Transcription
Essentially, what happened before the Big Bang? Right? You have to be careful with the language. So, if you define the Big Bang really carefully as the time when the universe was very hot and very dense, and as I said, you you can't argue with that because we can see it as we can look out into the sky, our best theory of how the universe got into that state is that there was a time before that, and it's called inflation.
What existed before the Big Bang? This question has always been a challenge for scientists, but now it seems they found the answer to it. But it has left scientists shocked, as Brian Cox revealed that something terrifying existed before the Big Bang. So, the idea is, the universe was, it was there in a sense, cold and empty, and expanded extremely fast. And that expansion slowed down and stopped. And the the energy that was driving that expansion got dumped into space, heated it up, made all the particles out of which we're made. That's what we call the Big Bang.
So, what existed before the Big Bang? Why has it left scientists terrified? Let's find out. And that theory has a kind of an extension called Eternal Inflation, which is that the inflation essentially goes on forever, and it just stops in little patches. So, you imagine this this str the fabric of the universe, space, time, stretch, stretch, stretch, stretch, and then it slows down and stops in little patches. And each one of those patches is basically a Big Bang and a universe of which ours is one. So, you end up with this sort of picture of an infinite fractal universe of of basically an infinite number of Big Bangs. And that's called the inflationary Multiverse.
In the vast cosmos, the idea of absolute nothingness seems theoretical rather than real. Even if all energy were removed from the universe, it wouldn't be truly empty. Currently, the universe is full of matter, radiation, antimatter, neutrinos, dark matter, and dark energy. Even without energy, the universe still creates new forms of energy. This phenomenon confuses us. It seems the universe doesn't understand our concept of complete emptiness. If we removed all energy, leaving a void, one might expect the universe to reach absolute zero with no particles. Yes, that's not the case. Even in an empty universe, its expansion would still produce radiation. This extends far into the future, or even back to the time before the hot Big Bang. The universe, it appears, never truly becomes void.
Given all of this, is it plausible that the universe originated from nothing? We can be certain that something always persists. Even if particles, antiparticles, photons, and quanta are removed, empty space remains. If we move away from any mass or energy sources, clear the space of external electric, magnetic, and gravitational fields, and prevent photons or gravitational waves from entering, a kind of physical emptiness still exists in this space. Quantum fields endure, and the fundamental constants and laws of physics endure. There is an inherent finite, positive, and non-zero value of zero-point energy in that space. This represents the closest approximation to nothing within our universe. While you might envision an even more nothing-like state, it lacks physical reality. No experiment can replicate such a condition. By adhering to scientific principles, we acknowledge that something always exists because true nothingness cannot coexist in our universe. Yet, the question of why remains unanswered by science.
Presently, our universe appears far from it's teeming with stars, gas, dust, galaxies, quasars, cosmic rays, and radiation from both starlight and the remnants of the Big Bang. With improved observational tools, we could potentially detect additional signals that we anticipate. A present this encompasses gravitational waves generated by any mass moving through a changing gravitational field, the mysterious signals from the constituents of dark matter, and a broader perspective on black holes, but both active and dormant, aside from those emitting the most radiation.
Everything we observe occurs in a universe that isn't static but is continuously changing. From a physical standpoint, it's intriguing to comprehend the evolution of our universe on a grand scale. The fabric of our universe, known as spacetime, is expanding. This implies that if you position two points far apart in your spacetime, the proper distance between those two points, the time it takes for light to traverse between them, and the wavelength of the light traveling from one point to the other, all increase over time. The universe isn't just getting bigger; it's also getting colder. As it expands, as light stretches to longer wavelengths, it moves towards lower energies and cooler temperatures. The universe was hotter in the past and will become even colder in the future. During this process, objects with mass or energy in the universe attract each other, forming clusters and creating a vast cosmic network.
If you were to somehow remove everything, all matter or radiation, every bit of energy, what would remain? Essentially, you'd have empty space itself, still expanding, still governed by the laws of physics, and still influenced by quantum fields that fill the universe. This is the closest physical approximation to true nothingness, yet it still adheres to specific physical principles. To a physicist, in this reality, removing anything else would create an unrealistic state that no longer reflects the cosmos we inhabit. This suggests that dark energy, as we currently understand it, would still be present in this hypothetical universe devoid of matter. In essence, if every quantum field in the universe was set to its lowest energy state, we would arrive at the zero-point energy of space, where no additional energy could be extracted for mechanical work. In a universe containing dark energy, a cosmological constant, or the zero-point energy of quantum fields, it's plausible that the zero-point energy wouldn't be truly zero.
