Cosmology: A Big Bang and the Beginning of the Universe

Summary

Professor Dave delves into cosmology, the study of the universe's origin and evolution. Starting with the Big Bang 13.8 billion years ago, he outlines key epochs: from the Planck epoch where all forces were one, through grand unification and electroweak epochs, to inflation and the formation of fundamental particles. He discusses the transition from quark-gluon plasma to hadrons, the dominance of leptons, and nucleosynthesis. The script culminates with the universe's expansion, the formation of neutral atoms, and the eventual emergence of stars, painting a vivid picture of the cosmos's development.

Takeaways

• 🌌 Cosmology is the subfield of astrophysics that studies the origin and development of the universe.
• 🔴 The Big Bang is the prevailing scientific model for the beginning of the universe, estimated to have occurred around 13.8 billion years ago.
• 🤔 The concept of the Big Bang is often misunderstood as a loud explosion, but it was actually the emergence of the universe from a singularity.
• 🕒 Our understanding of the universe's history begins at around 10^-36 seconds after the Big Bang, with much still speculative before this point.
• 🌐 The universe underwent a series of epochs, including the Planck epoch, grand unification epoch, electroweak epoch, and inflationary epoch, each characterized by different physical conditions and force symmetries.
• 🔬 The universe expanded rapidly during the inflationary epoch, dispersing fundamental particles and setting the stage for the formation of cosmic structures.
• 💥 The quark epoch saw the universe cool enough for the electromagnetic and weak nuclear forces to separate, with the Higgs field giving particles mass.
• 🌟 The hadron epoch led to the formation of protons and neutrons, and the lepton epoch saw the dominance of leptons over antileptons due to a matter-antimatter asymmetry.
• 🌡️ The universe continued to cool through the photon epoch, leading to the formation of light nuclei during big bang nucleosynthesis.
• 🌌 The recombination and photon decoupling era around 377,000 years after the Big Bang made the universe transparent and marked the first time it was visible.

Q & A

What is the field of science that specifically studies the origin and development of the universe?

The field of science that specifically studies the origin and development of the universe is called cosmology.

What is the prevailing scientific theory regarding the birth of the universe?

The prevailing scientific theory regarding the birth of the universe is the Big Bang, which suggests that the universe began around 13.8 billion years ago from a single point.

Who coined the term 'Big Bang' and in what context was it originally used?

The term 'Big Bang' was coined by astrophysicist Fred Hoyle, originally as an attempt to criticize the model, but it eventually became the widely accepted name for the theory.

What is the Heisenberg Uncertainty Principle, and how does it relate to the concept of the universe's origin?

The Heisenberg Uncertainty Principle states that the more certainty associated with one complementary variable (like energy), the less certainty that can be associated with another (like time). This principle allows for quantum fluctuations, where particles can pop in and out of existence, suggesting that the universe itself could be seen as a quantum fluctuation.

What is the Planck epoch and what is significant about it in the context of the universe's early development?

The Planck epoch is the earliest period of the universe's development, where all four fundamental forces were unified into one. The temperature was extremely high, making it too hot for familiar particles to exist.

What is meant by the term 'grand unification epoch' and what occurred during this time?

The grand unification epoch is a period shortly after the Planck epoch when the universe cooled enough for gravity to decouple from the other three forces, which could be collectively described by a grand unified theory.

What is the electroweak epoch and why is it significant?

The electroweak epoch is a period in the universe's early development when the strong nuclear force decoupled from the electrostrong force, leaving only the electromagnetic and weak nuclear forces together, known as the electroweak force.

What is the inflationary epoch and how did it affect the universe's size?

The inflationary epoch was a brief period of extremely rapid expansion of the universe, increasing its size by around 26 orders of magnitude, triggered by the separation of the electrostrong force into the strong nuclear force and electroweak force.

What happens during the quark epoch and how does it transition to the hadron epoch?

During the quark epoch, the universe cooled enough for the electromagnetic and weak nuclear forces to decouple, and the Higgs field began bestowing mass on particles. The hadron epoch followed, where quark-gluon plasma condensed into hadrons, including protons and neutrons.

What is the significance of the photon epoch in the universe's history?

The photon epoch is significant because it marks the period when the universe cooled enough for protons and neutrons to fuse into hydrogen and helium, an era known as big bang nucleosynthesis, which established the early elemental composition of the universe.

How does the recombination and photon decoupling era relate to the visibility of the universe?

