I've been thinking about the why and how of Equestria coming into contact with Earth. Up until now, the only "reason" that could fly in my mind was that Celestia did it on purpose - with or without malicious intent.

However, I had an idea. What if universes were like magnets? Earth has no magic - negative charge - and Equestria has lots of magic - positive charge. The two colliding could just be the result of a little too much magic in one area of Equestria, pulling the two universes together like a pin through two pieces of paper.

So Equestria is touching earth. Humans discover they can't touch Equestrian soil or airspace, or they'll die horribly to Thaumic Radiation. Ponification is invented, Bureaus open.

But that's a little stagnant. Where's the pressure? Why does the Purification happen/the world need to go pony?

Magic.
By touching Equestria, Earth is starting to absorb some of it's magic, like Osmosis. Normally, this would be great -- Magic on Earth.

Problem is, as has been proven earlier, thaumic radiation is bad for humans. If left to "equalize", all humans on earth will die a horrible death by burning.
It's not all sunshine and rainbows for Equestria, either; with the loss of what will turn out to be half their native magic in the air, Equestria will change -- magic will become less potent, and the magic of the land will fade. Clouds will become unmanageable, which could lead to some very nasty disasters (like Cloudsdale falling out of the sky)

The solution: One of the universes has to go. But how do you decide?

Tension!

Of course, that's just me and my "Losing Is Fun" sensibilities.

Got any alternative theories or takes you want to show off or flesh out? I guess this is the thread for it.

That's similar to my theory for the way the two came into contact. The universes drifted a hairsbreadth apart from each other at the same time Equestria's reality expanded (due to the repeated uses of the Elements of Harmony, which in my 'verse draw their power from the greater multiverse) As for the greater fate of the two worlds and their sentient species, that'd spoil things to come

Your theory has perked my interests further

This idea is very similar to my non-TCB story The Good of The Many

In that story I was exploring how ideas cross between Equestria and Earth, and the tension came from a possible m-brane collision leading to total annihilation of both universes.

However, I like your idea of a transfer of magic between the two worlds. It actually makes what is happening on the Equestrian side much more interesting than in the usual TCB setting. Also, the loss of potency of magic also provides impetus for trade between the two sides, and some social development of Equestrian Society (can anypony else smell steam-punk Equestria in this?)

443716
Well, there can be trade...

But that's not the intent. The whole point of that is to force a binary decision. Only one or the other can survive, and to take no action will be to doom both worlds. By the time magic potency drops to a noticeable level, everyone's probably boned anyway.

*sigh*

I once had a great vision of things, but I doubt the story is coming out any time soon. The plot, however, I have written out. Briefly said, magic manifests differently on Earth, and with enough knowledge it can be utilized to counter Equestrian magic. Earth and Equestria have always been relatively "close" to each other in the multiverse. The Equestrian side finds out Earth's getting pretty close to understanding these "magical" secrets, thus a portal is opened to ensure the survival of both worlds. Nevertheless, for some reason things don't go as hoped (can't say "as planned" since they were poking the unknown anyway). Purification is the sort of "conversion" of Earth's place in the multiverse to match that of Equestria, otherwise Equestria would violently push into Earth, wreaking untold havoc.

There you have it. In the end it's an expansion/combination of CoL's and LMS's settings (though when I say LMS, I mean the original before Windchaser rewrote it into a hideous pile of potato peelings).

Let's just say this question occurred to me, and I have a completely thought out answer in Gammaverse that does *not* involve 'Celestia did it' or 'physics happened randomly' or 'Humans did it.'

You'll have to wait for Genesis to find out though.

445946
tl;dr

445946
When you write it out, please, put up a reference link to the specific chapter and lines to make it easier for the rest of us. Thanks in advance.

446148
Yep, sure thing. I might just summarize too, depending.

446157
Dammit, you just out unsarcasticated ('tis a word) my sarcastic comment.
Have a moustache!