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# Negative mass vs Positive mass

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If we had a ball made of negative mass and a ball made of positive mass would they attract each other, repel each other, or would each only attract the same mass + or - . In other words would negative mass attract another negative mass like positive mass does but repel or attract a mass of the opposite mass?

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"Although no particles are known to have negative mass, physicists (primarily Hermann Bondi in 1957,[7] William B. Bonnor in 1964 and 1989,[13][14] then Robert L. Forward[15]) have been able to describe some of the anticipated properties such particles may have. Assuming that all three concepts of mass are equivalent according to the equivalence principle, the gravitational interactions between masses of arbitrary sign can be explored, based on the Newtonian approximation of the Einstein field equations. The interaction laws are then:

In yellow, the "preposterous" runaway motion of positive and negative masses described by Bondi and Bonnor.
• Positive mass attracts both other positive masses and negative masses.
• Negative mass repels both other negative masses and positive masses.

For two positive masses, nothing changes and there is a gravitational pull on each other causing an attraction. Two negative masses would repel because of their negative inertial masses. For different signs however, there is a push that repels the positive mass from the negative mass, and a pull that attracts the negative mass towards the positive one at the same time.

Hence Bondi pointed out that two objects of equal and opposite mass would produce a constant acceleration of the system towards the positive-mass object,[7] an effect called "runaway motion" by Bonnor who disregarded its physical existence, stating:

I regard the runaway (or self-accelerating) motion […] so preposterous that I prefer to rule it out by supposing that inertial mass is all positive or all negative.

— William B. Bonnor, in Negative mass in general relativity.[14]

Such a couple of objects would accelerate without limit (except a relativistic one); however, the total mass, momentum and energy of the system would remain zero. This behavior is completely inconsistent with a common-sense approach and the expected behavior of "normal" matter. Thomas Gold even hinted that the runaway linear motion could be used in a perpetual motion machine if converted to circular motion"

From Wikipedia      Negative mass - Wikipedia

But others, in particular R L Forward ( yes, the sci-fi author of Dragon's Egg ) have shown that the phenomenon violates no conservation laws and is mathematically consistent.

So yes, Moon, there is a very slight possibility that exotic matter, with negative mass, and which violates positive energy conditions could exist ( though I find the idea ludicrous ), and would allow forstabilization of wormholes and travel to the past/future/far-away regions of space at FtL speeds.

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Interesting, I was thinking that two negative masses would attract the same way two positive masses would and both would repel each other. Thank you for the clarification.

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