Aliens may only be at the prehistoric time.

This is also the reason why we cannot find traces of aliens in this vast universe.

If there is really a civilization in the universe, perhaps that text is still in its infancy . That's what concludes Dimitar Sasselov, an astronomer at Harvard University.

This conclusion is his explanation for a concept called "Fermi paradox". This paradox stems from the fact that there are billions of galaxies in the universe, billions of stars and planets that can be accommodated. However, by this time, we still have not been able to find out any alien life. And according to Sasselov, the reason is simply because they haven't developed yet.

The planets in the universe are still very . young.

Sasselov said the planets in the universe are still really . young . Based on his calculations, the universe and galaxies only created a stable environment to form the planet about 9 billion years ago. In particular, planets with rocky surfaces like Earth are about 7-8 billion years old. In addition, the complex chemical compound needed for life also appeared during this time.

Therefore, it can be said that humans have come too early, so we cannot find aliens yet.

In the next 10-20 years, we will find life beyond Earth in the form of bacteria.

NASA also seems to agree with Sasselov, claiming that in the next 10-20 years, we will find life beyond Earth in the form of bacteria.

Previously, an Australian scientist had another theory, that aliens might be extinct. During the study, Aditya Chopra - Ph.D. of the Australian National University - found that the newly formed life in the universe often died very quickly due to unstable environmental conditions on young planets.

He said: "Early life was very fragile, and rarely evolved quickly enough to survive. Most of the environment on early planets was unstable. To create a planet conducive to survival , life forms need to regulate greenhouse gases as well as water and carbon dioxide to maintain stable surface temperatures.

This can be considered a reason why alien creatures cannot evolve at the same time as our human species.