Dark Matter

Not really understanding but knowing it’s important!

I recently read a glowing review of the latest book by Sir Roger Penrose, the eminent mathematical physicist, called The Road To Reality. Having previously read his book The Emperors’ New Mind and just understanding it, I thought

Roger Penrose

his next one would be a welcome companion for long winter evenings.  Wrong!

I managed to the bottom of the third page of the preface before “According to the mathematician’s “equivalence class” notion …..” had me grasping for meaning.  Well over a 1,000 pages of content was destined to gather dust on the bookshelf.

But wrong again!

The idea of matter out there in the universe that is essential to the universe as we know it but is unseen has been sufficiently fascinating for the popular media to refer to it from time to time.  Most people are familiar with the term even if like me don’t really have a clue as to what dark matter is all about.

So a recent press release in a popular English newspaper suggesting that dark matter has been ‘discovered’, if discover is the appropriate term, had me reaching out for Penrose’s book again.  There under the chapter headed Speculative theories of the early universe was, on page 773, a few sentences that almost made sense.  Let me quote them:

For many years, it had become clear that the dynamics of stars within galaxies does not make sense, according to standard theory unless there is a good deal of more material in the neighbourhood of the galaxy than is directly seen in stars.  A similar comment applies to the dynamics of individual galaxies within clusters.  Overall, there seems to be about 10 times more matter than is perceived in ordinary baryonic form.  This is the mysterious dark matter whose actual nature is still not agreed upon by astronomers, and which may even be of some material different from any that is definitely known to particle physicists – though there is much speculation about this at the present time.

So the article in the British Guardian newspaper was worth reading and, subsequently, sharing with you on this Blog.  Here’s are the opening paragraphs of that article:

For 80 years, it has eluded the finest minds in science. But tonight it appeared that the hunt may be over for dark matter, the mysterious and invisible substance that accounts for three-quarters of the matter in the universe.

In a series of coordinated announcements at several US laboratories, researchers said they believed they had captured dark matter in a defunct iron ore mine half a mile underground. The claim, if confirmed next year, will rank as one the most spectacular discoveries in physics in the past century.

Tantalising glimpses of dark matter particles were picked up by highly sensitive detectors at the bottom of the Soudan mine in Minnesota, the scientists said.

Hence the first line of this Post “Not really understanding but knowing it’s important!” If this find is confirmed then, without me knowing the reasons why I say this, it may well serve as one of the huge discoveries of mankind.  Others who know better are encouraged to comment.

Dark Matter Ring

Finally, I was amused when searching for an image to add to this Post, bearing in mind that dark matter is unseen, to find a Google Images search on dark matter produced 23,000,000 results.  Surprised the astronomers didn’t do a Google search ages ago – would have saved a lot of bother!  Oh, nice introduction to Dark Matter on NASA’s web site.

By Paul Handover

3 thoughts on “Dark Matter

  1. OK, although I agree entirely with the preceding, let me bring my little grain of salt. I would be careful about the “tantalizing glimpses”. We have had them before, with all sorts of mysteries. Physicists need jobs too (the search in the USA for Dark Matter is supposed to move to Canada…)

    The deep mine experiments look for WIMPs (Weakly Interacting Massive Particles). In Europe and the USA, the world’s two largest elementary particle accelerators have targeted detectors in said mines, through hundreds of Kilometers of Earth’s mantle. Claims have been made of tentative events.

    The idea for the WIMP search is a bit the same as with neutrino detection. Neutrinos are traditionally supposed to have mass zero (neutrino means the small neutral one, an Italian neologism invented by Enrico Fermi, Nobel prize winner, refugee from Mussolini, and scientific head of the nuclear bomb project in the USA; the concept was from Wolfgang Pauli, to explain the continuous spectrum of beta decay). But it turns out that neutrinos have mass, and they oscillate between types. A whole slew of experiments will try to know more soon.

    It has been known since 1933 (by the Swiss astronomer Zwicky, a supernova specialist, discoverer of the concept of neutron star) that galaxies and clusters of galaxies are missing mass by a factor of at least ten, if one uses straight Newtonian gravity on the observed motions of galaxies or their disks.

    Now Newtonian gravity is the first order of the modern (“Einstein’s”) theory of gravitation. Both theories differ only at very high speeds or fields. Hence the observed discrepancy would mean that our theory of gravitation is false. A class of modification of Newtonian theory was proposed (MOND = MOdified Newton Dynamics, where the gravitational attraction is the same for high acceleration, proportional to the inverse of the square of the distance, but slips into simply the inverse of the distance for weak accelerations).

    But the way science proceeds is to milk a theory to death, until it dies. The Newton-Einstein theory of gravitation is correct in the Earth’s neighborhood, as far as we can see. So the reflex of experimentalists was to look for missing mass under the form of WIMPs. The search was on well before it became obvious neutrino had mass. Now that later fact is a game changer, since supernovas emit copious quantities of neutrinos. Indeed there is less of a missing mass now (maybe only a factor of five instead of ten…)

    Apparently the apparent Dark Matter is concentrated in strange ways: halos, lobes…

    Please remark that in today’s physics, photons have mass zero. All other particles have some mass. The mass zero of the photon has been turned into religion in Relativity theory, but, ultimately, it ought to be considered an experimental fact, to be continually verified. If photons did have a mass, that would be much more of a game changer. It would most probably imply that gravitons have mass too, so gravity would have to be recomputed…

    However, for reasons of logical completeness, Pauli (again!) noticed that Quantum Field Theory would work well if and only if each particle had a symmetric partner across the fermion-boson line. This is called SUSY (“SUperSYmmetry”). That would give plenty of WIMPs. So the search is on. 2010 will bring on line plenty of experiments worldwide, and the LHC in Geneva will ramp up in power.

    As the preceding indicates, Dark Matter could be something radically new (new WIMPs), or simply explained: say by massive neutrinos (?).

    Or then may be gravity was not as we extrapolated it to be, from around our little blue and white spaceship.

    But the real mystery is DARK ENERGY. That, if confirmed, is way out of imagined physics (although it could be claimed that the ad hoc “cosmological inflation” used to explain the homogeneity of the Big Bang was just such a possible prediction!). The universe is expanding, as if there was out there a mysterious anti-gravity. There is no mechanism to explain this (although it can be written down in Einstein’s gravitation equation by re-introducing a scalar term, the cosmological constant, Einstein had introduced to make the universe static, before Hubble discovered the expansion, leading an opportunistic Einstein to declare the cosmological constant was “his greatest mistake”).

    In conclusion, we are extremely far from a final “theory of everything”, contrarily to what some physicists have claimed with profit motivated outrageous naivety (there is great profit in books and fame). Profit is most often a bad adviser to the sharpest thinking (something profit obsessed American regressive economists fail to integrate).

    Verily, in 25 centuries or so of official physics history, I do not know of one period when so much has been officially not known, and blatantly darkly mysterious. Anything could happen. For example, there is not one force theory, but two, and they do not agree conceptually. The explanatory scheme in gravitation (no force, just inertia), is completely different from the explanatory scheme for forces in Quantum Field Theory (whatever that mystery wrapped in an enigma, shrouded by immense Lagrangians, renormalized by reality turns out to want to say).

    Patrice Ayme

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  2. big bang…universe is created…matter…acceleration…momentum… and gravity is created…acceleration…momentum…and gravity …powers the universe… by all standards we understand all power and movement of any and all things must come to a stop at some point … when gravety ceases… all matter will seperate and become what is being called dark matter…at some point …another big bang and the process will happen again….and again and again…

    john l. mccowen
    fitzgerald, ga.

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