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We know that the earth is rotating from west to east (anti-clockwise) Has the earth ever rotated from east to west in past,in early times after earth has formed? And/or is there any scientific foresight that the earth may rotate from east to west (clockwise) in future? If it happens,what changes would occur?

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  • $\begingroup$ have you done any research trying to find an answer to this question like looking here solarsystem.nasa.gov/solar-system/our-solar-system/in-depth $\endgroup$ Apr 8, 2022 at 13:45
  • $\begingroup$ "Clockwise" and "anti-clockwise" are meaningless here, because it all depends on which pole you're looking down on. "East" and "west" are defined by sunrise and sunset, so they don't help either. The terms "prograde" and "retrograde" (i.e. rotation relative to orbit) do actually mean something. $\endgroup$
    – Spencer
    Apr 8, 2022 at 15:25
  • $\begingroup$ @Spencer There are different definitions of east and west, they can either be defined by rotation or with respect to the ecliptic. Venus is very commonly described as having a western sunrise, although I agree there are more precise terms. $\endgroup$ Apr 8, 2022 at 16:27
  • $\begingroup$ @NuclearHoagie But if you look at just the etymology of the words, you'll see they're related to sunrise/sunset or morning/evening. $\endgroup$
    – Spencer
    Apr 8, 2022 at 16:34
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    $\begingroup$ I’m voting to close this question because it likely belongs in astronomy.stackexchange.com. There is even a very related question there: astronomy.stackexchange.com/questions/40768/… $\endgroup$
    – arkaia
    Apr 11, 2022 at 12:51

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No.

  • I'm not aware of any evidence that Earth ever rotated in the opposite direction in the past.
  • It's very unlikely that it will have its direction reversed, e.g. by a very large bolide, in the future.

For future reversals, I can think of 2 scenarios: slowing down and reversing, or flipping the rotational axis.

Slow down and reverse

I think we can discount the case of reversal by abruptly (in the geological sense) stopping it then accelerating in the opposite sense. For example, assuming the Earth has rotational kinetic energy of 2 × 1029 J, reversing its direction would require a change of twice this number. This is at least a million times the energy released in the Chicxulub impact (about 3×1023 J).

This is all very rough, we're ignoring its total orbital momentum and assuming its a spherical solid, but it seems like it would be hard to find this much energy, especially in today's solar system.

There's an old question about the possibility of the Earth eventually running out of angular momentum. If you accept that this might happen in several (probably tens of) billions of years, then I suppose it could be started again by a bolide impact... except that bolide impacts will be impossibly rare events by then.

Flip the axis

Most of the answers I could find are just as speculative as the question itself, and they seem to focus on a reversal of rotation direction. But none of them address the possibility of the Earth's axis flipping 180 degrees with respect to the ecliptic, which would effectively reverse the rotation. (Really, since it's already titled by 23.4 degrees, only another 68 degrees would push the North pole over the ecliptic.). There's a Physics Stack Exchange question about this, and thanks to the gyroscope effect, the energy required to shift the axis is almost the same as that required to reverse the spin.

Conclusion: this is just as unlikely as the first scenario.

Further reading

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    $\begingroup$ I think you've given the formula for torque, not work - the energy required to flip the earth's rotation shouldn't depend on how long it takes to do it, it should just be double the value of the earth's current rotational kinetic energy. And if we're assuming this is the result of an impact, the acceleration time will be on the order of a second, not a year (although the time will just determine the power needed, not the total energy requirement). $\endgroup$ Apr 8, 2022 at 13:56
  • $\begingroup$ @NuclearHoagie Admittedly I didn't give it a massive amount of thought, I probably got confused about angular momentum. Please feel free to edit or create another answer with a better analysis. As for the year, definitely a fair point. Somehow I couldn't imagine it taking ~1s but I guess it would have to be ~instantaneous. I think then it would exceed the binding energy and bash us out of orbit and/or into smithereens. Either way, it's bad. $\endgroup$
    – Matt Hall
    Apr 8, 2022 at 16:25
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    $\begingroup$ @NuclearHoagie Okay, I tried casting in terms of kinetic energy... see what you think. Definitely simpler. $\endgroup$
    – Matt Hall
    Apr 8, 2022 at 16:27

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