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In this issue:
symmetry: What is Dark Matter?
Science Today: John Harris to Deliver Lecture on Origin of Hot 'Quark Soup'
Correction: One More Globie!
ES&H to Offer Window for Training Courses

SLAC Today

Thursday - April 26, 2007

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symmetry: What is Dark Matter?

Dark matter is, mildly speaking, a very strange form of matter. Although it has mass, it does not interact with everyday objects and it passes straight through our bodies. Physicists call the matter dark because it is invisible.

Yet, we know it exists. Because dark matter has mass, it exerts a gravitational pull. It causes galaxies and clusters of galaxies to develop and hold together. If it weren't for dark matter, our galaxy would not exist as we know it, and human life would not have developed.

Dark matter is more than five times as abundant as all the matter we have detected so far. As cosmologist Sean Carroll says, "Most of the universe can't even be bothered to interact with you."

Whatever dark matter is, it is not made of any of the particles we have ever detected in experiments. Dark matter could have—at the subatomic level—very weak interactions with normal matter, but physicists have not yet been able to observe those interactions. Experiments around the world are trying to detect and study dark matter particles in more direct ways. Facilities like the Large Hadron Collider could create dark matter particles.

Read the latest issue of symmetry online...

(Daily Column - Science Today)

John Harris to Deliver Lecture on Origin of Hot 'Quark Soup'

In the beginning, there was an extremely hot, dense soup. Just 10 millionths of a second after the Big Bang, the universe consisted of a plasma of tiny particles called quarks and gluons that was 100,000 times hotter than the center of the sun. That quark-gluon plasma is the origin of all the matter that we know today.

Yale physicist John W. Harris will talk about this amazing primordial state of matter during this year's Robert Hofstadter Memorial Lecture at 8 p.m. Monday, April 30, in Room 200 of the Hewlett Teaching Center in the Science and Engineering Quad. The title of his talk, which is free and open to the public, is "What Is That Black Hole Doing in My Quark Soup?" He also will give a more technical colloquium, titled "Evidence for a Quark-Gluon Plasma in the Laboratory," at 4:15 p.m. Tuesday, May 1, in Room 201 of the Hewlett Teaching Center.

"Everything that we don't understand [about the origin of the universe] happened in the first 10 millionths of a second," says Harris. "And we are trying to understand what the matter in the universe was at that time and to determine its properties." 

Harris, who is a professor of physics and leader of the Relativistic Heavy Ion Group at Yale, will discuss the importance of studying this hot soup to understand the origins of the universe.  Read more...

One More Globie!

Yesterday's article about the 2007 Employee Recognition Awards neglected to list one recipient: Lisa Adair. Our apologies—and congratulations—to Lisa!

ES&H to Offer Window for Training Courses

Beginning Monday, April 30, SLAC's Environment, Safety and Health (ES&H) Division will offer employees and users a 90 day window to complete newly assigned ESH Training. The new rules will afford employees and users time to take training so that they will not be automatically considered overdue for a course that has just been assigned.

A restrictive period means that even though you have 90 days to complete the training, the work you are allowed to do during this period may be restricted. The level of work restriction varies depending on regulations or SLAC policy governing the hazards mitigated by the training. For example, you may not under any circumstances work with radioactive material without the proper training but you will be allowed to work at a computer until you receive the appropriate ergonomics training. A matrix of ES&H courses has been created to help you determine what work can be done within the restricted period for each course.

A list of all ES&H courses and their associated restrictive periods is available online

All employees and users are asked to please work with their safety coordinator and supervisor to ensure that they have an understanding of their training requirements. As always, the ES&H Training team is available to answer any questions. Please send an email to

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