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# Physics/Train tunnel at the bottom of the Atlantic ocean

Question
Hi! I just read news of a mag-lev train that travels in a tunnel depressurized to one tenth of the atmospheric pressure, at the speed of 2900km/h. The average depth of the Atlantic ocean is 3349m froma quick googling. If we built the tunnel from stainless steel how thick should the ''skin'' of the tunnel be?

It's not that simple.  The tunnel would have to withstand the massive vibration an forces associated with a train of that size and moving that speed.  You really need a structural engineer, and even one of those couldn't give you a good estimate of how thick the walls of the tunnel would have to be.  That's because nothing remotely like this idea (I saw an episode on TV on the science channel about exactly what you're talking about) has ever been built.  To build one in the Atlantic Ocean, to account for the massive wave forces on the tunnel, the forces as the tunnel bends due to those forces and yet still handle the pressure and stay straight enough not to destroy the train as it passed through...it's inestimably strong.  I'm not convinced that several feet would be enough, but I don't know enough about wave forces and building structures of that scale.  Again, check for an engineer, but if their answer is less than several feet (maybe they just plugged in pressure and found out how thick a pipe would have to be just for that) then I wouldn't trust it.  Keep in mind, such a tube wouldn't go all the way to the bottom.  It would have to float under the surface.  The pressure at the bottom would be ridiculous.

Physics

Volunteer

#### Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.