The modified gravity lightcone

The modified gravity lightcone simulation project I: Statistics of matter and halo distributions

We introduce a set of four very high resolution cosmological simulations for exploring f(R)-gravity, with 20483 particles in 768 h-1Mpc and 1536 h-1Mpc simulation boxes, both for a |fR0| = 10-5 model and a ΛCDM comparison universe, making the set the largest simulations of f(R)-gravity to date. In order to mimic real observations, the simulations include a continuous 2D and 3D lightcone output which is dedicated to study lensing and clustering statistics in modified gravity. In this work, we present a detailed analysis and resolution study for the matter power spectrum in f(R)-gravity over a wide range of scales. We also analyse the angular matter power spectrum and lensing convergence on the lightcone. In addition, we investigate the impact of modified gravity on the halo mass function, matter and halo auto-correlation functions, linear halo bias and the concentration-mass relation. We find that the impact of f(R)-gravity is generally larger on smaller scales and increases with decreasing redshift. Comparing our simulations to state-of-the-art hydrodynamical simulations we confirm a degeneracy between f(R)-gravity and baryonic feedback in the matter power spectrum on small scales, but also find that scales around k = 1 h Mpc-1 are promising to distinguish both effects. The lensing convergence power spectrum is increased in f(R)-gravity. Interestingly available numerical fits are in good agreement overall with our simulations for both standard and modified gravity, but tend to overestimate their relative difference on non-linear scales by few percent. We also find that the halo bias is lower in f(R)-gravity compared to general relativity, whereas halo concentrations are increased for unscreened halos.


DAMIC experiment at SNOLAB

The DAMIC experiment at SNOLAB

The DAMIC (Dark Matter in CCDs) experiment at the SNOLAB underground laboratory uses fully depleted, high resistivity CCDs to search for dark matter particles with masses below 10 GeV/c2. An upgrade of the detector using an array of seven 16-Mpixel CCDs (40 g of mass) started operation in February 2017. The new results, obtained with the current detector configuration, will be presented. Future plans for DAMIC-M, with a total mass of 1kg and a ionization threshold of 2 electrons, will be discussed.


Breakthrough Listen: Green Bank

The Breakthrough Listen Search for Intelligent Life: A Wideband Data Recorder System for the Robert C. Byrd Green Bank Telescope

The Breakthrough Listen Initiative is undertaking a comprehensive search for radio and optical signatures from extraterrestrial civilizations. An integral component of the project is the design and implementation of wide-bandwidth data recorder and signal processing systems. The capabilities of these systems, particularly at radio frequencies, directly determine survey speed; further, given a fixed observing time and spectral coverage, they determine sensitivity as well. Here, we detail the Breakthrough Listen wide-bandwidth data recording system deployed at the 100-m aperture Robert C. Byrd Green Bank Telescope. The system digitizes up to 6 GHz of bandwidth at 8 bits for both polarizations, storing the resultant 24 GB/s of data to disk. This system is among the highest data rate baseband recording systems in use in radio astronomy. A future system expansion will double recording capacity, to achieve a total Nyquist bandwidth of 12 GHz in two polarizations. In this paper, we present details of the system architecture, along with salient configuration and disk-write optimizations used to achieve high-throughput data capture on commodity compute servers and consumer-class hard disk drives.


Breakthrough Listen: Parkes 64m

The Breakthrough Listen Search for Intelligent Life: Wide-bandwidth Digital Instrumentation for the CSIRO Parkes 64-m Telescope

Breakthrough Listen is a ten-year initiative to search for signatures of technologies created by extraterrestrial civilizations at radio and optical wavelengths. Here, we detail the digital data recording system deployed for Breakthrough Listen observations at the 64-m aperture CSIRO Parkes Telescope in New South Wales, Australia. The recording system currently implements two recording modes: a dual-polarization, 1.125~GHz bandwidth mode for single beam observations, and a 26-input, 308~MHz bandwidth mode for the 21-cm multibeam receiver. The system is also designed to support a 3~GHz single-beam mode for the forthcoming Parkes ultra-wideband feed. In this paper, we present details of the system architecture, provide an overview of hardware and software, and present initial performance results.


