=============== Cosmology 101 =============== Katie Mack has produced an excellent series of short videos explaining the current cosmological beliefs. :: Cosmology is the study of the universe's evolution. It's the narrative of the creation of the smallest particles and atoms that make up our own bodies and the unseen forces that govern our existence. It's the tale of black holes and dark matter, of spectacular explosions, and of the quiet, growing dark. Join Katie Mack, Perimeter Institute’s Hawking Chair in Cosmology and Science Communication, on an incredible journey through the cosmos in our new series, Cosmology 101. You can find the series here: https://youtu.be/gB6GPdkyBx8?si=98fG1RmT1Dsg8zwQ This presents an excellent opportunity to outline how the ideas in Professor Colin Rourke's, The Geometry of the Universe, contrast to those of modern cosmology. There are just two ideas: Sciama Principle and de Sitter Space. Underlying everything: The Perfect Coperncian Principle. Introducing: Cosmology 101 ========================== :: ... it is easy to feel that stars and galaxies and the cosmos itself are eternal and un-changing, just fixtures of nature that have always been and always will be ... The field of cosmology is defined as a study of evolution and change. The field, apparently, does not consider the possibility that the universe, like de Sitter Space, has the Perfect Copernican Principle, that it has looked pretty much the same for a very long time indeed. The belief in a truly ancient universe was shared by Einstein and many other astrophysicists of his era. It was one reason for his introduction of the cosmological constant. When the Universe was seen to be expanding, he withdrew his cosmological constant. In contrast, de Sitter's solution removes the mass term from Einstein's equation, leaving just the lambda term. The lack of matter perterbed Einstein, as he had hoped his General Relativity equation would embody Mach's Principle, providing an explanation for inertial frames. In what follows, Dennis Sciama comes to the rescue, with an additional assumption to General Relativity that re-instates matter, in particular the distant stars, as the origin of inertia. More on this later. If cosmology is to be defined as a study of evolution and change then it is a study of the evolution and change of galaxies. Expansion of the Universe Explained =================================== The Universe is uniformly curved. The geometry of our universe is non-Euclidean, we live in a Poincare disk world. In a curved spacetime, each galaxy that enters our visible universe bursts on the scene highly blue-shifted, before accelerating away and showing the familiar redshift. As noted by Robert MacKay, "We see every galaxy redshifted for all but a small finite part of the infinite time we see it". In short, red-shift is an extreme example of an observer selection bias. How do we know it is expanding? ------------------------------- Distant galaxies all appear to be moving away from us. Redshift is introduced with the familiar ambulance siren, dropping in pitch as it passes by. Note that, an amulance travelling an appreciable percentage of the speed of sound, bursts on the scene with a high pitch, but the high-pitched period does not last long compared to the time we hear it low-pitched as it travels away from us. The relationship between distance and redshift is noted to be so exact that we use redshift synominously with distance and time. The blue shift observations, in the form of gamma-ray bursts are being ignored, or rather mis-interpretted as the result of dramatic events such as neutron star colloisions. Another thing to note from the ambulance anology, whilst the fact that it is moving away from us means we were closer in the past, it does not mean that we were at the same point some time in the past, rather it means there was a point of closest approach. And where is all that space going? ---------------------------------- It is not going anywhere, there is no overall expansion. The expansion we see is exactly balanced by new, blue-shifted arrivals in our visible universe. Cosmic Microwave Background =========================== Cosmology 101 states that any time we look out into the Cosmos, we are looking into the past. With the Perfect Copernican Principle, we should expect the past to look like the present. Can we see the primordial fire of the Big Bang? The answer is no, the Big Bang did not happen. The Cosmic Microwave Background is thermalised radiation from distant galaxies in the universe. We should expect it to be very uniform, since the universe is assumed to be ancient, it has had a lot of time to get into equilibrium. Note that in an ancient universe there has been plenty of time for very distant regions to communicate, so no problem with the uniformity we see. Likewise, large scale spherical harmonics are not a surprise. Why is it the temperature it is? -------------------------------- The gravitational waves which create the curvature of the universe also mean that there is a limit to how far light can get from its source before it is comprehensibly scattered in both intensity and direction. The same scattering also limits the total energy of gamma-ray bursts and takes some of the intensity out of them. Based on the temperature of the CMB this distance is likely a handful of Hubble distances, say six or seven. Note there should be balance between the energy of the CMB and the energy of the gravitational waves. What about the