Bitul Torah means the very severe sin of not learning Torah when one is able.

What is considered a part of "learning Torah" is extremely important because of the sin of "bitul Torah".[Bitul Torah means the very severe sin of not learning Torah when one is able. ]

So when some rishonim [mediaeval authorities]like Ibn Pakuda and the Rambam include Physics and Metaphysics in the category of learning Torah, the significance is great. What I mean is that one is obligated to learn Torah all the time. And if Physics was not a part of Torah, then it would be possibly bitul Torah. [Unless one was doing it for the sake of making a living.] 

The significance of the concept of bitul Torah is not just to make one guilty if e is not learning when he could. Rather it is to point out the awesome sweetness of Torah that one would not give up after having tasted it even once. The only thing is thatt I am saying that to some rishonim, math and physics come under the heading of "Learning Torah"

To so degree you can see this in Psalms 77, 105 and other places where it says to speak of God's wisdom in his creations.

picture of my Dad with the U-2 camera.

 

That was after he invented the Infra Red telescope. Then he was offered a job at to make a camera to put on the U-2 airplane to see if the Soviets were about to launch a military strike against the USA. [That is, to see if there was any indication anywhere inside the USSR if they were planning on a strike of any sort against the USA. No one in the USA had any info, and President Eisenhauer had been advised to launch a preemptive strike against the USSR. Instead, he exercised caution, and decided to create the U-2 project. 

[In fact, the U-2 camera showed that the USSR was not planning any sort of attack on the USA. So the U-2 had the great merit of avoiding WWIII.]

 One is not allowed to mention the name of an idol and certainly not to swear an oath by an idol. Now for a regular prohibition of the Torah one gets lashes. [That is the punishment unless something else is stated openly.] But here things are a little different. One who swears by an idol has not done an act. The Gemara in Sanhedrin 63 side A says the opinion that one gets lashes for swearing by an idol is coming like R Yehuda who holds one can get lashes even for a prohibition that does not have an act. 

The Rambam brings that one does get lashes for this and the Raavad asks that that is only like R. Yehuda. But the law is not like R. Yehuda but rather R Yose who held one does not get lashes for a prohibition that does not have an act. 

Rav Shach answers that Rabin who stated the original version of the law before the Gemara made its corrections to his statement said simply one does not get lashes for a prohibition that does not have an act except swearing and vowing. [And that original statement was said according to the law which is like R Yose. And the way that original statement was said involved not just swearing a false oath but also swearing in the name of an idol.]

I am trying to figure out what possible reason the Rambam would have had to ignore the correction of the Gemara.

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 "The evil inclination is dressed in mitzvot". [This is from the LeM of R.Nahman of Breslov. vol I. perek 1. ] The Satan never comes to  a person and says come and do a sin. Rather it is always "come and do a mitzvah." But hidden in the mitzvah is some poison that is unseen. You you this same idea in the commentary of the Gra on Mishlei in the beginning where the evil inclination comes and says: "Come and bring peace offerings."

So my approach is to avoid anything and everything that has any connection with the religious world unless it is straight from the Gra  according to the approach of Rav Shach and Rav Kinyesvsky. [The trouble is the aspect of the trojan horse that has seeped and infiltrated everything in the religious world] 

Without the Litvak approach based on the Gra, one lacks the backbone

 I see sometimes in the books of Rav Nahman statements that need to be taken with a grain of salt. His approach is basically to get to the core essence of Torah. But that is not to say that his approach is the whole shebang. Without the Litvak approach based on the Gra, one lacks the backbone [the structure]. It would be like a a person with no bones. 

the emphasis of the Litvak world was to learn in depth along the lines of Rav Haim of Brisk and Rav Shach.

 Rav Nahman has in one Torah lesson the idea that when one finds that he learns but does not understand the advice is to shout  the words. On occasion I have tried that myself and it works, but it seems to be advice for occasions that present the opportunity to do so. Because in general, I find it simpler to take the basic path of learning of Rav Nahman of just saying the words and going on more practical.

Also Rav Nahman did bring the idea of review both in the LeM and Sefer HaMidot. But clearly according to the Conversations of Rav Nahman 76, that is only a part time affair. Still I want to bring one way of review that I have tried and seems to work for me. As I progress through a book, I go one page forward and then keep my place and then review all the way back to the beginning. Then I go one more page forward and then from that new place also review back to the beginning. 

[But I should add that there were different ideas of how to learn in depth in Shar Yashuv in NY and the Mir in NY. But in any case, the emphasis of the Litvak world was to learn in depth along the lines of Rav Haim of Brisk and Rav Shach. [That is a more global approach than the previous achronim later authorities [like the Pnei Yehoshua and Maharsha] that concentrate more on local issues.]