Can we travel in time? Time machine and Aliens

A time machine is a virtual machine for the implementation of time travel. Such machines, which any forward and backmovement should allow in time are fictions: While taking advantage of time dilation, time travel into the future according to current knowledge possible, but the construction of a machine that accomplishes a journey into the past is, after current knowledge, not possible.
Time machines are a popular theme of science fiction. Seriously engaged in science among others on the basis of Einstein'sassumptions of a modifiable space-time and recent findings of reduced spontaneous formation of matter in addition to largemasses only with the transmission of 'information' in the past.