Would you recognize a time machine if you saw one? Would you know what to look for - or to borrow a phrase from Douglas Adams (author of "The Hitchhiker's Guide to the Galaxy"), would you overlook it as an S.E.P. (Somebody Else's Problem)? We literally do not see what our brains are not prepared for! Would a month-old baby recognize the gaudy, fringed thingy atop the lit-up thingy as being a lampshade - without some previous conception of either lamps or shades? In some ways, we are like the infant, with too few points of reference from which to glean the otherwise obvious.
If a caveman saw an airplane, would he not think it a bird? How many UFOs have we missed noticing, I wonder ... how many time machines? I'll take this one step further. Perhaps we are looking in all the wrong places for our elusive time machine. Perhaps the human mind itself is a time machine! We have memory, don't we? If we reflect intently on a past event, do we not feel present with it? Memories conjure the sights, smells and feelings of the past quite well. Often we don't pay nearly as much attention to sights and sounds around us as we do to choice memories.
When stuck in a hot summer traffic jam, wouldn't the memory of a cool ocean dip impress the mind more vividly than one's take on current surroundings?
While "re-membering" the past, we also retain memory of our present points of departure ... where we do our remembering from! That's why we may (hopefully) remember to take the goose out of the oven before it burns to crisp, whilst strolling down memory lane from a kitchen point of perspective!
If we traveled into the past in mind or body without recalling the future present, would we even notice that we traveled to the past at all? Of course not - we'd be literally lost in the past - and don't you travel into the future daily? If not, then you've probably reached the end of your road ... literally!
I'm not saying that a silicon-based technological wonder of a time machine with chrome siding and a sun roof is not possible. I'm saying that if you saw one parked on your neighbor's lawn, you might disregard it as an S.E.P. ... or not notice it at all.
As for time travel itself, perhaps some of us do too much of it! Many have heard the admonishment "Stop living in the past!"... good advice, especially if you overlook that your goose is about done - and have failed to notice that silvery, humming, otherwise indescribable contraption parked on YOUR lawn - yes, look out the window! Somebody else's problem?