The two key factors that would turn such a fall into a lengthy endeavor are the resistance of air filling the tunnel, which would gradually increase to a point where air would behave more like a solid than a gas, and the friction caused by the tunnel’s sides.
"The time it takes to fall down a tunnel through the center of the Earth to the other side takes approximately 42 minutes, but only when given several simplifying assumptions: a uniform density Earth; a gravitational field that varies linearly with radial position; a non-rotating Earth; a tunnel evacuated of air; and zero friction along the sides of the tunnel," the scientists remarked.
But while this problem was fun for them to think about, both scientists remark that the technology needed to conduct such an experiment won’t be available anytime soon.
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