Einstein invented the photon, and Goedel proved that by General Relativity there can be no such thing as time. If time travel exists, time does not. If time does not exist, causality is gone also. We'll need to do some more work on meaning and purpose, also.
With the 'conventional' notion of dimension Time, someone might 'prove' through relativity that it doesn't fit the conventional conceptualization. However, the theory I'm describing is not the 'conventional' concept of Time because I'm describing it as a dimension having three variable expressions which combine with dimension Space of three variable expressions.