Others trying to crack physics concept (6,6)
I believe the answer is:
string theory
'physics concept' is the definition.
'others trying to crack' is the wordplay.
'to crack' is an anagram indicator (I've seen 'cracked' mean this).
'others'+'trying'='otherstrying'
'otherstrying' anagrammed gives 'STRING THEORY'.
(Other definitions for string theory that I've seen before include "One idea in particle physics" , "Idea relating to subatomic particles" , "Cosmological hypothesis concerning all fundamental particles - retrying tosh (anag)" .)