# The Naked Scientists Forum

### Author Topic: Mysterious Gravity  (Read 2550 times)

#### latebind

• Sr. Member
• Posts: 248
• Hello World
##### Mysterious Gravity
« on: 21/03/2009 19:47:02 »
Gravity is one of those forces that is just downright mysterious.

One thing I find fascinating is the fact that gravity can move massive objects together, converting something into kinetic energy, but what is it converting?

We know that E=MC2, so we also know that matter and energy are equivalent,so I would assume there is matter being converted into energy somewhere? So where does the matter come from to move objects together?

If I understand general relativity correctly, it has an explanation for this which further adds to its mystery. Einstein said that the objects are'nt actually moving, its just that the space between them is being distorted by their mass. I wonder if this is really true, because an apple that falls has enough 'energy' to split when it hits the ground, if it was just a distortion of spacetime then surely the apple would just land softly with no energy involved in its motion??

I think what this really boils down to is whether an object moving under gravitational force is really moving or not? And if they are not moving(IE: space distortion) then why do they experience newton's third law upon impact?

« Last Edit: 21/03/2009 19:54:12 by latebind »

#### LeeE

• Neilep Level Member
• Posts: 3382
##### Mysterious Gravity
« Reply #1 on: 21/03/2009 21:36:56 »
If it were just a case of the apple existing in curved space, why should it move at all?  The answer seems to be that in curved space you've also got curved time and this means that any object that has non-zero size will be existing within a temporal gradient as well as within a spatial gradient.

Now the consequence of this, as I understand it, is that unless the temperature of the apple is at absolute zero K the atoms that the apple is made out of will not be stationary within the apple but will be vibrating, and this will give them a frequency associated energy.  However, because the atoms and their sub-atomic particles appear to occupy a volume of space there will be an energy gradient across them and this means that the energy at one side of a particle won't equal the energy at the other side.  It's in an effort then, to reconcile this entropic difference in energy across itself, and at a sub-atomic level, of all the particles that make the apple, that the apple moves down the gradient.

This explanation of gravity seems to imply that anything cooled to absolute zero (which is impossible) would be weightless, as would anything with zero length in the direction of the gradient.

• Sr. Member
• Posts: 112
##### Mysterious Gravity
« Reply #2 on: 22/03/2009 17:37:12 »
Quote
We know that E=MC2, so we also know that matter and energy are equivalent,so I would assume there is matter being converted into energy somewhere? So where does the matter come from to move objects together?
I think that statement is very mislead. That formula applies only when you are converting energy to matter and visa versa, but doesn't mean that whenever energy is being used up then matter is being created or anything of that nature. Different forms of energy are very different from each other. The energy you are talking about is radiation energy and is very different from kinetic energy.

#### latebind

• Sr. Member
• Posts: 248
• Hello World
##### Mysterious Gravity
« Reply #3 on: 22/03/2009 19:49:04 »
I think that statement is very mislead. That formula applies only when you are converting energy to matter and visa versa, but doesn't mean that whenever energy is being used up then matter is being created or anything of that nature. Different forms of energy are very different from each other. The energy you are talking about is radiation energy and is very different from kinetic energy.

Fair enough, I acknowledge your point.

Although I am yet to see energy that comes from nowhere.

We all know nothing is for free, and energy included, wrong or right?

So let me modify my question.
Regardless of energy type,  where does the energy for gravity come from?

« Last Edit: 22/03/2009 19:50:50 by latebind »

#### lyner

• Guest
##### Mysterious Gravity
« Reply #4 on: 23/03/2009 19:22:52 »
The (potential) energy is there by virtue of the positions of the two objects.
I suppose you could say that the potential energy is there because they have moved apart as a result of the big bang. So the potential gravitational energy can be looked upon as having come from the BB originally.

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##### Mysterious Gravity
« Reply #4 on: 23/03/2009 19:22:52 »