What does it mean to have a "quantum universe"?
Figuring out what the universe is made of and how it works has long been a challenge for research in particle physics. The Quantum Universe presents us with a new paradigm for explaining the universe in terms of quantum physics, the laws that govern the microscopic and subatomic world. It describes a revolution in particle physics, a leap forward in our understanding of the mystery and beauty of the universe.
What is the nature of the universe and what is it made of?
What is matter, energy, space and time?
How did we get here and where are we going?
Throughout human history, increasingly powerful and advanced scientific theories and experiments have addressed these fundamental questions about the universe. The resulting knowledge has led to revolutionary insights into the nature of the world around us.
Over the past 30 years, physicists have gained a profound understanding of fundamental particles and the physical laws that govern matter, energy, space and time. Researchers have tested this 'standard model' in countless experiments; and, time and time again, its predictions have been confirmed. A series of experimental and theoretical breakthroughs combined to produce the Standard Model, which can truly be celebrated as one of the greatest scientific triumphs of the 20th century. celebrated as one of the great scientific triumphs of the 20th century.
Now, in a development that some have likened to Copernicus' admission that the Earth is not the centre of the solar system, startling new data show that only 5% of the universe is made up of the normal, visible matter described by the Standard Model. 95% of the universe is made up of dark matter and dark energy, the fundamental nature of which is a mystery. The ordered and elegant view of the universe of the Standard Model must be incorporated into a deeper theory to explain the new phenomena. The result will be a revolution in particle physics no less dramatic than any that has gone before.
Doubts about the Universe
A worldwide programme of particle physics investigations is underway to explore a mysterious new scientific landscape. Nine interrelated questions define the way forward.
This feature takes a three-pronged, nine-question approach to questions about the universe.
Einstein's "unified field" theory
1. Is there an undiscovered principle of nature: a new symmetry, a new physical law?
The quantum ideas that have so successfully described familiar matter have failed when applied to the physics of the universe. Solving this problem requires the emergence of new forces and new particles, marking the discovery of new symmetries - undiscovered principles of natural behaviour.
2. How can the mystery of dark energy be solved?
The dark energy that pervades empty space and accelerates the expansion of the universe must have a quantum explanation. Dark energy may be related to the Higgs field, a force that fills space and gives particles their mass.
3. Are there additional dimensions of space?
String theory predicts seven undiscovered dimensions of space that give rise to most of the apparent complexity of particle physics. The discovery of additional dimensions would be an epoch-making event in human history; it would change our understanding of the birth and evolution of the universe. String theory could reshape our conception of gravity.
4. Can all forces be unified into one?
At the most fundamental level, all the forces and particles in the universe could be related, and all forces could be manifestations of one grand unified force, fulfilling Einstein's dream.
The world of particles
5. Why are there so many particles?
Why do three families of particles exist, and why do their masses vary so much? Patterns and variations in the fundamental particle families suggest as yet undiscovered fundamental principles linking quarks and leptons in the Standard Model.
6. What is dark matter? How can we make it in the laboratory?
Most of the matter in the universe is unknown dark matter, probably heavy particles created in the Big Bang. Although most of these particles annihilate into pure energy, some remain. These remaining particles should have a small enough mass to be produced and studied in an accelerator.
7. What are neutrinos telling us?
Of all the known particles, neutrinos are the most mysterious. They have played a crucial role in the evolution of the universe, and their tiny non-zero masses may signal new physics at very high energies.
The birth of the universe
8. How did the universe come to be as it is?
According to the theory of the universe, the universe began with a single explosion, followed by a burst of expansion. After inflation, the universe cools and undergoes a series of phase transitions that allow the formation of stars, galaxies and life on Earth. Understanding inflation requires breakthroughs in quantum physics and quantum gravity.
9. What happened to antimatter?
The Big Bang almost certainly produced equal amounts of matter and antimatter, yet the universe does not seem to contain antimatter. How did this asymmetry arise?
Opportunities for exploration
We live in a time when the search for great questions is leading to revolutionary new insights into the universe.
"The opportunity to discover the fundamental nature of the universe has arisen in a way we never anticipated," said John Marburger, the President's science advisor, recently." Technology has put these discoveries within our reach, but we need to focus our efforts on realising new opportunities in widely separated disciplines."
The Quantum Universe is a response to this challenge. It provides us with a guide to where the quest for understanding has taken us so far, and where it is going. The chapters that follow describe how existing and planned particle physics experiments in accelerators and underground laboratories, as well as space probes and ground-based telescopes, are opening up new opportunities for discovering the fundamental nature of the universe.