harmonics? ------------------------- Maps of local (<500 million light years) show structure on that scale, likely due to giant elliptical galaxies with central black holes 10^15 solar masses or more, with around 10^5 galaxies in the local cosmic web. The Sciama Principle implies that any two bodies should move towards harmony, subject to the distance between them. So galaxies 500 million years apart can follow the same 500 million year oscillation. Stellar Evolution ================= The central black holes of active galaxies eject streams of plasma in jets from the galactic centre. The conditions at galactic centres are very similar to those of the early stages of the Big Bang. As the jets travel from the centre, they cool and condense into population II stars of very low metallicity. These are short lived and stars forming further out have higher metallicity. Note that mature galaxies are could be orders of magnitude older than the 13.7 billion years of the big bang. This gives plenty of time for heavy elements to accumulate in the proportions that we observe. It also gives time for black holes the size of Sgr A* to form by accretion from the surrounding medium. Galaxy Formation ================ Galaxies grow very slowly over time by acretion of matter by its central black hole. Quasars are baby galaxies, often ejected from a parent galaxy. Perhaps Sagittarius A* will one day be ejected from the Milky Way and form a baby galaxy. Note that without the 13.7 billion year time limit, galaxy formation is much easier to explain. JWST pictures are mentioned. Note that the observations were exactly what is expected in a de Sitter Universe: galaxies as far as you can see, like the ones nearby to the Milky Way. Looking out into a negatively curved universe is like wearing glasses to correct short-sightedness: objects appear nearer and smaller than they actually are. In the Big Bang theory, this is modelled by the cosmic scale factor, giving the size of the universe at a given redshift. In a de-Sitter Universe, it is simply what it is like to live inside a Poincare disk. A galaxy at 7 Hubble distances only appears to be 7/8 of the Hubble distance away. The Big Bang model, argues that galaxies grow through mergers in the early universe. It should be noted that the Sciama Principle makes galaxy mergers and mergers of black holes highly unlikely. It is like expecting two Atlantic hurricanes to merge into one storm, it just does not happen. The Sciama Principle is what is used to explain galactic rotation curves without the need for dark matter, so it is important to understand all the consequences. As two rotating masses approach each other the Sciama Principle adds to their rotation about each other, the system is stable with feedback that prevents in-spiral. What abouth the waves LIGO et al are detecting? ----------------------------------------------- It is suggested that the waves we are seeing are the gravitational analogue of gamma-ray bursts: new quasars entering our visible universe. Just as curvature boosts the light into the gamma-ray range, it also boosts the waves emitted by the rotation of the central black holes. The reason we do not see a gamama-ray burst every time we detect a wave is because the small quasars, with fast rotating black holes, are radio sources and the attenuation of the radio signal is not sufficient to generate a gamma-ray burst. One thing on the to-do list is to estimate the paramaters of each gravitational detection, with a quasar arrival model, and see how the parameters are distributed. With the O4 run having several detections per week there is now a good data sample to investigate. Cosmic Web explained ==================== Copernican Principle: extend to Perfect Cosmological Principle by including time. Cosmic web: it is old, together with the Sciama Principle. Dark matter is back: rotating masses to the rescue. Cosmic Inflation ================ No big bang, no cosmic inflation. Also no problem to explain uniformity of the CMB. Dark Matter Explained ===================== Sciama Principle. Galactic rotation curves without need for dark matter. Assume the rotation of a black hole at the centre of a galaxy causes the space time around it to rotate. 10^10 or more solar masses required for a typical galaxy. Note that Sciama Principle is too weak to affect wide binaries of stellar mass. Also Sgr A* is too small to drive a galaxy the size of the Milky Way. It is suggested that it is a moderate sized quasar, roughly on line to the centre of the galactic bulge, but not actually the centre, with the true centre likely twice as far away. Dark Energy =========== The evidence for dark energy is the following plot from the Dark Energy Survey: .. image:: images/supernova.png The observation is that there are some distant galaxies that are not as redshifted as they should be given their distance. The conclusion is that the expansion rate of the universe has increased. What we appear to be seeing is just what we might expect in a de Sitter model: the redshift v distance relationship is an asymptotic relationship, but there are many galaxies that have not yet reached that asymptote. .. image:: images/zvr.png The End of the Universe ======================= is likely a very, very long way away. The Future of Cosmology ======================= Re-define the subject to admit the possibility that the Universe is essentially static, but does not appear to be so. Embrace non-Euclidean geometry and a model that does not have all the problems outlined in this series.