So there are no aliens but they are super advanced no aliens...i think i understand!!!
Einstein said something along the lines of 'nothing travels faster than light'. So far this has been proven to be true. To get a particle to a close approximation of light speed requires tremendous energy, the energy required to get an exploring, advanced alien and a containing vessel to light speed (or above) comes into the realms of a large suns output. Is this feasible?
I understand the closest planet considered capable of sustaining life is about 350ly from us. (Although that changes often as new proto planets are discovered). So exploring, advanced aliens would need exceptionally long lives lives dont you think?
Life is not complex, in its basic form, DNA it comprises of 5 chemicals and a base. But there is a lot of DNA in a human, cat, bird, snake, even an ant. I think you are confusing complexity and quantity.