Since gravity is energy, and energy is related to mass, and all objects release gravity "waves", then shouldn't the mass of these objects decrease over time?

This is partly correct, though you must be careful about what is meant by 'mass'.

Consider a universe containing two stars in orbit. As they orbit, they emit gravitational waves and lose energy (and hence 'mass').

If you take a third 'test' mass far away, you can measure it's gravitational acceleration towards the binary pair, from a fixed distance away from the center of mass of the binary pair.

Over time, the gravitational acceleration of the test mass will DECREASE. This is because the binary star pair is losing energy (and hence mass) to gravitational radiation.

But the rate of energy loss from most objects is far to small to ever be observable.

Aye, we are, a bit, although how many 'right paths' can there be? :) Sorry if I've been intruding, Guido.

Not a problem. After quantum mechanics was mentioned it went over my head so now I'm just reading it to try and learn something new.
But I still don't understand how a stationary object can create an energy source (gravity) out of nothing. So if we can make a contraption that can harness this energy, then we would have an endless energy supply... which doesn't jive with Newton.

Already being done with hydro-electric power stations. Of course it is not a truly endless energy supply because the Sun provides the energy to evaporate water which then falls as rain at some higher elevation.
None of this implies energy is being created. The energy is changing form. One example would be an old fashion grandfather clock. You use a key or crank to winch up a weight, which is the same as saying you have increased it potential energy. As the weight falls the extra potential energy is then release through various escapements and gears to drive the hands and ring the chimes.

Guido
None of this implies energy is being created.

My current understanding is the earth IS creating energy out of nothing. Gravity (that pulls the water down) is a form of energy.

If gravity was being created by converting something else... what is this "something else"? Mass? (Which would make sense because zero mass = zero energy).

Maybe we cannot measure the mass consumption, but if it is diminishing then eventually the entire universe would be converted to gravity, with a mass of zero. OK, now I'm just confusing myself, haha.

I know my thinking is wrong here, I just don't know if "I" don't understand, or if science doesn't understand it yet.

My current understanding is the earth IS creating energy out of nothing. Gravity (that pulls the water down) is a form of energy.

There is no experimental evidence that any NEW energy has been created in the universe since its beginning.

In the Newtonian theory of gravity each bit of mass (mass1) is surrounded by a field which gives every other bit of mass (mass2) a mutual potential energy with a value of minus G*mass1*mass2/(distance between the masses); G is a constant that depends on the units used. If a pair of masses moves closer their potential energy becomes more negative and the kinetic energy of each mass increases by increasing the relative velocity of each mass. If a pair of masses moves apart their potential energy becomes less negative and the kinetic energy of each mass decreases by decreasing the relative velocity of each mass. In both cases the increase/decrease of the kinetic energy exactly matches the decrease/increase of the potential energy. In neither case is energy created or destoried.

In General Relativity the details are different but the overall situation is much the same. One of the details is that the increase/decrease in velocity i.e. acceleration/deceleration results in the emission of gravity waves. This carries off some of total energy of the pair of masses. However the sum of the masses kinetic energy the potential energy and gravity wave's energy remains constant.

In neither Newtonian theory nor General Relativity is their any explaination of how or why the gravity field exists or take the form they do. There is just the fact that decades and even centuries of careful calculation and comparision to observation indicate that these theories accurately model the phenomenon. You would not be the first person to object the form of the theories, even Newton had reservations.

Perhaps a different approach might be easier. Start with the Newtonian idea the masses attract each other with a force of G*mass1*mass2/ (distance between the masses)^2 and this force is directed from each mass directly at the other mass. Using this as a starting point and using the standard equation of force equals mass times acceleration you will have six differential equations. Three equations for each mass to cover the three dimensions of space. You can manipulated these equations and integrate the result to create a energy equation. This new equation will match the equation for the energy of a pair of free particles except it will contain an extra term which matches the potential energy I suggested.

In General Relativity the details are different but the overall situation is much the same. One of the details is that the increase/decrease in velocity i.e. acceleration/deceleration results in the emission of gravity waves. This carries off some of total energy of the pair of masses. However the sum of the masses kinetic energy the potential energy and gravity wave's energy remains constant.

This I understand perfectly. The emission of gravity waves is related to velocity. Maybe what I don't understand is when you have zero velocity, why is there still gravity? You mentioned earlier that it is a different type of gravity, and not to be thought of as an emission (like radio waves), but it is still an energy that seems to appear from nowhere.

Quote:

In neither Newtonian theory nor General Relativity is their any explaination of how or why the gravity field exists or take the form they do.

So there is currently no answer to my question, which would explain why I'm having a hard time understanding how gravity works.

So there is currently no answer to my question, which would explain why I'm having a hard time understanding how gravity works.

Hi, Guido, maybe this quote will help you understand gravity better:

"Spacetime grips mass, telling it how to move, and mass grips spacetime, telling it how to curve" - John Archibald Wheeler

I got it from this Wikipedia page on General relativity, which you also might find helpful...

The best non technical book on GR I"ve come across is "The riddle of gravitation" by Peter G.Bergmann, a coworker of Einstein, 1968, but I don't know if is still available and not out of print.I edited its Italian edition in 1969 for Edizioni Scientifiche Mondadori.
Tullio

The best non technical book on GR I"ve come across is "The riddle of gravitation" by Peter G.Bergmann, a coworker of Einstein, 1968, but I don't know if is still available and not out of print.I edited its Italian edition in 1969 for Edizioni Scientifiche Mondadori.
Tullio

I can look for this book, but even if I find it could it be out of date? Maybe our understanding has changed somewhat since 1968?

