[HN Gopher] Negative Mass
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Negative Mass
Author : thunderbong
Score : 58 points
Date : 2023-04-22 18:07 UTC (4 hours ago)
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| daxfohl wrote:
| First example is wrong. Both would shoot off at infinite speed.
| https://en.m.wikipedia.org/wiki/Elastic_collision
| Freire_Herval wrote:
| 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.
| wardedVibe wrote:
| They're literally just plugging in negative numbers for
| freshman physics equations. I wouldn't think too deeply about
| it..
| goldenkey wrote:
| Very good point!
| brtv wrote:
| 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.
| phkahler wrote:
| 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 wrote:
| Antimatter just has the opposite _electrical_ charge. It
| doesn 't do anything weird at all with gravity.
| sycren wrote:
| 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 wrote:
| 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
| phkahler wrote:
| Could anti-quarks behavior be explained by them having
| negative mass instead?
| phkahler wrote:
| >> 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.
| thfuran wrote:
| 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.
| fooker wrote:
| >. We absolutely know that its electric charge is
| opposite that of the normal matter counterpart.
|
| Here is a contrived example calculating a hypothetical
| quantity X = m * Y.
|
| Suppose we observe that X is always negative.
|
| By your logic, we would then assume that Y is always
| negative.
|
| This is true if m is never negative, but it is somewhat
| possible that we would eventually find a situation where
| m is negative and Y is positive.
| phkahler wrote:
| 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.
| p1mrx wrote:
| "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/2022/202
| 2...
| lambdasquirrel wrote:
| 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.
| phkahler wrote:
| No, that doesn't cover the correct situation WRT gravity.
| JumpCrisscross wrote:
| > _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 wrote:
| But are they more paradoxical than relativity itself?
| JumpCrisscross wrote:
| > _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.
| MagicMoonlight wrote:
| 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 wrote:
| 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.
| nojs wrote:
| > Negative mass is attracted to positive mass but it pushes it
| away when it gets closer.
|
| Uh, what?
| firstlink wrote:
| The best explanation is that this post is two days late.
| tyronehed wrote:
| [dead]
| xwdv wrote:
| 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.
| eigenman wrote:
| 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.
|
| See, e.g., https://physics.stackexchange.com/a/8616
| [deleted]
| retrocryptid wrote:
| Nice. But I when I clicked the link I thought it was going to be
| a bunch of jokes about Boston.
| readthenotes1 wrote:
| I didn't have the patience to weight for the punchline
| canjobear wrote:
| 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.
| hinkley wrote:
| 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.
| tomrod wrote:
| > wiping out the entire visible universe at the speed of
| light and replacing it with something new
|
| ... and wonderful?
| joko42 wrote:
| Would negative mass make time contraction and length dilation
| possible?
| [deleted]
| nimbius wrote:
| "Let's weigh nikocado and some balloons"
|
| Who gave this absolute savage a website, I nearly choked on my
| coffee.
| colordrops wrote:
| So all you would need is a little negative mass to create endless
| energy? How does this not break the laws of conservation?
| CrampusDestrus wrote:
| Show me something with negative mass and I'll tell you
| colordrops wrote:
| I know you are joking but isn't the idea that negative mass
| works with current models of physics?
| DiscourseFan wrote:
| I think that says more about the model than the world it's
| based on.
| CrampusDestrus wrote:
| "Works" in what sense? Nobody is stopping you from plugging
| negative values everywhere, but the laws were formulated
| with sctrictly >=0 mass in mind.
|
| What would need to happen for you to claim that negative
| mass "doesn't work"? Some infinities somewhere? A division
| by zero in some place?
| ChrisClark wrote:
| Flubber? (From the original? haven't seen the remake)
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