If a particle had negative mass where would it go?

[Hurkyl]

i just don't know fundamentally how to test an E field without plopping in a test charge and watching it go somewhere. wouldn't a negative mass test charge move the same way as if it were positive mass with opposite charge?

Use the same test charge for both!

Put an electron next to an electron. Which way does the electron go?
Put an electron next to a positron. Which way does the electron go?

Those answers will be the same if and only if the electron and positrion have the same charge, no matter what their masses are.


Oh, here's another one. Place two identical charged particles next to each other. They repel each other if and only if their mass has the same sign as the k in kqQ/r^2.

 

[NoTime]

I am not asking for experimental evidence. My opinions are not carved in stone; I am not dogmatic about this issue. But since you cannot perform this Etovos experiment, using that specifically as an example hardly constitutes an argument, does it?

If you have some sound logic, however, to dispute my logic, I'm ready to listen - seriously. If there is a flaw in my reasoning, I'd prefer to be mildly embarrassed now than walk around for the next n years thinking something that is foolish.

I guess I didn't make myself clear.
It isn't currently possible to prove this by logic or math.

Perhaps someone might come up with a good idea that would allow us to discriminate between the various possibilities.
Which is likely why this thread isn't locked already.

As to your exact argument, other people have pointed out some items.

Personally I don't see anything wrong with being foolish as long as you are paying attention to what may or not may not be allowed.
Some of my best ideas have been destroyed by ugly reality.

 

[NoTime]

but that is not correct. two neutrally charged masses, one of +M, the other of -M will accelerate, but they will accelerate in the same direction. the -M mass will acclerate toward the +M mass and the +M mass will accelerate away from the -M mass.

Only if you flip the sign of curvature AND the sign of inertia. It isn't clear to me that this is necessary.

 

[rbj]

Only if you flip the sign of curvature AND the sign of inertia. It isn't clear to me that this is necessary.

we don't decide what is necessary or not, nature does. you have to show what reason you would not flip the signs in any case of negative mass. why would nature bother to essentially apply an absolute value operator to any of the three types of masses (that the Equivalence Principle says is one-and-the-same)?

negative intertial mass means the object moves in the opposite direction that it is pushed. negative passive gravitational mass means that the object in a regular gravitational field (from a much larger planet of positive mass) will have an upward force. so if both inertial mass and passive gravitational mass is the same mass, the two minus signs cancel and the small negative mass still falls toward the planet. from a GR perspective, this is consistent, because the curvature is determined by the much larger planet mass which is positive, in this case. the geodesic path is the same no matter what the quantitative value of the test mass is (as long as it's small and not contributing significantly to the curvature), whether it is positive or negative.

now consider a small test mass with positive mass and a big planet of negative mass. does that test mass fall toward the planet or get repelled away? does the curvature (when translated to flat Euclidian space) curve in toward the planet of large negative mass or away from it?

once you answer that, tie together all of the concepts and ask what happens when you have two planets of opposite signed mass and equal magnitude separated by some distance. what are the geodesic paths like that are created by the negative mass and in the vicinity of the positive mass? and vice versa? that's when you get a nice accelerating (from the POV of Newtonian 3-space) pair of planets that will accelerate indefinitely.

 

[rbj]

Use the same test charge for both!

Put an electron next to an electron. Which way does the electron go?
Put an electron next to a positron. Which way does the electron go?

Those answers will be the same if and only if the electron and positrion have the same charge, no matter what their masses are.


Oh, here's another one. Place two identical charged particles next to each other. They repel each other if and only if their mass has the same sign as the k in kqQ/r^2.

Hurkyl, I'm with you.

i was thinking about the test charge being the one with possible negative mass and the charge setting up the field being constant.

i think we're on the same page, at least now.

 

[NoTime]

once you answer that, tie together all of the concepts and ask what happens when you have two planets of opposite signed mass and equal magnitude separated by some distance. what are the geodesic paths like that are created by the negative mass and in the vicinity of the positive mass? and vice versa? that's when you get a nice accelerating (from the POV of Newtonian 3-space) pair of planets that will accelerate indefinitely.

Far be it from me to complain that Forward has his math wrong.
OTOH, ignoring any QFT, in GR gravity isn't a force. It's a condition of space.
What force is pushing against the -inertia to make it push back?

we don't decide what is necessary or not, nature does.

Exactly. And this is one of the things where nature hasn't divulged her secrets.

you have to show what reason you would not flip the signs in any case of negative mass. why would nature bother to essentially apply an absolute value operator to any of the three types of masses (that the Equivalence Principle says is one-and-the-same)?

I think that might be more like "observed to be the same".

The only way we know energy is thru photons.
Photons exhibit no net space-time curvature.
However, photons are considered to have momentum, a vector quantity.
If you bounce a bunch of photons off something it will move, as shown by experiment.
Now if you toss -e at +e and they annihilate, you might think everything would vanish.
They are after all anti-particles.
However, two 511mev photons are generated traveling in opposite directions.

Is +Energy and -Energy already absolute?
Only the relative direction the momentum vector points in designates the sign?
In any event you seem to end up with two electrons worth of momentum.
If energy is absolute then inertia needs to be as well to satisfy E=MC^2.
Can you have |+- curvature| = inertia?

 

[rbj]

Far be it from me to complain that Forward has his math wrong.
OTOH, ignoring any QFT, in GR gravity isn't a force. It's a condition of space.
What force is pushing against the -inertia to make it push back?

i think that gets answered when you come to the conclusion that there ain't no negative mass. (this is why i said it leads to contradiction.)

