# Talk:Exotic matter

## Just a hypothesis

Changed theoretical to hypothetical since there is no empirical support for the existence of such particles.

For example, neutrinos were once "purely theoretical" in that they had not been observed, but their existence was predicted to explain certain mass defects in nuclear processes, and the resulting violation of the law of energy conservation.

For these particles with negative mass, however, as well as for tachyons, for example, not even indirect or theoretical evidence for their existence exists.

Aragorn2 18:56, 25 Sep 2003 (UTC)

## Negative energy??

the article states

"The closest known real representative of exotic matter is a region of negative energy density produced by the Casimir effect."

but it is my understanding that vacuum energy has negative pressure, not negative energy. someone defend the "Casimir vacuum has negative energy" standpoint? Lethe

It's my understanding that the reason that the Casimir effect produces negative pressure is because it excludes long-wavelength virtual particles from the region of space between the two plates, resulting in a region of space with fewer virtual particles than is present in "normal" empty vacuum. This means there's less "stuff" there than in empty space, so the vacuum energy is lower than the vacuum energy of empty space - which is equivalent to "negative" energy density, if one defines vacuum as having zero energy density. Bryan 06:16, 19 Dec 2004 (UTC)
Which is a pretty big if. I've never heard of people defining vacuum soup as having zero energy, but then again I'm no expert by a long shot. --fvw* 06:21, 2004 Dec 19 (UTC)

Negative mass would produce "negative gravity" that repels ordinary positive mass, but would be attracted to positive mass and other negative mass particles in a normal matter.

The sentence contradicts itself. First it says that negative mass repels positive, but then it says that it attracts it. Paranoid 23:10, 18 Dec 2004 (UTC)
Not quite. A negative mass particle repels positive mass particles away from it, and is itself attracted towards positive mass particles. So if you had two particles sitting next to each other, one positive mass and the other negative mass, the two particles would both start accelerating in the direction of the positive mass particle. This doesn't violate any conservation laws since as the positive mass gains positive energy and momentum the negative mass gains equal amounts of negative energy and negative momentum. Bryan 06:07, 19 Dec 2004 (UTC)
This doesn't violate any conservation laws since as the positive mass gains positive energy and momentum the negative mass gains equal amounts of negative energy and negative momentum.

omg thnx for telling me that i always wondered lolz

## negative energy

redirects here, but there's nothing in the article about it. please don't do that. - Omegatron 00:55, May 2, 2005 (UTC)

I removed the redirect, as you mentioned this article doesn't at the moment have anything to do with negative energy. Intangir 16:56, 3 May 2005 (UTC)
Negative mass has negative rest energy, which is why I had created the redirect (the previous "negative energy" page was gibberish). This was discussed on Wikipedia:Pages needing attention/Physics, though the thread was archived to the discussion page after months of inactivity. This is the only suitable place I could see redirecting to, as it doesn't seem to be treated elsewhere, and the term "negative energy" most often comes up in context of negative mass (when discussing stabilization of wormholes and similar scenarios). The closest other context is discussions involving particles moving faster than light, but these typically posit complex rest masses, not negative ones. --Christopher Thomas 19:34, 1 September 2005 (UTC)

negative energy redirects here again, it seems that after i removed the redirect that article was deleted, remade, filled with gibberish, and finally redirected here. Whether or not redirecting here keeps it from being gibberish doesn't justify it to be linked here, there is simply no information about negative energy here. I'm pretty sure that neither of the negative mass theories expressed here even have any negative energy consequences, which seems to invalidate the reason that User:Christopher Thomas gave for redirecting: "Replaced gibberish with redirect (negative energy and negative mass are equivalent)."

