The quantum realm, the cosmological realm, and the multiverse, in 69 minutes | Hakeem Oluseyi

Introduction to the Nine Realms and the Quantum Realm

• The discussion begins with an introduction to the topic of the nine realms of the universe, focusing on three specific realms: the quantum realm, the cosmological realm, and the multiverse realm, with the first chapter exploring the strange world of quantum physics 10s.
• Quantum physics is described as weird because it breaks every intuition of the physics that is normally experienced in the regular world, with rules and certainty breaking down, and things becoming probabilistic, allowing objects to pass through walls and come into and out of existence 42s.
• Quantum particles are not things like the world around us, but rather the fundamental constituents of matter that come together to build up the world, with examples including protons and neutrons being made up of quarks, light being made up of photons, and electrons being a fundamental quantum particle 1m6s.
• The traditional artist's description of an atom, with electrons orbiting a nucleus like planets around the sun, is not accurate, as electrons are not falling around the nucleus and are not tiny spheres, but rather have a particular property that makes every electron identical 2m6s.

Quantum Physics and the Nature of Quantum Particles

• The concept of quantum fields is introduced, which permeate all of space and time, and particles are described as energy injected into these fields, with electrons being excitations in the quantum electron field, and the universe being a symphony of musical notes in quantum fields 4m10s.
• The analogy of musical notes is used to describe quantum particles, with the idea that just as a musical instrument can vibrate and create a note, quantum fields can fluctuate and create particles, and even when not plucked, the string is still vibrating, just like quantum fields are always fluctuating, giving rise to virtual particles 5m40s.
• The concept of virtual particles is explained, which are tiny vibrations in the quantum fields that can exist even when no energy is inserted, and the idea that quantum fields do not have a source like other fields, such as magnetic or electric fields, is discussed 6m50s.
• Quantum fields are entities that exist throughout all space and have no source, and they were confirmed to be real with the discovery of the Higgs field in 2012, which imbues mass to quantum particles 10s.
• The term "field" in physics refers to something that has a value everywhere, such as an electric field, which can be characterized by its strength and direction, and exerts a force on electric charges 42s.
• Potential energy is associated with the location of an object in a field, whereas kinetic energy is related to the object's motion, and quantum fields appear to be real physical entities that are everywhere 1m14s.
• Quantum particles can be modeled in different ways, such as waves or particles, depending on the calculation being made, and each model can provide the right answer using the physics of quantum mechanics 2m6s.

Quantum Fields and Their Properties

• The wave function is a mathematical description of a quantum entity that lives in a mathematical vector space, and it provides the right answers to measurements made with high precision, despite lacking intuitive basis for humans 3m20s.
• Quantum mechanics is based on complex mathematics, including vector math, which can be difficult to understand and translate to others, but is a valuable tool for making precise calculations and predictions 4m30s.
• The wave function is a vector that uses physical observables, such as locations, momenta, and energies, as its axes, rather than the traditional x and y axes, and this concept is fundamental to describing quantum entities 5m40s.
• When a measurement is made in a quantum system, the state of the system changes from a combination of possible states to one specific state, which is a fundamental concept in quantum mechanics, and this change is not accurately represented by a simple analogy of a vector rotating in space 10s.
• The wave function of a quantum system can be thought of as a vector in a high-dimensional space, where each axis represents a possible location or state, and when a measurement is made, the vector "collapses" to one of these axes, with the probability of each outcome determined by the initial state of the system 42s.
• In physics, models of systems such as a block of iron or a pendulum can be used to understand the behavior of the system, but these models do not always reflect the actual location or state of the system, as the atoms in the iron or the pendulum are in constant motion and only spend a small amount of time in their equilibrium positions 2m6s.
• The concept of a quantum state vector or wave function is still not fully understood, and it is unclear whether the vector is constantly moving around in its space or if it is just a mathematical representation of the system, and this uncertainty is due in part to the fact that the vectors live in a Hilbert vector space, which has no physical manifestation in our regular world 4m30s.
• The Schrödinger equation and the wave function are used to describe the behavior of quantum systems, and they represent a fundamental shift in our understanding of the physical world, as they describe how physical systems change over time based on energy and force, but the nature of the wave function itself remains a mystery 6m15s.

