1) We will never have time machines; if we did, we would ALWAYS have had time machines.
2) Time machines, like telephones, are useless if you only have one. Of course, the same machine is a “different” machine a day later, or a year later (or a hundred years later), so you can travel anywhere in time so long as time machines exist then. That fits the scenario above. But I suspect that, if a machine such as Randolph’s were built, the moment you turned it on someone from the future would pop up holding the plans for the best time machine imaginable. They’d then be everywhere, needing only the necessary time to build them. Time would then essentially collapse, since every technological advance possible would be available instantly, and every major event of the future could already be studied (without, alas, any hope of preventing future calamities). Perhaps, though, this state would only exist relatively briefly before time travel is outlawed and every time machine is destroyed.
Two possibilities:
1) We will never have time machines; if we did, we would ALWAYS have had time machines.
2) Time machines, like telephones, are useless if you only have one. Of course, the same machine is a “different” machine a day later, or a year later (or a hundred years later), so you can travel anywhere in time so long as time machines exist then. That fits the scenario above. But I suspect that, if a machine such as Randolph’s were built, the moment you turned it on someone from the future would pop up holding the plans for the best time machine imaginable. They’d then be everywhere, needing only the necessary time to build them. Time would then essentially collapse, since every technological advance possible would be available instantly, and every major event of the future could already be studied (without, alas, any hope of preventing future calamities). Perhaps, though, this state would only exist relatively briefly before time travel is outlawed and every time machine is destroyed.