I've been reading more about the philosophy of fatalism, in particular our ability, or lack of ability, to change the future, compared with our certain lack of control over the past. This seemed wrong to me, that it is possible (just as possible, or just as impossible) to change the past.
Yesterday I had soup for lunch and porridge for breakfast. This is a certain fact that occurred, but, what if I told the world that I had soup for breakfast and porridge for lunch. People could examine the contents of my kitchen and find empty soup cans and conclude that I had soup, but could not prove when. I did not tell anyone about my meals in the day, or document these events. There are no cameras. My body may absorb foods at different rates, so perhaps a skilled doctor could calculate that I had soup at 12pm rather than 9am and vice versa for porridge, but I think that this is extremely unlikely given the complex nature of biology. I expect that those results would be inconclusive.
We are close to a situation where the only evidence of what occurred yesterday is my memory and testimony, and, that if my memory were flawed, and my testimony stated that I had soup in the morning and porridge for lunch, then all of the evidence would indicate that that was the case, and that therefore the past would be changed.
Now, you might say that evidence, belief, testimony, or likelihood is one thing, but that in the universe itself there is a fundamental reality where I had porridge for breakfast and soup for lunch, irrespective of my memory, my belief, or the belief of others; but I attest that this is not the case. If the impact on the universe is identical in both cases (soup for breakfast, soup for lunch) then both events are identical, thus is is possible to change the order of my meals yesterday, and so change the past. If one reality or another cannot be distinguished between, then both are equally as likely.
For this we must discount physical changes to the world and universe, for example the heat expended when heating the soup in the afternoon or morning. This could be eliminated by having cold soup. Perhaps there are gas records in the gas company which could show when I had soup. If you ignore those for the moment, assuming I used a small gas cylinder, then perhaps the time of my having soup could be ascertained by a gentle warmness at a certain hour of the day versus another hour - but this warmness would decay or be affected by the 'noise' or other events, the sun in the afternoon, other meals, or various other things which seek to destroy the information about yesterday. This same principle of decay of knowledge would apply to gas company records, perhaps not in a few days but in a few years or decades the records may be lost or distorted. Over time, it would become more and more difficult to establish whether I had soup in the morning or for lunch, and in the universe as a whole the differences in effect between the two occurrences would become increasingly small as to be irrelevant; and again, the 'actual' order of meals becomes a moot point, both orders of meals would be increasingly likely to be true, as true as each other.
Uncertainty of truth regarding quantum-level events is well known, and it is conceivable to design an experiment involving quantum entanglement to prove that changing the past is possible in these extraordinary and sub-microscopic environments, but switching meals is no quantum event but one on a large scale. What about changing the past for even bigger events?
What if we changed the past now, and stated that Abraham Lincoln was not assassinated by John Wilkes Booth, but lived a long life and died of natural causes. This is more difficult to change because many more people know about Abraham Lincoln than my meals of yesterday. To change the past in this case, at very least, would involve changing every document about Abraham Lincoln, and changing the mind of everyone who knows about his assassination. Being such a distant event in time, the physical evidence may be easier to change; his Earthly remains, if in good order, could be altered to look as though he had died of natural causes. The total effort is greater than the changing of my meal order. There is much more information about the assassination of Abraham Lincoln, spread across many agencies, and to change this event, more energy is needed to overcome these facts, this information, the combined web of accurate knowledge of the event.
Information decays over time so it seems that the more distant an event in the past, the easier it is to change. We can easily change, for example, what Julius Ceasar ate on his 9th birthday because almost no agent knows this, and any evidence about is probably destroyed. Events which are well documented and verified among many agents are, by the same token, more difficult to change. Each event has something like a 'coefficient of certainty' relative to these two factors; closeness in time, and clarity of documentation.
There is at least one agent which does know what Julius Ceasar ate on his 9th birthday: a beam of light is now flying from the Earth which bounced up from Julius Ceasar's meal and was, by chance, deflected into outer space. That beam, a little piece of a 'photograph' of Julius Ceasar's meal, is now flying away from the Earth at the speed of light. Alas, we can never intercept it, but perhaps distant eyes could. Perhaps distant planets and extraterrestrial eyes may now be gazing on our planet as it was millions of years ago, and if their telescopes were good enough, they may see dinosaurs, or even (eventually) Julius Ceasar's 9th birthday party, but this is massively unlikely. Due to decay, distortion, damage, their fuzzy images may show some indication of the primordial Earth's atmosphere, but the detail needed to see individual dinosaurs, or the vague glows of light from a meal, is probably impossible to achieve. That beam of light which hit Julius Ceasar's meal is but a fragment, and alone would probably contain no conclusive, or even useful evidence, and combining multiple light beams from multiple sources to build an image would require a huge amount of energy.
So, we could say that he ate soup, and thus change the past.
The ideas here throw up all sorts of questions and implications. For a start, events in the distant future are more difficult to predict than events in the near future, as weather forecasters know too well. This indicates some sort of relation between the future and past. It also makes the present, whatever that is, important, and the present must be a unique present for each observer and agent. It seems that there are two universes which operate at once; one of all time and equality, and a one of transient time which is certain only in the present and increasingly uncertain towards distant past and future. This is perhaps something for a future examination.
Another implication is that reality, in our temporal universe, is relative to the knowledge of it, that the coefficient of certainty defines how real something is, and that an event which is unknown does not exist. If the unexamined life is not worth living, then the unknown life does not exist, and the more known a life is, then the more it exists.
