It is often cited that as a fundamental of relativity absolute time as a concept is no longer valid. I understand that absolute time was once accepted as a reality but Einstien found that this was not the case. a quote from JamesR in discussion with MacM (twins paradox thread) What is it that relativity has put aside? But I ask, what are we talking about when we refer to this concept "Absolute time"? What does it mean? Care to discuss?