Dark matter: we can't see it, but it's believed to make up 85 percent of all matter in the universe and without it we almost certainly wouldn't be here. Particle physicist and New York Times bestselling author Lisa Randall joins us to discuss her new book "Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe."

Joshua Bell has been a violin virtuoso since he was teenager in Bloomington, Indiana back in the 1980s. He talks with "Chicago Tonight" about his early years, the greatness of the Stradivarius and his favorite collaborators in this encore presentation. He'll also treat us to a live performance with pianist Sam Haywood.

Official rules for the Chicago Tonight Puzzle Challenge.

Today is the first day of medical marijuana sales in Illinois. Who is buying, who is selling, and is the program here to stay? Paris Schutz has the latest.

The U.S. Department of Education ruled that Palatine Township High School District 211 violated a transgender student's right not to be discriminated against when it refused the student unfettered access to the girls' locker room.

The violence in Chicago continues to spark rage and national headlines. Last week it was the murder of 9-year-old Tyshawn Lee, then 20-year-old Kaylyn Pryor, an aspiring model, was gunned down. This weekend 14-year-old J-Quantae Riles was killed. Eddie Arruza reports on steps being taken on the city’s West Side to combat the violence.

The museum sold five antique trains from its collection at a public auction last month. 

The veteran journalist who was anchor and managing editor of "Nightline" on ABC from 1980 until 2005 discusses his new book about the risk of cyberattack facing the power grid in the United States and the inadequate measures being taken to protect it.

Puzzle lovers, put on your thinking caps and prepare for the first-ever Chicago Tonight Puzzle. We'll stimulate your cerebrums with the first installment of a monthly segment in which we challenge our viewers to solve a puzzle for a chance to win a "Chicago Tonight" prize package.

An original and a reproduction – one of only two in the world – will be on display as part of the Field Museum's "Greeks" exhibit opening Nov. 25.

Joel Weisman and his panel of guests discuss the top stories of the week, including the announcement by Lake County officials that police Lt. Joseph Gliniewicz’s death was a suicide; the tragic murder of 9 year old Tyshawn Lee; the new trailer for Spike Lee's controversial film "Chi-raq"; and news that CPS schools may see thousands of layoffs this winter.

The general consensus: Last week's GOP presidential debate on CNBC was a disaster, but it has led to a lot of discussion over what sort of format and approach upcoming debates should take. Newton Minow, who has been called the father of televised presidential debates, joins our discussion.

The new head of the Chicago Urban League joins "Chicago Tonight" to talk about the city's gun violence and how the 99-year-old organization aims to help foster a new generation of black leaders.