The reason travel into the past is, at the least, a dangerous proposition, is due to the logic underlying the Heisenberg Uncertainty Principle. One cannot perceive without interaction, and that interaction may alter the subsequent flow of events in unpredictable (and perhaps catastrophic - see sensitive dependence on initial conditions and the butterfly effect) ways. Even the gravity of our bodies could alter things in unexpected manners. To travel into the past would be to alter the past's future, our present. If it were ever found to be possible, it should be forbidden in the interests of self-preservation. Joe