In discussing time it is essential to first distinguish between what I call personal time, measured time, and cosmic time.
Personal time is what we humans and other sentient creatures experience. It is based on input from our senses, plus input from our memories, imagination, and emotions. It is also based in part on events that are periodic like our sleep/wake cycle, the rising and setting of the sun, and changes in the seasons. For all these reasons, personal time is elastic. We each sense the passage of time differently from one another and differently from device-measured time, i.e. watches, cell phones, and clocks. The experience of personal time is also influenced by specific circumstances in which we find ourselves, such as on a roller coaster, on vacation, under pressure or stress such as in solitary confinement or war, in youth or old-age, and presumably on the degree to which we are sane or insane.
It is often said that the experience of personal time slows down during an accident, or when one takes psychotropic drugs. Personal time is so varied it is hard to categorize and quantify it. To get an entertaining idea of what personal time means to a comedian, visit George Carlin at https://www.youtube.com/watch?v=zaR3sVpTB98.
The fact that personal time exists at all is because it is created by sentient beings. We sense the passage of what we call time because our memories create a sense of events that have passed and our imaginations create a sense of events that could happen in the future. ‘Consciousness’ provides a sense of now. Because personal time is a variable construct resulting from cerebral/emotional processes, it should not be confused with the standardized, instrument-based increments of clock–measured time.
Measured time is a human invention. What we call the passage of time is displayed on man-made devices that were invented to transcend the arbitrariness and unreliability of personal time. Clock time, or measured time, is based on nature’s periodicities. Timepieces measure the duration of an event and/or the duration between events that are shorter than the natural units, i.e. such as a day (a revolution of the earth), a lunar month (a revolution of the moon around the earth), or a year (a revolution of the earth around the sun). Today we can account for not just a single second, but even a billionth of a second (a.k.a. a nanosecond). The average lifespan of certain molecules, such as positronium hydride, actually occur in half a nanosecond.
Throughout history, man focused on making clocks that were more accurate and more consistent, with the goal being that any two clocks would be able to keep exactly the same time or close to it. However, just as clocks became accurate (eventually substituting atomic vibrations for the movement of mechanical gears), it was discovered by Einstein that certain clocks accounted for the passage of time at different rates. If clock A moved faster through space relative to clock B, then clock A ‘ticked’ more slowly than clock B and time was deemed to run more slowly. Moreover, if clock A was closer to a particular gravitation field than clock B, then clock A, in these circumstances, also ‘ticked’ more slowly than clock B. This clicking hasn’t measured the passage of some ultimate, external, absolute cosmic entity we call time. The variable clicking simply reflects changes in the atomic processes and structure of the devices that record uniform intervals. Not only do clocks tick at different rates but all physical entities (organic and inorganic), tick – that is to say age – at different rates given their specific circumstances in space.
The reason that otherwise ‘perfectly’ synchronized clocks must measure duration at different rates when the clocks exist in different circumstances (motion and gravitational fields) is because clocks are made of baryonic matter, that is to say ordinary matter. Ordinary matter does not vibrate at unchanging rates, but as stated above, is subject to external forces. It is reasonable to conclude that what is commonly called ‘time’ and what I call ‘measured time’ could not exist in our universe in a cosmic era before ordinary matter existed.
Einstein and others have said that time is what clocks measure. In certain respects that is true, and yet this seemingly obvious definition might also be regarded as overly simplistic and confusing when other expressions of time are accounted for, such as cosmic time.
Cosmic time is a complex concept that challenges human imagination because it is so counter-intuitive. It is woven from a fabric wholly different from personal time and measured time. My thinking today on this subject builds on my earlier hypotheses and goes beyond my previous notion of a phantom instant. I suspect some readers will be inclined to immediately reject my current hypothesis simply because it is more aligned with Newton’s idea of ‘absolute time,’ that was supposedly supplanted by Einstein’s more accurate theories of relativity.
Cosmic time is composed of several challenging conceptual components. They are as follows:
The idea of cosmic time is based on the precept that the past and the future do not coexist with the present. Past, present and future are sometime represented as either a river or a loaf of bread with the past and the future existing upstream and downstream in the river, or to the right and left of now in the loaf of bread. These analogies are flawed and lead to misconceptions about cosmic time.
