Is it possible to steal time by flying west?

 By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

02 June 2013

Simon Mumbere wonders if it possible to steal time. He writes: “If I started a journey at mid-day, I am curious to know the speed at which I would have to walk, drive or fly so that its mid-day all through my journey (regardless of the duration of the journey). Will I have succeeded in stopping time – albeit figuratively? If my journey takes a whole year, will I have added a year onto my age?”

The answer is that you have to move westwards at the rotational speed of the Earth. The calculation is quite straightforward; only two quantities are required: the time taken to rotate once and the circumference of the planet.

Now, even though we normally say that the earth takes 24 hours to rotate once on its axis, this is not accurate. The correct duration is 23 hours and 56minutes. I do recall explaining the reason for the discrepancy during the early months of this column in the year 2004. Nonetheless, we can still work with 24h for now.

The second quantity required is the circumference of the earth. This can be evaluated easily from the diameter of the planet which is about 12,800km. Thus at the equator, the journey round the globe would be about 40,000km (pi-D = 3.14x12,800).

Therefore the speed comes to1,675km/h (40,000km divided by 24 hours). Now I don’t know any person who can run that fast (not even Usain Bolt!) and I also don’t know of any car that can reach that speed. Therefore, Simon is left with only one option: flying.

But even regular aeroplanes don’t reach higher than 1,000km/h – most of the commercial jets cruise at between 800km/h and 900km/h. The Concorde is the only civilian jet that flies faster at 2,100km/h… but it is no longer in service! Therefore Simon might have to talk to some one at the Air Force to take out on a joy-flight in a fighter jet. Good luck with that one!

Assuming that he gets one, the jet must fly due west in order for Simon to experience the effect he desires – the sun remaining stationary in the sky. But would he manage to steal time? If he remained in flight for 12 months, would he add a year to his age?

Of course not! If he started the journey from Nairobi at noon today (Sunday), he would fly back through here tomorrow (Monday) at the same time. And he would find the time to be noon at all the places that he flies over. But when would it change from noon on Sunday to noon on Monday?

We know for sure that when he would get back here at noon tomorrow, Monday. But when flies over Uganda, DRC and all the way to Gabon at the West African coast, it will still be Sunday. Same day as he crosses the Atlantic Ocean into Brazil.

So the question is: where (not when) will it change to Monday? The day would change when Simon crosses the International Date Line somewhere just before the island of Kiribati. By the time he reaches Christmas Island, he’d find the people preparing for Monday lunch.