Why Your Map Would Be Wrong By Lunchtime

Your phone knows where you stand because it is, in effect, eavesdropping on clocks in space. Satellites broadcast the time, relentlessly, and your phone calculates its position from how long each signal took to arrive. It is, at bottom, a timing problem masquerading as a map.

Simu yako inajua uko wapi kwa sababu, kwa hakika, inasikiliza kwa siri saa zilizoko angani. Satelaiti hutangaza muda, bila kukoma, na simu yako huhesabu mahali ilipo kutokana na muda ambao kila ishara ilichukua kufika. Kwa msingi wake, ni tatizo la muda lililojivalisha vazi la ramani.

Here is the inconvenient detail. Those clocks do not tick at the same rate as the one on your wrist. Further from the planet's mass, time runs slightly faster; moving at speed in orbit pulls the rate the other way. The two effects fail to cancel out, and the satellites end up gaining roughly thirty eight millionths of a second every day.

Hapa kuna jambo lisilo la kufurahisha. Saa hizo hazipigi mwendo sawa na ile iliyoko mkononi mwako. Mbali zaidi na uzito wa sayari, muda huenda kwa kasi kidogo zaidi; kusonga kwa kasi katika obiti hurudisha mwendo huo upande mwingine. Athari hizo mbili hazilingani kikamilifu, na hatimaye satelaiti hizo hupata ongezeko la takriban sehemu thelathini na nane za milioni ya sekunde kila siku.

That sounds like nothing. It is not. Light travels about thirty centimetres in a billionth of a second, so an uncorrected error of that magnitude compounds into roughly ten kilometres of position error per day. Your blue dot would wander off the street, then off the town, before dinner. The clocks are therefore built, deliberately, to run at the wrong rate on the ground, so that they arrive at the right one once they reach orbit.

Hiyo inasikika kama si kitu. Si kweli. Mwanga husafiri sentimita thelathini hivi katika sehemu ya bilioni ya sekunde, hivyo kosa lisilorekebishwa la ukubwa huo hujilimbikiza hadi kufikia kilomita kumi hivi za kosa la mahali kwa siku. Nukta yako ya buluu ingetangatanga kutoka barabarani, kisha kutoka mjini, kabla ya chakula cha jioni. Kwa hiyo saa hizo hujengwa, kwa makusudi, kuendesha kwa mwendo usio sahihi ardhini, ili zifike mwendo sahihi mara zinapofika obiti.