This is a nice exposition, but it would have been more clear if they laid out the difference between inertial and gravitational masses. So far, these two varieties of mass are equivalent in all our observations, but they need not be so. Negative inertial mass is pretty weird, as the examples illustrate; but negative gravitational mass (i.e., normal and negative mass repel according to inverse square law) would be something exciting to observe.
> wouldn’t that mean that something with negative mass can then go faster than the speed of light?
No. You can construct a theory of tachyons (particles that go faster than light) using special relativity, but they have imaginary masses!
The key is that the quantity that actually appears in the equations you refer to in special relativity is the mass squared. So ordinary objects have positive mass squared, light has zero mass squared, and tachyons have negative mass squared.
(Note that this means that some of the things that the article under discussion here says about "negative mass" are only valid in Newtonian mechanics, not in relativity.)
All negative mass that exists probably moved away in the opposite direction of the expansion of the universe. It’s out there, but we’ll never reach it.
i thought this was made by friends of jean-pierre petit and his Janus model...
I love the idea of negative mass ( because i love symetries in the laws of nature) but i've got a hard time believing the geniuses of the early 20th century haven't already explored the idea.
It's interesting because negative mass is a prerequisite for superluminal travel via Alcubierre warp drives. What these examples show is that negative mass is an incredibly counterintuitive concept, probably impossible in the real world.
Or we drop the Higgs field to a lower state trying to create it, wiping out the entire visible universe at the speed of light and replacing it with something new.
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.
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.
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_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.
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.
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)
> 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.
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.
That’s negative charge though, not negative mass. We haven’t been able to experiment with negative mass. No particle physics experiment has produced any evidence it exists.
IIRC, we don't actually know that for sure yet. I've seen some proposals for for experiments that use the relative stability and neutral charge of the exotic atoms muonium and anti-muonium to validate that anti muons don't have negative mass as well as flipped charge.
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).
That would require a re-formulation of conservation of color charge. You could probably come up with an alternative formulation where everything is consistent, but all of the formulas would almost certainly be more complicated. The most obvious way would end up replacing color by the sign of mass times color everywhere, but then you've just renamed ant-red, anti-blue, and anti-green, with no obvious benefit.
>> Antimatter just has the opposite electrical charge.
We don't know that. It may have the regular charge but after computing the force it may experience the opposite behavior via F=ma since the mass is negative.
We don't really know if the charge is opposite or the mass. Blindly using the equations you may get similar results depending where you stick the negative.
Also, I seem to recall Dirac predicting the existence of antimatter because some solution to an equation had an m^2 term and when you take a square root to solve for m there are two solutions. Then the positron came along and this was forgotten and people just assumed it had positive charge rather than negative mass.
Antimatter isn't some unobserved theoretical thing. It's produced daily at most large hospitals. We absolutely know that its electric charge is opposite that of the normal matter counterpart.
How do we know that? Because of how it behaves in electric and magnetic fields. In particular, how it accelerates. It obviously has a negative sign in it somewhere. My point is that we don't know if that sign flip is in charge or mass. A lot of the math behaves in accordance with observation whether we flip the charge or the mass.
Unfortunately this isnt correct. We know it has the opposite charge. This is due to conservation laws which include, among other things, the conservation of charge.
In a given interaction, charge is always conserved. So we see interactions where an electron and a positron collide they produce a chargeless photon. So it must have the opposite charge to an electron
Thank you. That's the first thing anyone has said that disambiguation it for me. My first thought was "but what if mass is concerned and the positive and negative mass cancel out?" But I quickly remembered the photons have the mass-equivalent energy, so the mass doesn't cancel, it gets "converted".
Is there energy in an electric field? If so it must be signed or it wouldn't cancel out.
> Is there energy in an electric field? If so it must be signed or it wouldn't cancel out.
The energy contained in the electromagnetic field is nonnegative: as I understand it, within a given volume, it's simply the sum of the photon energy of all of the photons.
Meanwhile, electrons and positrons exist in their own particle field, and have both positive mass energy and nonnegative kinetic energy. When an electron and positron annihilate and produce photons, they convert their combined mass energy into kinetic energy in the photons. The only thing that gets "canceled out" is the positive and negative electric charge.
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
See, e.g., https://physics.stackexchange.com/a/8616