In the tenach, there is
“for a thousand years in Thy sight are but like yesterday when it past“ (Psalm 90:2)
By the way , and this is really significant..
there is a kabbalistic teaching that the world(I guess universe not just earth) is 15 billion years old
That does correspond with science of today!
So it's a very significant thing.
note- I may have made an error in my maths here, but it seems ok to me. This is a well known thing, the 15.3 billion calculation by rabbi yitzchak of akko
Rabbi yitzchak of Akko based it on the kabbalistic teaching that the world is created and destroyed 6 times, lasting 7000 years each time.
So that's 42,000 years passed by before our world was created.
Rabbi Yitzchak of Akko points to
“for a thousand years in Thy sight are but like yesterday when it past“ (Psalm 90:2)
says that these 42,000 years the kabbalists speak of are to be taken as divine years.
A divine day is 1000 earth years (see tenach verse)
(it's 1000 times longer than an earth year)
A divine year is 365.25 divine days.
So,
equate them, earth years are of course the smaller unit.
divine day . = 1000 earth years
so we want to know how many earth years, are 42,000 divine years.
Because the world was created after 42,000 divine years.
divine year = 365.25*1000 earth years
= 365,250
42,000 divine years = 42,000 * 365,250
= ~15.3 billion years.
note - there is a dispute as to which cycle we are in, so some say final cycle, so 42,000 divine years passed, meaning indeed, 15.3 billion years.
others say second cycle (which I guess is 5.1 billion 14000*365250).
Here are 2 sources
http://www.jewishmag.com/8MAG/WORLDS/worlds1.htm (Classic webpage)
http://www.thehope.org/toreng0.htm (something I just picked up now)
To repeat myself..
rabbi yitzchak of akko has it htat,
1 divine day is(=) 1000 earth years.
our world was created after 42,000 divine years
divine day is the bigger unit,
we want to have the number of divine days to however many are in 42,000 divine years.
so times LHS by 365.25(days in a divine year)*42,000(to get days in 42,000 divine years)
Do the same on the RHS, which already has 1000 , so it's 1000*365.25*42,000
Another way to look at it is,
1 divine day = 1000 earth years
1 divine year = 365,250 earth years
42,000 divine years = 15.3 billion.
Another way is
365.25*42000=1.5 million
that's how many divine days before earth was created.
earth days are a smaller unit by 1000, so
1.5 million *1000= 15 billion.
sometimes it's worth thinking of it in a few ways to check yourself and not get tripped up in the mental arithmetic.