Summary
Highlights
The Large Hadron Collider (LHC), the biggest machine ever built by humans, is about to turn on. Physicists anticipate testing theories about how matter was created and the fundamental theory of nature. The LHC represents a fork in the road, either leading to a golden era of discovery or a quiet stagnation if no new particles are found. The collaboration between theorists and experimentalists is crucial for this endeavor. The design of the experiment began in the mid-80s and involves 10,000 people from over 100 nationalities, including countries that are mortal enemies. The LHC uses 7-ton superconducting magnets cooled to the coldest temperatures on Earth, and 100,000 computers globally manage its data, a system that evolved from the World Wide Web, which was invented at CERN for physicists to share data. The US had its own project, the Superconducting Super Collider, but it was canceled due to political and financial reasons. The LHC's purpose isn't military or commercial, but to understand the basic laws of physics. Theorists, like the speaker, construct theories, while experimentalists build machines and analyze data to discover new particles. The expectation of new discoveries is high, with the Higgs particle being the most anticipated.
Since the mid-70s, the Standard Model of particle physics has been highly successful, but it contains conceptual problems, such as why the universe is so big and why gravity is so weak. These questions suggest a missing piece in our understanding. A crucial prediction of this theory is the Higgs particle, without which the model doesn't make internal theoretical sense. The Higgs is believed to be responsible for giving particles mass, allowing atoms, molecules, planets, and people to exist. The LHC was designed to create a Higgs particle by smashing tiny protons together at nearly the speed of light within its 17-mile ring. The Atlas experiment, a seven-story camera, records these collisions, hoping to find the Higgs and other unexpected new physics. The scale of this project is compared to building the pyramids, driven by the desire to understand nature's basic laws and the universe's origins, replicating Big Bang conditions.
Atoms are made of electrons, protons, and neutrons. By the 1960s, hundreds of new particles were discovered, but theorists simplified this chaos by realizing most were made of three fundamental quarks. This led to the Standard Model, which explains most known particles, except for the Higgs boson. Peter Higgs's theory from the 1960s proposed a field that permeates all space, giving particles mass and enabling the formation of stable structures like atoms and galaxies. Discovering the Higgs would confirm this fundamental mechanism. Justifying such a massive scientific endeavor, which cost over $5 billion, is not about economic return but about advancing basic science and understanding the unknown. The initial turn-on of the LHC sparked public interest, but also generated fears about creating black holes, which scientists dismissed as scientifically unfounded. The first operation involved sending single beams around the ring, a critical first step towards collisions.
The first attempt to circulate a beam was successful, causing immense excitement among the scientists who had waited 19 years for this moment. This initial success confirmed the machine's magnetic properties and clear aperture. However, a significant setback occurred several days later: a faulty electrical connection caused a ton of liquid helium to leak into the 27km tunnel, damaging magnets. This catastrophic failure led to a shutdown for at least two months, requiring extensive repairs and cooling down/warming up of magnets. This incident highlighted the inherent risks of such a complex machine and the intensive, dirty work involved in maintaining it, a stark contrast to the clean environment of theoretical physics. The accident also created a 'PR disaster' for CERN, which had hyped the initial beam launch, making the subsequent failure more impactful.
Despite setbacks, the fundamental human curiosity drives physicists to ask big questions about the universe. The pursuit of science is like art, seeking patterns and symmetries in the seemingly chaotic world. The Standard Model, though successful, is incomplete; it doesn't account for dark matter or other unknown particles. Scientists hope these unknowns are part of a larger, more beautiful theory, much like discovering a pyramid from its scattered ruins. Super-symmetry (SUSY) is a leading candidate for this 'bigger picture,' proposing that every known particle has a heavier 'superpartner.' Its discovery would be experimentalists' dream, generating tons of new particles and data. The idea of the Multiverse, where the laws of physics vary across different universes, offers an alternative explanation for observed constants like the cosmological constant. This concept challenges the traditional scientific quest for universal laws and suggests our universe's parameters might be accidental, leading to a philosophical divergence in the physics community.
After repairs, the LHC successfully circulated beams at high energy, leading to the first collisions. This marked the culmination of 19 years of effort and brought immense pressure, especially given media expectations. Despite initial technical glitches and challenges in coordinating with the media, the first collisions were achieved, marking a historical moment for CERN. The focus shifted to analyzing the massive amounts of data generated, eagerly awaiting signals of new physics, particularly the Higgs boson. The excitement was palpable as data started coming in, allowing scientists to rediscover the Standard Model and hunt for the elusive Higgs. In July 2011, initial data hints suggested a 'bump' near 140 GeV, potentially indicating the Higgs. This sparked debate: if the Higgs was at 115 GeV, it supported super-symmetry, implying more particles. If it was at 140 GeV, it aligned with the Multiverse theory, implying no new particles and a possible 'end of physics' by explaining fundamental parameters as random accidents.
On July 4, 2012, a major announcement was made regarding the Higgs boson. Both CMS and Atlas experiments presented their combined results, indicating the discovery of a new boson with a mass around 125.3 to 126.5 GeV, with a statistical significance of 4.9 to 5.0 Sigma. This confirmed the existence of the Higgs boson, a momentous achievement that completed the Standard Model. The discovery was met with widespread celebration among scientists and the public, acknowledging the power of the human mind to understand the universe at sub-nuclear scales. The Higgs mass being in 'no man's land' between 115 and 140 GeV presented a new puzzle. It doesn't strongly favor super-symmetry or the Multiverse, leaving both possibilities open. This puzzling result has intensified the quest for new physics, and the upgraded LHC, operating at higher energy after a two-year shutdown, aims to provide more definitive answers. If no other new particles are found, a 125 GeV Higgs could imply an unstable universe. Conversely, new discoveries would rewrite our understanding of reality, reinforcing the continuous nature of scientific exploration.