Exploring the Limits of Space-Time, Marco Bersanelli

One of the most striking features of the universe as revealed by modern cosmology is that the expanse of space-time accessible to our observation is intrinsically limited. The existence of on ultimate cosmic horizon results from the combination of two fundamentally bounded quantities in nature: the speed of light and the finite age of our universe. When approaching the edges of the observable universe we probe physical conditions at ever increasing energy densities and temperatures up to fantastically large values. Recent precision measurements of the cosmic microwave background (CMB), such as those reported by the Planck satellite and by the Bicep2 experiment, probe some of the closest features to the very boundary of space-time. I will describe these measurements and discuss three different types of limits that are directly relevant to these observations and, in general, to contemporary cosmology: (a) limits arising from our technology and observing capabilities; (b) limits that are intrinsically contained in the laws of nature; and (c) epistemological issues, in particular the status of the scientific method when dealing with aspects of the world that are intrinsically unobservable.

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This talk was delivered during the conference “The Limits of Physics and Cosmology” organized by Copernicus Center for Interdisciplinary Studies.

There exist various kinds of limits which are inherent in cosmological research and physics.

The most conspicuous one is connected with scientific method itself. It manifests itself during attempts to construct (or discover) suitable mathematical structures to model the physical world. However, this limit may be even more profound. Over the past 300 years we have become accustomed to the mathematical and empirical method which has proven to be uncannily successful in describing the enclosing universe. But is there a fundamental limit to the method itself which is intrinsic to the structure of the world?

Another group of limits which are more connected to ourselves – as human beings – are conceptual ones. The two monumental theories of physics of the 20th century – General Relativity and Quantum Mechanics - are incompatible and this inconsistency is not only on the mathematical level, but also on the conceptual. Usually scientists believe that the reconciliation between the relativist and quantum realms is possible. But is there a conceptual limit within ourselves as elements of the world?