The Expanding Universe and the Cosmological Constant

• John Barrow

Room: 122:026 An introduction to the expanding universe and those questions that everyone asks about it –What is it expanding into? Are we at the centre of the expansion? What is expanding? We will then introduce the ‘cosmological constant’ and its effects on the expansion of the universe, see why was it invented by Einstein, and discover how it can be made to appear inevitably in Newton’s theory of gravity. Particle physics provided a new interpretation of the cosmological constant as the vacuum energy of the universe. We will then see why this meant that almost no one believed it existed before it was discovered.

Why the Cosmological Constant turned into Dark Energy

• John Barrow

Room: 122:026 We will begin with a brief introduction to the hot early stages of the universe and the background radiation and the differences between decelerating and accelerating universes. This leads to definition of ‘inflation’ which will look like the appearance of a temporary cosmological constant in the very early universe. We will look at some of its unusual consequences. We show how the concept of ‘dark energy’ generalises the simple idea of a cosmological constant and some of the candidates for it. We then summarise the different pieces of observational evidence for dark energy, including the simple anthropic bound, and the prospects for future discoveries. Finally, we draw together the big unexplained features of the dark energy, look at some attempts to resolve them, and conclude by seeing what dark energy may mean for the far future of the universe.

Q&A

• George Musser
• Sabine Hossenfelder

Room: 122:026 Question and answer session to the topics of this morning's lectures.

The CMB Bonanza, Part I

• Stefan Hofmann

Room: 122:026 The lectures aim at explaining the basic mechanisms at work in the origin of the cosmic microwave background and at a global characterization of our Universe in accordance with the relic microwave background.

The CMB Bonanza, Part II

• Stefan Hofmann (Nordita)

Room: 122:026 The lectures aim at explaining the basic mechanisms at work in the origin of the cosmic microwave background and at a global characterization of our Universe in accordance with the relic microwave background.

Q&A

• George Musser (Scientific American)
• Sabine Hossenfelder

Room: 122:026 Question and answer session to topics of this afternoon's lectures.

Gravitational Waves: Whole Lotta Shakin' Goin' On

• Patrick Sutton

Room: 122:026 Gravitational waves -- ripples in the fabric of spacetime - - were one of the first major predictions of Einstein's General Theory of Relativity, and are the last to be directly measured. These waves are produced by some of the most violent phenomena in the universe, such as collisions of black holes, the explosive deaths of massive stars, and the big bang itself. Gravitational waves could provide novel probes of matter and gravity under extreme conditions, but they are so fantastically weak that they have so far eluded direct observation. A worldwide effort to detect gravitational waves has been building over several decades, and is approaching culmination with the upcoming operation of a new generation of detectors that are expected to finally catch these elusive signals. I will review the physics of gravitational waves, experimental efforts to detect them, and the scientific potential of this new window on the universe.

Q&A

• Sabine Hossenfelder
• George Musser (Scientific American)

Room: 122:026 Question and answer session to today's topics.

Gravitational Lensing Boot Camp

• Robert Nemiroff

Room: 122:026 What is gravitational lensing, what has it told us about the universe, and what more can it tell us about the universe? Lenses such as black holes, stars, galaxies, clusters of galaxies, and the universe as a whole will be covered. Concepts such as Einstein rings, photon spheres, image pair creation events, and shear will be defined and briefly discussed. The intersection of gravitational lensing with current research frontiers will be reviewed including how microlensing is being used to search for extra-solar planets, how radio telescopes are being used to probe galaxy-center black holes, and how weak lensing is being used to probe galaxy evolution in the early universe. Possible lensing signals in continuing and upcoming missions such as Planck, DES, LSST, Euclid, and WFIRST will be reviewed. Relevant parts of the lecturer's own research will also be briefly mentioned.

Gamma Ray Burst Boot Camp Room: 122:026 Gamma Ray Bursts (GRBs) are the furthest explosions known. As such they are valuable probes of energetic explosions and fluctuating beacons seen through nearly the entire intervening universe. Although almost every physical mechanism behind GRBs is debated, leading theories will be reviewed including expansion physics and candidate progenitor objects. The phenomenology of GRBs will be reviewed including prompt emission, afterglows, common light curve features, and candidate standard candles. Searches for GRB coincidences with detectors sensitive to neutrinos, gravitational radiation, cosmic rays, and extremely high energy photons will be reviewed. Searches for gravitational lensing by intervening dark matter and Lorentz invariance violations by intervening quantum foam will be reviewed, as will possible effects GRBs could have on the Earth. Relevant parts of the lecturer's own research will also be briefly mentioned.

