If we were able to dig a stretch of tunnel that went straight to the centre of the Earth, jumping into it would spell immediate peril. Before you had even travelled one per cent of your journey, your body would be crushed by the immense pressure and scorched by the building heat. Then whatever remnants of you met the core itself would be completely incinerated.
But let’s pretend that we carved straight through the core and you are invulnerable to the other hazards. If that were the case, you would swiftly reach terminal velocity as you fell – about 200kph – and it’d take you just over a day of falling to arrive at the centre. Once there, you would be tugged by gravity in all directions equally, rendering you weightless – and also stuck there, floating forever!