We've made incredible scientific and technological strides as a society, but do we as individuals know anything more than we ever have? Everything I know about science I've learned from books, magazines, newspapers, teachers, family and friends. I mean, I haven't done any of the research myself, and I can't imagine being able to do enough of the research myself to really know even a small fraction of what the scientific facts we take for granted. So do I just take all these books, teachers, friends, etc. at their word? If so, how is my situation any different than somebody who lived 500 years ago and also got all his information from books, teachers and friends?

When it comes to the justification of many of our beliefs--particularly those about the way the world works, and the way it is beyond our immediate environment--I don't think we are in a qualitatively different position now than we were 500, 5,000 or even 50,000 years ago. It's plausible to think that homo sapiens of that vintage shared our lingiuistic ability; and if so, this presumably helped them rely upon the testimony of others in their band (who in turn often stood at the end of long chains of such testimony) to form beliefs about the state of things across the mountains, or in the generations before they were born, or in their causal connections (e.g., how you start a fire), or in their cosmic ordering. As you point out, we too rely--and can't really help but rely--upon the claims other people make about the way the world is and works. Of course, there are differences in degree. We have available to us many, many more sources of testimony (along with many more sources of quasi-observational...

In an illegal drug such as LSD, the chemical reaction with your brain causes you to see things, such as motion trails or lighting effects, that cannot be seen by someone who is not on the drug. Assuming that is true, would it be possible that LSD gives its user the ability to see something that actually exists but cannot be seen by the human eye without the chemical adjustment of the drug in the brain?

I suppose it depends upon how you understand these effects. Take "motion trails". If we regard these as illusions--that is, we hold that there aren't really colored trails that follow a moving object like colored silk scarves attached to the end of the object--then the drug may be allowing us to have certain illusory experiences that we might not otherwise achieve, but it isn't allowing us to see colored trails that actually follow objects, since there are none. So LSD allows us to have an experience as of a motion trail, but not to actually see one in the world. (This is just what we should say about the straight pencil that looks crooked in a glass of water: I have a visual experience as of a crooked pencil, but am not actually seeing one, since there is none to be seen.) This is not to deny, though, that drugs may heighten our veridical perception of our environment. That to me is the most interesting feature of drugs. Perhaps LSD does this at times, but I wouldn't know.

If enough people believe in something, will it be true? For example, does reality conform to the laws that we, as a group, choose to believe in?

It might be worth adding, nevertheless, that there are some facts that obtain in virtue of enough of the right people believing that they do. You and I are "going out" if and only if we each believe that we are--or so it seems. It also seems that the market will go up if and only if enough of the right people believe that it will. As Alex rightly points out, though, these cases cases don't extend very far--e.g., to making the sun rotate about the earth.