With Mathematics, Physics and Chemistry in Hand, You Can Walk Sideways Through Ancient Times

What should I do if I suddenly travel to ancient times and I don't have enough to eat? What, the man is about to be beaten, the government has given him a beautiful wife, and he must have a baby next year? What, foreigners are invading the Central Plains again? ... It doesn't matter. If you learn mathematics, physics and chemistry well, you won't be afraid of traveling all over the world! Are the prairie cavalry unstoppable? Is the Japanese pirate ship indestructible? Joke!