[brtv]

Also the last one: "Negative mass is attracted to positive mass". How? With gravity 2 positive masses attract to each other. I don't know what happens if 1 mass is negative , but to me it's not obvious that they still attract.

And I don't see how this relates to the previous examples. In my mind, impact and friction has nothing to do with gravity.

[at_a_remove]

Alright. We are supposing for the moment that both inertial and gravitational contexts for mass give the same number.

The force between two masses, F is equal to G multiplied m-sub-1 multiplied by m-sub-2, and then all of that divided by the square of the distance between m-sub-1 and m-sub-2. Here G is the gravitational constant and the number being positive indicates a force toward, say, the first partner, m-sub-1.

Now, imagine m-sub-2 is negative mass.

Our force then becomes negative, so a force away from the first partner, m-sub-1.

BUT ...

Acceleration is equal to force divided by mass. Here the mass, m-sub-2 is negative, but so is the force. And so the acceleration is back to being positive and the negative mass "falls toward" the positive mass of m-sub-1.

In other words, positive matter ends up being a "falling toward" field.

Negative matter, however, well, run the numbers, only do everything from the m-sub-2 vantage point. The positive mass, m-sub-1, flees! Even as it attracts the other one.

And so once you have a negative/positive pair, they lock on, one fleeing, one chasing. One ends up with ever increasing positive kinetic energy, the other with ever increasing negative kinetic energy (all starts to sound a little silly here) and they cancel out, from a distance.

Gets wacky once you start imagining this for charged particles, which immediately bunch up into staggering Coulombs of negatively-charged nega-mass particles, and ditto for the positively-charged nega-mass particles. They just rapidly self-sort into these clumps due to the "electrostatic repulsion" going up against negative inertia. The EM force quickly dominates.

These two blazing opposite poles of charge, Q-pos and Q-neg, should naturally attract one another, but for that pesky negative inertia again.

And so all of the negative mass in the universe sorts into Q-pos and Q-neg, then promptly tries to approach the speed of light fleeing from one another, leaving just the slightest of electrical fields evident, but always asymptotically approaching zero as they more or less banish themselves to the further regions of normal matter.

(Some normal matter would be torn along for the ride)

It's a fun thought experiment.

[daxfohl]

I feel like the first example plus https://en.m.wikipedia.org/wiki/Bell%27s_spaceship_paradox reveals a need for something beyond Newtonian gravity.

[JumpCrisscross]

> don't know what happens if 1 mass is negative , but to me it's not obvious that they still attract

The physics of negative mass/energy are paradoxical to the point that they mathematically enable transluminal transport.

[daxfohl]

But are they more paradoxical than relativity itself?

[phkahler]

Yeah I've never looked at collisions. But if you blindly plug a negative mass into newtonian gravity F=GM1M2/r*2. And then use F=ma or a=F/m you get a=GM/r*2 where M is the other mass, and a is our acceleration toward that mass. Positive masses attract everything where negative masses repel everything. One of each held at constant separation should accelerate together.

This is why I want to know if antimatter falls up. Or I guess it might fall down but repel regular matter in which case it'll be very hard to detect.

[p1mrx]

"the BASE collaboration has shown, within strict boundaries, that antimatter does in fact respond to gravity in the same way as matter"

https://www.riken.jp/en/news_pubs/research_news/pr/2022/2022...

[Dylan16807]

Antimatter just has the opposite electrical charge. It doesn't do anything weird at all with gravity.

[MagicMoonlight]

Positive mass draws things towards it (gravity) so negative mass would push things away (anti-gravity), therefore they would just cancel out if they were the same magnitude