NB Einstein actually pondered over to call his theory the theory of the absolute because besides showing that space, time simultaneity, mass (and more) were relative he also showed what was absolute
e.g. c the velocity of light in vacuum and "interval " in spacetime
I don't know the sayings in English but in Sweden many people says "Allt är relativt"
that is "It's all relative" But this is not what Einstein said!
The starting point for my idea of six-dimensional relativity
Dr E A B Cole mathematician who have published basic work on six dimensional relativity.
On his homepage you find all references and an article. Among else he has written about
Prediction of dark matter using six-dimensional special relativity
Dr Matej Pavsic physicist who have published on generalised LT, three times and tachyons
He solve the causality paradox with tachyons using Everett's many worlds interpretation of QM.
As argued in my abstract I think Everett's interpretation is doubtful.
Prof Howard Wiseman have written an interesting history about Einstein and Bell's theorem
and which to my mind shows how shaky it was when the Copenhagen interpretation was put together.
My view is that to believe in solipsism is intellectual hubris,
I think Plato's ideals The True. The Beautiful and The Good are a valid base for all human activities including science