Lifeboat Foundation

As physicists continue their struggle to find and explain the origin of dark matter, the approximately 80% of the matter in the universe that we can’t see and so far haven’t been able to detect, researchers have now proposed a model where it is produced before the Big Bang.

Their idea is that dark matter would be produced during a infinitesimally short inflationary phase when the size of the universe quickly expanded exponentially. The new model was published in Physical Review Letters by three scientists from Texas in the US.

An intriguing idea among cosmologists is that dark matter was produced through its interaction with a thermal bath of some species, and its abundance is created by “freeze-out” or “freeze-in.” In the freeze-out scenario, dark matter is in chemical equilibrium with the bath at the earliest times—the concentration of each does not change with time.

Was dark matter created some time after the Big Bang? Gravitational wave detectors could soon find the answer.

For now, the duo’s results suggest that the Dark Big Bang is far less constrained by past observations than Freese and Winkler originally anticipated. As Ilie explains, their constraints could soon be put to the test.

“We examined two Dark Big Bang scenarios in this newly found parameter space that produce gravitational wave signals in the sensitivity ranges of existing and upcoming surveys,” he says. “In combination with those considered in Freese and Winkler’s paper, these cases could form a benchmark for gravitational wave researchers as they search for evidence of a Dark Big Bang in the early universe.”

Continue reading “Delayed Big Bang for dark matter could be detected in gravitational waves” »

Space-time may not be continuous but instead made up of many discrete bits – and we may be able to see their effects near the edges of unusually bright black holes.

By Karmela Padavic-Callaghan

Black holes are some of the most mysterious phenomena in space that have puzzled scientists ever since their discovery. Extreme levels of gravitational pull suck in everything around the black hole, even light. Black holes are the complete absence of any source of light, resulting in total darkness.

According to a video posted by the popular YouTube channel Riddle, a black hole’s origins can be traced back to a star that has burnt up and turned into a supernova. One of the largest known black holes has a mass that is forty billion times larger than our sun in our solar system. This black hole is situated in a galaxy called “Holmberg 15A,” which is approximately 700 million lightyears away.

Continue reading “Video: Black holes — here’s what they are and why scientists are still puzzled” »

When a star dies in a supernova, one possible outcome is for the remains to become a neutron star. Inside a neutron star, the protons and electrons combine into uncharged neutrons. This substance is called neutron matter.

A team of researchers from the United States, China, Turkey, and Germany has performed ab initio (i.e., from the most fundamental principles) simulations to calculate spin and density correlations in neutron matter. They used realistic nuclear interactions at higher densities of neutrons than previously explored. Spin and density are the probability of finding a neutron in a particular position with a particular direction of spin. These correlations determine key aspects of how neutrinos scatter and heat up in a core-collapse supernova.

The research is published in the journal Physical Review Letters.

A unique Einstein zig-zag gravitational lens refines Hubble constant measurements and probes dark energy, solving key cosmological puzzles.

The universe just got a whole lot bigger—or at least in the world of computer simulations, that is. In early November, researchers at the Department of Energy’s Argonne National Laboratory used the fastest supercomputer on the planet to run the largest astrophysical simulation of the universe ever conducted.

The achievement was made using the Frontier supercomputer at Oak Ridge National Laboratory. The calculations set a new benchmark for cosmological hydrodynamics simulations and provide a new foundation for simulating the physics of atomic matter and dark matter simultaneously. The simulation size corresponds to surveys undertaken by large telescope observatories, a feat that until now has not been possible at this scale.

Continue reading “Record-breaking run on Frontier sets new bar for simulating the universe in exascale era” »

Particle physicists have been looking for so-called “sterile neutrinos” for a few decades now. They are a hypothesized particle that would have a tiny mass like the three known neutrinos but would not interact by the weak force or any other Standard Model force, only through gravitational interactions.

Its existence—or their existence—would solve some anomalies seen in neutrino experiments, help answer questions beyond the Standard Model of particle physics, and, if massive enough, could explain cold dark matter or warm dark matter.

But sterile neutrinos have not been seen in any particle experiments, despite many attempts. Now an experiment by the IceCube Collaboration has used 10.7 years of data from their detector near the Amundsen-Scott South Pole Station to lower the probability that at least one sterile neutrino does not exist. Their paper appears in Physical Review Letters.

Observations of the cosmic microwave background, leftover light from when the Universe was only 380,000 years old, reveal that our cosmos is not rotating. Infinitely long cylinders don’t exist. The interiors of black holes throw up singularities, telling us that the math of GR is breaking down and can’t be trusted. And wormholes? They’re frighteningly unstable. A single photon passing down the throat of a wormhole will cause it to collapse faster than the speed of light. Attempts to stabilize wormholes require exotic matter (as in, matter with negative mass, which isn’t a thing), and so their existence is just as debatable as time travel itself.

This is the point where physicists get antsy. General relativity is telling us exactly where time travel into the past can be allowed. But every single example runs into other issues that have nothing to do with the math of GR. There is no consistency, no coherence among all these smackdowns. It’s just one random rule over here, and another random fact over there, none of them related to either GR or each other.

If the inability to time travel were a fundamental part of our Universe, you’d expect equally fundamental physics behind that rule. Yet every time we discover a CTC in general relativity, we find some reason it’s im possible (or at the very least, implausible), and the reason seems ad hoc. There isn’t anything tying together any of the “no time travel for you” explanations.