<prompt> Bheka isigaba esingezansi bese uphendula umbuzo emva kwalokho ngolimi olufanayo nesigaba: Ukudlula: Ngokwezimfundiso ezivamile zokulinganisela, ayikho into ebonakalayo engafinyelela noma idlule ukushaya kokukhanya. Ayikho ithonya lomcimbi A elingafinyelela kunoma iyiphi enye indawo X ngaphambi kokuthi ukukhanya okuthunyelwe ku-A kuye ku-X. Ngenxa yalokho, ukuhlola yonke imigqa yomhlaba yokukhanya i-null geodesics kunikeza imininingwane ebalulekile ngesakhiwo esibangela isikhala nesikhathi. Lesi sakhiwo singaboniswa ngokusebenzisa amagrafu kaPenrose-Carter lapho izifunda ezinkulu ezingenamkhawulo zesikhala kanye nezikhathi zesikhathi ezingenamkhawulo ziyancipha zihlanganisiwe ukuze zilingane ebalazweni eliphelele, kuyilapho ukukhanya kusahamba ngama-diagonals njengasemagrafu ajwayelekile wesikhala nesikhathi. Beqaphela ukubaluleka kwesakhiwo esiyimbangela, uRoger Penrose nabanye basungula lokho okwaziwa ngokuthi i-geometry yomhlaba. Ku-geometry yomhlaba wonke, into efundwayo akuyona isisombululo esisodwa noma umndeni wezixazululo kuma-Einsteins equations. Kunalokho, ubudlelwano obuyiqiniso kuwo wonke ama-geodesics, njenge-Raychaudhuri equation, nemibono engeziwe engaqondile mayelana nemvelo yendaba ngokuvamile ngesimo samandla isetshenziselwa ukuthola imiphumela ejwayelekile. Umbuzo: Ukukhanya kumelwe kuthunyelwe kusuka kuphi kuya kuphi?  <response>: A kuya ku-X 