Chapter 13 (A Short History of Our Universe)

Timeline

-13.8 billion years-the big bang

-5 billion years-our sun forms

-4.5 billion years-earth forms

-3.5-4 billion years- primitive life emergences on earth

-850 million to 1 billion years-ancestors of algae exist

-800 million years-first multicellular organisms appear

-650 to 700 million years-sponge like organisms exist

-530 million years-fish-like vertebrates evolve

-470-500 million years-aquatic green algae begin colonizing land.

-420–450 million years-animals began colonizing land

-420 million years-more complex plants with stems and roots appear

-390–400 million years- tetrapods (amphibians, reptiles, birds, mammals) begin to appear

-230 to 240 million years- dinosaurs appear

-140 to 250 million years -flowering plants begin to appear

-66 million years- dinosaurs become extinct

-66–90 million years- first primates evolve from small, tree-dwelling mammals

-25 million years-true primates (old world monkeys/apes) appear

-6-8 million years the hominin family (humans) split from chimpanzees.

-300,000 years modern humans (Homo sapiens) appear.

-5,000 to 6,000 years- human civilization begins

Today

+5 billion years-life on earth ends as our sun becomes a red giant

+20 billion years to infinity-our universe ends

Did our universe have a beginning?

To this question nearly all religions answer “yes” the world had a beginning. Most religions have their own creation stories. Hinduism does. All three of the monotheistic Western religions do. China does. Buddhism can be seen as an exception. There are the questions that the Buddha refused to answer known in the tradition as the Avyākṛta which includes questions like did the universe have a beginning? Will it have an end? The Buddha didn’t say that he didn’t know the answers to these questions but seems to have thought that this was knowledge that you didn’t need to know. It was unnecessary for pursuing the spiritual journey. Western science has not been afraid to propose answers to this question. Those answers concerning our universe will be the subject of the rest of this chapter. I won't take up the subject of multiverses. I wouldn't be surprised if they exist but since at this point, we only know that one universe exists let's keep our focus here.

The big bang

Current views in Western science are that “yes” the universe had a beginning. From the 1940s to 1960s, scientists were divided between the steady-state theory and the big bang theory. The core idea of the steady state theory was that our universe is eternal, with no beginning or end. It was a static universe that looked the same everywhere at all times. The alternative was known as the “big bang” which proposed that the universe began from an incredibly hot, dense single particle that contained all the energy of the universe. At some point this particle exploded. Our universe developed from that explosion.

The steady state theory was largely abandoned in the 1960s for several reasons. Firstly, it became clear that the universe is not in a static steady state. Edwin Hubble observed that distant galaxies are moving away from us, indicating a universe that is stretching and expanding, a universe consistent with one that began from a point source. To maintain constant density the steady state theory had to postulate that new matter was being created to fill the voids being created by expansion, a process never observed. A major prediction of the big bang theory was the existence of a cosmic microwave background, a faint afterglow of the big bang, representing this oldest light in the universe which fills all space in the universe. When this background was discovered in 1965, the balance of evidence clearly shifted away from the steady state theory and by the early 1970s the scientific community overwhelmingly accepted the big bang as the most explanatory of the two theories. Interestingly the term "big bang" was coined by English astronomer Fred Hoyle, one of the founders of the steady state theory. Hoyle meant the term as a pejorative, but it was so memorable it stuck.

The big bang is estimated to have occurred about 13.8 billion years ago. After the bang, in a period known as cosmic inflation the universe rapidly expanded. Within a fraction of a second space stretched from subatomic size to much larger than a galaxy. After this rapid expansion ceased the inflation field's energy converted into a hot, dense soup of particles and radiation. As the soup cooled, protons and neutrons formed, subsequently fusing to create the first light, atomic nuclei and eventually creating the particles of the standard model of particle physics. As matter formed, the effects of gravity became apparent pulling matter into stars and galaxies. As the universe continued to expand and cool, it entered its current phase dominated by dark energy which has accelerated the expansion. What existed before the big bang, where that hot substance came from as well as what caused it to bang, modern theories say little.

