Registered User regular
edited June 2009
Ok here goes:

I know that energy cannot be created or destroyed, and that it is only transferred from one state to another. Where, then, does the energy needed for gravity come from? I mean, I'm assuming that energy is needed to hold all of us in place, yeah?

Thanks.

DarwinsFavoriteTortoise on

Posts

• Registered User regular
edited June 2009
Gravity is not an energy form to start with. It is the basis for potential energy (e=mgh) that might be what you're looking for.

Gravity is also something that we cannot explain yet. Matter just attracts other matter for some reason. There are some speculations with gluons and whatnot but nothing that explains why. It's more like models to calculate it, not explain it.

Gravity, like, just exists, man.

Movitz on
• Registered User regular
edited June 2009
Current Talk about gravity uses General Relativity.

When Einstein was writing down his theory he guessed an equation of the form "geometry=matter", and ended up with http://bit.ly/FieldEquations

Which says that the presence of matter in space causes space to curve, and that curving tells the matter how to move. The more matter, the more curving, which we interpret as gravity. So the more curving, the more gravity.

So I would argue the energy due to gravity comes from the energy contained in masses.

Fuzzywhale on
• Registered User regular
edited June 2009
Fuzzywhale wrote: »
Which says that the presence of matter in space causes space to curve, and that curving tells the matter how to move. The more matter, the more curving, which we interpret as gravity. So the more curving, the more gravity.

So I would argue the energy due to gravity comes from the energy contained in masses.

The whole curvature thingymajigger isn't really an explanation, it's a theory that makes some calculations possible.

And I disagree that gravity=energy. If you "make" energy by dropping a ball, it's because the carbs from your ham sandwich lunch allows you to place the ball in a position to fall. It's more like you=energy.

So the answer to the question from the OP "Where, then, does the energy needed for gravity come from?" would be "the ham sandwich"

....sorta

Movitz on
• Registered User regular
edited June 2009
I thought this was one of the big questions they think the LHC and CERN can actually provide an answer for, the hunt for the graviton and such?

dispatch.o on
• Registered User regular
edited June 2009
dispatch.o wrote: »
I thought this was one of the big questions they think the LHC and CERN can actually provide an answer for, the hunt for the graviton and such?

Yeah people are excited because the LHC is meant to uncover 'physics beyond the standard model'. If we start to see things like supersymmetric partners and such, that would be really great. It would also be mind blowing if we didn't see anything new...

Fuzzywhale on
• Registered User regular
edited June 2009
The whole curvature thingymajigger isn't really an explanation, it's a theory that makes some calculations possible.

Why isnt general relativity an explanation? It is saying "Gravity is in fact a geometric effect and here is why".
Granted it is only relevant on astronomical scales, and is definitely not the final answer, But right now there is no nice theory of quantum gravity.

Fuzzywhale on
• Registered User regular
edited June 2009
Fuzzywhale wrote: »
The whole curvature thingymajigger isn't really an explanation, it's a theory that makes some calculations possible.

Why isnt general relativity an explanation? It is saying "Gravity is in fact a geometric effect and here is why".
Granted it is only relevant on astronomical scales, and is definitely not the final answer, But right now there is no nice theory of quantum gravity.

It doesn't say "Gravity is in fact a geometric effect and here is why". That's just the way it's simplified to make nice pictures, but that's not the point.

We're kind of heading into semantics here, which is almost always boils down to personal opinion. But for me an explanation is when we know why something happens. We don't know why gravity happens or how, that is sort of the end point of human knowledge.

Movitz on
• Registered User regular
edited June 2009
I've always found that one of the weirdest things on gravity is that when you drop something and it falls to earth, that body falling to earth is exerting an equal and opposite gravitational force on the earth. You just don't notice the earth moving towards the object because of the difference in scale.

At least, I think that's how it works.

RUNN1NGMAN on
• Registered User regular
edited June 2009
Yup.

For a science project waaaaay back I calculated the amount of dropped pencils it would take to move the earth 1 meter. Turns out the correct amount was "many"

Movitz on
• Registered User regular
edited June 2009
I would suggest that the basic problem here is that the OP doesn't understand enough about what gravity, energy and force actually is.

I could suggests remediating to a high school physics textbook first, followed by something like "Relativity Simply Explained", which I very much enjoyed, and then on to things like "Gravity's Arc: The Story of Gravity from Aristotle to Einstein and Beyond"

NotASenator on
• Registered User regular
edited June 2009
Ok here goes:

I know that energy cannot be created or destroyed, and that it is only transferred from one state to another. Where, then, does the energy needed for gravity come from? I mean, I'm assuming that energy is needed to hold all of us in place, yeah?

Thanks.

It's closer to think of gravity as a spring. If you think of the Earth's surface as the neutral point of the spring, where it's not extended or contracted, no energy is required to keep us at that point. However, it takes energy to move us from the neutral point of the spring. This energy goes into the spring and is used to pull us back to the neutral position.

Of course, the actual neutral position is at the center of the Earth, but that makes my explanation a little harder to write :P

Klorgnum on