Book Review: Connecting Quarks with the Cosmos

Connecting Quarks with the Cosmos: by Committee on the Physics of the Universe, National Research Council

Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century is a study encompassing astrophysical phenomena that give insight into fundamental physics as well as fundamental physics that is relevant to understanding astrophysical phenomena and the structure and evolution of the universe. The study team identified 11 questions and soliciting ideas from the community, prepared the answers for each, as given below.

-What Is Dark Matter?

We know that the objects in the universe are held together by a form of matter different from what we are made of and that gives off no light. Does this matter consist of one or more as-yet-undiscovered elementary particles, and aggregations of it produce the gravitational pull leading to the formation of galaxies and large-scale structures in the universe?

-What Is the Nature of Dark Energy?

We know that the expansion of the universe is speeding up rather than slowing down. This contradicts the fundamental idea that gravity is always attractive. It calls for the presence of a form of energy, dubbed “dark energy,” whose gravity is repulsive and whose nature determines the destiny of our universe.

-How Did the Universe Begin?

We think that during its earliest moments the universe underwent a tremendous burst of expansion, known as inflation. The underlying physical cause of this inflation is a mystery.

-Did Einstein Have the Last Word on Gravity?

Black holes are ubiquitous in the universe, and their intense gravity can be explored further. 

-What Are the Masses of the Neutrinos, and How Have They Shaped the Evolution of the Universe?

We think of neutrinos as abundantly present in the universe today. Physicists have found evidence that they have a small mass, which implies that cosmic neutrinos account for as much mass as do stars. The pattern of neutrino masses can reveal much about how nature’s forces are unified, how the elements in the periodic table were made, and possibly even the origin of ordinary matter.

-How Do Cosmic Accelerators Work and What Are They Accelerating?

We are seeing an amazing variety of energetic phenomena in the universe, including beams of particles of unexpectedly high energy but of unknown origin. In laboratory accelerators, we can produce beams of energetic particles, but the energy of these cosmic beams far exceeds any energies produced on Earth.

-Are Protons Unstable?

The matter of which we are made is the tiny residue of the annihilation of matter and antimatter that emerged from the earliest universe, and in not-quite-equal amounts. The existence of this tiny imbalance may be tied to a hypothesized instability of protons, the simplest form of matter, and to a slight preference for the formation of matter over antimatter built into the laws of physics.

-What Are the New States of Matter at Exceedingly High Density and Temperature?

The theory of how protons and neutrons form the atomic nuclei of the chemical elements is well developed. At higher densities, neutrons and protons may dissolve into an undifferentiated soup of quarks and gluons, which can be probed in heavy-ion accelerators. Densities beyond nuclear densities occur and can be probed in neutron stars, and still higher densities and temperatures existed in the early universe.

-Are There Additional Space-Time Dimensions?

In trying to extend Einstein’s theory and to understand the quantum nature of gravity, particle physicists have posited the existence of space time dimensions beyond those that we know. Their existence could have implications for the birth and evolution of the universe, could affect the interactions of the fundamental particles, and could alter the force of gravity at short distances.

-How Were the Elements from Iron to Uranium Made?

Scientists’ understanding of the production of elements up to iron in stars and supernovae is fairly complete. Important details concerning the production of the elements from iron to uranium remain puzzling.

-Is a New Theory of Matter and Light Needed at the Highest Energies?

Matter and radiation in the laboratory appear to be extraordinarily well described by the laws of quantum mechanics, electromagnetism, and their unification as quantum electrodynamics. The universe presents us with places and objects, such as neutron stars and the sources of gamma ray bursts, where the conditions are far more extreme than anything we can reproduce on Earth that can be used to test these basic theories.