What If We Dug A Tunnel Through The Earth? The Fastest Way to Get Anywhere

Follow us on Twitter: @universetoday

Team: Fraser Cain - @fcain
Jason Harmer - @jasoncharmer
Susie Murph - @susiemmurph
Brian Koberlein - @briankoberlein
Kevin Gill - @kevinmgill

Created by: Fraser Cain and Jason Harmer

Edited by: Chad Weber

Music: Left Spine Down - “X-Ray”

Long distance air travel sucks. Anyone who’s ever had to sit on an airplane for 17 hours, enduring screaming babies, terrible internet, and the constant threat of deep vein thrombosis knows how bad it sucks. I know, I know, it’s the miracle of flight, and I really shouldn’t complain. But there’s got to be a better way.

Well, I’m happy to inform you, there is a better way. A faster way, where you can travel halfway around the world in less than an hour, with no pesky seats, or even an airplane at all. All you need to do is jump… down. Into that enormous tunnel bored right through the Earth connecting your location with the exact opposite spot on the Earth - your antipode.

Oh, you don’t have a tunnel like that nearby? That’s probably because it’s a terrible idea, completely impractical when you consider the massive engineering challenges to make something like that happen.

But if you could, it would be pretty sweet. Here’s how it would work:
The circumference, or distance around the Earth, is approximately 40,075 km, but that depends on where you measure it; around the equator, or from pole to pole. So, to travel overland from one location to its antipode, you’d need to travel 20,037 km.

A tunnel, dug from one side of the Earth to the other would be, on average, 12,742 km. So it’s a shorter trip, sure, but that’s not the best part.

If you jumped into the tunnel, you’d fall down towards the center of the Earth, accelerating constantly, thanks to gravity. By the time you reached the halfway point, after falling for 21 minutes, you’d be traveling at 28,000 kilometers per hour.

Once you crossed the halfway point, the velocity would carry you back up the other side of the tunnel for another 21 minutes. This time, however, gravity is slowing you down, so by the time you reach the other end, you come to a perfect stop, just as you arrive at your destination.

In other words, the trip didn’t require any energy. You exchanged gravitational potential energy for kinetic energy on the way down, and then exchanged it back on the way up again. No energy was created or destroyed. We obey all the laws of thermodynamics here on the Guide to Space.

The trick is that you need to make sure the tunnel is a complete vacuum, so that you don’t experience any air resistance during your journey. That would cause you to fall at terminal velocity, and you’d end up stuck at the center of the Earth, completely weightless and helpless.

I’m sure the engineer in you is screaming obscenities at the screen right now. We can barely dig a tunnel just a few kilometers into the reasonable outer crust of the Earth. Forget digging down through the hotter part of the crust, into the mantle, where rock squishes and oozes around like jello. And you can completely forget digging through the Earth’s metal inner core, which probably spins faster than the Earth itself.

Now, this is practically impossible on every level. However, this idea isn’t completely terrible. Here’s the cool part.

If you dig a tunnel between any two points on Earth, you can still take advantage of the Earth’s gravity. Instead of traveling between two antipodes, you could travel a much shorter distance, without piercing so far down.
------
What two spots on Earth should be connected by a gravity train? Would you ride in one? Let us know your thoughts in the comments below.

In our next episode, we’ll let you know what it takes to become a NASA astronaut; including the “right stuff”, whatever that is. Make sure you subscribe to our channel, so you’ll get notified the moment we publish it.

Oh, and make sure you stick around for the blooper.

Speaking of bloopers, our Patreon community sees entire blooper reels, gets advanced access to all our videos, and sees no ads on Universe Today.

Join the club of 511 amazing people who support us in making great space and astronomy content. The people who make these shows even possible, like Tony Barry and David Whitlow. Want to get in on the action? Click here.

[unvergebeneid]

So you're telling me that, on a very slow Sunday morning, when it takes me three hours just to get out of bed, if I had a tunnel to my living room, I'd be there in 42 minutes without any energy expenditure on my part? That sounds like a really good deal actually.

