If we understand our minds as we understand the physical world — that will change everything.
Because I've been writing about the history of a particular form of mental activity, I've been especially aware of the limits of what we know about the brain and the mind, this new entrant on the stage of science. Think about it: what we know about the human mind comes from data gathered for little over a hundred years. In actuality, only since mid 20th century do we have anything approximating the sort of activity that we would call a science of the mind. For a half century's work we've done pretty well, but the bald fact is that we have almost no understanding of how the thing that affects all aspects of our lives does its work. The state of our decision making — whether it is about global warming or the human genome, about big bailouts on Wall Street or microfinancing in Asia, about single payer healthcare or not — is what it is because the machine that does all the heavy lifting is something we barely understand. Would we trust the furnace in our house if we understood it as little?
I anticipate that many of the viable candidates for "everything changers" will be striking single events such as encountering new intelligent life, the ability to live forever, and a permanent solution to the problem of the environment. Indeed, any of these will produce enormous change and deserves to be on the list. But if we are to take seriously the question of what will change "everything", then the candidate really has to be something that underlies all other changes, and hence my candidate remains understanding the mind.
From the little we do know, we can say that good people (we, us) are capable of incredible harm to others and even themselves. That daily moral decisions we make are not based on the principles of justice that we think they are, but are often a result of the familiarity and similarity of the other to oneself. These two simple types of bias happen because the mind and its workings remain invisible to us and until we unmask it meanderings, the disparity between what we do and what we think we do will remain murky.
That we have spent no more than a few decades of our entire history scrutinizing the mind should be both frightening and give hope. Whether the question is how we will deal with new life forms when we encounter them, or how we will design our lives as we prepare to live forever, or how we will generate the courage to stop environmental devastation, understanding the mind will change everything.