Anyways, this problem needs some kind of resolution which will stick. Perhaps we could start a real article on negative energy, or alternatively add some negative energy content to this page? Intangir 06:57, 28 August 2005 (UTC)

Hardly an expert here, but doesn't the classic E=mc2 formula indicate that negative mass is equivalent to negative energy? Substitute in a negative number for m and you get a negative result for E. The article also has some stuff on negative kinetic energy in the Forward's analysis section. Bryan 20:46, 28 August 2005 (UTC)
Actually, the full equation is e2=m2c4+p2c2, where p is momentum. Assuming no momentum gives us e2=m2c4. Normally from there, we take the principle square root, assuming mass and energy must be positive. But if we can't make that assumption, I don't see how that equation would imply that negative mass and negative energy are equivalent. Also, yeah i guess negative temperature would be a form of negative energy. Intangir 00:55, 29 August 2005 (UTC)
If inertial mass = rest mass and is seen as the modulus of the gravitational mass (which can be +ve or -ve) then E=mc2 would always be positive. This ties in with the idea that negative energy would consist of negative photons, which are undefined since they are their own anti-particles. The only form of negative electromagnetic radiation I can think of is a reversed vibration in space-time ie real waves 1800 out of synch.Brian O'Donnell (talk) 19:07, 17 July 2008 (UTC)
I think it should be a real article about negativ energy. Negtive energi exists in quite non-exotic forms, for example the potential energy in a gravity field or the potential energy in an eletromagnetic field. That IS negative energy. In fact, matter/antimatter pair can be created in strong elektromagnetic fields so that the particles "pays" the energy for the mass by the energy of the potential energi. So it has nessecary not anything to do with exotic matter. There is also possible to argue that the universe total energy can be zero, because the gravitational potential energy is negative and the total sum may be zero. 83.241.133.2 12:20, 16 September 2005 (UTC)
The distinction is that negative potential is completely arbitrary; it depends on what you define to be zero. Example: does a rock two meters above the ground near sea level have the same potential as a rock two meters right above the top of a mountain? They will have (virtually) the same kinetic energy when they hit the ground. If you defined 0 height to be the top of the mountain, then the rock at sea level would have negative energy. If you defined 0 height to be sea level, then the rock at the top of the mountain would have a lot of potential. Potential is relative. - mako 22:32, 16 September 2005 (UTC)
The problem here is straightforward, ladies and gentlemen. This article is very uninformative on the topic on which I intended to be informed. Something relevant has been lost. Need there be further debate? 75.170.37.221 (talk) 00:08, 18 October 2010 (UTC)

## so does it repel or attract positive mass?

"would produce a system with "negative gravity" that repels ordinary positive mass, but which would be attracted to positive mass and other negative mass particles in a normal manner."

which is it? - Omegatron 00:58, May 2, 2005 (UTC)
• Un-fixed. The accuracy of the sentence in question depends on your definitions of "repel" and "attract". A positive and a negative mass both repel each other in terms of force. However, the negative mass will accelerate in the opposite direction in which it is forced, effectively acting as though it was attracted. This sentence needs to be clarified as there has already been two comments by confused readers on this talk page. I'm not quite sure of the best way to do this though. —TeknicTalk / Mail 05:16, 2 May 2005 (UTC)
• refixed. Intangir 16:31, 3 May 2005 (UTC)

"However, the negative mass will accelerate in the opposite direction in which it is forced"

I don't buy this; this is implying that gravity, inertia, and momentum are the same "force", and that's not true. The repulsive gravity between a postive mass and a negative mass would push them apart, and that's all.

-[User:Qolonoscopy|Qolonoscopy] Sunday, Jan. 8, 2006, 2:04AM EST

• The gravitational behaviour of negative mass bodies can be predicted from first principals as follows:
According to Newtons law of universal gravitation the magitude of gravitational forces felt between two bodies is directly proportional to the product of their masses:
    ${\displaystyle F_{g}={\frac {k(m_{1})(m_{2})}{r^{2}}}}$

The introduction of one body of negative mass into a two body gravitational system would thus result in the following gravitational force being excerted:
    ${\displaystyle F_{g}={\frac {k(m_{1})(-m_{2})}{r^{2}}}=-F_{g}}$

