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EDG
2009-Nov-13, 04:52 PM
In a SF story I recently read (by Alastair Reynolds, in "Zima Blue") the author uses something called "Shadow Matter" as one on the big plot elements. This is basically matter that's opposite in every way to normal matter, that doesn't interact with normal matter in any way except gravity. Otherwise, it forms atoms and molecules and planets and stars in exactly the same way as normal matter... just undetectable except by gravitational interaction.

In the story, he has a star with a higher gravity than it should (which means it burns brighter than it should), and a planet with a shadow matter component.

I understand that it's a conjectural scientific concept usually referred to as "Mirror Matter"... but it sounds rather similar to Dark Matter, doesn't it? If it's not supposed to be the same, then what are the differences between Mirror Matter and Dark Matter? And if Mirror Matter is opposite to normal matter, then how would that make it different to Antimatter (which is still detectable by other means, at least).

Between Mirror Matter, Dark Matter, Negative Matter, and Anti Matter I'm getting rather confused :).

Cougar
2009-Nov-13, 06:07 PM
..."Shadow Matter"... doesn't interact with normal matter in any way except gravity.

Well, antimatter does interact with normal matter.

I don't know of any consistent theories involving "negative matter."

See here (http://en.wikipedia.org/wiki/Mirror_matter) for more on mirror matter.

Nick Theodorakis
2009-Nov-13, 06:22 PM
Here's another article on mirror matter, (http://www.daviddarling.info/encyclopedia/M/mirrormatter.html) which also compares it to supersymmetric (SUSY) particles that are also theorized.

It's possible that dark matter might be composed of either mirror matter or SUSY particles, but neither have been proven to exist yet.

Nick

DrRocket
2009-Nov-13, 06:28 PM
[QUOTE=EDG_;1621924 And if Mirror Matter is opposite to normal matter, then how would that make it different to Antimatter (which is still detectable by other means, at least).

Between Mirror Matter, Dark Matter, Negative Matter, and Anti Matter I'm getting rather confused :).[/QUOTE]

Detection of antimatter is pretty simple.

You insert your detector. If it disappears, that was antimatter.

trinitree88
2009-Nov-13, 07:19 PM
Here's another article on mirror matter, (http://www.daviddarling.info/encyclopedia/M/mirrormatter.html) which also compares it to supersymmetric (SUSY) particles that are also theorized.

It's possible that dark matter might be composed of either mirror matter or SUSY particles, but neither have been proven to exist yet.

Nick

Nick Yep I find it interesting that with regular baryonic matter, all the particles in the Standard Model couple both to gravity, and to the weak force, but the proponents of dark matter, mirror matter and SUSY particles conveniently have their putative particles fail to couple to the weak force while still coupling gravitationally, unlike anything we actually have data on.
To date, the weak force is also shown to be universal in it's coupling. After some twenty+ years, supersymmetry with it's 17 particles and 17 antiparticles has a perfect record.....none found. :shifty::naughty::eek: pete

EDG
2009-Nov-14, 02:32 AM
I had a look at the mirror matter wiki page before I asked here... it gave some background but didn't really explain the differences too well IMO.

So mirror matter could actually be dark matter?

trinitree88
2009-Nov-14, 04:18 PM
I had a look at the mirror matter wiki page before I asked here... it gave some background but didn't really explain the differences too well IMO.

So mirror matter could actually be dark matter?

EDG. Nobody knows at this point. pete

JohnD
2009-Nov-14, 05:23 PM
EDG,
That was a 'story', from the shelf marked Science Fiction. It's not real science. SF writers are most original, but their stories are imaginary!

Rather more interesting is the New Scientist article ("In SUSY we trust", NS, 14/11/09, p.37)) on supersymmetry theory - and practice, in the LHC - that points out that SUSY can explain dark matter, sort of. The massive supersymmetrical counterparts to the particles of the standard model will, by this time in the Universe, have decayed into neutralinos. Enormous amounts of neutralinos, with mass and low interaction with normal matter that matches observed dark matter effects.

No doubt Dr.Rocket et al wiil pointout where this doesn't match observation.

John
(PS See: http://www.newscientist.com/article/mg20427341.200-in-susy-we-trust-what-the-lhc-is-really-looking-for.html )

Cougar
2009-Nov-14, 07:08 PM
Rather more interesting is the New Scientist article ("In SUSY we trust", NS, 14/11/09, p.37)) on supersymmetry theory - and practice, in the LHC - that points out that SUSY can explain dark matter, sort of. The massive supersymmetrical counterparts to the particles of the standard model will, by this time in the Universe, have decayed into neutralinos. Enormous amounts of neutralinos, with mass and low interaction with normal matter that matches observed dark matter effects.

That was a pretty good article! So neutralinos would be fermions, and they wouldn't be 'hot' like neutrinos....

I'd be happy with that result. :)

blueshift
2009-Nov-14, 09:43 PM
There was a book out long ago that I read at a nearby library called "Mirror Matter" and it simply referred to antimatter, not DM nor supersymmetric particles. This is likely where some SF writers found the terminology, depending upon the age of the writer. If the writer is in his or her 50s or older than that could be the source and the description in the OP seems to describe a complete misunderstanding of differences between antimatter and DM, something I do expect from SF writers.

cjameshuff
2009-Nov-15, 02:57 AM
There was a book out long ago that I read at a nearby library called "Mirror Matter" and it simply referred to antimatter, not DM nor supersymmetric particles. This is likely where some SF writers found the terminology, depending upon the age of the writer. If the writer is in his or her 50s or older than that could be the source and the description in the OP seems to describe a complete misunderstanding of differences between antimatter and DM, something I do expect from SF writers.

It's not called antimatter and doesn't act remotely like antimatter, why would you think it's a mistaken term for antimatter?

I'm pretty sure Alastair Reynolds knows what antimatter is, and is not using "mirror matter" in the long obsolete and never popular sense as an alternative term for antimatter while also confusing its properties beyond all recognition. "Mirror matter" is a distinct concept, with a mirror counterpart for every particle...there would be mirror antimatter as well.

If overall symmetry is unbroken, mirror matter would behave just like normal matter, except for being observable to us only by gravity...the mass of mirror matter in the universe would equal the mass of normal matter, and it would clump up into stars and galaxies...it would not act much at all like dark matter, and there wouldn't be enough of it. If the symmetry is broken, the mirror particles could be more massive and might behave quite differently as a result...perhaps this could account for dark matter, but it would seem to weaken the original case for mirror matter as a way to retain unbroken symmetry.