Gravity got you down?

(Oh yeah, this one's going to be fun...)

Well fret no more. I'm here to tell you that gravity doesn't exist!

There, feel better? No? Still tethered to your planet, at the bottom of a gravity well hundreds of miles deep (unless I have readers on the space station)?

Okay, then, let's back up a little. Gravity exists, but no one knows what it is or why.  If you go by the old rule of "if you can't define it's limits, it doesn't exist", we could argue that gravity doesn't.  (Hrm, still not floating...)

Gravity's a bit like time in that respect. We have it, we can measure it, we can even use it, but we have no way of describing it fundamentally. We have no real notion of what is taking place, other than a grade-school concept of "the attraction between two bodies".

First, let's give what we *do* know: gravity seems to be an attractive force. This doesn't mean it's pretty: I mean that it brings two objects together. The amount of gravity any one object "inflicts" on any other can be calculated based on their relative masses and separation distances. We also know that gravity is indistinguishable from acceleration.

That's pretty much it. We don't know how it works: most interactions between objects require a medium of interaction, and despite searches for the almighty graviton, no such particle has ever been detected. Einstein got around this by stating that the "medium" was spacetime itself, and while it's a neat little answer, it's a bit too neat - and too black-boxy - for most modern physicists. We also haven't really been able to determine whether gravity operates within discreet units like other forces; this is important, because discretion would imply a quantum nature whereas a lack of discretion would seem to imply - well, something else. We also know that gravity is related to mass, but we don't know *why* it's related to mass.

We also have to reconsider the whole "attraction between two bodies" concept, not because it's wrong but because it's a simple statement that really doesn't make its full impact apparent. When we say "between two bodies", we really mean "between two things that exist" - again, since gravity is related to mass, and mass is interchangeable with energy, and everything in the universe has mass and/or energy, everything inflicts some gravity. Also, everything is affected by gravity. So, our little "attraction between two bodies" really means "attraction between everything in the universe and everything in the universe". That's right, gravity is trying to pull together everything in the universe; most of the time the force is too small to be measured or effective, but it's always there (and yes, while this means you're technically being drawn however slightly towards that bag of potato chips, it doesn't explain why you had to eat the whole bag in one sitting).

There is also, noteably, no such thing as "anti-gravity", which is one more trait gravity shares with time: whereas most forces or actions have an opposition, gravity (like time) does not. Even antiparticles - which are just mass like anything else - are attracted to each other and to standard particles. We've never encountered anything that has a reverse gravitational effect - basically, a repulsion instead of an attraction - that isn't based on some other force.

That's not to say a lot of people aren't trying to solve the unknowns. Quantum gravity, quantum loop gravity, holographic theory - there are a lot of approaches to answering the big question of how gravity works. There are even a few that state that gravity, like centrifugal force, "doesn't really exist" and is instead just something else being (mis)interpreted as a separate force - usually acceleration (again!) or entropy.

We'll have to see where it all goes. Since much of our future scientific and cultural expression will rely on overcoming gravity efficiently (at least locally), I expect this area of study to be one of the biggest for the next 50-100 years or until a major paradigm shift takes place.

Until then, it helps to realize that even something as familiar as gravity isn't all that familiar and remember all the good things that gravity permits - like a nice day in the waves at the beach.


david said...

its been my experience that gravity always wins....

- cheers.... d

AndyDrewby said...

Gravity is a habit that is hard to shake off.
Terry Pratchett, "Small Gods"
I have to say I thoroughly agree with him.