Did the burning down of the library at Alexandria really destroy most of the knowledge that the west had acquired up to that point?

I've always heard that I would be unable to communicate were I to travel back in time any farther than the 1900's, but the documents that exist from that time are still comprehensible by today's standards. Would I still be able to communicate with contemporary English?

Is there any evidence that the Jolly Roger ever flew or there was such a person as Blackbeard or Bluebeard?

To be clear, I understand the controversy surrounding the movie ie. arguably propaganda by the Chinese government as part of its one China policy etc. That said, I was wondering if there was any truth in its claims that Qin Shi Huang Di's actions laid the bureaucratic/pseud-nationalist/cultural framework for a united "Chinese" country.

I understand that cost would probably be the main issue, but were they really bleeding that much cash? And did this outweigh the benefits? It seems that (mostly) electrified rail systems, often with their own right-of-ways, would be massively useful in urban transportation. Were they just another victim of the increasing popularity of the automobile?

For example, would Peter or John have been pronounced the same way during Christ's life?

Were ironclads effective against wooden ships? If so, by how much?

Indigenous peoples of the Americas make up 52 million people, of less than 1% of the world's population, according to Wikipedia. This number is in the hundreds of millions if including Mestizos. Before apocalyptic plagues erased Native American societies from the face of the planet, and New World crops increased the population of the Old World, what percent of humans were Native American?

How exactly did this sect of Christianity become a relatively large part of the European population? The reason I don't understand why is because the basic tenants of Calvinism seem incredibly depressing. To me personally, the idea of likely being damned without any possibility of changing that fate is not a belief system that sounds appealing. Add on to that that you still have to live an incredibly moral life of work and praying despite your predestinated fate, and I simply can not understand it. How did this form of Christianity catch on with people? What was appealing about it?

I understand that the British didn't want the fleet falling into German hands to challenge their naval superiority, but why didn't they allow the fleet to retreat to a port in the UK?

I'm not that well-versed in the JFK assassination, but I do know there seems to be a lot of dispute about the Warren Commission's official account. Do the alternative scenarios hold any water?

Are the 'multiple gunmen' theories actually considered credible (or even likely) by historians, or are they simply a cultural phenomenon, and fun to speculate about due to the huge amount of attention surrounding the event?

If so, how?

I have read a few books about the Spanish civil war and I still can't quite understand how the constitution of 1931 was so liberal. I realize that most people were more leftist but obviously the right still had a lot of power and influence.