Dark matter?

Question

Does any one know what dark matter is? my teacher was talking and i wasn't listening. Thank You!

Answer 1

Well as far as they know - and we are still largely talking theoretical - it is the opposite of matter - anti-matter. Very dangerous stuff indeed - I believe they have actually been daft enough to produce some of it in California - if it comes into contact with matter - very, very, very, big bang !

I have just seen the two answers preceding mine - I answered your question the best I could as apposed to some people who JUST want to collect two points !

Answer 2

Dark matter is what cosmologists believe make up the major portion of our universe. It is not detectable by any of our technologies; its existence is only inferred from its effects on visible matter. If I remember correctly, dark matter is a theory still? I could be wrong, it has been a while since I looked over my old books. Check out the Wikipedia article link I posted below. It explains the major points very well.

Answer 3

Dark Matter is the thoerized force driving the universe at an accelerated pace. Astronomers and asrophysicists have come up with this theory to explain why red shifts in our galactic neighbors don't nessesarily add up to the distance a galaxy's position ahould be according to the accepted age of our universe. It appears that some galaxies are further apart than should be possible at this point in time needing something to explain the eccellerated expansion of the universe.

Answer 4

Dark Matter
What do scientists look for when they search for dark matter? We cannot see or touch it: its existence is implied. Possibilities for dark matter range from tiny subatomic particles weighing 100,000 times less than an electron to black holes with masses millions of times that of the sun . The two main categories that scientists consider as possible candidates for dark matter have been dubbed MACHOs (Massive Astrophysical Compact Halo Objects), and WIMPs (Weakly Interacting Massive Particles). Although these acronyms are amusing, they can help you remember which is which. MACHOs are the big, strong dark matter objects ranging in size from small stars to super massive black holes . MACHOs are made of 'ordinary' matter, which is called baryonic matter. WIMPs, on the other hand, are the little weak subatomic dark matter candidates, which are thought to be made of stuff other than ordinary matter, called non-baryonic matter.

Answer 5

Since scientists can't explain how the universe works based only on what they can see, they assume there is more matter that exists that we can not see called dark matter (doesn't emmit or reflect light). The mass of the dark matter makes up the difference in what they theorize exists and what they can actully show exists.

Answer 6

no more than four percent of dark matter can be ordinary matter, but the rest is unknown. there is about six times as much dark matter as ordinary matter. dark matter seems to interact with ordinary matter only thru gravitation so it is unseen. fritz zwicky discovered dark matter in 1933, but there is recent direct evidence for its existence.

look here:
http://en.wikipedia.org/wiki/Dark_matter
http://en.wikipedia.org/wiki/Bullet_cluster

Answer 7

In astrophysics, dark matter is matter that does not emit or reflect enough electromagnetic radiation (such as light, X-rays and so on) to be detected directly, but whose presence may be inferred from its gravitational effects on visible matter. Among the observed phenomena consistent with the existence of dark matter are the rotational speeds of galaxies and orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter also plays a central role in structure formation and Big Bang nucleosynthesis, and has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than is directly observable, indicating that the remainder is dark.

The composition of dark matter is unknown, but may include new elementary particles such as WIMPs and axions, ordinary and heavy neutrinos, dwarf stars and planets collectively called MACHOs, and clouds of nonluminous gas. Current evidence favors models in which the primary component of dark matter is new elementary particles, collectively called nonbaryonic dark matter.

The dark matter component has vastly more mass than the "visible" component of the universe. [1] At present, the density of ordinary baryons and radiation in the universe is estimated to be equivalent to about one hydrogen atom per cubic meter of space. Only about 4% of the total energy density in the universe (as inferred from gravitational effects) can be seen directly. About 22% is thought to be composed of dark matter. The remaining 74% is thought to consist of dark energy, an even stranger component, distributed diffusely in space. [2] Some hard-to-detect baryonic matter (see baryonic dark matter) makes a contribution to dark matter, but constitutes only a small portion. [3] [4] Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics. It has been noted that dark matter and dark energy serve mainly as expressions of our ignorance, much as the marking of early maps with terra incognita. [2]

[...]

A proposed alternative to physical dark matter particles has been to suppose that the observed inconsistencies are due to an incomplete understanding of gravitation. To explain the observations, the gravitational force has to become stronger than the Newtonian approximation at great distances or in weak fields. One of the proposed models is Modified Newtonian Dynamics (MOND), which corrects Newton's laws at small acceleration. However, constructing a relativistic MOND theory has been troublesome, and it is not clear how the theory can be reconciled with gravitational lensing measurements of the deflection of light around galaxies. The leading relativistic MOND theory, proposed by Jacob Bekenstein in 2004 is called TeVeS for Tensor-Vector-Scalar and solves many of the problems of earlier attempts. A similar theory proposed by John W. Moffatt is Nonsymmetric Gravitational Theory.

In August 2006, a study of colliding galaxy clusters claimed to show that even in a modified gravity hypothesis, the majority of the mass must be some form of dark matter by demonstrating that when regular matter is "swept away" from a cluster, the gravitational effects of dark matter (which is thought to be non-interacting aside from its gravitational effect) remain [1]. However, a study claims that TeVeS may be able to produce the observed effect but needs the majority of the mass to be dark matter, possibly in the form of ordinary neutrinos [17]. Also Nonsymmetric Gravitational Theory has been claimed to qualitatively fit the observations without needing exotic dark matter [18].

In another class of theories one attempts to reconcile gravitation with quantum mechanics and obtains corrections to the conventional gravitational interaction. In scalar-tensor theories, scalar fields like the Higgs field couples to the curvature given through the Riemann tensor or its traces. In many of such theories, the scalar field equals the inflaton field, which is needed to explain the inflation of the universe after the Big Bang, as the dominating factor of the quintessence or Dark Energy. Using an approach based on the exact renormalization group, M. Reuter and H. Weyer have shown [19] that Newton's constant and the cosmological constant can be scalar functions on spacetime if one associates RG scales to the points of spacetime.

Answer 8

it does not matter

Answer 9

you should have listened