As the universe continues to expand and cool, there will come a time in the distant future when radiation becomes the dominant component, surpassing other forms of matter and radiation, leaving dark energy as the primary influence. However, there's also a period in the universe's history, not in the future, but in the distant past, when something else besides matter and radiation held dominance. During cosmic inflation, prior to the hot Big Bang, our universe underwent extremely rapid and constant expansion. Instead of being dominated by matter and radiation, the cosmos was controlled by the field energy of inflation, akin to today's dark energy, but much more potent and expanding at a significantly faster pace.
If eternal inflation is accurate, but time remains finite, where might the universe have originated? There must have been a beginning, correct? To address this question thoroughly, let's unravel three commonly conflated concepts and discuss each individually: the hot Big Bang in relation to our universe, the theory of cosmic or cosmological inflation and its role in proceeding and preparing for the Big Bang, and the issue of an ultimate beginning or origin for our universe and why both inflation and the original concept of the Big Bang might not offer a satisfactory solution to this question.
In the early 20th century, a significant synthesis took place when four key pieces of information came together. A breakthrough by Alexander Friedman in Einstein's general relativity, showing that a universe filled uniformly with any form of matter and energy cannot remain static but must either expand or contract. The rate of this expansion or contraction depends on the overall energy density of space. Henrietta Leavitt's observational work established a connection between the period of brightness and dimness of variable stars and their inherent brightness, known as the period-luminosity relation. Observations by Vesto Slipher, measuring the shift in light (either redshifted or blueshifted) from our solar system's perspective in spiral and elliptical nebulae, which were later identified as galaxies, indicated that these galaxies were moving away from us at incredibly high speeds. Edwin Hubble, alongside Milton Humason, identified similar types of variable stars to those identified by Henrietta Leavitt in spiral and elliptical nebulae. This enabled them to gauge the distances to these galaxies and confirmed they were beyond our own. These findings, combined with other data, led to the concept of the universe expanding.
If the universe expands, it suggests that over time, space itself stretches, causing the matter within it to become less dense. As space expands, radiation like light waves not only becomes less concentrated but also stretches, leading to the universe cooling. If we rewind the clock, the opposite would occur to matter and radiation in the universe. In earlier times, when the universe was younger, it was denser and hotter. If we rewind further, all matter and radiation would have been squeezed into a smaller space, increasing the density of the universe. The light, which stretched due to cosmic expansion, when we reverse time, would have had a shorter wavelength, resulting in hotter temperatures. If you envision going back as far as physics permits, you'd reach a singular state where all matter and radiation existed within a single point of infinite density and temperature.
The initial idea of the Big Bang Theory resulted in the formation of five key expectations regarding the early universe's hot and dense conditions. These forecasts became the foundation of the Big Bang Theory:
1. The universe ought to demonstrate expansion, as indicated by a distinct redshift-distance relationship among extragalactic objects.
2. Initially, the universe should have been relatively uniform, with structures like stars, galaxies, and clusters of galaxies gradually forming and evolving over time.
3. In the past, the universe was hotter, preventing the formation of stable neutral atoms. This prediction led to the discovery of the cosmic microwave background, which is observable today.
4. In the initial stages of the universe, when it was extremely hot, atomic nuclei couldn't form stably. This led to the creation of light elements such as hydrogen, helium, lithium, and their isotopes.
5. The universe was so hot that neutrinos played a significant role. Recently, this prediction was confirmed, indicating that cosmic neutrinos should have detectable effects on both the large-scale structure and the leftover radiation from the Big Bang.
With strong observational evidence supporting these predictions, the Big Bang Theory has remained uncontested as the primary explanation for the early universe since the mid-1960s, coinciding with the discovery of the cosmic microwave background.
As evidence supporting the hot Big Bang Theory grew in the 1960s and 1970s, certain challenges surfaced that the Big Bang alone couldn't resolve. Several observations contradicted the concept of the universe originating from a singular state of incredibly high temperatures and densities. Three of these challenges stand out:
Firstly, there's the Horizon Problem. When we observe different directions, the universe seems to possess uniform temperatures and density throughout. However, since the onset of the hot Big Bang, these regions have never had the opportunity to communicate, exchange information, or achieve thermal equilibrium with one another. This raises the question: how did they evolve to exhibit uniform temperature and conditions across the board?
Next, let's consider the issue of Flatness. In a universe that's expanding, there's a continual tug-of-war between the initial expansion pushing things apart and gravitational forces attempting to pull everything back together. Remarkably, in our universe, these opposing forces appear to be perfectly balanced, resulting in a spatially flat universe. The question arises: why did our universe come into existence with these particular characteristics?
