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The Early Universe Adam: The Early Universe April 1, 2020 Wednesday, April 1, 2020 Adam, brief report: The Early Universe The early universe Hey everyone, here is my presentation on the early universe. Will try to answer any questions asap. Adam Q & A: Question from Clayton: 1. You say In the beginning that the 4 fundamental forces were combined, do you have any extra infor- mation on that? Such as how it would interact with the early universe at the time? Answers: Adam: As for your first question, I actually only found rather hopeful text on the matter of the 4 forces. I read that it is coined “Theory of everything” but from my understanding there isn’t any headway on that. Than again, when reading about it, it does bring up string theory a lot so may Dr. Wheeler could shed some light on that. JW: There is evidence from particle accelerators that the strength of the strong, weak, and electromagnetic interactions changes with energy, and that at high enough energy these forces have the same strength. Even without such evidence it is tempting to suppose these interactions are different aspects of a single one, in the same way that electricity and magnetism are now unified into electromagnetism. Since the 1970s a great deal of work in high energy field theory has been devoted to finding such a unifying theory, a Grand Unified Theory, or GUT. Beginning in the 70s as well, theorists developed supergravity theories that include the other inter- actions. Containing all the known interactions – gravity, strong, electroweak – these theories are whimsically called Theories Of Everything, or TOEs. The only currently successful quantum TOE is string theory, which does succeed at giving a unified quantum theory of all known interactions, including gravity. Most predictions yet made from TOEs or GUTs focus on low energy; it is difficult to compute the ultra-high energy behavior expected in the early cosmos. In any case, at the earliest times, the Planck era, we must have a quantum theory of gravity such as string theory because the available energy is enough to spontaneously produce small black holes, which (being small) would quickly evaporate. Questions from Clayton and Noah: Clayton In the lepton age particles and antiparticles are created, and most of the antiparticles are destroyed. Do you know if there were the same amount of particles and antiparticles made? And what happened to the matter/energy of the antiparticles after they were destroyed? 1 Noah On slide 6 you mention that most antiparticles were destroyed due to annihilation or instability. Could you expand more on what you mean by instability? Answers: Adam: As for your second question, Clayton, that leads into something called the Baryon asymmetry problem. The standard model nor general relativity explain this issue as both would assume an equal distribution of matter and anti matter. If you are still curious about the matter anti-matter problem I highly suggest looking up the Baryon asymmetry problem. Pretty fun to read about. I mostly said instability due to the proposition that there MAY have been more matter than anti-matter in the beginning. Probably poor wording on my part there. JW: In known particle creation events, particle-antiparticle pairs occur so the expectation is equal numbers of particles and antiparticles arising from the quark plasma. However, a certain very few particles, notably the K meson, violate both Parity and Charge Conjugation. There is a fundamental theorem in quantum field theory called the CPT theorem, which states that the combination of three symmetries: Parity, Charge conjugation, and Time Reversal – must be conserved. If the CPT theorem holds then since the K meson decay violates CP it must also violate T. If time reversal, T, is violated then there will be slightly different numbers of particles and antiparticles in the early universe. It is assumed that these particles and antiparticles annihilated, leaving the slight excess of ordinary particles as the ones we see today. The energy of the annihilations would have heated the Universe and contributed to the overall expansion. Clayton I looked up the baryon asymmetry like Adam had suggested, and one of the theories was a university-antiuniverse pair where our universe ended up mostly particles and time travels forward. Then the antiuniverse ended up mostly antiparticles, and time travels backwards, I thought that was really interesting and wanted to know your thoughts on it JW I think that view makes a lot of sense! The best understanding of antiparticles in field theory is that they are normal particles traveling backward in time. It would be totally consistent for the Big Bang event, whatever it was, to send particles both directions in time, with the antiparticles the ones that went the other way. No surprise we don’t see them! Question from Noah: Noah: How does the big bang theory predict the existence of the CMB? Also, aside from the redshift of galaxies and the existence of the CMB, what are the main sources of evidence for the big bang theory? Answers: Adam: The Big Bang theory predicts that the early universe was a very hot place and that as it expands, the gas within it cools. Thus the universe should be filled with radiation that is literally the remnant heat left over from the Big Bang, which is the CMB. Another piece of evidence for the Big Bang are primordial gas clouds. In 2011, astronomers found pristine clouds of primordial gas by analyzing absorption lines in the spectra of distant quasars. Before this discovery, all other astronomical objects have been observed to contain heavy elements that are formed in stars. These two clouds of gas contain no elements heavier than hydrogen and deuterium. Since the clouds of gas have no heavy elements, they likely formed in the first few minutes after the Big Bang. Other than that, the CMB and red shifted galaxies are the main pieces of evidence that I know of. JW: This is the most important point about the Big Bang. Wikipedia Big Bang gives a clear list with detailed descriptions (below) and you should be familiar with these! 2 1. Hubble’s law and the expansion of space 2. Cosmic microwave background radiation 3. Abundance of primordial elements 4. Galactic evolution and distribution 5. Primordial gas clouds "[The] big bang picture is too firmly grounded in data from every area to be proved invalid in its general features." Lawrence Krauss Observational evidence The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble’s law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by BBN. More recent evidence includes observations of galaxy formation and evo- lution, and the distribution of large-scale cosmic structures,[69] These are sometimes called the "four pillars" of the Big Bang theory. Precise modern models of the Big Bang appeal to various exotic physical phenomena that have not been observed in terrestrial laboratory experiments or incorporated into the Standard Model of particle physics. Of these features, dark matter is currently the subject of most active laboratory investigations. Remaining issues include the cuspy halo problem and the dwarf galaxy problem of cold dark matter. Dark energy is also an area of intense interest for scientists, but it is not clear whether direct detection of dark energy will be possible. Inflation and baryogenesis remain more speculative features of current Big Bang models. Viable, quantitative explanations for such phenomena are still being sought. These are currently unsolved problems in physics. Hubble’s law and the expansion of space Main articles: Hubble’s law and Expansion of the universe See also: Distance measures (cosmology) and Scale factor (cosmology) Observations of distant galaxies and quasars show that these objects are redshifted: the light emitted from them has been shifted to longer wavelengths. This can be seen by taking a frequency spectrum of an object and matching the spectroscopic pattern of emission or absorption lines corresponding to atoms of the chemical elements interacting with the light. These redshifts are uniformly isotropic, distributed evenly among the ob- served objects in all directions. If the redshift is interpreted as a Doppler shift, the recessional velocity of the object can be calculated. For some galaxies, it is possible to estimate distances via the cosmic distance ladder. When the recessional velocities are plotted against these distances, a linear relation- ship known as Hubble’s law is observed: v = HD, where v is the recessional velocity of the galaxy or other distant object, D is the comoving distance to the object, and H0 is Hubble’s constant, measured +1:3 km to be 70:4−1:4 s·Mpc by the WMAP. Hubble’s law has two possible explanations. Either we are at the center of an explosion of galaxies— which is untenable under the assumption of the Copernican principle—or the universe is uniformly expanding everywhere. This universal expansion was predicted from general relativity by Friedmann in 1922 and Lemaître in 1927, well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang theory as developed by Friedmann, Lemaître, Robertson, and Walker. The theory requires the relation v = HD to hold at all times, where D is the comoving distance, v is the recessional velocity, and v; H, and D vary as the universe expands (hence we write H0 to denote the present-day Hubble "constant"). For distances much smaller than the size of the observable universe, the Hubble redshift can be thought of as the Doppler shift corresponding to the recession velocity v.
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