We have never seen definitive proof of aliens. Some people think they have seen aliens, but they were never seen again, or they had no evidence, so we think they might have just seen aliens in a dream.
This does not mean that real aliens don’t exist though. We think there’s 35 trillion (35,000,000,000,000) planets in the universe, so I think one of them might have aliens !
The REPORTS of aliens are a really fascinating phenomenon. It turns out that all of them have alternative explanations. Some are flat-out hoaxes, like the ‘alien autopsy’, but a lot more are people fooling themselves – for instance, there’s a big increase in ‘mysterious alien lights in the sky’ reports around any celebration when people are sending up fire lanterns!
As Nike says. given how many planets there are estimated to be in the universe, scientists have been interested for a long time in the possibility that life could exists on some of them. So there are plenty of people LOOKING for signals from outer space that might indicate there’s something out there. These projects often involve radio astronomy (monitoring radio ‘noise’ from space looking for signals). You can read about this here. Some people even ‘donate’ the computing power of their home computer to help sift through the radio noise from space in the hunt for signals. Nothing’s turned up yet, though.
If by aliens you mean the little grey or green men in films, then I do not think that they have really visited us! It is a long way to come simply to kidnap people! It is more likely that alien life in our solar system exists in the form of bacteria under the surface of some of Jupiter’s moons.
There are predicted to be many, many planets in the galaxy similar to ours that could support life. There may even be planets that support life that is silicon based, rather than carbon based like on earth. It is entirely possible that whole advanced civilisations have evolved, developed and died multiple times through the life of the universe, as the universe has been around for an incredibly long time. I do believe that aliens are real, but it is unlikely that we will meet aliens from civilisations like ours, as the distances between stars is unimaginably vast.
However, there are lifeforms on earth right now, possibly even in your back garden, that are so incredible they could almost be alien! Have you ever heard of a creature called a tardigrade? A tardigrade, or water bear, is an animal about 1mm long that can survive anything. They are capable of essentially dying to protect themselves from changes in the environment. Once they are ‘dead’, they can be exposed to the vacuum and cold of space, frozen to 1 degree about absolute zero (around -273 degrees C), boiled, dehydrated and exposed to radiation thousands of time stronger than the dose that could kill a human. A tardigrade has been recovered from a 120 year old dry bit of moss in a museum simply by adding water!