Anyway, it looks like there's more reading I need to do. (The hard part is remembering everything I read!)

## RE: Since gravity is

)

This is partly correct, though you must be careful about what is meant by 'mass'.

Consider a universe containing two stars in orbit. As they orbit, they emit gravitational waves and lose energy (and hence 'mass').

If you take a third 'test' mass far away, you can measure it's gravitational acceleration towards the binary pair, from a fixed distance away from the center of mass of the binary pair.

Over time, the gravitational acceleration of the test mass will DECREASE. This is because the binary star pair is losing energy (and hence mass) to gravitational radiation.

But the rate of energy loss from most objects is far to small to ever be observable.

Bruce

Director, Einstein@Home

## RE: Aye, we are, a bit,

)

Not a problem. After quantum mechanics was mentioned it went over my head so now I'm just reading it to try and learn something new.

But I still don't understand how a stationary object can create an energy source (gravity) out of nothing. So if we can make a contraption that can harness this energy, then we would have an endless energy supply... which doesn't jive with Newton.

## Guido Already being done

)

Guido

Already being done with hydro-electric power stations. Of course it is not a truly endless energy supply because the Sun provides the energy to evaporate water which then falls as rain at some higher elevation.

None of this implies energy is being created. The energy is changing form. One example would be an old fashion grandfather clock. You use a key or crank to winch up a weight, which is the same as saying you have increased it potential energy. As the weight falls the extra potential energy is then release through various escapements and gears to drive the hands and ring the chimes.

## RE: Guido None of this

)

My current understanding is the earth IS creating energy out of nothing. Gravity (that pulls the water down) is a form of energy.

If gravity was being created by converting something else... what is this "something else"? Mass? (Which would make sense because zero mass = zero energy).

Maybe we cannot measure the mass consumption, but if it is diminishing then eventually the entire universe would be converted to gravity, with a mass of zero. OK, now I'm just confusing myself, haha.

I know my thinking is wrong here, I just don't know if "I" don't understand, or if science doesn't understand it yet.

## RE: My current

)

There is no experimental evidence that any NEW energy has been created in the universe since its beginning.

In the Newtonian theory of gravity each bit of mass (mass1) is surrounded by a field which gives every other bit of mass (mass2) a mutual potential energy with a value of minus G*mass1*mass2/(distance between the masses); G is a constant that depends on the units used. If a pair of masses moves closer their potential energy becomes more negative and the kinetic energy of each mass increases by increasing the relative velocity of each mass. If a pair of masses moves apart their potential energy becomes less negative and the kinetic energy of each mass decreases by decreasing the relative velocity of each mass. In both cases the increase/decrease of the kinetic energy exactly matches the decrease/increase of the potential energy. In neither case is energy created or destoried.

In General Relativity the details are different but the overall situation is much the same. One of the details is that the increase/decrease in velocity i.e. acceleration/deceleration results in the emission of gravity waves. This carries off some of total energy of the pair of masses. However the sum of the masses kinetic energy the potential energy and gravity wave's energy remains constant.

In neither Newtonian theory nor General Relativity is their any explaination of how or why the gravity field exists or take the form they do. There is just the fact that decades and even centuries of careful calculation and comparision to observation indicate that these theories accurately model the phenomenon. You would not be the first person to object the form of the theories, even Newton had reservations.

Perhaps a different approach might be easier. Start with the Newtonian idea the masses attract each other with a force of G*mass1*mass2/ (distance between the masses)^2 and this force is directed from each mass directly at the other mass. Using this as a starting point and using the standard equation of force equals mass times acceleration you will have six differential equations. Three equations for each mass to cover the three dimensions of space. You can manipulated these equations and integrate the result to create a energy equation. This new equation will match the equation for the energy of a pair of free particles except it will contain an extra term which matches the potential energy I suggested.

## RE: In General Relativity

)

This I understand perfectly. The emission of gravity waves is related to velocity. Maybe what I don't understand is when you have zero velocity, why is there still gravity? You mentioned earlier that it is a different type of gravity, and not to be thought of as an emission (like radio waves), but it is still an energy that seems to appear from nowhere.

So there is currently no answer to my question, which would explain why I'm having a hard time understanding how gravity works.

But I did learn a lot. Thanks to everyone!

## Guido A mass moving at a

)

Guido

A mass moving at a constant velocity does not emit gravity waves. Only when the velocity changes are gravity waves emitted.

## RE: So there is currently

)

Hi, Guido, maybe this quote will help you understand gravity better:

"Spacetime grips mass, telling it how to move, and mass grips spacetime, telling it how to curve" - John Archibald Wheeler

I got it from this Wikipedia page on General relativity, which you also might find helpful...

## RE: RE: So there is

)

The best non technical book on GR I"ve come across is "The riddle of gravitation" by Peter G.Bergmann, a coworker of Einstein, 1968, but I don't know if is still available and not out of print.I edited its Italian edition in 1969 for Edizioni Scientifiche Mondadori.

Tullio

## RE: The best non technical

)

I can look for this book, but even if I find it could it be out of date? Maybe our understanding has changed somewhat since 1968?

Anyway, it looks like there's more reading I need to do. (The hard part is remembering everything I read!)