Most of what passes for "Torah" is false. The way you know this is by the Mishna in Sanhedrin [perek Chelek] where it lists those who have no portion in the next world. Then there is added to this category "he who reads outside books." The Rif and Rosh both explain "outside books" as books that give explanations of Torah that are not from the sages of the Mishna and Gemara.
[What are books of Chazal (the Sages) that explain verses of the Old Testament? The Midrash. e.g. Midrash Raba. Tanchuma, Sifrei Sifra, Mechilta, etc.]
Therefore most of what passes as "Torah" nowadays thus comes under the category of "outside books".
So outside books do not refer to Natural Sciences. Rather this refers specially to books that claim to be books of Torah but give different explanations from what is brought in the Midrash and Gemara.
