# Do Moving Masses Slow Down Due to Gravitational Waves?

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• Cato
In summary, gravitational waves are produced by accelerating masses, but they are so weak that their effect is probably something like a rounding error in the 15th decimal place. Objects in free fall don't produce gravitational waves, but objects that merge will speed up.
Cato
TL;DR Summary
Gravitational waves are produced by accelerating masses. Since all space is curved -- more curved near large masses stars, less curved in intergalactic space -- all moving masses are being accelerated to some degree. Do all moving masses therefore produce gravitational waves? If they do, will all moving masses lose energy and slow down?
Gravitational waves are produced by accelerating masses. Since all space is curved -- more curved near large masses stars, less curved in intergalactic space -- all moving masses are being accelerated to some degree. Do all moving masses therefore produce gravitational waves? If they do, will all moving masses lose energy and slow down?

Technically, yes, gravity waves are produced but they are so weak in the kind of situation that you describe that their effect is probably something like a rounding error in the 15th decimal place.

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Objects in free fall aren't accelerating in any meaningful sense. The source of gravitational radiation is stress-energy with a changing quadropole moment.

That does mean that any pair of objects ought to emit gravitational radiation unless they are at rest with respect to one another (I think - there might be exceptions). And that does mean that they'll slow down with respect to one another, but that may or may not mean slow down with respect to whatever coordinate system you are using.

Back-of-the-envelope, the kinetic energy of Earth in its orbit is 1031J. The power output from gravitational radiation is around 100W, if memory serves. So I think that this effect is rather weaker even than @phinds says - even for a system as massive as our planet.

Finally, extending this argument to "every object" is risky. We strongly suspect that GR is not an accurate description of gravity when quantum effects are important for its source. So gravitational radiation may or may not be emitted by very small objects.

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phinds
Ibix said:
That does mean that any pair of objects ought to emit gravitational radiation unless they are at rest with respect to one another (I think - there might be exceptions). And that does mean that they'll slow down with respect to one another, but that may or may not mean slow down with respect to whatever coordinate system you are using.
Looking at the the merger of two compact objects I think they speed up independent of the chosen coordinate system. Or do you think of non-inertial frames here?

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timmdeeg said:
speed up independent of the chosen coordinate system.
Can “speed up” ever have a coordinate-independent meaning? “Experiences proper acceleration” has a coordinate-independent meaning and in an inertial frame does imply what most people would mean by “speed up”... but we’re talking gravitational effects here, so are considering regions of spacetime that aren’t properly described by any inertial frame.

I don't know this kind of physics enough to discuss the details. "Finally, extending this argument to "every object" is risky. We strongly suspect that GR is not an accurate description of gravity when quantum effects are important for its source. So gravitational radiation may or may not be emitted by very small objects." So perhaps objects where quantum effects are important don't produce gravitational waves. Thanks for all your answers.

## 1. How do gravitational waves affect moving masses?

Gravitational waves are ripples in the fabric of spacetime that are created when massive objects accelerate. As these waves pass through a region of space, they cause the space itself to stretch and compress. This stretching and compressing can affect the motion of objects, including moving masses.

## 2. Do gravitational waves cause moving masses to slow down?

Yes, gravitational waves can cause moving masses to slow down. This is because the waves transfer energy to the objects they pass through, which can result in a loss of kinetic energy and a decrease in speed.

## 3. How significant is the effect of gravitational waves on moving masses?

The effect of gravitational waves on moving masses is very small. For most everyday objects and motions, the impact of gravitational waves is negligible and cannot be detected. However, for extremely massive objects such as black holes or neutron stars, the effect can be significant.

## 4. Can gravitational waves completely stop a moving mass?

No, gravitational waves cannot completely stop a moving mass. While they can cause a decrease in speed, they cannot bring an object to a complete halt. The effect of gravitational waves is limited and cannot overcome the inertia of the object.

## 5. How do scientists study the impact of gravitational waves on moving masses?

Scientists study the impact of gravitational waves on moving masses through various experiments and observations. This includes using highly sensitive instruments such as interferometers to detect the stretching and compressing of spacetime caused by gravitational waves. They also use computer simulations and mathematical models to understand the effects of gravitational waves on different types of moving masses.

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