This is the third part of my "Time and Entropy" series. Why doesn't time run backwards? If you have missed the former ones, don't miss to read them, which are about
Part 3: The direction of time
Between past and present
We experience progression of time as irrevocable flowing into a specific direction. But is this true independent of our perception? We witness future as changeable, compared to the past, which we don't. Both are seperated by present.
The infinitesimal small moment separates past from present. Our brain processes the present as time units of about 3 seconds, that's what psychologists and brain researchers found out. The smallest distinguishable time difference amounts to 30 milliseconds.
Time travel - Possible in our imagination
A time machine is possible in
science-fiction, but not in reality
© palau83/ thinkstock
This irreversibility of past excites imagination: Particularly popular descriptions of time travel to the past are found f.e. at H. G. Wells or in younger times at J. K. Rowling. Apart from the fact, that one doesn't need to hope about implementation of such travels according to the knowledge of physics, one can imagine if they would be desirable.
The effects of a changeable past on the present could only be sustained, if - like in a popular comedy - after a surprising variation of time, the coming day would begin again as the same morning at 6 o'clock.
Inside out
© SerKucher / thinkstock
A lot of fundamental laws in physics actually allow us to reverse the direction of time. For instance, if somebody films the collision of two billiard balls, the video can be played backwards, without the viewers noticing it.
On the other hand, a lot of natural processes only elapse in one specific direction. Neither a movie about the burning of a candle in the wrong direction of time would convince anybody, nor would the reversed cooling down of a cup of coffee in the kitchen. These processes are irreversible. The first push at the billiard table towards the 15 balls is also implausible in reversed time direction.
What makes it differ from the first example?
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