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Articles: Devotion | Quest for Infinity - 08
- Prof. venkata ramanamurty mallajosyula
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Have MACHOs been observed? Yes, many of them; so we can say dark matter does exist. OK, MACHOs exist but do they account for all the dark matter that could be present? Any other types of dark matter possible? Of course, say the scientists, and they suggest that certain types of elementary particles called WIMP [Weakly Interacting Massive Particles] could exist, and physicists are busy looking for them; thus far, none have been found.
Cosmic Census
What I want to impress with the above is that one thing leads to another, and dark matter, the value of Ω, the fate of the Universe, elementary particle physics, all have begun to influence each other in ways never before imaginable. Let me now give you some more taste of this! Suppose we do a Cosmic Census, meaning, adding up all the known masses in the Universe; and we represent the result as a pie chart. This was done some years ago, and it was found that if one added all the known masses, including a good estimate of the dark matter, then it all added up to just about 30 % of the mass needed to make Ω equal to 1; remember, Ω is the magic parameter that determines the fate of the Universe, and the value of Ω depends on the amount of matter in the Universe. Current estimates suggest that Ω is in fact pretty close to 1; in which case, the question becomes: “What is it that is missing to make up for the mass needed to make Ω equal to 1?”
This pie chart is essentially an approximate “census’ report of the Cosmos. [The percentages do not add up exactly to 100 because of rounding-off errors.] Many decades ago, people thought the Universe was filled only with matter and radiation, with matter being made up of galaxies, which in turn were made up of stars and their planets [if any]. As the figure above shows, the view is now very different. Ordinary visible matter forms only a very small part; besides this, there is a lot of dark matter. But that is still not the end of the story. The requirement that the value of Ω be close to 1, now suggests that besides dark matter, there is also dark energy! In fact, the contribution due to dark energy seems to dominate the contents of the Universe!
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