This content explores the scientific understanding of the universe's origin and ultimate fate, contrasting ancient philosophical ideas with modern cosmological discoveries, ultimately presenting a cyclical view of existence from birth to death, mirrored in both the cosmos and human life.
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Dad, Dad. How was I made?
That was yesterday’s question. Ask another one.
How long will the sun keep shining?
Until the end of the world. Then it fades.
-Will the world really end? -Yes.
-Why? -Because everything has an end.
-Why? -Because physics says so.
-Why? -Physics is applied science.
Math is applied philosophy. And philosophers said so.
-Why? -They were bored in Ancient Greece.
Stop asking why. New questions!
So you and Mom will fade too?
Yes. Everything will fade.
Your mom, dad, grandpa, aunt, and uncle.
-Why? -Because biology follows physics.
What’s going on here? Why are you crying?
Dad said everything will end, even the sun and my uncle.
He’s lying. I said the sun will stop shining.
It’s burning gas. When it’s done, it goes dark.
Then comes an ice age. Then the uncle fades.
These are basic physics. What’s the problem?
He’s just a kid!
I told you a hundred times not to mention the end of the world!
Sorry, but it’s my right.
I agreed with your family to discuss it anytime.
Enough!
Come on, sweetheart. Don’t cry.
I’ll tell you about the multiverse.
There are lots of your uncle there. Let’s go.
Hello my dear viewers.
Welcome to a new episode of Al-Daheeh.
Let’s head to Vatican Palace
and look at one of the most famous murals ever painted.
The School of Athens.
It was painted by the Italian artist Raphael in the early 16th century.
The painting brings together the greatest philosophers and early scientists.
You see figures like Pythagoras, Heraclitus, and Euclid.
But the most important part is this exact scene.
The scene that brings Plato and Aristotle together.
Plato stands on the left and points his finger to the sky.
Aristotle stands on the right and points his hand to the ground.
Two gestures pointing in opposite directions.
Art here captures the biggest disagreement in philosophy.
Plato points upward to what is called the World of Forms.
In Plato’s philosophy, it is a perfect, unseen world.
Everything there exists in a state of absolute perfection.
Our earthly world is only a reflection of it.
It was created as an imperfect copy of an ideal world.
What matters to us is the word created.
It means our world did not exist, then suddenly came into being.
In the 4th century BC, Aristotle speaks to his students at the Lyceum in Athens.
He begins arguing an idea far stranger than Plato’s.
He sums it up in one bold sentence.
"Nature abhors a vacuum."
Nature hates a vacuum.
"What does that mean, Abu Hamid?"
It means nothing in the universe ever truly becomes nothing.
There was never a time of nothing before the universe existed.
There will never be a time when the universe ends into nothing.
The universe has no beginning and no end!
That is why Aristotle, in the painting, points down toward the earth.
He is saying the universe is made of eternal matter.
It has no beginning and no end.
The painting places both ideas side by side.
But which idea will eventually win?
At first, Aristotle’s students are completely shocked.
His idea contradicts Greek philosophy
and even contradicts his own teacher, Plato.
But gradually, Aristotle’s idea takes over philosophy and natural science
for almost two thousand years.
His idea created enemies everywhere.
Religious scholars in Europe and the Islamic world oppose it.
They reject Aristotle’s view and call it the eternity of the world.
They claimed the world had a beginning.
In religion, after all, the universe is created.
But the idea also finds supporters who want it to be true, like alchemists.
They dream of turning cheap metals into gold.
Aristotle’s idea says the matter of the universe is constant.
Only the forms of matter change from one state to another.
That gives them hope.
they believe gold and tin are just different forms of the same substance.
And maybe, one day, tin could become gold.
The eternity of the universe remains a major philosophical problem.
It is extremely hard to disprove with solid science.
Some people believe the universe was created and will one day come to an end.
Others believe the universe has no beginning and no ending at all.
But in the early 20th century, all of this changed.
On October 6, 1923, at the top of Mount Wilson in California.
The mountain hosts the Hooker Telescope, the largest in the world at the time.
It can observe stars anywhere in the Milky Way.
That day, a young American astronomer arrives to take a routine photo
of a spiral-shaped cloud in our galaxy, M31.
Like any young astronomer, he was monitoring the galaxy,
but then he noticed something very strange.
The photos he took that day looked different
from those taken the previous two days.
