How is affected the thermodynamic description of physical systems when   gravity is incorporated?
  This research is aimed at the revision of the thermodynamic concepts and their relationship with the General Relativity Theory (GRT) and how physical systems are affected when gravity is included in their thermodynamic description. We found that in the case of light, the entropy in an extreme stage is proportional to the area. This is due to a reduction of freedom degrees of the system, since gravity imposes constraint on the number of microstates which are accessible to the system and this is consistent with the holographic principle. 
W. A. Rojas C. and R. Arenas S
gr-qc