The recombination and photon decoupling era is when electrons combined with nuclei to form neutral atoms, allowing photons to travel freely without being scattered by charged particles. This marked the first time the universe became transparent and visible as we understand it.

Outlines

00:00

🌌 Introduction to Cosmology and the Big Bang Theory

Professor Dave introduces the concept of cosmology, a subfield of astrophysics that focuses on the origin and development of the universe. He explains that while early civilizations had mythological explanations for the universe's beginning, modern science has provided empirical evidence pointing to a beginning around 13.8 billion years ago, known as the Big Bang. Despite skepticism, the theory is grounded in physics and astronomy, contrasting the common misconception of a loud explosion with a more complex and gradual process. The tutorial promises to explain the current model of the universe's birth and early development, with a later discussion on supporting evidence involving galaxies and other celestial objects.

05:01

🔬 The Quantum Beginnings and Early Epochs of the Universe

The script delves into the quantum origins of the universe, suggesting that the entire cosmos could be seen as a quantum fluctuation with net energy close to zero. It discusses the Heisenberg Uncertainty Principle and how it allows for particles to appear from nothing, setting the stage for the universe's emergence. The narrative then explores the Planck epoch, where all four fundamental forces were unified, and the subsequent grand unification epoch, where gravity decoupled from the other forces. The electroweak epoch and the inflationary epoch are described, detailing how the universe expanded rapidly and fundamental particles began to take shape.

10:02

🌠 The Evolution of Forces and Matter in the Early Universe

This section continues the cosmic timeline, discussing the quark epoch where the universe cooled enough for the electromagnetic and weak nuclear forces to manifest distinctly. It describes the hadron epoch, where quarks combined to form hadrons, including protons and neutrons. The lepton epoch follows, with hadrons and antihadrons annihilating, leaving a surplus of matter. The photon epoch is introduced, detailing the period of nucleosynthesis where hydrogen and helium were formed, and the universe's expansion into a filament-like structure under the influence of gravity.

15:07

🌟 The Formation of Atoms and the Universe's Visibility

The final paragraph discusses the recombination and photon decoupling era, where electrons combined with nuclei to form neutral atoms, allowing photons to travel freely and making the universe transparent. This marked the first time the universe was visible. The script then describes the 'dark ages', a period of relative inactivity where the universe continued to cool and hydrogen and helium gas clouds collected due to gravity, eventually leading to the formation of stars and the ignition of the universe's luminous history.

Keywords

💡Cosmology

Cosmology is the branch of astronomy concerned with the study of the origin, evolution, and eventual fate of the universe. It is central to the video's theme as it sets the stage for understanding the scientific narrative of the universe's development. The script discusses cosmology as the science that takes us from mythology to empirical evidence, guiding us through the timeline of the universe's history starting from the Big Bang.

💡Big Bang

The Big Bang refers to the prevailing cosmological model that suggests the universe began as an extremely hot and dense point and then expanded. It is a key concept in the script, marking the beginning of the universe's timeline. The term is used to describe the event that started the cosmic clock, from which all subsequent events and developments in the universe can be traced.

💡Quantum Fluctuation

Quantum fluctuation is a phenomenon in quantum mechanics where particles can temporarily 'borrow' energy to pop in and out of existence. In the context of the video, quantum fluctuation is proposed as a possible mechanism for the birth of the universe, suggesting that the entire universe could be seen as a large-scale quantum fluctuation, which challenges our understanding of the origin of everything.

💡Planck Epoch

The Planck Epoch is the earliest period in the history of the universe, when it was incredibly small and hot, and all four fundamental forces were theorized to be unified. The script refers to this time as the period where our understanding is speculative, indicating the extreme conditions that would have existed and the challenges in studying this era.

💡Grand Unification Epoch

The Grand Unification Epoch is a period shortly after the Planck Epoch when the universe cooled enough for gravity to separate from the other three forces. This concept is integral to the video's explanation of the force unification and symmetry breaking that occurred as the universe expanded and cooled, leading to the distinct forces we observe today.

💡Electroweak Epoch

The Electroweak Epoch is a stage in the universe's early development when the strong nuclear force separated from the electrostrong force, leaving behind the electroweak force. This term is crucial in the video's discussion of the sequential breaking of symmetries and the formation of the forces we understand today.

