NEW HOT-to-COOL COSMOLOGY: Amazing Progress Yet Greater Questions
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This document summarizes the progression of cosmological theories from astrology to the modern precision cosmology of the hot big bang model. It describes key developments like Lemaitre predicting the expansion of the universe from Einstein's general relativity in the 1930s. Later, the cosmic microwave background radiation was discovered, confirming the hot origins of the universe. Current measurements still have discrepancies to resolve, like differences in the Hubble constant. Theorists have proposed ideas like inflation and the multiverse to further explain observations, but greater understanding of dark matter and energy is still needed.
NEW HOT-to-COOL COSMOLOGY: Amazing Progress Yet Greater Questions
- 1. NEW HOT-to-COOL COSMOLOGY:Amazing Progress Yet GreaterQuestions by Paul H. Carr We live on an island of knowledge surrounded by a sea of mystery. As our knowledge island continues to grow, the boundary on the shoreline with mystery increases1. ABSTRACT Astronomy has progressed from astrology to precision, hot-to-cool, cosmology. Georges Lemaitre, using Einstein’s General Relativity, predicted in 1930s that our universe expanded from at primeval atom in a hot big bang. In 1964, radio astronomers detected the whispering cosmic microwave background radiation from this hot cosmic explosion. Since 1993, an increasing number of satellites have measured that this Planck black-body radiation has cooled, as it expanded, to a very cool 2.725 K. It also has fluctuations of one part in 100,000. Alan Guth’ inflationary universe theory predicted this as arising from quantum fluctuations at the “Beginning.” Some aspects of Guth’s theory have been verified. His theory also predicts that the process that created our observable universe did not stop, but continued to make other universes. It was a gift that kept on giving. Will we ever be able to observe these multi- universes? The atomic mass/energy that we earthlings experience, is only 5% of the universe. The other 95% is cold dark matter, that has gravity but does not emit light, and dark energy a repulsive anti-gravity that is causing our the expansion of our universe to accelerate. There are some discrepancies between different methods for measuring the Hubble expansion constant. Wouldn’t it be better to resolve these discrepancies and to more deeply understand the dark matter and dark energy in our universe before we take the existence of multi-universes seriously? INTRODUCTION During the 20th century, we have experienced amazing progress in our understanding of the size and age of the cosmos. In the late 1800s, physicist Lord Kelvin, using thermodynamic cooling arguments, calculated the age of the earth to be 20 to 40 million years. This implied the other planets and the sun were similar in age. This brought him into conflict with geologists who concluded from fossil evidence that our earth was billions of years old. This was resolved when British astrophysicist Arthur Eddington suggested that stars get their energy from the nuclear fusion of hydrogen into helium. Hans Bethe’s proof of this in 1938 resulted in his 1967 Nobel Prize. Our present knowledge is that sun and our solar system are 4.5 billion years old. There is enough nuclear fuel left in our sun to let it shine for billions of years. In 1995, the Hubble telescope gave us images of galaxies, 12 billion light years away, that formed 2 billion years after the hot big bang explosion at the beginning of our “Whispering Cosmos” (See Fig 1). “Whisper” is a metaphor for the cosmic background radiation noise or hiss
- 2. that we hear as we tune between radio and TV stations.2 There was no medium to transmit the implied sound of the Big Bang . Fig. 1. Hubble Deep Field Photo of Galaxies 12 billion light years away, 2 billion years after the “Beginning.” We will trace emergence of precision measurements of the remnant fossil microwave radiation noise from the big bang. The atomic matter, with which we earthlings are familiar, is only 5 per cent of the mass/energy of the cosmos. The remaining is dark matter/energy, that has gravity but does not radiate energy, and dark energy/matter. It is manifest as a sort of repulsive force that in 1998 was discovered to cause our universe to accelerate its expansion. Alan Guth’s inflationary theory also predicted that the expansionary explosion that created our universe, could have continued to create other universes. Will we ever be able to observe these multi- universes? Physicists have been searching for years for dark matter particles, to no avail. EINSTEIN’S GENERAL RELATIVITY THEORY Modern cosmology originated with Einstein’s General Relativity Theory. When Einstein applied this to the universe, he noted that the gravitation attraction of the stars and plants would cause