Q&A

• George Musser (Scientific American)
• Sabine Hossenfelder

Room: 122:026 Question and answers to this morning's lectures.

Finding Exoplanets

• Ray Jayawardhana

Room: 122:026 Two decades ago, we knew of only one planetary system: our own. Since then, astronomers have found nearly a thousand confirmed planets and thousands more planet candidates around other stars. These discoveries --most of which have been made by measuring the subtle effects that planets induce on stars-- have revealed a remarkable diversity of worlds, from close-in super-Earths to far out super-Jupiters, blurring the very definition of what constitutes a "planet". They have challenged our preconceptions about the origins and architectures of planetary systems many times over. Now we stand on the verge of identifying the first crop of terrestrial worlds in the habitable zone where rocky planets could sustain liquid water on the surface. Our picture is far from complete, however, and more surprises are likely in store. I will review the emerging view of the planet population, highlight the strengths and limitations of different search techniques and discuss future prospects for extending their reach.

Characterizing Exoplanets

• Ray Jayawardhana

Room: 122:026 Remote sensing of distant worlds, across tens or even hundreds of light-years, to pin down their characteristics ain't no easy task. The whopping brightness contrast between the glaring suns and their faint planetary embers makes it particularly difficult. Yet, despite daunting hurdles, astronomers have begun measuring physical properties of alien worlds in earnest: in other words, the era of "comparative exoplanetology" is here. Planets caught in transit and those imaged directly are best suited for detailed characterization. I will review how we can determine not only the masses and orbital parameters of exoplanets but in some cases also learn about their bulk composition, day- and night-side temperatures, and upper atmospheres. I will discuss how we might adopt similar techniques to target terrestrial planets with a view to assessing their habitability and to search for biosignatures.

Q&A

• Sabine Hossenfelder
• George Musser

Room: 122:026 Question and answers to this morning's lectures.

The Search for Dark Matter

• Green Anne

Room: 122:026 Most of the matter in the Universe is invisible. This dark matter is also exotic, made of new elementary particles. I will briefly describe the observational evidence for dark matter, on scales ranging from individual galaxies to the entire Universe. One of the best dark matter candidates are WIMPs, Weakly Interacting Massive Particles. I will describe how WIMPs arise in particle physics models designed to unify the fundamental forces and are generically produced in the early Universe with the required abundance. WIMPs can be detected directly, via their rare interactions with conventional matter, or indirectly, via the gamma-rays and anti-matter produced when they annihilate. WIMPs can also be produced at particle colliders such as the LHC. I will conclude by describing the principles, current status and future prospects of these experiments.

The Sun's Enduring Mysteries

• Axel Brandenburg (Nordita)

Room: 122:026 The realization that stars like the Sun are giant gas balls is less than 100 years old, and for much of this time, astrophysicists have remained deeply perplexed about our nearest star. For example, in the Sixties, our simple physical understanding was challenged, because it led to estimates for the rate of neutrinos that exceeded measurements by a factor of 3. This controversy took decades to put to rest. A crucial tool has been helioseismology, which allows scientists to peer beneath the Sun's surface and create a map of its interior structure. In solving one mystery, however, these measurements only created others. For instance, the Sun's surface was long known to rotate non-uniformly: faster at the equator and about 30% slower at the poles. Helioseismology was able to provide information about the Sun's internal angular velocity as well. Curiously, the lines of constant angular velocity do not lie on cylinders, as was predicted by simulations, but are spoke-like. This puzzles scientists, as there is still no good agreement between measurements and simulations. In addition, helioseismology provides crucial measurements about internal flow speeds and their temporal variation during the 11-year solar cycle. Theory and simulations suggest turbulent flow speeds of about 100 m/s, but new helioseismic measurements suggest much smaller values. Something must clearly be wrong somewhere. Theorists are also puzzled by what generates magnetic fields in the Sun. Understanding this is crucial for being able to predict space weather. This is now a major concern to airlines, who routinely reroute transcontinental flights to lower latitudes during times of strong magnetic storms.

Q&A

• George Musser (Scientific American)
• Sabine Hossenfelder

Room: 122:026 Question and Answers to today's lectures.

Closing Discussion

• Sabine Hossenfelder
• George Musser (Scientific American)

Room: 122:026