💡Inflationary Epoch

The Inflationary Epoch describes a brief period of extremely rapid expansion in the early universe, which dispersed fundamental particles evenly across a much larger volume. The script uses this concept to explain the vast scale of the universe and how it transitioned from a hot, dense state to a more expansive, cooler one.

💡Quark Epoch

The Quark Epoch is a phase where the universe had cooled enough for quarks to form, but not yet for protons and neutrons. This term is used in the script to illustrate the progression of particle formation and the cooling of the universe, marking a transition from a plasma of quarks and gluons to the formation of hadrons.

💡Hadron Epoch

The Hadron Epoch is characterized by the formation of hadrons, particles composed of quarks, including protons and neutrons. This period is highlighted in the script as a critical step towards the formation of atoms, as it sets the stage for the creation of the building blocks of matter.

💡Lepton Epoch

The Lepton Epoch is a phase following the Hadron Epoch, where leptons and anti-leptons dominated the universe before largely annihilating each other. The script mentions this epoch to explain the asymmetry between matter and antimatter, which allowed for the remaining matter to form the universe as we know it.

💡Photon Epoch

The Photon Epoch refers to a period in the universe's history when photons began to travel freely, marking the transition from an opaque to a transparent state. This concept is used in the script to describe the cooling of the universe and the beginning of the era where light could travel unimpeded, leading to the formation of the cosmic microwave background.

Highlights

Cosmology is the study of the origin and development of the universe.

The universe is estimated to be around 13.8 billion years old, originating from a single point known as The Big Bang.

The Big Bang theory was initially criticized but has become the prevailing cosmological model.

The misconception of the Big Bang as an explosion is clarified; it was a rapid expansion from a singularity.

Our understanding of the universe's initial moments is limited, with concrete models starting around 10^-36 seconds post-Big Bang.

The Heisenberg Uncertainty Principle allows for quantum fluctuations, suggesting the universe could be a large-scale fluctuation.

The Planck epoch, the earliest period of the universe, is theorized to have unified all four fundamental forces.

The grand unification epoch saw gravity decouple from the other forces, leading to the electrostrong force.

The electroweak epoch marks the separation of the strong nuclear force from the electrostrong force.

Inflationary epoch describes a rapid expansion of the universe by 26 orders of magnitude, dispersing fundamental particles.

The quark epoch is when the universe cooled enough for the electromagnetic and weak nuclear forces to decouple.

The hadron epoch is characterized by the formation of hadrons, including protons and neutrons, from a quark-gluon plasma.

The lepton epoch saw hadrons and anti-hadrons annihilate, leaving a matter-antimatter asymmetry.

Big Bang nucleosynthesis during the photon epoch led to the formation of light elements like hydrogen and helium.

The universe's structure evolved into a filamentary pattern due to gravitational attraction of hydrogen and helium nuclei.

Recombination and photon decoupling around 377,000 years post-Big Bang allowed electrons to form neutral atoms, making the universe transparent.

The dark ages of the universe lasted for about 150 million years, with no stars and a cooling universe.

Matter continued to clump due to gravity, eventually leading to the conditions necessary for star ignition.

Transcripts

It’s Professor Dave, let’s talk about cosmology.

While astrophysics is the field of science that studies the universe and everything in

it, the subfield of astrophysics that specifically studies the origin and development of the

universe is called cosmology.

That means that if we are going to start our story from the beginning, we have to start

with cosmology.

How did the universe begin, and when?

Early civilizations had all kinds of mythology surrounding this question.

But ever since the 20th century, we have begun to answer it not with stories, but with science.

Actual empirical evidence that provides clues as to how it all began.

And what does this evidence tell us?

Overwhelmingly, it tells us that the universe was born around 13.8 billion years ago, from

a single point.

Scientists and laypeople alike refer to this event, the beginning of our universe, as The

Big Bang, a name coined by astrophysicist Fred Hoyle in an attempt to criticize the

model, but ironically it stuck.

Many people are incredulous of such a big bang, considering the whole idea to be completely absurd.

But the main reason for this is nothing more than a cosmic gap in understanding of principles

in physics and astronomy.

When most people imagine the Big Bang, they think of a loud kaboom, a cartoon explosion

graphic, and the present-day, fully-formed universe spilling out of it, with a comet,

and the planet Saturn, and other complex objects.

This would indeed be impossible to believe, and in fact, it could not be further from

the truth.

In this tutorial we will describe, in a basic way, our current model for the birth and early

development of the universe, as understood by modern cosmologists.

