The cosmos is a particularly attractive laboratory as it provides particles (cosmic rays) or objects (black holes, neutron stars) which are not produced in manmade laboratories. They will be addressed from different research corners and with different experimental methods: - Ultracold atoms - High stability and accuracy atomic clocks - Matter-wave interferometry - Classical and quantum links.

The open problems in fundamental physics investigated in this white paper are: - Validity of the Einstein's Equivalence Principle - Origin and nature of dark matter and dark energy - Decoherence and collapse models in quantum mechanics - Quantum many-body physics. With that respect the Einstein's Equivalence Principle assumes a central role in the search for a quantum theory of gravity. String theory or loop quantum gravity are good candidates to solve this puzzle and interestingly both of them foresee violations of the Einstein's Equivalence Principle. This is one of the biggest challenges that theoretical physics is facing today. Furthermore, the lack of a self-consistent theory of Quantum Gravity prevents the unification of SM and GR at ultraviolet scales. In summary, the clustering of large-scale structure and the accelerated behaviour of cosmic fluid could be addressed whether finding out new (unknown) forms of matter or assuming that gravity behaves in different ways at infrared scales. Today, dark matter and dark energy have an unknown origin and there is a great deal of experimental and theoretical activity to solve this puzzle. Yet, dark matter and dark energy represent 95% of the energy content of our universe while known matter (atoms, molecules) amounts to only 5%. However, they fail to explain dark matter, dark energy, or the imbalance between matter and anti-matter in the universe. Both theories have been probed individually with ever increasing precision and are consistent with nearly all experimental observations. The Standard Model (SM) of particle physics and General Relativity (GR) are the two pillars of our current understanding of Nature.

Orbital antimatter uplink