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Well, in that case... I'm not sure I would use the word 'opinions' though. Anything taken seriously must be, at the very least, a well thought out hypothesis. Of course, a hypothesis must extend from what is known already. However, even pretty convincing evidence can be overturned by something new and more powerful.

One such situation, which I teach to students, and involves lactic acid. Most think it's a waste product and makes our muscles sore after exercise. It does nothing of the sort as we now know. Interestingly, if you remove the newer data about lactic acid the old theory becomes convincing again, albeit with gaps.

This is why it's so important to view science kind of like a perpetual lava flow. Always moving steadily, with new lava covering the old, but the old is still there if you look for it. Or something like that anyway <img src="/forums/images/graemlins/cyclops.gif" alt="" /> Of course some theories, no matter how much you scrutinize them, using new tools and technology they still make complete sense to those who care to understand them. Newton, Darwin, Einstein for example <img src="/forums/images/graemlins/cheers.gif" alt="" />