So, in the first episode of "Phineas and Ferb", the evil Dr. Doofenshmirtz tries to reverse the rotation of the earth. His plan fails in show, and there are several reasons why his plan would have never worked. But, it got me wondering, what would happen if you could reverse the rotation of the earth?

We can probably assume that Dr. Doofenshmirtz wanted this to happen quickly, within a day, so from normal rotation speed to reverse rotation within 24 hours. We can also probably assume that he wanted to get to the same speed in reverse, so from $460 \ m/s$ or $1000 \ mph$, in our current direction, to zero, to $460 \ m/s$ or $1000 \ mph$ in the other direction all within 24 hours.

My first thoughts is that this would be very apocalyptic, my second thoughts were that the forces necessary would tear the earth apart. I am asking for a description of either what would happen on earth, or a confirmation that the planet would be torn apart.

Addendum to original question. In the show itself, Doofenshmirtz essentially tries to reverse the rotation of the earth by yanking on the eastern seaboard of the United States. If one could "yank" on the entire eastern seaboard with an even force, what would happen then?

  • 1
    $\begingroup$ Please specify the mechanism used to reverse the rotation. The effects are VERY different depending on the mechanism. $\endgroup$ – SRM May 28 '18 at 23:58
  • $\begingroup$ The rotational kinetic energy of the Earth is large. Very very large. Large enough to convert the Earth into a ball of molten rock. See, on this very site, "How much energy to destroy the crust of a planet". $\endgroup$ – AlexP May 29 '18 at 1:02
  • 3
    $\begingroup$ Toilets would drain the opposite direction afterwards, right? $\endgroup$ – manassehkatz-Moving 2 Codidact May 29 '18 at 1:23
  • 1
    $\begingroup$ @manassehkatz, that might be the least of your problems.... $\endgroup$ – Thucydides May 29 '18 at 2:21
  • $\begingroup$ @manassehkatz what toilets? $\endgroup$ – Dubukay May 29 '18 at 3:57

If the evil doctor can somehow decelerate and accelerate all the interior and exterior parts of the earth in unison (including the sea) - for example some hyper-technology tractor beam - then there should be no ultra-catastrophic problems. The surface acceleration required to do the reversal in 24 hours is around $0.01 \ m/s^2$, or about 1/1000 of the acceleration due to gravity. If you were standing still on the surface you probably wouldn't even notice it. But there might be subtle effects due to the temporary reduction in centripetal force on the earth's crust that could result in earthquakes, volcanic activity etc. Note that in the future, tides would occur around every 11-12 hours rather than every 12-13 hours. And I almost forgot to mention, if all rotational motion is 'near-instantaneously' reversed then the earth's generated magnetic field would also want to switch polarity. This might have interesting effects on the ionosphere, national grids and the like.

If he neglected to accelerate the air, then we would experience pretty massive atmospheric shear. Insanely powerful tornadoes and hurricane-like winds blowing over most of the earth's surface.

If he neglected to (de/ac)-celerate the seas, then there would be fairly major flooding. Applying $0.01 \ m/s^2$ sideways acceleration is equivalent to 'tilting' the surface of the sea by $1 \ m/km$. So it would 'slop' into (or away from) the shore like the worst tsunami ever. Note that being on the slop-away-from side would only give you a few hours to escape the coast, as it would pour back again when the acceleration stopped.

If his mechanism only worked on the crust (or even the crust and outer mantle) then we would be toast. The friction between the crust and molten interior would tear the crust to pieces, fluid dynamics in the interior would cause magma-plumes like nothing seen in the last 4.5 billion years and cause hyper-volcanoes. Things would get messy quickly.

  • $\begingroup$ You must dissipate 2.1E29 J of rotational energy. That's very much more than enough to boil the oceans and melt the crust. $\endgroup$ – AlexP May 29 '18 at 1:07
  • 1
    $\begingroup$ @AlexP That is why I suggested the need for some form of hyper-technology.As the final retro-rotated earth has exactly the same rotational energy as it began with we don't actually need to dissipate rotational energy as heat. We do have to somehow 'magically' change the rotational inertia of the earth though, so might have to find somewhere to dump that to maintain conservation of momentum in the visible universe. But I am guessing that the evil Dr. has the technology. $\endgroup$ – Penguino May 29 '18 at 1:36
  • 4
    $\begingroup$ Its all very simple, you see. We just open up the pocket universe, put the Earth inside through the wormhole, translate the "X" axis then release the Earth back into the initial inertial frame. Piece of cake, really. You should see some of the difficult experiments we do here..... $\endgroup$ – Thucydides May 29 '18 at 2:24
  • 2
    $\begingroup$ side note: for rotational motion one doesn't measure acceleration in $m/s^2$ $\endgroup$ – L.Dutch May 29 '18 at 2:32
  • 2
    $\begingroup$ @L.Dutch True, but to get a sense of the 'surface effect', it is probably more usefully descriptive than using radians/sec^2 $\endgroup$ – Penguino May 29 '18 at 3:30

Over 24 hours the deceleration isn't the biggest problem as long as the whole planet is shut down in a reasonably uniform way, and since you need the energy for the reversal you wouldn't waste too much as heat so that's not an issue either. There are still two big problems:

  1. EM field; if you don't shut down the outer core the Earth gets shredded when you stop the rest of it, if you do shut it down then the Earth's Electromagnetic Field shuts down and just about everything on the surface of the planet dies within a couple of hours due to raw solar radiation and charged particles hammering the planet.

  2. Rotational stretch; the Earth is not a sphere, it's wider at the equator, this is entirely because it's spinning, if you shut that down the equatorial bulge will start collapsing. The bulge makes the world 68km off spherical if it had time to collapse fully the poles would extend by about 34km and the equator shrink by the same. The earthquakes and tsunamis caused by even the start of that process will dwarf anything in recorded history.

These two things start happening once the world starts slowing down so even if it hardly stops in the middle of the process they're still going to be major issues.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.