Do you know the answer?
Prof. Dr. Lutz Köpke from the Institute of Physics at Johannes Gutenberg University Mainz knows the answer:
Preparations
First of all, this is quite a crazy idea... The interior of the Earth consists of a molten iron core whose heat would be unbearable; there is also no material that is heat-resistant enough to build the necessary tube. But who knows what the future will bring.
You should also dress warmly, because the ideal starting point is the South Pole. You should also bring enough breathing air and an astronaut suit, because the tube must be airless. As every skydiver knows, air resistance hardly allows speeds above a few hundred kilometers per hour. You would reach the center of the Earth, even slightly beyond it, but then you would inevitably be pulled toward the center of the Earth and "evaporate" there.
Jumping into a deep hole
Okay, no one could dissuade you from your plan. You're sitting at the South Pole, shivering, and you jump into the deep hole. After 21 minutes, you race past the center of the Earth at a speed of 29,000 kilometers per hour, and after another 21 minutes, you reach the North Pole and watch a few more fish through the glass tube. You can even see the polar bears from a lofty height, because you shoot almost 3,000 meters past your target.
Unfortunately, you can only enjoy the daylight for a short time, because you fall back into the hole and make your way back to the South Pole. Once there, you have to be careful and grab the helping hand, otherwise you will swing back and forth between the two poles.
Alternative "fall route"
Okay, so you're a down-to-earth kind of person, you hate the cold, and you know a smart tunnel builder. Then you can start from Mainz. However, the tunnel must not lead straight down, but in a gentle arc.
Why? In Mainz, you are rotating with the Earth at a speed of around 1,070 km per hour, but the rotational speed decreases to zero towards the center of the Earth. This means that after a few hundred meters, you would hit the wall and damage your beautiful astronaut suit.
But if the tunnel is built in an arc that compensates for the effect of the Earth's rotation, you could make it; however, you would arrive in the South Pacific at a slightly different location.
About the researcher
Prof. Dr. Lutz Köpke from the Institute of Physics at Johannes Gutenberg University Mainz conducts research on neutrinos at the South Pole, among other places. Some of the 5,000 sensors frozen in the ice are named after Mainz characters and expressions, such as Dibbegugger, Dollbohrer, Permediggel, and Margittche.