Hal Finney wrote:
> Dan Fabulich, <firstname.lastname@example.org>, writes:
> > FTL movement => arbitrary backwards time travel.
> > Now suppose, for example, that your flavor of time machine uses special
> > limiting "gateways." You build the gateway today, wait a week, walk into
> > the gateway, and you've just travelled one week back in time.
> > It would appear that the inventor's ability to time travel is limited: If I
> > build the gateway tomorrow, I can't travel back to today, though I can
> > travel back to tomorrow from any arbitrary point in the future.
Actually, if Feynman's Transactional Interpretation of QED holds true, then travelling in to the past should be no more difficult than a device that converts the traveller's mass into antimatter in the future, then back to matter in the past. Of course, this necessitates that time travel will only be possible where/when a matter/antimatter converter is in existence. If your mass is instantly converted to antimatter, you should start travelling back in time, as anti matter is merely matter that is travelling backward in time, according to the transactional interpretation. Granted, building a device that not only turns normal matter into antimatter, but will maintain the biological structure of the human body is a technological acheivement in and of itself.
Now, given this idea, since no matter/antimatter converters are in existence of the type needed, then of course we will not have seen any time travelers come back to this date from the future. They will be limited to traveling within their own era.