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human
[Contact] Why do the aliens send back Jodie Foster with no evidence of her trip?

So the alien in the form of her father tells her this (introduction to new species presumably) is hows it been done for millions (billions?) of years. But why would they only have introduction to one life form from the planet and have almost no evidence of the contact (bar the hours of static on the video recording) she could bring back?
gpt
It's all about faith, that's the message of the film. Due to her father's death and her nature in general, Foster claims to reject faith and religion, she dedicates herself to science. There is no God, no nothing.

Yet we see that despite her anti-religious stance, she is not dissuaded by the lack of evidence that there are other intelligent creatures in the universe. She spends her time listening for messages from people that might not exist, she's trying to prove that her belief that something else is out there is true. Foster's character actually wants to believe in something she can't see, so is using science to justify her faith. She claims she's unwilling to accept God because there's no proof, yet she's willing to believe in other intelligences in spite of there being no proof.

When she encounters the father/alien, her faith is rewarded. She believed something was out there, now she can prove it. There are aliens and she's talked to them. But when she returns, there is no proof, there's seemingly no evidence that her story is credible. Foster spent the day with an alien who claimed he took the guise of her father, she is now trying to get everyone else to take it on faith that she's being honest about her encounter. Can she convince everyone that it's possible to believe something you can't prove? Don't believe in God the father, just believe in Foster's alien father?

When we learn that there's a blank recording that matches up with the experience she claimed, we know that her contact was real. Is her claim that she had contact with aliens more valid than the apostles' claims they witnessed the Resurrected Christ? The alien suggests that there will be further contact in the future, a second coming of the aliens, will people be in a better position to understand them then or will we still insist on rejecting things we can't yet explain?

That's the message of the movie, that without believing in things you can't see, you can't discover them. Foster rejects God but it's her faith that leads her to discover that were are not alone in the universe. Her belief that there was something more led to the discovery of aliens.