There's an interesting article on the PhysOrg science news site about a possible solution to the "arrow of time" problem.
The "arrow of time" problem (it's sometimes called a paradox, but it isn't, really) is as follows: the laws of nature aren't time-dependent. They work just as well in reverse as forward. When something falls, it releases energy. Put energy in, and you raise it up. The energy in the system remains constant. And yet we never see things spontaneously rise up into the air as the surroundings become slightly cooler. There's no law that says they can't, we just don't observe it. Over time the amount of entropy (disorganized, unusable energy) in the universe increases, it never spontaneously reverses itself.
Physicists have been puzzling over this for years. Why does time go in one direction only? Stephen Hawking speculated that it's somehow related to the expansion of the Universe -- and proposed that if the Universe were to begin contracting, everything would start working in reverse.
Now, Dr. Lorenzo Maccone has proposed that time-reversed processes may well happen -- may be happening around us all the time -- but we have no way of observing or remembering them because the process of reversing entropy erases the memory of the event.
This sounds like some spooky psychic phenomenon, but it's really just a consequence of the fact that our brains are physical objects in the Universe, operating by the same physical laws as everything else. Which means that memory is a physical process, and thus would be part of any reverse-entropy event.
Going back to my example of an object -- let's say an apple -- falling upward, all the normal "consequences" of that event have to reverse themselves. So the sound waves made by the apple hitting the ground spontaneously assemble themselves out of random air movements, rush inward at the speed of sound to the point of impact, and the energy transfers itself back to the apple, lofting it into the air back to the stem on the branch. My memory of hearing the thump is caused by those sound waves, so my brain has to unremember the thump and push a tiny pulse of sound out of my eardrum to help put that apple back on the stem.
This could happen. This may happen all the time. But we don't know about it, and cannot know about it, because knowing and remembering are part of the flow of time and entropy.
I'm not sure if under Dr. Maccone's theory reverse-entropy events could easily coexist with a positive-entropy world. In other words, can apples fall up to their trees and then turn right around and fall again later? Or does it mean that there is a ghost world of counter-entropy coexisting with us but not interacting? The latter does remind one of dark matter. Perhaps the Universe is mostly counter-entropy and we are part of the entropic minority?
The Universe just got spookier.
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