Fun With Physics #5 · 12:55am Nov 23rd, 2012
How exactly would Nightmare Moon go about creating eternal night?
I've actually been toying with this issue for a little over a month now. Of course, I'm assuming a heliocentric solar system with natural planetary rotation and orbit (because that's just how physics works). From what I could figure, there are three feasible options:
1. Stop the rotation of the planet.
Believe it or not, this is possible. Planetary rotation is simply a result of angular momentum left over from the debris orbiting the sun. When a star has just formed, the planets aren't really there. However, there's plenty of dust swirling around the infantile star that isn't quite in an inward spiral. Instead, it's gone into an equilibrium, and stays in orbit. Because this dust is swirling around the sun, it has angular momentum, which doesn't just vanish when is coalesces into a planet. Instead, it remains, and due to conservation of angular momentum (basically conservation of energy), the momentum increases as the radius of rotation decreases.
In any case, there's no specific force causing planets to rotate. So it's not unfeasible to find planetary bodies that don't rotate at all. In fact, Earth's own rotation is gradually slowing: the day becomes longer by about twenty millionths of a second each year. This is due to tidal forces generated by the Moon's gravity.
But I digress. What would this do? Well, depending on how abrupt the slow-down is, the results could range from unnoticeable to catastrophic. Since I've always had a penchant for the dramatic, I'll envision an abrupt slow-down, where the planet's rotation stops completely over a period of a day.
Earth's equatorial rotation speed is 465.1 m/s, giving a deceleration of 0.00538 m/s^2... which really isn't that much. If you drop something, the acceleration due to Earth's gravity is nearly two thousand times that. However, this is a small acceleration applied to an obscene amount of weight. That atmosphere alone has a weight of about five billion billion kilograms. So, the resultant momentum would be extreme. It would probably take months, or even years for the atmosphere to stop moving, which, once the planet's rotation ceased, would create winds that put a Category 5 hurricane to shame. Not to mention that every volcano on the planet would erupt, along with major tidal waves, coupled with severe earthquakes at just about every fault line on the... you know, take half the scenes from the movie 2012 and imagine them occuring at about the same time. That should give you a good idea.
Then, of course, there's the matter of the oceans. Because of Earth's rotational momentum, the planet has taken on a slight ellipsoid shape that bulges outward at the equator. The water of the oceans does the same. Once the rotation stops, the planet will eventually resume a spherical shape, and the bulge of ocean water will migrate evenly over the planet, submerging northern areas and exposing equatorial landmasses.
After all that, there's still something else. The Earth's magnetic field is generated by a dynamo effect that's a direct result of its rotation. This magnetic field allows us to navigate, creates the polar regions' auroras, and, most importantly, deflects charged particles ejected by the Sun. Without that, the planet would be bombarded by positrons, beta particles, neutrinos, protons... all those lovely things that make particle physicists salivate. And, upon exposure, die horribly.
But the main problem with this method isn't the planetwide devastation: it doesn't create eternal night. The planet would continue to orbit the Sun, and so eventually, light would reach every corner of the globe. A day would just take the same amount of time as an orbital year.
2. Deflect the light coming from the Sun.
What happens at night? Well, the face of the planet you happen to be on is turned away from the sun. Because light can't penetrate opaque matter, it's dark. But how do you make the entire planet like this? Easy. Just take all the light coming from the Sun and bend it around the planet. If no light hits it, then it's always dark. Foolproof, right? Sure, you'd end up with a big black spot in the sky where the Sun usually is, but darkness is complete on the entire surface.
Nope. Because of the utter lack of solar radiation striking the planet, it would be as if there was no Sun at all. That means no harmful cosmic radiation (a boon to tanners, most definitely), no irritating sun glare (a boon to the light-sensitive), and... oh. No heat.
Heat, or infrared radiation, is part of the electromagnetic spectrum, as is visible light. Visible light makes up a relatively small part of it: between wavelengths of 390 nm and 750 nm. Infrared radiation extends out from the red range, from 740 nm to 300,000 nm. And because you can't deflect only specific wavelengths, that means the planet would be devoid of a heat source. Sure, greenhouse gases in the atmosphere would hold on to it for a while, but eventually, temperatures will plummet to a level similar to that of Pluto: about 50 K, or -223 degrees Celsius – about 30 degrees colder than liquid nitrogen. Needless to say, that's too cold for anything to survive.
But I'm not done yet. There's still one more option to contemplate. One that is probably the subject of countless B science-fiction movies.
3. Blow up the Sun.
This actually isn't as difficult as it might seem. Actually, if left alone for five billion years or so, our Sun will do just that. Well... not quite. I don't think the mass of that particular star is quite enough to go supernova. But, once it's started fusing iron and silicon (the heaviest elements a star can fuse), fusion begins to grind to a halt. And at that point, the amount of energy the star releases declines sharply. See, the only thing keeping a star from collapsing in on itself is the energy released from fusion (so technically, a star is a massive, continuous explosion). Once that energy declines to a critical point, the star undergoes gravitational collapse.
