Wavelengths are huge, but a tsunami (like the tides) is a shallow-water wave, and its velocity is proportional to sqrt(water depth). In the open ocean waves move at 700-800 km/hr. Damage when the wave hits the shore is related to the total volume of water displaced (which, in the case of the tides, is huge).
The wave of tides travels around the earth at twice a day, or about two thousand miles an hour at the equator. It would continue to do so, pretty much uninterrupted, for a while. I have no idea how long, but my seat of the pants feeling is for a few days, maybe a month. It would be smaller every day, and eventually just run out.
The sudden loss of power source is not realistically going to suddenly start the tides slamming into the continents. It makes no sense whatsoever to think it would. Stir a cup of tea for a while, and then pull the spoon out. Does the water suddenly slosh out of the cup? No, of course not.
Tris
I’m not sure that the cup of tea is an adequate analogue - the moon is doing more than just moving the tides around the earth, it’s holding them up too. If it stops holding them up, they’re going to fall.
But it wouldn’t change the average depth of water in the ocean, would it? While the tidal bulge would flatten out that water would be moving into the space that is normally lower than it would be without the tidal bulge.
After all, it’s not like the factors of ‘amount of water’, and ‘layout of ocean bottom’ would change appreciably. So the water that fills the ocean still has to fill up the same volume…it’s just going to do it slightly differently.
As a global average, it shouldn’t change, but the moon is not only pulling the water into a heap east/west-wise, it’s also pulling water from north and south towards the equator (or thereabouts, if the plane of orbit is different), so the sudden loss of the moon should mean a lower mean sea level at the equator and a higher mean sea level at higher latitudes in both hemispheres.
And they’re going to fall with enormous force in a split second. That’s the key, given the OP. As Mangetout says, the volume of water being held up by the moon above the level where it would otherwise exist is unimaginably massive. The sudden drop of this volume would slosh a lot of water over the “edges” of the ocean. Imagine a shallow tea cup full of water with a good portion of the water pulled a significant distance up above the edges of the cup by some gravitational force. Now kill that force in a split second. The water drops and some of it is going to slosh over the edges. I’m not sure the OP has a lot to do with waves, tides, etc. It has more to do with what happens when you drop water onto water in a very shallow bowl.
The mean difference between high and low tides in the central oceans is (within variable differences because of continent shapes, and ocean depth) somewhat less than 40 cm. This is the height of the bulge, compared to the depth of the basin caused by both the sun and moon. Depending on the timing of the SMEF event, it could be slightly more or slightly less because of solar tides. Most of the time it would be only a minor difference.
The event is instantaneous, so the thinking seems to be that the bulge instantly hits the earth with meteoric, or earthquake type effect. Actually, the bulge will instantaneously begin accelerating toward the earth at the difference between earths normal gravity, and the gravity of the moon which is what piled it up over the eons. It would not crash, it would slump. It is already accelerating toward the Earth at 32 feet per second per second. Now it would be “crashing” down at 32.0004 feet per second. (number made up, for dramatic effect.)
Another factor being ignored is that the crest of the bulge is, by geometric coincidence surrounded on all sides by the trough. Not only does the bulge have less acceleration than the imagined amount, but it has a place to go, that has room for it to spread out. So, a lot of places would simply experience somewhat decreased tides sooner, and a few, because of continental influence, somewhat increased tides.
The imagined SMEF consequences are also mediated by the the major energy component of the tide. Inertia. The tidal bulges will continue to act as they now act until the absence of the force of the gravity of the moon changes the vectors. The tidal bulges will continue to move around the earth in the same direction, and at the same velocity, until dampened out by normal forces. No sudden crash there.
Poets might leap from sea cliffs and hit sand, because of the loss. Lovers on lover’s lanes might find themselves in the dark, if they noticed. But the megaSMEF ain’t coming.
Tris
I don’t see how a wave caused by this hypothetical event could be larger than the height of the tides. If the tides are 40 cm (as earlier stated) and they suddenly fall, they’re not going to fall 400 cm causing huge waves. They’re going to fall 20 cm and the ocean in between will rise 20 cm. It may go back and forth a few times, but it’s not going to be a 20 foot tsunami.
That’s assuming they even fall. I’m thinking they’d probably carry momentum and continue circling the planet slowly dissipating.
