Wehaveperson A floatingnearby a massiveobjectwith a lotofgravityandperson B justcasuallyfloatinginanemptyvoidofspace.
Person A shines a greenlaserbeamtowardsperson B.
Becauselightis a formofvibration, thelaserbeamhas a colorthatcorrespondsto 600 trillionvibrationseachsecond.
Nowlightisalso a formofenergyandasthatbeamoflightcomesoutofthatgravityofthemassiveobjectitloses a lotofenergy.
Thislossmeansthatthereis a decreaseinfrequency.
Sobythetimethatbeamoflightreachesperson B itsfrequencywillhavedecreasedbysomefactor.
Thatmeansinsteadofthegreenlightat 600 trillionvibrations a second, person B getsonlylet's say 10 billionvibrationspersecondwhichis a microwaveradiobeam.
Sinceperson A creates 600 trillionwiggleseverysecondwhileperson B onlygets 10 billioneverysecond, theonlywaythiscanhappenisifonesecondononeastronaut's clockisnotthesameasonesecondontheotherastronaut.
Inotherwords, itonlytakesonesecondforperson A tocreatethose 600 trillionwiggles.
Butitwilltake 60,000 secondsornearly a dayforperson B toreceivethem.
Sothisiswhathappens.
Ourclocksrunat a wildlydifferentratesandbyclocks I don't meanjustmechanicalorelectronicdevicesbutalsobiologicalclockslikeyourheart, lungs, yourbrains, etc.
Person A takes a breathandtakesanotherbreathandmeasures a fewsecondsbetweenthetwo.
Forhim, everythingfeelsnormal.
Clocksticksthewaytheyaresupposedto.
Ontheotherhand, person B, watchingperson A through a telescope, seeseverythinginslowmotionwithseveraldayspassingbetweenthetwobreaths.
Sonowwe'revisitingthissceneagainfromInterstellar, youshouldget a betterunderstanding.