Well, to be fair, the ability to send messages to the past really only becomes useful once such messages are receivable. For the messages to be receivable, we m

Well, to be fair, the ability to send messages to the past really only becomes useful once such messages are receivable. For the messages to be receivable, we must know the properties of the medium that the messages are to be sent on. Basically, this limits the very earliest that such backwards going messages can be received to around now-ish.[1] As a consequence it may not be a paradox anymore, since there will be no point at which we can operate without a suspicion of future interference, thereby reducing the paradox effect, and in fact encouraging it by divining the outcomes of our actions. Of course this divining rapidly loses power anyway, as multiple messages are sent conflicting with one another - it gets messy quick. It gets messier quicker if you choose to go with a "many worlds" interpretation of the universe. Further, there are questions regarding observation: does observing a message from the future cement that future into being, possibly incurring an absurd chain of events but not causing any paradox (the 12 monkeys thing)? What I am really driving at here is this: Your paradox claims are amusingly simplistic, the real deal here is that we just don't know enough to say. [1] I am ignoring two big possibilities: 1. that this has been known for some time by, say, evil wall street bankers with secret labs (and their ilk -- governments, supervillians and such). 2. That there aren't aliens at some point in the very distant past whom we get messages to, and convince to do our bidding, who show up at various key stages of history an change everything. This may or may not have happened, depending on what you believe from the history channel (ancient aliens) and Stargate.