We are taught that the world is to exist for 6,000 years. Then there will be another thousand years of Tohu. The cycle then starts again. The Talmud (Sanhedrin 97a) comments:

Rav Katina said: “Six thousand years the world will exist, and one [thousand] it shall be desolate (harov), as it is written, ‘And the Lord alone shall be exalted in that day.’ (Isaiah 2:11)” וְהָיָה֙ בַּיּ֣וֹם הַה֔וּא שֹׁ֣רֶשׁ יִשַׁ֗י אֲשֶׁ֚ר עֹמֵד֙ לְנֵ֣ס עַמִּ֔ים אֵלָ֖יו גּוֹיִ֣ם יִדְרֹ֑שׁוּ וְהָֽיְתָ֥ה מְנֻחָת֖וֹ כָּבֽוֹד: And it shall come to pass that on that day, Hashem shall continue to apply His hand a second time to acquire the rest of His people, that will remain from Assyria and from Egypt and from Pathros and from Cush and from Elam and from Sumeria and from Hamath and from the islands of the sea. Abaye said: “Two [thousand years it will be] desolate, as it is written: ‘After two days will He revive us, on the third day He will raise us up, that we may live in His presence.’ (Hosea 6:2).A tanna taught per Rav Katina: “Just as the Shmita year occurs one year out of seven years, so too does the world have one thousand years out of seven thousand that are fallow (mushmat), as it is written, ‘And the Lord alone shall be exalted in that day’ (Isaiah 2:11); and further it is written, ‘A psalm and song for the Shabbat day’ (Psalms 92:1) – meaning the day that is altogether Shabbat – and also it is said, ‘For one thousand years in Your [God’s] eyes are but a day that has passed.’ (Psalms 90:4)”

The Tanna deBei Eliyahu Rabbah taught,

The world consists of six thousand years: two-thousand years are unformed (Tohu), two-thousand years of Torah, two-thousand years the era of the Moshiach, but due to our many sins many of those years have already been lost.

In the 600th year of the sixth thousand [i.e., 5600, or 1839–1840 CE], the gates of wisdom on high and the wellsprings of lower wisdom will be opened. This will prepare the world to enter the seventh thousand, just as man prepares himself toward sunset on Friday for the Shabbat.

The Zohar explains further,

The redemption of Israel will come about through the mystic force of the letter “Vav” [which has the numerical value of six], namely, in the sixth millennium. … Happy are those who will be left alive at the end of the sixth millennium to enter the........

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