Understanding the yovel year

This year is the shmita year in Israel, following the Torah rule according to which the land should be let to lie every 7 years. 7 shmita years are considered the jubilee. However, although we are required to observe the shmita, we are not requested to observe the yovel until all the Jewish people will dwell in the land of Israel, according to their portion assigned to them as tribes. Practically, since 600 BCE, when the tribes of Gad, Reuven and almost half of Menashe went into exile, the yovel is no more applicable. It occured the destruction of the second Temple and the disbandment of the Sanhedrin.

According to Rambam (Mishne Torah, 10:15), the laws of letting the land rest on the yovel year are the same in all respects, to the laws for shmita years. Whatever agricultural work is forbbidden in the shmita year is also forbidden in the yovel and whatever is permitted in the shmita year is also permitted during the yovel. In both cases, the requirements regarding not working the land are similar when it comes to the release of the land. 'You shall make a shmita means' to refrain from plowing, sowing and reaping, leaving the land to rest, 'to make the day of Shabbat'. 

However, which do have their own mitzvot, with some slights differences are between the two. During the yovel years, the indentured servants should be emancipates and during the seventh year, all the debts should be canceled which is not required during the jubilee. 

There is a shmita of the money and a shmita of the land, as a year when all economic development, from the financial to agricultural activities are meant to stop. 'All the work should stop' during this Shabbat Shabbaton. 

The exile occured as a consequence of ignoring these requirements too. According to Gemara on Shabbat 33a, 'As a punishment for incest, idolatry and the non-observance of the years of shmita and yovel, exile comes into the world: (the Jews) are exiled, and others come and dwell in their place'. Thus, according to Vayikra (25:10), the jovel is only observed when all the 12 tribes of the Jewish nation are living in Israel, when the Jewish nation will be back again: "And you shall sanctify the fiftieth year, and proclaim freedom throughout the land for all who live in it", most specifically when each tribe is living its assigned part of the land. 

Rambam, in Mishne Torah, Hilchot Shmita VeYovel (10:4,8) made his own calculations of the years since the destruction of the Temple, but assumes that his calculations are not relevant anyway. Although not even Torah observant Jews are keeping the yovel year, there are some opinions according to which the yovel can be in fact respected because each of the 12 tribes is already represeted in the land, even only partially.