<p>Strictly speaking, the Earth will never cease to rotate in the technical sense... not while Earth is intact at least. No matter what the Earth might eventually become tidally locked with, whether the Moon or the Sun, it will be rotating, at the same rate as either the Moon's or the Sun's orbital period. For example the moon is tidally locked with the Earth, which means its rotation rate is equal to its orbital period, so it always shows (roughly) the same face, although it wobbles on a regular pattern during each orbit, showing somewhat closer to 60% of its surface area to us rather than a flat 50%.</p>

CC BY-SA 4.0
2018-05-25T08:29:33.190Z
Seems to me that this is a matter of frames of reference :-) But, a fair point in an intuitive sense.
Semidiurnal Simon
CC BY-SA 4.0
2018-05-25T08:03:56.337Z
2018-05-25T08:03:56.337Z
seanion
<p>Strangely, the hypothesis (well supported) that Earth's rotation is slowing got its modern start from Immanuel Kant of all people ironically, who pointed out that tidal friction must be dissipative (we might presume by heat transfer) with geophysical consequence, which Kant claimed to be a lengthening of the day. His then novel idea was evidently supported by none other than Lord Kelvin. I am no physicist, but Earth's orbit has many nuances and influences, such as from other planets and its eccentricity, precession, axis motion in three dimensions and so forth. As the Sun burns away, it loses mass (extremely slowly) and all orbits increase, including the Moon's. So over a few billion years, a calculated effect of the role of any drift toward lunar tidal lock is exceedingly complicated. Perhaps a future supercomputed simulation will shed light on a model that is actually verifiable by physical measurements from a satellite (think ESA Hipparcos). Then we will know something about this question.</p>

CC BY-SA 3.0
2016-04-17T19:35:05.333Z
This all seems very speculative and doesn't actually help to answer the question. This is not a discussion forum.
bon
CC BY-SA 3.0
2016-04-17T23:03:41.163Z
This answer would be improved by a reference or two, at least to Kant's _Allgemeine Naturgeschichte_ or whatever the source is. I think it would also be useful to state categorically that your answer is "We don't know.". Split the answer into a couple of paragraphs, and I think it's a better answer than the accepted one.
Matt Hall
CC BY-SA 3.0
2016-04-17T18:28:41.793Z
2016-04-17T18:28:41.793Z
GuestinArizona
<p>No not really, because the earth will be engulfed by the sun as a red giant at which point it might accrete mass or fall into the sun, still rotating at 50hrs/day... we d be talking well above 20/50 Gya.
It's alse enough time for the solar system to be disrupted by galactic events like local supernova destruction and being captured by a passing star which migh render it into multiple fragments.</p>
<p><a href="https://i.sstatic.net/2o62i.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/2o62i.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2021-01-28T04:18:16.270Z
2021-01-28T04:30:04.250Z
2021-01-28T04:30:04.250Z
bandybabboon
<p>The short answer is "Probably Yes".</p>

<p>The longer answer is that it is debatable whether Earth's rotation will become tidally locked to the moon due to tidal drag, at which point it will not be rotating <em>relative to the moon</em>, or whether the sun's exhaustion of hydrogen and the fusion of Helium will result in the sun's expansion vaporizing the earth first.  As tidal drag slows the earth's rotation, the moon moves further away, reducing its effect on the earth's rotation, and making the calculations fairly complex.</p>

<p>In either case, unless something really unexpected happens to the earth first, such as it being ejected from the solar system, which is completely improbable, it <em>will</em> stop rotating, if only due to it ceasing to be a planet at all.</p>

CC BY-SA 4.0
2018-09-04T21:40:54.657Z
Do you have rough time estimates for when these events would occur? (rotation stopping and sun consuming earth)
Phylliida
CC BY-SA 4.0
2021-01-23T06:59:18.597Z
Could the earth gravitationally lock with the sun? (I assume it is some kind of 'gravitational friction' that slows down the rotation)
Amphibio
CC BY-SA 3.0
2014-04-17T05:10:19.023Z
2014-04-17T05:10:19.023Z
Monty Wild
<p>It is well known that the Earth's rotation is slowing down and that millions of years ago there was a point in time where there was only a mere 20 hours in a day on Earth.</p>

