Talk:Exotic matter

Contents

1 Just a hypothesis 2 Negative energy?? 3 Contradiction 4 negative energy 5 so does it repel or attract positive mass? 6 antimatter negative mass or charge 7 How many supporters

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. &#0xfeff; --fvw* 06:21, 2004 Dec 19 (UTC)

Contradiction

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)

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)

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)

• Fixed —Teknic^{Talk / Mail} 05:05, 2 May 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. —Teknic^{Talk / Mail} 05:16, 2 May 2005 (UTC)

• refixed. Intangir 16:31, 3 May 2005 (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] (http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/antimatterFall.html) - Omegatron 18:45, May 3, 2005 (UTC)