Zenith Grant Awardee
Dr. Alexander Vilenkin
Tufts University
Co-Investigators
Jaume Garriga, <i>Universitat de Barcelona</i>
Project Title
The Measure Problem in the Inflationary Multiverse
Project Summary
Recent developments in cosmology suggest that much of the universe is in a state of explosive, accelerated expansion, called inflation. We live in a finite "bubble" where inflation has ended, and other bubbles with diverse properties are constantly being formed. All possible events will happen an infinite number of times in such an eternally inflating "multiverse." Unless we learn how to compare these infinities, we will not be able to make any predictions at all. This is known as "the measure problem''. Some of the proposed probability measures predict that "Boltzmann brains'' – hallucinating disembodied brains appearing as quantum fluctuations – greatly outnumber regular observers. We shall investigate how this and other paradoxes can be used to restrict the set of possible measures. We shall also explore how the probability measure can be derived from the fundamental theory, such as quantum gravity. Another direction of the proposed research is the study of bubble collisions. The most spectacular observational test of the multiverse scenario would be a direct observation of a collision of our bubble with another one. We shall investigate observational signatures of such a collision and the probability for us to be close enough to detect one.
Technical Abstract
One of the most intriguing problems of inflationary cosmology is that of calculating probabilities in models of eternal inflation. The crux of the problem is that the numbers of all possible observations performed in the course of eternal inflation are infinite. We have to figure out how to compare these infinities, since otherwise we will not be able to make any predictions at all. We shall explore different proposals for the probability measure, making sure they are not riddled with inconsistencies or obvious conflict with the data. We shall also explore what constraints on the measure are imposed by the global structure of the universe, having in mind in particular the "persistence of memory'' effect.
The most spectacular observational test of the multiverse scenario would be a direct observation of a collision of our bubble with another one. We shall study observational signatures of such a collision and the probability for us to be close enough to detect one. We shall also explore some conceptual issues related to the measure problem. These include the choice of reference class, the choice of prior probabilities for different models, and the possibility of deriving the measure from quantum gravity.
QSpace Latest
PressRelease: Shining a light on the roots of plant “intelligence”
All living organisms emit a low level of light radiation, but the origin and function of these ‘biophotons’ are not yet fully understood. An international team of physicists, funded by the Foundational Questions Institute, FQxI, has proposed a new approach for investigating this phenomenon based on statistical analyses of this emission. Their aim is to test whether biophotons can play a role in the transport of information within and between living organisms, and whether monitoring biophotons could contribute to the development of medical techniques for the early diagnosis of various diseases. Their analyses of the measurements of the faint glow emitted by lentil seeds support models for the emergence of a kind of plant ‘intelligence,’ in which the biophotonic emission carries information and may thus be used by plants as a means to communicate. The team reported this and reviewed the history of biophotons in an article in the journal Applied Sciences in June 2024.