Seriously, have you thought about it? There, it did it again, where did that last moment just go? We were there, it was as real as anything can be, and now it’s gone. Where in the vast universe and beyond does the past, a second ago and ancient past, go? It has to go somewhere doesn’t it?
Many have tried to explain it. The notion of entropy, in the “arrow of time”, is presented as an irreversibility. That the universe is a system with a certain known macrostate order regardless of the variability of what occurs in the microstate. That the cosmological arrow of time points in the direction of the universe’s expansion (above diagram2). It may be linked to the thermodynamic arrow, with the universe heading towards a heat death (Big Chill) as the amount of usable energy becomes negligible.1 That the radiative arrow of time moves away from its source, with a causal arrow of time notion that each event has a cause with the causal event preceding the event.
,An epistemological problem with using causality as an arrow of time is that, as David Hume maintained, the causal relation, per se, cannot be perceived; one only perceives sequences of events. Furthermore, it is surprisingly difficult to provide a clear explanation of what the terms cause and effect really mean, or to define the events to which they refer. However, it does seem evident that dropping a cup of water is a cause while the cup subsequently shattering and spilling the water is the effect. 1
Physically speaking, the perception of cause and effect in the dropped cup example is a phenomenon of the thermodynamic arrow of time, a consequence of the second law of thermodynamics. Controlling the future, or causing something to happen, creates correlations between the doer and the effect, and these can only be created as we move forwards in time, not backwards.1
All of this speaks to the how of time passing but nothing of the location of the past beyond our own memories. Does it pass into a new universal dimension? Some papers theorize that the past does remain physically with us, no different than the present. That the future is out there in the ether waiting to “happen”. So, if the past is somehow physically available, how do we, or is it possible to, “visit” the past as well as the future? These are all notions considered by what’s called the “A Theorists and the B Theorists”.
The “A Theorists” notions are akin to the Arrow of Time view with us traveling down a metaphorical “road”. There is the past, the portion of the road already traveled, the present, and the future, the portion of the road yet to be traveled. The A Theorists propose that the past may be a “real thing” that exists beyond just in our memory. Those subscribing to a physical past appear to gain support from the nature of mathematical space-time. The metaphysical view has the past only existing in memory.
The “B Theorists” in contrast, suggest the past and the future have the same physical or metaphysical status of existence as the present. The “Bs” theorize that the future does exist but has an element of indeterminacy, with a kind of physical free will causality. It is said that time travel buffs bend more toward the “B” perspective with a more metaphysical view as time travel presents a number of very difficult mathematical obstacles.
So, if the past does physically exist could we travel to it? Wouldn’t we have to travel faster than time? If we could travel to the past, in what state would we be in? If the past were physical is it still like a photograph or fluid like video or film? Could we interact with it or is it as fixed as our memory of it?
Future generations may conceive of and create answers to these many questions, problems and conundrums. When we stop to think about what just occurred, there, that moment that just past, whether cosmically consequential or not, it would be fascinating to know if that moment still exist somewhere not just in our memory.