<p>My question is in two parts.  Firstly why is the Earth's rotation slowing given that angular momentum is conserved, and secondly given that understanding, will the Earth either (a) stop rotating in the future, or (b) eventually begin rotating in the reverse direction to what it is now or will it (c) reach a constant rotational velocity in the same direction it is rotating now and why?</p>

<p>I think the answer to the question will depend on whether the Earth's rotation is slowing at a decreasing rate or at a constant rate.</p>

CC BY-SA 3.0
2014-04-20T01:20:45.887Z
This question appears to be on-topic because it fits the scope of the proposal as defined in area51. Voted to reopen.
Kenshin
CC BY-SA 3.0
2014-04-20T20:53:35.287Z
Even if it falls short of "expert," this seems like a deep, complex question that considers multiple scenarios.
Tom Au
CC BY-SA 3.0
2014-04-16T23:51:23.693Z
How do you know Earth is slowing down, and that there was only 20 hours a day millions ago?
amorfis
CC BY-SA 3.0
2014-04-16T23:54:13.243Z
@amorfis I recommend asking that as a separate questions (we *do* know).
gerrit
CC BY-SA 3.0
2014-04-16T23:55:01.883Z
If I recall correctly, Earth will eventually be tidally locked with the moon, with a day lasting exactly a month.  But I leave it to others to answer because my knowledge is based entirely on popular science.
gerrit
CC BY-SA 3.0
2014-04-17T00:32:29.013Z
My feeling is that the sun's expansion will have some say about this.
Neo
CC BY-SA 3.0
2014-04-17T02:04:24.423Z
The Earth's rotation is gradually slowing due to tidal drag.  Oddly enough, there's a nice explanation of it (and leap seconds) on the xkcd blog: http://what-if.xkcd.com/26/  In a nutshell, rotation wouldn't ever completely stop, the Earth would just eventually become tidally locked with the moon just like the moon is tidally locked with the Earth (i.e. the same side of the earth would always face the moon and vice versa).  (I can't back enough of that up to make a complete answer, though.)
Joe Kington
<geophysics><planetary-science><earth-rotation>
Will the Earth ever stop rotating?
Kenshin
# Will the Earth ever stop rotating?

(Asked by: username_0 on 2014-04-16)

It is well known that the Earth's rotation is slowing down and that millions of years ago there was a point in time where there was only a mere 20 hours in a day on Earth.

My question is in two parts. Firstly why is the Earth's rotation slowing given that angular momentum is conserved, and secondly given that understanding, will the Earth either (a) stop rotating in the future, or (b) eventually begin rotating in the reverse direction to what it is now or will it (c) reach a constant rotational velocity in the same direction it is rotating now and why?

I think the answer to the question will depend on whether the Earth's rotation is slowing at a decreasing rate or at a constant rate.

**Tags:** geophysics, planetary-science, earth-rotation

> **Comments:**
> **username_2**: How do you know Earth is slowing down, and that there was only 20 hours a day millions ago?  
> **username_3**: @username_2 I recommend asking that as a separate questions (we *do* know).  
> **username_3**: If I recall correctly, Earth will eventually be tidally locked with the moon, with a day lasting exactly a month.  But I leave it to others to answer because my knowledge is based entirely on popular science.  
> **username_4**: My feeling is that the sun's expansion will have some say about this.  
> **username_5**: The Earth's rotation is gradually slowing due to tidal drag.  Oddly enough, there's a nice explanation of it (and leap seconds) on the xkcd blog: http://what-if.xkcd.com/26/  In a nutshell, rotation wouldn't ever completely stop, the Earth would just eventually become tidally locked with the moon just like the moon is tidally locked with the Earth (i.e. the same side of the earth would always face the moon and vice versa).  (I can't back enough of that up to make a complete answer, though.)  
> **username_0**: This question appears to be on-topic because it fits the scope of the proposal as defined in area51. Voted to reopen.  
> **username_1**: Even if it falls short of "expert," this seems like a deep, complex question that considers multiple scenarios.  