The only way we know energy is thru photons.
Photons exhibit no net space-time curvature.
However, photons are considered to have momentum, a vector quantity.
If you bounce a bunch of photons off something it will move, as shown by experiment.
Now if you toss -e at +e and they annihilate, you might think everything would vanish.
They are after all anti-particles.
However, two 511mev photons are generated traveling in opposite directions.

Is +Energy and -Energy already absolute?
Only the relative direction the momentum vector points in designates the sign?
In any event you seem to end up with two electrons worth of momentum.
If energy is absolute then inertia needs to be as well to satisfy E=MC^2.
Can you have |+- curvature| = inertia?

dunno why all of this is germane. i would still suggest taking it up with John Baez (that sci.physics.research post i cited earlier). in GR, gravity is not a force, but when spacetime is flat enough and speeds are slow enough, the Newtonian model in 3-space is a very good approximation and it's easier to look at intuitively when you look at it. you count the minus signs and a negative mass repels anything while a positive mass attracts anything. two equal sized and opposite masses will result in one always attracting the other, while that other always repels the first.

 

[Hurkyl]

Photons exhibit no net space-time curvature.

Photons have energy and momentum. Energy and momentum contribute to the stress-energy tensor. The stress-energy tensor affects controls how space-time is curved.

So yes, photons do curve space-time.

Now if you toss -e at +e and they annihilate, you might think everything would vanish.

An alternative is to create a pair of photons traveling opposite directions through time as well as space.

Hrm... I'll have to mull over what the consequences of that are!

 

[NoTime]

Photons have energy and momentum. Energy and momentum contribute to the stress-energy tensor. The stress-energy tensor affects controls how space-time is curved.

So yes, photons do curve space-time.

I tried to get away from that by saying net.
If they had a net curvature then wouldn't a photon have mass?
I do think they curve space-time, but with equal amonts of positive and negative curvature.
Thus, no mass.

I'm no GR expert, but at one time I could stumble through MTW. Doubt I could still do the math or at least not without a tremendous amount of rework.

An alternative is to create a pair of photons traveling opposite directions through time as well as space.

Hrm... I'll have to mull over what the consequences of that are!

They do!
But time isn't anything like whatever you think it might be.

 

[rbj]

...Thus, no mass.

this is a good reason for why i think that physics curriculums have made a pedgagical mistake in the last 2 decades by deciding to ignore the differentiation between rest mass (or "invariant mass") and relativistic mass.

photons have mass:

m = \frac{E}{c^2} = \frac{h \nu}{c^2}

this mass causes the same amount of curvature in space-time as would any other mass of the same quantity (but sometimes that is represented as energy density divided by c^2).

however, the rest mass

m_0 = m \sqrt{1 - \frac{v^2}{c^2}}

is zero because v = c.

Photons have mass, but no rest mass.

you've also done nothing to support your use of an absolute value function to apply to either gravitational mass or inertial mass. the reality of negative mass leads to perpertual motion machine and the obsolesence of the conservation of energy.

 

[WhyIsItSo]

but that is not correct. two neutrally charged masses, one of +M, the other of -M will accelerate, but they will accelerate in the same direction. the -M mass will acclerate toward the +M mass and the +M mass will accelerate away from the -M mass.

...and there will be some net acceleration. Assuming you are correct of course. I have no idea on this issue, yet I question your certainty about the behavior of +M and -M. From the discussions so far, I don't see that any negative mass (or negative matter even) is known. On what do you base your assurance concerning their behavior?

 

[Hurkyl]

If they had a net curvature then wouldn't a photon have mass?

I don't see why.

I do think they curve space-time, but with equal amonts of positive and negative curvature.

I'm not really sure that that means -- but I will point out that "light in a box" will gravitate almost identically to a massive object with the same total energy. (Because the momentum terms will roughly cancel out. I'm not really sure what to think of the momentum flow terms, but I suspect that would be negligible too)

this mass causes the same amount of curvature in space-time as would any other mass of the same quantity

No, it wouldn't. The 0,0 components of the stress-energy tensor would be the same, but at least the other momentum terms would be very different.

the reality of negative mass leads to perpertual motion machine and the obsolesence of the conservation of energy.

Conservation of energy still holds -- the kinetic energy of the particle with negative mass will be negative.

 

[NoTime]

you've also done nothing to support your use of an absolute value function to apply to either gravitational mass or inertial mass.

Don't know that I have, don't know that I havn't.

the reality of negative mass leads to perpertual motion machine and the obsolesence of the conservation of energy.

Math works fine. No problem with conservation of energy.
But, no one has told me what force is acting on the -inertia.

 

[NoTime]

I'm not really sure that that means -- but I will point out that "light in a box" will gravitate almost identically to a massive object with the same total energy. (Because the momentum terms will roughly cancel out. I'm not really sure what to think of the momentum flow terms, but I suspect that would be negligible too)

I don't know how to put light in a box.
At least not enough to make more than electron or two worth of weight change.
Don't think anybody else does either.
Won't argue with the math, but like negative mass I'd have to see it done.
Trouble is a lot of mathamatical solutions are non physical.
I suspect that negative mass/inertia is one of them.

 

[Andrew Mason]

i think that gets answered when you come to the conclusion that there ain't no negative mass. ...

Rbj, you seem to be coming around on this (although I would not be emphatic that negative mass actually exists).

AM

 

[firstme]

Hey guyz, what are you talking about?
Antimatter or Negative matter?
Why can't you understand this all is a foolishness! what's is good with giving matter a sign? it is signless, just like mass.
just think, can you give sign to an Apple? (Negative apple and positive apple, what thiz means?)
i'm sorry if I'm wrong, ok?