Some fundamental beliefs
I believe that the power of the human mind can explain everything that has happened after the universe began; this is a belief because we have not actually achieved that and we never will. However, the scientific method is incomparably superior to anything else humans have ever used to explain the world. We can maniuplate things we can't see. We can make predictions. We can understand and observe phenomena which takes place over millions of years despite our short lifespan. We can wield some of the fundamenal powers of nature. We can cure disease. To humans from only a few centruies ago, we would seem like gods, except for our lack of immortality. Our capabilities would be even more beyond their ken than the most extreme natural phenomenon. Yet our method for achieving all of this can be taught to a child in a few years. The ideas of science are powerful, liberating and destructive to people who relied on other ways of defining the truth (usually religions based around supernatural explanations). Science has always had enemies and it always will.
I believe that we can explain the universe by rules which do not change arbitrarily, and I do not believe there are forces or entities above nature which have the power to modify these rules. I believe that there has never been a reliable observation that proves the existence of a supernatural power.
I believe that an observation is only reliable when it can be repeated and observed by independent people. I believe that an explanation which can make a prediction confirmed by a reliable observation is truth. I believe that if there are two explanation for an observation, the preferred observation is the one which has less assumptions about unknown factors. I believe that things which are held to be true may be proven to be untrue by later observations. In this definition, I don't define what "independent" is. Accepting this creed relies on cultural values; it only works if we can broadly agree on what "independent" means, and exactly how reliable we need to be. Science is not black and white: one school of thought says that science can never prove anything is true, only that something is false, and that we measure our progress by the ever-growing pile of things which are false.
So it is important that these ideas be broadly understood and broadly agreed upon. If I was able to travel back in time 10000 years, I would be the only person on earth who knew the volcanoes were not an act of angry god, but this knowledge wouldn't do me any good since I couldn't compress the entire Renaissance into a few years.
I believe that life after death is impossible because the human mind is a material organ existing only in the observable universe, and that entropy explains that brain death is irreversible. The essense of human existence is at the very least our memories and senses. Our senses, such as vision, are clearly material (they exist in the human body). Our memory is a vast database of information stored in the cells of our brain. Since neither of these disappear into thin air after death, the concept of life after death is contrary to rational thought and observed facts.
I believe that people can collectively decide what is right and what is wrong. I do not believe that humans need the concept of eternal punishment or eternal reward to motivate decent behaviour.
I therefore do not believe that any human can speak with authority conferred by a god.