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With all the hype of the impending "2012 Mayan doomsday" I was thinking it might be interesting to see what principles of physics prevent the theories of doomsday from occurring. One overarching theory is that on December 21, 2012, the two magnetic poles will reverse as a result of a solar flare equivalent to 100 billion nuclear bombs, enough to reverse the geomagnetic poles.

Is there any way a solar flare could lead to reversal of the magnetic poles? If not, what prevents it from happening?

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Hi Andrew, and welcome to Physics Stack Exchange! Although your curiosity is certainly a good thing, there were a few problems with your original question, among them that you were really trying to ask two questions in one, and they weren't clearly defined. I thought it would be simplest to just propose a different way of writing your first question so that it would be more acceptable here. Feel free to make other edits (it is your question, after all), but if you'd like to ask about the stellar alignment thing, that should go in a separate post. – David Z May 15 '12 at 2:28
Just a note to point out that new archeological findings of a Mayan Calendar give us 6000 years grace!… . This confirms the opinion that the 2012 end date was just because the chiseler had run out of wall :). – anna v May 15 '12 at 4:34

Theory one

a solar flare equivalent to 100 billion nuclear bombs

This is about how strong they already are.

reverse the geomagnetic poles

The Earth's magnetic field is created by the spinning of the core as well as the flows within the mantle. Reversal of the field requires a series of strong, persistent changes over hundreds to thousands of years, and no run-of-the-mill astrophysical event can just "flip" it like a switch. And even if it did, the result would probably not be classified as "catastrophic".

Theory two

the black hole Saggitarius A

Yeah, no. Not unless it suddenly warped to within a few dozen parsecs of us. Which probably won't happen. And without that, the oceans just keep going up and down like they always do.

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FYI I edited the question for acceptability, so you may want to edit your answer in response. Or you could wait until Andrew comes back and sees my edit to see if he's going to change anything else. – David Z May 15 '12 at 2:29
@David: I'll hold until he decides what to do. – Ignacio Vazquez-Abrams May 15 '12 at 2:30

It has been suggested that external events could influence the magnetism of the core. See for some examples, but it seems unlikely that solar flares could do this. In principle if the core were in a critical state, i.e. right on the cusp of changing, it's conceivable that a sufficiently strong external magnetic field could have some effect. However the mantle is believed to screen out fast changes to the magnetic field (because it's semi-conducting) and a flare wouldn't last long enough to have much effect.

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