Full Idea
In classical theory we assume past and future are separated by an infinitely short time interval called the present moment. In relativity it is different: future and past are separated by a finite time interval dependent on the distance from the observer.
Gist of Idea
In relativity the length of the 'present moment' is relative to distance from the observer
Source
Werner Heisenberg (Physics and Philosophy [1958], 07)
Book Reference
Heisenberg,Werner: 'Physics and Philosophy' [Penguin 1989], p.103
A Reaction
Not sure I understand this, but it is a revelation to realise that not only is time made relative to observers, but the length of the 'present moment' also becomes relative. The infinitesimal present moment has always bothered me.