0

*I'm a writer, not a physicist, so please bear with me in my 'ham'-handling of physics and its terminology!

My question is about whether repulsive forces over large distances could exist.

My starting point: I (think I) understand that gravitational fields differ from electromagnetic ones in that they have only one sign of charge. Also, that gravitational fields are generated by and proportional to the density of energy, while electromagnetic fields are generated by separations of charge. This density is never negative, and so any repulsive force is precluded.

My central question is: All unfounded analogies between the two forces aside, can gravity be conceived of as acting on an energy-density gradient in a mirror-image way to the way that differences of electrical charge tend toward equilibrium? So that, in gravity's case, rather than energy out-flowing from regions of high density to regions of lower density, like electrical charge, the opposite occurs.

Second: In a finite, unbounded space, could this allow one to conceive of such a gravitational field as exerting a negative pressure on regions of lower energy density?- Not in an absolute sense, but as part of a system, relative to any region of higher density, like oil 'pushed' to the surface of water.

Lastly: If that's all baloney and I'm a dumbbell for trying to draw analogies between these two different forces, what might be the most pronounced oddities of a universe in which such a repulsive quality of gravity Did exist in a finite, unbounded space? Disclaimer: Yes, I really want to use this idea in my story!

Thanks!

Kyle
  • 1

1 Answers1

1

If "regions of lower energy density" are, e.g., rigid spherical shells filled with vacuum; and if "regions of higher energy density" are, e.g., filled with CO2 gas; then yes, gravity repels regions of low energy density. Of course that's what buoyancy is and it's why hot air balloons and helium balloons float.

You didn't specify what you really mean by "regions of lower energy density", but I get the feeling that you're imagining some sort of "nega-field" analogous to an electromagnetic field, that conveniently has negative energy density, rather than the gas-filled regions I invoked.

However, a magical "nega-field" is not needed. Suppose we arranged for a large volume of space to be filled with a very strong, uniform electric field. Within that volume, place a gravitating mass; and near the gravitating mass place a hollow conductive sphere whose mass is much less than the mass-energy density of the surrounding electric field.

In this situation the conductive sphere would indeed be repelled by the gravitating mass, because now the total energy would be more negative the farther the conductive sphere is from the gravitating mass. The surrounding electromagnetic field would act, in effect, very much like the CO2 in the buoyancy example; and the interior of the conductive sphere would act like the evacuated cylinder in the buoyancy example. Unfortunately it's not practical as a space drive.

However, if you're writing a SciFi story, you could postulate existence of a uniform field that fills space and interacts with almost nothing, but has a positive energy density. Then postulate a technology that can generate a "bubble" in that field the way the hollow conductive sphere generates a "bubble" in an electric field. This "bubble" would be repelled by any gravitating mass.

S. McGrew
  • 24,774