There’s a star in the image that isn’t a normal nova.
A nova lights up for a while then fades completely.
This star is completely different.
Astronomers call it a Cepheid variable.
This star becomes a key marker in studying space.
It lights up and dims in a regular pattern, as if it is giving pulses.
At that moment, the young astronomer changes the star’s symbol
from "N" for nova to "VAR" for variable.
This young astronomer is Edwin Hubble.
He is the one the Hubble Space Telescope is named after,
which gave us the most important images of the universe.
The photos Hubble took, later labeled H335H,
will become the most famous astronomical image in history.
-Wow! -Let me explain it to you.
When Hubble discovered the Cepheid variable in that cloud,
he could calculate the number of its pulses.
He then measured the time between each pulse,
and from that, determined the star’s brightness.
This allowed him to find the Cepheid’s distance from Earth.
"How did he do all this?"
Stellar calculations weren’t magic.
They were available at the time.
Thanks to astronomer Henrietta Swan Leavitt
and her team of researchers, known as Harvard Computers.
There wasn’t a machine back then,
but the word "computer" referred to anyone who did calculations manually.
Anyone doing calculations by hand.
Hubble finally calculated the distance to the star using Henrietta’s work.
He discovered the Cepheid was 800,000 light-years away.
The Milky Way galaxy is about 100,000 light-years across.
Here Hubble realized the star was in a completely different galaxy.
Later, we’d learn this galaxy is Andromeda.
He distance isn’t 800,000 light-years, it’s actually 2.5 million light-years.
That means light takes 2.5 million years to travel that distance.
This was the first time in history
humans knew there were other galaxies in the universe.
Because of this, Edwin Hubble is called
"The man who discovered the universe."
In 1929, Hubble began studying 12 galaxies beyond our own.
He noticed most of the light from these galaxies leaned red.
"Maybe they’re just shy?"
Galaxies? Shy? No, it’s the moon that hides its face!
The red color had another meaning.
Hubble applied the Doppler effect, which looks at frequency changes in light.
Through it, he could measure their motion in space.
If stars move closer, their light shortens and shifts blue.
If they move away, their light stretches and shifts red.
Hubble discovered that the galaxies with red light
were moving away from Earth and from the Milky Way.
He also noticed the farther a galaxy is, the faster it moves away.
To understand this better, imagine the universe as a balloon.
Dots on its surface represent galaxies.
The more you inflate the balloon, the farther apart the dots move.
But not all at the same speed.
Dots near the balloon’s edge move faster than those near the center.
"What does this have to do with the universe’s beginning, end, or Aristotle?
Do you know them personally or what?"
Just wait, and everything will make sense.
Hubble’s discoveries inspired Belgian physicist Georges Lemaître.
For the first time, he proposed it in the idea of the expanding universe.
Lemaître said if the universe expands steadily,
like a balloon inflating over time,
we can rewind to the beginning
and see the very moment it was born.
Did you catch the word "born"?
The universe had a beginning, contrary to Aristotle!
Its start was like the balloon inflating from the smallest possible point.
This moment would later be called the Big Bang.
Ironically, the moment science uncovered the universe’s beginning
also revealed the idea of its eventual end.
Georges Lemaître was a clergyman as well as a physicist.
The universe expanding over time, like its birth in the Big Bang,
revived an old 19th century idea called heat death.
This theory comes from one of physics’ most important laws,
the second law of thermodynamics.
Let’s imagine two glass cubes.
The first holds hot gas, with fast, energetic particles.
The second holds cold gas, with slow, calm particles.
Now connect the two cubes.
The hot cube with fast, energetic particles
starts to cool down,
while the cold cube heats up.
This continues until both reach the same temperature.
The second law of thermodynamics fully explains this process.
It says that in isolated systems, with no outside influence,
energy always flows from hotter systems to colder ones.
Here I need to introduce a term. Entropy.
It measures disorder and change in a system.
In our experiment, energy transfer continues
until entropy reaches its maximum.
At that point, temperatures become equal.
This process cannot be reversed
unless an external force steps in.
If you look closely, you’ll notice the second law of thermodynamics
is one of the very few laws in physics
where time shows up.
Let me explain it to you.
Matter changes from one state to another,
but time never runs backward.
In physics, most processes are time agnostic.
They don’t care about time.
They don’t have to move in one direction through time.
