Saturday, September 8, 2012

Uniting dark matter and dark energy

One of the most elusive topics in physics right now are dark matter and dark energy. We know they exist because their effect is measurable, but we do not exactly know what it is. We observe their effects by looking at the orbits of planets and stars: we know pieces of matter attract each other by the force of gravity, but this effect alone cannot explain what we see. Hence dark matter: which is matter we cannot see but does have gravitational effects. On the other hand, there is dark energy, that opposes the force of gravity and is supposedly responsible for the expansion of the universe. While the details are still incredibly fuzzy, some scientists have come up with a way to unite the two into one single theory and are thereby challenging Einstein himself.

Like most things in physics, phenomena can be described by giving a set of equations. Because they are usually incredibly complicated, and truthfully a bit boring, I will not mention them. However, they are very important to accurately describe physics, and several of Einstein's ideas have turned into very famous equations, the most prominent of course being E=MC2. He also described how the universe is curved instead of 'flat', something which is bundled in his theory of general relativity, and it functions as a geometric description of gravity.

Dark matter and dark energy were only discovered after Einstein's death, like many other theories in physics. Nevertheless, most of his ideas have hold their ground, although we have seen some adaptations to various theories. Mathematicians from the Sichuan University in China think they can expand on the theory of gravity by incorporating equations that describe the behaviour of dark matter and dark energy. According to them, it is necessary to unite them in order to accurately describe basic laws of physics, such as the conservation of energy. The Chinese researchers claim that by incorporating energy-related equations describing dark matter and dark energy, we get better models for the phenomena we observe in our universe.

It is an interesting, albeit extremely complicated, idea to unite dark matter and dark energy into the set of gravitational field equations that were originally developed by Einstein and others. Intuitively, it makes sense because dark matter and dark energy both have an effect on gravity, even though they are on opposite ends. Of course, mathematical models are only valid when we can put them to the test, which means experimental validation and accuracy in predicting observations needs to be shown. Because gravity still holds many mysteries, the Chinese concept is a refreshing one in the field of physics.

Einstein failed to unite gravity with the other universal forces (electromagnetism, the strong and weak nuclear force), but better understanding of its behaviour may help us reach that goal. Because we already have a set of equations that incorporates all universal forces except gravity, being able to unite them all would be a great step forward in our understanding of the universe.

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