Brian Clegg’s entertaining pop-physics book Build Your Own Time Machine: The Real Science of Time Travel (2011) has a couple of amusing examples of how grammar gets wonky when you’re talking about time travel. The first example comes in a discussion of what’s called the block universe model, which encompasses “all of space and all time that will ever be”:
If the block universe is the correct picture, even if we managed to travel backward in time, we could never do anything that would change the future, at least within a particular quantum version of the universe. Because the future and the past already exist in the block, any action we take must already exist. (We have trouble with tenses emerging from time travel here. It might be more accurate to say that any action must will have existed.)
Later, Clegg talks about “Destination Day” in Perth, when a time and place were announced to welcome possible visitors from the future. (Similar events have taken place in MIT and Baltimore.) Note that the DD website is no longer directly accessible and can be reached only in cached form via tools like the Wayback Machine – the internet equivalent of time travel. Clegg:
I can’t find any official description of what happened that day in Perth, but I suspect there was some form of welcoming committee, eagerly anticipating visitors from the future to pop into existence. Of course now March 31, 2005, is in the past, and we aren’t so much awaiting them as we have been were awaiting them.
Have been were awaiting: lovely. I recently noted that English has no future tense, but whether the grammar of time travel would be easier if it did is a question for another day. As things stand English verb tenses, Clegg concludes, “definitely aren’t designed to cope with time travel”. This is good to already will have known.
Update:
A nice example from Futurama, season 6 episode 16, ‘Law and Oracle‘ (brief clip here):
No! No! What have I will have done?
Posted by Stan Carey 
Sentence first 