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We like to think of time and space as continuous, that you can divide time and space into infinitely small quanta. This is fundamental to everything we know about the universe, and something that should be rock solid science.
Think again.
Most of us already know that matter isn't continuous at all but instead constructed from atoms and they in turn from sub-atomic particles. Our perceptions of the nature of matter have been adjusted to accept that it isn't the continuous stuff that we once thought it was. But what about time and space?
If we look at the theory of loop quantum gravity, it is not only matter that is made up of discrete components, but also time and space as well. How on Earth can this be?
As a computer programmer, working with machines with finite-accuracy processors, the division of a simulated world into discrete units is very natural and something that I'm well used to doing. But, I only do this because I work with finite-accuracy processors and for no other reason. Why would nature do the same thing? Is this the Matrix all over again? Hmm.
Loop quantum gravity theory has been around for years, as a theory. Lately however, it has started gaining a lot of ground as it has helped to explain a number of real-world observations, and experiments that are due to happen in the near future will determine whether space could really be made from atomic pieces. The theory is simple, and nature adores simple. It fits so well with established quantum physics and Einstein's theory of general relativity that it does seem like a dream come true. Perhaps this is the grand unified theory that everybody has been searching for.
The theory itself came about because of that hole in our knowledge, between quantum physics and the theory of general relativity. We still cannot, after all these years, properly explain gravity at a quantum level - we still don't know quantum-gravity. Loop quantum gravity theory, is the best theory we have so far that attempts to fill this huge void.
The theory predicts that volumes of space are measured in units of approximately 1 Planck length, which in English is around 1.6 x 10 raised to the power of -35 metres, or 0.000000000000000000000000000000000016 metres. Extrapolating that a little further, it predicts that there are around 10 raised to the power of 99 discrete units of volume per cubic centimetre of space. That's a lot. To put it into context, there are more of these units of volume in a cubic centimetre of space, than there are cubic centimetres of space in the known universe. Therefore, the unit of measurement is, to all intents and purposes, infinitesimally small, but it is measureable.
Interestingly, this measurement is pretty close to the smallest value that an IEEE floating point number can express, being 1.175 x 10 raised to the power of -37. Hmm, maybe this is the Matrix after all?
So, space is said the be constructed from a huge number of discrete points. But what does this mean in reality? Simply put, matter, or sub-atomic particles, can only exist at certain points in space. They cannot exist between these points, but only at these points. It seems rediculous, matter can exist here and here, but not there or there. If there is a space there, why can matter not exist there? There is already a precedent in quantum theory though that makes it easier to believe that this could indeed be the case. It's very similar to the story of electrical charge of electrons. Originally, we thought that they could hold any charge within a specific range. But we now know, through refinement of quantum theory and subsequent observation, that electrons can in fact only hold certain specific electrical charges.
Time is said to work in a similar way, with very small units expressing points in time, and that time isn't the continuous stream that we have always thought it to be. According to the theory, time 'ticks' at a given rate, and that rate is approximately 10 raised to the power of -43 seconds.
In this context though, what does time mean? That is a difficult thing to explain, as time and space are tied up together in the fabric of the universe - one cannot exist without the other. This is what Einstein called 'spacetime'. Fundamentally, the 'shape' of space affects the passage of time. According to loop quantum theory though, matter can only exist at certain points in space and time - it being impossible to make observations between those points in either space or time.
This whole concept of 'pixels' of space and time is a little bewildering, but very easy to understand. As a theory, it is born out of pure mathematics rather than some sort of concocted hypothesis specifically designed to fit some prior observations. That it works at the quantum level, and explains Einstein's relativistic gravity theory is pure gold. Allied with the fact that some real-world observations that have been difficult or impossible to explain with well-established theories, but are explained perfectly with loop quantum theory, it would seem that it might indeed be truth.
Either way, the future for the theory is looking very interesting. Only now are we at a point where we can start to perform some real experiments to test the theory in any kind of rigid way. The problem thus far has been that we are talking about such small numbers in the realms of time and space, that no instrumentation yet exists that can possibly observe either at anything like the required granularity. That, is only going to be the case for so long though, and viable experiments are already being planned for the near future to test the validity of the theory.
So, it's only a matter of time (if you'll excuse the pun) before we discover if we are indeed, all just batteries for a machine world.
[Posted 07/21/2008] |