- 3. them to move together. At that time, however, astronomers believed that the universe was static, so Einstein added a cosmological constant or “fudge factor” to cancel out the gravitational attraction. This Cosmological Constant or anti-gravity has recently become evident as dark energy. In the 1930s, Georges Lemaitre, using Einstein’ general relativity, postulated that the universe originated from a tiny cosmic “egg” or primordial atom in a hot big bang. Initially, this was not taken seriously The atheist astronomer Fred Hoyle never believed it, partly because it seemed too much like the biblical creation story with its “Beginning.” In 1949, Hoyle coined the term “LeMaitre’s Big Bang” to express his disbelief.2 And there was light! In 1964 radio astronomers Penzias and Wilson discovered the “fossil” radiation from the big bang, for which they received the 1978 Nobel prize . This confirmed George Gamow’s earlier prediction that glowing gas plasma in the big bang would have extremely high temperatures that would be released when the universe became transparent. This temperature was hot enough to fuse the primordial hydrogen into 25% helium. The measurement of the 73% to 25% hydrogen to helium ratio, with 2% other atoms, confirms the universe’s very hot beginning. In 1993, the cosmic background Explorer satellite (COBE) measured the light at many frequencies and found that it fit exactly the Planck black-body spectrum of thermal radiation. Due to cosmic expansion, the temperature of the radiation has cooled to 2.725 degrees K above absolute zero – the Cosmic Background Radiation (CBR). This discovery confirmed the prediction that the universe had indeed expanded from a point about 13.8 billion years ago. This is indeed “hot” to very “cool” (-270 degrees C) cosmology. In 2001, NASA launched a cosmic radiation satellite (called WMAP) was launched to measure and map the CBR in more detail. It was found that the temperature of the CBR varies by a tiny amount (about 1 part in 100,000) over the celestial sphere. Astrophysicist Max Tegmark played a significant role in analyzing the data from the WMAP satellite over nine years.3 Tegmark separated the cosmological signal from other noise using information theory and his ability to do sophisticated computational number-crunching. He made beautiful high-resolution plots of the light that began to shine about 380,000 years after the Big Bang. The plots in Fig 2 suggest that these tiny variations in temperature formed the “seeds” that allowed gravity to pull matter together to form the first stars, galaxies and planets. The nonuniform patterns in this radiation is the same as that of the galaxies. Lambda Cold Dark Matter theory (Lambda CDM) can account for both the nonuniformities in the primordial cosmic radiation that gravity magnified into the nonuniform distribution of the galaxies. The fundamental parameters of Lambda CDM theory are the same for both.
- 4. Fig 2 WMAP data. The temperature scale shows the variations in micro-K from the mean temperature of 2.725 K. Precision cosmology Measurements of the CBR by the WMAP satellite were followed in 2009 by the European Space Agency’s Planck satellite, which measured the CBR at an even greater level of detail. The data from these satellites has been used to describe many of the features of the early universe. These efforts in space science and mathematical analysis over the past 20 years, have led to the era of precision cosmology. For example, we now have determined values of these parameters: Age of the universe: t0 = 13.8 Gyr Hubble parameter: H0 = 67.4 +/- 0.5 Km/s/Mpc Atomic Baryon density / critical density: b = 4.9% Cold dark matter density / critical density: c = 27% Spatial curvature: = 0.000 +/- .005 (i.e. flat) Dark Energy Lambda: 68% One of the first questions that arose about the CBR is known at the Horizon Problem. How can parts of the universe over 13.8 billion light years apart be in thermal equilibrium at almost the same temperature everywhere it is measured? MIT Professor Alan Guth’s Inflationary Universe theory solved this problem.4 A tiny fraction of a second after the beginning, the big bang was in thermal equilibrium and expanded at very much faster rate than we measure today. Guth’s theory of quantum fluctuations at the Beginning also explained the small, one part in 100,000 nonuniformity observed in the cosmic microwave background radiation. He also predicted that there is no spatial curvature in the universe.
