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Author Topic:   Missing Matter
Hoof Hearted
Junior Member (Idle past 3388 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


(1)
Message 1 of 104 (481237)
09-10-2008 5:07 AM


One of the purposes of the new LHC at Cern is to search for dark matter. My understanding is that this has been so elusive thus far, because it has been completely undetectable by current technology. 'Normal' matter is completey oblivious to it and unaffected by it.

I understand that we are only aware of it's existence because the observed motion of galaxies cannot be explained just by the mass of the matter which we know about.

So how can it be that dark matter affects the motion of galaxies when 'normal' matter is not affected by dark matter? Because the we know the motion of observable matter in galaxies is affected by dark matter, am I not correct to suggest that it should be possible to detect dark matter?

I'm sure there's a simple explanation to this.

Edited by Hoof Hearted, : No reason given.

Edited by Hoof Hearted, : No reason given.


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AdminModulous
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Posts: 897
Joined: 03-02-2006


Message 2 of 104 (481249)
09-10-2008 7:11 AM


Thread moved here from the Proposed New Topics forum.
    
Percy
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Posts: 18842
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.5


Message 3 of 104 (481254)
09-10-2008 7:42 AM
Reply to: Message 1 by Hoof Hearted
09-10-2008 5:07 AM


There'll be better answers coming when Cavediver and Son Goku find this thread, but I can tell you a little bit.

Just as you say, normal matter is affected by the gravity of dark matter. That's how we know it's out there, from its gravity. But we can only detect the gravity of massive amounts of matter. The paltry number of particles produced by colliders quickly decay and/or flit and scatter away.

Some of the theorized candidate particles for dark matter exist at higher energy levels than can be detected by existing colliders, and the LHC may find some of these particles. But I don't know how scientists expect to establish a connection between new particles detected by the LHC and the dark matter detected by our telescopes.

--Percy

Edited by Percy, : Grammar.


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Son Goku
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Posts: 1150
From: Ireland
Joined: 07-16-2005
Member Rating: 7.2


Message 4 of 104 (481256)
09-10-2008 7:48 AM
Reply to: Message 1 by Hoof Hearted
09-10-2008 5:07 AM


Noninteracting
Dark Matter interacts either not at all or very weakly with other matter through electromagnetic, strong or weak forces. Hence you can't see it and it passes through normal matter.
It does however interact gravitationally and hence its combined mass influences the motion of the cosmos.
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Hoof Hearted
Junior Member (Idle past 3388 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 5 of 104 (481259)
09-10-2008 7:52 AM


If normal matter is affected by the gravity of dark matter, then I would assume that dark matter is similarly affected by the gravity of normal matter.

Our earth is held together by the force of gravity. So if dark matter is affected by the gravitational forces of normal matter, I would expect dark matter to be attracted towards our earth.

So I wonder therefore, if there is a sphere of dark matter occupying the same region of space as our earth.


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Hoof Hearted
Junior Member (Idle past 3388 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 6 of 104 (481261)
09-10-2008 8:17 AM
Reply to: Message 5 by Hoof Hearted
09-10-2008 7:52 AM


Of course that probably would be dependent on dark matter having similar physical properties as normal matter. What I mean is that normal matter can form planets because it is capable of becoming complex molecules which can have a solid state.
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Modulous
Member (Idle past 363 days)
Posts: 7789
From: Manchester, UK
Joined: 05-01-2005


Message 7 of 104 (481262)
09-10-2008 8:22 AM
Reply to: Message 1 by Hoof Hearted
09-10-2008 5:07 AM


So how can it be that dark matter affects the motion of galaxies when 'normal' matter is not affected by dark matter?

Hi Hoof,

Dark matter is a catchall term for matter that cannot be seen. It might be argued that a brick orbitting Alpha Centauri at 10AU is dark matter since it does not emit light and the amount of light it reflects is below the level of detection. Bricks are unlikely, but difficult to detect Brown Dwarfs or massive compact halo objects or neutrinos.
Theory suggests that these can only account for some of the dark matter.

There are large amounts of 'exotic' matter that does not interact (or only weakly interacts) in an electromagnetic fashion, but still interacts gravitationally. Examples are the theoretical particle the sterile neutrino, the axion or Weakly Interacting Massive Particles (WIMPs). Different cosmology models predict the existence of different types of candidate exotic dark matter. LHC may well discover which flavour of dark matter can actually exist, providing some evidence in support of one model or another.

Enough of these particles of non-zero mass travelling at relativistic speeds (or perhaps just very 'hot') can generate significant gravitational fields which in turn can affect the structure of galaxies etc.

Edited by Modulous, : No reason given.


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rueh
Member (Idle past 1920 days)
Posts: 382
From: universal city tx
Joined: 03-03-2008


Message 8 of 104 (481263)
09-10-2008 8:33 AM
Reply to: Message 7 by Modulous
09-10-2008 8:22 AM


It might be argued that a brick orbitting Alpha Centauri at 10AU is dark matter since it does not emit light and the amount of light it reflects is below the level of detection
I thought that ordinary matter that is not detectable through radiation or ordinary matter that is so dispersed as to render it undetectable was referred to as invisible matter and the term dark matter was used to reference matter that does not interact with ordinary matter execpt gravitationaly. See graphic for an example.

