Space Travel - Gravity

Everyone knows what gravity is, don't they? It keeps us grounded right? But what exactly is it? It is listed as one of the four fundamental forces of nature along with electromagnetism and the weak and strong nuclear forces. But is it really a force?

If you ask most people they would say yes. They would claim it is an attractive force that pulls you to an object of mass. But is it an attractive force? Does gravity somehow act like a magnet pulling other objects of mass towards it? If it is an attractive force, why doesn't the earth pull the moon into itself and the two collide? Why does the moon just orbit us and not come in contact like we do?

Well, let's look at it and you decide what it is. Gravity manifests itself by warping the space-time continuum (whatever that is). It causes depressions in the fabric of space (if that even exists).

A common way gravity is explained is by the trampoline example. If you place a bowling ball in the middle of a trampoline it depresses it. The bowling ball is the earth and the trampoline the "fabric" of space-time. Now, envision rolling a marble around the circular depression the bowling ball creates. The angular momentum would continue the circular or orbital path of the marble. But eventually the marble loses its angular momentum and "crashes" into the bowling ball, right?

I could discuss Kepler's laws here but that would simply confuse the matter. I never thought laws were all that interesting anyway. Theories are what interest me as they stand on the precipice of new knowledge. Theories unfold new adventures and stories whereas laws are simply the termination of old knowledge.

Well, why doesn't the moon do the same thing with the earth as the marble on the trampoline? Why doesn't it lose its angular momentum and come crashing down? Because of friction, of course. If that marble didn't experience friction against the trampoline fabric and the earth's atmosphere, it would continue on a circular or orbital path inside the well indefinitely.

The moon does not experience these frictional forces (let's ignore tidal acceleration for now). So it continues in its orbit within the "well" the earth creates in space-time. So now you can sleep better tonight knowing the moon won't come crashing down on your bed!

So, what do you think? Is gravity actually a force? I guess in the sense it warps space-time it is. But not in the sense of some invisible attractive force that pulls us into it. When we "feel" gravity it is in the form of acceleration. That's how it is measured, 9.8 m/s2 as any engineer has memorized. That means for every second an object is moving (falling in this case), its velocity increases by 9.8 meters per second.

Einstein realized that's exactly what gravity is. It is indistinguishable from ordinary acceleration. The "force" of gravity you feel in the form of your mass "pushing" against the earth, is no different than that force you feel when you step on the accelerator of your car and your back pushes against the car seat. The forces are the same, just of different magnitude.

But gravity is not really pulling on you. You are simply free falling into the "well" of space-time the earth's mass has created. You would continue down this well to the center of the earth if the surface of the earth did not prevent you. In fact, and this a mind blower, if you could indeed fall to the center of the earth, where the mass of the earth is equal on all sides of you, then you would feel no gravity at all. You would simply free float as if you're in space. Crazy, huh? I'd like to try that.

Wouldn't it be great if you could buy the center of the earth's real estate and then collect for "gravity-free" experiences? Ok, let's just forget about all the logistics stuff.

Gravity is really still a mystery. Little is understood of it despite Einstein's great discoveries. The warping of space-time is fascinating to me. But we haven't looked at the more interesting aspect of it. We looked at the warping of space, but what about time? Follow me in this journey next week and we'll look at that too.....