TU München: Cluster of Excellence Fundamental Physics: Origin and Structure of the Universe
This cluster of excellence will embark on a joint investigation by astrophysicists, particle physicists and nuclear physicists aiming to explore the three biggest questions of modern physics, the innermost structure of matter, the nature of the fundamental forces and the origin of the structure and content of our Universe. In recent years, remarkable progress has been made in understanding the evolution of the Universe and in tracing back its formation history (figure). We have strong evidence that the Universe started with the Big Bang, a singularity in space and time. During the Superstring/Supergravity Era, 10-43 s after the Big Bang, at enormous densities of 1094 g/cm3 and temperatures of 1032 K all four fundamental forces of nature were unified in an as yet unknown way. As the Universe expanded, gravity established itself first as a separate force while the 3 remaining interactions remained unified. The nature of most of the particles that existed in this Era of Grand Unified Theory (GUT) is still unknown. At this time our Universe experienced a short phase of accelerated expansion, inflation, that has been incorporated in current models of the evolution of the Universe in order to explain its otherwise puzzling global homogeneity and flatness. At the Electroweak & Quark Era, symmetry breaking disintegrated the GUT-field into 3 fundamental forces that, in combination with gravity, now dominate the evolution of structure in the Universe. Symmetry breaking might also be the cause for the overabundance of matter with respect to anti-matter that left behind the baryonic material out of which the visible components of galaxies formed.
After passing through a phase dominated by free quarks, the protons and neutrons which dominate the current baryon budget formed, and then, 10 seconds after the big bang and still at temperatures of 109 K, these baryons formed the first complex atomic nuclei, producing the helium, and lithium observed today in the oldest stars. After 400,000 years the Universe had cooled to temperatures of a few thousand Kelvin, and radiation decoupled from baryonic matter, allowing small density fluctuations in the gas to condense within dark matter halos producing a first generation of massive stars. The epoch of stellar nucleosynthesis started with the violent deaths of these stars which ejected heavy elements into their environment while at the same time collapsing into black holes that may have acted as seeds for the massive black holes that later grew at the centres of many galaxies. Subsequently, galaxies like the Milky Way formed by condensation of gas within large dark matter halos and these aggregated by hierarchical merging into ever larger systems, a process that was dominated by the interplay between the two unknown fundamental components of our Universe, dark matter and dark energy. Eventually, 4.5 billion years ago our solar system formed inside a dense molecular cloud that had been enriched with dust and heavy elements by previous generations of massive stars.
Exploring the history of the Universe as outlined above requires close interaction between astrophysics, nuclear physics and particle physics. This interaction has been very fruitful in the past. For example, the explanation of how the light elements formed shortly after the Big Bang is a result of a very successful interplay between all three research fields. Another famous example is the fact that the first indications for neutrino oscillations came from comparisons of detection rates for solar neutrinos with theoretical models of stellar structure. This has led to solar neutrino spectroscopy, while quantitative analysis of neutrino fluxes from distant supernova explosions has initiated the new science of neutrino astronomy, providing unique information about stars and their explosive demise. Finally, models for supernova explosions and for the production of the heavy elements require the determination by nuclear physicists of nuclear reaction cross-sections at very low energies.
Enormous progress has been made recently towards solving some of the major outstanding questions of astrophysics, nuclear and particle physics. The Standard Model for particle physics as a gauge theory is now fully established, both through high precision experiments, and through its theoretical formulation as a quantum field theory. On the astrophysics side, we now enter the era of high-precision cosmology through new measurements of the cosmic microwave background by the WMAP satellite or in the future by Europe’s Planck satellite, and through large surveys of the distribution of galaxies such as the Sloan Digital Sky Survey. These independent achievements appear to make it possible to establish for the first time a consistent and quantitative cosmological model that, as a result of a concerted effort between astrophysicists, nuclear and particle physicists, can describe the origin of matter and of fundamental forces as well as the evolution of the Universe from a tiny fraction of a second after the Big Bang until now, and indeed into the distant future.
This deeper insight also raises new and interesting questions about fundamental physics which can only be answered in a combined interdisciplinary effort, guided by astronomical observations and by laboratory experiments, as well as by new theoretical models and a new generation of high-precision computer simulations. In the following we briefly outline a few of the most important questions that will be investigated by members of our proposed Cluster of Excellence. The nature of dark energy is still mysterious and may be linked to fundamental physics at very short length scales. Most of the matter density of the Universe consists of dark matter, yet no candidate particle has so far been seen in any particle physics experiment. Until this mystery is solved one cannot claim to have a complete picture of all the particles in the Universe. Another spectacular and at the same time puzzling discovery is that of the presence of massive black holes at the centres of almost all bright galaxies. The origin of these exotic objects is not understood. On very small scales, where quantum gravity is effective, the quantum properties of black holes are still an open problem. The excess of baryons over antibaryons in the Universe remains mysterious and may be related to new symmetries linking matter and forces at very high energies, thus very early in cosmic history, which allow leptons to turn into baryons. Finally, there are deep theoretical questions about the origin of the masses of elementary particles, and about the structure of space and time in a theory of quantum gravity. Such a theory is needed to describe the Universe immediately after the Big Bang.
The physics and astrophysics institutes in Garching and Munich constitute an outstanding and unique research environment that is ideally suited for an interdisciplinary investigation of these fundamental problems of physics, astronomy and cosmology. New instruments that are unmatched world-wide (telescopes like the ESO-VLT, satellites like Planck, accelerators like the LHC and FAIR, and facilities like the Garching neutron source) and in which the Garching/Munich institutes have a leading role will produce an enormous volume of qualitatively new data with an extraordinary potential for new discoveries. Our proposed Cluster of Excellence will coordinate scientific research with these unique data, concentrating on the above problems at the interface between nuclear/particle physics and astrophysics. During the initial funding period, research will be focussed on the following 7 fundamental scientific questions:
1. How does matter behave at extremely high energies and short distances?
2. Is there symmetry between matter and forces?
3. What is the origin of particle masses and the reason for their hierarchy ?
4. What are the properties of cosmic phase transitions and what is their role on the evolution of the early Universe and what is the origin of the asymmetry of matter and antimatter in the Universe ?
5. What are the dark components of the Universe ?
6. How did black holes form and evolve ?
7. How was the Universe enriched with heavy elements?
Each of these questions is the basis of a special Research Area of the cluster. In each area a set of research projects is defined. Many experimental projects are performed within international collaborations with large-scale research facilities (satellites, multipurpose experiments, underground experiments, telescopes etc.) which are operated by international organizations. Thus, one facility can be used for different measurements and can be relevant for several of the research fields.
We note, that the problems addressed by this cluster belong to the class of fundamental problems that in principle require independent treatment by a number of research groups. In practice, financial constraints often do not permit the setting up of more than one international facility with the required capabilities. Many investigations are therefore carried out in collaboration with other international scientists. Competition is nevertheless still strong in many of the fields of research of this cluster and is critical to stimulate efforts to make original, robust, convincing and fully validated contributions. Both, competing scientists and close collaborators are included in the group of strategic partners, who will be invited to this centre for joint research and discussion.
To our knowledge, this Cluster of Excellence will become the largest centre in astro-, nuclear and particle physics worldwide, with key access to some of the largest and most expensive research facilities (VLT, LHC, etc). This will place us in a unique position worldwide, guaranteeing a leading role in basic physical science.