End of the Universe

Apart from the well known long-term “heat-death” describing a gradual end to the universe, it has been postulated the more abrupt possibility that the quantum vacuum might only be in a quasi-stable state, and that its reversion to a stable state would set about a radical restructuring of the laws of physics which spreads at the speed of light from source of its reversion – this would cause the end of chemistry, and therefore life, as we know it.

Now a new proposal for an abrupt end has been published. This involves some obscure quantum physics which predicts the ‘instanton’ – a kind of bubble in the Higgs field, which would expand at the speed of light, swallowing everything. However their calculations suggest that this would happen on average once every 10^100 years! (present age of the universe is only 10^14 years)

Space.com article

Paper in Physical Reviews

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The Still Silent Night of Dark Matter

Two major experiments are reporting (8th Nov 2017) that they have been unable to detect any signals at all from dark matter – XENON1T in Italy and PandaX in China.

WEB_P1190369_FC-XENON

These experiments were based on the favoured theory of SuperSymmetry in which dark matter consist of Weakly-Interacting Massive Particles (WIMPs) that would interact, but only rarely with ordinary matter, and carry large mass.

Such detectors will continue to be developed, but alternative theories are now being taken more seriously – axions (a type of massive exotic photon) are one candidate. But it is also possible that the dark matter (whose gravitational effects are not disputed) exists in a ‘sector’ of the universe completely hidden from us, or that the theory of gravity needs modification in the large scale.

Click for more detailed Nature article

Update 19th Nov 2017: Despite the above failure to detect WIMPs, the Astroparticle Physics European Consortium (APPEC), which coordinates funding plans, has proposed scaling up the same experiments – instead of using 3 tonnes of noble gas, they would use 30 tonnes! There has been criticism that following this same line of research “will turn the dark-matter field into a desert of ideas.”

Update 2nd Dec 2017: A Chinese spacecraft (DAMPE) which is designed to measure cosmic ray properties, has confirmed an anomolous disruption in the curve when plotting number of particles against energy of those particles. This cannot be explained within existing physics knowledge, and is possible a pointer to darm matter WIMP annihilation. Futurism article

Update 4th April 2018: The DAMA collaboration have just released results showing that they are still seeing the signal, allegedly from dark matter, which they announced some years back, before upgrading their equipment. They record flashes of light in sodium iodide crystals caused by particles colliding with crystal nuclei. Although there are background sources for these collisions, the dark matter signal should peak in June as the Earth plows slightly faster into the supposed dark matter headwind, in concert with the solar system’s orbit round the galaxy.
Update 9th Dec 2018: The COSINE-100 experiment, designed to use the same methodology as DAMA above, has reported finding no evidence of dark matter after allowing for background radiation.
Update 7th April 2018: A paper, published March 23 in the journal Physical Review Letters, describes a mechanism whereby during the inflation stage of the universe, after the big-bang, the Higgs field, in a quasi-stable state, could exhibit quantum fluctuations sufficient to cause the local ‘stuff’ to clump together sufficiently to form a black hole. These primordial small mini black holes would be formed in the weight region of 10 trillion kilograms, their calculations suggest, and the existence of these in great numbers, growing over time, could explain away dark matter. other commentators are more conservative primordial black holes might explain only a few percent of dark matter.
Update 4th July 2018:  Published today in the journal Nature, is a study showing that the Equivalence principle, the idea that Gravitational Mass is equal to Inertial Mass, holds, even with very high mass objects like neutron stars and white dwarfs. This in turn rules out several theories in which gravity might vary from Relativity in extremes, and therefore makes the theoretical existence of Dark Matter seem even more likely.