I have a theoretical question. I have been reading on what would happen if the earth suddenly stopped rotating around its axis, and I have learned that would result in the annihilation of all life on the planet. I also learned that the earth rotates currently at 465 meters/second.

Now, my question. What is the optimal deceleration factor that would allow the earth to stop over time (and not suddenly), while allowing live to continue? How do I build a machine to slow down the earth to a complete stop, without destroying all life on planet?


  • $\begingroup$ You don't have to build such a machine, because it already exists: the Moon. The deceleration factor (+0.00001542857 seconds a year) worked pretty well in the last billion year. ;-) $\endgroup$ – klanomath Aug 27 '19 at 21:25
  • $\begingroup$ @klanomath, thanks for the information. Can I assume that if a planet, of a mass equal to earth, passed slowly near us, that it could cause the earth to slow down to a full stop without ending all live on the planet? $\endgroup$ – Kacihoh Aug 27 '19 at 22:23
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    $\begingroup$ I'm voting to close this question as off-topic because it belongs on Worldbuilding $\endgroup$ – Jan Doggen Aug 28 '19 at 7:17

Slowing the planet would have major consequences. Stopping the planet would have major consequences (here are some: Effect on sea level if the Earth stopped rotating).

Doing either of these things too quickly would have even greater consequences, but trying to predict these consequences and the effects for life on earth would be (a) a major primary research project, and (b) perhaps impossible. The answer is that we just don't know, and I doubt that anybody is about to fund the research ;-)

How to do it is, as I suspect you realise, also a very big question. I mean, if for some reason you wanted to. The difficulty is conservation of angular momentum: for the planet to have stopped turning, you need to have shifted that angular momentum somewhere else. That probably means firing stuff into space, or using tidal mechanisms (as somebody noted re the Moon), or maybe building a giant / massive flywheel on the Earth's axis and spinning it really fast the other way..... all of these are, of course, well into the realm of science fiction.

  • $\begingroup$ Thanks for the information, Semidiurnal Simon. I am trying to theorize based on several articles I read about natural disasters. I am trying to bring the theoretical points stated in those articles into some science (or semi-science). If the earth was showered with several heavy meteors over the years, can the added mass cause the earth to slow down and come to a complete stop? Also, if the earth was to go into a World War 3, and all the countries that own superior rockets, fire everything they got at each other, would that have any effect on earth rotation? $\endgroup$ – Kacihoh Aug 27 '19 at 23:00
  • $\begingroup$ Yes, a lot of big enough meteor(ites) hitting at the right angle could potentially stop the planet... but I'm pretty sure the amount you'd need would be well beyond enough to cause mass extinction without the need for any change to rotation. And yes, if everybody fired their rockets in the same direction, this could slow the earth, by a very little bit. Not enough that you could notice without careful measurements. The Earth is really, really, heavy, such any way I can think of of stopping its rotation in human timescales would destroy it, or kill us all, by other means anyway. $\endgroup$ – Semidiurnal Simon Aug 28 '19 at 0:25
  • $\begingroup$ Thanks a lot for the information. I was under the impression that if all countries fired their high yield rockets they would actually cause the earth to slow down and eventually to a complete stop. I guess no amount of firepower we currently got can do that. What originally peaked my interest into this topic is the research done on the question "what if earth spun into the opposite direction?" They made a simulated model to depict what would happen (climate changes and all). That is when I wondered. What if they know something I don't? How could the earth spin into the opposite direction? $\endgroup$ – Kacihoh Aug 28 '19 at 1:52
  • $\begingroup$ I mean, I haven't done the maths re the rockets, but I would be very surprised if the effects weren't tiny. $\endgroup$ – Semidiurnal Simon Aug 28 '19 at 5:40

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