It'd probably accelerate, then get stuck in t'middle. That's the centre of gravity (in our little region of space) so it'll be pulling everything toward it.
Otherwise the aussies would fall off the planet.
For the second thing, I'd probably presume you'd get squashed like a tin-can rather than exploding. - Kinda like a mechanical meat recovery machine, without the mechanical bit. We could send down a bass- or banjo-player to test this theory.
Or would you simply float in the middle (zero gravity), if it were possible to create an open tunnel?
The pressures and heat would be immense though, so making a tunnel that remains 'open' would be - currently - far beyond impossible. Diamond melts at 3800K, while the centre of the Earth is allegedly 5000-7000K, so even if the tunnel was made of diamond it would still melt.
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PS > And another thing! Will the Ti|3 have user customisable/importable wavetables?
A ribbon-controller or XY-Pad might be nice, too, please! Thanks!