Time Machines and the Eternal Now

I just watched "Arrival" - not a bad SF piece. Possible spoiler - these days conquest of time seems to be a favorite theme. as it is in "Back to the Future", one of the best movies on the theme which appropriately makes a joke of the concept of time travel.

We are obsessed with time. Can we "travel" in it aside from the 60 seconds per minute pace we are stuck with? Does the future exist or has fate laid it all out like the road ahead? Does it all exist in one "eternal now"?

You would think Science is immune to such fantasies, but there are serious scientists who would seem to say that time is an illusion. We supposedly live in the "eternal now" - whatever that could possibly mean. Others say time is basic. Lets face it, they are dreaming and guessing like the rest of us. The skeptical part of me suspects that if we paid our physicists better they would not need to write books for the general public challenging the reality of time.

As for myself, I think that the present moment is real and the future is open, not like the road ahead and not compatible with the idea of "fate". I have reasons for this, but of course I could be wrong.

• Einstein's discovery of "space-time" lead many to picture time as "space like" - something you could "travel" in. This was an unfortunate spin-off of his analogy. In fact, special relativity showed that you cannot send any message, let alone a souped-up Delorian, into the future. Einstein showed that my "future" is in the "future" of every other observer in the Universe, although it's farther in the future for everyone but me.
• Quantum mechanics seems to show that, at a small scale at least, events occur without what we normally think of as a "cause". There is a probabilistic connection between "now" and the next moment. Historically speaking, the idea of probability has had a hard time sinking in. I do understand that Schrodinger's famous wave equation is deterministic - reversible in time, but when it "collapses" into specific measurable events, it does so with a cosmic "roll of the dice".
• The second law of thermodynamics (not really a "law" but a "theory") is not reversible in time. It more or less defines the "arrow of time" in Science. There is a lot of carping around the edges of this issue from Scientists (as there should be). For example, for some reason the "law" is violated at the moment of the Big Bang (also a theory not an observation).
• Our daily experience deeply depends on time. Even if it is an "illusion", one may ask what use it would be to "know" this, since life is full of "decision points" and unexpected events.

Given this, it is still important to understand some of the ways that time violates our expectations in our  daily experience.

For example, we know that our experience of time, even the way that machines such as clocks "measure" it, is "local". Famously, if one twin went on a round trip to the nearest star at near the speed of light and came back to Earth, he would be years younger than his brother when he got back. His "clocks" would really run slower than the clocks back on Earth. Time "flows" at a different rate for different observers. That's an observable fact. Another case that fascinates me is how time slows to a crawl, closer and closer to stopping, flinging the observer into the far future as he falls into a black hole. Of course this is assuming the observer would survive the atoms of his body being pulled apart as he nears the event horizon. But if he could survive, he'd get a quick ride to the end of time (not, as depicted in too many movies, a quick survivable ride back in time).

But in all these cases, time "flows" in one direction, like a river, with different rates of flow in different parts of the river.

I think time is flowing differently for my dog than for me. Her reactions are implausibly quick. Birds flying full-speed through a forest are another example. Whatever a dog's "experience" is like, its clock runs very fast (relative to my own). It's also possible that it runs slowly at times  - she can stare at me for 20 minutes waiting for me to feed her. Is she aware how long she's been doing that or has time somehow stopped for her? I'd also love to know how my dog's experiences of the future. Watching her run at full speed through an obstacle course of logs on the beach, it's plain that she is very good at anticipating the "future" a split second ahead. This is also evident in her ability to catch a treat thrown at her face. As to the long range future, she "runs on rails", anticipating the "normal"course of events (especially meal times) and seems to be able to carry out rudimentary "planning". But I doubt that she's aware of the "future" like you or me. In this sense, the future is a construction of the human brain and, in this sense, it is an "illusion". It is not time itself that's the illusion. Just the future.

Brain Science also teaches us that the "present" is a construction of our nervous system. The "present" of our consciousness lags behind events in the world by a few milliseconds and can actually get the order of events wrong. For example, the signal to move our hand away from a shock originates in our brain before we "decide" to move our hand. In this narrow sense, the present is also constructed by the brain and is therefore a kind of "illusion". Like many aspects of consciousness, the "present moment" is a "magic trick" pulled on us by our brains to make sense of what is happening.

What would happen if we had some way of measuring time at a very small scale and super-short time intervals? This leads us into the realm of Quantum Mechanics, where we learn that measuring tiny intervals of time runs into the same problems of measuring tiny intervals of space. At sub-atomic scales, space-time is subject to quantum rules. Our ideas of "causality" may not apply to quarks for example. Even so, none of this turns time into an illusion. It just says that our ideas of time need fine tuning (like all our ideas) at very small scales. We have, in fact, conducted experiments where time intervals are in the pica-second range (the time it takes a photon to traverse a proton) and no overhaul of our concept of time seems to be required.

Feynman Diagram of Particle Interaction

For me, the Feynman diagram is a picture of what happens in space and time at all scales down to the "bottom". These diagrams successfully depict what is happening at quantum scales all the way down to the range where observation is impossible in principle (the "foam" of empty space). One axis of the Feynman diagram is time. In fact, the diagrams summarize fundamental equations of Quantum Mechanics which also fundamentally involve time. So far, these equations successfully predict behavour of the Universe down to the limits of observation. Interestingly, these diagrams (and the equations they summarize) depict possible interactions when the "meaning" of the axes are reversed (time to space and space to time). I'll let you know the implications of this fact once I complete my Ph D in physics but intuitively, the above diagram "makes sense" if you read time as going from bottom to top or left to right (or from right to left or top to bottom).  Momentum is depicted by the slope of the lines in the diagram (space per unit time). It is preserved in any case at any moment in time. I'm also aware that, strictly speaking, the particles shown in the diagram don't exist - only the corresponding fields. However the very concept of a field involves something that has a value at every point in space and time.

I guess that I would say that time is perhaps the ultimate mystery - an irreducible part of the Universe. Trying to unravel its mysteries is perhaps the most interesting part of the human journey.