GPS, relativity, and nuclear detectionYouTube↗  IA↗(long shot)
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Dutch Stef van Schie
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We take navigation for granted these days - GPS receivers guide airplanes, cars, and
Tegenwoordig zijn wij gewend aan navigatie - GPS ontvangers sturen vliegtuigen, auto's en
even cell phones!
zelfs mobiele telefoons!
But did you know that the Global Positioning System is basically a big clock in space?
Maar wist je dat het Globale Positie Systeem eigenlijk een grote klok in de ruimte is?
There are thirty GPS satellites in orbit, and they just broadcast where they are and
Er zijn dertig GPS satellieten in een baan om de aarde, en zij versturen gewoon waar ze zijn en
what time it is.
hoe laat het is.
All your phone GPS has to do is receive signals from four satellites and it can triangulate
Het enige dat je telefoons GPS hoeft te doen is signalen ontvangen van vier satellieten en dan kan het
its location in the four dimensions in which we live – three space and one time.
zijn locatie in de vier dimensies waarin we leven bepalen - drie in ruimte en één in tijd.
But actually it's not that simple! In order for navigation to work, the satellites carry atomic clocks accurate to the nanosecond – otherwise your GPS receiver might tell you you're halfway across town when you're
Maar het is niet zo makkelijk! Om navigatie te laten werken, hebben de satellieten atoomklokken met een precisie van een nanoseconde - anders zegt de GPS ontvanger misschien dat je in het
still in the driveway.
midden van de stad bent, terwijl je nog op de snelweg bent.
And special relativity tells us that moving clocks run slow, while general relativity
En de speciale relativiteitstheorie zegt dat bewegende klokken langzaam lopen, terwijl de algemene relativiteitstheorie
tells us that clocks run faster higher in a gravitational field.
zegt dat een klok sneller loopt in een hoger zwaartekrachtveld. Deze effecten heffen
These effects don't quite cancel – general relativity wins out and time indeed runs faster
elkaar niet precies op - de algemene relativiteitstheorie wint en tijd gaat inderdaad sneller in een baan om de aarde met
up in orbit with the satellites!
de satellieten!
But some of the engineers working on the first GPS satellite couldn't bring themselves to
Maar sommige ingenieurs die werkten aan de eerste GPS satelliet konden maar niet
believe that their clock would actually run fast just from being higher up, so they sent
geloven dat hun klok echt sneller zou lopen, omdat ze hoger waren, dus stuurden ze
it up uncorrected! Within minutes it was off by enough to impair GPS navigation, and by the end of the day,
het ongecorrigeerd de ruimte in! Binnen een paar minuten week het genoeg af om GPS navigatie aan te tasten, en tegen
GPS receivers would have been wrong by tens of kilometers!
het einde van de dag, GPS ontvangers zaten fout met tientallen kilometers! Vanzelfsprekend,
Needless to say, the engineers turned the correction back on, and these days they trust
zetten de ingenieurs de correctie weer aan, en vandaag de dag vertrouwen ze de algemene
general relativity!
relativiteitstheorie!
Oh, and one last thing - GPS is also a nuclear weapons detector: there are always at least
Oh, nog één ding - GPS detecteert ook nucleaire wapens: er zijn altijd tenminste
four GPS satellites visible from any point on earth, and because of this, any nuclear
vier GPS satellieten zichtbaar vanuit elk punt op aarde, en vanwege dit, elke nucleaire
detonation will be seen by enough satellites to pinpoint exactly where and when it took
ontploffing wordt gezien door genoeg satellieten om exact te bepalen waar en wanneer het
place.
ontplofte.
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