The most satisfying way of searching for life outside this Solar System would be to encounter beings from another planet. Unfortunately distances to even the closest stars, such as Alpha Centauri (about 4 light-years away), are so great that human travel to a planet of a Sun-like nearby star seem unfeasable for a long time to come. NASA Pioneer-type of spacecrafts travel at speed of 10 Km/sec, or 36,000 Km/hr. Although this speed seems quite high, even compared to the speed of jets (which travel at about 900 Km/hr), it would take 120,000 years to reach the closest star.
The speed of a spaceship can be increased, but then one would neeed much more energy to get it going. Actually, in interstellar space there is no drag or friction; thus there will be no need of energy to keep the spaceship going at constant speed. The problem is that the spaceship needs to be accelerated from rest to the desired speed, and this takes energy, lots of energy.
One could think that would be desirable to have interstellar travel
at speeds close to the speed of light. Unfortunately, according to the special theory of relativity by Albert Einstein, as the spaceship approaches the
speed of light, enormous amount of energy are required since, due
relativistic effects, the mass of the spaceship becomes increasilngly
The most efficient way would be to use an engine based on fusion, or
an engine based on the collision of matter with antimatter (antimatter
particles have the same mass but opposite electric charge of the
matter particles). When a matter particle and its antimatter counterpart meet, their rest mass is converted in energy according the
Einstein's equation E=mc2, where m is the mass and c is the
speed of light. This energy is then available for propulsion.
Machine to smash particles of matter into their anti-matter
counterparts have been built on Earth in order to study the physics of
elementary particles. To build an engine based on matter-antimatter
fuel is well beyond our current engineering capabilites.
Throughout history, human beings who have thought about meeting creatures from other regions of the universe have relied on their human intuition and experience to imagine what such an encounter would be like. This common-sense approach has led them typically to picture a physical interchange with extraterrestrial aliens, a face-to- face confrontation perhaps ending in friendship or in violence. The example of Orson Wells radio broadcast of the "War of the Worlds" is emblematic. But the insights that astronomy offers suggest that the best means of interstellar communication consists of radio messages, not spaceflight. If we can rely on scientific analysis, we should anticipate an exchange of television programs, not a showdown in space, as the first encounter with other civilizations.
Related link: see section "Contact"