Number 657, October 14, 2003
by Phillip F. Schewe, Ben Stein, and James Riordon
Cosmology Theories Come and Go
Cosmology theories come and go as new information becomes available.
The geometry and nature of the universe must be one of the most fascinating
questions for the human species. Early Egyptians thought the universe
was a rectangular box. Alexandrian Greeks pictured the cosmos as a set
of concentric crystalline spheres, a view adopted by the medieval Catholic
Church, which executed Giordano Bruno for holding that the universe
was infinite in extent. In the 20th century Hubble's surveys of receding
galaxies supported the idea of an expanding spacetime scaffolding. This
model, now called the big bang, is generally the accepted overarching
theory, but it has been amended several times to include an early "inflationary"
phase and, more recently, the existence of dark energy, an entity or
mechanism which apparently allows the expansion of the universe visible
to our telescopes to be speeding up, and not slowing down. Also not
slowing down is the list of new cosmological ideas. Last year's entrant
was the "ekpyrotic"
model, according to which our universe and all the energy and matter
residing therein arises from the collision of two immense membranes
embedded in an even larger multi-dimensional volume. Last week's interesting
new cosmology development was the suggestion that the universe is finite
and has a dodecahedral (soccerball) geometry (Luminet et al.,
Nature, 9 October 2003). Meanwhile,
this week's leading cosmology news, presented at a meeting in Cleveland,
featured observations of very distant (8 to 10 billion light years away)
and unusually bright supernovas, recorded by the Hubble Space Telescope.
This accords with the dark energy model which holds that the general
expansion of the universe was relatively slow 10 billion years ago and
afterwards got much faster, owing to the propulsive effects of the dark
energy winning out over the attractive and slowing effects of gravity
(paper by Adam
Reiss; also see Science News
Online, 11 October ).
Why Don't Alcohol and Water Mix Very Well?
Bartenders who make cocktails shouldn't worry about trying to get
alcohol and water to mix completely. Nature prevents even the most patient
drink-makers from fully blending the two. Studying methanol, a simple
non-drinkable alcohol that nonetheless can provide insights into ethanol,
or drinking alcohol, a US-Swedish collaboration (Jinghua
Guo, LBL, 510-495-2230) has obtained new molecular-level details
of why water and alcohol don't mix very well. Using LBL's Advanced Light
Source, the researchers performed x-ray emission (XE) and x-ray absorption
(XA) spectroscopy, which allowed them to study such things as the chemical
bonds that form between molecules in the liquid over timescales of picoseconds
to femtoseconds. Looking first at a liquid of pure methanol, the researchers
observed the presence of rings and chains made of 6-8 methanol molecules.
When they mixed methanol and water, they found that the 6-8 molecule
chains connected with water molecules to form larger water/methanol
clusters (see image).
These clusters are very stable, because of the (hydrogen) chemical bonds
that hold them together. But the water/methanol clusters also have a
high amount of order, thereby reducing the liquid's overall disorder
(entropy). Yet entropy must stay the same or increase in the liquid.
So nature discourages the formation of more clusters in the liquid,
and this can explain why alcohol and water don't like to mix completely.
In addition, the research sheds light on a 40-year controversy over
the molecular structure of pure methanol liquid, and the structures
that are formed when water and methanol combine. For example, other
researchers had suggested that water surrounded methanol in a static,
ice-like structure. (Guo
et al., Physical Review Letters, 10 October 2003).
A New Type of Medium Interface Features Negative
Refraction
A new type of medium interface features negative refraction or, depending
on the angle of incidence, positive (conventional) refraction. This
switch-hitting optical ability (the technical name for it is "amphoteric"
refraction) is a first. Furthermore, the same type of interface can
be used to refract (negative or positive) a ballistic beam of electrons
(electrons traveling, as waves, over a very short distance in a straight
line). Refraction, a change in direction, is what happens when light
waves (or other kinds of waves) move from a material with one index
of refraction (say, air) into a medium (water, say) with a different
index. Physicists at the National Renewable Energy Lab in Colorado have
devised their material sample not from a collection of tiny rods and
split rings mounted on boards, as was the case with previously reported
negative-refraction materials. Instead they used a YVO4 bicrystal. Negative-refraction
materials are also called "left handed materials," or LHM,
because they refract light in a way which is contrary to the normal
"right handed" rules of electromagnetism (see past summary
in Update
#628). LHM researchers hope that the peculiar properties will lead
to superior lenses, and might provide a chance to observe some kind
of negative analog of other prominent optical phenomena, such as the
Doppler shift and Cerenkov radiation. According to Yong
Zhang (303-384-6617), an additional feature of their material is
that it inhibits all reflection. When considering the refraction process,
reflection can be thought of as a sort of energy-loss penalty paid by
waves when they are refracted, and so a reflection-less lens would be
of enormous value in, for example, the transport of high-power laser
beams. (Zhang
et al., Physical Review Letters, 10 October 2003;
see figure)
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