In my former lecture I paid attention to one of the two views on time, time as an absolute, a structural dimension of our universe. It is often metaphorically described as a stream or flow and in that sense understandable in relation to time traveling.
The opposing view is that time does not refer to any kind of "container" that events and objects "move through", nor to any entity that "flows", but that it is instead part of a fundamental intellectual structure (together with space and number) within which humans sequence and compare events.
This second view, in the tradition of Gottfried Leibniz and Immanuel Kant,holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be travelled.
It is related to an ongoing discussion about words like past, present and future. What do these words mean. Do they describe real mind-independent properties of events, which would put the events in some linear relation to eachother? Time travelers will like this approach.
The other position is, that these words are so called token-reflexive, they refer to themself and can be translated in specific relations. These are the relations of earlier than, simultaneous with, and later than.
Thus, past, present. and future do not exist, or rather they have no mind-independent existence. This is not to deny the reality of time simpliciter, but only time conceived along certain lines.
Dividing time into present and future is roughly analogous to dividing space into here and there. There is, of course, nothing inherent in the structure of space that so divides it; it is divided into here and there only from the perspective of a particular observer.
Similarly, the division of time into past and present is a function of the way we experience reality, and is just as much dependent upon the perspective of a particular observer as is the division of space into here and there.
This approach deals with a kind of analysis like this: Ceasar crossed the Rubicon (E) contains a reference to a past tense, however, this reference doesnt mean more than the statement "E was earlier than this utterance"
One word on Duration. The only philosopher who emphasized this concept in relation to time was Bergson (1911) According to him, physical time is something spatialized and intellectualized, whereas the real thing, with which we are acquainted in intuition (inner experience), is duration.
Unlike physical time, which is always measured by comparing discrete spatial positions—for example, of clock hands—duration is the experienced change itself, the directly intuited nonspatial stream of consciousness in which past, present, and future flow into one another.
It is interesting in the context of the philosophy of time, but I don't see much relation with the issue of time traveling here.
One word on the spatio-temporal relation. Einstein had realized in 1905, that space and time, are intimately connected with each
other. One can describe the location of an event by four numbers.
Three numbers describe the position of the event. The fourth number, is the time of the event. Thus one can think of space and time together, as a four-dimensional entity, called space-time.
For a detailed discussion on the possibility of time traveling, based on Einstein's Relativity Theory I'd like to refer to a lecture of Stephen Hawking "Space an Time Warps'. I have the text for you available in a notecard.
This is all way over my head, but there is one important difference with the time traveling we discussed last Tuesday. In fact in this case it isnt the real SF-like time traveling, but only a matter of clocks running slower or faster.
And here we see that the time traveler isnt immune at all for this moving in time. It has serious consequences. So, I would conclude that there is time traveling and "time traveling" (with time machines and the like).
Let me finish with a quote from Stephen Hawking: "The conclusion of this lecture is that rapid space-travel, or travel back in time, can't be ruled out, according to our present understanding. They would cause great logical problems, so let's hope there's a Chronology Protection Law, to prevent people going back, and killing our parents."
Check also this superb articles:
Time Traveling : http://www.iep.utm.edu/t/timetrav.htm
Time : http://www.iep.utm.edu/t/time.htm