The appearance of life on earth

Life on Earth is thought to have begun through a process of abiogenesis, a process whereby non-living elements formed self-replicating organic molecules especially ribonucleic acid (RNA), then simple cells, simple organisms and finally more complex organisms. However, this was not a process that could happen just anywhere. It required a planet with a stable orbit positioned in a solar system away from the threats of supernovae. This planet had to be the right distance from a sun that could provide the energy necessary for life to form. It had to be free from heavy bombardment by asteroids. It had to be protected from harmful solar radiation by a magnetic field and kept neither too warm nor too cold by an insulating atmosphere. In the early Earth other factors such as volcanic activity likely aided this process by releasing gases including CO₂ and recycling minerals essential for sustaining life. In this environment, the chemical ingredients necessary for life, including water, carbon and other organic molecules could form.

Earth formed about 4.5 billion years ago. Around 3.5-4 billion years ago in various settings including ocean depths and volcanic ponds, simple organic molecules accumulated in a primordial soup and the basic building blocks needed to create life formed. From these early building blocks, amino acids and nucleotides assembled into proteins and nucleic acids and a self-replicating RNA world emerged that could store information and catalyze reactions. The first cells formed when lipids spontaneously formed liposomes (bubbles of lipid) and encased self-replicating RNA. A key event occurred about 2 billion years ago when a larger cell engulfed smaller bacteria, and the engulfed bacteria became mitochondria and chloroplasts (the energy producers of later cells) allowing formation of eukaryotic cells with a nucleus and specialized organelles. As cellular evolution continued a gradual shift occurred from RNA to deoxyribonucleic acid (DNA) as the self-replicating material with DNA becoming the genetic material and RNA taking on functions in protein synthesis. These gradual, interconnected steps, from basic chemistry to specialized cells and cooperative organisms, laid the foundation for the diversity of complex organisms that exist today.

Single cells became cell colonies, and then multicellular organisms with many specialized cells. Distinct specialized cell types evolved with roles including feeding, and reproduction leading to true multicellular organisms. Sexual reproduction allowed for greater genetic variation. Natural selection favored beneficial mutations, accelerating adaptation and driving evolution over long timescales. The development of traits such as cell adhesion allowed multicellular organisms to become established.

The evolution of plant and animal species.

Ancestors of algae existed 850 million to 1 billion years ago. 470 to 500 million years ago descendants of aquatic green algae resembling modern liverworts began colonizing land. More complex plants with stems and roots appeared around 420 million years ago. The appearance of plants played a crucial role in reducing atmospheric carbon dioxide, leading to global cooling and allowing marine life to expand. Flowering plants appeared between 140 and 250 million years ago.

The first fish-like vertebrates evolved approximately 530 million years ago in the form of jawless, small, soft-bodied creatures with a notochord (a precursor of a true backbone), a head, and rudimentary gills. Jawed fish appeared about 420–450 million years ago. A massive diversification of fish occurred between 359-419 million years ago.

Animals began colonizing land roughly 420–450 million years ago starting with invertebrates like arthropods (insects, spiders, crustaceans, centipedes). Invertebrates, similar to modern millipedes and arachnids, were the first to move onto land with the earliest land fossils including millipedes, scorpions, and spiders. Fish with limbs evolved from lobe-finned fish and moved onto land. Vertebrates (the tetrapods-amphibians, reptiles, birds, mammals) followed around 390–400 million years ago. Early land animals first developed in moist environments relying on habitats close to water before becoming fully terrestrial.

The dinosaurs

Dinosaurs appeared on Earth during the late Triassic Period, 230 to 240 million years ago. They emerged during a time when all continents were connected in a single supercontinent and evolved from reptile ancestors into small, mostly bipedal creatures. Early dinosaurs were generally small and meat eaters. As dinosaurs evolved, they increased in size reaching massive proportions, with the largest, weighing over 60-70 metric tons (130,000–150,000+ lbs.) and exceeding 30–37 meters (100–120+ feet) in length, becoming the largest land animals to ever live on Earth. During the Jurassic and Cretaceous periods, dinosaurs became the dominant vertebrates on land.

The dinosaur’s extinction occurred about 66 million years ago. While different theories exist concerning why the dinosaurs became extinct the most commonly accepted seems to be the Chicxulub asteroid impact in what is modern-day Mexico. This asteroid which is believed to have been about 10–15 km wide, struck the Yucatán Peninsula, creating a 150 km diameter crater. The impact caused massive earthquakes, and global forest fires. Particulate matter, dust and debris blocked sunlight for years creating an effective “nuclear winter”. Without sunlight photosynthesis stopped, and plants died, leading to starvation of plant eating dinosaurs. The carnivorous dinosaurs that fed on them soon followed. While there are alternate theories that don't involve an asteroid impact, they mainly invoke ideas that some type of catastrophic climate change occurred which led to the dinosaur’s demise.

