Are there ghosts in the world? Since there are no ghosts, what makes the ancients say that there is a heavy yin at midnight, and how did a "ghost" come from?

Your question is a bit big, it's hard to say. Whether there is a ghost or not, then judge for yourself. If you think there is, there is. If you think not, then not. Because this is subjective, not objective.

As for 12, it is not accurate, or "the ancients" is not accurate at the moment. In fact, most of these so-called ancient legends you have seen are legends or sayings of the Ming and Qing Dynasties. For example, you are "ancient", so-called Yin Qi is the heaviest, and the time to meet ghosts is from 5 pm to 7 pm. All this is just some statements made by different people in different times.

The source of the word "ghost", the word "ghost Oracle Bone Inscriptions", should be the letter A above, symbolizing tortoise shell and divination, and there is a man kneeling below. So the word "ghost" originally refers to things like sacrifice and divination. In the early history of China, people in Shang Dynasty were more keen on divination and sacrifice, and many important things were decided by God through divination. Therefore, it is recorded in the book that "businessmen still worship ghosts". Later, after many changes, the word has become countless different concepts, often mixed, and different countries call it different.