The negative sign of ${\displaystyle F_{g}}$ implies that a repulsive force will be exerted on each of the bodies with respect to the centre of gravity of this two body system. By virtue of Newtons second law of motion the two bodies will accelerate as follows:
   ${\displaystyle a_{1}={\frac {F_{g}}{(m_{1})}}=-a_{1}}$

   ${\displaystyle a_{2}={\frac {F_{g}}{(-m_{2})}}=+a_{2}}$

Remember these values are measures with respect of the CoG and thus imply that both bodies will accelerate in the same direction. The body of positive mass will accelerate in the same direction as the repulsive gravitational forces exerted upon it, while the body of negative mass will accelerate in the opposite direction to the repulsive gravitational forces exerted upon it (i.e. in the same direction as its neighbouring body).
The implications of mass inequaties are as follows:
• ${\displaystyle (m_{1})=(-m_{2})}$ results in the two bodies accelerating mutually (in same direction while maintaining the same relative positions) "forever". This form of perpetual motion, known as negative mass propulsion, requires zero input energy (gravity provides the thrust) while not violating the laws of conservation of energy and momentum.

Newtonian mechanics isn't good enough. Negative mass is attracted to positive mass, if a mass is neglible relative to another, it will move the same path, along the geodesic, regardless of positive/negative, size of mass(As long as neglible, if it isn't it will affect the other mass and change spacetime, and change its own path through that.) 88.159.72.240 (talk) 15:18, 14 November 2009 (UTC)

-Anubeon January 22nd 2006, 21:07 GMT.Talk / Mail

Negative mass can be visualised as a bump in space-time just as +ve mass can be seen as a dent. From here there are two possible kinds of behaviour. Type 1 is where all test masses roll 'downhill'. Type 2 is where +ve masses roll 'downhill' and -ve masses go 'uphill'.
Type 2 shows an internal symmetry and has a kind of symmetry with electrical chrges. Also, -ve masses would be repelled from +ve matter and end up in the empty space between galaxies.
To go back to F=ma, inertial mass is a resistance to change in momentum and ought to be the same for +ve and -ve masses of the same magnitude. For type 1 to be valid, we need a working definition of negative resistance to change in momentum.
Brian O'Donnell (talk) 11:13, 17 July 2008 (UTC)

One potential problem, common to the preceding analyses, is that QM is being ignored. It is widely known that physicists want to be able to describe gravitation in terms of exchanges of virtual gravitons between objects. This means, inevitably, that Planck's constant will become invovled in the equations. Currently we might suspect that Planck's constant is buried somewhere inside of "G", the gravitational constant in the ordinary equations. We could imagine "G" as being a shorthand description of the result of exchanges of virtual gravitons between objects. Anyway, look again at that article on Planck's constant, and note how it is used in the description of the energy of a photon. An ordinary photon has ordinary positive energy, right? What should the equation look like if we wanted to describe a photon that carried negative energy instead? LOGICALLY, Planck's constant should be a negative number, per Dimensional analysis. The "units" of Planck's constant are "energy multiplied by time", so if the energy of the photon is negative, then the energy-dimension of Planck's constant should also be negative, for consistency. Heh, it is reasonable to think that all through this article on Exotic Matter, whenever Negative mass/energy is discussed, a negative Planck's Constant should also be mentioned --and a number of results of interactions between particles would change. For example, two ordinary protons have the same electric charge and accelerate away from each other as a result of (A) the electrostatic force between them and (B) the fact that they have ordinary mass. If they have negative mass, however, then while the article currently talks about how (B) is affected, it ignores the effect of a negative Planck's constant upon (A). It could very well be that the force is reversed, and the effect of that upon the two negative-mass protons is: they still accelerate away from each other. This leaves us with a major question, "How would we describe an ordinary proton interacting with a negative-mass proton?" Which version of Planck's constant should be used? Both??? How!?!? I don't have an answer for that, but I can say that with respect to Gravitation, a negative Planck's constant would allow Quantum Mechanics to say that two negative masses should accelerate toward each other, compatible with the "bumps" in curved spacetime of General Relativity that should be associated with negative masses. That is, two negative masses should strive to make a bigger "bump", just as two ordinary masses strive to make a bigger "dent", in the fabric of spacetime. Here's a more extensive explanation that's been posted on the Web for several years: http://www.nemitz.net/vernon/BALANCD2.pdf —Preceding unsigned comment added by Objectivist (talkcontribs) 16:58, 11 November 2008 (UTC)

