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So let’s say you want to lose weight.
You have some options.
You could join Weight Watchers, you could stop eating carbs, you could train for a marathon,
you could cut off an appendage, or you could just move to the Hudson Bay region of Canada.
Why?
Because the Hudson Bay is missing gravity.
If you weigh 200 kilo-pounds normally, by moving to Hudson Bay, you will, in an instant,
automatically weigh 0.01 pounds or kilograms less—and you don’t even have to stop eating
pasta.
You see, back in the 1960s, scientists were mapping the Earth’s global gravitational
fields to make a thing that looks like this, and, if you look here, you’ll notice that’s
it’s a different color from the not-here parts.
This is Canada’s Hudson Bay and this means that there is literally less gravity here
than everywhere else on earth.
Based off science stuff, this should not have been the case.
The scientists looked everywhere for the missing gravity—the cupboard, their pants pockets,
all the usual places—but they couldn’t find it anywhere.
Over time, two major theories have developed to try to solve the mystery of Hudson Bay’s
missing gravity.
But before we go into them, a quick primer on how gravity works.
Gravity, of course, was a 2006 song written by John Mayer as the third single off his
album Continuum.
It works by following a basic chord progression in the key of C and combining that with lyrics
that are just vague enough to mean whatever you want them—oh you know what, this is
the wrong gravity.
I should really stop having the AI write my scripts.
Gravity is, put as simply as possible, an attraction that relies on mass and distance
and then there’s the Higgs-boson field and Higgs-boson particles and Higgs-boson…bosenhiggs
or whatever…you know what, for the purposes of this video, we’re going to oversimplify—
not because I don’t understand it, or anything, but because I don’t wanna explain.
The basic idea you need to understand is that gravity is proportional to mass and to distance.
The more mass, the more gravity.
The more distance, the less gravity.
The reason that if you slip on a banana peel, you fall on the ground, is that you are pulled
down to earth by the Earth’s mass.
If the earth was twice as massive, assuming it was the same size, then we would experience
twice as much gravity.
Basically, the more mass below you, the more gravity you experience, but the further you
are from something, the less its gravity pulls you.
That’s why, if you get far enough from the earth, and you slip on a banana peel, you
will no longer be pulled down to the ground, you’ll just float around in space which
is way cooler than falling down on earth and then having all the kids in the 7th grade
laugh at you and then getting called banana man Sam for the rest of your life.
Not that that ever happened to me.
So, here are the two theories on why the Hudson Bay is missing gravity.
The first has to do with what’s called convection.
Basically, something like 60ish miles or 100ish kilometers beneath the ground is the earth’s
mantle and this mantle is full of super-hot magma.
But the magma doesn’t stay still—it swirls and whirls and twirls and churls and flurls.
The reason that magma is in motion is because of convection.
There’s heat coming from the Earth’s core and that heats up magma at the bottom.
That magma then expands, because it’s hot.
Once it’s expanded, it’s lighter, so it floats up and when it floats up, it pushes
colder magma down.
Eventually that magma heats up, and does the same thing, and the cycle repeats over and
over and over.
So it creates a current, that looks like this, that goes around and around and around like
a giant, terrifying, hot magma merry-go-round.
The convection current can pull down the Earth’s tectonic plates.
If the tectonic plates are pulled down in an area, like Hudson Bay, there’s less mass
below you, and therefore less gravity.
The second theory has to do with something called the Laurentide Ice Sheet.
Back in the Ice Age, there was this giant sheet of ice that covered most of where Canada
and the northern US are now.
It was like an ice skating rink, except 2.5 million square miles across, and about 2 miles
or 3.2 kilometers thick, so actually, not like an ice skating rink at all, and in two
places in Hudson Bay, it was even thicker—closer to 2.3 miles or 3.7 kilometers.
About 10,000 years ago, the ice melted, and it left behind a massive dent in the earth.
That dent pushed a bunch of earth to the sides.
So now, if you stand in that dent, there’s less mass below you.
And like we said before—less mass equals less gravity.
The earth is slowly rebounding from the dent, but at a rate of half an inch or one and a
quarter centimeters a year, so it’s going to take a while for things to get back to
normal, and therefore until then, there’s less gravity in the area.
Now it’s important to note that when you’re in the dent, you’re also closer to the center
of the Earth’s gravity, which makes gravity stronger.
After all, the closer you are to something, the stronger the gravity, but in this theory,
the loss of gravity caused by the reduction in mass below you is more than the gain in
gravity resulting from being closer to the Earth’ center.
So which theory is right?
Well, as a certain taco ad once wisely said: “Por qué no los dos?”
As it turns out, both theories were right.
Geophysicists at the Harvard-Smithsonian Center for Astrophysics satellite data from the Gravity
Recovery and Climate Experiment, or GRACE, were finally able to calculate that that rebounding
ice sheet and the swirling magma are each causing about half of the missing gravity,
and so, the mystery solved.
And just to think, gravity might have gotten away with it if it weren’t for those pesky
geophysicists.
Now, there is one other type of gravity that I’m not sure you understand—the gravity
of this situation.
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