This law describes how particles, and everything in the universe,
move from an ordered state, with low entropy,
to a more random, chaotic state, with higher entropy.
Most importantly, this process cannot be reversed under the same conditions.
Most physical processes can run in either direction.
But with entropy, you can only do it from one side.
If you drop a cup of tea and it shatters into pieces,
the only law stopping it from reassembling itself like nothing happened,
is the second law of thermodynamics.
Now look at the whole universe. You’ll see the same law applies.
In 1852, the British physicist Lord Kelvin published a paper titled…
In it, he used the first and second laws of thermodynamics
to predict the fate of the universe.
If we assume the universe is a closed, isolated system,
then energy moves from its most dense, complex state,
the singularity, where the Big Bang began,
through the gradual expansion of the universe,
where stars, galaxies, and even life itself form.
As expansion continues, galaxies drift farther apart,
just as Hubble saw through his telescope.
Until the universe reaches a stage
where its temperature drops and energy dissipates.
When energy dissipates in an irreversible way,
the entire universe enters a state of equal temperature.
Or as Lord Kelvin called it, heat death.
Kelvin wrote:
If the finite universe is left to obey existing laws,
the inevitable result will be stillness and cold death.
Our universe will be like a corpse, cold and lifeless.
"The laws of physics are ruthless!"
Kelvin saw the idea of heat death as a paradox.
It could challenge the notion of an eternal universe.
It challenged the 19th-century idea
that the universe has no beginning or end.
If the universe were eternal, there shouldn’t be any motion.
Every movement consumes mechanical energy,
but our universe moves like stars, planets, everything we can observe.
With 20th century discoveries, Hubble’s contributions,
Einstein’s relativity, and others,
it was easy to bring back the heat death hypothesis
to fit the laws of physics.
But in the second half of the 20th century, the theory ran into problems.
If galaxies move quickly, as Hubble proved,
their speed could slow over time.
From this came a new idea, the Big Crunch.
Its proponents assumed the universe’s expansion would slow.
Over time, expansion would reverse,
galaxies would collapse and collide.
Gravity would compress them,
causing explosions and…
forming massive black holes.
The end of the universe would lead to a new singularity and Big Bang,
creating a whole new universe.
"Oh no! So we get our lives replayed,
back to school, work, and marriage?!"
Relax! These are just guesses.
We won’t live twice… as far as we know!
For years, scientists treated galaxy motion like a projectile,
like a football kicked into the sky.
Over time, it slows, stops briefly,
and then gravity reverses its motion,
sending it crashing back.
But in 1998, two teams of astronomers were shocked
while studying a supernova explosion.
They discovered the supernova was not just moving away from Earth,
it was accelerating.
This meant the galaxy it belonged to was also accelerating.
So the speed not only stays constant or slows down, but also accelerates.
Contrary to the Big Crunch idea,
which expected the universe’s expansion to slow down,
what actually happened was the opposite: the universe sped up its expansion.
What we have discovered is an unknown force in the universe
called Dark Energy
that pushes galaxies apart and drives cosmic expansion.
It is a force we know exists in the universe.
But we cannot measure it, or know its true value.
Is it positive or negative?
Will it stay within safe limits, or could it grow in the future?
Because if it does increase, the universe would expand at an extreme speed,
which could cause a tear in the fabric of space.
Imagine the universe ripping open, like a busted zipper, exposed to all realities.
A cosmic scandal across the multiverse.
This is known as the Big Rapture.
Even though recent scientific papers suggest
that dark energy changes strength over time, rising and falling,
the heat death theory remains the most realistic scenario so far.
So let us try to picture it using our most important energy source on Earth.
The Sun.
The Sun is a medium sized star.
It is roughly the same age as our planet, about 4.6 billion years old.
It is the main energy source for Earth and the planets orbiting it.
To remain a stable energy source, the Sun must burn hydrogen in its core.
This process causes two things.
First, it releases the energy we depend on, and a fraction of it reaches us.
Second, it produces helium, which slowly builds up in the Sun’s core.
But recently, we discovered something strange during this burning process.
As long as the Sun keeps holding everything inside,
helium builds up, and it slowly kills itself.
Why not just be like the Moon?
Cold, frozen, doing nothing, just borrowing sunlight and shining quietly.
Civilizations adore moonlight.
