Hey guys, I'm Jon and welcome to Respect
Your Intellect. It came to my attention
that there are a lot of misconceptions
and misunderstandings when it comes to
the Big Bang so we'll be talking about
that today. So in this video, we'll cover
the history of how the Big Bang was
discovered, the other early theories that
were discarded in favor of the Big Bang
Theory, we'll address some of the biggest
misconceptions and misunderstandings
about the Big Bang and we'll talk about
the four pillars of evidence that we
have that support the Big Bang. We'll
also cover the five main periods of the
expansion of the universe. Let's get
started!
[Music]
There will be a few things about light
in this video so if you haven't seen my
video on light yet, you should definitely
go check that out first to understand
everything in this video. I'll leave a
link in the description or you can check
it out right here and come back
afterward. Let's start with a bit of
history about the discovery of the Big
Bang. It all starts in 1922 when
Alexander Friedmann predicted a
universal expansion of the universe
using Einstein's General Relativity. A
bit later in 1927 Georges Lemaître was the
first to propose that the expanding
universe could be traced back to a
single point. This is because if we
measure at different intervals and
record the movements of objects we can
then extrapolate their movements and
positions backward through time. Then in
1929 Edwin Hubble made the first direct
observations of the expanding universe
when he recorded the redshift of distant
objects and realized that there was a
correlation between distance and
redshift. This led him to develop
Hubble's Law that states that the
further an object is, the faster it's
moving away from us. Hubble's law only
has two possible explanations either
we're at the center of an explosion of
galaxies or the universe is uniformly
expanding everywhere.
The former goes against the Copernican
principle that states that humans, earth,
or our solar system, are not privileged
observers of the universe.
Hubble's Law became the cornerstone of
the Big Bang Theory. After that, in 1948,
Ralph Alpher and Robert Herman
predicted that there would be a cosmic
microwave background radiation left over
from the Big Bang. And finally, in 1964,
Arno Penzias and Robert Wilson
discovered the cosmic background
radiation and were awarded the Nobel
Prize in Physics in 1978. When the Big
Bang Theory was first conceived it was
contending with another theory called
the Steady State Theory. The Steady State
Theory was a model that theorized that
the density in an expanding universe
stayed proportional due to a continuous
creation of matter.
This theory is now rejected by the vast
majority of cosmologists, astrophysicists,
and astronomers. This is because the
observational evidence that we call the
four pillars of the Big Bang all point
to a hot Big Bang event
with a universe of a finite age while
the steady state theory makes no such
predictions. Now let's talk about the
misconceptions and misunderstandings
about the Big Bang.
Contrary to what its name suggests, the
Big Bang is not an explosion "in" space
but rather an expansion "of" space. A lot
of people just tend to call it an
explosion because it avoids having to go
into a tangent to explain the expansion
of space; but that's ultimately incorrect.
Another misconception is that the Big
Bang is the creation of matter from
nothing but this is very far from what
the Big Bang Theory claims. When the
universe was very young it was a very
different place; much hotter, much more
dense, and much smaller. All the matter we
can observe today was already there at
the beginning of the universe and a lot
of it even annihilated each other to
leave us with only a small fraction of
the matter. So the Big Bang Theory
actually predicts that we "lost" the
majority of the universe's matter rather
than the popular belief of the Big Bang
having "created" matter. Alright, now that
we got the misconceptions out of the way,
let's talk about the evidence we have
for the Big Bang. When it comes to
evidence for the Big Bang we have four
main points that we call the four
pillars of the Big Bang Theory. The first
pillar is Hubble's Law that states that
the farther an object is, the faster it's
moving away from us. Hubble's Law can be
observed directly by looking at various
distant objects like galaxies. What it
does is support the claim that space is
expanding uniformly from everywhere. The
second pillar is the discovery and
measurement of the cosmic microwave
background radiation. This background
radiation was theorized to be visible
from anywhere you look at in space and
that it would be the remnant of the Big
Bang. Arno Penzias and Robert Wilson were
the first to detect it in 1964 and they
were awarded the Nobel Prize in Physics
for it in 1978. Since then we had better
and better maps made of it with the WMAP
spacecraft and this map is in
agreement with the large scale
structures we can directly observe in
space today. The third pillar is the
abundance of light elements in the
universe. This is not light as in photons
but light as in very little mass like
helium, deuterium, lithium, and a few
others. Everything else in the universe
was created much later inside of stars
during their evolution
or when stars exploded as
supernovae. This is also directly
observable and correlates well with the
predictions made from what we know about
the Big Bang. And the fourth pillar comes
from more recent observational evidence
of galaxy formations and evolution as
well as the distribution of large-scale
cosmic structures. Our observations and
simulations show that the first quasars
and galaxies formed when the universe was
only about 1 billion years old. Quasars
are essentially extremely luminous black
holes that can be thousands of times
brighter than our entire Milky Way
galaxy. This is because the gas around
them releases insane amounts of
electromagnetic radiation as it falls
towards the black hole. Since those first
quasars and galaxies formed, larger
structures like galaxy clusters and
superclusters have continued to form.
