Baryon （重子）
https://zh.wikipedia.org/zh-tw/%E9%87%8D%E5%AD%90
https://en.wikipedia.org/wiki/Baryon
What is the Difference Between Dark and Baryonic Matter?
https://www.futurelearn.com/info/courses/mysteries-of-the-universe/0/steps/217637
Dark and baryonic matter are believed to be two completely different substances, with the former still being a mystery as to its true identity and composition, while the latter being the usual substance that we always encounter in our daily lives.
Baryonic Matter vs Dark Matter
First and foremost, baryonic matter are composed of baryons – mostly protons and neutrons. However, the composition of dark matter is yet to be discovered. The existence of dark matter has been backed up by evidences related to astronomical observations (e.g., galaxy light curves, observations of galaxy clusters and gravitational lensing), but it is possible that dark matter may exist also in Earth.
Dark Matter Undetectable
The reason why it is hard to detect dark matter is because it interacts very weakly, or there is no interaction at all, with most forces. For instance, as its name suggests, dark matter does not absorb, emit, or reflect light. This suggests that dark matter does not interact greatly with electromagnetic force (recent studies found out that dark matter may possess electrical charge, though very weak). However, dark matter is found to interact with gravitational force.
Evidence of Dark Matter
One of the evidences of dark matter, gravitational lensing, shows that objects behind galaxy clusters become “lensed”, and the total mass of the galaxy cluster can be inferred from the lensed image. Calculations show that the total mass derived from the observable/visible matter is less than the total mass needed to produce the lensed image, hence there should be some kind of matter that we haven’t discovered yet.
This is an additional video, hosted on YouTube.
Baryonic Matter Matters
Baryonic matter is, of course, important as it is. Without it, we will be nothing. However, dark matter is important too. One reason is because without dark matter, galaxies will not be able to rotate the same way as we observe it from its light curve (as what Prof. Goto showed in his previous video). It is also crucial to explain the formation of the Universe.
Certain events in the Big Bang caused the creation of elements such as hydrogen, helium and many others. They needed to clump together to form stars, and as stars get old they explode into a supernova.(超新星) The materials that are ejected by supernova will be recycled to form more complex molecules, and to do this, the materials should stay into the galaxy by a decent amount of gravitational pull. Without dark matter, this required gravitational pull will not be enough and so the ejected materials will fly very far away for it to be recycled again, making molecular life impossible to achieve.
