Can gravity be reversed

[swansont]

Would that also result in a violation of conservation of momentum and conservation of energy? It seems if the bolded part could happen you could use it to turn something, and yet technically the negative mass would cancel the energy and momentum. Peculiar indeed.

 

I haven't followed this through; negative mass implies momentum opposite to the direction of travel and negative kinetic energy. It would seem that two objects of opposite mass starting at rest could accelerate each other up arbitrarily close to c and have zero momentum and zero kinetic energy the whole time.

[michel123456]

Unless you can show that inertial and gravitational mass are not the same, negative mass does not really yield repulsion, at least the analogue to electrostatics that is usually implied. F=-GmM/r^2 is now positive, but for a negative mass a = F/m is negative, so the resulting acceleration vector gives you attraction toward the positive mass. You now have some peculiar situations — for the positive mass you get acceleration in the same direction, owing to the loss of the minus sign, and two negative masses feel an attractive force, but repel each other in terms of acceleration.

 

IMHO this peculiar situation is due to the fact that we forgot to reverse one last thing: distance.

Distance is always positive, like mass, gravity, time & energy. When we reverse mass, we have to reverse everything, distance included.

[swansont]

IMHO this peculiar situation is due to the fact that we forgot to reverse one last thing: distance.

Distance is always positive, like mass, gravity, time & energy. When we reverse mass, we have to reverse everything, distance included.

 

A) no, we are reversing mass only, and B) gravity depends on r^2 anyway, so it's moot