What is interesting is the question of if evolution is a natural process, that is if the conditions are right, it will just happen and if it was natural for dinosaurs to evolve and become the dominant land animal, why didn't dinosaurs re-evolve? The answer to why dinosaurs did not re-evolve is likely that evolution is not a repetitive process. It adapts existing creatures to current environments, not those of the past. Following their mass extinction, environmental conditions changed. Oxygen levels were lower and different plants populated the environment. Mammals and birds which survived adapted to take over the ecological niches previously held by dinosaurs. The ancestral populations required to restart the evolution of large, non-avian dinosaurs no longer existed. Conditions were no longer right and there was no room for dinosaurs to re-evolve. There is also likely a stochastic (random/probabilistic) quality to evolution. Evolution is driven by a combination of deterministic factors and natural selection. But there are effects of random mutations and genetic drift in populations. Natural selection provides direction, but stochastic factors shape which mutations arise and are available to contribute to evolution. Birds are the only surviving, direct descendants of dinosaurs. Some modern reptiles including crocodiles and turtles, are considered the close cousins of dinosaurs. Although dinosaurs were once the dominant land creatures, they were a dead end in the evolution of life on Earth.

Human evolution

Primates evolved from small, tree-dwelling mammals 66–90 million years ago, with the first true primates appearing around 55–65 million years ago after extinction of the dinosaurs. The earliest primates were likely small, nocturnal, and lived off eating insects. They adapted to tropical forests by developing grasping hands and feet with nails instead of claws. What are considered the earliest true primates (old world monkeys/apes), appeared about 25 million years ago and adapted for life in trees.

In Africa humans (the hominin family tree) split from our closest living relatives, the chimpanzees (who share 96-98% of their DNA with modern humans) around 6-8 million years ago. Early hominins living about 2.3 million years ago (e.g., Lucy, Australopithecus afarensis) started walking on two legs. About 2 million years ago Homo erectus with more human-like bodies developed. Homo erectus mastered fire, and learned to create and use relatively sophisticated tools. Homo erectus was the first to migrate out of Africa. Modern humans (Homo sapiens) appeared in Africa around 300,000 years ago. Their development included larger brains, complex language, and culture. They spread globally.

Human civilization arose 5,000 to 6,000 years ago (4000–3000 B.C.E.) in Mesopotamia although some archeological sites in Turkey dating back as far as 9000–10,000 B.C.E suggest that advanced civilizations existed earlier. Civilization in Egypt emerged shortly after Mesopotamia, establishing complex, centralized states along the Nile. Other early civilizations appeared in the Indus Valley (c. 2500 B.C.E.), China (c. 1500 B.C.E.) and modern-day central America (c. 1200 B.C.E.).

The key drivers of human evolution are believed to be shifting African climates which favored adaptations like bipedalism and broader diets. Increased brain size allowed for tool-making, and control of fire as well as more complex communication. Development was however not a straight line but more of parallel streams of species interbreeding with Homo sapiens and breeding with other hominins like Neanderthals and Denisovans. The development of agriculture drove the transition from nomadic hunter-gatherer societies to civilization with permanent settlements, labor specialization, and complex social structures.

Is there life elsewhere in our universe?

The western scientific view of evolution implies that it is a natural process. If there was planet orbiting a star that was not too bright where the temperature, atmosphere, and other conditions were just right it would happen. But to truly believe this it would be nice to see that it has happened more than once. I’m not going to consider the evidence for UFOs and other claims that the earth has been visited by beings from other planets as convincing. Astronomers have found many planets (called exoplanets) orbiting other stars in our galaxy that might possess an earth like atmosphere. While the right conditions may be rare it is a vast universe and hard to believe that if the evolution of life on earth was so inevitable, that evolution of some kind of life would not happen elsewhere. Unfortunately, until we visit those distant locations or are contacted by beings from other planets we have no confirmation.

