Gravity

[Cmitchell]

Hi Folks

Can anyone tell me in plain English how gravity works?

Many thanks in advance

Kindest regards, Mitchell

[magicdice]

umm, we don't really know to be honest...

essentially, there's a force that means that all masses are attracted to each other. of course, it's quite a weak force and so only really noticeable when there are very massive bodies involved. what gravity does do is keep us all together (as in, stop our internal organs floating around and keep our feet on the earth) and also means that planets can orbit each other.

[Dave.B]

There are only theories about how gravity works. Basically, it's a very weak force between two (or more) objects that varies according to their mass.

As said above, it only really affects massive bodies (i.e. planets and things), although what you feel when you are sitting on your nice comfy chair is the force of the Earth pushing up against you due to your mutual gravitational actraction - because it is so very massive and you are very close to it.

The current fashion seems to be to explain gravity with the hypothetical 'graviton' - a particular flavour of force-carrying particle that falls under the "Boson" category.

However, as yet, there is no proof of the graviton's existence, much to the chagrin of modern physicists.
Explaining and proving the graviton's existence would fulfill Einstein's dream of a Grand Unified Theory (GUT) - which so far proves that 3 of the 4 fundemental physical forces are actually pretty much the same thing (the 3 are: Strong Nuclear force, Weak Nuclear Force and Electromagnetic force; Gravity being the fourth, troublesome force).

[thikasabrik]

Air has a weight (feel the difference between a full scuba tank and an empty one). The atmosphere presses down on us and  the force it exerts is 1kg per cm2. (Imagine a tiny cube measuring 1 cm square and imagine a bag of sugar pressing down on it). That's the pressure the atmosphere exerts on us - imagine how many square centimetres there are on our bodies. That's why we don't all float away. This is a bit of a simplified explanation but I hope it's OK for you.

[Dave.B]

No offence to Thikasabrik, but that's completely wrong.

Think about Neil Armstrong standing on the Moon. He didn't float away, and there is no atmosphere on the Moon.

The reason he didn't float away was because his body and the moon were mutually attracted to each other - with a force one sixth of that we experience on Earth. That's because the Moon is one sixth of the mass of the Earth. It's got nothing to do with the weight of air above us.

[rojash]

What's more thikasabrik, when you talk about the weight of air pressing down, you are actually talking about the gravitational attraction between the earth and the mass of the air.

[slimfandango]

Isn't there a perspective on it which explains it in terms of the lattice of space/time? If you think of the fabric of spacetime as a big rubber sheet, then having an object on the fabric causes a distortion on the fabric. Just like placing a ball bearing on your thin rubber sheet. This causes a distortion in the spacetime fabric (actually propagated in 'waves') which obviously has an effect on the way other objects then behave in their locally modified spacetime. In extreme situations, you have a huge local mass in a neglibible space (eg blackholes) it's like having a very very heavy but small ballbearing on your sheet. It doesn't affect much of the fabric, but it does drag it down an awfully long way, and other objects in the vicinity appear to vanish in its locale.

I love this quote from MIT Professor Alan Guth "Space tells matter how to move. Matter tells space how to curve."

[Sequin]

Very simple - Gravity sucks!

[Bob A Job]

OK... Imagine this

Far out in space, away from any other forces and in a vacuum (no air present) a single rock will not move in any direction. if two rocks are near each other they will move towards each other. this is because:-

Matter (the rock) bends the universe around it. hard to imagine but it does, picture a sheet of cling film spread out in mid air, now place two golf balls on it and they stretch the cling film making it curve and the two balls move towards each other.

The hard part is picturing the idea in three dimensions.

Matter bends spacetime, the larger the matter the larger the curve... the stronger the pull.

We can never truly understand the universe, in the same way a sheet of paper can never understand a sphere.

There is not a 4 dimensional solution to a 5 dimensional problem, simple mathamatics.