Another interstellar object

This asteroid came from another solar system—and it’s here to stay

By Daniel Clery |

While astronomers around the world had their eyes fixed last year on ‘Oumuamua, a lump of rock from another planetary system that whizzed through ours, little did they know that another interstellar interloper was quietly living among us. And this one appears to have been here for billions of years.

Astronomers first spotted the object, an asteroid called 2015 BZ509 that is orbiting close to Jupiter, in 2014. They knew it was unusual because it was traveling around the solar system in the opposite direction as almost everything else. (Its motion is shown in the animations above, with 2015 BZ509 circled.) Astronomers have found other objects in “retrograde” orbits, perhaps knocked off course by passing too close to a giant planet, but 2015 BZ509’s orbit was the weirdest of all because it is also elongated and out of alignment with the planets and other bodies.

To find out why, a pair of astronomers ran a series of 1 million simulations of the asteroid’s orbit, each with slightly different parameters. Jupiter’s orbit is a busy part of the solar system where the risk of being knocked off course is high, so eccentric orbits that are stable long term are unlikely. But the researchers found a number of possible orbits that were stable and concluded it is much more likely that 2015 BZ509 is in one of them, rather than that it happened to arrive for a short-term visit. Some of those stable orbits, if wound back in time, would mean that 2015 BZ509 has been with us since the beginning of our solar system, about 4.5 billion years ago.

There is no known mechanism that could have produced 2015 BZ509 in such an orbit when the planets were forming, the researchers report today in the Monthly Notices of the Royal Astronomical Society: Letters. Instead, the asteroid must have been drifting through space and was captured by the sun’s gravity.

That’s not as far-fetched as it seems. The sun and its planets formed inside a closely packed cluster of stars—which have since moved on—and any object ejected from one planetary system by gravitational interaction could conceivably end up in another. The discovery of 2015 BZ509 quietly living in the solar system suggests we should look again at some other oddball asteroids; the team’s simulations suggest that some of them may be interstellar interlopers as well. And if space agencies deemed it worth visiting one of them, we could find out whether other planetary systems are made of the same stuff as ours.


ELT-AO with Intel Xeon Phi Architecture

ELT-scale Adaptive Optics real-time control with the Intel Xeon Phi Many Integrated Core Architecture

We propose a solution to the increased computational demands of Extremely Large Telescope (ELT) scale adaptive optics (AO) real-time control with the Intel Xeon Phi Knights Landing (KNL) Many Integrated Core (MIC) Architecture. The computational demands of an AO real-time controller (RTC) scale with the fourth power of telescope diameter and so the next generation ELTs require orders of magnitude more processing power for the RTC pipeline than existing systems. The Xeon Phi contains a large number (> 64) of low power x86 CPU cores and high bandwidth memory integrated into a single socketed server CPU package. The increased parallelism and memory bandwidth are crucial to providing the performance for reconstructing wavefronts with the required precision for ELT scale AO. Here, we demonstrate that the Xeon Phi KNL is capable of performing ELT scale single conjugate AO real-time control computation at over 1.0 kHz with less than 20 μs RMS jitter. We have also shown that with a wavefront sensor camera attached the KNL can process the real-time control loop at up to 966 Hz, the maximum frame-rate of the camera, with jitter remaining below 20 μs RMS. Future studies will involve exploring the use of a cluster of Xeon Phis for the real-time control of the MCAO and MOAO regimes of AO. We find that the Xeon Phi is highly suitable for ELT AO real time control.


An Open Letter on AI

Research Priorities for Robust and Beneficial Artificial Intelligence

Artificial intelligence (AI) research has explored a variety of problems and approaches since its inception, but for the last 20 years or so has been focused on the problems surrounding the construction of intelligent agents – systems that perceive and act in some environment. In this context, “intelligence” is related to statistical and economic notions of rationality – colloquially, the ability to make good decisions, plans, or inferences. The adoption of probabilistic and decision-theoretic representations and statistical learning methods has led to a large degree of integration and cross-fertilization among AI, machine learning, statistics, control theory, neuroscience, and other fields. The establishment of shared theoretical frameworks, combined with the availability of data and processing power, has yielded remarkable successes in various component tasks such as speech recognition, image classification, autonomous vehicles, machine translation, legged locomotion, and question-answering systems.

