Archaeologica.org

Watch the program June 25 on PBS, or come back June 26 to watch it online here.

For decades, many scientists have theorized that the universe is made up of nearly undetectable mysterious substances called dark matter and dark energy. But until yesterday there was no proof that the subatomic matter actually exists.

After studying data from a long-ago collision of two giant clusters of galaxies, researchers now say they are certain dark matter does exist and plays a central role in creating and defining gravity throughout the universe....

... Stacy McGaugh, an astrophysicist at the University of Maryland, has been one of the dark-matter skeptics, and he said yesterday that he remained unconvinced.

"I've been aware of this result some time, and I agree that it is interesting and may make more sense in terms of dark matter than alternative gravity," he said. "However, it is premature to say so."

He said that a definitive detection of dark-matter particles would mean "grabbing them in the laboratory, not just inferring that their effects can be the only possible explanation for an observation before the alternatives have actually been checked."

The NASA-affiliated team that announced its findings yesterday said that the next step in trying to understand dark matter (and related dark energy) is, in fact, to identify it in a laboratory. That task has proved difficult so far, they said, because dark matter leaves no detectable traces, except to create a gravitational pull.

"This finding doesn't tell us where dark matter comes from," Carroll said. "It tells us that dark matter exists, but it doesn't say what it is, or why there's so much of it. The real adventure is ahead of us."

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…… 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 the names "dark matter" and "dark energy" serve mainly as expressions of human ignorance, much as the marking of early maps with "terra incognita."

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 adjusts 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. However, a study in August 2006 reported an observation of a pair of colliding galaxy clusters whose behavior, it was claimed, was not compatible with any current modified gravity theories.[21]

In 2007, astronomer John W. Moffatt proposed a theory of modified gravity (MOG) based on the Nonsymmetric Gravitational Theory (NGT) that accounts for the behavior of colliding galaxies.[22]

Digit wrote:Also of course Ish the idea is pretty old, it used be known as the 'Ether' or 'Aether'.

UK astronomers, as part of an international team, have reached a milestone in the construction of one of the largest ever cameras to detect the mysterious Dark Energy component of the Universe. The pieces of glass for the five unique lenses of the camera have been shipped from the US to France to be shaped and polished into their final form. The largest of the five lenses is one metre in diameter, making it one of the largest in the world.

Each milestone in the completion of this sophisticated camera brings us closer to detecting the mysterious and invisible matter that cosmologists estimate makes up around three quarters of our Universe and is driving its accelerating expansion. Observations suggest that roughly 4% of the Universe is made up from ordinary matter and 22% from Dark Matter; this leaves 74% unaccounted for - the so-called Dark Energy.