Time Travel

Time is a subject that has always interested me. I once stated that time is change and that our age is best measured by the amount of time that we have left. If we see a twenty year old man walking down the road with a fifty year old, which one is older? The first answer most people would give is the fifty year old man. If the twenty year old is scheduled to die at the age of twenty-two and the fifty year old is scheduled to check out at the age seventy-five, which is younger? The fifty year old, for he has more time on this Earth.
When the talk of time comes up the subject of time travel always finds its way into the conversion. If time travel is possible a few things must be true:
1. The present, past, and future continually exists. Somewhere in the universe the past events are still taking place and the future events are taking place. Our past must be someone's present and our future must be someone's present.
2. The time machine must already be built. Time travel must be taking place as we speak.

Now, someone once told me that history is always being rewritten. I read somewhere that history is rewritten to fit the current political and social attitudes of man. But, what if the real reason is that history is being rewritten is the fact that a time machine exists and someone goes back in time and makes subtle changes to our past history.