This is also all in agreement with our
simulations based on the information we
have. In 2011 we also found pristine
clouds of primordial gas by analyzing
the absorption lines of the spectra of
distant quasars. This was the first time
that we found clouds of gas with no
elements heavier than hydrogen and
deuterium which means that those clouds
were likely formed in the first few
minutes after the Big Bang. On top of
these four pillars, our estimate of a
13.8 billion year old universe is now in
agreement between the Hubble expansion,
the Cosmic Microwave Background, and the
oldest stars. As for the future, we're
hoping we can add a fifth pillar by
detecting gravitational waves from the
very early universe. This would give us a
direct observation of something that
occurred less than one second after the
Big Bang; giving us a glimpse at what
we're having trouble seeing right now. So
now that we know we have strong evidence
that all agree with each other, let's
talk about the timeline of the Big Bang
itself as well as what we know and
what's still up for speculation. The
first period is what we call the
singularity. We don't have much
information about it just yet so this
period is still open to a lot of
speculation. It's essentially the point
at which everything converges to an
infinitely dense and infinitely hot
universe when we use general relativity
to extrapolate backwards. This suggests
that our current laws of physics are
insufficient to explain this early
period of the universe. Perhaps in the
future we'll be able to unify General
Relativity and Quantum Mechanics under a
Quantum Gravity Theory that will yield
more answers; but we're not there yet. The
main problem with General Relativity is
that it resides in classical physics
while the other three fundamental forces
are described in quantum mechanics.
Unfortunately, we can't consistently
combine classical physics with quantum
mechanics and that presents a
substantial problem in our quest to
understand the very early universe. The
second period is what we call Inflation
and Baryogenesis. This entire period
takes place when the universe was only
an extremely small fraction of a second
old so it's too early and different for
us to explain everything at this point.
What we believe happened in this period
is that the very small universe was
uniformly dense and experienced very
rapid heating and cooling temperature
fluctuations. During this period, a phase
transition happened that caused a cosmic
inflation and the universe grew
exponentially. This growth left ripples
of varying densities which became the
large-scale structures we see today like
clusters of galaxies. When the inflation
stopped, the universe reheated and was
able to produce the first elementary
particles. The temperature of the
universe at this point was so high than
everything in the universe was moving at
just under the speed of light. All this
energy caused particles and
antiparticles to continuously be created
and destroyed in collisions. Then we
believe something happened that we call
baryogenesis. This baryogenesis event
would be responsible for violating the
conservation of the baryon number which
is just a fancy way of saying the total
value of particles in a system in
quantum mechanics. What this led to is an
excess of matter over antimatter by
about 1 part in 30 million and
resulted in the predominance of matter
that we see today in the universe. The
next period is called the Cooling period.
Everything before this point happened in
a tiny fraction of a second but when the
universe becomes one second old, things
start to slow down significantly. There's
much less speculation at this point
because we can directly observe these
conditions in large particle
accelerators. During this period, the
universe continued to decrease in
temperature and density so the particles
in it were less and less energized. This
is the period in which the fundamental
forces of physics came into existence in
the form that we observe them today.
This is also the time where the
elementary particles formed that will
later become atoms. This period also
includes a mass annihilation event
between matter and antimatter and left
the universe with no more antimatter and
only one ten-billionths of the matter it
previously had. The same mass
annihilation event also happened between
electrons and positrons when the
universe was about one second old. After
this mass annihilation, everything slowed
down and the universe was left with
light as its main source of energy. At
about 379,000
years old, electrons and atomic
nuclei combined to form the first atoms
which were mostly hydrogen. At this point,
radiation decoupled from matter and
became known as the cosmic microwave
background radiation; which is one of the
pillars of the Big Bang Theory. We can
actually see the cosmic microwave
background radiation from when the
universe was about 400,000 years old and
it's considered the best observable
evidence that confirms the Big Bang. We
also think that during this period, when
the universe was 10 to 17 million years
old,
there may have been a habitable epoch
that contributed to the chemistry of
life. The next period is what we call
Structure Formation. During this period,
the universe was still pretty uniformly
distributed but there were slightly
denser regions and slightly less dense
regions. The slightly denser regions
started attracting nearby matter by
gravity and continued to grow denser.
This resulted in the formation of gas
clouds, stars, galaxies, and other
structures that we can observe today. We
actually have a map of this from the
Cosmic Microwave Background and it
allows us to perform real measurements
and observations about the early
universe. The spacecraft that imaged it
was operating from 2001 to 2010 and it
was called Wilkinson Microwave
Anisotropy Probe; or WMAP for short. And
finally, we have the last period which is
called Cosmic Acceleration. We believe
that space is infused with dark energy
that's responsible for space
accelerating its expansion. When the
universe was much smaller and denser
gravity was able to dominate over dark
matter and acted like a braking
mechanism
to slow the expansion of space. As space
continued to expand, gravity had less and
less effect in the universe as a whole
and became overpowered by dark matter.
This means that as the universe
continues to expand it also continues to
accelerate as well. So to conclude, the
four pillars of the Big Bang as well as
a few other observable pieces of
evidence are the reason why it's the
predominant model today. It wasn't just a
choice we made because we liked the idea.
It's a conclusion that was drawn from
many observations that all agree with
each other
and seem to only be explained by a Big
Bang event. Since the Big Bang is not an
event that suggests creation from
nothing, it doesn't require a belief like
many people think. We have a "lot" of
evidence that supports it and we're able
to trace it back to very near the
beginning. We still need to figure out
parts of the very early periods that we
can't yet observe directly but that
doesn't invalidate all the other
evidence that we can observe and are in
agreement. We currently have a lot of
studies and experimentation happening
right now for these periods as well as
dark matter and dark energy that we
don't have much information on as of yet.
Hopefully each advancement in those
fields will help us explain more and
more of the events of the Big Bang. If
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