Click the first one to enlarge.
When I visit the desert I think deeply about time: past and future.
If you grab some sand with your hand and let it fall, is quite easy recall the sand falling down inside a hourglass.
Also, it happens that desert is a high entropy system.
Entropy is the number of ways in wich you can rearrange the parts of a system and not notice that you’ve done so. When there is a force acting, like wind in the desert, things will be messy just because there are more ways to be disordered than ordered. Entropy always increases. Past has less entropy than future (this is called the Arrow of Time), and that is the very reason because of you can’t back to past. Everything we’ve built, that once was full of structure, is slowly being returned to a less ordered state. Universe tends to entropy, to Chaos.*
But,…what is Time?
According to Isaac Newton (17th century), ”time flows equably without reference to anything external.”
The passage of time, according to Einstein, is in the eye of the beholder: Clocks that are in relative motion or that are subject to different gravitational fields tick off time at different rates; the more these factors come into play, the further out of synchronization the clocks will fall. Numerous terrestrial experiments and astronomical observations leave no doubt that Einstein was right.
Einstein said in a letter sent to a widow for grieving the loss of a friend : “… the distinction between past, present, and future is only an illusion, however persistent.”*
*1. Excerpt from Brian Cox’s “Wonders of Universe” (BBC)
*2. Excerpt from Brian Greene’s article “The Time We Thought We Knew” (New York Time, Jan 1, 2004) and books “The fabric of universe” and “The hidden reality”