are defined relative to something.

The answer is further up in the thread - it's defined relative to the earth's orbit round the sun. A prograde rotation is not the same as a retrograde rotation.
posted by Dysk at 3:43 AM on April 17, 2018 [1 favorite]

I think I get what zompist is trying to say, and he's almost right.

Imagine three copies of our solar system: O (original) will remain unchanged from the one we know, while A and B will be modified.

Oliver is placed in a spaceship in a vantage point which is colloquially called "above" the plane of solar system O. More specifically, it is a point from which the planets' orbit around the sun appears to be counterclockwise. The moon's orbit around the earth is also counterclockwise from this vantage point, and the rotation of most planets, including earth, is counterclockwise.

We similarly place Alice in a spaceship "above" solar system A, but we place Bob in a spaceship "below" solar system B.

Note that from Oliver's view, the earth's rotation carries San Francisco towards New York City, NYC towards London, London towards Moscow, etc. Earth's rotation is prograde both with respect to the earth's motion around the sun and the moon's motion around the earth.

Now, modify solar systems A and B as follows:

In solar system A, reverse the rotation of the earth. (Alice now sees SF rotating away from NYC, NYC away from London, etc.)

In solar system B, "flip" the earth 180° so the poles are exchanged, so the side with Russia and Canada is now pointing towards Bob, but keep it rotating the same way. (SF still towards NYC, NYC still towards London, etc.)

I believe the point zompist is trying to make is that solar system A as seen by Alice and solar system B as seen by Bob are exact mirror images of each other.

Alice is looking at the side of the earth with Canada and Russia, sees the earth rotating clockwise, and all the planets orbiting counterclockwise, and the moon also orbiting the earth counterclockwise. Alice's earth has a retrograde rotation, both with respect to its orbit around the sun and with respect to the moon's orbit around the earth.

Bob is looking at his earth's Canada and Russia, sees it rotate counterclockwise, and the planets orbiting the sun clockwise, and the moon orbiting the earth clockwise; Bob's earth also has a retrograde rotation.

As system A, as viewed by Alice, and system B, as viewed by Bob, are exact mirror images, they should have climatologically equivalent earths, argues zompist. (Note that the mirror symmetry breaks down if Alice and Bob can view not only the position and rotation of solar system bodies other than earth, but also their surface features. E.g., if they are far enough from the plane of the solar system, Alice can see Saturn's polar hexagon, as in system A, it is on the same side of the plane of the solar system as Canada and Russia, but Bob cannot; in system B, it is on the opposite side. But those features seem unlikely to make a climatological difference to earth.)

One objection, and one comment:

1. This holds only if orbits — especially the earth's orbit — is circular, or nearly enough so that the variation in distance makes no climatological difference. As I pointed out in my previous comment, this is not the case. The elliptical orbit of the earth breaks the mirror symmetry between Alice's and Bob's view. Alice sees the Canadian/Russian pole tilted roughly away from the sun at the earth's closest approach to the sun, while Bob sees the Canadian/Russian pole tilted roughly towards the sun at the earth's closest approach.

The difference is small but non-negligible; the earth receives about 3% more solar radiation at perhelion than at aphelion. For a given point on the earth, the difference in solar radiation between summer and winter is slightly more extreme in the Australian hemisphere (where the effect of the distance to the sun enhances the effect of the earth's axial tilt), and slightly more moderate in the Russian/Canadian hemisphere (where the distance to the sun slightly counteracts the effect of axial tilt), on both Oliver's and Alice's earth, but on Bob's earth, the difference is more extreme in the Canadian/Russian hemisphere and more moderate in the Australian hemisphere.

2. Even if all orbits were perfectly circular so Alice and Bob saw exact mirror images...so what? The climatological models of A and B would then be exactly the same. This strikes me as having about the same level of interest as a stoned college freshman who says, "Dude...what if the universe were suddenly replaced with its mirror image? Then most people would be left-handed, but we wouldn't know it because we'd call left 'right' and right 'left,' and we'd still say that most people were right-handed. Writing would be reversed, but since our brains and eyes were also reversed, writing would look normal to us. Whoa. We'd have no way of knowing. Far-out."
posted by DevilsAdvocate at 7:27 AM on April 17, 2018 [1 favorite]

Also: mirrors only reverse good/evil.
posted by DevilsAdvocate at 7:31 AM on April 17, 2018 [5 favorites]

Wait, no, Alice's earth and Bob's earth themselves are not mirror images, so my lengthy analysis above does not hold, and I am giving zompist more credit than he deserves. Bob sees sunrise in New York about three hours before sunrise in San Francisco, while Alice sees the reverse. Please disregard the entirety of that comment.