Moving on, we encounter the Monopole or Ancient Relic Dilemma. If the universe underwent extreme temperatures and energy conditions in its early stages, why do we not observe any exotic remnants, such as right-handed neutrinos and magnetic monopoles? Theoretically, these particles should be detectable and still present today.
Rather than just taking these conditions as how the universe came to be, which contradicts the scientific method, scientists are looking for a mechanism that would establish and arrange these initial conditions. Alan Guth introduced a solution to these cosmological mysteries in 1980 with a groundbreaking paper. He suggested that an early phase of rapid and continuous expansion, where the universe's energy wasn't spread among matter and radiation particles but was an intrinsic part of space itself via a field or another mechanism, could solve all three issues.
Regarding the Horizon Problem, the uniformity of temperature and density throughout the universe is attributed to the past interconnectedness of everything. This connection, stretched during the early expansion phase, is called inflation, resulting in the current conditions observed.
For the Flatness Problem, inflation expanded the universe so much that regardless of its initial state, the visible part now appears uniformly flat.
As for the Monopole Problem, the absence of ancient remnants is explained by inflation preventing the universe from reaching excessively high energies or temperatures. The maximum temperature reached after inflation avoids the formation of these remnants.
Inflation not only explains these phenomena but also presents a compelling alternative to the standard hot Big Bang model. Additionally, a further issue was addressed: to demonstrate how a uniform, anisotropic early universe could be reinstated after inflation, it became evident that inflation could act as a quantum mechanism for seeding the universe with initial imperfections or the origins of cosmic structure, ultimately leading to the intricate formations we see today.
In the 1980s, inflation theory made precise and testable forecasts about the beginnings of cosmic structure that should be detectable in both the cosmic microwave background and the large-scale layout of the universe. These forecasts, crafted decades ago, have been validated by observations spanning from the 1990s to the present day, encompassing an almost, though not entirely, scale-invariant spectrum of imperfections, variations in density and temperature, density irregularities that are entirely adiabatic and not at all isocurvature, in essence, fluctuations on scales larger than what a signal traveling at the speed of light in an expanding universe could generate, and a maximum temperature limit for the universe during the hot Big Bang, notably smaller than the Planck scale.
Because inflation involves a rapid expansion of space rather than culminating in a singularity like the original model for the Big Bang, it presents an alternative depiction of the beginning. Instead of time and space gradually emerging from a single state, inflation proposes a rapid expansion leading to the Big Bang. This raises a fundamental question about the actual beginning of the universe, if such a notion even makes sense within the framework of the hot Big Bang. Without inflation, we could trace back and reach a singular state where the universe's size approaches zero in a finite time. However, inflation complicates this scenario. Its exponential growth makes it challenging to trace back to a singularity size, since reaching a state where the universe had zero size would require an infinite amount of time due to the exponential nature of inflation. Adding to the complexity, the observable evidence for inflation, such as quantum fluctuations leaving imprints on our visible universe, corresponds to just the final 10 to the power of 32 seconds before inflation leads to the hot Big Bang. If we were hoping to delay the start of an earlier grand event, inflation ruins those hopes. There's nothing observable that gives us clues about what, if anything, caused inflation.
A fascinating aspect of inflation is called Eternal Inflation. When exploring how inflation works, almost any model that effectively addresses the issues with the original Big Bang and creates the necessary quantum effects to initiate the universe with imperfections will result in a scenario where, while inflation ends in certain areas like our own, there will be countless more surrounding regions where inflation continues, creating more space that keeps expanding. Essentially, once inflation starts, it wipes out any information about what existed before, and the inflationary state will persist indefinitely into the future. At times, quantum fluctuations, akin to those shaping the universe's structure, cause certain areas where inflation ceases, resulting in a hot Big Bang. However, these regions are far fewer compared to those where inflation persists indefinitely. Notably, no two separate regions with Big Bangs will ever overlap because the expanding universe drives them apart.
Despite its appeal, Eternal Inflation has limitations. It's eternal only into the future, not into the past. In fact, it's been demonstrated that inflationary spacetime doesn't extend into the past infinitely and must have originated from a prior non-inflationary and possibly singular state. The issue of past time-like incompleteness can't be avoided by considering alternatives like bouncing cosmologies or cyclic cosmologies, as they face similar challenges. However, this doesn't necessarily imply that the universe originated from a singularity. While it could have, it's not a strict necessity. For example, one can envision a spacetime resembling the past where inflation takes place by modeling the universe's expansion rate through a scale factor composed of a growing exponential plus a constant, rather than just a pure growing exponential.
