Here's my second-to-last review of Stephen Hawking's Universe, a series
broadcast on PBS last Fall. I really don't know anything about dark matter
and how much to believe the results presented in this episode, so I'd
appreciate comments from those who do. I hope you enjoy this interlude
from the discussions about Noah and evolution.
Stephen Hawking's Universe
Episode 4: On the Dark Side
This episode discusses the end of all things. How will the Universe end?
The answer depends upon the amount of matter in the Universe. It will
either expand forever, getting cooler, or end in a Big Crunch. What we
know of the Universe now is that it is flat, on the edge of the two
possibilities. But we may not be able to see all the matter. As part of
the discussion, the strange acronyms of astronomers and particle physicists
are used: MACHOs and WIMPs (GUT and TOE are saved for the last episode).
In the 1960s, Vera Rubin at Kitt Peak Observatory measured the rotation of
galaxies and found that star orbit speeds were the same from center to
edge-unlike what is expected from Kepler's equations. Something else must
be producing gravity at the edges of the galaxies, which we can't see,
dubbed "dark matter." She and her coworkers inferred that 90% of the mass
of spiral galaxies are dark.[for more about her experiments, see ref. 1]
Christopher Stubbs at the University of Washington is hunting for dark
matter. He says, "There's an infinite amount of science to do." That seems
naive, as we know that there are limits to science. In any case, the
science he does is to look at the edges of galaxies for machos (massive
compact halo objects). Machos are a type of dark matter, perhaps
compressed corpses of stars (brown dwarfs). If the macho is heavy enough,
its gravity will focus a star's light like a lens, causing it to
momentarily appear brighter (Einstein's relativity). After 2 years of
collecting data on thousands of stars, his group found one star whose
intensity increased and decreased in a manner predicted by relativity.
Stubbs: "Our experiment has detected a previously unknown component of this
galaxy." The narrator of the program states that "Dark matter is no
fantasy." But not enough machos to account for rotation of stars. How do
we know how numerous machos are? I hope that there has been more than one
Another possible source of dark matter is the neutrino, one of the many
types of particles produced in the Big Bang and which suffuses the
Universe. But do neutrinos have mass? They are hard to catch, since they
move rapidly and interact weakly with matter (a type of wimp--weakly
interacting massive particle). For example, 100 trillion neutrinos fly
through your body in a sec. Fred Rinnes was the first neutrino hunter, and
received the Nobel prize for detecting them in 1956.
Neutrinos are also produce in nuclear reactors. Yves Declais of the Chooz
Neutrino Project sets traps near nuclear reaction under ground, to reduce
background noise from cosmic rays. His experiment is to see if neutrino
undergoes some kind of transformation from source to detector, 1km away.
If so, then it has mass.
In the recent PSCF, Loren and Deborah Haarsma report that it has been
discovered that some neutrinos have non-zero mass. But the actual value of
the mass isn't known, so we are still unable to determine mass density of
Carlos Frenk of the University of Durham makes computer models of early
universe. His calculations depend upon the characteristics of dark matter,
since aggregates of exotic (dark) particles produced 100 sec after Big Bang
may be responsible for the gravity to produce stars and galaxies. When he
plugged the neutrino hypothesis (assuming the neutrinos have mass) into his
evolutionary cosmology, the model Universe produced was similar to ours,
but upon closer inspection it didn't match. Since we now know some
neutrinos have mass, what are the implications for his negative
calculations? He then used "invented" cold dark matter (unobserved wimps
that particle physicists theorize were produced in the Big Bang) and the
calculations worked. But does cold dark matter really exist?
Neil Spooner, from Sheffield University, has set up a wimp detector in a
water tank in the bottom of Bogley (sp?) mine, the deepest shaft in Europe.
In the one mile deep salt mine, cosmic rays are blocked. So far, he?s seen
nothing, but he thinks he still needs 100x more sensitivity. Then if he
doesn?t see anything, wimps don't exist. But why can't we keep saying we
just need more sensitive instruments? Despite these negative results, he
believes that 99% of the matter in the Universe is dark matter--not protons
and electrons. He thinks that not only are humans not at the center of the
universe [see references in my review of episode 1 for a response to this],
we aren't composed of ?normal? matter. . Since we aren?t normal, should
we think of humanity as insignificant or unique?
Sandra Faber, from the University of California, Santa Cruz, is mapping the
Universe. Galaxies are not distributed evenly: more like at the edges of
bubbles. The Milky Way and our neighboring galaxies are moving at
600km/sec towards a supercluster of galaxies, called The Great Attractor.
Why? "Dark matter is key...it's in charge." She bets the Universe will
expand forever, ending in a sea of elementary particles. On the other
hand, Hawking thinks it'll Crunch.
Hawking end this episode by saying, "I can assure worried investors, either
way, the Universe is good for many billions of years more. The end may be
coming, but not just yet." As Christians, we look forward to the end of
the World. Our Lord Jesus will return, but we don't know when.
1. V. Rubin, _Sci. Am._, *1983*, Jun, 96.
2. L. D. Haarsma and D. B. Haarsma, _Perspectives on Science and Christian
Faith_, *1998*, _50_, 160-1.
3. G. O. Abell, D. Morrison, S. C. Wolff, _Realm of the Universe_,
Saunders: New York (1988), pp. 460- 1.
4. Matthew 24: 36-44.