Tuesday, October 11, 2011

Particle physics may shed light on reversal of time

Experiments on a simple particle that consists only of one proton and one neutron, elements that make up the core of an atom, could unravel a phenomenon called time reversal violation. This means, particles that travel through time in the opposite direction, compared to what we are used to, but with a little twist. Basically, what scientists think is that certain particles move through time the way we perceive, and other particles balance this by travel back in time as part of their 'natural course'. A violation in time reversal could explain why the universe consists of  the elements we see today, and why there is no balance between particles going through time the way we perceive it, versus particles moving in the opposite direction.

To discover the spectacular and mind boggling phenomenon called time reversal violation, the University of Arizona proposed experiments on a particle called deuteron. This is basically a hydrogen atom, but instead of an electron cloud, this particle possesses a neutron. Therefore, the deuteron consists of one positively charged proton and a neutral neutron. Technically, it is not an atom, as there are no electrons present. The atom variant of the deuteron would be called deuterium: a heavier version of hydrogen consisting of a proton, neutron and an electron. Apparantly, the deuteron has a special property called a magnetic quadrupole moment. This could reveal violation of time reversal.

But why would time reversal exist in the first place? It seems that all matter moves through time the same way we do: everything gets 'older', nothing seems to travel back in time. Apparently, that is only what we perceive. For every piece of matter, there is a mirror image, called antimatter. Antimatter has opposite quantum mechanical properties, including the direction of time. When the universe was created, scientists think there was an equal amount of matter versus antimatter. Balance. University of Arizona researcher Bira van Kolck explains time reversal with an analogy of billiards:
"Let's suppose you're playing billiards. You have two balls and you knock them against each other on the table. Suppose you film this, but you play the movie in reverse. If you don't tell the person who is watching which version is forward and which is backward, the person wouldn't be able to tell."
There is symmetry in this example. With our laws of physics, scientists expected symmetry when using equations describing matter and time. However, in certain experiments, something called an electrical dipole moment has been found in particles: an unequal distribution of the negative charge that an electron carries. That basically means particles spin in a way that is different than what one would expect when there is balance.

When looking at time reversal, scientists expected a reverse spin compared to their counterpart, that moves through time in the way we perceive it. Because there is basically no antimatter anymore in our present universe, something in this balance is disturbed. Violation of the principle of time reversal may explain this phenomenon. The electrical dipole moment is caused by spin of the particle, so measuring it tells you something about the direction of the spin.

However, the electrical dipole moment is not enough to explain how particles can spin to violate time reversal. The magnetic quadrupole moment of deuterons are apparently more suitable to establish time reversal violation. Performing measurements on deuterons may explain why particle spin causes a glitch in time, that results in the reverse version to be a tad bit different to what we would expect. To make another anology; what scientists want to know is why your car is not going as fast on the way back.

Scientists assume our universe was created, during the Big Bang, with equal amounts of matter and antimatter. When matter and its corresponding antimatter counterpart meet, they annihilate each other, which creates energy equal of e=mc2, Einstein's famous equation linking energy and matter. In this case, the universe would consist merely of the particles of light: photons. There would be no matter. Because this is obviously not the case, the apparent assymetry is one of the biggest unsolved problems in the world of physics. Experiments on deuterons and its magnetic quadrupole effect could reveal a disbalance in time reversal of antimatter, possibly explaining why this asymmetry exists.
You and your antimatter version meeting each other.
Though this seems like an important question in physics, there is only 4 percent matter in the universe. The remainder is unexplained stuff we dubbed dark energy and dark matter. Forms of energy and matter we can not detect, but we know must exist. While the disbalance between matter and antimatter, and its link with time travel is extremely interesting, there are more mysterious forces at work in our universe. These things will keep us busy for many more decades to come.
What the universe consists of; a pie chart.

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