In our own solar system, the one planet where some form of life might have emerged is Mars. While Mars is now cold and dry there is credible evidence that in its past liquid water existed that formed rivers, lakes and oceans suggesting that Mars once had a warm and wet environment where life might have emerged. While there is no strong belief that life currently exists on Mars, NASA’s Mars rovers have found potential biosignatures that life once existed. The most promising findings come from NASA's Perseverance rover, finding in a rock called “Cheyava Falls” which had organic molecules, and evidence of redox reactions involving iron and silver consistent with microbial metabolism. Although non-biological explanations remain possible, these findings could indicate that conditions may have once existed on Mars but never progressed further or life was forced underground as Mars lost its magnetic field, and solar winds stripped away its protective atmosphere leading to Mars becoming cold and bombarded by intense radiation.

How will life on earth end?

Life on Earth is intimately linked to our Sun and stars have lives. A supernova is the colossal explosion of a star that occurs during the during the final stages of its life when a star runs out of fuel and its core collapses. Supernovas occur primarily in massive stars. Our Sun will never become a supernova. It lacks the mass (it would need about 8-10 times more) to trigger as it runs out of fuel, a core collapse that would lead to an explosion into a supernova. Our Sun is currently a long-lived, stable yellow dwarf star that provides consistent energy. It is about halfway through its 10-billion-year life span. It won't truly "burn out" but it will exhaust its core hydrogen which it fuses into helium and gradually swell into a red giant in about 5 billion years. As this occurs, the Sun will get hotter and brighter causing Earth's oceans to evaporate and making life on Earth as we know it impossible. Earth will become uninhabitable due to the Sun's increasing brightness in roughly 1 billion years. As it becomes a red giant the Sun may engulf the inner planets including Mercury, Venus and Earth which would end any life that might possibly remain. The Sun will then evolve into a white dwarf which will cool over potentially trillions of years eventually becoming a black dwarf but life on earth will have ended long before that.

Will our universe end?

Our current universe is believed to be about 13.8 billion years old. The consensus is that the universe will have some kind of end. However, how it will end gets more speculative, not that what we've been discussing up until now doesn't contain a healthy dose of speculation. However, I think it is fair to say that what we have been discussing up until now is reasonably accepted speculation in the Western scientific tradition.

As the energy from the initial big bang dissipated you might expect that gravity would slow the expansion and maybe at some point pull the universe back together. This was a reasonable theory until in the late 1990s when astronomers discovered that the expansion of the universe was not slowing down and was in fact speeding up. Distant galaxies were moving away from us faster and faster. These observations made no sense based on theories at the time and forced physicists to postulate the existence of a dark energy, which would have a repulsive effect, pushing space apart and expanding the universe at increasing rates. The nature of dark energy is still unknown but it makes up about 70% of the energy in the universe. Much of the uncertainty over the universe’s fate rests on the future behavior of dark energy.

One theory on the universe's future which is probably the most widely accepted is the "slow fade" or "big freeze". This theory postulates that the universe's expansion will continue, and as it does galaxies and all matter will drift further apart. New stars will stop being formed and old stars will die. Black holes will evaporate. Matter will become so spread out that the universe will be mostly empty. According to this theory the universe will not really have an end. It will last for infinity, but it will fade away becoming cold and dark in about 10¹⁰⁰ years.

An alternative theory more recently proposed is called the "big crunch". This theory is based on some recent evidence that dark energy may not be constant over time and may be weakening. If so the expansion of the universe would slow and if dark energy weakened enough at some point expansion might stop. If expansion stopped gravity could pull everything inward, causing the universe to contract and collapse back into a single point, effectively resulting in the big bang in reverse. Contraction back into a single point particle might trigger a new big bang. This theory raises the intriguing possibility of a cyclic or oscillating universe in which endless cycles of expansion and contraction occur. A big crunch might happen in 20 billion years.

A third theory is called the "big rip." This theory postulates that rather than weakening dark energy may strengthen and becomes so strong that it overcomes gravity, leading to a violent expansion of the universe which would rip all matter apart disrupting galaxies, and tearing stars, planets, and perhaps even atoms into pieces. Probably needless to say when all this might happen is speculative but according to the big rip theory, the universe could end in approximately 22 billion years.

References

Donald R. Prothero (Author), Carl Buell (Illustrator). Evolution: What the Fossils Say and Why It Matters. 2017.

Richard Dawkins, The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design. 1986.

Mark Whittle. Cosmology: The History and Nature of Our Universe, The Great Courses, 2008, www.thegreatcourses.com

"Why Didn't The Dinosaurs Ever Re-Emerge?" YouTube