is to assume that they are a biological beings like us, we automatically assume that they are biological beings that travel the universe. None of the videos, pictures about ufos, has been proven as extraterrestrial spacecrafts, but we assume that those UFOS are extraterrestrial.
We know that there is extraterrestrial life out there, you do not need proof for this, is common sense.
The real problem comes here, the nearest star is alpha centauri, it would take 5 years at the speed of light to reach that star, the only technology that extraterrestrials are using would have to do with traveling at the speed of light or travelling by bending space and time, like a black hole or warp travel.
Problem is that a biological being would be destroyed by traveling at the speed of light, not only that, all the energy required to travel at such speed would incinerate the beings inside ships, any biological being would be destroyed by traveling through time or warp travel, a biological body would not be able to stand these kinds of travels
Maybe extraterrestrials are some type of artificial intelligent beings, this would allow them to be completely unaffected by the energy required to travel at such speeds or allows them to travel through time.
Maybe they are biological beings that send artificial intelligence inside their ships, to explore the universe just like we send robots to explore the universe for us, the only difference is that their robots are as intelligent if not more intelligent than us.
In retrospect I am just assuming too but I can't be the only one who believes that aliens don't have to be creatures similar to us?