The most likely method of communication with extra-terrestrial life-forms is probably through...

Question

A. Interstellar space travel (spacecraft).

B.  Radio

 C. Smoke Signals.

Answer 1

Physical law implies that interstellar travel requires enormous amounts of energy or long travel times. Sending signals, on the other hand, requires only modest energy expenditure, and the messages travel at the speed of light.

major reference

Seth Shostak 

1. Astronomer, SETI Institute, Mountain View, California. Author of Sharing the Universe: Perspectives on Extraterrestrial Life and numerous professional papers and popular articles extraterrestrial life: Life beyond the solar system