If there is nothing after death how do we find out?

[Angrboda]

When our bodies die,afterlife isnt possible,posthumously mental life REQUIRES to restart the biological and physical life. If we would like to live again we would need our bodies.

This is not necessarily true. While I would agree that it's improbable that there is a naturally occurring process which would "takeover" the hosting of our mind after the death of the physical, it's not impossible in principle. Nor is it necessary that said process involve a biological vessel. In fact, one of the proposed methods for exploring and colonizing space would involve digitizing the information necessary to describe our brain/mind, and transmitting that at the speed of light across the galaxy to a distant planet, where it would be recreated in another vessel, likely a robot or similar, or perhaps a surrogate species.

Ultimately it would at minimum require understanding the mind and the universe to either rule in or rule out the hypothesis to a reasonable degree of certainty. At present we aren't there. We're left with a situation similar to what some people term pseudoscience. Not only has no good evidence been provided, no plausible underlying mechanism exists. (See Type I error and extraordinary claims. It's not impossible that the paranormal exists, it's just much, much harder to demonstrate without a plausible mechanism. In its absence, poor evidence is virtually useless.)

(I just attended my first meeting of a local group for psychics, mediums, healers and similar people. We performed a remote viewing experiment. The experiment was interesting in and of itself, but there were a number of ways in which the thinking involved in discussing and reasoning about such things had an entirely "other" character that I didn't expect. I should write it up. But I probably won't.)