This question was prompted when a mate of mine came around last night at 2030hrs, after being kicked out by his Mrs after an argument. We had a beer together, and after seeing me on this forum, started asking questions about scientific theories. His question was simply... "If Scientific Theories keep changing, then how can we [lay people] trust science?" What a great question I thought! I informed him that scientific theories are always open, because as technology advances, and as we are able to make more and more observations, things may change. A new unexpected observation may lead us to modify a theory I used the fact that the "advance in the perihelion of Mercury" which was unpredicted by Newtonian gravity. I told him that Einstein and GR being a more precise theory, was able to explain it. I explained that Newtonian mechanics was still correct, and still used everyday on Earth and even in relation to space probes etc. I explained that GR, even though it is more precise, [on large scales] was lacking at quantum/Planck scales. I explained the fact that as scientific theories continue to make correct predictions and match further and further observations, they become more and more certain. I gave a couple of examples. I named six scientific theories so well supported that all we can expect in the future is some tinkering and additions with the main theoretical application not changing. I explained how the BB, GR particle physics fit well together without contradiction. I explained the incompatibility of probably our two greatest theories, GR and QM. I explained the fact, that limitations in our observations, just means that some scientific theories are incomplete. Finally, I gave him two old books of mine by Hawking and Sagan..."A Brief History of Time" and "Cosmos" I then sent him home to his Mrs at 2200hrs, went to bed contented in what I had achieved. He is 64 years old, but you are never to young to learn! Please Register or Log in to view the hidden image!