The Relationship Between Spacetime and Quantum Fields

• The concept of spacetime is a combination of every aspect of the universe, expressed by a mathematical equation known as a metric, which includes distance, time, and the curvature of spacetime, as well as the change in spacetime coordinates with time 10s.
• Quantum fields are thought to exist in spacetime, but it is unclear whether spacetime emerges out of quantum fields or if spacetime is a fundamental aspect of the universe that allows quantum fields to exist, with some arguing that spacetime is emergent and others arguing that it is fundamental 42s.
• The relationship between spacetime and quantum fields is complex, with physicists attempting to quantize spacetime and develop a quantum theory for it, but so far, they have been unable to do so, especially in high-energy regimes 1m6s.
• Quantum fields can be thought of as existing in the same space at the same time, similar to a mesh or a swimming pool filled with different colors of jell-o, where some fields interact with each other and others do not, but they all coexist throughout the space 1m30s.
• The concept of reality is multi-layered, with spacetime and quantum fields appearing to be fundamental, and energy being the driving force behind change, which requires the existence of space and time 2m6s.
• The origin of spacetime and quantum fields is unclear, with it being possible that they came into existence simultaneously, similar to the relationship between supermassive black holes and galaxies, where it is unclear which one came first 2m42s.

Quantum Entanglement and the Nature of Correlation

• Quantum entanglement is a phenomenon that occurs in quantum mechanics, where two or more entities behave as if they are a single entity, following certain rules and existing in complementary states 4m10s.
• The concept of quantum entanglement is a topic of debate among physicists, with some considering it a correlation and others believing it to be a more complex phenomenon, and the speaker takes a neutral stance, acknowledging the strangeness of the correlation that can be measured across vast distances 10s.
• The analogy of twins separated by light years, with each twin having a set of scribes recording their actions, is used to illustrate the concept of quantum entanglement, where the correlation between the twins' actions holds even when they are separated by vast distances, but this concept is complicated by the definition of "now" and the relativity of simultaneous events 42s.
• The definition of "now" is based on a set of simultaneous events, but according to Albert Einstein, events that are simultaneous to one observer may not be simultaneous to another observer if they are moving differently or are in a different state of gravitational energy, and this effect compounds over distance, leading to the Andromeda paradox 2m6s.
• The Andromeda paradox shows that observation breaks down at great distances, and while quantum entanglement has been measured across relatively short distances, such as from the surface of Earth to a satellite, it has not been measured across the vast distances of the universe, leaving the underlying reality unclear 2m6s.

Understanding the Cosmological Realm and Astronomical Scales

• The quantum realm is difficult to understand because it is unlike anything in our everyday experience, and trying to relate it to familiar concepts can lead to confusion, requiring a new and distinct understanding of reality based on complex math 4m30s.
• The cosmological realm, on the other hand, is the realm of dynamic spacetime, characterized by spacetime curvature and motion, including stretching and waving, and is a distinct area of study that involves understanding the dynamics of the universe on a large scale 6m40s.
• The solar radiance is a significant number, approximately 10 to the 30s per second, which is essential for a solar physicist to know, and understanding such numbers helps in grasping reality at the astronomical scale 10s.
• The moon is 1% the Earth's mass and one quarter the Earth's diameter, while Mars is 10% the Earth's mass and half the Earth's diameter, and the sun is a hundred times the Earth's diameter, which are crucial numbers to comprehend the astronomical scale 42s.
• One night, while leaving the observatory, the realization that the moon is one quarter the Earth's size and approximately 60 Earth radii away helped in visualizing the sky in 3D, and the presence of Jupiter, which is 10 times bigger than Earth, further enhanced this understanding 2m6s.
• The observation of Jupiter in the night sky, knowing its distance from Earth, revealed its massive size, and this experience highlighted the importance of understanding distances in the astronomical scale 2m6s.
• A friend, who was not an academic but had curiosity, pointed out a fuzzy thing in the sky, which turned out to be the Andromeda galaxy, visible to the naked eye in a dark enough place, and this discovery led to a deeper understanding of the cosmological realm 4m0s.
• The Andromeda galaxy, which is 2.5 million light-years away, appears as a bulge in the night sky, approximately 3° across, and its enormous size, despite being at such a vast distance, is a testament to the immense scale of the cosmological realm 6m0s.
• The experience of seeing the Andromeda galaxy with the naked eye and comprehending its enormous size had a profound impact, as it helped in feeling the vastness of the cosmological realm and the incredible scale of the universe 8m0s.