## antimatter negative mass or charge

"Certainly, this observation implies that their ratios differ only in sign, but it does not make clear whether it is charge or mass which is negative."

but earlier you said that if a particle had negative mass, it would accelerate indefinitely and other bizarre effects. i think this sentence may be talking about "intertial mass" and not just "mass" in general, though it's not clear to me what the difference is. - Omegatron 01:04, May 2, 2005 (UTC)
Yes, i meant to say inertial mass there, I think I have clarified it now Intangir 16:37, 3 May 2005 (UTC)

## How many supporters

Supporters of the theory that antimatter has negative gravitational mass

Are there any significant supporters of this? - Omegatron 16:48, May 3, 2005 (UTC)
Good question, seems doubtful but it is a fringe topic people sometimes babble about. That whole section about antimatter is too POV, it needs some good criticism Intangir 16:53, 3 May 2005 (UTC)
Yeah, I figured. Definitely leave it in; just demonstrate that a little evidence does exist for the standard view. - Omegatron 17:04, May 3, 2005 (UTC)
Indeed. The SN 1987A event is given as empirical evidence that antimatter reacts identically to matter under gravity, but I don't understand it enough to explain how. Intangir 17:13, 3 May 2005 (UTC)
Yeah. This link explains it too: [1] - Omegatron 18:45, May 3, 2005 (UTC)
I've found no significant support for the negative gravity idea on the web. However, there seems to be wiggle-room in the evidence, so I'm not writing off the posibility. A recient paper talking about this topic is “Precision Experiments with Antimatter” by Rolf Landua in 2003 PDF file. IMO the SN 1987A event does not prove that anti-matter falls down, just that anti-neutrinos travel straight. Since space is curved, their paths bent as expected, confirming General Relativity applies to both matter and antimatter. Had they traveled differently, that would have been very weird. I have yet to see convincing evidence that antimatter falls down. However, if it did not, a lot of what we think we know would need to be revisited. Bill Cox Aug 5, 2005

## Why redirect

Why is "negativ energy" redirected to "exotic matter"? Negtive energi exists in quite non-exotic forms, for example the potential energy in a gravity field or the potential energy in an eletromagnetic field. That IS negative energy. In fact, matter/antimatter pair can be created in strong elektromagnetic fields so that the particles "pays" the energy for the mass by the energy of the potential energi. 83.241.133.2

There are two talk sections in this page (both with "negative energy" in their headers) that discuss the whys of this. Bryan 15:20, 15 September 2005 (UTC)

## Confusion

This phrase is found in this article "The closest known real representative of exotic matter is a region of negative pressure density produced by the Casimir effect."

However, if one goes to the negative pressure article, one finds this: "The Casimir effect is mistakenly thought to produce a region of negative pressure."

Can someone confirm which is correct and edit the corresponding article?

