He changed his surname from "Björkén" to Bjorken upon arriving in the US; he moved to Chicago to work as an electrical engineer, which was where he met his future wife, Edith.

After graduating from Maine East High School in 1952, he decided to attend Massachusetts Institute of Technology (MIT) over the University of Chicago.

Despite being offered more financial aid to attend the University of Chicago, his parents advised him that he should move further away to find his independence.

[4] At MIT, he quickly decided to major in physics; one of the main reasons was his enjoyment of the lectures that Hans Mueller gave.

[4] Bjorken discovered in 1968 what is known as light-cone scaling (or Bjorken scaling), a phenomenon in the deep inelastic scattering of light on strongly interacting particles, known as hadrons (such as protons and neutrons): Experimentally observed hadrons behave as collections of virtually independent point-like constituents when probed at high energies.

This observation was critical to the recognition of quarks as actual elementary particles (rather than just convenient theoretical constructs), and led to the theory of strong interactions known as quantum chromodynamics, where it was understood in terms of the asymptotic freedom property.

In Bjorken's picture, the quarks become point-like, observable objects at very short distances (high energies), shorter than the size of the hadrons.

It states that in the Bjorken scaling domain, the integral of the spin structure function of the proton minus that of the neutron is proportional to the axial charge of the nucleon.

Richard Feynman subsequently reformulated this concept into the parton model, used to understand the quark composition of hadrons at high energies.

[8] The predictions of Bjorken scaling were confirmed in the early late 1960s electroproduction experiments at SLAC, in which quarks were seen for the first time.

The general idea, with small logarithmic modifications, is explained in quantum chromodynamics by "asymptotic freedom".

[9] Bjorken died from melanoma at a care facility in Redwood City, California, on August 6, 2024 at the age of 90.