At this point, the entire mass of the star hurtles toward the core at a significant fraction of the speed of light. The unthinkable heat and pressure generated by this facilitates the fusion of even heavier elements: elements like gold, copper and uranium. Of course, this burst of fusion generates a new burst of energy... one that rips the star apart in an explosion that would send Michael Bay into paroxysms of orgasmic joy. (This is the only case where it's technically possible to blow up an explosion, by the way)
One can also make a star explode simply by hitting it with a burst of energy – enough to accelerate its entire mass to escape velocity. Based on some obscenely complicated calculations that are just too difficult to format to put here (the formula and derivation is here, if you're curious), the amount of energy required to do that is about 1.12 x 10^42 J. Which, incidentally, is close to the amount of energy required to sling the Sun around the Earth (See Fun With Physics #1).
So there we go. No more Sun, no more day. Also, no more light and heat (creating the same result as Method 2), and likely no Earth (Or Equestria, or whatever you want to call the planet ponies live on). The energy involved in blowing up the sun is so ridiculous that the resulting blast would probably take out most of the solar system. Even if it didn't, the massive burst of gamma rays, neutrons and neutrinos from the explosion would unquestionably scour everything within a significant distance clean of life. (One school of thought believes that it was a supernova about 50 or so light-years away that caused the Cambrian extinction, where between 70 and 80% of life on Earth died off)
Huh. I'm no analyst... but it seems that any possible method to create eternal night will basically screw everything. Guess Nightmare Moon didn't quite think that through all the way.
The third isn't a possibility simply because of how it occurs within the show, though. Nightmare Moon was stopped and day returned, while blowing up the sun would be pretty damn irreversible if you ask me.
Also, have you taken into account geocentrism?
Adiabatic lapse rate. The pressure of the atmosphere would keep it relatively warm even without the sun. Combined with that, there's probably enough energy within the planet to maintain a gaseous atmosphere given the current volume of gas around us. Wouldn't be particularly healthy for humans, but it'd be enough to stop it freezing out as snow.
what if the earth rotated at such a speed, that equestria always remained on the furthest side away from the sun?
Oh... Hello...
images4.wikia.nocookie.net/__cb20120621172639/half-life/en/images/thumb/8/88/GLaDOShd_Portal_2.png/250px-GLaDOShd_Portal_2.png
I see somebody has been doing science... I approve.
- Or end up like this...
texturbation.com/blog/fallout.jpg
- Face it, this is why people love physics.
As for the implications of this to the show. It fits very well with my idea, the eviler a person is, the bigger of an idiot they are. And yes, by this account I would be inclined to call Hilter, Stalin, and Chairman Mao the three stooges.
images4.wikia.nocookie.net/__cb20120621172639/half-life/en/images/thumb/8/88/GLaDOShd_Portal_2.png/250px-GLaDOShd_Portal_2.png
Or maybe just Wheatley.
528992
With the magic of tidal locking, it is possible to have eternal night for half the planet. Everyone on the planet would be kind of screwed as half the planet freezes and the other half burns. Life would only be able to survive on the border between the two extremes. We will call that area the twilight zone, just for fun. Radiation would probably still kill what life is left, unless the earth's core was kept spinning to keep the magnetic field intact. Radiation proof bunkers would probably be more cost affective then controlling the earths core.
My explanation. It's magic. I don't got to explain nothing
>The planet would continue to orbit the Sun, and so eventually, light would reach every corner of the globe
What if Le Earth rotated while going around Le Sun? Sure, it would fry the zebras on the other side, but who gives a fuck about them? //e.deviantart.net/emoticons/moods/love/lust/suggestive.gif
>This is the only case where it's technically possible to blow up an explosion, by the way
So you can explode twice?
I've always thought of the MLP universe as occurring on a disc, like in Under the Northern Lights or in Discworld. The sun and moon are moved under and over the disc, and all Nightmare Moon would need to do would be to keep the sun under the disc.
No, that's only how physics works in our universe. Equestrian physics probably works differently.
Not actually correct! The particle-level nuclear reactions involved in fusion are different from the atom-level chemical reactions involved in explosions.
530349
From the Wikipedia explosion entry:
According to this definition, an explosion can be driven by nuclear, chemical, or even strictly mechanical reactions. On the other hand, the sun probably does not qualify as a "continuous explosion" by this definition because the volume stays fairly close to constant. There are stars that do change volume and brightness (see variable star at Wikipedia for a long list of types), but most of them would probably not be a lot of fun to live under.
Couldn't an eternal eclipse do the job? But, then again, I'm not the one spending copious amounts of time over-analyzing the laws of a fictionall universe.
After all that, there's still something else. The Earth's magnetic field is generated by a dynamo effect that's a direct result of its rotation. This magnetic field allows us to navigate, creates the polar regions' auroras, and, most importantly, deflects charged particles ejected by the Sun. Without that, the planet would be bombarded by positrons, beta particles, neutrinos, protons... all those lovely things that make particle physicists salivate. And, upon exposure, die horribly.
I actually knew enough to follow this part, scenario #2 and the basis of scenario #3 (except for the actual math behind it. It sucks when I'm only a Sophomore in High School and have yet to even get into that kind of math.). The rest was just partial understanding or of interest. Man, I can't wait until Physics...
Also, that number 3...
530852
How about magic? That works too. Or by placing a hollow sphere around a planet that blocks all light that attempts to come through.