Digging a hole straight through the Earth is an extremely popular thought experiment. It can teach people about so many properties of our planet as well as some pretty cool physics. However, the process of digging such a hole is impossible, and not just because the interior of our world goes through molten and liquid layers before meeting the solid inner core. Even on a planet or moon that is solid throughout, the pressure experienced by a deeper layer would be impossible to cut through.
But we are armed with our sophisticated thought technology, and we have dug our hole. Our beautiful hole of roughly 12,756 kilometers (7,926 miles) is ready. I am about to cut the ribbon to inaugurate the completion of the work when you run past me and jump in shouting “Cannonball!” A solitary tear runs down my cheek. You have just jumped to your death.
Some like it hot
Our hole through the Earth is a death trap, for many reasons. The first thing that would kill you is the temperature. If you have ever been down a mine, you might have noticed that it gets hot. The deepest humans have ever drilled is the Kola Superdeep Borehole, which reached just over 12 kilometers (7.5 miles) or about 0.1 percent of the length of our imaginary hole.
The reason why they stopped drilling was the temperature. Just 12 kilometers down, the bottom of the hole reached a temperature of 180°C (356°F). The scientists working on the project did not expect such a value, it was much higher than the models had estimated.
If it is any consolation, it won’t take long. The journey through a hole across our planet is estimated to take 38 minutes and 11 seconds. You would be roasted much sooner than you get to the other side.
Saddened by your loss, I turned on my time reversal machine (another patented invention in Thought Space) to before you jumped. I explain what happened in that other timeline, and ask you to wear a heat protection suit but not to interrupt my ceremony. As I go to cut the ribbon once again, you barge in and jump. Despite the protection of the suit, I know you are going to die once again.
This time, the killer is pressure. You will be crushed by the massive increase in pressure. At sea level, you are experiencing about a few tens of kilometers of air above you. In the hole, you’d get thousands of kilometers. The air will become so pressurized and compressed that it will experience phase transitions, likely becoming a superfluid. And you will become part of that concoction.
Once again, the time reversal is put to work. I explain the situation, and you point out that if the pressure gets so high, we probably have evacuated all the air from the surface of the planet, killing most life forms, including all 8 billion of us on the surface. Cross with you for pointing this out, I go back in time again to the design phase and make sure the hole is under vacuum.
You are now slowly lowering yourself into the airlock. And dive, safe from temperature and pressure. And then you die. Ok, this one is on me. The design has the hole going from outside your house to the other side of the world, and you are bringing with you the rotational acceleration you had when you left, due to the spin of the Earth. But as you move inside the Earth, this makes you drift into the walls. At high speed. So you will be banging on the walls, faster and faster, like a ragdoll. That's got to hurt.
We had a good run
The solution to that is having the hole through the axis of rotation of the Earth. Having relocated it there, you can now jump safely from the North Pole, arriving in the South Pole 38 minutes and 11 seconds later.
You might still die because no vacuum is perfect, so a bit of air might slow you down in the middle and make you lose the momentum you need to attach yourself to the opposite airlock. This could be fixed with a strong push from the beginning.
Well, that depends on whether I have forgiven you for pointing out the dark, apocalyptic nature of my thought experiment.