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about meabout

quick facts
Anna

I am a theoretical cosmologist. My research is aimed at the most fundamental questions about the universe: what is the mechanism that set the big bang initial conditions? how can we better understand the cosmic evolution on large scales? what is the universe composed of? and how will it be changing in the future? I use the tools of both general relativity and quantum field theory to address these problems. More specifically, I have been studying different models of the very early universe with the aim of ultimately developing an improved cosmology that provides an explanation of observational data.

Check out my research page to learn more about what I do or my publications page to download reprints. The misc page has a variety of media related to my work, including videos and links to recent news coverage.

Currently, I am the John A. Wheeler Postdoctoral Fellow at the Princeton Center for Theoretical Science (PCTS). Before coming to Princeton, I completed my doctoral dissertation at the Max Planck Institute for Gravitational Physics (a.k.a. Albert Einstein Institute) in 2014. The last two years of my PhD studies, I have been supported by prize fellowships that enabled me to conduct research abroad; I was the Fritz Thyssen Fellow at the Harvard-Smithsonian Center for Astrophysics during 2012-3 and spent the academic year 2013-4 at the Physics Department of Princeton University.

I wrote another, award-winning thesis at Munich University, studying philosophical implications of quantum physics. The Philosophy of Science remains an interest. Besides my research in Cosmology, I am actively participating in the dialogue with Philosophy and the Humanities in general.

To learn more about me, download my CV .

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researchresearch

theoretical cosmology

questions Cosmology@2016. Shortly after the idea of big-bang cosmology emerged about 75 years ago, it was realized that the properties of our universe including its composition, structure, and evolution are fully determined during the very first instants after its birth. By the 1970’s, though, it was clear that big-bang cosmology fails to provide a dynamical explanation of cosmic origins, i.e., how the particular primordial conditions needed to explain the observed features of the universe naturally emerged from the big bang. For the past thirty-five years, the conventional view has been that, during the very first instances after the big bang, the universe underwent a period of accelerated expansion, ‘inflation,’ that flattened and smoothed the cosmological background and generated a nearly scale-invariant spectrum of density fluctuations that seeded the formation of planets, stars, and galaxies in the late universe. But, with better understanding of inflationary theory, major shortcomings have been revealed. In my research, my goal is to find ways of developing a new, more powerful cosmological theory that can simply explain observations and predict new phenomena. My strategy has been to; (1) identify the strengths and weaknesses of current theories, including comparisons with recent observations; (2) develop essential building blocks for constructing new theories; and (3) explore new approaches drawing from the new building blocks and lessons learned from existing theories.

inflation Observational Issues for Inflation. Recent results from the Planck satellite measurements combined with earlier observations from WMAP, ACT, SPT, and other experiments eliminate a wide spectrum of more complex inflationary models and favor models with a single scalar field, as reported by the Planck Collaboration early 2013. In a series of papers, I have shown that all the simplest inflationary models are disfavored statistically relative to those with plateau-like potentials. However, a restriction to plateau-like models has three independent serious drawbacks. First, a new kind of conceptual difficulty arises: simply using the inner logic of inflationary theory, small-field plateau-like models that are currently favored by experimental data are, at the same time, disfavored by the inflationary paradigm (unlikeliness problem). In addition, the very same plateau-like models suffer from a new multiverse problem and a new initial condition problem because inflation starts at energy densities well below the Planck scale. I showed that this new initial conditions problem becomes even more serious if our current vacuum is metastable, as suggested, for example, by recent LHC results assuming a standard model Higgs. Forthcoming searches for B-modes, non-Gaussianity, and new particles should be decisive. Accordingly, further consideration of these observational issues is one of my ongoing research projects.

Bouncing Cosmologies. I have been developing novel cosmological scenarios that have the common feature of replacing the bang with a “bounce.” According to this idea, the bang was not the beginning of everything but today’s expanding phase was preceded by a contracting phase with a crossover from contraction to expansion that we call a “bounce.” The idea of bouncing cosmologies was inspired by the recognition that, by using the same physics (Einstein's General Relativity), smoothing and flattening of the universe can be achieved during a slowly contracting phase before a bounce (rather than rapid inflation after a bang). The challenge for contracting models is to find a simple and robust dynamical mechanism of generating (nearly) scale-invariant, adiabatic squeezed modes and carry them through the bounce.

ekpyrosis Ekpyrotic universe. One class of contracting models is known as the “ekpyrotic universe” (from the Greek meaning “out of the fire”). In contrast to inflation, smoothing by ekpyrotic contraction does not require special arrangements of energy and is easy to trigger. Furthermore, contraction prevents quantum fluctuations from evolving into large patches that would generate a multiverse. However, making the scale-invariant spectrum of variations in density requires more ingredients than in inflation. I have figured how to construct the simplest type of ekpyrotic models and shown that it naturally fits current observations, including the Planck satellite data, and I have shown how the scenario can arise naturally as a result of fundamental symmetries in nature.

