In quark–diquark models, a diquark, or diquark correlation/clustering, is the hypothetical state of two quarks grouped inside a baryon (that consists of three quarks) (Lichtenberg 1982). The diquark is often treated as a single particle with which the third quark interacts via the strong interaction. The existence of diquarks inside the nucleons is a disputed issue, but it helps to explain some nucleon properties and to reproduce experimental data sensitive to the nucleon structure. Diquark–antidiquark pairs have also been advanced for anomalous particles such as the X(3872).

The forces between the two quarks in a diquark is attractive when both the colors and spins are antisymmetric. When both quarks are correlated in this way they tend to form a very low energy configuration. This low energy configuration has become known as a diquark.

Many scientists theorize that a diquark should not be considered a particle. Even though they may contain two quarks they are not colour neutral, and therefore cannot exist as isolated bound states. So instead they tend to float freely inside hadrons as composite entities; while free-floating they have a size of about 1 fm. This also happens to be the same size as the hadron itself.

James Randi (born Randall James Hamilton Zwinge; August 7, 1928) is a Canadian-American stage magician and scientific skeptic best known as a challenger of paranormal claims and pseudoscience. Randi is the founder of the James Randi Educational Foundation (JREF). Randi began his career as a magician named The Amazing Randi, but after retiring at age 60, he began investigating paranormal, occult, and supernatural claims, which he collectively calls "woo-woo".

Although often referred to as a "debunker", Randi rejects that title owing to its perceived bias, instead describing himself as an "investigator". He has written about the paranormal, skepticism, and the history of magic. He was a frequent guest on The Tonight Show Starring Johnny Carson and was occasionally featured on the television program Penn & Teller: Bullshit!. The JREF sponsors The One Million Dollar Paranormal Challenge offering a prize of US$1,000,000 to eligible applicants who can demonstrate evidence of any paranormal, supernatural or occult power or event under test conditions agreed to by both parties.