- 5. In 2018, a new challenge in precision cosmology was discovered. The value of the Hubble expansion constant derived from the cosmic microwave black body data is 67.4 Km/sec/Mpc. (This means that at large scales, space is expanding at a speed of 67.4 kilometers per second for every 3.3 million light-years farther away we measure). Another approach to measure the Hubble parameter was developed by Adam Riess5 and colleagues. The difficult part of astronomy is to measure the distances to the stars. Through a complicated series of steps, a “distance ladder” is calibrated: first by means of stellar parallax, which calibrate distances to some nearby stars, then this scale is used to measure distance to Cepheid variable stars that have a known brightness-cycle relationship, then to Type Ia supernovae that have a uniform brightness – “standard candles” that allow the distance scale to be extended to millions of light years. Recent measurements of the Hubble expansion constant by Riess et al. give a Hubble constant of 74 Km/sec/Mpc. Experimental error cannot explain the discrepancy. The cosmic microwave background value of 67.4 Km/sec/Mpc is from beginning of the universe. The value of 74 Km.sec.Mpc is measured from supernovae formed more recently. A deeper understanding of dark energy and matter might help in resolving the discrepancy. According the present cosmology, only 5% of the atomic matter in the universe is well understood. The remaining 27 % is dark matter, that has gravity but does not emit light, and 68% is dark energy. For many decades, scientists have been unsuccessfully searching for candidate dark matter particles. The theoretical understanding of dark energy, whose repulsive anti-gravity is similar to Einstein’s Cosmological Constant, is limited. The multiverse Several cosmologists such as Alexander Vilenkin have recognized that Guth’s inflation theory leads logically to a shocking idea: that inflation generally refuses to stop, forever producing more space: eternal inflation. Tegmark thus describes Guth’s inflationary universe beginning as “the gift that keeps on giving.” In other words, the process continues and could be creating an infinity of universes – the “multiverse”. Could the the multiverse be more metaphysics (beyond physics) than physics? Cosmologist George Ellis asks, “Does the multiverse really exist?” Ellis questions whether Vilenkin’s eternal inflation idea is correct. Inflation may not go on forever. "It's very unfortunate that one thinks of the beginning whereas in fact, we have no good theory of such a thing as the beginning," 2019 Nobel Laureate James Peebles said in an interview. By contrast, we do have a "well-tested theory of evolution from an early state" to the present state, starting with "the first few seconds of expansion"—literally the first seconds of time, which have left cosmological signatures referred to as "fossils."
- 6. Max Tegmark, like all theoretical physicists, is good at mathematics and loves it. This attitude places him in a long tradition going back to the Pythagoreans, about 500 BC. Even then, mathematics took on an exalted and semi-religious status, which persists to this day in the Mason. Tegmark’s arguments for mathematics as an ultimate reality resonate with Thororeau’s, “The most distinct and beautiful statement of any truth must take at last the mathematical form.” Paul Carr in his book “Beauty in Science and Spirit,” defined beauty as “at delicate dance between mystical subjective forms and mathematical objective functions that maintain the universe and life.” 6 This description is similar to Tegmark’s Chapter 9 “Internal Reality, External Reality, and Consensus Reality.” External Reality has a mathematical description. Internal Reality is subjective perception. Consensus Reality is what we agree upon in a classicalphysics sense, such as our heliocentric solar system. Tegmark states, “Our Universe does not give life meaning, but life gives our Universe meaning.” One “top down” source of meaning is that we are part of something much greater than ourselves, as embodied by many of the world’s religions. This is in contrast to anti- religious scientists who say that the universe is meaningless blind chance. Tegmark himself finds “bottom up” meaning in small things such as the “the beauty of the little flowers by the roadside. CONCLUSIONS Astronomers have made amazing progress in understanding the origin and age of our universe in the last century. Yet greater questions remain. Wouldn’t it be better to resolve the Hubble constant discrepancies and to have a better understanding of dark matter and dark energy in our universe before we take the existence of multi-universes seriously? Will be ever be able to measure the properties of these multi-universes? We live on an island of knowledge in a sea of mystery. As our knowledge expands, so does the shoreline with mystery. RERERENCES 1. M. Gleiser, The Island of Knowledge: The Limits of Science and the Search for Meaning. Basic Books. (2015) 2. P. Carr. 2007. “Not with a Bang, but a Whisper.” America Physical Society News. Letter to the Editor, (December 2007) http://www.mirrorofnature.org/NotBangButWhisper.pdf
- 7. 3. M. Tegmark, Our Mathematical Universe: My Quest for the Ultimate Nature of Reality. Vintage Paperback (2015) 4. P. J. E. Peebles, B. Ratra. “The cosmological constant and dark energy” Rev. Modern Physics, vol 75, (April 2003) 5. A. Guth. The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Basic Books (1998) 6. A Riess, et. al. New Parallaxes of Galactic Cepheids from Spatially Scanning the Hubble Space Telescope: Implications for the Hubble Constant. The Astrophysical Journal, vol 855, No. 2 (2018) 6. P. Carr 2006. Chapter 3 “From the ‘Music of the Spheres’ to the Big Bang’s Whispers,” Beauty in Science and Spirit. Beech River Books, Center Ossipee, NH (2006). Couronne, Ivan ( "Top cosmologist's lonely battle against 'Big Bang' theory". Phys.org. November 14, 2019.