Anamorphic Cosmology. anamorphosis More recently, I have introduced a new alternative, anamorphic cosmology; the novel feature is that, by amending Einstein’s theory of general relativity, I have shown how it is possible for contraction and expansion to morph one into one another (hence, the name “anamorphic”). In the anamorphic smoothing phase, the Compton wavelength is fixed in time and, as measured by rulers made of matter, space is contracting. Simultaneously, the Planck length is shrinking so rapidly that space is expanding relative to it. And so, surprisingly, it is really possible to have contraction (with respect to the Compton wavelength) and expansion (with respect to the Planck length) at the same time! The anamorphic smoothing phase is temporary. It ends with a bounce from contraction to expansion (with respect to the Compton wavelength). As the universe expands and cools afterwards, both the particle Compton wavelengths and the Planck mass become fixed, as observed in the present phase of the universe. By combining contraction and expansion, anamorphic cosmology potentially incorporates the advantages of the inflationary and ekpyrotic scenarios and avoids their disadvantages. Because the universe is contracting with respect to ordinary rulers, like in ekpyrotic models, there is no multimess problem. And because the universe is expanding with respect to the Planck length, as in inflationary models, generating a scale-invariant spectrum of density variations is relatively straightforward.

Cosmological bounces. bounce A key missing building block needed to make scenarios with cosmic contraction viable was a theory of a cosmological bounce, i.e., a smooth transition from a period of contraction to a period of expansion. Until recently, attempts to construct a theory of the bounce had failed and there were even recent mathematical arguments, so-called ‘no-go theorems,’ suggesting that bounces are not possible. My response to these challenges was to study the no-go theorems and look for weaknesses. Having found them, I showed that these weakness can be exploited to evade the theorems and construct examples of well-behaved cosmological theories with a non-singular cosmological bounce. These examples proved that the universe can go through a cosmological bounce after contracting to a small but finite size at which potentially disruptive quantum gravity effects are so tiny that they can be ignored, and rebound into an expanding phase without requiring superluminal sound speed of co-moving curvature modes or creating instabilities. This result removes the most challenging roadblock for models of the early universe that propose that smoothing and flattening of the cosmological background occurred during a contracting phase before a bounce.

publicationspublications

journal articles, books, etc.

For a complete list of my publications, see my CV.

Selected journal articles:
Books:
  • A. Ijjas, B. Loewer (eds). Introduction to the Philosophy of Cosmology, under contract with Oxford University Press, to appear in 2017.
  • A. Ijjas. Der Alte mit dem Würfel. Ein Beitrag zur Metaphysik der Quantenmechanik, Göttingen: Vandenhoeck & Ruprecht 2011, pp.223. [In German, English title: The old one with the dice: a contribution to the metaphysics of quantum mechanics.]
Other publications:
  • A. Ijjas, P.J. Steinhardt, A. Loeb. Pop goes the universe Scientific American, to appear February 2017.
  • A. Ijjas, P.J. Steinhardt. Do we live in an anamorphic universe? PBS NOVA: The Nature of Reality 01/2016 |

miscmisc

my research in the media
Featured press:
  • Pop goes the universe, Scientific American, to appear February 2017. | invited feature article
  • Did the Universe Boot Up with a “Big Bounce?”, Scientific American August 3, 2016 | LINK.
  • Do We Live in an Anamorphic Universe?, PBS Nova January 12, 2016 | LINK.
  • Joint Dust Analysis Deflates Big Bang Signal, Quanta Magazine January 30, 2015 | LINK.
  • Evidence for Universe Inflation Theory May Lurk in New Data, space.com January 21, 2014 | LINK.
  • Pop-Up Universe, New Scientist 2937 (2013) 38–41 | LINK.
  • New Study Challenges Planck Result, SciTechDaily April 12, 2013 | LINK.
Recent multimedia:

Here are the records of a few selected talks that I gave recently.

Introduction to anamorphic cosmology

Invited seminar talk at the Perimeter Institute in June 2015.

Harvard Lectures on Inflation

In light of the BICEP2 announcmenet, I was invited to present two lectures reviewing the principals of inflation at Harvard's Department of Astrophysics in April 2014.

contactcontact

how to reach me

E-mail is the best way to get in touch with me.

email

aijjas@princeton.edu

address
Princeton Center for Theoretical Science
Princeton University
411A Jadwin Hall
Princeton, NJ, 08544
USA
phone

(+1) 609-258-4721