What are we talking about here? Time? Death? Hoping for something that I could wrap my brain around, I started with its definition. By the time I got embroiled in wiki pages on physics (which BTW I didn't pursue after high school) and thermodynamics, I decided on what I am calling Old Woman's Observations or OWO.
Under that heading, let's talk about Climate Change aka global warming. It is almost too late to reverse the effects of global warming. Things that have changed will be VERY difficult, and some impossible, to reverse. Those species that are extinct will not be re-born. Those that are in danger, like the Monarch butterfly, may have a chance of re-invigoration. Those islands that are being flooded by sea water, will not be habitable in the same way, even in the event of sea level fall, after having soaked up all the saline in the sea water.
I did read an interesting article in today's New York Times newspaper. Studies are linking belly microbes to the brain...seriously...who could imagine that what's in your gut could effect changes in your brain? There is the radical idea that diseases treated as irreversible may not be. Alzheimer's. Autism? Epilepsy? Parkinson's?
The whole idea is really hard for this Old Woman with Observations to understand. I'm going to re-read this article. Maybe you would like to: https://www.nytimes.com/2019/01/28/health/microbiome-brain-behavior-dementia.html