A Few Thoughts about Gravity.

Gravity; it’s what holds you firmly to Terra Firma. If I ask you what holds you firmly to Terra Firma you’d answer “gravity”. But if then asked to explain exactly what it is and how it works you’d be stumped. Giving that the Newtonian equations makes predictions but doesn’t give explanations.

However, there are two explanations for gravity if I read the textbooks correctly.

Gravity Is Just Another Force: Firstly, there are in this worldview four fundamental forces: the electromagnetic force, the strong and weak nuclear forces, and gravity. Forces have accompanying elementary particles witch convey the force. In the case of the electromagnetic force, the particle is the photon. The particle associated with gravity has been dubbed the graviton. Unfortunately, it has never (to date) been detected. That aside, the graviton is still considered to be an essential part of the Standard Model of Particle Physics. Now the central issue here is try as they might, physicists cannot unify the four forces into one whole, called a Theory of Everything or TOE [#]. Since everything should be related to everything else, gravity should be, if not a brother or sister to the other three force-related siblings, at least a kissing cousin. Alas, it’s an unrelated hermit that wants no ancestry with the other three.

Gravity Is Just the Geometry of Space-Time: The second is that mass ‘tells’ space-time how to warp, and warped space-time ‘tells’ mass how to move – seemingly experimentally verified more than several times over. The movement of mass in warped space-time is what we interpret as the ‘force of gravity’, but gravity is actually the actions of mass moving in space-time geometry. If gravity is just geometry and mass deviates from the straight and narrow path because lots of other mass has warped space-time from the flatland Great Plains to the peaks and valleys of the space-time Rockies, then there’s no apparent need or reason that I can see to unify gravity with the other forces and their particles. There is no graviton. If there is no causality link with the other three (quantum level) forces, there’s no need for a TOE. There’s no need to reconcile the 98 pound of weakling gravity with the Atlas physiques of electromagnetism, etc.

Gravity is highly anomalous. One mystery is why gravity is so absolutely weak when compared to the other fundamental forces. Apart from the fact that gravity is the 98 pound weakling of all the forces (you can pull a paperclip up into the air with just a tiny magnet even though the entire Planet Earth’s gravity is tugging back); and that the graviton hasn’t been spotted anywhere, anytime, anyhow; and that TOE is a no-go; but lastly there are those cosmic twin anomalies, Dark Matter and Dark Energy.

We can’t see, or even detect directly, 96% of the Universe! We have no idea what 96% of the Universe is composed of. If that’s not anomalous, I don’t know what is. Both however have revealed themselves indirectly via their gravity (in the case of Dark Matter) or their antigravity (in the case of Dark Energy). Some of that ‘missing’ part of the Universe is matter of unknown composition, but like all good matter, has gravity. It’s the gravitational effect on matter we can see that gives the game away. Some more (way more) of that ‘missing’ part of the cosmos is Dark Energy which is that unknown stuff which is accelerating the expansion rate of the Universe and if that’s not anomalous, I don’t know what is since by rights the expansion rate of the Universe should be decelerating under the force of gravity. The fact that it’s accelerating suggests that Dark Energy is a form of antigravity, a repulsive force driving things apart at ever faster and faster rates. Though antigravity is really outside the accepted realm of physics (though not sci-fi), there is a symmetrical parallel with the electromagnetic force, which is both attractive like gravity (north pole to south pole) and repulsive (north pole to north pole, or south pole to south pole).

So, gravitational anomalies abound.

[#] The exception is that the highly theoretical (read purely mathematical) String Theory, Superstring Theory or M-Theory can produce a TOE. The downside is that it takes a whole potful of highly theoretical (read purely mathematical) extra dimensions of which we have no awareness of and can’t (yet) detect. That’s just a bit too ad hoc for me, though many a theoretical physicist goes to sleep by counting their strings instead of their sheep.