-
--------------------- 2665 - AXIONS - how to explain the universe?
-
- The Earth, solar system, entire Milky Way and the few thousand galaxies closest to us move in a vast “bubble” that is 250,000,000 light years in diameter, where the average density of matter is half as large as for the rest of the universe.
-
- This is the hypothesis used to learn what speed is the universe expanding? Until now, at least two independent calculation methods have arrived at two values that are different by about 10% with a deviation that is statistically irreconcilable.
-
- The universe has been expanding since the Big Bang occurred 13.8 billion years ago, a proposition first made by the Belgian physicist Georges Lemaître (1894-1966), and first demonstrated by Edwin Hubble (1889-1953). The American astronomer discovered in 1929 that every galaxy is pulling away from us, and that the most distant galaxies are moving the most quickly.
-
- This suggests that there was a time in the past when all the galaxies were located at the same spot, a time that can only correspond to the Big Bang. This research gave rise to the Hubble-Lemaître law, including the Hubble constant (H0), which denotes the universe’s rate of expansion.
-
- The best H0 estimates currently lie around 70 (km/s)/Mpc (meaning that the universe is expanding 70 kilometers a second more quickly every 3.26 million light years, that is 156,600 miles per hour for every 3.26 lightyears distance). The problem is that there are two conflicting methods of calculation.
-
- The first calculation is based on the cosmic microwave background. This is the microwave radiation that comes at us from everywhere, emitted at the time the universe became cold enough for light finally to be able to circulate freely, about 370,000 years after the Big Bang.
-
- Using the precise data supplied by the Planck space mission, and given the fact that the universe is homogeneous and isotropic, a value of 67.4 is obtained for H0 , rather than 70 km/sec, using Einstein’s theory of general relativity to run through the scenario.
-
- The second calculation method is based on the supernovae which appear sporadically in distant galaxies. These very bright events provide the observer with highly precise distances, an approach that has made it possible to determine a value for H0 of 74 km/sec, rather than 67.4 km/sec.
-
- These two values becoming more precise for many years while remaining different from each other. It didn’t take much to spark a scientific controversy and even to arouse the exciting hope that we were perhaps dealing with a ‘new physics’.”
-
- To narrow the gap the idea that the universe is not as homogeneous is claimed, and a hypothesis that may seem obvious on relatively modest scales. There is no doubt that matter is distributed differently inside a galaxy than outside one. It is more difficult, however, to imagine fluctuations in the average density of matter calculated on volumes thousands of times larger than a galaxy.
-
- If we were in a kind of gigantic ‘bubble’ where the density of matter was significantly lower than the known density for the entire universe, it would have consequences on the distances of supernovae and, ultimately, on determining H0, the rate the Universe is expanding.
-
- All that would be needed would be for this “Hubble bubble” to be large enough to include the galaxy that serves as a reference for measuring distances. By establishing a diameter of 250 million light years for this bubble, the physicist calculated that if the density of matter inside was 50% lower than for the rest of the universe, a new value would be obtained for the Hubble constant, which would then agree with the one obtained using the cosmic microwave background.
-
- The probability that there is such a fluctuation on this scale is “1 in 20” to “1 in 5”. This could mean there are a lot of regions like ours in the vast universe.
-
- A new study, conducted to better understand the origin of the universe, has provided insight into some of the most enduring questions in fundamental physics: How can the Standard Model of particle physics be extended to explain the cosmological excess of matter over antimatter?
-
- What is dark matter? And what is the theoretical origin of an unexpected but observed symmetry in the force that binds protons and neutrons together?
-
- A compelling case can be presented in which the “quantum chromodynamics” (QCD) “axion“, first theorized in 1977, provides several important answers to these questions. The rotation of the QCD axion can account for the excess of matter found in the universe.
-
- Infinitesimally light, the QCD axion, at least one billion times lighter than a proton, is nearly ghost-like. Millions of these particles pass through ordinary matter every second without notice.
-
- However, the subatomic level interaction of the QCD axion can still leave detectable signals in experiments with unprecedented sensitivities. While the QCD axion has never been directly detected, this study provides added fuel for experimentalists to hunt down the elusive particle.
-
- The QCD axion is capable of filling three missing pieces of the physics jigsaw puzzle simultaneously:
-
- First, the QCD axion was originally proposed to explain the so-called strong CP problem, why the strong force, which binds protons and neutrons together, unexpectedly preserves a symmetry called the Charge Parity (CP) symmetry.
-
- The CP symmetry is inferred from the observation that a neutron does not react with an electric field despite its charged constituents.
-
- The second is that the QCD axion was found to be a good candidate for dark matter, offering what could be a major breakthrough in understanding the composition of approximately 80 percent of the universe’s mass that has never been directly observed.
-
- Also thirdly, the QCD axion could explain the matter-antimatter asymmetry problem.
-
- As matter and antimatter particles interact, they are mutually annihilated. In the first fraction of a second following the Big Bang, matter and antimatter existed in equal amounts. This symmetry prevented the predominance of one type of matter over the other.
-
- Today, the universe is filled with matter, indicating that this symmetry must have been broken. The QCD axion as the cause, Kinetic energy, resulting from the motion of the QCD axion, produced additional baryons , or ordinary matter. This slight tipping of the scale in favor of matter would have had a pronounced cascade effect, paving the way for the universe as it is known today.
-
- Greater understanding of the newly discovered dynamics of the QCD axion could potentially change the expansion history of the universe and thus inform the study of gravitational waves. It could also explain the origin of the tiny neutrino mass.
-
- Knowing how fast the Universe is expanding and what is ratio of matter to energy will help astronomers explain the results of measurements these new methods are giving us. Stay tuned there is a lot more to learn.
-
- March 13, 2020 2665
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Sunday, March 15, 2020 --------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment