In 1905 Albert Einstein did away with the concept of absolute space and absolute time. Today, more than a century later we still, however, are very much emotionally invested in the concept of the ‘absolute past’. We argue about it. We fight about it. We disagree about it, completely overlooking the fact that the universal, one and only ‘absolute past’ does not exist.

The absolute past does not exist because we cannot experience it. We do not (yet?) have a time machine that can take us to any moment in the past and show us exactly how it was. Immutable. Constant. Undisputed. The same for everybody who wants to see it.

Therefore, until the time machine is invented we are forced to conclude that the ‘absolute past’ is a mere fantasy that has no practical value. What has practical value, however, is the concept of ‘relative past’, which is the concept we use daily in our life, the concept that we simply refer to as ‘the past’. But this past is relative and here is why.

The concept of the past is nothing more than an ‘informational construct’, which we build in our minds when trying to reconcile the present values of observable variables with what we know and understand about the dynamics of the system. In other words, we have a set of facts that are known to us. And we have some understanding on how a system in consideration behaves. And using these facts and of this understanding we are making an inference of what the system must have looked like in the past, or rather what the observable variables (the observables) must have been in the past.

However, our grasp of the present is not unique or absolute. Each observer has his own set of observations and their own understanding of the dynamics of the system being observed. But even if the understanding of the dynamics of the system is the same (e.g. by way of education or censorship), the set of observations (or the values of the observables) is invariably different. Measurement errors (human error), measurement uncertainties (due to quantum effects), measurement discrepancies due to Einstein’s relativity and other factors result in different observers having a different set of observables that they use to infer the past. Also, our understanding of the dynamics of the system is neither complete nor correct ever, as the Universe is a very complex and wondrous place and we only hope to be able to approximate it’s true behavior. Therefore, intentional malice aside, even our best intent is likely to produce versions of the past that are vastly different for different observers. In fact, the past is likely to be chaotic since the world is generally speaking a complex system, and most complex systems tend to be chaotic the further we go in time in either direction.

Therefore, we should quit arguing and fighting and resign to the fact that there is no absolute past as there is no absolute space nor absolute time. The past is relative and depends on the information at hand.

Does this mean that different observers will have different versions of the past for the system they observe? Sure. Does this present a problem? No, it does not. The notion of the past is a utilitarian one. We need the past in order to explain the present. We need the present to make projections about the future. In both cases we are dealing with complex systems, and in both cases we are likely to be wrong due to the chaotic nature of the complex system’s dynamics. But we can try nonetheless, and hopefully make useful inferences.

When constraining the notion of the past to mathematics, we can define ‘the past’ or, more accurately, the ‘relative past’ as the collection of the observables that gives us their present value given our understanding of the dynamics of the system. Such a definition has clear mathematical and practical utility, although the answer is not a unique one. We need to take a deep breath and accept this uncertainty in the same way we accept the uncertainty of the quantum world and relativity of space time. We use this definition all the time, this definition is utilitarian and therefore a highly practical one. What we need to change is to stop arguing about it, as our discomfort resides in the false concept of the ‘absolute past’, which simply does not exist.

From a humanitarian point of view, this means that different people, different groups or nations may have their own version of the past. In fact they are entitled to it and the disagreement is unavoidable, unless and until we agree on the common set of facts and on the common rules describing the evolution of the dynamic system such as the World. Is the latter practical or necessary? Not necessarily so. The people are entitled to different perspectives. The accuracy and completeness of our information and knowledge is always questionable. There cannot be one version of the past. Instead there are multiple pasts by different narrators. These relative pasts coexist in our collective human mind where the perspectives clash and we argue. This is to be expected and there cannot be any other way since no group or individual can claim supremacy in the accuracy of the information and completeness of the model of the dynamic system, which is the World. This is another fact we must resign to and ultimately accept. There is no single version of the ‘absolute past’. Instead there are multiple (relative) pasts, which are equivalent. As uncomfortable as the philosophical implication of this conclusion may be, this is something to be reckoned with. We do not know everything – our knowledge is incomplete. What we think we know may be inaccurate. Our mind is not infallible. Human intent is often a malicious one. The world is chaotic. Therefore we may never agree about the past, and this is OK.

P.S.

The famous often cited quote by Daniel Moynihan “You are entitled to your opinion. But you are not entitled to your own facts.” is invariably wrong. We are entitled to our own facts, every scientist knows this. We take measurements and derive conclusions. Some accurate, some wrong. We argue about them. We challenge each other’s findings a lot before we accept any of them as ‘facts’.

Then the time passes and we discard many of these facts as new information becomes available. In fact, scientific (and general) progress is only possible exactly because we come up with new facts every so often and discard the old ones. This is happens all the time. The are no absolute facts. ‘Absolute facts’ are a construct of authority. 150 years we all knew that space and time were absolute. That was a fact. Today we know that faster than light travel is impossible. This is a fact. What we will know tomorrow? So hold on to your facts and your opinions! You are entitled to both. Just don’t think that either is an absolute.