Stephen Hawking wrote in his book, A Brief History of Time, that time is a relative, personal concept unique to the observer who measures it. The laws of science do not distinguish between the past and the future. Backward time movement is forbidden by the second law of thermodynamics. This particular law, as we watch it play out in physical experiences on Earth, is bound by the rule of Earth’s gravity. In the example Mr Hawking gives, a cup of water falls to the floor, the cup shatters and the water scatters. Whilst water droplets might coagulate into a puddle and are molecularly unchanged, the pottery or glass cup is reduced to shards that will never reassemble themselves in any way. More importantly, time will not reverse. The cup of water will not go back to its intact state on the table. Time does not stop, reverse, and move forward again. This ‘always going forward’ behavior is called an “arrow of time.” Mr Hawking states there are three distinct arrows of time: thermodynamic (where entropy gradually increases); psychological (our perception of the passage of time and how we remember the past but not the future [more on that later]) and cosmological. This latter, he says, is evident by the expanding universe. (PS p.183 Loc.2953 “…the expansion of the universe is [truth]..”)
The psychological arrow is determined by the thermodynamic arrow and these necessarily always point in the same direction. Using the same analogy of the cup of water, I can follow along with Mr Hawking’s entropy analogy (he uses a puzzle, but I like the water cup better). His scattered puzzle pieces represent disorder vs. the put-together puzzle that represents order. If a system begins with some kind of order (put-together puzzle or full cup of water) then over time it will become disordered, because disordered states outnumber ordered states.
I don’t necessary agree that the nature of our universe can be reduced down to a single concept of entropy or order because it then becomes dependent on a fixed beginning, i.e. the big bang. Don’t misunderstand me. I’m not saying there wasn’t a big bang. I just don’t believe it was the first. I have never believed in the beginning there was nothing. The way I see it, the universe is in a constant state of life and death. Think of the Klein Bottle, or the Ouroboros, and there’s another one I can’t remember the name of at this moment. I don’t ascribe to a singular beginning any more than I can ascribe to the boundary condition. I’m also not saying that the 2nd law of thermodynamics isn’t a thing, of course it is. It just isn’t the thing. Mr Hawking uses it to substantiate the psychological arrow of time by concluding that our brains use energy to recall a memory, and the by-product of that energy increases entropy, and therefore “we must remember things in the order in which entropy increases.” Disorder increases with time, he says.
As he weaves through his chapter on the arrow of time, he evolves – saying, “The collapse of a star to form a black hole is rather like the later stages of the collapse of the whole universe.” The universe expands and expands until at some point it begins to contract. It contracts and contracts, condensing down until it reaches that moment of singularity – or collapse. (I am reminded that this process is a lot like the birth, growth, decline and death of a person). He hypothesizes that the thermodynamic arrow reverses at the beginning of contraction and entropy decreases towards order. But, I’m not convinced that the arrow reverses, instead it seems to me it would just curve along with us and continue to move forward toward a new, albeit violent, outcome. Boom! The big bang again. But, as Mr Hawking points out, life won’t be around to witness much of that contraction phase. In fact, we won’t come along (again) for a really long time.
I started this topic to help myself work through the idea of getting over the past and look toward the future, and as always, Solace in Science! I’m reminded how my oldest daughter always teases me, “Mom, your sense of humor is ridiculously diminished each day you work in that humorless job,” so I take my ha-ha’s where I can get them. Thus, it’s humorous to me that Hawking started this chapter from the point of view that we humans can only see now and the past. And that’s how we know that the arrow of time moves forward. That’s why we don’t see time pause, reverse and start again. I think I find this overall approach to understanding time to be a faulty one. If you are the Curiosity Rover on Mars (literary license here, please) and the little computer eyes look up away from the dusty, seemingly dead landscape, and ponder the concept that there are no beings anywhere in the solar system, time still marches forward. The fact that We Humans see now, but we only remember the past doesn’t prove anything about the nature of time itself. Human remembering is really dependent on how strong our recall mechanism is. The information is there, stored perfectly unless our storage mechanism is faulty through some trauma or illness. Our recall mechanisms can be amazing or awful or any shade in between. Just because we can’t remember it doesn’t mean it didn’t happen – anymore than if we can’t see it doesn’t mean it isn’t there.
It’s my opinion and maybe I’m alone in this – we do perceive the future. I’m not sure how it works though. We don’t see it the same way we see the Right Now. Right Now is gone at the speed of light. The future is always just a SOL increment away.
Once upon a time I thought about how a multiverse would have independent bubbles of time, and what would happen when bubbles bump into one another and merge. (Also see ekpyrotic theory.) A topic for another day…
PS: check this out Arrival