Some hindus love bragging about how the ancient scriptures of full of science and how modern science is just re-discovering those ancient truths. One of the most frequently cited "proofs" for this ancient knowledge is the time of one day of Brahma which is equal to 4.32 billion years. That is close to the age of Earth (around 4.54 billion years) and those proud hindus wildly thump their chests with "You see! It matches with the value given by science. Hinduism has all the truths!"
Let us take a closer look at hindu cosmology. (The timelines are from Wikipedia)
One day of Brahma (4.32 billion years ) consists of 1000 mahayugas. Each mahayuga has 4 yugas. In the current Brahma's day, 27 mahayugas have elasped. 28th is in progress with the present yuga being Kaliyuga. So around 120 million years (1 mahayuga = 4.32 million years. 27*4.32 + (4.32 - 0.43) = 120.096) have elapsed out of the 4.32 billion years of the current Brahma's day. So according to hindu cosmology, the age of the current cosmos is just around 120 million years.
Also at the end of a mahayuga, Kalki appears and cleans up the Earth of sin. This usually involves some sort of catastrophe. According to hindu cosmology, 27 such cleansings should have taken place at 4.32 million years apart. But modern science has no record of such cleansings.
According to science humans evolved around 400,000 - 250,000 years ago. But as per hindu cosomology humans have always existed, so in the current cycle they have been around for 120 million years. Even if we consider only the current mahayuga, at least 3.88 million years have elapsed and humans were there in all of that time. Again science has no evidence of humans dating back to 3.88 million years ago.
Even if we extend the creation/destruction cycle of the cosmos to 100 years of Brahma and not to one day of Brahma, and given that 50 years of Brahma have elapsed, it would give the current age of the cosmos to around 155 trillion years. Again science doesn't agree with that number.
So out of all the numbers spouted by the hindu texts for the age of cosmos, just one number comes close to a scientific value. But that is enough proof for the hindus who think their scriptures are the ultimate science. It doesn't matter most numbers don't match with the observed Universe.
