Hey Crazies.
There are 3 big misconceptions about the universe people still don’t get.
Let’s set the record straight!
There’s a whole playlist on cosmology, but I’m spastic sometimes, so I could believe
you might have missed them.
One!
How much bigger will I be at 80-years-old after you account for the expansion of the
universe?
Exactly the same size.
Well, maybe not exactly the same size.
Most people are shorter when they’re older because of biological changes.
But the expansion of the space has exactly zero effect on your size.
Are you saying the universe isn’t expanding inside us?
Oh, it is!
It just isn’t strong enough to stretch you.
Think of it like this.
Imagine you and the love of your life are holding hands,
but you’re each standing on your own conveyor belts that move in opposite directions.
You know, because the universe is always against you.
Anyway, the belts try to pull you apart, but they’re not strong enough to overcome the
grip you have on each other’s hands.
You stay together as the belts move beneath you.
The force from your hands holds you together.
The same kind of thing happens with space except in 3 dimensions.
Space stretches through you while you stay the same size
because there are forces between your atoms and molecules that hold you together.
They’re strong enough to overcome the expansion of space.
Solar systems, galaxies, and even clusters of galaxies are held together by gravity,
so they don’t expand either.
However!
The expansion of space is uniform throughout the universe,
but gravity gets weaker with distance.
At a sufficiently large distance, the expansion wins and can start spreading things out.
That happens between super-clusters of galaxies.
That’s clusters of clusters of galaxies!
The universe is big enough that one point of light in this image is a super-cluster
of galaxies.
Space is big.
Really big.
Two!
Why does it look like we’re the center of the universe?
Because we are the center of the observable universe.
We can’t see the whole entire universe because light doesn’t travel fast enough.
The universe might be infinite, it might be finite, but either way,
Light hasn’t had enough time to travel all the way across it,
so this is all we get to see of it.
That’s the observable universe.
That’s how far light could have possibly traveled since the big bang.
And, this is the light that’s traveled the farthest:
the Cosmic Microwave Background.
The observable universe and the entire universe are not the same thing.
Unfortunately, some people call both of these things “the universe”
and it causes a lot of confusion.
Anyway!
Since light takes the same amount of time to travel from every direction,
we can see the same distance in every direction, which makes us look like the center of the
universe.
Even though we aren’t.
Three!
How can a 3D universe be flat?
It’s not!
It’s not actually flat!
You know how words can have multiple meanings?
When we say the universe is flat, we’re not using the word in an ordinary way.
These shapes are just visual representations of math.
“Flat” just means “Zero Curvature.”
The universe doesn’t actually look like any of these shapes.
Honestly, we should probably stop using them, but people like pictures.
If you want to understand anything involving general relativity, then remember this:
The easiest way to see curvature is by drawing parallel lines.
For example, if you draw parallel lines on a flat piece of paper
those lines will stay parallel across the entire piece of paper.
If we live in a flat universe and the data suggests that we do,
then parallel lines in our universe should do the same thing.
Let’s say there are two spaceships.
Each ship plots out a course they think will be parallel to the other ship’s course.
If the universe is flat, those courses will stay parallel as the ships travel.
No matter how far they go, they’ll always be the same distance apart.
What other option is there?
Oh! Oh! I'm glad you asked!
On a sphere like the Earth, two parallel lines come closer together over time.
If the spaceships are flying in a positive curvature universe,
then their paths will come closer together over time.
On a saddle, two parallel lines spread apart over time.
If the spaceships are flying in a negative curvature universe,
then their paths will spread apart over time.
Planes, spheres, and saddles are just lower-dimensional examples of curvature.
It’s the curvature that matters, not the shape.
So I hope that clears things up!
As usual, if you have questions, please ask in the comments.
Thanks for liking and sharing this video.
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I wanted to just take a few seconds to thank thedeemon for
diligently and accurately helping me answer questions in the comments.
There’s just too many for me to answer by myself.
Thank you and thanks to everyone for watching.