You need at least 2,000 days to walk around the Earth

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

12 April 2009

Peter Wanjohi is still not convinced that the Earth is round. He says: “You contradict yourself…when you say that there is a triangle originating at an observer at the seashore to a ship at the horizon. Doesn't that prove exactly what you are trying to disapprove, a flat earth, or does the curvature of the world only start at the horizon?”

Peter further argues that if the observer had a powerful telescope able to “see around the world, there would still be a triangle extending all the way.” This, he says would be proof “that light travels in a straight line and that the sea level is truly level.”

He therefore concludes: “This creates a paradox of a flat yet round earth, which in my opinion is resolved by a weird conclusion that the earth is not three-dimensional but multidimensional with spatial singularities or boundary conditions all over. What do you think?”

Well, you lost me on that last statement regarding “…multidimensional spatial singularities or boundary conditions….”, nevertheless, I must hasten to correct one false assertion: No matter how powerful a telescope is, it cannot see around the world!

In fact, all telescopes mounted at eye-level at the sea shore can view only 5km of water surface…after that, there are clouds and stars beyond the horizon. The reason is simply that light travels in a straight line – as Peter rightly says.

Therefore, light from “below” (as opposed to “beyond”) the horizon can never reach the telescope…so it cannot be seen. The problem is not the magnifying power; it is the direction from where the light is coming.

Let me also clarify a point about the triangle I alluded to last week. It has three straight sides: one from the eyes to the horizon, a second one from the eye to the feet, and the third line from the feet to the horizon.

Now the third line does not run on the surface of the sea. If it did, then Peter would be right to conclude that the surface is flat. Since the Earth is round, the third line of the triangle runs under the sea. You may want to visit my website (www.MungaiKihanya.com) to see a picture showing how this is done.

 If you are still not convinced, then this question from Muita Wangoko might help: “If I start moving from one point on earth and move straight ahead, is possible that I will come back to the same place one day and time?”

Yes you will, Muita: assuming that there will be bridges over the seas, lakes and rivers that you will find on your straight path, your journey will be at least 40,000km.

I say “at least” because I assumed the Earth to be a smooth round object. In reality it isn’t: there are hills and valleys that increase the actual distance walked. Thus you might find yourself walking 50,000km.

At the average walking speed of 5km per hour, that would take you 10,000 hours. If you walked five hours a day and rested the remainder of the time, the journey would take you 2,000 days, or five and a half years…but since there are no bridges, this might prove an impossible expedition!