Meanwhile, the Moon is just sitting there doing nothing.
Every billion years, the Sun’s burning rate increases.
As a result, its brightness and energy output rise by 10 percent.
This is extremely dangerous.
Because the heat reaching Earth would increase dramatically.
As a result, the atmosphere protecting the planet would begin to erode.
Then rising temperatures would start evaporating oceans and water bodies.
Their vapor would gradually get trapped in the upper layers of the atmosphere.
When that happens, we would see the greenhouse gas effect,
raising the planet’s temperature to unprecedented levels.
All surface water would evaporate at extremely fast rates.
Once all the water is trapped in the upper atmosphere,
the Sun’s intense heat would break water molecules into hydrogen and oxygen,
which would escape the planet entirely.
In a short time, our planet would become a barren desert.
It would completely leave the habitable zone of the solar system.
Earth would leave the habitable zone,
and Mars would take its spot as the new planet within that zone.
"You have relieved me!"
Wait… the disaster hasn’t come yet.
"It still hasn’t, after all that?"
Unfortunately, after 4 billion years of our planet burning,
the Sun will reach its final days.
It will start transforming from a medium star into a massive red giant.
Its surface temperature will drop as it swells.
Remember when I told you burning hydrogen produces energy and helium?
Five billion years from now,
the Sun will exhaust all hydrogen in its core and turn it into helium.
Because the Sun is affected by gravity like everything else,
the pull on its outer layers will transfer inward, compressing the core.
To prevent collapse in its heart,
it will start burning the leftover hydrogen on the outer core.
Over 10 billion years, the Sun’s lifespan,
when it burns this hydrogen rapidly to save its core,
it will expand twenty times its normal size.
This swelling will swallow all the planets in its path,
including Earth, Mars, and others.
After swallowing all planets up to Mars,
it will burn all remaining core hydrogen, shrink down from that giant size,
but never return to its original form.
Gravity will keep pressing hard,
so it will start burning the accumulated helium.
Burning helium produces explosions and ejects parts of the Sun itself.
It will expand again, but this time for the last time,
until the Sun, which once cradled life on this planet,
detonates in its greatest explosion.
Its core temperature reaches 100,000 Kelvin
after exhausting all hydrogen and helium.
Only heavy elements remain, like carbon and oxygen,
whose fusion in the core will leave the Sun as a white dwarf,
a witness to the Sun’s death, like a gravestone.
These are the Sun’s final days.
That was the story of the Sun’s final days.
Now let us talk about our galaxy’s fate.
Remember the spiral cloud cluster,
that Hubble proved was a separate galaxy called Andromeda.
It is moving southeast from its current position in space.
When we calculated its speed, we found it travels at 110 kilometers per second.
Heading where?
"Do not say it is heading straight for us!"
Exactly. It is moving straight toward our Milky Way.
"Why are you smiling? That is a disaster!"
From 2000 to 2010, astronomers studied Andromeda’s stars
using the Hubble telescope.
They compared them to stars in distant galaxies
to calculate the distance between us and Andromeda.
By measuring its angles and speed with high precision,
they found a chance of a Milky Way collision.
"What? What if it hits us? How do we fix that?
Go ask if there is a way to save our galaxy!"
Calm down. That is still 10 billion years away.
Still, they will drift past like a cosmic wind!
In fact, we can already see Andromeda in the sky.
Over millions of years, it will become clearer and clearer,
like a car speeding straight toward a crash.
In 4 to 5 billion years, the first collision will occur.
Then each galaxy will pass by with little effect.
Over time, they will drift closer,
as if the two galaxies are dancing flamenco in space.
After 2 billion years, they collide again,
beginning full merger.
The black holes at their centers merge too,
forming a massive black hole,
the single giant core of a brand new galaxy.
"So if God gives us billions of years of life,
and we see the galaxies collide, what will happen to Earth?"
what optimism is this?
The Sun is already hot, and it will get even hotter in a billion years.
If we survive it, and manage to leave Earth
before the Sun swallows it turning into a red giant,
and move to a new planet in our solar system…
Even if we do all that, like a Nolan movie plot,
there’s a very high chance the new planet won’t feel the galaxy collision at all.
That’s because distances in space are unbelievably huge.
For example, the distance between Earth and the nearest star is 4 light-years.
Let me make it clearer to you.
Imagine the Sun as a ping-pong ball, and the closest star to Earth as a pea.