The Concept of Spacetime and Its Mathematical Foundations

• The size of an atom is approximately 10 micrometers across, with its nucleus being even smaller, and the galaxy is enormous, with a size of 10 to the 15th power in smallness and 10 to the 21st power in bigness, making it challenging to comprehend the vast range of sizes in the universe 10s.
• The concept of spacetime, which describes the relationship between space and time, is often attributed to Albert Einstein, but it originated with Minowski, and it suggests that space and time are interconnected in a more fundamental way than people experience in everyday life 42s.
• The relationship between space and time is intuitive, as people can describe distances in terms of either space or time, such as saying a location is a certain distance away or a certain amount of time away, and this relationship is also used with light, where the distance to the sun can be described in miles or light seconds 1m6s.
• When describing a line in a 2D space using the Pythagorean theorem, the equation is a^2 + b^2 = c^2, but when a time coordinate is added, the equation changes to a^2 - b^2 = c^2, indicating that space and time have a complex relationship where they "tug at each other" 2m6s.
• The consequence of this relationship is that everything in the universe is moving through spacetime at the speed of light, but the speed through space and time can vary, and since nothing can move at the speed of light, everything is always moving through time, resulting in different speeds through time for different objects 3m15s.
• The speed of an object through spacetime is constant, but the speed through space and time can change, and gravity can cause this change by turning speed through time into speed through space, which is why objects accelerate near gravitational bodies 5m30s.
• The concept of spacetime and the relationship between space and time can be difficult to understand, as it challenges human intuition, which perceives time as passing at a regular rate, but in reality, time can be affected by motion and gravity, causing time to pass differently for different objects 7m20s.

Relativity and the Nature of Time and Motion

• The concept of relativity can be brain-breaking, but it also solves mysteries, such as why the speed of light is considered a speed limit in the universe, because when an object moves rapidly through space, it must move more slowly through time, and the maximum speed it can borrow from is the speed of light 10s.
• According to the mathematics of relativity, if an object is at rest relative to an observer, they are moving through time at the speed of light, but if the object starts moving rapidly through space, it must subtract from its speed through time, and if it brings its speed through space up to the speed of light, it will have no speed left to move through time 42s.
• The phenomenon of time dilation and length contraction occurs when objects move at high speeds, causing time to appear to pass more slowly and distances to appear shorter, but this does not apply to light because light does not have a rest frame, making it nonsensical to say that light does not experience space or time 2m6s.

The Curvature and Expansion of the Universe

• The universe can be considered both curved and flat, depending on the scale at which it is observed, with local areas such as those near planets, stars, and galaxies exhibiting curvature, while the universe as a whole appears smooth and flat when viewed from a larger scale 5m30s.
• The curvature of spacetime is affected by the presence of mass and energy, with dense objects such as black holes creating significant curvature, while less dense areas have less curvature, and the universe can be thought of as having a complex, locally curved structure that appears smooth when viewed from a distance 7m10s.
• The universe has a large-scale, curvatureless spacetime and local, highly curved spacetime with various sizes and intensities based on mass, density, energy, and pressure, and this overall spacetime behavior takes place in an expanding universe 10s.
• The expansion of spacetime and its curvature must be taken into account when discussing the universe at the cosmological scale, which breaks our intuition and is difficult to understand because space is flowing, waving, and stretching in ways that have no analogy in our everyday existence 42s.
• To create an analogy for understanding space-time expansion, a sphere with lines of latitude and longitude can be used, where galaxies are placed at the intersections, and when the sphere expands, the line segments between the intersections get longer, but the galaxies remain at those intersections, illustrating that space has expanded but the galaxies haven't moved 2m6s.
• The expansion of the universe means that most of the motion of galaxies observed is due to the expansion of the grid itself, rather than their intrinsic motion, and this concept is referred to as expansion drag, where the faster the expansion, the more it slows down the intrinsic motion of galaxies 2m6s.
• An example of expansion drag is the movement of tadpoles in a river, where the water near the edge interacts with the bank and moves more slowly than the water at the center, and similarly, galaxies are carried away by the expansion of spacetime, with their motion characterized by the spacetime motion rather than their intrinsic motion 2m6s.
• The expansion of spacetime can result in objects moving away from each other faster than the speed of light, which breaks our intuition that nothing can move through spacetime faster than the speed of light, and this phenomenon occurs when observing objects at great distances 2m6s.
• The universe's expansion can make things move away from each other at varying speeds, but locally, nothing can move faster than the speed of light, and the concept of a universal present is broken in multiple ways due to the effects of gravity and speed on time 10s.