A 20 cm wave in midocean is many meters tall in littoral reaches. As the wavefront moves inland, the energy remains the same (neglecting viscous losses) but the amount of mass it has to act upon wil be substantially less. As for momentum, you have to realize that the waves aren’t result of a different in momentum between the rocky Earth and her blanket of oceans, but rather of the result of the difference between the Earth’s rotational rate and the Moon’s orbital period; while the energy for this comes almost entirely (>99%) from the Earth’s rotational momentum, without an external influence there are no tides. It’s not as if the tides are the result of water moving across the ocean, but rather water being pulled up in coastal regions, or drawn out to sea depending on the relative position of the Moon. If the Moon suddenly disappears, water plops down in a splash.
Aside from Chronos’ concerns about mathematical discontinuities in the fabric of spacetime and the introduction of a small but significant nutational disturbance in the motion of the Earth, you’re also going to disrupt delicate ecosystems in littoral regions that depend upon regular tidal action to bring in food and remove waste. You’ll probably have significant impacts upon circulating currents as well, which will have substantial climate impacts. And of course, surfers of the world will be eternally saddened while poets, lovers, and advertising executives will have to come up with a new iconography for romance. All in all, it’s a bad plan.
Stranger
The moon is far enough away from the earth that the ‘vacuum effect’ wouldn’t really exist. There’s no atmosphere out there, and the particles that are there aren’t concentrated enough to do much of anything. It would just kind of like. . . turn out the nitelite.
Although, I will raise this question: gravitational forces on the water is one thing, but what about the molten iron in the Earth’s core? I betcha there’d be some damn funky stuff with the magnetic poles of the Earth.
Tripler
A disappearing moon? Personally, I blame the Communists.
OK, guys, let’s keep the magnitude of forces in mind.
The acceleration of objects on earth toward the moon due to the gravitational attraction of the moon is 0.000033135 m/s[sup]2[/sup]. The tidal bulges will suddenly be accelerating downward at 9.765966865 m/s[sup]2[/sup], instead of 9.7766 m/s[sup]2[/sup]! (at the equator, neglecting angular vectors if the moon is not along the ecliptic.)
Head for high ground! Chicken little was wrong!
Tris
Okay, yes, I should have thought of that.
But whatever part of the ocean is under the moon or opposite it has more water. It’s as if part of the ocean’s water is following underneath the moon. I still don’t see why the tidal bulge wouldn’t continue like an ordinary wave once the moon disappeared, at least until it hit the next continent to the west. The tides are kept stable by the moon, but it doesn’t seem like the disappearance of the moon would cause them to instantly drop. Maybe it would, but I just can’t imagine why.
It would solve that pesky werewolf problem.
There’s something I’m finding very disturbing about this entire thread. I may be wrong about this, but . . .
For the moon to instantaneously blink out of existence, wouldn’t some fairly basic physical laws have to be stretched to the point of being actually violated? IOW, is such an event even possible, without at least violating Cause and Effect? If so, then the only answer to the question is, literally, ***anything ***can happen. Any answer, regardless of probability, is just as valid as any other.
How about this one: Existence, itself, will suddenly vanish along with the moon.
By my armchair understanding of quantum mechanics (those who actually know this stuff well, please correct me if I am wrong) it actually would be possible for the whole moon to vanish, but the probability for such an event is so low that the post size limit here would prevent me from get anywhere near typing out the number.
I reiterate:
One can answer the OP’s question by, say, constructing a computer simulation of the Earth-oceans-Moon system, and then at some time abruptly overwriting the value of the Moon’s mass with 0. Such an answer, of course, completely ignores the implications which disturb you and I so much, and is probably more or less what the OP is looking for.
Eh, yes and no. The particles which make up the Moon could spontaneously all tunnel to some other location or locations, but the energy associated with them cannot be created nor destroyed, nor can it be transferred at greater than the speed of light. I’m unsure what the gravitational implications of such an unlikely event would be, and they might even require a theory of quantum gravity to describe (though semiclassical gravity would probably be enough… That’s comprehensible, but a lot more trouble than I’m going to go through for a message board post).
If The Earth Had No Moon is a very enlightening program shown frequently on either the Science Channel or National Geographic Channel (maybe both).
Minor nitpick: Once a day, two waves on opposite sides of the Earth.
The moon is also responsible for the tilt in the earth’s axis. If the moon were to disappear, then the axis, which if I remember correctly is tilted around 10-15 degrees, would fluctuate more wildly. It would perhaps go to 60-90 degrees.
