Gravity vs. Pressure: The battle that formed the universe - Fabio Pacucci
Welcome one and all!
It’s time to grab your seat
for the biggest battle
in the soon-to-be-formed universe.
That’s right—
the Big Bang is about to go down!
In one corner is the force that brings
all matter together.
It acts on any particle with mass,
and its range is infinite—
give it up for gravity!
In the other corner, our contender can
push matter away
with spectacular strength.
When the going gets tough,
this fighter just gets tougher.
That’s right, it’s pressure!
Over the next several
hundred thousand years,
these two contenders will be wrestling
for the fate of the universe.
That’s right folks, the ripple effects
of this historic match
will shape the structure of the universe
as we know it today.
But what are these powers fighting over?
We’ll find out when the Big Bang
hits right... now!
Let’s zoom in for the play-by-play.
This epic event has brought three
components into our infant universe.
Dark matter, which only interacts
with gravity.
Baryonic matter, which makes
up all matter you’ve ever seen,
is affected by both gravity and pressure.
And radiation composed
of innumerable particles of light,
also known as photons.
In the moments just after the Big Bang,
all three components are in equilibrium,
meaning no one location
is denser than another.
But as the universe starts expanding,
differences in density start to emerge.
Gravity immediately gets to work
pulling matter together.
Dark matter begins to collect
at the center
of these increasingly
dense regions,
forming the foundations
of future galaxies.
Meanwhile, pressure begins gathering
its strength.
In this hot, high-energy environment,
protons and electrons can’t come
together to form atoms,
so these loose particles zip around,
freely interacting with ambient photons.
The result is almost a fluid
of baryonic matter and radiation.
But the closer these baryonic particles
get, the hotter the fluid becomes,
pushing photons to ping
around with incredible force.
This is the power of pressure,
specifically radiation pressure,
battling to push things apart.
With each of gravity’s vicious tugs
squeezing photons and matter together,
pressure exerts a forceful shove back.
And as the two giants struggle,
they heave this fluid back and forth—
creating massive waves called
baryonic acoustic oscillations.
Moving at almost two thirds
the speed of light
these BAOs ripple across space,
impacting the universe
on the biggest scale imaginable.
These rolling waves determine the
distribution of matter throughout space,
meaning that today— almost 14 billion
years after this fight began—
we're more likely to find
galaxies at their peaks
and empty space in their troughs.
And that’s not all.
We can still see these ripples in the
background radiation of the universe,
a permanent reminder of this epic brawl.
But after being locked in a stalemate
for roughly 370,000 years,
the tide of our battle finally
begins to turn.
After all this time, the heat from the
Big Bang has dissipated significantly,
cooling the universe down to a temperature
at which loose electrons
start to pair up with protons.
Known as the “era of recombination,”
this stops electrons
from recklessly pinging around.
This allows light to stream freely
for the first time,
illuminating the universe.
These photons now only exert a tiny force
on the neutral atoms they interact with,
gradually reducing the power of pressure.
And with that, it’s time to crown
our champion!
The undefeated force,
the most pervasive power in the universe:
it’s gravity!
And yet, this rivalry isn’t over.
A similar battle continues between these
two sworn enemies today,
within every single star.
As gravity pulls a star’s gas inward,
pressure increases and pushes
the matter back outward.
This push and pull keeps the Sun,
and all other stars,
stable for billions of years.
In fact, this clash of the titans
is the same reason
Earth’s atmosphere doesn’t collapse
to the ground.
So while their greatest fight
might have ended,
these two warriors are still
to be locked in combat—
even as a new challenger approaches.
even as a new challenger approaches.