I think this is a problem of phrasing, more than one of content. The Casimir effect produces a region where the energy density of vacuum is lower than the energy density in free space. This is the closest thing to a region of "negative energy" that we've observed, but it's only "negative" due to arbitrarily setting the zero point at the energy density of vacuum in free space. As for "negative pressure", I believe what the article is trying to say is that it's not an attractive force being produced, but a lessened repulsive force, resulting in unequal forces acting on the two sides of each plate (same argument that says you're blown out an airlock, not sucked out). By all means take a stab at rewording it; I'm still on Wiki-Sabbatical, myself. --Christopher Thomas 20:37, 23 September 2005 (UTC)
As for editing the heading part, a decent explanation would probably take too much space. I suggest adding a section about it somewhere in the body of the article. One way to explain the Casimir Effect involves the "virtual particles" that fill the vacuum, even when a volume of space is totally empty of ordinary matter and energy. All possible types of particles constantly pop into a very temporary existence, and then vanish again; this is an important consequence of the Uncertainty Principle. The energy-content of that otherwise-empty volume of space is required to be Uncertain in magnitude, so we are granted a miniscule and impossible-to-directly-detect loophole in the Law of Conservation of Energy. We can only detect some of the side-effects of the virtual particles having been there, of which the Casimir Effect is one. Now, different virtual particles can persist for different amounts of time; the less mass/energy they have, the longer they can persist. All virtual particles can pop into existence with a lot of "virtual energy", moving at nearly the speed of light. That energy is required to disappear before it can be detected; analysis of the equations of the Uncertainty Principle indicate that virtual energy vanishes in a way that at its prettiest mimics the mathematical curve of 1/x (nothing keeps it from vanishing faster or irregularly; Uncertainty is the rule here!). When some particle's total virtual energy drops to a point equal to the mass of a given virtual particle, that particle is required to vanish. For some particles like massless photons or gravitons, they have no lower limit of energy, so they can persist essentially forever. This is actually necessary for Quantum Mechanics to explain how forces like ElectroMagnetism work; virtual photons are "exchanged" between electrically charged particles, and since the EM force has infinite range, the virtual photons need to be able to persist forever. One key fact here is that low-energy photons are bigger (have longer wavelength) than high-energy photons; a given volume of empty space therefore must be presumed to be quite full of large low-energy virtual photons. Finally we arrive at the Casimir Effect, in which two sheets of metal are placed face-to-face with a tiny gap between them. There is no room between them for those big virtual-energy photons! (The plates have to be metal since other materials are basically transparent to low-energy photons.) The net effect is that there are more particles of virtual energy "outside" the two plates than between them. Think of all those virtual particles as being equivalent to a kind of "atmosphere". Fewer particles bouncing against a given surface --or reflecting off metal-- is equivalent to a lower pressure. In the Casimir Effect, the "lesser pressure" exists between the two metal plates, so they seem to attract each other, as they are literally pressured together by the greater numbers of external virtual particles bouncing off them. The Casimir Effect is considered to be the best proof available that virtual particles do actually exist. On another hand, some workers have connected this phenomenon to something known to chemists as "van der Waal's force":

## absolute zero

At absolute zero, does an object have a mass of zero? If so, could it be possible if you were to have an object with a temperature of below absolute zero then it would have a negative mass? And according to Einstein's famous equation ${\displaystyle E=mc^{2}}$ negative energy can exist as long as the mass is negative. Also, what would the mass of a tachyon be, could it possibly be negative? Just some thoughts. --William and Sean 05:10, 2 November 2005 (UTC)

Temperature does not affect mass (it is only the measure average velocity of a group of atoms) and the scale only goes from "moving really fast (real hot)" - "moving around a bit (room temp)" - "not moving at all (absolute zero)". There's no "moving backwards".
Actually, velocity of the particle affects particle's (relativistic) mass, and energy has mass too, thus heating (absorbing energy) means gaining mass while cooling (losing energy) means reducing mass. However, this effect is, supposedly, too minute to measure in a laboratory. Perhaps it could be observed in stars, quasars and black hole accretion disks? —Preceding unsigned comment added by 147.91.1.45 (talk) 08:47, 15 October 2009 (UTC)
As for negative mass / energy, sure. But they are only a consequence of the math we use, and not something that has been observed or even postulated. I think I read from the exotic matter article that a certain pair of + and - masses, accellerating together forever, do not violate the law of conservation of momentum. It's fun to think about (and use in scifi) but not really practical. Tzarius 09:54, 4 November 2005 (UTC)
lmao tachyon with negative mass lolz. dude, its like so friggin obvious it cant be negative cuz its fukin mass is complex, ur e=mc squared is not complete in describing the energies of all object in classical theories. and no no1 nos wat that looks like :P. btw there no such thing as abosutle 0 its only dubbed that name cuz its the ground state of teh vacuum. so because there no such thing as 'absolute 0' ur sentence does an object have a mass of zero is false for all non-zero locally positive/negative rest mass objects (it means everday object cant be turned to zero mass by cooling it). lolz i feel like i just explained how to use paper towel to a kid -NOOBLET

