Absolyutnyi nul' temperatury - nachalo otscheta absolyutnoi temperatury po termodinamicheskoi shkale (shkale Kel'vina). Absolyutnyi nul' temperatury raspolozhen na 273,16 K nizhe temperatury troinoi tochki vody (na 273,15S nizhe nulya temperatury po shkale Cel'siya; sm. Temperaturnye shkaly). Soglasno tret'emu nachalu termodinamiki (teoreme Nernsta), pri stremlenii temperatury sistemy k absolyutnomu nulyu temperatury, k nulyu stremyatsya i ee entropiya, teploemkost', koefficient teplovogo rasshireniya. Pri absolyutnom nule temperatury prekrashayutsya haoticheskie dvizheniya atomov, molekul, elektronov, opredelyayushie temperaturu sistemy, no ostayutsya ih regulyarnye dvizheniya, podchinyayushiesya kvantovoi mehanike, naprimer nulevye kolebaniya atomov v reshetke, s kotorymi svyazana nulevaya energiya.

Poluchenie temperatur, predel'no priblizhayushihsya k absolyutnomu nulyu temperatury, predstavlyaet slozhnuyu eksperimental'nuyu problemu