Sunday, November 25, 2012

Time is not symmetrical, new study shows

We experience time as a straight line; it only goes forward and never backwards, unless you are playing back a piece of video or audio in reverse. This is something that is never questioned, but the wondrous world of quantum mechanics has taught us to look differently at things that seem obvious. Einstein already proved with his theory of relativity that time differs depending on the observer, but individual particles appear to go one step further. There supposedly is an anti-particle for every particle that has exact opposites characteristics, and that also means that it has a different direction in time. An associated theory is dubbed supersymmetry, but scientists have revealed that time is actually asymmetrical.

It may seem obvious that time is asymmetrical, as there is no observable backwards direction that would complete the symmetry of time. However, things look different on the scale of individual particles. This is where supersymmetry comes in. Particles can be symmetrical in charge (C, plus or minus), parity (P, spatial coordination, meaning there is a 'mirror image') and in time (T). If everything would be symmetrical, then for every decaying particle there would be an event 'mirroring' what happens.

We can prove that there are mirror images by the fact that there is antimatter. Antimatter consists of particles that have the exact opposite characteristics of their respective matter counterparts, which is what we observe in our daily life. We are able to artificially 'produce' antimatter, but there is not much of it. And that is not surprising, because when matter and antimatter collide they annihilate each other, which means energy is released based on the famous E=MC² equation. For those with a little understanding of this famous equation by Einstein: complete annihilation of matter would mean a release of an enormous amount of energy.

Symmetry violation
The existence of antimatter raises questions about the origin of our universe. If there is almost exclusively matter present today, where did all the antimatter go? One of the hypotheses is that the symmetry of the C, P and T was broken during the Big Bang. That means formation of antimatter and matter and its corresponding annihilation did not happen at equal rates, and this supposedly resulted in more matter being left over today.

CP violation
Each individual component of symmetry, the C, P and T, can be combined: C and P can form CP symmetry, and if you add time to the mix, you get CPT symmetry. While this is rather complicated, it means something along the lines of everything being symmetrical in all aspects. CPT symmetry is actually a different name for supersymmetry, and if it were true, it would explain a great deal about our universe. However, physicists have already shown that under some condition, CP violation occurs. That means that the laws for particles and their corresponding anti-particles are not the same (C), and that for two particles that are 'mirror images' of each other, the laws of physics are not the same either (P).

T violation
This leaves time. So far, time was thought to be symmetrical: the decay of a particle that goes forward in time is exactly the same as the decay backwards in time, just as watching a video in reverse would not mean it takes longer or shorter (given the same playback speed). While this is known to be not true in some conditions for C and P, T symmetry has so far 'survived' the experimental procedures that were set up to test this hypothesis. Until a group of researchers from the SLAC National Accelerator Laboratory looked closely at a large number of particle collisions. They were able to prove that the rate of decay is not the same for each direction of time. An analogy is that when you play a tape that takes one hour, and then choose to rewind it at exactly the same playback speed, time will either take longer or shorter in reverse. However, it is impossible to make an accurate real life analogy when it comes to quantum mechanical phenomena.

While asymmetrical characteristics of individual particles are almost impossible to grasp, it does have important implications about our understanding of the universe. If these results can be replicated, it means that we can toss the theory of supersymmetry out of the window. That also means we need to find new hypotheses to explain certain phenomena in our universe, such as dark energy and dark matter. While this concept of time violation, along with charge and parity violation, is almost impossible to grasp, it is amazing to see that how deeper we dive into the world of individual particles, the laws of physics get stranger and stranger.
A graphical explanation of time violation. The particle is switching from its red state to its blue state, and its symmetrical counterpart is doing the exact opposite. Under symmetrical conditions, the time this event takes should be the same, but this is found to be not true. A similar representation can be made for C, P and CP violation.

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