Unfortunately, we will not yet be ready to discuss the evidence that supports this model,

because understanding that evidence will require a discussion of galaxies and many other objects

that we will get to later in the series.

So for now, try to simply take this model at face value, and I promise that later on,

we will examine several independent threads of evidence that all corroborate this model

of origin and specific age for the universe to great precision.

So now, let’s start at the beginning.

To be fair, at present, we don’t know what happened at the beginning.

By the beginning, we mean t equals zero.

The first instant.

Our understanding begins to take shape at around 10 to the negative 36 seconds after

the big bang.

That’s a trillionth of a trillionth of a trillionth of a second.

From that moment forward, we start to have an increasingly solid grasp of how things

must have gone, which is pretty darn impressive when you think about it.

As for the imperceivably small increment of time before that, we must admit that our current

models just don’t work.

We will still talk about this earliest period here, but to be clear, it will be largely

speculative, including some of my own personal conjecture.

But don’t worry, we will quickly get back to the real science.

I’m already exhausted.

Let’s just start at the first moment, and picture blackness, since that’s kind of

the best we can do.

Now, the first thing, time zero.

Freeze the clock.

A single point.

The uncaused cause.

How could this have happened?

Let’s first recall some things about the Heisenberg Uncertainty Principle.

This tells us that when looking at complementary variables, like energy and time, the more

certainty associated with one, the less certainty that can be associated with the other.

This is what allows for quantum fluctuation, the very real and very measurable phenomenon

by which particles pop into and out of existence, all over the universe and at all times.

This means that the idea that something could simply appear is actually not without precedent.

Of course, to go from virtual particles to the entire universe is quite a leap, for a

number of reasons, but if you really think about it, with nothing else in existence yet

to be compared to, would this fluctuation have been large or small?

Is it a lot of energy or a little?

In comparison to what, precisely?

What if, taking into account both positive and negative energy, the net energy is very

close to zero?

Then the entire universe could be regarded as a quantum fluctuation, borrowing energy

it will pay back later.

If we take for granted that without any other frame of reference, a quantitative amount

of energy appearing from nothing can be of any arbitrary amount, then we are acknowledging

that the appearance of some energy from no energy is the only thing we must explain.

It is the emergence of an initial duality.

Plus and minus.

Yes and no.

Whatever you want to call it.

It is not planets and stars tumbling out of a kablooey graphic.

It is the emergence of the simplest possible thing that is a thing, rather than no-thing.

Everything else follows from there.

Now we get to 10 to the negative 43 seconds after the big bang.

What do we know about this time?

Still not much.

But if we recall some things about the standard model of particle physics, experiments in

particle accelerators have allowed us to begin the incredible task of unifying the four fundamental forces.

These are the electromagnetic force, the weak nuclear force, the strong nuclear force, and gravity.

In that earliest period that we know almost nothing about, also called the Planck epoch,

given the universe’s minuscule size, the temperature of the universe must have been

over 10 to the 32 Kelvin, which is nearly a billion trillion trillion degrees, far too

hot for familiar particles to exist, and all four forces must have been unified into one

single force.

The search for quantum gravity is the search for the quantum particle that would mediate

this singular force, thus it is sometimes called the search for the theory of everything.

Particle accelerators can’t yet achieve this incredible energy, so we must hope for

bigger and better technology.

But in the next epoch, from 10 to the negative 43 seconds until 10 to the negative 36 seconds,

also called the grand unification epoch, temperatures cooled down to 10 to the 29 Kelvin.

This allowed for gravity to decouple from the other three forces, which can be collectively

referred to as the electrostrong force, and which we believe could potentially be described

by a grand unified theory.

This act of forces breaking off from other forces is the result of symmetry breaking,

a phenomenon that can occur when extreme temperatures cool below certain transition temperatures.

In this way, we can understand that all the disparate fundamental particles in the universe

were once part of the same thing, that only manifested as different objects as a result

of a series of successive symmetry breakings while the universe cooled.

Next, we enter the earliest era for which theoretical physics has some reasonable basis,

taking place from 10 to the negative 36 seconds until 10 to the negative 32 seconds after

the Big Bang.

This is called the electroweak epoch.

It is marked by the decoupling of the strong nuclear force from the electrostrong force,

leaving only the electromagnetic and weak nuclear forces together, which we call the

electroweak force.

This is possible now with the universe having cooled to a frosty 10 to the 28 Kelvin.

