[paul.fr]

Is it possible to have negative mass? I remember (think i do) that anti-particles could have negative mass, but anti-particles have positive mass....

Negative mass, is it possible?

[syhprum]

In the strange world of strings and alternative universes it might exist but not here.

[lightarrow]

Is it possible to have negative mass? I remember (think i do) that anti-particles could have negative mass, but anti-particles have positive mass....

Negative mass, is it possible?

Anti particles exist but they have positive mass. Negative mass doesn't exist. If it existed, it would have very strange properties, between which the fact that pushing it would make it accelerate in the opposite direction: a = F/m; if m is negative, a has the opposite direction of F.

[another_someone]

As you say, negative mass would both have anti-gravity as a property, but would also respond negatively to force.

The problem is, aside from gravity, the other long range force is the coulomb force, but that already exists in two forms, and so one has to ask how one could differentiate between a negative mass or merely a reversal of polarity of the coulomb force?

It would also have negative energy, and negative quantum wavelength; but I am not sure how that would manifest itself.

One possibility I can think of is that if an object of negative mass were to be travelling backwards in time, would it then appear as an object with positive mass to someone travelling in the opposite direction in time?  I believe I have seen speculation that anti-matter is actually matter travelling backwards in time, and if this were the case then maybe it is a requirement for anti-matter to be regarded as having negative mass (this might allow for a conservation of mass when matter/anti-matter pairs are created)?

[lightarrow]

As you say, negative mass would both have anti-gravity as a property, but would also respond negatively to force.

The problem is, aside from gravity, the other long range force is the coulomb force, but that already exists in two forms, and so one has to ask how one could differentiate between a negative mass or merely a reversal of polarity of the coulomb force?

I don't get this. It is always possible to establish if a body has charge or mass or not. If it has not charge and it has a mass, then the repulsion must come from a negative mass.

It would also have negative energy, and negative quantum wavelength; but I am not sure how that would manifest itself.

Which energy are you considerating? Self energy or grav. potential energy?

One possibility I can think of is that if an object of negative mass were to be travelling backwards in time, would it then appear as an object with positive mass to someone travelling in the opposite direction in time?  I believe I have seen speculation that anti-matter is actually matter travelling backwards in time

It could be considered this way for virtual particles but not for real particles: if this were true, we should detect as many positrons as electrons, for example, but this is not true.

and if this were the case then maybe it is a requirement for anti-matter to be regarded as having negative mass (this might allow for a conservation of mass when matter/anti-matter pairs are created)?

There is no need for a mass conservation law, since we already know that mass doesn't conservate: it can be converted into energy (and vice versa).

[another_someone]

As you say, negative mass would both have anti-gravity as a property, but would also respond negatively to force.

The problem is, aside from gravity, the other long range force is the coulomb force, but that already exists in two forms, and so one has to ask how one could differentiate between a negative mass or merely a reversal of polarity of the coulomb force?

I don't get this. It is always possible to establish if a body has charge or mass or not. If it has not charge and it has a mass, then the repulsion must come from a negative mass.

How do you detect is a particle has charge or mass, except by its effect on other particles.

Particles without any charge are extremely difficult to detect at medium distances at cosmic distances, you can detect gravity as a force, but in laboratory conditions, almost the only force you can directly detect is the coulomb force, and everything else is merely inferred from that).  If the coulomb force is reversed, how would that differ from negation of mass (i.e. two particles which previously had a mutually attractive force, by reversing the coulomb force one can cause the particles to repel, but by retaining the same coulomb force but negating the mass, one could have the same effect).

But, by negating the mass of a particle, one would also negate its response to gravity.  This may not be measurable within a laboratory, but on a cosmic scale, it might explain why we don't find very much anti-matter in the same vicinity of the universe as we find matter (we cannot say whether anti-matter exists elsewhere in the universe, except that we can detect when matter and anti-matter interact; but if they are gravitationally repulsive to each other, then we would not expect to find many places where they do collide on a cosmic scale, although one should be able to see regions of the universe which are gravitationally repulsive to each other).

It would also have negative energy, and negative quantum wavelength; but I am not sure how that would manifest itself.

Which energy are you considerating? Self energy or grav. potential energy?

Both mass energy (E = mc²) and kinetic energy (E = ¹/²mV²), although both ofcourse merge in the relativistic energy of the particle.

One possibility I can think of is that if an object of negative mass were to be travelling backwards in time, would it then appear as an object with positive mass to someone travelling in the opposite direction in time?  I believe I have seen speculation that anti-matter is actually matter travelling backwards in time

It could be considered this way for virtual particles but not for real particles: if this were true, we should detect as many positrons as electrons, for example, but this is not true.

As I recollect what I had read was that an anti-particle was a reflection of a particle in time at some point in time.  If this were to be the case then the number of anti-particles to exist would depend on the number of refection events that occur at a future time.  Since these refection events would send the anti-particle backwards in time, it would actually explain why we do have fewer ant-particles than particles.  It would imply that at the moment of the Big Bang, we would have two universes, our universe moving in one direction in time (arbitrarily labelled as moving forward in time), and another universe moving in the opposite direction in time.  In the early universe, there would be many reflection events, but those particles that are moving backward in time (anti-matter) would move towards our anti-universe, while those particles that are moving forward in time would tend to move towards our universe.  As the two universes moved away from each other, it would be more difficult for a particle to slip from one universe to the other, and so some of the wrong type of matter for each universe would remain in each universe.  Anti-particles would continue to be created, but only insofar as time reflection events exist in the future, and as the energy density of the universe diminishes, so the number of time reflection events diminish, and so the number of anti-particles created in the future (that we can see today) also diminishes.

On the other hand, I cannot see both negative time and negative mass co-existing, since their effects would in many contexts (particularly in the key areas of reaction to force) would be the same, and if they both happened at the same time, the effects would cancel each other out (I don't believe the effects on kinetic energy or mass energy would cancel out, but I am not so sure how those would be manifest in experiments).