In the movie, the inability to change the past is emphasized. The idea is that one can't change the past. Once something happens, it cannot be reversed. What do you think?
One thing among many others attracted my attention the most. When the photonic cited the name Alexander Hartdegen, 1869 to 1903, Alexander asked questions about Hartdegen, but no avail, there was not enough info as he had not told anyone that he had achieved making a time machine.
What if a scientist makes it and does not tell anyone about that? Do you think there are real Alexanders? And last but not least, why would one declare it if he/she succeeded in making a time machine?