The Expansion of Spacetime and Its Implications

• The rate at which time passes for every entity in the universe depends on its energy situation, with gravity slowing down time, and the faster an object moves relative to another, the slower its clock goes, resulting in varying clock speeds across the universe 42s.
• The gravitational landscape of the universe varies, with vast voids between galaxies and the cosmic web, a filamentary structure where dark matter and matter come together, affecting the passage of time, making it difficult to define a universal now 1m14s.
• The evolution of the universe, including the formation of elements and the emergence of complexity, can serve as a convenient clock, as well as the cosmic microwave background radiation, which averages out variations in the universe's expansion 2m6s.
• The cosmic microwave background radiation is strongly coupled to spacetime, and as spacetime expands, the radiation's wavelength is stretched, providing a uniform clock that can be used to define a time slice for the universe 2m50s.
• The cosmological principle, which states that the universe is homogeneous and isotropic, allows cosmologists to talk about the universe at any given time slice, despite the lack of a universal now, and this principle is based on the idea that the universe is made of the same stuff everywhere, with no special locations or orientations 4m10s.

Cosmological Principles and the Cosmic Microwave Background

• The homogeneity of the universe is an average property, and while every point in space is unique, the universe can be described as being made of the same stuff over large enough averages, and the pattern of emergence, including the formation of stars, galaxies, and structures, can be used to define a time slice 5m14s.
• The cosmic microwave background radiation provides an average clock, and when modeling the universe, cosmologists make assumptions based on the cosmological principle and the properties of the cosmic microwave background radiation 6m30s.
• The universe is assumed to be a uniform gas, allowing for the creation of equations for conservation of energy and acceleration, which enable calculations about the past and future of the universe 10s.

Observational Limits and the Speed of Light

• Looking at objects in the universe means looking into the past because light takes time to travel, and the universe is so big that light takes 2.5 million years to reach the nearest galaxy 42s.
• It is possible to look at the universe as it existed at different points in the past by observing objects at varying distances away, but it is not possible to look at oneself or objects on Earth in the past because that would require moving faster than the speed of light 1m30s.
• The speed of light acts as a limitation on what can be observed, and understanding this limitation is essential for comprehending the universe and how it is observed 3m20s.
• The expanding universe has multiple horizons that define how far away objects can be seen, and the rate of expansion varies with distance, meaning that everybody in the universe sees the same thing and is at rest relative to themselves 5m10s.

Horizons in the Expanding Universe

• As an observer looks out into the universe, the limit of their observations forms a sphere that grows with time as light from more distant objects reaches them, but the expansion of the universe means that objects at greater distances are moving away faster 6m40s.
• The expansion rate of the universe will eventually reach the speed of light, defining the Hubble sphere, and even if something is moving away from us at the speed of light and emits light in our direction, we will be able to see that light eventually 10s.
• There is a point beyond the Hubble sphere known as the cosmic event horizon, which is the boundary beyond which objects that emit light today will never be seen by us because their light will be pulled back by the rapid expansion of space-time 42s.
• The cosmic event horizon works like a treadmill that is moving away from us, and if the treadmill's speed is faster than our ability to move forward, we will not make progress and will be carried away, similarly, if space-time is expanding away from us too fast, light emitted today will never reach us 1m6s.
• The particle horizon is defined as the distance from us to objects whose light is arriving at us today, and those objects were closer to us in the distant past, but the expansion of space-time has taken them beyond our cosmic event horizon 2m6s.
• The cosmic event horizon is around 16 billion light-years away, the Hubble sphere is around 14 billion light-years away, and the particle horizon is around 46 billion light-years away, allowing us to see light from objects that are now 46 billion light-years away from us 3m10s.

The Age and Future of the Universe

• The universe is still in its infancy, and if we compare its age to a human being that is 100 years old, the universe would be equivalent to a couple of days old, and it will exist for a very long time, with stars in it, for example 4m20s.
• In the distant future, the expansion of the universe will take all galaxies, except for those gravitationally bound to us, outside of our cosmic event horizon, and we will not be able to see them, but we can still make measurements using pulsars to detect gravitational waves and do cosmology 6m0s.
• The cosmic microwave background radiation can still be measured, allowing for cosmology, but observing galaxies is no longer possible 10s.

The Concept of a Universe and Multiverse

• A universe is defined as a volume that is separate from the rest of existence, with its own set of physical constants, such as the gravitational constant, Planck's constant, and the Boltzmann constant, which characterize the physics within that universe 1m5s.
• Every universe has its own set of constants that define how physics takes place within it, and it is a volume cut off from the rest of other such volumes 2m6s.
• The many worlds interpretation of quantum mechanics is trying to solve the measurement problem, which questions what happens when a quantum measurement is made and the state of the system changes from a combination of possible states to only one state 3m20s.
• The Copenhagen interpretation suggests that the measurement causes the system to collapse into one state, while the many worlds interpretation proposes that every state actually exists and corresponds to its own universe, resulting in multiple universes with different copies of everything 4m40s.
• The many worlds interpretation seems counterintuitive, appears to go against conservation of energy, and raises questions about what constitutes a measurement, such as whether an interaction between particles, like the Compton scattering experiment, qualifies as a measurement 6m10s.

