So how do you define truth? Again, "truth is relative" is an absolute statement, and so must be false to be true. It doesn't make any sense.

Christians believe one truth. Muslims another. Hindus another. Scientists also have different truths.

No, all these groups believe different things. Just because one believes something doesn't make it true. Like I said before, for the better part of human history, we believed the earth was the center of the universe. That didn't make it true.