Lifeboat Foundation

Researchers for the first time showed, how gravity can exist without mass, providing an alternative theory that could potentially mitigate the need for dark matter…

Dark matter is a hypothetical form of matter that is implied by gravitational effects that can’t be explained by general relativity unless more matter is present in the universe than can be seen. It remains virtually as mysterious as it was nearly a century ago when first suggested by Dutch astronomer Jan Oort in 1932 to explain the so-called “missing mass” necessary for things like galaxies to clump together.

Now Dr. Richard Lieu at The University of Alabama in Huntsville (UAH) has published a paper in the Monthly Notices of the Royal Astronomical Society that shows, for the first time, how gravity can exist without mass, providing an alternative theory that could potentially mitigate the need for dark matter.

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The American theoretical physicist, Brian Greene explains various hypotheses about the causation of the big bang. Brian Greene is an excellent science communicator and he makes complex cosmological concepts more easy to understand.

The Big Bang explains the evolution of the universe from a starting density and temperature that is currently well beyond humanity’s capability to replicate. Thus the most extreme conditions and earliest times of the universe are speculative and any explanation for what caused the big bang should be taken with a grain of salt. Nevertheless that shouldn’t stop us to ask questions like what was there before the big bang.

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Primordial black holes are hypothetical objects formed during the earliest moments of the universe. According to the models, they formed from micro-fluctuations in matter density and spacetime to become sand grain-sized mountain-massed black holes.

Discover the groundbreaking Self-Interacting Dark Matter (SIDM) theory that suggests dark matter particles might collide and interact with each other. Learn how recent studies on the El Gordo galaxy cluster support this revolutionary idea, potentially changing our understanding of the universe’s structure and evolution. Dive into the cosmic dance and stay updated with the latest space discoveries!

Chapters:
00:00 Introduction.
00:44 The Dance of Self-Interacting Dark Matter.
02:39 Unveiling the Strengths and Weaknesses of CDM and SIDM
05:14 Exploring Dark Matter: Methods and Future Prospects.
09:20 Outro.
09:37 Enjoy.

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In this Astrobite, the authors search for primordial black holes, a dark matter candidate, by calculating the effect their gravity would have on objects in our Solar System!

As opposed to black holes, white holes are thought to eject matter and light while never absorbing any. Detecting these as yet hypothetical objects could not only provide evidence of quantum gravity but also explain the origin of dark matter.

No one today questions the existence of black holes, objects from which nothing, not even light, can escape. But after they were first predicted in 1915 by Einstein’s general theory of relativity, it took many decades and multiple observations to show that they actually existed. And when it comes to white holes, history may well repeat itself. Such objects, which are also predicted by general relativity, can only eject matter and light, and as such are the exact opposite of black holes, which can only absorb them. So, just as it is impossible to escape from a black hole, it is equally impossible to enter a white one, occasionally and perhaps more aptly dubbed a “white fountain”. For many, these exotic bodies are mere mathematical curiosities.

The expansion of the universe has been a well-established fact of physics for almost a century. By the turn of the millennium the rate of this expansion, referred to as the Hubble constant (H ₀), had converged to a value of around 70 km s ^–1 Mpc ^–1. However, more recent measurements have given rise to a tension: whereas those derived from the cosmic microwave background (CMB) cluster around a value of 67 km s ^–1 Mpc ^–1, direct measurements using a local distance-ladder (such as those based on Cepheids) mostly prefer larger values around 73 km s ^–1 Mpc ^–1. This disagreement between early-and late-universe measurements, respectively, stands at the 4–5 σ level, thereby calling for novel measurements.

One such source of new information are large galaxy surveys, such as the one currently being performed by the Dark Energy Spectroscopic Instrument (DESI). This Arizona-based instrument uses 5,000 individual robots that optimise the focal plane of the detector to allow it to measure 5,000 galaxies at the same time. The goal of the survey is to provide a detailed 3D map, which can be used to study the evolution of the universe by focussing on the distance between galaxies. During its first year of observation, the results of which have now been released, DESI has provided a catalogue of millions of objects.

Small fluctuations in the density of the early universe resulted not only in signatures in the CMB, as measured for example by the Planck probe, but also left imprints in the distribution of baryonic matter. Each over-dense region is thought to contain dark matter, baryonic matter and photons. The gravitational force from dark matter on the baryons is countered by radiation pressure from the photons. From the small over-densities, baryons are dragged along by photon pressure until these two types of particles decoupled during the recombination era. The original location of the over-density is surrounded by a sphere of baryonic matter, which typically is at a distance referred to as the sound horizon. The sound horizon at the moment of decoupling, denoted r _d, leaves an imprint that has since evolved to produce the density fluctuations in the universe that seeded large-scale structures.

“… living systems evolve to exploit any aspect of physics that enables exploration of all possible ‘fitness landscapes’.”

Indeed!

In 1990, within the intellectual haven of Haverford College, I embarked on a transformative academic journey into biophysics – the captivating intersection of physics and biology.

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The much-hyped planetary alignment of June may not have been the jaw-dropping naked-eye spectacle some made it out to be, but it still made for some stunning astrophotography.

Josh Dury of Somerset, England caught the planetary parade on June 1, 2024, from atop Crooks Peak, a popular and historic outcropping of rock in the Mendip Hills.