Science has revealed that our solar system consists of 9 (or 8) planets and the sun, the star of the system, and that there are more than 300 billions of stars in our galaxy, the Milky Way. It is estimated that there must be about half a trillion planets in the Milky Way. If only 1 in every 10.000 planets have the conditions to sustain life, then there must be 50.000.000 planets in our solar system that might contain life.
Our earth is about 4.5 billion years old, and began to form approximately when our solar system began to form, some 7 billion years after the Big Bang. So some of the previously mentioned planets must have been born millions of years before earth. We could then assume that life on these planets would have more than enough time to develop science and technology times higher than ours. You only need to think how much our technology developed within 100 years...
If we are now able to talk about time travels and black holes and wormholes and staff, imagine what these civilizations would have done within a million years of evolution... Most probably a spacecraft like the Enterprise would be an obsolete model...
So, where is everybody??? Why don't we see evidence of their existence?