5 ms·

I don't know about the friction part. Seems like friction is modeled as a force that is dependent on mass but I don't think that's what's actually occurring.

goldenkey 3y ago
Very good point!
brtv 3y ago
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.
- JumpCrisscross 3y ago
  > 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 3y ago
    But are they more paradoxical than relativity itself?
    - JumpCrisscross 3y ago
      > are they more paradoxical than relativity itself I think so. For most purposes, we can build intuition for special relativity without having to do the math. (General is more fucked.) We don’t understand negative energy/mass enough to even do that.
- phkahler 3y ago
  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.
  - Dylan16807 3y ago
    Antimatter just has the opposite electrical charge. It doesn't do anything weird at all with gravity.
    - sycren 3y ago
      Since it focuses on electrical charge, would it be worth renaming it to Anti-charged-matter Are there other types of Antimatter that focus on different properties?
      - mayoff 3y ago
        Antimatter also has anti-color-charge. Quarks have a ‘color charge’ (unrelated to visible colors) which is ‘red’, ‘green’, or ‘blue’. An antiquark is antired, antigreen, or antiblue (and has the opposite electrical charge from its corresponding normal quark). https://en.wikipedia.org/wiki/Color_charge https://en.wikipedia.org/wiki/Color_charge
        phkahler 3y ago
        Could anti-quarks behavior be explained by them having negative mass instead?
        monocasa 3y ago
        I don't believe so; color charge isn't a scalar like mass is.
- MagicMoonlight 3y ago
  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
- at_a_remove 3y ago
  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 3y ago
    I feel like the first example plus https://en.m.wikipedia.org/wiki/Bell%27s_spaceship_paradox https://en.m.wikipedia.org/wiki/Bell%27s_spaceship_paradox reveals a need for something beyond Newtonian gravity.
wardedVibe 3y ago
They're literally just plugging in negative numbers for freshman physics equations. I wouldn't think too deeply about it..
- daxfohl 3y ago
  It's wrong anyway. The friction force would be the opposite direction, but then the acceleration due to a force on the negative mass would flip direction again. So it would slow down like a positive mass.
  - gus_massa 3y ago
    Inside a crystal, electrons act weirdly like an electron that travels with a "perturbation" around it, so the mass for calculations is not the mass of an electron traveling in vacuum. It's call "effective mass" m* https://en.wikipedia.org/wiki/Effective_mass_(solid-state_physics) https://en.wikipedia.org/wiki/Effective_mass_(solid-state_ph... The weird part is that it can be negative, so we already know quasi-particles with negative mass. This quasi particle with negative mass and negative charge is a fermion so it's mathematically equivalent to a quasi particle with positive mass and positive charge. We call them "holes" and people that work with semiconductors think about "holes" instead of weird particles with negative mass. Anyway, inside semiconductors they slow down and follow the conservation of energy law, they don't get faster and faster like in the simulation. The weird behavior of the simulation is not realistic.
    - daxfohl 3y ago
      Or just realize that the formula for stopping distance due to friction is independent of mass.

goldenkey 3y ago

Very good point!

brtv 3y ago

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.

JumpCrisscross 3y ago
> 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 3y ago
  But are they more paradoxical than relativity itself?
  - JumpCrisscross 3y ago
    > are they more paradoxical than relativity itself I think so. For most purposes, we can build intuition for special relativity without having to do the math. (General is more fucked.) We don’t understand negative energy/mass enough to even do that.
phkahler 3y ago
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.
- Dylan16807 3y ago
  Antimatter just has the opposite electrical charge. It doesn't do anything weird at all with gravity.
  - sycren 3y ago
    Since it focuses on electrical charge, would it be worth renaming it to Anti-charged-matter Are there other types of Antimatter that focus on different properties?
    - mayoff 3y ago
      Antimatter also has anti-color-charge. Quarks have a ‘color charge’ (unrelated to visible colors) which is ‘red’, ‘green’, or ‘blue’. An antiquark is antired, antigreen, or antiblue (and has the opposite electrical charge from its corresponding normal quark). https://en.wikipedia.org/wiki/Color_charge https://en.wikipedia.org/wiki/Color_charge
      - phkahler 3y ago
        Could anti-quarks behavior be explained by them having negative mass instead?
        monocasa 3y ago
        I don't believe so; color charge isn't a scalar like mass is.
MagicMoonlight 3y ago
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
at_a_remove 3y ago
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 3y ago
  I feel like the first example plus https://en.m.wikipedia.org/wiki/Bell%27s_spaceship_paradox https://en.m.wikipedia.org/wiki/Bell%27s_spaceship_paradox reveals a need for something beyond Newtonian gravity.

wardedVibe 3y ago

They're literally just plugging in negative numbers for freshman physics equations. I wouldn't think too deeply about it..

daxfohl 3y ago
It's wrong anyway. The friction force would be the opposite direction, but then the acceleration due to a force on the negative mass would flip direction again. So it would slow down like a positive mass.
- gus_massa 3y ago
  Inside a crystal, electrons act weirdly like an electron that travels with a "perturbation" around it, so the mass for calculations is not the mass of an electron traveling in vacuum. It's call "effective mass" m* https://en.wikipedia.org/wiki/Effective_mass_(solid-state_physics) https://en.wikipedia.org/wiki/Effective_mass_(solid-state_ph... The weird part is that it can be negative, so we already know quasi-particles with negative mass. This quasi particle with negative mass and negative charge is a fermion so it's mathematically equivalent to a quasi particle with positive mass and positive charge. We call them "holes" and people that work with semiconductors think about "holes" instead of weird particles with negative mass. Anyway, inside semiconductors they slow down and follow the conservation of energy law, they don't get faster and faster like in the simulation. The weird behavior of the simulation is not realistic.
  - daxfohl 3y ago
    Or just realize that the formula for stopping distance due to friction is independent of mass.