I propose that intelligent life is improbable generally speaking. The other issue is distance. Assuming there is an energy breakthrough and relativistic speeds are possible, the craft will be destroyed long before arriving at a destination. Think collisions and blueshifting of radiation. At non-relativistic speeds, you are looking at extremely long transit times. Think 40,000 years to 200,000 years. No energy source can last that long. You ship would have lost it's energy long before arriving at a destination. Biological entities would have died in the first 100 years. Robotic entities cannot function without an energy source.