31 December 2011

Time Please

Time Please

For those who have suffered my thoughts on time before, you will know that time is something that concerns my little brain. In fact, what exactly time is has concerned much brainer people than me. And perhaps reconciling time with the two main paradigms in theoretical physics is key, for in the Einsteinean world time merges into space-time and is relative and has no standalone life, while in the standard model of the quantum world, time is fundamental to the theory. So in one, there is no "real" time while in the other there is. This anomaly needs mediating.

Anyway, what I have been pondering on for some months this year is a thought experiment: take an electron now, then consider where it is in the future, but also where it was in the past.

Now, in the quantum world, we do not know where that electron is in the future. In fact, it is everywhere in the universe, but that smearing of the electron throughout the universe collapses down to a point roughly where it was now at that point a nanosecond in the future. That is pretty much understood since Bohr proposed it in the early 20th century and then others like Heisenberg, for example, expanded these ideas further with his uncertainty principle and Feynman later with his diagrams. However much we do not like it, this idea works and has been tested by loads of scientists and shown to work.

But what perplexed me more was no-one ever mentions the past. If we take that electron and move backwards in time, do we know where it was?

At first, I decided that the inherent uncertainty worked both ways, so we could only be certain of a point in time now, but, because we had not measured (or observed) the electron in the nanosecond beforehand or a minute or year previous, then its past would also be uncertain and it would exist throughout the universe. So in this concept, the present is a unique point in time with uncertain existence on either side, and you can only be certain about that which you have measured and so brought into existence.

But I am not so sure now and think this idea is wrong. I now believe that the past is very different from the future.

Even if we have not measured or observed a particle in the past, its position/existence/velocity etc are effectively known (or at least knowable) and so the past is not uncertain in a theoretical sense, even if we do not actually have the evidence or answers or data measured.

But so what?

Well, it would mean that the past is fundamentally different from the future. For example, in the past, the world would be deterministic, so a particle has definite momentum and position at any point in time. In this classical Newtonian world, cause leads to effect. In other words, this is the world and universe of our experience, and does fit with our understanding of how the world seems to us to work. However, the future is more mysterious and a particle does not exist until it is measured, while between measurements such a particle does not exist anywhere specific but everywhere in the universe. This world is one of probabilities and possibilities, where cause does not lead necessarily to effect but to a whole array of different probabilities of outcomes.

So when it is said that an electron is a wave or a particle, is the difference in result how you are measuring it, i.e. when you are measuring in time rather than what you are observing? This is close to the Copenhagen Interpretation which effectively said energy quanta were a particle or wave, but not both, and what it was depends on how you set up your experiment. However, it gives no interpretation of why the how of setting up an experiment changes the answer. My suggestion is that it depends on what time-frame you are looking at.

As I have argued before scientists are very focused on "what" they are looking at and "how" they are observing, but perhaps not "when" they are looking at, yet Einstein was very interested in what time really is. For me, the present is a strange chimeral zone that is not quite the past nor the same as the future and is full of kooky mystery, and this is the strangeness that quantum physicists are looking at.