The premise of the existence of Time machine is that, there exists a future where a time machine has been invented or in the past, time machine was invented but never revealed or went unnoticed.<p>But, lets consider the Future:
If indeed there is a future where time machine has already been invented, then there would already have been visitors from the future.<p>From this reasoning, two conclusions can be made.
1.) Time Machine is impossible to make.
2.) Or, there is no future. Just Past and Present<p>So either Time machine and time travel is an impossibility or the concept of Future does not exist.<p>--OR--<p>Time machine has already been invented, visitors have already travelled, but they are doing an incredible job of concealing it for reasons their own.<p>What do you think?
I think this topic is a lot deeper than you realize. For example, consider the theory that a working time machine is required on the receiving end; it follows that no one could travel back before the invention of the first time machine.<p><a href="http://plato.stanford.edu/entries/time-machine/" rel="nofollow">http://plato.stanford.edu/entries/time-machine/</a>
<a href="http://plato.stanford.edu/entries/time-travel-phys/" rel="nofollow">http://plato.stanford.edu/entries/time-travel-phys/</a>