This would have the affect of changing climate everywhere on earth, as now the north pole is where the desert used to be (at some point).
So whoever said it had minimum affect on climate is completely WRONG.
sigh I’m not sure you could pack more wrong into such a short space if you tried. First of all, the tilt of the Earth’s axis with respect to the solar ecliptic plane is approximately 23.4 degrees, with about a 2 degree overall variation in a 23,000 year cycle. The orbit of the Moon about Earth is at an angle of 5.2 degrees to the solar ecliptic. The Moon may provide some moderating influence to the variation, but it is highly unlikely that the polar orientation of the Earth would “fluctuate more wildly…60-90 degrees”. However, as rotational momentum is leeched from the Earth via tidal interactions with the Moon, it will actually become more susceptible to external influences. Far from being a stabilizing influence, the Moon is actually contributing to the loss of Earth’s natural gyroscopic stability. Mars, which essentially lacks any moons (Deimos and Phobos are captured asteroids that have no calculable effect on the rotational behavior of their parent), has an axial tilt of 25.2 degrees to the ecliptic and an estimated tilt range of 15 to 35 degrees. Mars is also significantly less dense than the Earth and smaller, and thus presumably more affected by external couples that would cause variations in axis tilt.
Second, I’m not really clear what you mean in your statement, “…the north pole is where the desert used to be (at some point).” I’m not sure to which desert you are referring, but there is no credible evidence that the axis of the Earth has ever varied dramatically (though what evidence we have is limited by the age of the crust). It’s certainly possible that a land mass crossed the North Pole during tectonic movements from the breakup of Pangaea through the modern day, but that has nothing to do with the rotation of the Earth.
Third, even a modest axial tilt would have an effect on the climate by altering the duration and intensity of the seasons, and additional nutational modes resulting from the sudden disappearance of the Moon would certainly contribute to this, but again such variations would be minor (fractions of a degree) over periods of centuries or larger. If the Earth were to somehow undergo some massive rotational shift–say even one of five or ten degrees–the resultant effect on Earth’s climate and the ecosystems adapted to that regular variation would be extreme, probably killing off all megafauna and much flora, leaving simpler and more adaptive organisms to rebuild. More dramatic variation might destory virtually all life entirely by permanently disrupting the critical vapor cycle, making the planet uninhabitable by anything more complicated than single cell organisms.
While the force of the Moon’s influence on any small collection of water may be tiny, the whole amount of energy is huge. If that force is released all at once, that energy goes somewhere, and because it can’t really go down (water and the seafloor below it being pretty much incompressible) it’ll spread out in an expanding wave, which will become higher as the depth gets shallower. Once expended, however, there is nothing else to drive tidal forces; after the inital tidal blast, there won’t be any more lunar tides, ever. There’ll still be solar tides, of course, but these will be less dramatic.
Any system of fundamental particles can be considered a superposition of the probabilities of the individual particles. However, by the time you get up to the level of molecules the molecular structures themselves are considerably larger than the amplitude of the waveform (so that the molecule always appears to be almost exactly where you expect it) and quantum effects at that level are very small, limited to the tiny variations that cause statistical mechanics to be, well, statistical. At the level of stuff you can even examine optically–say, a speck of dust–the waveform is so much smaller than the object that you can treat it classically in terms of mechanical interactions. For an object the size of the Moon its variation from its nominal position is far less than it is possible to measure, even in theory, even on quantum scales. For all intents and purposes, the Moon is exactly where it appears to be. While it is nominally possible to calculate a possibility that the Moon is across the Solar System, the likelyhood of this occuring in the lifetime of the Universe is virtually infinitesimal. In any case, as Chronos notes, the energy bound up in the Moon (i.e. its mass and momentum) can’t just disappear, and even if it flitted across the Galaxy for an instant, it would be back the next. (The average speed can’t exceed the speed of light without creating a lot of problems even before you get to relativity, but that’s another problem entirely.)
I don’t know how you’d cope with the gravitational implications of this, since there’s no accepted way to cope with the gravitational force in quantum mechanics. Presumably the field would remain centered on the nominal position of the Moon, but that doesn’t seem to make sense, either. The idea underlies the whole problem between General Relativity and quantum mechanics, which makes a lot of people very nervous so they prefer to think about reality television shows and midget pornography instead, hence the popularity of the Internet. Bizarre how it all comes around, init?
Stranger