SUR 1.2

Science, 2012

Inflationary cosmology has been widely accepted due to its successful predictions: for a “generic” initial state, inflation produces a homogeneous, flat, bubble with an appropriate spectrum of density perturbations. However, the discovery that inflation is “generically eternal,” leading to a vast multiverse of inflationary bubbles with different low-energy physics, threatens to undermine this account. There is a “predictability crisis” in eternal inflation, because extracting predictions apparently requires a well-defined measure over the multiverse. This has led to discussions of anthropic predictions based on a measure over the multiverse, and an assumption that we are typical observers. I will give a pessimistic assessment of attempts to make predictions in this sense, emphasizing in particular problems that arise even if a unique measure can be found.

There are growing indications today that complex dynamics of far-from-equilibrium systems lies at the root of primordial cosmology and the ultraviolet (UV) sector of particle physics. We recently pointed out that dimensional fluctuations of the UV sector can reproduce the morphology of the cosmic web. Expanding on the same line of inquiry, this provisional report explores the link between the long-range temporal correlations of critical phenomena and primordial cosmology. Excluding systematic measurement errors, our report sheds new light on the tension in the age of the Universe sparked off by the latest observations of the James Webb Space Telescope (JWST).

Astronomy & Astrophysics, 2013

Context. Theoretical stellar evolutionary models are still affected by not negligible uncertainties due to the errors in the adopted physical inputs. Aims. In this paper, using our updated stellar evolutionary code, we quantitatively evaluate the effects of the uncertainties in the main physical inputs on the evolutionary characteristics of low mass stars, and thus of old stellar clusters, from the main sequence to the zero age horizontal branch (ZAHB). To this aim we calculated more than 3000 stellar tracks and isochrones, with updated solar mixture, by changing the following physical inputs within their current range of uncertainty: 1 H(p, νe +) 2 H, 14 N(p, γ) 15 O, and triple-α reaction rates, radiative and conductive opacities, neutrino energy losses, and microscopic diffusion velocities. Methods. The analysis was conducted performing a systematic variation on a fixed grid, in a way to obtain a full crossing of the perturbed input values. The effect of the variations of the chosen physical inputs on relevant stellar evolutionary features, such as the turn-off luminosity, the central hydrogen exhaustion time, the red-giant branch tip luminosity, the helium core mass, and the ZAHB luminosity in the RR Lyrae region are analyzed in a statistical way. Results. We find that, for a 0.9 M model, the cumulative uncertainty on the turn-off, the red-giant branch tip, and the ZAHB luminosities accounts for ±0.02 dex, ±0.03 dex, and ±0.045 dex respectively, while the central hydrogen exhaustion time varies of about ±0.7 Gyr. For all examined features the most relevant effect is due to the radiative opacities uncertainty; for the later evolutionary stages the second most important effect is due to the triple-α reaction rate uncertainty. For an isochrone of 12 Gyr, we find that the isochrone turn-off log luminosity varies of ±0.013 dex, the mass at the isochrone turn-off varies of ±0.015 M , and the difference between ZAHB and turn-off log-luminosity varies of ±0.05 dex. The effect of the physical uncertainty affecting the age inferred from turn-off luminosity and from the vertical method are of ±0.375 Gyr and ±1.25 Gyr, respectively.

1993 (2nd) International Symposium on Uncertainty Modeling and Analysis

The time trends in the sequential series of measurements of the same physical quantity show a general pattern: the normal distribution grossly underestimates the probability of large deviations from the true values; the probability is well described by exponential functions. By analogy with physical measurements, the results indicate that the usual 95% confidence intervals in epidemiology and environmental studies should be expanded to account for unsuspected systematic errors.

Physical review. E, 2018

Complex dynamical systems often have tipping points and exhibit catastrophic regime shift. Despite the notorious difficulty of predicting such transitions, accumulating studies have suggested the existence of generic early-warning signals (EWSs) preceding upcoming transitions. However, previous theories and models were based on the effect of the intrinsic noise (IN) when a system is approaching a critical point, and did not consider the pervasive environmental fluctuations or the extrinsic noise (EN). Here, we extend previous theory to investigate how the interplay of EN and IN affects EWSs. Stochastic simulations of model systems subject to both IN and EN have verified our theory and demonstrated that EN can dramatically alter and diminish the EWS. This effect is stronger with increasing amplitude and correlation time scale of the EN. In the presence of EN, the EWS can fail to predict or even give a false alarm of critical transitions.

SCIENCE ANNUAL CONFERENCE SEPTEMBER 29 TH-OCTOBER 1 ST 2010 THE UNIVERSITY OF SYDNEY, 2010

We report on the initial findings of a study aimed at developing ways to address threshold concepts in the design of undergraduate curricula, involving academics in two disciplines (physics and law) from four Australian universities The present paper compares two different processes by which physics academics identified and characterised a candidate threshold concept, measurement uncertainty, using student interviews and their own experiences as teachers.

There are different kinds of uncertainty. I outline some of the various ways that uncertainty enters science, focusing on uncertainty in climate science and weather prediction. I then show how we cope with some of these sources of error through sophisticated modelling techniques. I show how we maintain confidence in the face of error.

2024

This paper presents the Theory of General Uncertainty, a framework that unifies relativity and quantum mechanics through the lens of uncertainty. By expanding the Heisenberg uncertainty principle to encompass energy, time, mass, position, distance, and momentum, we derive key relativistic and quantum phenomena. We propose an experiment to test the theory's predictions on gravitational wave interactions with light and predict specific X-ray phenomena generated by gravity due to general uncertainty. These predictions are compared to actual observed data for validation. We also address the distribution of mass-energy in the universe and its implications for predicting the motions of intergalactic bodies. Furthermore, we propose a novel approach to solving the cosmological constant problem and make a testable prediction.

Physical Review D, 2014

Recent observations have led to the establishment of the concordance ΛCDM model for cosmology. A number of experiments are being planned to shed light on dark energy, dark matter, inflation and gravity, which are the key components of the model. To optimize and compare the reach of these surveys, several figures of merit have been proposed. They are based on either the forecasted precision on the ΛCDM model and its expansion, or on the expected ability to distinguish two models. We propose here another figure of merit that quantifies the capacity of future surveys to rule out the ΛCDM model. It is based on a measure of the difference in volume of observable space that the future surveys will constrain with and without imposing the model. This model breaking figure of merit is easy to compute and can lead to different survey optimizations than other metrics. We illustrate its impact using a simple combination of supernovae and BAO mock observations and compare the respective merit of these probes to challenge ΛCDM. We discuss how this approach would impact the design of future cosmological experiments.