DARK MATTER

Dark matter was proposed by  Fritz Zwiky in 1933 based in the influence of a not vissible mass that affected the velocity of the oribits of th galaxys. Another activities where this influence can be noticed is in the temperature of hot gas in galaxys and in the rotation of them. It is call dark because we cant see it like the stars or planets.

The theoretical model of the composition of the Universe propose that it is composed in the next way: 68% dark energy, ~27% dark matter, ~5% normal matter. 

''Dark matter is one of the great scientific mysteries of the time, but once astronomers accepted its existence, the answers to many other cosmic nmysteries fell into place.''

This unknown material may be, it seems to explain why the disk of our milky way galaxy has such a pronunced warp at its outer rim. Orbiting satellite galaxies naturally tend to distort the galaxy, but their gravitational effect would be to weak without the amplification that dark matter provides.
Another question dark matter answers is why the Milky Way appears to have fewer such satellite galaxies that models predict it should. It turns out that the satellites are probably out there, composed almos enterly of dark matter, making them hard to detect.


October 2011, ScientificAmerican

Time

Could time end?

Before the theory of Einstein's theory of relativity it was believed that time was like a steady drumbeat, never stopping. Einstein proved that time can slow down or even stretch out. Time affects and responds to what matter is doing, the moments when time goes up or down are called singularities, a beginning or an end. For example, the big bang which is when our universe bursted into existence and began expanding.

Relativity explains that everything, even timeline might end with a big black hole sweeping up matter, where molecules can't get recycled to start a new life. "It is not logically possible for time to have an end" says Richard Swinburne. It is absurd to think that infinity is no more than a mathematical idealization. There are six ways of how time might end, with a big crunch (dark energy makes gravity matter go into reverse making everything collapse), with a big whimper (the universe expands forever), big rip (the universe tears itself into peaces), big freeze (phantom energy fills everything up making it enable to move, and time seizes up), big brake (dark energy retards cosmic expansion) and big lurch (where pressure forces go infinite). 

The theory of relativity is not taken very seriously because it fails to capture important aspects of gravity and matter, so physicists moved on to a quantum theory of gravity, which stipulates that time may not end.  Physicists argue in both ways, some think it might end, others not. The bottom line is that physicists struggle with the contradiction no less than philosophers do.

September 2010, Scientific American

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