The Past

You’ve probably heard the expression, “the past is prologue to the future,” suggesting that events and experiences of the past inform outcomes in the future. But what if I were to tell you that experiments conducted in quantum physics suggest that the past can be influenced by the present? Seems wholly counter intuitive, doesn’t it? Nevertheless, a group of scientists have just won a Nobel Prize for experiments that demonstrate quantum retrocausality. In simple terms, they have demonstrated that seemingly unrelated actions in the present can predetermine the outcome of experiments begun in the past. Let that sink in for a minute. It isn’t exactly time travel, but it does defy logic.

Maybe the place to begin is to first talk about causality. When we look at a thermometer we can observe the temperature, but we would never suggest that the thermometer is causing the temperature to be either hot or cold, it is merely measuring what is being caused by other forces. On the other hand, if we were to drink a glass or two of whiskey, our reflexes, speech and behavior would be affected, and we could conclude that the whisky was the cause. In the latter case there is a correlation between an action and an outcome, albeit the temporal sequence is from past to present. Retrocausality suggests that there can be a correlation between an action—drinking the whiskey in the present and feeling tipsy in the past. Of course, I just simplified this to a degree that is likely to be a bit misleading.

Causal correlations refer to the outcomes of variables. If we change how we hold the thermometer, or whether it is marked in Fahrenheit or Centigrade the temperature itself will be unaffected. There is no causal correlation. But if we drink more or less alcohol we are likely to be more or less tipsy. There is a causal correlation that we can alter by changing a variable—the amount we drink, for example. It isn’t the only variable, drinking a beer or a glass of wine rather than whiskey affects the amount of alcohol we imbibe hence it would alter the outcome and our body weight is another variable since it can impact how much alcohol we need to consume before we are affected.

A lot of science –especially in quantum physics these days is based on trying to figure out what changes when one or more variables in an experiment is altered. What outcomes change, and based on the correlations that are uncovered, what does that tell us about how the Universe functions.

Now on to the question at hand, can the present affect the past? Here is a thought experiment. Imagine two physicists unknown to each other and separated by great distance are conducting experiments with particles they have obtained from a common source. They each independently decide how they will measure the outcomes of experiments they conduct using these particles. Now here is where it gets downright weird. A physicist by the name of John Bell predicted back in the 1960’s that when the results of their independent experiments were tallied up there would be inexplicable correlations between the results of the physicist’s work. Bell assumed that particles cannot ‘know’ what measurements they will encounter in the future so these correlations must be the product of something else. Real world experiments have now shown that this force –what we call a superdeterminer is the measurement choices each of the physicists made in the present which affected the particles back at their source in the past.

In the example of the thermometer, conductivity acts as a superdeterminer that correlates and controls both the temperature and its measurement. In our thought experiment involving the two physicists it is the choice of measurement—even though those choices were made independently. The variable—the choices of measurement controlled the unexpected correlations and could only have done so at the source, and in the past, even though the choices were made in the present.

The study of retrocausality still has a long way to go. We aren’t at a point where we can send messages to the past that would alter the present and we still must contend with the time travel paradox. But for now, at least, we may have to coin a new concept, the present as prologue to the past.