Time Travellers

There is only one:

"Time Machine" (Wells'):

"Time Traveller" (also Wells');

"Future History" (Heinlein's) -

- although there are many subsequent "time machines," "time travellers" and "future histories."

We owe the archaic term, "time machine," entirely to Wells. We no longer refer to "flying machines" or to "thinking machines."

The Time Traveller and Poul Anderson's mutant time traveller, Jack Havig, describe their experiences of "time travelling," i.e., of remaining invisible and intangible while watching the rest of the universe either fast forward or rewind. Other time travellers usually either remain enclosed inside a temporal vehicle or experience a subjectively instantaneous transition between different sets of spatiotemporal coordinates.

Heinlein was the master of the Future History and of the circular causality paradox whereas Anderson became a master of future histories and of every aspect of time travel.