As capabilities in these areas and others cross the threshold from laboratory research to economically valuable technologies, a virtuous cycle takes hold whereby even small improvements in performance are worth large sums of money, prompting greater investments in research. There is now a broad consensus that AI research is progressing steadily, and that its impact on society is likely to increase. The potential benefits are huge, since everything that civilization has to offer is a product of human intelligence; we cannot predict what we might achieve when this intelligence is magnified by the tools AI may provide, but the eradication of disease and poverty are not unfathomable. Because of the great potential of AI, it is important to research how to reap its benefits while avoiding potential pitfalls.

The progress in AI research makes it timely to focus research not only on making AI more capable, but also on maximizing the societal benefit of AI. Such considerations motivated the AAAI 2008-09 Presidential Panel on Long-Term AI Futures and other projects on AI impacts, and constitute a significant expansion of the field of AI itself, which up to now has focused largely on techniques that are neutral with respect to purpose. We recommend expanded research aimed at ensuring that increasingly capable AI systems are robust and beneficial: our AI systems must do what we want them to do. The attached research priorities document gives many examples of such research directions that can help maximize the societal benefit of AI. This research is by necessity interdisciplinary, because it involves both society and AI. It ranges from economics, law and philosophy to computer security, formal methods and, of course, various branches of AI itself.

In summary, we believe that research on how to make AI systems robust and beneficial is both important and timely, and that there are concrete research directions that can be pursued today.

Prof. Max Tegmark

LIFE 3.0:

I’m fascinated by AI and the the future of life. There’s been much talk about AI disrupting the job market and enabling new weapons, but very few scientists talk seriously about the elephant in the room: what will happen once machines outsmart us at all tasks? That’s why I wrote this book, to help you join the most important conversation of our time.

Max Erik Tegmark


China’s moon mission

China’s moon mission is set to probe cosmic dark ages

Daniel Clery

On 21 May, China plans to launch a satellite with a vital but unglamorous mission. From a vantage point beyond the moon, Queqiao, as the satellite is called, will relay data from Chang’e 4, a lander and rover that is supposed to touch down on the lunar far side before the end of the year. But a Dutch-made radio receiver aboard Queqiao will attempt something more visionary. In the quiet lunar environment, it will listen to the cosmos at low frequencies that carry clues to the time a few hundred million years after the big bang, when clouds of neutral hydrogen were spawning the universe’s first stars. The mission is a proof of principle for other efforts to take radio astronomy above the atmosphere, which blocks key radio frequencies, and far from earthly interference. For Europe’s astronomers, it is also a test of cooperation with China, something their U.S. counterparts at NASA are barred from doing.


Neutron stars’ quark matter

Neutron stars’ quark matter not so strange

Adrian Cho

For decades, some theoretical physicists have speculated that in the heart of a neutron star, a bizarre type of matter might emerge: a soup of the subatomic particles called quarks. Now, a new analysis indicates the recipe for such “cold quark matter” needs revision. Atomic nuclei consist of protons and neutrons, which themselves consist of trios of particles called up and down quarks, bound tightly by the strong nuclear force. Since the 1970s, some theorists have predicted that under extreme pressures like those in neutron stars, quarks might break free to create a soup of cold quark matter. They also predicted that it should include a third flavor of quarks known as strange quarks. Stable bits of such strange quark matter—or strangelets—might emerge in cosmic rays or linger from violent astrophysical events. Now, a trio of theorists argues that cold quark matter should consist of just up and down quarks. The analysis suggests that particle accelerators on Earth might just be able to produce stable bits of the quark matter. It would also dispel a far-fetched notion the Large Hadron Collider in Switzerland could produce negatively charged strangelets that would gobble up positively charged atomic nuclei—a possibility already ruled out by cosmic ray observation. Up-down quark matter would definitively rule out the doomsday scenario, as it would be positively charged and repel atomic nuclei.