In essence, the hot Big Bang, while our most accurate model of the early universe, wasn't its absolute genesis. There's a limit on how far back we can extrapolate the temperature and density of a matter and radiation-filled universe. Prior to the hot Big Bang, there existed a period of cosmic inflation, which initiated and led to the hot Big Bang. During inflation, space was saturated with energy, devoid of matter and radiation, and expanded exponentially. However, inflation couldn't have persisted indefinitely and must have emerged from some pre-existing non-inflationary state. Unfortunately, our knowledge of this earlier state is limited, aside from knowing many things it couldn't have been.
We don't live in a universe where matter drifts in empty space. We live in a universe filled with energy fields that interact to form everything we see. When considering the vastness of emptiness, the endless void, and mortality, it's striking how the idea of nothingness can provoke such fear. Did William Shatner, at 90, go on a space journey expecting to find the universe's mysteries, only to realize there was no mystery or grandeur? He encountered only death, witnessing a cold, dark black void unlike any darkness on Earth. It was overwhelming and all-encompassing. Yet, in another paradox of nothingness, Shatner wasn't truly observing a void; rather, he was looking at a vacuum where a lot was happening that he couldn't see.
Quantum field theory is one of the most accurate theories in physics, known for predicting the outcomes of many experiments. According to this theory, the universe is not made of matter floating in empty space but of energy fields that permeate space and interact, creating everything we observe, including ourselves. Some physicists describe these fields as fluid-like, similar to water in a pool. While others compare them to a room filled with varying levels of energy, like a field of distributed heat. These fields are constantly moving due to quantum fluctuations, brief changes in energy, similar to ripples in a wave caused by external forces exciting the particles within the field. For example, an electromagnet can cause changes in an electromagnetic field. Even in their lowest state, known as the vacuum state, fields remain active. Pairs of positive and negative particles continuously borrow energy from the vacuum, briefly appear, and then disappear, returning the energy. These temporary entities are called virtual particles. When the field is excited or at a higher energy level, it has ripples or waves that produce elementary particles that persist and interact with each other, forming the world we know.
The type of particles created depends on the field. Different matter particles are associated with specific types of fermions, such as electrons, up quarks, down quarks, and neutrinos, which are fundamental components of all atoms. These fermions interact through three types of field: electromagnetism, involving photons; the strong nuclear force, involving gluons; and the weak nuclear force, involving W and Z bosons. According to Cambridge theoretical physicist David Tong, without these force fields, matter particles would drift aimlessly in the universe without interactions or interesting behaviors. Then there's the Higgs field, which Tong compares to molasses spread throughout the universe. The Higgs field gives mass to other particles, stopping them from moving at the speed of light. Tong notes that this comparison is not perfect because it suggests friction, while in reality, different particles interact with the Higgs field in various ways.
All fields, including matter and force fields, exist everywhere but interact differently. Some particles in these fields ignore each other, while others interact, leading to reactions and complex structures. The collaboration of these fields covers everything we understand and observe, along with much that remains unknown and beyond our perception. Oddly, the creation of matter particles is an exception. For instance, an atom forms when there's enough energy in the quark fields to produce quarks that aren't destroyed by antimatter quarks, though the reason for this is not fully understood. Gluons, which are particles related to the strong force, bind with two up quarks and one down quark to form a proton. Gluons then connect protons with neutrons to create a nucleus. Physicists propose that the visible universe consists of remnants that survive the constant creation and destruction of virtual particles. However, the particles making up dark matter are a different issue.
Although the universe is full of virtual particles, it doesn't completely negate the idea of nothingness. First, there's the nothingness before the Big Bang, which we don't yet understand. Additionally, this nothingness, made up of vast fields of quantum energy, seems to produce matter and force, leading to the creation of our world. Physicists are still unsure why some elemental particles persisted after the Big Bang. In his book, "A Universe from Nothing," Lawrence Krauss, a theoretical physicist and cosmologist, argued that the evidence holds the answer: the inherently unstable nature of nothingness produces elementary particles. There's also the idea that the entire universe might be a large virtual particle. The vacuum genesis hypothesis proposes that the universe began as a large fluctuation in the nothingness that preceded it. Although this hasn't been proven, it's an intriguing concept. Ultimately, everything, you, me, the whole universe, amounts to a big bunch of nothingness.
Even if you can picture an empty universe, this doesn't match reality. Adhering to the laws of physics is enough to dismiss the idea of a truly empty universe. As long as there is energy within it, even the zero-point energy of the quantum vacuum, there will always be some form of radiation that can't be eliminated. The universe has never been completely empty, and as long as dark energy exists, it never will be. The universe is the way it is, and while we try to understand it as much as we can, we should remain humble in the face of its vast unknowns. My only advice is to embrace the curiosity that drives us to explore, question, and uncover its mysteries.
So, that's all for this video. We'd love to hear your thoughts on this, so leave them in the comments below and stay tuned for more content like this.