This also means mirrors reverse Lawful/Chaotic, not Good/Evil.
posted by DevilsAdvocate at 7:45 AM on April 17, 2018 [1 favorite]

If you modify B not by flipping the earth, but but mirroring the earth through its equatorial plane, then I think my analysis still holds.
posted by DevilsAdvocate at 7:59 AM on April 17, 2018

If you are asked to spin clockwise you will spin directionally toward your right hand. It's unambiguous.
There speaks a person with no problem at all differentiating left from right.
posted by glasseyes at 3:12 PM on April 17, 2018

It's nice that you finally get it while managing to throw out a bunch of gratuitous insults. I guess understanding that there is no universal reference frame is exactly like being a hippie. Wait till you get to Einstein and his thought experiments. Haha, what a doofus, with his "relativity"! Well, at least he had the hair for it.

The bit in the original article I found curious (and no more than that, it's not like this is a big problem) is that their simulation changed the reference object for directions, without seeming to realize it. It's as if they said "Let's switch east and west, and see what happens in the northern hemisphere," without noticing that "north" would be affected by their change.

As a maybe less contentious analogy, it's like saying "In our simulation, we changed the cesium-133 atom to vibrate twice as fast. Now, ten seconds later..." But seconds are defined by vibrations of the cesium-133 atom; do they mean "old seconds" or "new seconds"?

This may all be the journalists' fault— the abstract doesn't refer to directions at all, but to "retrograde rotation".

Now, reversing the earth's spin is something you probably don't want to do. The article doesn't describe simulating an actual change; they zeroed out all motion first and changed some physics parameters. (They talk about changing the sun's path, which suggests that their astronomical model was Ptolemaic. Whether they include the eccentricity of Earth's orbit, or even the effects of the moon, isn't clear.)

So it seems like they were modeling what the earth would be like if it had always rotated the other way. But if it had, we'd have called the direction the sun rises "east" in that world.

We don't live in that world, so we don't know what people would do when they found out that the sun rotates the opposite way. Do they say that "east" must now be redefined as the direction of sunset?

It seems a bit parochial to define east with reference to the earth, but most use of language is not astronomical, so too bad. Pretty obviously we've applied the earth's directional system to the rest of the solar system; happily, there's no conflicts except for weirdo places like Venus.
posted by zompist at 3:14 PM on April 17, 2018 [1 favorite]

It's as if they said "Let's switch east and west, and see what happens in the northern hemisphere," without noticing that "north" would be affected by their change.

does your beef really boil down to them saying "northern hemisphere" instead of "the hemisphere analogous to the real earth's northern hemisphere"
posted by PMdixon at 4:25 PM on April 17, 2018 [2 favorites]

Thats nice and all, but what really interests me is what the climate would be like if the Earth's rotation were more like that of Uranus? If the rotational pole were parallel to the plane of the orbit, instead of quasi-perpendicular.
posted by Xyanthilous P. Harrierstick at 5:48 PM on April 17, 2018 [1 favorite]

Mirrors don't reverse left and right and they don't reverse up and down.

Ah, you people are so earnest!
posted by Segundus at 2:34 AM on April 18, 2018

We don't live in that world, so we don't know what people would do when they found out that the sun rotates the opposite way. Do they say that "east" must now be redefined as the direction of sunset?

If we're going to be talking about how stuff changes climatologically across two different rotation scenarios, it makes sense to use a constant location reference system across both scenarios, for ease of communication. Maybe counter roasting earth people have Australia in the northern hemisphere, but it's still a good idea for understanding, when comparing and contrasting the two worlds, to have "the northern hemisphere" refer to the same half of the planet in both instances. Otherwise it becomes way too confusing to talk about.

(And if you're concerned that people on a counter rotating planet would have defined cardinal directions differently, so why are we using our system, why are you okay with them using country ie city names? Surely in the counter rotating earth with significant climatic differences, our cities and borders would be in different places, so comparing what is different in China, say, is no less parochial than calling magnetic North North. Parochial, but necessary to communicate in a meaningful manner.)
posted by Dysk at 4:14 AM on April 18, 2018 [4 favorites]

This is really cool and a great demonstration of the effects of the Coriolis effect on prevailing winds and ocean currents and in turn their roles in determining climate. My environmental science students got a kick out of it, especially since here in Georgia would be a desert comparable to the current Sahara while the UK, whose climate I'm constantly reminding them is controlled by our Gulf Stream, would be tundra.
posted by hydropsyche at 8:48 AM on April 18, 2018 [2 favorites]