If there were a river of time, then the past would lie upstream and the ‘riverwaters’ of time would flow into us in the present moment and then flow out of us into the future, which would show up downstream. If this were so we should be able to look somewhere in the universe and see the past upstream and see the future downstream. But there is no upstream or downstream anywhere to be seen. There is only the now, the cosmic instant in which we exist and experience the moment. Nevertheless, theorists believe they can tunnel through time into the past and into the future.
One might say ‘but I can see the past in the light that comes to us from distant galaxies that may no longer even exist.’ But the light that enters our eyes or instruments, as well as the light that is still on its way here, exists only at any instant of the present now. The configuration (energy level and quantity) of those arriving photons provide information about what happened in previous ‘present’ instances but they themselves do not constitute the past itself arriving at our eyes and telescopes. Those photons en route and upon arrival are always of the present instant. Upon arrival they become embedded in the operations of the material world and carry past-presents into the current present. Moreover, the future is only what we imagine the present to become as a mental construct. The future is only a transformed present. In short, it is only the present that exists at any instant of time and the duration of that instant is zero.
The river analogy is flawed in the same way that the loaf of bread analogy is flawed. The slices to the left (say) of the slice representing the present is only a mental construct. So, too, with the slices on the right (the future). The only slice that is real is the slice representing the present moment and the width of that slice, like the duration and the present instant, is also zero. Based on the above analysis, logic suggests that the past does not exist at any present instant but is ‘embedded’ in the present, much as the past becomes embedded in the geologic record of the present and in the current thoughts of all thinking organisms on earth and elsewhere.
Likewise, the future does not exist anywhere in the universe. The future exists only as a set of imagined conditions in currently living brains. One can go nowhere in the universe to visit the past or the future. Slicing the loaf of bread at an angle as Brian Greene has proposed is not feasible if there is no loaf to slice. All that exists is the knife slice, not the cooked dough. Consequently, logic suggests that the much-discussed notion of time travel is a logical and physical impossibility.
I prefer to liken time, first, to a single piece of photographic film that someone is carrying as he or she walks from one end of a block to another. The walking aspect of this model is intended to suggest the passage of what we call time. Imagine that what appears on the piece of film represents, say, what is physically happening on a slice taken through a galaxy (clarification; what appears on the film is not intended to be a picture — not intended to be a photograph of the galaxy but rather just what is in the plane of the cross -section). What appears on the film at any instant represents what is happening along that cross-section slice. There are no other sheets of film in front or behind the single sheet held by the person walking, which would suggest the concurrent existence of a past ad a future.
If it were possible to make the sheet of film thinner and thinner, in the same way that a second can be divided into, say, 1 billionth of a second, or even thinner, then the duration of the present instance continues to be reduced to what might be regarded as an infinitely thin sliver of time with neither the past nor the future existing on either side.
Now imagine that that infinitely thin slice of film is replaced with an infinite large expanse of three-dimensional space. Represented on that snapshot of space then is what would exist at any particular instant throughout the universe. There would be no hidden pocket of space that contained the past or the future. Only the present would exist in that ‘snapshot’ at any particular instant.
Now consider that what ever images/forms appear on that single snapshot of the universe will appear in subsequent durationless snapshots but in slightly different configurations. In combining those individual snapshots a ‘picture’ emerges of photons moving through space and matter forming various physical entities.
The rate of change in each of those configurations will be seen to vary, suggesting that atomic processes are occurring at different rates due to local effects of gravity and local effects of motion. But changes in what might be called the flow of time will not alter what is captured on each snapshot. The present will always and exclusively be the present but atomic processes will be seen transforming at different speeds from snapshot/instant to snapshot/instant. In short, the flow of events will be seen to be the absolute, eternal progression of dimensionless instants (snapshots) that contain within them the variable rates at which processes occur and energy forms evolve and increase (and sometimes decrease) in complexity. The above model represents my notion of absolute cosmic time. Cosmic sequentiality (subject to no variability) is the non-physical womb, so to speak, in which measurable physical phenomena are subject to relativistic effects.