Q. How can you know for sure that there really is life after death, instead of the other belief that we are just mechanistic organisms that live and then die and then are nothing?
A. There are different processes of acquiring knowledge, such as by direct perception, by experiment, by logic and example, by hypothesizing etc. But none of these methods bring us to the point of conclusive knowledge, especially about something that lies beyond our sense perception; all these processes are subject to defects. The best way of acquiring knowledge is therefore to hear from qualified authorities. We accept the Vedas as authority on all subjects, because they are not man-made but given by the Supreme Lord, the creator Himself. It would be a big mistake to think that Vedic knowledge is nothing but a set of blind beliefs or that it is fictitious; the Vedas are very scientific and reasonable. From Vedic evidence, such as Bhagavad-gita, we can get very clear and scientific understanding of our true nature as spiritual entities beyond the combination of material ingredients, in the shape of the material bodies which we presently occupy.