Gravity affects many things. How plants grow. How fire flickers. Even how our clocks tick in our kitchens and on our phones. We know what gravity does, but we do not know what gravity is. A mystery that our bodies, and all bodies, possess.
So let me catch you up a bit for those who may not necessarily know about one of the (relatively) weakest forces in our universe.
There is a story of a man under a tree and a piece of fruit with great aim and impeccable timing. The story goes that Sir Isaac Newton sat under an apple tree. One day an apple broke free of its branch and bounced on the head of the unsuspecting scientist. From that interaction Newton discovered gravity and the rest is history.
Like many stories of discoveries this one isn’t true. Newton did mathematically show the relationship that gravity, matter, and distance have, sure. But it was not because of a bit of fruit that chanced a landing upon his head. Just like the story of Benjamin Franklin using a key and a kite to see electricity or Thomas Edison creating the lightbulb, this story is missing a plethora of details.
Long ago we did not have calculus. In fact, before calculus was invented many people believed reality was not real because they could not calculate the area under a curved graph of motion. Sound weird? It is. Imagine not being able to calculate the area of a bell curve, looking up from the paper, and then say, “Well. I guess I’m not real then.”
Newton created calculus to be able to show mathematical concepts and area under a curve of a graph. From there he gave the relationship that we see with mass, distance, and gravity.
Gravity is… weird to say the least. It cannot be observed on the atomic level because, relatively speaking, gravity is an extremely weak force. Take a magnet above something metal. That metal object will go against gravity and attach itself to the magnet. A small neodymium magnet (the size of an eraser) can exert more force than an entire planet can with gravity.
But gravity is not without its own special effects. Space and time are warped by gravity. But what has gravity? And what is space time? Let me answer that.
First. Anything that is made up of atoms and quarks essentially has a mass. An ant that is relatively small to us has a force of gravity. Rocks have gravity. Dogs, cats, and all living organisms have gravity.
You have a gravitational field that you create because you are made of stuff.
You have mass.
Keep this in mind as I come back to it later.
Now. Space-time is often referenced as a sheet of rubber. It serves its purpose well in this form. Now an object, let’s say a planet is placed on that rubber sheet and what happens? The rubber stretches downward and you get a “dent” in space and time.
You walk amongst that fabric daily. And because you have gravity you also put a dent (however very small relative to planets) in space-time. But your gravitational field is still there.
So what does gravity do to time? It slows it down. On average your feet will be 90 billionths of a second younger than your head by the time you reach 70 years of age. You see, the more gravity that acts on an object the slower its clock goes in relation to other objects that experience less gravity. But your feet are attached to your body. Why doesn’t your whole body stay the same? And that is where Sir Isaac Newton comes into play.
Here is an equation for you.
G x (Mass of object 1 x Mass of Object 2) / distance between both objects squared.
Or
G(m1 x m2) / r^2
This equation is Newtons own. This equation shows the relationships between mass, gravity, and distance. So let’s think about it.
What is closer to the Earth, your feet or your head? Because your feet are closer to the Earth the effects of Earths gravity is greater. Thus, the internal clock of your feet runs slower than your head. Albeit a very small, almost negligible difference.
But think about satellites. Satellites are much farther away from the center of Earth (where distance is measured from the center of a body of mass). Does this effect it more?
Yes.
Satellites must be calibrated for how high they are because their clocks run “faster” in relation to the clocks on the surface. Astronauts in the International Space Station will age a second older in space than they would have stayed on Earth!
And you see gravity has infinite range. Another aspect that you need to remember. In the equation above you can put trillions of kilometers. While the overall force will get smaller and smaller, it never will be zero.
And that’s what I want to talk about now. We have discussed that you are mass and therefore have gravity. All things with mass have gravity. And gravity has an infinite range. We also have an equation for this.
The big letter G in the equation is known as the gravitational constant which equals 6.67 x 10^-11. Or, written out that would be:
.0000000000667
Very small number, huh. This is the amount of gravity that a kilogram has.
Now how much mass do you have? We need this in kilograms. 1 kilogram is basically equal to 2.2 pounds. So if you way 220 pounds, divide that by 2.2 and you get 100 kilograms. Figure out your weight now in kilograms.
Next I want you to think of someone you hold dear. How much do they weigh? Do the same thing to them. Estimate how much mass they have in kilograms.
Good! Now this is where things get tricky. How far away are they? Let’s say they are 600 miles. Well we need kilometers. How do you get kilometers from miles? Divide miles by 0.6. 600 ÷ .6 = 1,000 kilometers.
Now we are not quite done. In order to get the unit we need we need to convert kilometers to meters. Move the decimal over three places to the right. Thus 1,000 kilometers becomes 1,000,000 meters. Make sense?
So you have G, your mass, a loved ones mass, and distance. Now we can put that into Newtons equation.
Multiply your mass in kilograms by your loved ones mass in kilograms. Now multiply that number by 6.67×10^-11 or .0000000000667.
Now divide that new number by your distance squared. If your distance was 100 kilometers that is 100 x 100. If it was 1,000,000 then it is 1,000,000 x 1,000,000.
To recap divide your first number (two masses times G) by your distance squared (r^2).
You should now have a very, very….. very small number.
But it’s not zero.
What is this small number? So small that it might as well be nothing?
That is the force you feel from your loved one. And the force they feel from you. You see, no matter how far apart you are from the people you love, you still “feel them.” This invisible, delicate, imperceptible spider’s thread that connects them to you and vice versa.
Even on the farthest reaches of our universe the atoms that are out there feel your presence. There is nothing in this universe that doesn’t feel you.
While the force is so small it can be stated as negligible, one thing remains the same. The mathematical number isn’t zero. And because of that mathematical fact every person, every planet, every star, and every atom has an invisible, delicate thread connected from it to you.
Throughout the universe, everything feels your presence
Yelling at Space 