## Negative energy (again)

Someone had replaced the negative energy redirect page with a short rehash of some of the exotic matter and Alcubierre drive material.

As there was substantial protest over negative energy redirecting here, and as people had correctly pointed out that it's a term used with respect to several phenomena, I've turned it into a disambiguation page.

I hope that this rewrite is acceptable to anyone involved in the original discussions. --Christopher Thomas 05:52, 12 November 2005 (UTC)

Excellent! Intangir 06:27, 13 November 2005 (UTC)

## Negative mass?

Negative mass would basicially result in the following:

• Negative moment of inertia
• Angular momentum switches sign
• Torque switches sign
• Kinetic energy switches sign
• Negative energy

However, if the length of such an object was imaginary:

• Imaginary velocity (velocity along one or more imaginary axes)
• Angular momentum has the same sign
• Torque has the same sign
• Kinetic energy has the same sign
• Positive energy

As long as their masses are of the same sign for every action there is an equal and opposite reaction (Push for Push, and Pull for Pull). But if their masses differ in sign, for every action their is an equal but not opposite reaction (Push for Pull, Pull for Push). A negative mass implies either negative energy or movement along the complex plane(s). Same sign masses would interact with less than 100% efficiency, where as the interaction between oppositely massed objects would have more than 100% efficiency.

Up. Down. Charm. Strange. Top. Bottom.

Push for Pull, Pull for Push.

10^23 + cycles per second. Non-stop. No collapse.

Kmarinas86 14:47, 19 July 2006 (UTC)

## Which way does antimatter fall?

The last section "Which way does antimatter fall?" is about antimatter. But the article is about exotic matter. What do I do with it?! --Yanwen 22:59, 24 September 2006 (UTC)

Actually, the section doesn't look entirely irrelevant because it's discussing whether antimatter has negative gravitational mass, which is a characteristic of exotic matter. There may be a bit much here, though. If you want to get rid of some of it I'd suggest moving it to Gravitational interaction of antimatter. Bryan 23:27, 24 September 2006 (UTC)
Its relativent because antimatter is often confused to have negative mass. This is because antimatter-matter reaction involves negative energy state(*), which Dirac discovered when he showed that the solution to combining quantum physics and special relativity. See Dirac Sea for more info. (*)Side Note for clarification: Honestly I cannot remember if its the antimatter, that actual photon, or the virtual photon, that we attribute the negative energy state, so I am using the word "involves" here.Physics16 (talk) 15:20, 2 November 2011 (UTC)

## Question

I have a question regarding F = ma implying that exotic matter would move in the opposite direction of the force applied. I thought that the acceleration term carried a direction aswell, wouldn't that then imply that it is accelerating in one direction and having a force applied in the opposite direction? I am probably missing something. Phoenix1177 20:49, 19 September 2007 (UTC)

