Lecture given by Professor Lawrence M. Krauss at the CERN Colloquium on Cosmological Physics. The last decade or two have represented the golden age of observational cosmology, producing a revolution in our picture of the Universe on its largest scales, and perhaps also its smallest ones. In this lecture, Prof. Krauss will argue that these recent development bring to the forefront some vexing questions about whether various fundamental assumptions about the universe are in fact falsifiable. In this he will focus on 3 issues: (1) "Proving" Inflation, (2) Dark Energy and Anthropic Arguments, and (3) Cosmology of the far future. In 2014, the potential "smoking gun" for inflation was thought to have been found with the following experimental techniques https://www.youtube.com/watch?v=QCbk4afiF1c, Super-sensitive, superconducting microwave detectors, built at NIST, and implemented at BICEP and Keck telescope arrays at the South Pole have allowed astrophysicists to find out some of the answers with new observational results. The Background Imaging of Cosmic Extragalactic Polarization (BICEP) results are indirect evidence for the existence of the elusive gravitational waves from the big bang itself. By using highly sensitive microwave detectors, developed at the National Institute of Standards and Technology (NIST), telescope cameras can detect the polarization direction of photons emitted from the moment of last scattering between the photons and electrons in the plasma of the early universe, before stars and galaxies could form. These photons make up the CMB Radiation, which radiated outward after electromagnetic radiation decoupled itself from the plasma state of matter in the early universe, as the plasma formed into a gas, making space transparent for the first time. The photons emitted at the moment of last scattering, 13.7 Billion years ago, were gamma ray photons. Since then, they have been travelling almost uniformly, in every direction across the universe. Since the universe is expanding, these photons have stretched with the fabric of spacetime as the universe expanded and this has stretched their wavelength from gamma rays to microwaves. The apparently uniform pattern of polarization in the CMB can be broken into two components. One, a curl-free, gradient-only component, the E-mode (named in analogy to electrostatic fields). The second component is divergence-free, curl only, and is known as the B-mode (named in analogy to magnetic fields). Cosmologists predict two types of B-modes, the first generated during cosmic inflation shortly after the big bang, and the second generated by gravitational lensing at later times. Now, the BICEP team has confirmed detection of the first type of B-modes, consistent with inflation and gravitational waves in the early universe However, there are now grave doubts over the validity of the results. The BICEP2 team underestimated how much dust in our own galaxy can polarize microwave radiation, which was tested with ESA's Planck Mission that observed these effects and compensated for them. In order to salvage any hope of a discovery claim they will have to take more data from BICEP2 and Planck, compensate for the effects of space dust, and then publish the paper before making any announcement as it is a big claim to make, to be sure whether they had in fact seen the first signs of gravitational waves from the Big Bang, or were fooled by the effects of intergalactic space dust. Either way the results were announced too early and without proper scrutiny. The results may yet be salvaged when the results are compensated for the intergalactic dust or they may have to go back to the drawing board and wait for a new series of experiments, including an orbiting satellite for observing B-mode polarization from the CMB. Either way, we are making progress as we now have a real opportunity to answer observational questions that would not have even been asked a decade ago.

• published: 21 Sep 2014
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