The unknown years of Jesus (also called his silent years, lost years, or missing years) generally refers to the period of Jesus's life between his childhood and the beginning of his ministry, a period not described in the New Testament.
The "lost years of Jesus" concept is usually encountered in esoteric literature (where it at times also refers to his possible post-crucifixion activities) but is not commonly used in scholarly literature since it is assumed that Jesus was probably working as a carpenter in Galilee, at least some of the time with Joseph, from the age of 12 to 29.
In the 19th and 20th centuries theories began to emerge that between the ages of 12 and 29 Jesus had visited India and Nepal for Spiritual enlightenment inspiring from Hinduism, or had studied with the Essenes in the Judaean Desert. Modern mainstream Christian scholarship has generally rejected these theories and holds that nothing is known about this time period in the life of Jesus.
The use of the "lost years" in the "swoon hypothesis", suggests that Jesus survived his crucifixion and continued his life, instead of what was stated in the New Testament that he ascended into Heaven with two angels. This, and the related view that he avoided crucifixion altogether, has given rise to several speculations about what happened to him in the supposed remaining years of his life, but these are not accepted by mainstream scholars either.
The 18 unknown years
New Testament gap
Following the accounts of Jesus' young life, there is a gap of about 18 years in his story in the New Testament. Other than the statement that after he was 12 years old (Luke 2:42) Jesus "advanced in wisdom and stature, and in favour with God and men" (Luke 2:52), the New Testament has no other details regarding the gap. Christian tradition suggests that Jesus simply lived in Galilee during that period. Modern scholarship holds that there is little historical information to determine what happened during those years.
The ages of 12 and 29, the approximate ages at either end of the unknown years, have some significance in Judaism of the Second Temple period: 13 is the age of the bar mitzvah, the age of secular maturity, and 30 the age of readiness for the priesthood, although Jesus was not of the tribe of Levi.
Christians have generally taken the statement in Mark 6:3 referring to Jesus as "Is not this the carpenter...?" () as an indication that before the age of 30 Jesus had been working as a carpenter. The tone of the passage leading to the question "Is not this the carpenter?" suggests familiarity with Jesus in the area, reinforcing that he had been generally seen as a carpenter in the gospel account before the start of his ministry. Matthew 13:55 poses the question as "Is not this the carpenter's son?" suggesting that the profession tektōn had been a family business and Jesus was engaged in it before starting his preaching and ministry in the gospel accounts.
Background of Galilee and Judea
The historical record of the large number of workmen employed in the rebuilding of Sepphoris has led Batey (1984) and others to suggest that when Jesus was in his teens and twenties carpenters would have found more employment at Sepphoris rather than at the small town of Nazareth.
Aside from secular employment some attempts have been made to reconstruct the theological and rabbinical circumstances of the "unknown years", e.g., soon after the discovery of the Dead Sea Scrolls novelist Edmund Wilson (1955) suggested Jesus may have studied with the Essenes, followed by the Unitarian Charles F. Potter (1958) and others. Other writers have taken the view that the predominance of Pharisees in Judea during that period, and Jesus' own later recorded interaction with the Pharisees, makes a Pharisee background more likely, as in the recorded case of another Galilean, Josephus studied with all three groups: Pharisees, Sadducees and Essenes.
Other sources
The New Testament apocrypha and early Christian pseudepigrapha preserve various pious legends filling the "gaps" in Christ's youth. Charlesworth (2008) explains this as due to the canonical Gospels having left "a narrative vacuum" that many have attempted to fill.
Jesus' childhood is described in the Infancy Gospel of Thomas, the Gospel of Pseudo-Matthew, and the Syriac Infancy Gospel, among other sources.