Exposing PseudoAstronomy

November 12, 2012

Falling through Earth

Filed under: general science,movies,physics — Stuart Robbins @ 8:18 pm
Tags: , , , , , ,

Just a quick post for today (busy busy here as usual, stuff should settle down a bit come December …). What would it be like to take an elevator trip through Earth from one side to the other?

Apparently, in the remake of the hilariously (poor science-)fiction movie Total Recall, the remake which I have not seen, there is a plot point of taking an elevator trip through Earth’s center from one side of the other. Apparently this is the only way to safely travel from one city to the other … I hope it’s not just some stupid thing that seems “cool” that serves no other purpose than to spend a budget on special effects.

Anyway, I came across a Wired article today where a physicist spends great detail explaining what would it actually be like to travel through Earth’s center. As with all great investigations when we have too much time on our hands, he even does numerical simulations, though it looks like he graphed in Excel … but I won’t hold it against him.

He shows several interesting things, including that the elevator would reach speeds no slower than 8 km/sec (around 5-6 miles/second). That’s really really fast. If he includes the higher density of Earth’s core, then you reach speeds up to 50% faster than that, even.

He also addresses the concept of weightlessness. This is something that all physics majors learn about in detail in Classical Mechanics classes (Physics I on steroids after your first and usually second year). But, I’ve always found it somewhat difficult to easily convey why, without drawing diagrams of circles and triangles, you would be weightless if you were stationary at Earth’s center. He goes through that in agonizing detail before letting you know that, actually, in the scenario in this version of Total Recall, you’d be weightless the whole time because you’re in free fall.

So, as I said, quick post for today, head over to Wired if you have a few minutes to reach about the physics of taking an elevator trip through the Center of the Earth.


  1. I would say plate tectonics could potentially make the trip a bit shaky before entering the deeper part of the earth.

    Comment by Johan Normark — November 13, 2012 @ 12:30 am | Reply

  2. I believe there is a solid ball bearing at the centre of eartth Principles of pressure transformation of gas into liquid into solid and reverse?

    Comment by sleeping8 — November 13, 2012 @ 2:01 am | Reply

  3. I need to find a book or document that will explain the variables in the equations, since the Dr. Allain provided none. He apparently assumes we all know or can easily access the definitions for ourselves, so no need for him to do so. Too many different variables, some with multiple meanings, depending on the context of the formula in use at the time, or even from moment to moment. For example, “m” can mean “meters” or “mass”. I can guess at some, but not enough to follow with any real understanding. I basically had to accept his assertion that people in the elevator would be weightless throughout the trip, without being able to follow the proof. Makes me feel a bit frustrated…

    Comment by Rick K. — November 14, 2012 @ 7:18 pm | Reply

    • In all of the equations, m is mass. Only in one of his graphs is it ever used as the unit “meters.”

      F = force
      G = gravitational constant
      r = distance from center (r-hat (r with the carot ^) means a vector)
      ME = mass of Earth
      ρ = density
      π = 3.1415926…
      k = Hook’s constant for a spring (varies by springs)
      T = time / period of oscillation

      Comment by Stuart Robbins — November 14, 2012 @ 7:24 pm | Reply

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