If we put the ping-pong ball here and the pea over there,
the distance between them would be 1,100 kilometers.
That’s an enormous distance for objects of that size.
Most calculations say stellar collisions are nearly impossible.
Most likely, our solar system will stay in the outer shell of the new galaxy,
without any noticeable change.
So we might witness the final days of Earth, the Sun, and the galaxy.
Next are the last days of the universe.
Unfortunately, the fate is the same: heat death,
the destiny of all elements in the cosmos according to physics.
From stars to galaxies, even black holes.
That’s because every element depends on energy to exist,
kinetic energy or stored potential energy.
When the universe reaches maximum entropy,
all this energy will disperse evenly across space,
after the universe reaches its maximum expansion.
Everything will die gradually and sequentially.
The Sun’s death will occur during the death of stars,
which begins 100 million years from now.
It will start with the death of red dwarfs,
the most common type of star.
At first, their fuel runs out, like I told you with the Sun.
Due to gravity, they collapse into black dwarfs, extremely dense remnants.
This process will continue for up to 100 billion years.
We will see stars disappearing from our sky, one by one.
The sky will turn into darkness.
No matter how we look with telescopes from anywhere,
we will see nothing.
Even radiation from the farthest places in the universe,
like the Big Bang’s glow, we won’t detect it.
Over time, we won’t be able to tell the universe’s age
or what happened at the beginning.
After a thousand trillion or quadrillion years, galaxies will start to break apart.
Planets will lose their orbital paths
and drift randomly through space,
marking the start of the era of galaxy death.
According to theoretical physicist Freeman Dyson,
after a quintillion years, 90 to 99% of planets will be scattered in space,
without any orbit or planetary system to belong to.
Smaller objects will drift randomly through the void.
Heavier objects will be drawn to the galaxy centers
and swallowed by black holes, making them even larger.
After that, very strange things happen.
At the end of the death of stars and galaxies,
the remaining basic elements are protons, black holes,
and star remnants turned into black dwarfs.
The proton is the core of every atom, giving matter its mass.
When a proton decays, it produces positrons and gamma-ray photons.
Until recently, the Standard Model,
the theory describing subatomic particles,
forbade proton decay under normal conditions.
A proton under normal conditions will not decay!
Unfortunately, after galaxies die, protons themselves will decay.
The assumption also says, for all protons in the universe to decay,
we need between 10^34 and 10^40 years,
that is, from 10 duodecillion to 10 quattuordecillion years.
Of course, you don’t know how many that is, and neither do I!
During that time, everything will decay:
planet remnants, stars turned into black dwarfs, even atomic dust itself.
If you think this is the end, not yet.
After proton decay, it’s the black holes’ turn,
which are dark, devouring, and expanding.
Even black holes lose mass and evaporate over time.
This is called Hawking radiation.
Black holes lose energy as very faint radiation from their event horizon.
Over time, they shrink, get smaller, and disappear completely.
For small black holes, say Earth-sized,
this takes about 10^67 years.
The largest black holes, swallowing matter at galaxy centers,
need 10^106 years to disappear,
a million googols of years.
After the last black hole dies, not much will remain in the universe.
Even dark matter will decay or already be swallowed by black holes.
All that’s left is vast empty space,
with energy evenly spread,
near absolute zero.
The universe dies.
Everything becomes dark and cold,
no vibrations, no motion, no energy.
Everything disappears.
Only random electrons and photons drift in infinite space.
In the end, the universe in our episode follows the rules of physics.
The universe is not as Aristotle imagined,
not eternal before or after us.
It appears like a living creature like us.
A child is born, grows, goes through adolescence,
and eventually weakens and dies.
We humans, every cell in our bodies is made of the universe’s elements.
Elements formed at its birth, like hydrogen and helium,
or later formed, like carbon, oxygen, and iron.
We are living witnesses to this universe.
Science can imagine its beginning and its end.
And what we experience is a cosmic death, just like our human death.
Just as the universe ends, our episode comes to an end.
Don’t forget to watch the new episodes and the old ones.
Check the sources below and subscribe if you're on YouTube.
Hope someone watching us in 10^67 or 10^106 years
can tell us if these predictions were right?
"But we will not be alive."
Speak for yourself. I am an idea, and ideas never die.
Physics never mentioned thoughts, so I am safe.
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