---

## 4 answers

### Answer by username_12 on 2014-04-17. Score: 18 | Accepted answer

The short answer is "Probably Yes".

The longer answer is that it is debatable whether Earth's rotation will become tidally locked to the moon due to tidal drag, at which point it will not be rotating *relative to the moon*, or whether the sun's exhaustion of hydrogen and the fusion of Helium will result in the sun's expansion vaporizing the earth first. As tidal drag slows the earth's rotation, the moon moves further away, reducing its effect on the earth's rotation, and making the calculations fairly complex.

In either case, unless something really unexpected happens to the earth first, such as it being ejected from the solar system, which is completely improbable, it *will* stop rotating, if only due to it ceasing to be a planet at all.

> **Comments:**
> **username_13**: Do you have rough time estimates for when these events would occur? (rotation stopping and sun consuming earth)  
> **username_14**: Could the earth gravitationally lock with the sun? (I assume it is some kind of 'gravitational friction' that slows down the rotation)  

---

### Answer by username_6 on 2018-05-25. Score: 5

Strictly speaking, the Earth will never cease to rotate in the technical sense... not while Earth is intact at least. No matter what the Earth might eventually become tidally locked with, whether the Moon or the Sun, it will be rotating, at the same rate as either the Moon's or the Sun's orbital period. For example the moon is tidally locked with the Earth, which means its rotation rate is equal to its orbital period, so it always shows (roughly) the same face, although it wobbles on a regular pattern during each orbit, showing somewhat closer to 60% of its surface area to us rather than a flat 50%.

> **Comments:**
> **username_7**: Seems to me that this is a matter of frames of reference :-) But, a fair point in an intuitive sense.  

---

### Answer by username_8 on 2016-04-17. Score: 2

Strangely, the hypothesis (well supported) that Earth's rotation is slowing got its modern start from Immanuel Kant of all people ironically, who pointed out that tidal friction must be dissipative (we might presume by heat transfer) with geophysical consequence, which Kant claimed to be a lengthening of the day. His then novel idea was evidently supported by none other than Lord Kelvin. I am no physicist, but Earth's orbit has many nuances and influences, such as from other planets and its eccentricity, precession, axis motion in three dimensions and so forth. As the Sun burns away, it loses mass (extremely slowly) and all orbits increase, including the Moon's. So over a few billion years, a calculated effect of the role of any drift toward lunar tidal lock is exceedingly complicated. Perhaps a future supercomputed simulation will shed light on a model that is actually verifiable by physical measurements from a satellite (think ESA Hipparcos). Then we will know something about this question.

> **Comments:**
> **username_9**: This all seems very speculative and doesn't actually help to answer the question. This is not a discussion forum.  
> **username_10**: This answer would be improved by a reference or two, at least to Kant's _Allgemeine Naturgeschichte_ or whatever the source is. I think it would also be useful to state categorically that your answer is "We don't know.". Split the answer into a couple of paragraphs, and I think it's a better answer than the accepted one.  

---

### Answer by username_11 on 2021-01-28. Score: 0

No not really, because the earth will be engulfed by the sun as a red giant at which point it might accrete mass or fall into the sun, still rotating at 50hrs/day... we d be talking well above 20/50 Gya.
It's alse enough time for the solar system to be disrupted by galactic events like local supernova destruction and being captured by a passing star which migh render it into multiple fragments.

[![enter image description here](https://i.sstatic.net/2o62i.png)](https://i.sstatic.net/2o62i.png)


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