# Negative Mass and Negative Inertia

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I have a question. Before I start, I want to say that I know negative mass itself has not been observed or proven to exist, if it does at all. That is why this is more of a what-if question if that is okay. Anyway...

Say an object has negative mass and therefore negative inertia. Now, considering inertial reference frames, or fictitious forces, objects with normal mass appear to move, such as going backwards seemingly when say, a car it is in speeds up. If a negative mass object were to exist, and were place inside the car before it speeds up, would the object appear to go the opposite direction of what a normal mass object would do when that car moves, as in that negative mass apparently going forward rather than backward when the car speeds up? As well as going backward apparently instead of forward when a car slows down, if I have inertial reference frames down correctly? All due to fictitious forces? Or would it be the same as normal, positive inertia?

I know this seems rather outlandish, possibly even for a hypothetical question in physics, but I have been thinking about it and I am rather curious. I hope nothing bad happens by asking this. So, is there anything to say about this question, if there is something?

Edited by SilentSky23

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Assuming you don't mean 'effective' mass, but actual inertial mass, which, by the equivalence principle, is identical to the mass which 'generates' the gravitational field, and to the mass which responds to an external gravitational field ( by momentum conservation ), then H Bondi, W B Bonnor an R L Forward ( one of my favorite sci-fi authors ) proposed the phenomenon of 'Runaway Motion'

An excerpt from the Wiki article

https://en.wikipedia.org/wiki/Negative_mass

follows, and you might want to give the whole Wiki article a good read...

"Although no particles are known to have negative mass, physicists (primarily Hermann Bondi in 1957,[6] William B. Bonnor in 1964 and 1989,[12][13] then Robert L. Forward[14]) 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,[6] an effect called "runaway motion" by Bonnor who disregarded its physical existence."

The article goes on to state that R L Forward showed that no conservation laws are violated by this effect, however, quite a few unphysical situations ( mentioned in the article ) result.

Edited by MigL

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Posted (edited)

Saoussen Mbarek and Manu Paranjape at the Université de Montréal in Canada say they’ve found a solution to Einstein’s theory of general relativity that allows negative mass without breaking any essential assumptions. Their approach means that negative mass can exist in our universe provided there is a reasonable mechanism for producing it, perhaps in pairs of positive and negative mass particles in the early universe.

Edited by SergUpstart

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49 minutes ago, SergUpstart said:

Saoussen Mbarek and Manu Paranjape at the Université de Montréal in Canada say they’ve found a solution to Einstein’s theory of general relativity that allows negative mass without breaking any essential assumptions. Their approach means that negative mass can exist in our universe provided there is a reasonable mechanism for producing it, perhaps in pairs of positive and negative mass particles in the early universe.

Any developments on that in the subsequent 5+ years?

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11 minutes ago, swansont said:

Any developments on that in the subsequent 5+ years?

J.Farnes theory, 2018

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5 minutes ago, SergUpstart said:

J.Farnes theory, 2018

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GR also predicts, and allows for, singularities.
Yet we know they are un-physical.

The model is never able to encompass all aspects of reality.

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2 hours ago, swansont said:

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