Steven Weinberg: ‘A Step Closer To The God Equation’

An image of particle physics
Christina Giallombardo

Steven Weinberg. It’s not a name most would have heard of, yet his contributions to science have been astounding. Weinberg, hailed as one of the greatest theoretical physicists of all time, whose conceptual breakthroughs revolutionised particle physics, quantum field theory and cosmology, passed away on 23 July, aged 88.

Weinberg was born in 1933 in New York City to a family of Jewish immigrants. His father encouraged his inclination towards science, and at around the age of 15 his focus turned to theoretical physics. Although his studies switched between particle physics and astrophysics, his love stayed firmly mathematical and theoretical.

His career was filled with outstanding work, earning him numerous awards including the coveted National Medal of Science and the Dannie Heinemann Prize for Mathematical Physics. But it was his work in the 1970s which was truly ground-breaking and forever changed the world of physics.

Within physics, there are four (known) fundamental forces that underpin and describe every interaction in nature: gravity, the strong interaction, the weak interaction and the electromagnetic interaction. These interactions are how one particle has a direct effect on another particle. (It is worth noting that the terms force and interaction are used interchangeably.)

The ultimate goal of theoretical physicists is to find a way to unify all four of these forces and form ‘The God Equation’, as theoretical physicist Michio Kaku phrases; also known as the ‘Theory of Everything’.

Their unification of the two forces to form the electroweak force won them the Nobel Prize in 1979

Steven Weinberg, with the help of Sheldon Lee Glashow and Abdus Salam, proved that the electromagnetic interaction and the weak interaction were simply two sides to the same coin. Their unification of the two forces to form the electroweak force won them the Nobel Prize in 1979.

To understand the electroweak force, we must first understand each force separately. The weak force is one that governs the decay of unstable subatomic particles. This interaction is the reason why the sun shines and sustains life on Earth. The weak interaction is stronger than gravity but acts at a distance so small (10-17 m which is 17 zeros after the decimal place!) that we cannot directly interact with it in everyday life.

Unlike the weak force, the electromagnetic interaction is one that can be felt in everyday life. It’s used to describe phenomena like rainbows, lightning and all human-made devices that use an electric current such as computers and televisions! It is essentially a force that acts over infinite distances and between electrically charged particles.

The electromagnetic interaction is already a combination of the electric and magnetic force that act on the charged particles as they move relative to one another. The unification of the electric and magnetic force was the work of Scottish physicist James Clerk Maxwell in 1865, a renowned physicist in his own right who won a Nobel Prize for his work in 1902 and gave us our first real understanding of the age-old question: what is light?

Both interactions work by the exchange of a force carrying particle. One being the massless photon which is responsible for the electromagnetic interaction, and the other being the massive W and Z bosons which are responsible for the weak interaction.

From a glance, the two interactions seem to have nothing to do with one another. One acts over an extremely small distance, the other over an infinite distance, and both use two different particles to complete the interaction.

The paper where he presented his theory has become one of the most cited theoretical works in high-energy physics

What Weinberg proposed in 1967, however, was that the photon and W and Z bosons were in fact members of the same family of particles – the boson! He also theorised the masses of the force carrying particles for the weak interaction. These predictions were successfully confirmed in 1982-83 in a series of experiments. The paper where he presented his theory has become one of the most cited theoretical works in high-energy physics.

This was a major step in furthering our understanding of nature and got us a tantalising step closer to the ultimate theory of everything. Weinberg was not one, however, to boast. When he was referred to as a model builder, he jokingly responded: ‘I am not a model builder. In my life, I have built only one model’.

Despite the modest statement, his ‘one model’ was one that earned him a spot amongst a group of a few individuals who, during the course of the history of civilisation, have radically changed the way we look at the universe. For this, he will forever have the respect of scientists everywhere, and will be greatly missed.

Christina Giallombardo

Featured image courtesy of Berkeley Lab via Flickr. Image license found here. No changes were made to this image.

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