Q ?   Eleven Big questions about the origins of collective behavior in Matter



1. What  fundamentally new classes of matter await discovery?

2. What is the origin of high temperature superconductivity?

3. What is the nature of  strange metals?

4. What new principles of the cosmos can be discovered from a study of  condensed matter?

5. Is quantum computation feasible?

6. Why don't glasses flow like liquids?

7. What principles govern the organization of matter away from equilibrium?

8. Can statistical mechanics be applied to a system as complex as the living cell?

9. How do singularities form in collective matter and in spacetime?

10. What principles govern the flow of granular materials?

11. What are the physical principles of biological self-organization?


Why do things do what they do?

Condensed Matter Physics is the science of connecting atomic-scale physics to the properties of everyday things. The astounding mystery of the subject is contained in ten short words:

"the whole is more than the sum of its parts."

When you put a lot of atoms together and you get strange, wonderful and sometimes useful new kinds of behavior: superconductivity; magnetism, rubber, superfluidity... Indeed, everytime we think we have classified all the different kinds of behavior, nature surprises us with something new (the quantized hall effect; high temperature superconductivity, collosal magnetoresistance).

Condensed Matter Physics proceeds via the discovery, understanding and control of new materials and phenomena by experimental, theoretical and computational means. Discovery can take place as a result of detailed experimental, theoretical, or computational efforts, or as a result of a well-interpreted chance event. Understanding is gained by careful research and analysis and often first takes place at an empirical level. Over time, as experimental and theoretical knowledge grows, understanding often evolves to a deep and profoundly detailed level, frequently involving the development of new physical principles or concepts.
Control of a new material or phenomenon can range from the ability to predict response or events based on an empirical or theoretical knowledge to the ability to manipulate the material or phenomenon in the form of a product or tool.

Unlike big science, the modest numbers of people involved in any one condensed matter research project, be it experimental or theoretical, make this an  individualistic science, not driven by agenda. Repeatedly, the history of this field has demonstrated the exceptional opportunity for young talent to express its virtuousity and brilliance through individual discovery. Remarkle individual discoveries   have changed technology, but they have also  had cosmic implications - ideas such as broken symmetry, the Higg's mechanism and universality began through understanding condensed matter physics.

The diversity and individuality of condensed matter physics do not lend it so naturally to a fixed list of "Big Questions". The big issues change in a rather fluid way with new discoveries. Nevertheless, there is a  great need for this remarkable field to articulate the dreams and questions for the future.    The following is a first draft attempt at articulating these big questions.

1. What  fundamentally new classes of matter await discovery?

When matter develops new forms of organization, its properties transform in unexpected ways. Crystals become solid. Magnets produce an external magnetic field. Superfluids flow without resistance. Superconductors expel magnetic fields.  These new states of matter were unexpectedly discovered, mostly in the 20th century.  There are roughly 100 elements, so each time we add one more element to a  crystal,  the number of new types of material that become possible grows by at least a  factor of 100. At the turn of the 21st century, scientists have barely begun to explore the 10,000,000 plus materials that become possible with four elements.  What new states of matter - beyond such recently discovered examples as high temperature superconductivity and the fractional quantum Hall effect hide out in this frontier, awaiting discovery?

2. What is the origin of high temperature superconductivity - and  is room temperature superconductivity feasible?

New materials have recently been discovered which lose all of their electrical resistance to become "superconducting" at a  transition temperature as as high as 160 degrees absolute. This is a far higher temperature than the previous generation of superconductors, much higher than ever thought feasible - but  still not room temperature. Room temperature superconductors- if they are feasible-  would be of tremendous importance for a wide range of applications ranging from the power to the medical industry.   Answering the vital question about the feasibility of room temperature superconductivity requires that we solve the mechanism of high temperature superconductivity. Many  believe that  its ultimate answer will  require a fundamentally new mathematical description of the collective behavior of quantum matter. 

3. What is the nature of  strange metals?

When we tune metals to tbe brink of instability, they develop strange new properties and a propensity to develop new forms of order, such as superconductivity.
Inside these materials, electricity  can no longer be described as a fluid of individual electrons, but appears to require a fundamentally new, collective description.

