Time travel. Conceptual computer artwork of a warp in space that acts as a gateway to other times and places. A sabre-toothed tiger of a past ice age is shown at left. The middle image represents the present-day era. The image at right shows future contact with an alien spaceship. Many scientists believe that time travel into the past (and hence returning from the future) is impossible because of the paradoxes it would cause. However, some solutions to Einstein's equations of space-time do appear to allow brief travel through time.