Imagine that the Hollow Earth theory is actually right. We've been living inside a planet shell. The gravity: we are "glued" to the ground, unlike this explanation that conclude we are should be in zero gravity.

I imagine that a person can sail/trek around the earth, and conclude that earth is spherical. Yes, but you're living in it, not on it.

So, by circumnavigation, can one deduce that they are living within earth, as opposed to on earth? I'm interested in "simple ways", and scientific ways.

Note: They've been living there for ages.

  1. Perpetual day, means no night. The light source is a "sun" in the center of the shell. The light is just similarly blinding like the sun.
  2. Atmosphere pressure is reduced when you go to the center.
  3. Opposite side is not visible.
  4. How the gravity works? Just like you got pulled to the ground perpendicularly.
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    $\begingroup$ you want scientific explanation for handwaved situation? $\endgroup$ – L.Dutch Nov 17 '17 at 5:02
  • $\begingroup$ @L.Dutch It looks like the question is "How can people determine that they're living inside a hollow earth?" I swear I've heard this question before. $\endgroup$ – sphennings Nov 17 '17 at 5:50
  • $\begingroup$ They have! I distinctly remember answering a couple $\endgroup$ – nzaman Nov 17 '17 at 6:31
  • $\begingroup$ I don't get this. You state in your commets that we still have a day/night cycle. If we had day all day, this would prove it, yeah. Do I understand it correctly that everything seems to appear exactly as we lived on this earth? Then nothing will prove it ... $\endgroup$ – Raditz_35 Nov 17 '17 at 7:23
  • $\begingroup$ @Raditz_35 and because they originally lived in perpetual day, I don't think day/night cycle will provide a clue to figure out they lived inside a shell. $\endgroup$ – Vylix Nov 17 '17 at 8:47

To answer core question of:

So, by circumnavigation, can one deduce that they are living within earth, as opposed to on earth?

Surprisingly, yes. When going in circles, you are pushed away from the center (by virtual force, that is, but anyway). So you "just" need to go fast enough for the chance to be measurable. Let's assume that your world is not rotating itself. Change of 1N would do in such situation. Let's also assume standard 100kg weight and radius from our own Earth. v = (√Fo · √r)/√m gives us "cruising" speed of ≈250 m/s — quite a lot. Thus, you would need a more precise force measurement, or heavier block of steel. Also if your world is rotating, you need to be able to factor it into your calculations. But in principle it is possible.

  • $\begingroup$ I love this answer, but I might be missing something: For this to work, you wouldn't have to (fly, sail, drive) in circles around earth but really any path - how short it can be would only be limited by the time it takes to measure - would yield the same result? Qualitatively of course, not the same number because they will not live inside a perfect sphere. $\endgroup$ – Raditz_35 Nov 17 '17 at 9:33
  • $\begingroup$ So if for example, the inhabitants use a train in a straight path, they will feel that the gravity is slightly amplified? Very interesting approach. $\endgroup$ – Vylix Nov 17 '17 at 9:36
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    $\begingroup$ @Raditz_35 long enough to stop accelerating along the path and measure, and then long enough to make few measures and minimize ±. It depends on their tech level, but I guess pretty darn long, especially at this speed. $\endgroup$ – Mołot Nov 17 '17 at 9:36
  • $\begingroup$ @Vylix yes, exactly. $\endgroup$ – Mołot Nov 17 '17 at 9:36

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