In the Newtonian description these changes are such that time is absolute: the movements of the observer do not influence whether an event occurs in the now (i.e., whether an event passes the horizontal line through the observer). However, in the relativistic description the observability of events is absolute: the movements of the observer do not influence whether an event passes the "light cone" of the observer. Notice that with the change from a Newtonian to a relativistic description, the concept of absolute time is no longer applicable: events move up and down in the figure depending on the acceleration of the observer. Arrow
Time appears to have a direction – the past lies behind, fixed and immutable, while the future lies ahead and is not necessarily fixed. Yet for the most part, the laws of physics do not specify an arrow of time, and allow any process to proceed both forward and in reverse. This is generally a consequence of time being modelled by a parameter in the system being analysed, where there is no "proper time": the direction of the arrow of time is sometimes arbitrary. Examples of this include the cosmological arrow of time, which points away from the Big Bang, CPT symmetry, and the radiative arrow of time, caused by light only travelling forwards in time (see light cone). In particle physics, the violation of CP symmetry implies that there should be a small counterbalancing time asymmetry to preserve CPT symmetry as stated above.
"The Problem of Boutonniere Deformity". Clinical Orthopaedics and Related Research. 104 (104): 116–133. doi:10.1097/00003086-197410000-00012. PMID 4607222. Nalebuff, Edward A.; Millender, Lewis H. (July 1975). "Surgical Treatment of the Boutonniere Deformity in Rheumatoid Arthritis". Orthopedic Clinics of North America. 6 (3): 753–763. doi:10.1016/S0030-5898(20)30987-1. PMID 1099508. Littler, J. William; Eaton, Richard G. (October 1967). "Redistribution of Forces in the Correction of the Boutonnière Deformity". JBJS. 49 (7): 1267–1274. doi:10.2106/00004623-196749070-00002. PMID 5622971. To, Philip; Watson, Jeffry T. (January 2011). "Boutonniere Deformity". The Journal of Hand Surgery. 36 (1): 139–142. doi:10.1016/j.jhsa.2010.10.032. PMID 21193133. Massengill, James B. (November 1992). "The boutonniere deformity". Hand Clinics. 8 (4): 787–801. doi:10.1016/S0749-0712(21)00744-7. PMID 1460075. Aiache, Adrien; Barsky, Arthur J.; Weiner, Daniel L. (August 1970). "Prevention of the boutonniere deformity". Plastic and Reconstructive Surgery. 46 (2): 164–167. doi:10.1097/00006534-197008000-00010. PMID 5423482. S2CID 39268503. Curtis, Raymond M.; Reid, Robert L.; Provost, John M. (March 1983). "A staged technique for the repair of the traumatic boutonniere deformity". The Journal of Hand Surgery. 8 (2): 167–171. doi:10.1016/s0363-5023(83)80009-4. PMID 6833725. Urbaniak, James R.; Hayes, Michael G. (July 1981). "Chronic boutonniere deformity—An anatomic reconstruction". The Journal of Hand Surgery. 6 (4): 379–383. doi:10.1016/s0363-5023(81)80048-2. PMID 7252114. Dolphin, James A. (January 1965). "Extensor Tenotomy for Chronic Boutonnière Deformity of the Finger: REPORT OF TWO CASES". JBJS. 47 (1): 161–164. doi:10.2106/00004623-196547010-00011. PMID 14256963. External links
Boutonniere Deformity at eMedicine