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'DARK ENERGY!'
HEY I'm back again! It's time to take a deep dive into our chasm of ignorance, let me tell you a story about the Single biggest SHOCK in the History of Astronomy!
So, take a deep breath and you might wanna sit down!
LET'S DO THIS
HEY I'm back again! It's time to take a deep dive into our chasm of ignorance, let me tell you a story about the Single biggest SHOCK in the History of Astronomy!
So, take a deep breath and you might wanna sit down!
LET'S DO THIS
One of the things I love about science is that whenever we look at nature in a new way, we come up with new discoveries, like the Universe itself throws such things at us that we didn't even know to talk about in the first place, that's just what happened with DARK ENERGY!!!
Let's go back in time, the year is 1915! Albert Einstein, after wrestling with nature for 10 years published his astounding General Theory of Relativity, this is our modern understanding of Gravity & oh my gosh this theory lies at the heart of theoretical physics!
Okay, a quick note on relativity again; so imagine space itself as a big huge rubber sheet which is nice and flat in the absence of any matter or energy! Now Put a heavy mass in that fabric of space, you'll see that the mass would curve and bend that fabric of space and time!
Roll little marbles in that curved environment and they'll start to orbit around that heavy ball, that's how Gravity communicates it's influence, that's how Gravity works on the big scale!
SO MANY THINGS WERE HAPPENING AROUND THIS TIME, soon after when Einstein was done with Relativity, two physicists Georges Lemaître and Alexander Friedmann Applied this theory to the WHOLE UNIVERSE!
Now, at that time nobody even imagined that the Universe which is all there is, could be doing anything at all! It's just there, it has always existed, even Einstein was so sure about it that he claimed that the Universe itself is static and unchanging!
He thought that since the universe is static then one day all matter will eventually come closer due to gravity & it will clump up together in on itself hence he added a term in his equations to cancel that effect so that the universe could remain static,the Cosmological constant
THEN, Alexander Friedmann & Georges lemaître independently came to same conclusion after solving Einstein's equations! An expanding or contracting universe was fitting better in the theory, Not the static one, but Einstein didn't pay much attention to that
Also, around the same time! Astronomer Vesto Slipher was taking the spectra of so called 'Spiral nebulae', these were blurry patches of light in the night sky! Nobody was quite sure what were actually they were and i'll get back to that in a minute 
It took him years of observations & speculations to do this, but when he saw the spectra of these spiral nebulae he was STUNNED! He noticed that ALL THESE SPIRAL NEBULAE WERE RUSHING AWAY FROM US AT INCREDIBLE SPEEDS! ALL OF THEM!
(Their spectra was highly redshifted)
(Their spectra was highly redshifted)
People in those days thought that our galaxy is the only one here, it is the whole universe, it is the only thing to exist and these spiral nebulae were nothing but cloudy patches of light and all residing in our own galaxy, that's how egoistic and hubristic we were 
BUT!
In the 1920's Edwin Hubble, figured out a way to measure the distance of a special type of Star(cepheids) in the great spiral of Andromeda! You know what he found?
*Drum rolls*
THOSE CEPHEID STARS WERE LYING OUTSIDE OF OUR MILKY WAY GALAXY!
In the 1920's Edwin Hubble, figured out a way to measure the distance of a special type of Star(cepheids) in the great spiral of Andromeda! You know what he found?
*Drum rolls*
THOSE CEPHEID STARS WERE LYING OUTSIDE OF OUR MILKY WAY GALAXY!
Ladies and gentlemen! Your Edwin Hubble just discovered a GALAXY OUTSIDE OF OUR OWN MILKY WAY, HOLY MOLY! Andromeda galaxy is wayyyy bigger than milky way!
You guys remember those Vesto Slipher's spiral nebulae, blurry patches of light in the night sky? Hubble discovered that THOSE SPIRAL NEBULAE WERE ENTIRE FREAKING GALAXIES SITTING IN THE VOID OF SPACE, LIKE A MONSTER
"This was like discovering island universes"
"This was like discovering island universes"
Overnight our entire egoistic picture of the Milky way was thrown out of the window, the last measure of our self worth shrank to an insignificant point in this multi-billion Galactic show & the universe was much larger than anyone had ever previously imagined! 
Yes, those spiral nebulae, what we now call galaxies are moving farther way from us! THE UNIVERSE IS DEFINITELY EXPANDING, now you'd think that this expansion might be slowing down, why? Because there's so much matter in the universe, it's gravity might be stopping that expansion
Turns out that this is NOT what's happening
In 1990's 2 independent teams of astronomers were using the world's biggest telescopes to peer deep into the cosmos! They were looking for type 1a supernovae, they are so bright that you can accurately measure their distances!
In 1990's 2 independent teams of astronomers were using the world's biggest telescopes to peer deep into the cosmos! They were looking for type 1a supernovae, they are so bright that you can accurately measure their distances!
Compare their distance to Slipher's redshifts spectra and boom! You'll get the rate of expansion of the universe.
But the results they got DIDN'T MAKE SENSE! those Supernovae were fainter than expected, they were much farther away!
THE EXPANSION OF THE UNIVERSE WAS SPEEDING UP
But the results they got DIDN'T MAKE SENSE! those Supernovae were fainter than expected, they were much farther away!
THE EXPANSION OF THE UNIVERSE WAS SPEEDING UP
WHAT? THAT'S NUTS? HOW IN THE WORLD COULD IT BE POSSIBLE? We were expecting the expansion to slow down but it's speeding up omg!! It's like tossing up a coin in the air & instead of it falling down back, it shot up upwards faster & faster defying gravity!!!
The universe is not only expanding but that expansion is getting faster & faster Everyday, it's speeding up! What can possibly cause such a thing? Tbh we don't know, but whatever this thing is, it is acting like an invisible energy suffusing through the fabric of space
A mysterious pressure that is pressing against the Gravity of all matter in the universe, forcing all the galaxies of the night sky to go farther from each other every second! We call this DARK ENERGY!
Don't let the name fool you, we don't even really know if it's energy or not, it's just a term to hide our ignorance, just a placeholder name! Dark energy makes up 73% of the universe, 23% is dark matter & normal matter that is you can see, touch, taste or smell is only about 4%
We clearly have no idea about this dark energy thingy, it's one of the longest standing MYSTERIES in modern Astrophysics, maybe it needs a new uneasy marriage of General Relativity and quantum physics, or maybe something else, we don't know!
As always, keep looking up
As always, keep looking up
Oh, by the way while you finish reading this thread the universe would have expanded by trillions of kilometres ok bye
