Saturday, May 3, 2014

G-Train through the Center of the Earth

Humans have always looked up in the sky, fascinated more by birds than moles, we built hot air balloons, the Wright brothers flew and finally NASA took us to the moon (Which is almost 5 decades ago, but that is a rant for another blog post). Humans have travelled 384,400 kms to the moon and the voyager is away from the Earth. What we have not done is scratched the Earth’s surface.

An old QI episode (G for Gravity) talked about drilling a hole through the center of the Earth and the travel time if the tunnel was frictionless through it would be 42 minutes and 12 second. This is called a “Gravity Train” and is quite a popular concept. The more interesting thing about the “Gravity train” is that it does not need to pass through the center of the Earth. Even if we cut a cord across any point of the Earth to another, the train will get from one end to the other in ~42 minutes in frictionless conditions.

A gravity train route that cuts through a chord of Earth looks like this –

If we move things around such that Gravity always points down then the gravity train looks like a massive roller coaster –

This seems to be a great solution to the world transportation problem. Get from anywhere to anywhere in less than 43 minutes and the only energy that is required be used to overcome friction and drag. You start at the top of the roller coaster, build momentum, go as far as you can up the other way and top up with some power when steam runs out due to friction.

However, it is difficult to drill a hole through the center of the Earth. It is surprising how quickly we will get to magma if we start digging downwards, after about 20-30kms of digging and you have almost created a man-made volcano! (More on this evil plan in a future blog post) Meanwhile, we will dig sideways. The furthest we have gotten in terms of drilling deep is the Al Shaheen Oil Field  ~12.5kms which is a surprising 0.19% of the distance to the center of the Earth, and this was a bore hole and not quite a tunnel. Suppose we could tunnel this deep – How far can our gravity train travel?

So from the plot above if we can dig a tunnel that has a max depth of 12.5 kms which is close to the deepest drilled hole we have today we can travel ~810 kms on the surface of the Earth. That is Bangalore – Mumbai, New York – Detroit and London – Zurich in less than an hour. That is an average speed of ~1000km/hr. What’s more, there is heavy return for development of technology, for every 1 km we can go deeper, we can travel ~ 30 kms more on the ground in the same time.

All we need is some focused energy to get this done. Half a century ago people thought going to the moon was a ludicrous idea. It’s difficult to convince investors why it is worthwhile to go to the moon today, but we can convince them that this will change the world and be profitable. It’s been almost 50 years since we were on the moon, come on engineers – Challenge Accepted?

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