4. What new principles of the cosmos can be discovered from a study of  matter in the laboratory?

The principles that govern the properties of matter studied in a laboratory environment - also govern cosmological matter. Tremendous insight into the cosmos at large has been gained in the past from laboratory experiments.  Studies of diamond led Einstein to propose the quantum nature of energy inside matter. Similarly, research into  how superconductors levitate provided the conceptual  insights that enabled physicists to understand the  weak nuclear forces that make the sun shine.  Many areas of current activity in condensed matter physics hold  promise of providing new insight into the cosmos at large. For example, the study of quantum phase transitions inside the cryostat  may provide new models for phase transitions in the early universe. The study of glasses, which have many stable minima, may have connections to many-valued solutions of string theory and  the study of superfluid Helium -3 may  provide insights into quantum gravity and unexplained smallness of the cosmological constant. 

5. Is quantum computation feasible?

Theoretically, quantum mechanics can be used to develop a fundamentally new type of computation, in which the computing power scales not linearly, but exponentially with the size of the computer.  Such computers could decode the most sophisticaed ciphers, could encode  unbreakable codes and may be able to solve the hardest "NP complete" problems in computer science. But can they  be made to work in practice? Scientists are only just discovering how to make the simplest element of the quantum computer - the qubit.  To make a fully functioning quantum computer will the development  of a new quantum technology that can successfully isolate and protect the coherent quantum computer from the incoherent classical world of its  environment.

6. Why don't glasses flow like liquids?

Glasses are liquids that have become frozen in time: window glass requires times longer than the age of cathedrals to flow. Analagous freezing arise in colloids and magnetic materials. What are the physical principles governing these various frozen fluids? In some cases, a flowing state can be restored by exceeding a threshold of external force. In others, such a force seemingly creates a glass where none was before ('jamming'). When, and why, do stressed glasses melt and freeze?

7. What principles govern the organization of matter away from equilibrium?

Most 20th century physics describes matter in equilibrium, governed by the overarching principles of thermodynamics and statistical mechanics. These directly relate the macroscopic properties of a system to its underlying 'energy landscape'. Increasingly we want to address systems far from equilibrium, such as turbulent fluid flow, waves at the sea-shore, electricity driven through an atom, and even life itself. Each of these systems is driven by an external force, often into parts of the landscape far from those explored in equilibrium. What are the new principles that govern the organization of matter in these new, non-equilibrium situations?

8. Can statistical mechanics be applied to a system as complex as the living cell?

Statistical mechanics describes the emergent properties of large collections of atoms and molecules caused by thermal excitation. Such excitation is certainly present in living cells, but there is much else happening too: the processes of life drive the system far from a state of thermal equilibrium. The growing field of nonequilibrium statistical mechanics addresses these problems, but which aspects of cellular life can it help us to understand? Are some of these aspects just too complicated for the 'physicists view' -- that simplification is the first step towards understanding -- to be useful?

9. How do singularities form in collective matter and in spacetime?

One basic behavior of matter---especially tenuous matter, is its characteristic of creating sharp, singular spatial structure spontaneously. The vortex in a draining sink and a crumpled sheet of paper are two examples. Often these structures are fundamental consequences matter's essential nature---its local connectivity and its inertia. What is the range of this singularity-forming behavior, to what degree does it condense the system's energy into the singularity, and what analogous singularities might occur in spacetime?

10. What principles govern the flow of granular materials?

Granular materials include sand in dunes, snow (or rocks) in avalanches, sediments on the sea floor, and powders used commercially e.g. to make pharmaceutical pills. As the grains collide with each other they dissipate energy, causing new and unpredictable behavior. Granular materials can sustain ripples and waves, including shock waves; can evolve spontaneous avalanches; and can unmix (rather than mix as fluids would) when stirred together. Even at rest, the grains can carry subtly imprinted memories of earlier flows, through the particular set of positions and contacts that remain. A deeper knowledge of the physical principles of granular flow will help understand how the earth's surface came to be as it is, and unlock the door to many other areas of science and technology.


11. What are the physical principles of biological self-organization?

We only partially know how DNA encodes the structure of proteins, While the "standard model" works for bacteria and viruses, we now are realizing that, for multi-cellular organisms the transcription from DNA to mRNA is a highly "editted" process.  What is the machinery that controls this editting process? Howdoes DNA encode the software and the large-scale organization of an organism? At a higher level, how do 109 bits of information in the human genome encode the information for the 1011 neurons and the 1015 synapses of the human brain?