What is gravity?
Don’t feel bad, no one else does either.
There are two ways to read that question, the first will get you answers about Newton’s Law of Universal Gravitation or even Einstein’s Theory of General Relativity. The former is fairly straightforward and understandable, the latter is the stuff doctoral theses try to understand.
But neither of those answer the question of what gravity is, they just relate to how gravity affects other things.
Now, I am no one you should be listening to when it comes to anything, so I will get all of this wrong, but when you talk to physicists, they will spend forever telling you what gravity does, pretending they are telling you what it is. Eventually they will break down and admit they don’t know. If you get a good one that admits it right away, you are in for a great conversation, grab on with both hands and enjoy the ride!
In The First Men On the Moon, H.G. Wells uses the idea of a substance that shields against gravity, much as lead shields against radiation. These shields are used to block the earth’s gravitational pull and allow the moon’s gravity to pull the spaceship up into space.
Is this pure fantasy? Of course it is! Or-not. No one really knows what gravity is, so how can they know if it can be blocked?
Physics describes four fundamental forces in our universe. These fundamental forces are Electromagnetic (light, microwaves, radio, etc.), Weak Nuclear (kind of like radioactive decay), Strong Nuclear (holds atoms together), and finally Gravitation (holds us on the planet). Interestingly, all of these are non-contact forces, meaning they act upon things at a distance -without direct contact. Unlike your brother’s fist to your face, and more like your mother’s worry/guilt complex she put on you when you left the house.
How do these things work at a distance? How does a magnet pull iron in? The quick and easy explanation is the magnetic field causes the positive and negative poles of the atoms in the iron to line up in the same directions, turning the iron into a magnet also, and the two magnets attract one another.
Great. That didn’t answer the question, did it?
What is a magnetic field? What is it made out of?
We don’t know. Nobody does.
Okay, where’s the angry physicist? Oh! There you are…yes..mmmhmm. Virtual photons, you say? Virtual particles? Uh huh. As opposed to real particles? Oh there is a difference? You don’t say? Thank you for your time, I appreciate your input. I think we all feel better now.
So what I got out of that, in case you didn’t catch it all, is they don’t know. We have fallen into the realm of quantum physics where nothing is as it seems and it is all examined, predicted, and explained with mathematics. And here is where the Uncertainty Principle comes into play. (For more on that check out my previous ravings on Schrödinger’s Cat Walks Into A Bar With Heisenberg And Steps On A Butterfly.)
We have moved into the realm of the unknown or is it the unknowable? The physicist is pretty irked at me right now, so I am moving on.
What is the big difference between those four fundamental forces? Well, obviously they all do different things, to different things. Don’t they?
Is the attraction between atoms really so different than that of a magnet and iron? Different in strength, for sure, but how much else? In distance acted? Okay. But what of the ‘force’ behind it? Pretty much described the same way -by mathematics and observation of action, not by the actual force, or substance composing the force, itself.
Some thoughts on gravity include the same idea as we just went through with magnetism, but rather than using a ‘virtual photon’ to describe the ‘thing’ the field is made of, a graviton is used instead. Unfortunately, a ‘gravity field’ is not so easy to observe as a magnetic field, and Einstein described it as not only affecting another body, but also light, the shape of space, and even time. So what is it? Well…
Why is it Electromagnetic Force and not Electric and Magnetic Forces? Because in 1864 James Maxwell Unified those theories – he showed they are different parts of the same force. Does that term sound familiar? (Unified, not force! This isn’t a Lucas Love Fest! Although I guess it could be…) Unified Theory. Those two very different things are part of the same thing!
Could anything else possibly be incorporated into the ‘unified’ theory? Yup. In 1979 the Nobel Prize in Physics was awarded for the 1973 development of the theory of the Electroweak force, showing the Electromagnetic and Weak Forces are different parts of the same force. Did that sound familiar?
Einstein had already tried to combine his Theory of General Relativity with Electromagnetism, calling it a search for a Unified Field Theory, but he was not successful.
Is gravity merely yet another part of the same force? I don’t know. Einstein seemed to think so, and who am I to argue?
Supposedly a strong enough magnet can affect anything, to some degree, however negligible, however you can’t bend light with a magnet, as light has no charge (positive or negative). But gravity certainly can bend light. Just think black hole. But how does it pull the light in? Mass. Light has mass. And the theory of relativity states that as an object approaches the speed of light, its mass increases towards the infinite. So light traveling at light speed has infinite mass? Right? Obviously not.
We just don’t really know what light is either. We get around this by saying light is both a particle and a wave. Or rather it has the properties of both. Or actually, sometimes one and sometimes the other. We don’t really know, so we have built mathematical formulas to describe and predict.
So we have forces that we don’t really understand acting upon things we don’t really know what are. Great! Pat your local physicist on the back reassuringly next chance you get, it is a stressful headache of a job they have, especially when running into people like me.
In fact, light can be bent with a magnet. Depending on the medium it is in, but then you are actually effecting change in the medium, which affects the light. Is this how gravity works? by effecting change in the medium (space) and thereby affecting the things within?
Unfortunately, none of this answers the original question. What is gravity? We don’t know.
H.G. Wells might not have been too far off with the idea of ‘blocking’ gravity waves. We already know how to block electromagnetic fields (it’s not easy, but it can be done), We know how to make them (well enough to contain anti-matter) and we (think we) know that most of the fundamental forces in our universe are all different aspects of the same force, and we are trying to prove they are all part of the same force (even if we don’t know what that force is), so there is no reason not to believe, one day, we will actually understand how they all work.
And if we do that, we may figure out what gravity is. And if we do that, we may figure out how to manipulate, control, use, and create it. And don’t forget, Einstein thought it could manipulate light, space, and time.
Don’t let anyone tell you space and time travel is impossible. Chances are they don’t even know what it is…
Not to mention we haven’t even figured out what dark matter is yet! Oh what a wonderful universe we live in! Mystery abounds!
* A note from Sam: I was fortunate enough to have this comment left. It was written by a physics professor, and I think it definitely adds fuel to the fire when you are feeding your brain the good stuff.
All interesting, and fairly accurate, except… The question itself. You ask as if gravity is a “thing.” You know, as in “A noun is a person, place, or thing.” Something concrete, something you can hold and touch and bounce off your brother’s head. How would you answer, “What is justice?” or “What is truth?” Justice, truth, gravity, charge, they’re all properties of something else. They’re concepts. Ideas. Ways or methods we have of describing actions in the universe. It’s hard to describe something that you can’t bounce off your brother’s head. Describe the wind. You can’t see it. You can experience it. And actually you don’t feel it. You feel the results of the wind. Simple answer it is the movement of the air. More complex answer, it is waves of pressure moving through the atmosphere. Gravity is the effects, the results, the force of matter. Which is related to energy. Which gives rise to electromagnetic waves. Electricity and magnetism both arise from charge, another property of matter. And we arrive back at the holy grail of physics. The Unified Theory Of Everything. How does it all fit together? I have my own theory, doesn’t everyone.