You seem to be asking in regard to the Growing Block Universe theory of time. If this is the case, then Einstein's relativity is relevant because the contradictions found by physicists in the idea of a time that passes and creates past, present, and future are only answered by the Growing Block Universe theory of an unpassing, full continuum, time.
Relativism as a philosophy has serious flaws in its fundamental structure: if nothing is objectively true, then the Law of Relativism is the exception that proves the rule... except that it cannot be an exception, because it clearly states that NOTHING is objectively true, and so it itself cannot be... meaning that there must be SOME objective truths, rendering Relativism false.
Honestly, I don't think relativism is at all relevant anymore. Science has proven absolute truths, and even though there is always more to learn, truth is usually augmented by new truths instead of being replaced by them.
I love truth questions!!! Discussions such as these remind me of two texts: Monster (Myers) and A Streetcar Named Desire (Williams). Both Steve Harmon and Blanche DuBois both live in a world where they "create" truths. I have to agree that this questions speaks to the eternal paradox about truth--given not all people accept all things as being truths for themselves. Truths belong to the individual only, never the whole.
In regards to post #3, what truths are we talking about? Are we talking about philosophical truths? If so, what are the philosophical truths we must admit to?
This is an honest question offered in the spirit of discussion. I am quite interested to hear what one person considers to be "evident, undeniable and/or obvious" philosophical truth and to find out if those views are shared across individuals and cultures.
#2 draws attention to the essential paradox that is at the heart of all discussions about relativism. Basically, it is a belief system that logically cancels itself out and proves itself to be impossible. Whilst there is a definite attraction in seeking to show respect and tolerance to those around us and their beliefs, at the end of the day, we have to admit that there are some truths that exist out there. Philosophy has been impacted by such ideas through postmodernity.
Do you mean the theory of relativity in physics, or do you mean relativism -- the idea that there are no absolute truths? If you mean the latter, then notice immediately the logical contradiction that relativism can seem to involve. If there I claim that there are no absolute truths, and I believe that that claim is an absolute truth, then I've contradicted myself. I don't mention this in order to deny the force of relativistic arguments, just to call attention to the difficulties of making them.