Quantum Interpretations and the Many-Worlds Theory

• The Compton scattering experiment demonstrates the particle property of light, showing that it exchanges momentum like particles, and in this interaction, both the electron and light behave as particles, despite being described as waves before the interaction 7m30s.
• The interaction between particles in a superposition state can create a new universe where each particle goes from a superposition state into a definite state, with many galaxy clusters containing hot X-ray emitting gas and galaxies with numerous electrons being bombarded by X-rays, potentially spinning off a universe with every interaction 10s.
• The concept of probability in the pre-measurement state, where the wave function has probabilities built within it, is questioned, as every measurement has a probability of one in some universe, leading to uncertainty about what these probabilities mean 42s.
• Some people think that the idea of the wave function collapsing is unphysical, and instead, they consider the many-worlds interpretation, where every measurement creates a new universe, which is one of the possible explanations, and it is acknowledged that there may be something missing in the current understanding 1m6s.
• The possibility of accessing other universes is considered, and if the many-worlds interpretation is found to be true, it could lead to new insights into nature, similar to how new technologies have created new economies, and researchers may find ways to interact between universes 2m6s.

The Multiverse in Cosmology and Inflation Theory

• The current understanding is that if the multiverse idea is true, universes may be forever isolated from each other, but if it is found to be true, researchers will likely explore ways to interact between universes, and some ideas, such as gravity leaking into parallel universes, have already been proposed and experimented with 3m42s.
• The exploration of the multiverse idea and its implications will continue, and it is expected that new discoveries and ideas will emerge, potentially leading to new areas of exploration and understanding, similar to how new mathematical concepts have created rich areas of exploration 5m6s.
• The concept of the multiverse is invoked in cosmology through a mechanism that solves the flatness problem and the horizon problem, which are issues that researchers noticed in the late 20th century, and the solution to these problems is called inflation 10s.
• Inflation is the notion that the universe doubled in size repeatedly in the very early moments of its existence, over a timescale of around 10 to the minus some double digit number of seconds, resulting in regions that appear to be outside of each other's cosmic event horizon but have the same temperature 42s.
• The horizon problem refers to the fact that regions of the universe that appear to be outside of each other's horizons today were once within each other's horizons due to the rapid expansion of the universe, which is explained by the concept of future light cones and the speed of light 2m6s.
• The inflationary event that allows regions to be inside each other's light cones is what led to the idea of multiverses being real in the cosmological realm, and the types of universes that exist in this multiverse are fundamentally different from those in the many worlds interpretation 4m10s.
• The multiverse in the cosmological realm can be thought of as a loaf of bread with air pockets, where each air pocket has its own history and is separate from the others, but in this case, the "bread" is an expanding universe that creates separate universes or "bubbles" that are forever separate from each other 6m20s.

Evidence and Implications of the Multiverse

• The process of eternal inflation generates multiple spacetimes, resulting in the creation of multiple universes that are separate from each other, and if this concept is true, then there are indeed multiple spacetimes 8m30s.
• The concept of the multiverse suggests that every universe has its own spacetime with its own history that evolves separately from a bigger spacetime, and the properties in each bubble universe will be slightly different, each having its own history and spacetime curvature 10s.
• Humans have made significant progress in understanding the universe, from breaking rocks to create tools to developing quantum technology and performing experiments to understand the evolving universe, including making measurements of the cosmic microwave background radiation 2m6s.
• The concept of the multiverse predicts the existence of super horizon fluctuations, and experimental verification of this phenomenon has been achieved through careful measurements, including the use of the Plunk satellite, which provides strongly circumstantial evidence for the multiverse 4m42s.
• While some physicists consider the evidence conclusive, others, including the speaker, are not convinced and require further understanding, highlighting the need for continued research and experimentation to fully comprehend the multiverse 6m15s.

The Role of Equations and Theoretical Predictions in Physics

• The history of physics has shown that equations can lead to new discoveries, such as Maxwell discovering that light is an electromagnetic wave, but also often produce results that are not true, requiring physicists to distinguish between reality and mathematical junk 8m30s.
• The development of equations, such as those for general relativity, has predicted phenomena like black holes and gravitational waves, which may take decades or centuries to measure, emphasizing the importance of taking predictions seriously and continuing to fund research into fundamental questions 10m50s.
• Research into avant-garde ideas and the edges of human understanding is essential for discovery and has led to new engineering and technologies, and it is up to humans to listen to the universe and ask questions, using observations and calculations to understand the universe's answers 13m10s.