Not to get too New-Agey, but with our current understanding of spacetime in physics and quantum mechanics, it seems possible that we live in a specific line of time. That would mean that the future and the past are equally fixed.

This is known as the deterministic principle, and it's currently the subject of debate between scientists. It isn't, strictly speaking, proven one way or the other. However, there are good arguments for determinism which elevate it beyond silliness, and they don't all depend on hidden variable theories.

That's because, using a Many Worlds interpretation, the specific world we're in might be fixed even if it's indistinguishable from another until a certain point in time. It's all rather technical, but my point is that determinism could very well be real and it's hard to imagine what a world would be like that has a "present" independent of subjective observers.