2 ms·

It is actually quite challenging to show that the earth is round in a way that does not require you to take anyone's word for anything Perhaps if you live nowh

by causi 5y ago

It is actually quite challenging to show that the earth is round in a way that does not require you to take anyone's word for anything Perhaps if you live nowhere near an ocean and have no trees from which to hang a pendulum and can't afford a rangefinder for lining up two boards with holes in them.

lisper 5y ago
You would be shocked at how many people there are who have never seen an ocean. You would be shocked at how many people there are who live within an hour's drive of an ocean who have never seen it. There are a lot of things that the typical HN reader takes for granted that are unimaginable luxuries for billions of people. I think you will also be surprised how hard it is to fill in the details of the experiments you are alluding to.
- causi 5y ago
  The only one you need details to is the aligned-holes experiment. The others are just observation. You watch the bottom of a ship vanish before the top. You watch a swinging pendulum deviate from its beginning alignment more and more over time.
  - lisper 5y ago
    You have obviously never actually tried to set up a Foucault pendulum. It is not so easy. You can't just hang a weight from a rope tied to a tree. That won't work. Also, Foucault's pendulum does not show that the earth is round, it merely shows that the earth is rotating. Flat disks can rotate. Also, ships do not always sink below the horizon. The right atmospheric conditions can refract the light in a way that causes them to be visible at a much greater distance than the straight geometry would allow. But this explanation can be inverted to claim that it is the vanishing that is due to atmospheric effects and that the non-vanishing ship is the accurate reflection of the geometry. Falsifying that hypothesis is, again, not so easy.
    - MatteoFrigo 5y ago
      In fact, the sun at sunset which appears to be above the horizon is already well below the horizon, precisely because the atmosphere is less dense at higher altitudes. See https://www.feynmanlectures.caltech.edu/I_26.html https://www.feynmanlectures.caltech.edu/I_26.html Fig. 26-7 (Presumably this is also true at sunrise, so the day is longer than it "should" be from purely geometric considerations.)

by causi 5y ago

lisper 5y ago

You would be shocked at how many people there are who have never seen an ocean. You would be shocked at how many people there are who live within an hour's drive of an ocean who have never seen it. There are a lot of things that the typical HN reader takes for granted that are unimaginable luxuries for billions of people. I think you will also be surprised how hard it is to fill in the details of the experiments you are alluding to.

causi 5y ago
The only one you need details to is the aligned-holes experiment. The others are just observation. You watch the bottom of a ship vanish before the top. You watch a swinging pendulum deviate from its beginning alignment more and more over time.
- lisper 5y ago
  You have obviously never actually tried to set up a Foucault pendulum. It is not so easy. You can't just hang a weight from a rope tied to a tree. That won't work. Also, Foucault's pendulum does not show that the earth is round, it merely shows that the earth is rotating. Flat disks can rotate. Also, ships do not always sink below the horizon. The right atmospheric conditions can refract the light in a way that causes them to be visible at a much greater distance than the straight geometry would allow. But this explanation can be inverted to claim that it is the vanishing that is due to atmospheric effects and that the non-vanishing ship is the accurate reflection of the geometry. Falsifying that hypothesis is, again, not so easy.
  - MatteoFrigo 5y ago
    In fact, the sun at sunset which appears to be above the horizon is already well below the horizon, precisely because the atmosphere is less dense at higher altitudes. See https://www.feynmanlectures.caltech.edu/I_26.html https://www.feynmanlectures.caltech.edu/I_26.html Fig. 26-7 (Presumably this is also true at sunrise, so the day is longer than it "should" be from purely geometric considerations.)