From:  thread on how to teach biology genetics science type topics in our schools:

On the age of the universe, there are likewise pieces of information that I believe are not well known which bring things like Big Bang cosmology as being more speculation than concrete science. Far from being the place to hang our hat on, Big Bang cosmology is so speculative that I believe it's a mistake. I would like to refer to the Rashi on the gemara in Hagigah, where it says that ten things were created on Day One, the last two are midas ha’yom and midas ha’lilah, the units of day and the units of night. Rashi says that this means the twenty-four hours of Day One. The Rambam says the same thing. He asks what about the time before the creation of the sun, and he said that the day was still a regular day, because it was just one revolution of the sphere. I have no less than ten Rishonim and Hazals like this that all talk about the young universe, six twenty-four hours. I think that people sense that it's a fudge to tell them that it’s millions of years when our whole mesorah indicates that we are talking about thousands of years.

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