Universe

I’ve allways wondered if Dark Matter and Antimatter were close together because Dark matter can’t been seen and I would think that antimatter couldn’t be seen either. Seeing as antimatter is the opposite of regular matter.

They are very different things!

Anti-matter has the same properties as ordinary matter except that the charges of the basic particles are flipped. For example, an electron is negatively charged, so the anti-matter particle for the electron is positively charged. It is called a positron. There are other, more subtle changes, so the anti-neutron is not the same as a neutron (although both are electrically neutral).

There is a collective term for heavier particles like protons and neutrons which are made out of quarks. They are called baryons. Anti-matter is ultimately made out of quarks also, so is baryonic.

Because anti-matter has charges, it interacts with light (electromagnetic waves) in essentially the same way as matter does. So, large quantities of anti-matter would be visible. Anti-carbon, for example, would have the same density as ordinary carbon and would be black (assuming it was anti-graphite).

Also, anti-matter interacts very strongly with ordinary matter. So strongly, in fact, that the two destroy each other: their mass is converted into energy when they meet.

Dark matter is very different. At this point, we only know about it from its gravitational effects: how it affects orbits of stars in galaxies, or how it bends light around galaxies. We know that it, unlike anti-matter, does not interact strongly with light. That is why it is invisible. We also know that dark matter is not baryonic, so it is not made from quarks at all.

At this time we don’t know what dark matter is made from, although there is a lot of speculation. The best guesses at this point all suggest that dark matter is like a heavy analog of a neutrino, which only interacts with ordinary matter through the weak force and gravity, not the electromagnetic force. In particular, dark matter does not destroy ordinary matter like anti-matter does.

I.L.Dark.Matter. Part 1.
This is only for fan purposes. No copyright infringement intended.

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Complete video at: http://fora.tv/2008/07/23/Leonard_Susskind_-_The_Black_Hole_War

Stanford University physicist Leonard Susskind differentiates the theoretical concept of “dark matter” from its somewhat more controversial cousin, “dark energy.”

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Recognizing a contradiction in Stephen Hawking’s claim that things disappear in black holes, Susskind and Gerard t’Hooft offered a counterargument aimed at disproving this controversial theory.

Susskind discusses the story behind the black hole conflict and how it has led to a better idea of how our universe works – The Commonwealth Club of California

Leonard Susskind is a theoretical physics professor at Stanford University in the field of string theory and quantum field theory. Susskind is widely regarded as one of the fathers of string theory for his early contributions to the String Theory model of particle physics.

Duration : 0:3:14

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Wouldn’t dark matter need to make up exactly 50% of the universes mass for the mirror matter hypothesis to be credible?
Yet dark matter makes up 96% of the Universes mass so this does not make sense. 4% and 96% seem no where near equal.

Your argument would be correct if symmetry was preserved. However if mirror symmetry is broken then the mirror matter could be either heavier or lighter than ordinary matter and would interact only weakly if not at all via the electromagnetic, strong and weak forces and only via gravity. Hence if mirror matter existed it would be by definition be dark matter.

The 96% includes dark matter and dark energy which may or may not be coupled. The dark matter is about 6 times the ordinary matter we interact with (we see less than 25% of that). These numbers may become important numbers if mirror matter can be shown to exist or string theory will ever be confirmed.

Stay tuned.

If dark matter makes up 96% of the universe, and visible matter only 4%, then is there dark matter around, on, or in the Earth or is it all out in space somewhere?

George is close. Dark matter exists in large halos which envelope galaxies. The dark matter halos can have an arbitrary shape, in fact many people have made "maps" of the dark matter by looking at gravitational lenses. The size of the halo can be a few to many tens of times larger than the galaxy which resides in side of the halo. Many very large halos can host several galaxies (though rarely more than a few galaxies per halo).

The mistake George makes is when he says that it’s "near the Galactic center". This is very false. The galactic center is *inside* a dark matter halo. In fact, the center of the halo and the galaxy need not be the same, such as in the case of this galaxy cluster:

http://en.wikipedia.org/wiki/Bullet_Cluster

Also, since the dark halos host galaxies, and earth is in a galaxy, then earth is in a dark halo. Therefore, dark matter *EXISTS* all around us, even here on Earth. There are several major experiments set up to detect dark matter and measure it’s properties. You can learn about a famous experiment at:

http://en.wikipedia.org/wiki/Cryogenic_Dark_Matter_Search

An international team of astronomers using the NASA/ESA Hubble Space Telescope has discovered a ghostly ring of dark matter formed long ago during a colossal collision between two galaxy clusters. This is the first time that dark matter has been found with a distribution that differs substantially from the distribution of ordinary matter. Read more at: http://www.spacetelescope.org/news/html/heic0709.html

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How does Dark Matter and Dark Energy in the universe determine the future of the universe in our current understanding of these materials? What is the Cosmic Jerk in the universe 6 Billion years ago? Help appreciated, thanks.

The Cosmic Jerk six billion years ago occurred when there became enough Dark Energy to start accelerating the expansion of the universe. Until then, the gravity of the Galaxies and matter was slowing the expansion down. But around six billion years ago, their became enough dark energy to start accelerating the expansion.

It is in this sense that Dark Energy will impact the future of the universe. If their becomes too much, it will eventually accelerate the universe so fast that everything will be pulled apart from each other, dooming all life. In this scenario, the future of the universe will end in the Big Rip, in which the universe accelerates so fast that even atoms and the smallest particles will be pulled apart.

If their isn’t so much dark energy, then the universe will just expand forever. This would result in something called the Big Freeze, where galaxies become solar systems, and everything becomes so spread apart that there is not enough stars being born and too many dying out. In this scenario, everything would become so spread apart that their would eventually be no light and no heat. This is what will most likely happen based off known info.

As for Dark Matter, it just contains the "extra" matter that holds everything together. It doesn’t really have and impact on the universe’s expansion.

Can someone help me with the topic dark matter?? I really dont know what it is. Any help will be appreciated. Thanks in advance

In astrophysics and cosmology, dark matter is a hypothetical form of matter that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter.

COSMOS Video News Release
For the first time ever, astronomers have been creating a three—dimensional map of how the dark matter is distributed across the Universe. An international team of scientists, among them groups from Marseille, the Max-Planck Institutes and Paris have been using data from the NASA/ESA Hubble Space Telescope. The results are published in nature online of 8 January 2007, and at the meeting of the American Astronomical Society in Seattle. This Video News Release discussed this discovery. More on: http://www.spacetelescope.org/news/html/heic0701.html

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http://www.pbs.org/nova/sciencenow We can’t see dark matter, and some skeptics doubt its existence, but many scientists think it makes up 20-some percent of our universe. Astronomer Doug Clowe explains how the Bullet Cluster, a group of galaxies billions of light years away, may shed some light on this mysterious stuff.

Don’t miss the new season of NOVA scienceNOW, airing every Wednesday at 9pm starting June 25 on PBS. Watch past episodes of the program, try out interactives, and more on our Web site: http://www.pbs.org/nova/sciencenow

Duration : 0:4:38

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