I've recently watched Season 3's War Without End, Parts 1 and 2 (spoilers about that episode in this question) and while I enjoyed it, I became confused about how time travel is supposed to work in Babylon 5. Particularly:
- Delenn and others say that they must use the White Star to save Babylon 4 because they "have already done it" (kind of a variation on the predestination paradox)
- At the beginning of War Without End, Part 1, Babylon 5 receives transmissions from 8 days in the future as the station is being destroyed, suggesting that other futures can happen. Also it implies that their timeline is not the first (i.e. if that future had not "happened" already, they would not be doing what they were doing)
- Despite knowing that they have "already done it", the characters strongly believe that they have a free will choice to save Babylon 4 and if they don't, the bad future will come to pass. This is consistent with statements like that of the Centauri seer in Season 1's Signs and Portents who indicated that there are different possible futures and that we have choices to change it.
- Despite knowing both that the Shadows were defeated 1000 years ago and that they will in the future send Babylon 4 back in time, Delenn specifically states that if they don't save Babylon 4, the Shadows will have won the first war in the past.
- Sheridan "slips into" his body in the future in which they have already won the Shadow War and future Delenn has already heard future Sheridan tell her about this meeting. And yet despite knowing that a future Sheridan told her about this very meeting, future Delenn still believes past Sheridan can change things and warns him not to go Zha'ha'dum.
- I seems that Valen only exists because Sinclair knew that Valen existed. There doesn't appear to be an original timeline when Valen doesn't exist and there is no causality. And if Minbari reincarnation is to be believed, this also creates a boostrap paradox with Sinclair's soul: Sinclair was born with a Minbari soul, Sinclair became Valen, and then Valen's soul was reincarnated into Sinclair a thousand years later.
In most time travel movies and novels (the ones that don't take a wibbly-wobbly timey-wimey approach), there are at least some consistent rules and you can generally say "time travel works this way, and you're just not supposed to think about X problem".
However with Babylon 5, it's not clear what those rules are. Sometimes it seems the future (or past!) can be changed, sometimes it does not. Sometimes it seems like they have a free will choice to change the timeline and sometimes it does not. Sometimes it seems like there is an "original timeline" and sometimes it does not.
Suffice to say, I find it fairly confusing. So could someone explain how time travel works in Babylon 5?