Dark energy and dark matter: What are they?

Dark energy and dark matter: What are they?

Dark energy and dark matter are prominent concepts in cosmology? What are they?

Think about our own solar system. Most stuff, such as planets, rotate around the Sun. Occasionally, some stuff, such as meteoroids, fall into the Sun of planets. Occasionally, some stuff fly out of the solar system.

Now look at the whole universe. According to current understanding, the whole universe is expanding rapidly, expanding in accelerating speed. It takes energy to accelerate. Where is the source of energy? It can’t be the gravitational energy. It is a contracting force. We can’t detect the energy source. We call it dark energy.

Think about our own solar system again. Venus rotates faster than Earth. Earth, in turn, rotates faster than Mars. Objects further away from the center, or center of the gravity, rotate slower. In the case of the solar system, more than 99% of the total mass is concentrated in the Sun.

But the edges of some galaxies move as fast as the center. This suggests that the mass of these galaxies must be spread out quite evenly. But obervations found no such matter. So much of matter is unobservable, at least with the current methods. We call this unobservable matter dark matter.

From the calculation based on current theory, dark energy constitute 68% of the total energy mass, dark matter constitute 27%, ordinary matter only constitute 5%.

If ordinary matter only constitute 5% of the universe from the current theory, you might be forgiven to suspect there is something wrong with the current theory. That is my suspicion as well.

Dark energy, which constitute 68% of the total energy mass of the universe, is required by the acceleratingly expanding universe. But is the universe really expanding? The conclusion is based on the redshift data. Could there be an alternative explanation for the redshift data?

I think so. Data shows that light source further away displays more redshift. This is interpreted as the accelerating universe. But it can be simply thought as light wears out more from travelling longer distance. From background radiation, we know that the vacuum is not truly empty. It is natural to think light wears out travelling through the space. This is a much simpler explanation.