Dark matter: A form of matter particles that does not reflect or emit electromagnetic radiation. The existence of matter is interfered from gravitational effects on visible matter e.g. stars and galaxies.
Dark matter - which does not emit or reflect enough light to be "seen" - is thought to make up 25% of the Universe. The ordinary matter we can see is believed to make up no more than about 5% of our Universe - http://news.bbc.co.uk/2/hi/science/nature/5272226.stm
MACHOs : stands for Massive Astronomical Compact Halo Objects. There is some evidence that lots of ordinary matter does exist in these groupings. These can be thought of as low mass 'failed' stars or high mass planets. They could even be black holes which produces little or no light.
WIMPs: stands for Weakly Interacting Massive Particles. these could be new particles which we do no know about. Many experiments around the world are in the search for WIMPs.
Why is the Density of the universe so difficult to determine?
- we can only see a maximum of 10% of matter that exists in the galaxy
- much of the mass of the galaxy and the universe is made out of dark matter - not sufficiently enough for us to detect
- dark matter is in the form of MACHOs or the undiscovered WIMPs
E4.12: State that current scientific evidence suggests that the universe is open
The current scientific consensus of most cosmologists is that the ultimate fate of the universe depends on its overall shape, how much dark energy (some unknown force that is opposing gravity which is pushing the universe apart) it contains, and how the dark energy density responds to the expansion of the universe. Recent observations have shown that, from 7.5 billion years after the Big Bang onwards, the expansion rate of the universe has actually been increasing, concurrent with the Open Universe theory.
E4.13: Discuss an example of the international nature of recent astrophysics research.
- The Drake Equation
http://www.astronomynow.com/news/n1005/24seti7a/
E.4.14 Evaluate arguments related to investing significant sources into researching the nature of the universe.
For:
- Understanding the nature of the universe sheds light on fundamental philosophical question like for example:
why are we here? and is there life elsewhere in the universe?
- fundamental research will give rise to technology and improve the quality of life
- life on Earth will be an impossibility and thus will be able to colonize new planets
Against:
- money could be spent elsewhere such as food, shelter, medical care to those who are suffering from hunger, homeless and disease
- worthwhile to spent the money on medical research as it will improve the quality of life as well as being able to save lives
- funding space research should not be a priority since it is expensive
- is the information gained worth the cost?
Source: Heinemenn HL Physics textbook by Chris Hamper
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