Click to enlarge

Edited by rueh, : No reason given.

Edited by rueh, : No reason given.


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Percy
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Posts: 18842
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.5


Message 9 of 104 (481268)
09-10-2008 8:52 AM
Reply to: Message 8 by rueh
09-10-2008 8:33 AM


There have been two candidates for the dark matter originally detected back in the 1930s, MACHOs and WIMPs. MACHO stands for MAssive Compact Halo Object, which would be objects too small or cold to give off detectable electromagnetic radiation. WIMP stands for Weakly Interactive Massive Particle, which is sort of self-explanatory. The possibility of MACHOs has fallen increasingly out of favor over the past decade or so. Astrophysicists are expecting to find that the vast majority of dark matter consists of WIMPs, which is why they think the LHC might detect the particle or particles that make up dark matter.

--Percy


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Hoof Hearted
Junior Member (Idle past 3388 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 10 of 104 (481269)
09-10-2008 9:08 AM


So am I to assume that particles such as WIMPs cannot practically be detected, because we don't have a means of detecting their gravitional forces amongst the gravity of conventional matter which surrounds us?
    
Son Goku
Member
Posts: 1150
From: Ireland
Joined: 07-16-2005
Member Rating: 7.2


Message 11 of 104 (481701)
09-12-2008 7:19 AM
Reply to: Message 3 by Percy
09-10-2008 7:42 AM


Dark matter particles
But I don't know how scientists expect to establish a connection between new particles detected by the LHC and the dark matter detected by our telescopes.

Neither do we!;) Establishing that a specific new particle found in the collider is directly related to Dark Matter is exceptionally difficult. It could easily be argued that any weakly interacting particle discovered in the LHC are not the as the Dark Matter particle, simply because there would be no direct connection.

One way of telling would be if the particle that was created was very stable, since Dark Matter doesn't seem to decay.


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cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 12 of 104 (481702)
09-12-2008 7:26 AM
Reply to: Message 11 by Son Goku
09-12-2008 7:19 AM


Re: Dark matter particles
One way of telling would be if the particle that was created was very stable, since Dark Matter doesn't seem to decay.

This is by far the key point, and why I would find such a discovery to be one of the greatest of the past fifty years or so.


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RAZD
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Posts: 20119
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


Message 13 of 104 (481819)
09-12-2008 7:24 PM
Reply to: Message 12 by cavediver
09-12-2008 7:26 AM


Re: Dark matter particles
I would think that it also would have to be inert (not attracted to other particles), only combine with other particles with great energy (= collider energy) - perhaps only with other dm particles - and not charged.

As such I would expect it to be difficult identify and to contain.

We've seen where atomic particles (protons, electrons and neutrons, etc) have been broken apart into sub-atomic particles, quarks and leptons (wiki: a proton is made up of two "up quarks" and one "down quark", yielding a net charge of +1, while a neutron contains one "up quark" and two "down quarks", yielding a net charge of 0), that explain the charges and attractions of the atomic particles.

Do you expect the quarks and leptons to be broken down into sub-sub-atomic particles?

Enjoy


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Son Goku
Member
Posts: 1150
From: Ireland
Joined: 07-16-2005
Member Rating: 7.2


Message 14 of 104 (481856)
09-13-2008 6:40 AM
Reply to: Message 13 by RAZD
09-12-2008 7:24 PM


Re: Dark matter particles
Do you expect the quarks and leptons to be broken down into sub-sub-atomic particles?

I would say it's unlikely for a few reasons. The first being and I'm not sure how to say this, the proton is not really "made" of three quarks. Rather the proton is a state produced by the interaction of about eleven different quantum fields. Three of those fields, if they didn't interact with the others, that is if they were free, would have excitations which we call quarks. So those fields are called the quark fields. However since the fields do interact, this picture isn't accurate and the fields never possess those excitations we call the quark particle. Usually when calculating things however we start of by having the fields being approximately free and so we use this fictitous notion of quark.
I hope that makes sense. In a way asking if the quark is made of anything wouldn't be sensible. One could ask if the quark fields are the results of fields interacting on a lower level. This is unlikely though, if the quark fields are made of something it's probably not a field.
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cavediver
Member (Idle past 1903 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 15 of 104 (481858)
09-13-2008 6:55 AM
Reply to: Message 14 by Son Goku
09-13-2008 6:40 AM


Re: Dark matter particles
Rather the proton is a state produced by the interaction of about eleven different quantum fields. Three of those fields, if they didn't interact with the others, that is if they were free, would have excitations which we call quarks. So those fields are called the quark fields.

Great way of putting this :)

However since the fields do interact, this picture isn't accurate and the fields never possess those excitations we call the quark particle.

Never's a bit too strong, don't you think? We eek out quark-like behaviour with our deep inelastic scattering, after all.


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