Roughly concurrent with the electroweak epoch is what we call the inflationary epoch.

This was a brief period in which the universe expanded by an incredible factor, around 26

orders of magnitude, triggered by the separation of the elecrostrong force into the strong

nuclear force and electroweak force.

We don’t know the precise size of the universe before and after this phase, but the magnitude

of the expansion would be like inflating something the size of a small molecule up to something

ten light years across, or about 60 trillion miles.

This nearly instantaneous expansion dispersed the earliest fundamental particles around

this much larger volume quite evenly, after which the immense potential energy from the

inflation was released, producing a hot plasma of quarks, anti-quarks, and gluons.

Plodding along to around 10 to the negative 12 seconds, or one trillionth of a second

after the Big Bang, we enter a period called the quark epoch.

Here, things have cooled enough for the third and final symmetry to break, decoupling the

electromagnetic and weak nuclear forces, thus resulting in the four distinct forces we know today.

As a result, the Higgs field bestows existing particles with mass for the first time, but

things are still too hot for protons and neutrons to form.

This is also the highest-energy epoch that we can currently probe with particle accelerators,

which means we are now transitioning from theoretical cosmology to experimental.

At around 10 to the negative 6 seconds after the Big Bang, things finally cool down enough

for the quark-gluon plasma that permeates the universe to congeal into hadrons, which

are particles made of quarks.

This includes baryons like protons and neutrons, which will eventually make up all the atoms

in the universe.

This is called the hadron epoch, lasting until one full second after the Big Bang.

The action will slow down a bit from here, but before we move on, take a moment to imagine

how much has happened in just one second, the void yielding merely some energy and a

singular force, which sequentially breaks into four forces, in turn yielding a sea of

massive particles.

From one second to ten seconds after the big bang lasted the lepton epoch.

Hadrons and antihadrons largely annihilate leaving leptons and anti-leptons to dominate,

which in turn also largely annihilate, and thanks to a slight asymmetry in favor of matter

over antimatter, this leaves just a fraction of the original matter behind.

From here, the start of the photon epoch, things start to look a little more familiar.

For about seventeen minutes, the universe is cool enough for baryons to be stable, but

also hot enough for them to fuse, so protons and neutrons fuse together to make lots of

hydrogen and helium, and trace amounts of other light nuclei, an era called big bang

nucleosynthesis.

After that, it gets too cold and sparse, so fusion halts, locking the universe into a

three-to-one ratio of hydrogen to helium by mass.

At this point, the universe is about 600 light years across, so we are no longer dealing

with a tiny universe.

Over the next several hundred thousand years, as the universe continues to expand, all of

these hydrogen and helium nuclei begin to collect in little patches, due to the effects

of gravity.

This force, now understood through Einstein’s general relativity to be the warping of spacetime

by massive objects, attracts all objects with mass towards one another.

So by virtue of the mass of these nuclei, and more so, all the dark matter around the

universe, which we will discuss later, the universe takes on a sinewy, filament-like structure.

Denser regions become more dense, and empty regions become more empty, as the photon epoch

draws to a close.

During the next era, recombination and photon decoupling, about 377 thousand years after

the big bang, things are finally cool enough for electrons to combine with nuclei to form

neutral atoms for the first time.

Electrons are captured, relax down to the ground state, and emit photons in doing so.

This marks the first time that the universe is actually visible, in the sense that we

consider something to be visible to our eyes.

It is no longer opaque, but transparent, with electromagnetic radiation now moving freely

over large distances, and with a diameter for the universe of nearly 100 million light

years, the distances are large indeed.

Then for around 150 million years, not much happened.

We call this era the dark ages.

There was plenty of hydrogen and helium around, and photons were traveling everywhere, but

there were no stars to produce all the light we see in the night sky today.

Things continued to cool, from around 4,000 Kelvin, down to 300 Kelvin, which incredibly

would allow for liquid water, if any were to exist, all the way to around 60 Kelvin,

a temperature that is finally cold enough by human standards to somewhat resemble the

cold outer space we normally conceive of.

But slowly, ever so slowly, all the clouds of hydrogen and helium gas continue to collect.

Over millions of years the minute gravity exerted by these particles, combined with

the more significant gravity exerted by surrounding dark matter, pulled matter together into clumps,

little dense pockets of matter.

Closer and closer, until all the atoms are pushing right up against one another.

What happens when you get enough atoms all together in the same place?

Ignition.

So let’s move forward and see what happened next.