Buddhism appears to be about the only major religion that fares quite well with modern science. After all, the Buddha himself exhorted his followers not to believe in his teachings merely he was their teacher, but to examine the teachings carefully and test them against their own understandings, reasonings and experiences. However, when it comes to the law of karma and the doctrine of rebirth, it seems to have a hard time explaining these concepts in light of modern science.
Here Buddhism appears to say the same thing as do the other religions, namely that things do not come to an abrupt end when one dies. There is a kind of afterlife. And this is the key issue regarding the relation between Buddhism and science. Buddhism may have an intricate system of cosmology and analysis of the mind and matter which could be compared to that of modern science, after all science has somethng to say about cosmology and analysis of mind and matter too. But when it comes to karma and rebirth, then modern science is competely silent. So if Buddhism is to be compatible with science, then how should karma and rebirth fit in?
One way out is to challenge sciene to come up with their own explanation of the phenomenon. That there is no scientific explanation of karma and rebirth yet is the failure of modern science, not of Buddhism, which has its own elaborate theory. This, of course, assumes that the phenomenon is real and is already there to be experienced. Many Buddhists believe that this is the case, so do followers of other related religions such as Hindus and Jains.
So instead of Buddhism having a problem of hot being able to explain karma and rebirth; it is science itself that finds itself with the problem of not being able to explain it. But how do we know that karma and rebirth are already there? Well, this doctrine is based on the idea that every event in the universe happens through causes and conditions. These are technical terms in Buddhism. A ’cause’ is that which changes to become another thing. So the seed is the cause of the oak. A ‘condition,’ on the other hand, is that which corroborates the cause’s effective becoming the result. Thus moisture is a condition without which the seed would not sprout to become the oak. There are a variety of conditions, and the intention of one who plants the seed in order to grow an oak counts as a condition too.
So our lives as human beings all arise out of causes and conditions. We see karma at work when we find that no one human being is exactly the same as others. Everyone is unique; the question is how to explain this uniqueness? I do not mean merely genetic uniqueness, since identical twins can lead very different lives, thus each of them is unique, even though their genes are identical. One twin perhaps gets richer than her sister. But why?
To look at another example. One buys a lottery and wins one million dollars, while his friend buys another lottery at the same place and at the same time but wins nothing. Here the most that science can do is just to leave the whole thing to chance. But the key idea in Buddhism (and in many others) is that there is no chance event in the universe. Everything that happens, happens because of some set of causes or conditions (Leibniz called this “The Principle of Sufficient Reason”). So there must be something that explains why this particular person won the lottery whereas nobody else did.
So karma and rebirth are a way to explain the phenomena mentioned above. Otherwise there just would be no explanation at all as to why this particular person and not another won the lottery, or why one twin got a rich husband and her sister got a so-so one.
However, believing in karma and rebirth does not mean that you are forever doomed to live within their influences with no way out. Nothing is further from the truth in Buddhism. It is true that what explains your current situation might refer back to your karmas, but that does not mean that you yourself have no free will to shape up your own causes and conditions for your future well being. Otherwise there just would not be any reason for practicing the Buddhist Teaching. There is always the cause and condition for your eventual Liberation lurking inside. It is there in all of us, all of beings in samsara. It just needs to be brought out and polished.