Properties of matter with negative gravity?

[robross]

First, I'm not proposing that any such thing as anti-gravity exists, but I want to ask a hypothetical question.

I know some discussions of dark energy refer to the negative pressure it exerts as acting like anti-gravity, but I want to specifically avoid talking about dark energy and just talk about regular everyday matter.

Also, I'm assuming our current universe applies (notwithstanding that anti-gravity doesn't exist), so it's expanding and finite and flat, and has all the usually accepted concepts. (I don't think it matters in this hypothetical if inflation occurred or not, but if you think it would affect anything feel free to choose one or describe how things would be different under each case).

Also, I don't know how GR's description of mass curving space would be interpreted in this scenario, so I'm going to stick with a quantum gravity model where gravitons exist, in order to be able to describe gravity as (possibly) having a different charge like the electric force (similar in concept but different in effect.)

Ok, all assumptions out of the way, say we have two normal matter neutrons (I choose neutrons so the EM force doesn't dominate in this example.) Since they both have mass, they are attracted by gravitation.

Now, say we have a hypothetical anti-gravity-neutron, which behaves the same way as a normal neutron in every way, except that instead of being attracted to a normal matter neutron, it is repulsed by the same amount. If the neutron and the anti-grav-neutron come near each other and no other forces are present, they repel each other as the inverse square of their distance.

My question is, under this scenario, would two anti-grav-neutrons attract each other, or repulse each other?

Rob

[korjik]

I think that it would depend on where your negative sign came from. If it acts as a negative mass in all ways, then two anti-grav particles should attract. However, you would end up with alot of other problems when the negative mass showed up in other equations.

[Jeff Root]

I've slowly been working on this idea for about 30 years. :) I don't
think it has any problems. The people at CERN think they will be able
to measure the response of antimatter to Earth's gravity by about
2015, six years from now, in conjunction with the ATHENA apparatus.
I intend to look for antigravitational lensing of light in the meantime.

-- Jeff, in Minneapolis

[DrRocket]

First, I'm not proposing that any such thing as anti-gravity exists, but I want to ask a hypothetical question.

I know some discussions of dark energy refer to the negative pressure it exerts as acting like anti-gravity, but I want to specifically avoid talking about dark energy and just talk about regular everyday matter.

Also, I'm assuming our current universe applies (notwithstanding that anti-gravity doesn't exist), so it's expanding and finite and flat, and has all the usually accepted concepts. (I don't think it matters in this hypothetical if inflation occurred or not, but if you think it would affect anything feel free to choose one or describe how things would be different under each case).

Also, I don't know how GR's description of mass curving space would be interpreted in this scenario, so I'm going to stick with a quantum gravity model where gravitons exist, in order to be able to describe gravity as (possibly) having a different charge like the electric force (similar in concept but different in effect.)

Ok, all assumptions out of the way, say we have two normal matter neutrons (I choose neutrons so the EM force doesn't dominate in this example.) Since they both have mass, they are attracted by gravitation.

Now, say we have a hypothetical anti-gravity-neutron, which behaves the same way as a normal neutron in every way, except that instead of being attracted to a normal matter neutron, it is repulsed by the same amount. If the neutron and the anti-grav-neutron come near each other and no other forces are present, they repel each other as the inverse square of their distance.

My question is, under this scenario, would two anti-grav-neutrons attract each other, or repulse each other?

Rob

Unless you have a self-consistent theory lurking somewhere it is impossible to answer that question, or even formulate it sensibly. The answer should lie in the model that represents your theory, a model that doesn't seem to exist.

If, as Korjik seems to assume, you simply have negative mass and plug it into the Newtonian formula for gravitation, then the negative signs cancel and you do get attraction.

But you don't have a theory that holds any water. It you have negative mass then you also get acceleration in the direction opposite to force, and negative kinetic energy, whatever that is.

Does this negative neutron come along with other particles of negative mass? Two negative mass protons ought to be interesting -- they attract because the electromagnetic forces are repulsive !!! And a negative mass proton and an negative mass electron repel because the electromagnetic forces are attractive.

You can't ask questions such as yours in isolation and expect meaningful answers. You need to put the whole package together and see if it is consistent with experimental data and with itself. Then and only then explore the other implications of the theory. You are a long way from that state.

[a1call]

I agree with DrRocket.

While fantasizing imaginary materials anything can be true or false depending on the constraints of the fantasy.

One (and only one) possible analogy of the positive and negative attraction/repulsion would be magnetism and diamagnetism (http://en.wikipedia.org/wiki/Diamagnetism).

I assume (confirmation/rejection appreciated) that generally magnetic materials attract each other under magnetic forces (North-North South-South repulsion considered) while diamagnetic materials repel each other under magnetic forces.