[tyreean]

You do realize that you said you can travel anywhere on Earth in 42 minutes and it makes me wonder if Deep Thought knew about this or if Douglas Adams because the answer to the Ultimate Question is ---

[tomasbortel]

42 minutes? It's the ultimate answer to Earth travel and everything!

[marktwain]

Your little science chats are quite good: comprehensible, accurate, and thought-provoking. Thanks for taking the time!

[brandonhall]

I had like a total recall to a scene in a movie where this happens. It didn't end well.

[siegfriedarmory]

I was under the impression that if you dug down through the crust of the earth, you would encounter four elephants balancing on the back of a giant turtle.

[nilsp]

If I dig a tunnel horizontally through a molehill in my garden, does a tiny gravity train need 42 minutes to cross it?

[KieranMetcalfe]

Would you have to ensure that the two endpoints were at the same distance from the centre of gravity? i.e. - if the ground at the start is slightly lower (closer to the CoG of the Earth) than the end, you might not have enough kinetic energy to make it right the way out?

Or does all this assume that the Earth is perfectly spherical, and not an 'oblate spheroid' (or indeed flat, as I've recently stumbled across many videos promoting... sheesh...)

[Dickking]

Neat video. You did however forget to mention that a gravity train would, in addition to being in a vacuum, also have to be a maglev train to eliminate friction from the wheels. Also, for the hole through center of the Earth, the Earth's rotation (the fact that it rotates faster at the edges in particular) would probably cause you to hit the wall at some point through your journey, which wouldn't be a pleasant experience.

[rhydlew]

Excellent video Fraser. Sorry, incorrect about coming to rest at the other side (great opportunity for a follow up video). You've assumed that the DURATION of acceleration at high and low gravitational effect are mirror images either side of the centre/core, they aren't. The first half of the distance starts with low velocity and ends at vmax. This means that the duration spent at high gravitation is far longer than the duration spent nearer micro gravitation. Loads of acceleration. Then, however the second half of the distance starts with vmax at low gravitation, far less TIME spent there than before, then the vessel is still at quite high velocity when entering the high gravitational effect nearer the surface, and spends less TIME in that effect. If anyone has trouble understanding this please familiarise yourself with the gravitational slingshot. Decades ago engineers used it to make the Voyager probes the fastest machines ever made. So actually you'd fly out of the other side and probably (not sure) break away from the atmosphere, then slowly get attracted back, but at extremely high altitude. It would actually repeat, think of it as a very UNSTABLE orbit (obviously ignoring air, the moon or other bodies).

[gw]

I have a question:

Do black holes accelerate things to faster-than-light speeds? So if i fall into a supermassive black hole will i fall faster than light speed before I got to the center?

[kylehazachode]

Would the rotation of the earth cause you to bounce off the walls of the tunnel as you attempt free fall to the other side?

[CMDR_Evolution]

Very interesting! Keep up the great work. Thank you

[tubedude]

Do you get stretched as what happens with black holes if you jump through it

[ClapBoomBoom]

If I'm observing from the other end and another person free falls from my side just as the other person who free-falled from the first end arrives. It can't be possible for two objects to be going different directions can they? Also me as an observer, how is it possible for me to see someone levitate back up instead of falling down?

[phoule]

cool concept to imagine, and the gravitation pull and push makes for an elegant system!

[michaelmacomber]

I think there should be a tunnel connecting Washington DC and the Sahara desert for obvious reasons.

[israelgonzalez]

As you travel deeper into the Earth would there be any pressures on the body by the Earths weight on top of you?

[MaRkPerHouR]

gravity decrease as you reach the centre of earth. so basically acceleration is decreasing the deeper you get. also, put in mind the mass of the earth that will be above you. this also exert gravitational forces on you. so there is a big chance you will be stuck in the middle of earth.

[doncarlodivargas]

tunnels between A and B will work if I am at A and want to travel to B, but if I for some reason want to travel elsewhere someone have to dig a tunnel to that destination, something tells me there will be a couple of tunnels criss-crossing inside the earth, where do we deposit all the materials from all those tunnels? out in the ocean?

and, what do we do if we hit valuable minerals while digging, start excavating and make a new tunnel elsewhere?