Salam Distinguished Lecture Series 2018

ICTP started off its new year of quality scientific activities with the Salam Distinguished Lecture Series. For 2018, the featured speaker was Alan Guth, the Victor F. Weisskopf Professor of Physics and a Margaret MacVicar Faculty Fellow at the Massachusetts Institute of Technology.

Guth delivered a series of three lectures, from 29 to 31 January, titled "Inflationary Cosmology: Is Our Universe Part of a Multiverse?". The Salam Distinguished Lecture Series is sponsored by the Kuwait Foundation for the Advancement of Sciences.

Missed the Salam Lectures livestream? Watch them on ICTP's YouTube channel:

• Lecture 1: "Inflationary Cosmology: Is Our Universe Part of a Multiverse?"
• Related slides
• Lecture 2: "Eternal Inflation and its Implications"
• Related slides
• Lecture 3: "Infinite Phase Space and the Two-Headed Arrow of Time"
• Related slides

According to Guth, inflationary cosmology gives a plausible explanation for many observed features of the universe, including its uniformity, its mass density, and the patterns of the ripples that are observed in the cosmic microwave background. Beyond what we can observe, most versions of inflation imply that our universe is not unique, but is part of a possibly infinite multiverse. Guth's first two lectures will describe the workings of inflation, the evidence for inflation, and why he believes that the possibility of a multiverse should be taken seriously. In the third lecture, he will discuss the arrow of time, and how it might originate in the context of inflationary cosmology. Abstracts of all three lectures are included below.

Trained in particle theory at MIT, Guth held postdoc positions at Princeton, Columbia, Cornell, and the Stanford Linear Accelerator Center before returning to MIT as a faculty member in 1980.  His work in cosmology began at Cornell, when fellow postdoc Henry Tye persuaded him to study the production of magnetic monopoles in the early universe.  Using standard assumptions, they found that far too many would be produced. Continuing this work at SLAC, Guth discovered that the magnetic monopole glut could be avoided by a new proposal which he called the inflationary universe. Guth's honors include ICTP's 2002 Dirac Medal (which he shared with Andrei Linde and Paul Steinhardt), the Breakthrough Prize in Fundamental Physics, and the 2014 Kavli Prize in Astrophysics.

Guth is still busy exploring the consequences of inflation. He has also written a popular-level book called "The Inflationary Universe: The Quest for a New Theory of Cosmic Origins" (Addison-Wesley/Perseus Books, 1997; available in ICTP's Marie Curie Library).

Abstracts

• Lecture 1, 29 January: "Inflationary Cosmology: Is Our Universe Part of a Multiverse?"
  Inflationary cosmology gives a plausible explanation for many observed features of the universe, including its uniformity, its mass density, and the patterns of the ripples that are observed in the cosmic microwave background.  Beyond what we can observe, most versions of inflation imply that our universe is not unique, but is part of a possibly infinite multiverse. Guth described the workings of inflation, the evidence for inflation, and why he believes that the possibility of a multiverse should be taken seriously.
  
  
• Lecture 2, 30 Janury: "Eternal Inflation and its Implications"
  This lecture further explored the connection between inflation and the multiverse.  Guth described the mechanism of inflation in more detail, showing why most versions lead to eternal inflation: once inflation starts, it never completely stops, but instead the inflating region grows forever, producing "pocket universes" ad infinitum.  Eternal inflation is in some ways very attactive, because, for example, it offers a possible explanation for why the energy density of the vacuum is so incredibly small. But it also leads to the "measure problem": how does one define probabilities in an infinite system in which any allowed event is expected to occur an infinite number of times?
  
  
• Lecture 3, 31 January: "Infinite Phase Space and the Two-Headed Arrow of Time"
  One of the unsolved mysteries of physics is the arrow of time: the laws of physics make no distinction between the future and the past, but in our experience they are entirely different. The arrow of time can be identified with the growth of entropy, but what caused the entropy to be lower in the past?  Guth described a speculative picture which shows how an arrow of time can develop naturally, provided that the available phase space is infinite, even in a system with time-reversible laws of physics, and with no special initial conditions. He also discussed the alternative possibility that the phase space available to the universe is finite, arguing that this assumption leads to serious cosmological problems.