The problem with exotic matter is that it never acts the way you'd expect. For so-called 'negative' matter, the gravitational mass and the inertial mass are opposite in sign. So if I pull on it with the gravity of a normal positive mass, it will move towards the positive mass. But at the same time, the negative mass repels the positive mass, so the positive mass is pushed away. So if you had a negative mass next to an equal positive mass, the pair would accelerate and keep on going, maintaining the same separation between them. Oddly, the pair's total kinetic energy apparently remains at zero. This sort of thing is why I hope exotic matter doesn't exist outside of science fiction. Michaelbusch 21:04, 19 September 2007 (UTC)
We would expect the same, if antimatter had negative mass, with a proton and an antiproton. The force between them would be attractive, causing the proton to move towards the antiproton. But since F=ma and m was negative, the antiproton would move away from the proton. So surely the fact that this behaviour is never observed serves as sufficient proof that antimatter has positive mass. So why, according to the article, is this considered questionable? Manwiththemasterplan 22:17, 30 October 2007 (UTC)
It isn't questionable, but it is very hard to observe due to the difficulty of making enough antimatter with sufficiently low energy to observe it interact gravitationally - although now that I think about it, something like CERN or Fermilab might not work properly if gravitational acceleration wasn't canceled out. Michaelbusch 22:32, 30 October 2007 (UTC)

To add to this idea, is there some reason why F = ma couldn't "actually" be F = |m|a (using the absolute vlue of the mass)? Supposing there is such a thing as negative mass that accelerates in the same direction as the force applied, would the substitution mess anything else up? I really don't know anything about this subject (wandering around on wikipedia...), but I read that part of the article and thought something like "hmm". Joelanders (talk) 21:49, 4 April 2008 (UTC)joelanders

## Citation needed for nanotube creation?

Come on... that's like common knowledge... Carbon nanotubes are talked about ALL the time. I mean, fullerenes and carbon nanotubes have been studied since the 50s. I think that particular "citation needed" should be removed. Man, you guys really go overboard with those sometimes. —Preceding unsigned comment added by 98.209.137.136 (talk) 07:47, 9 August 2008 (UTC)

## Reference list error

Reference 8 has an error at the end of it. It should read - http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/antimatter_fall.html Can someone who knows how to, please correct it.--83.105.33.91 (talk) 11:48, 1 October 2008 (UTC)

## Complex mass

So, we've addressed imaginary masses, but what about complex ones? They definitely have complex energies, and I have no idea what results that would have. —Preceding unsigned comment added by Po8crg (talkcontribs) 14:26, 19 March 2010 (UTC)

It is written: particle with imaginary rest mass would always travel faster than the speed of light.

I think the particle which always travel faster than the speed of light, has no rest mass. Nyunyuc (talk) 12:23, 24 August 2013 (UTC)

## Confusing sentence

If the reverse were true, and antiparticles had negative inertial mass and the same charge, then the normal particle with positive inertial mass would be repelled by its antiparticle.

But it doesn't explain why negative mass and opposite charge is not possible.

We don't know that they are NOT possible definitively. -G (talk) 15:18, 23 June 2011 (UTC)
Actually we kind of do, in that the particle cannot have both negative mass, negative energy, and negative charge. If it did then you would violate the principles of the Casmir Effect or particle would switch over to a positive charge and positive with less time than it takes for an atom to go a Plank second. Simply because the term we are talking about is either I believe the quotent of mass and energy (for one side to be dimensionless), it kind of has to be either/or, not both. Physics16 (talk) 15:13, 2 November 2011 (UTC)

## Difficulties with Negative Energy

Template:Hidden I have removed this from the article. I don't see what it has to do with exotic matter at all. Perhaps some of it could be sourced and adapted for the negative energy however. 05:20, 2 May 2010 (UTC)

## Moving content

Most of the content of this article is about the negative mass and this content is now present in negative mass article, and little content about imaginary mass is now present in tachyon article, which has section about mass and other possible meanings of term "exotic matter" (which are mentioned in intro) were included here.

If turning this article into disambiguation page is really too radical change, then perhaps negative mass section could be shortened with {{main}} on top of it pointing to negative mass article. Imaginary mass section wouldn't really need to be shortened because it is already short. --antiXt (talk) 07:44, 25 July 2010 (UTC)

Shortening with a {{main}} sounds reasonable. I could go for that. 13:23, 25 July 2010 (UTC)
It is done. --antiXt (talk) 17:13, 27 July 2010 (UTC)