What science can and cannot do

The scientific method has been a powerful tool for learning a great
deal about the physical world, but it is not a system for answering all
questions. The only questions science can attack are those that can be answered
by using the five human senses in one way or another. For example,
suppose that someone hypothesizes that the reason earthquakes
occur is that tiny invisible demons living under Earth’s surface cause those
events. That hypothesis is, by definition, untestable by scientific methods.
If the demons are invisible, there is no way for scientists to observe
them. One might look for indirect evidence of the demons’ existence, but
the problem is probably beyond scientific investigation.
It is for this reason that topics such as love, hope, courage, ambition,
patriotism, and other emotions and feelings are probably beyond the
scope of scientific research. That statement does not mean these topics
are not worth studying—just that the scientific method is not likely to
produce useful results.
Another question that the scientific method cannot solve is “why?”
That statement may startle readers because most people think that explaining
why things happen is at the core of scientific research.
But saying why something happens suggests that we know what is
in the mind of someone or something that makes events occur as they do.

A long time ago, scientists decided that such questions could not be part
of the scientific enterprise. We can describe how the Sun rises, how objects
fall, how baseballs travel through the air, and so on. But science will
never be able to explain why these things occur as they do.

Environmental risks of tropical deforestation

Trees in tropical rain forests store huge quantities of carbon in their
tissues, helping reduce the amount present in the atmosphere. The loss of
tropical rain forests and the increased use of fossil fuels (such as oil and
gas) have led to increased concentrations of carbon dioxide in the atmosphere—
what scientists call the greenhouse effect.
Old-growth tropical rain forests are the most highly developed and
diverse ecosystems on Earth. Tropical deforestation, mostly caused by
slash-and-burn agriculture, is the major cause of the great wave of plant
and animal extinctions that is presently plaguing Earth.

Human versus animal smell

There is no doubt that many animals have a sense of smell far superior
to that of humans. Most vertebrates (animals with backbones) have
many more olfactory nerve cells than humans. This probably gives them
much more sensitivity to odors. Also, the structure in the brain that processes
odors (called the olfactory bulb) takes up a much larger part of the brain in
animals than in humans. Thus, animals have a greater ability to process and
analyze different odors. This is why humans use dogs to find lost persons,
hidden drugs, and explosives—although research on “artificial noses” that
can detect scent even more reliably than dogs continues.
Still, the human nose is capable of detecting over 10,000 different
odors, even some that occur in extremely minute amounts in the air. Many
researchers are considering whether smell does not play a greater role in
human behavior and biology than has been previously thought. For instance,
research has shown that human mothers can smell the difference
between clothes worn by their baby and those worn by another baby only
days after the child’s birth.
Scientists are only beginning to understand the role that smell plays
in animal—and human—behavior. For example, animals release chemi-
cals called pheromones to communicate danger, defend themselves
against predators, mark territory, and attract mates.

The most studied stellar magnetic field

The Sun, the only star our solar system, has show that it has a magnetic
field that reaches all over its surface. Astronomers know that this
magnetic field affects the rotation of the Sun and the movement of chemical
elements around its surface. It has concentrated areas of magnetism
called sunspots (dark areas on the Sun that produce magnetic storms).
While astronomers remain uncertain of exactly how the Sun’s magnetic
fields work, the most widely accepted theory involves a stellar dynamo.
A stellar dynamo can be thought of like a generator (an engine
usually fueled by gas that spins a magnet wrapped in coil, producing electricity).
Astronomers theorize that in the case of the Sun, instead of producing
electricity, the stellar dynamo generates a magnetic field in two
ways, each involving powerful motions. The first involves the movement
of gases in the convection zone. (A convection zone is the upper layer of
a star.) In this zone, material close to the surface of a star rises as heat
moves outward from the lower layers of the surface. This process results
in hot gas rising from the surface, in a way that is similar to hot air rising
on Earth. Upon the release of the heat of the gas at the Sun’s surface,
the gas drops down again as it replaced by the hotter gases below the surface.
The second type of motion in a stellar dynamo is a result of the Sun
being made of gas (mainly hydrogen and helium). When the Sun rotates,
its speed is varied due to its gassy composition; this differs from planets,
whose solid composition produces a regular rotation. The irregular rotation
of the Sun is called differential rotation. It causes the equator (the
middle of the Sun) to spin faster than the poles (the top and bottom of
the Sun).

The stages in ecological succession

The changes that take place during any form of succession depend
on a variety of environmental factors, such as the amount of moisture,
temperature, and wind. One possible scenario for primary succession
might begin with the appearance of simple plants, such as lichens and
mosses. Such plants are able to spring up in tiny cracks in the rocks in
which water and dissolved minerals collect.
When these pioneer plants die, they decompose and begin to form
soil in which other, more complex plants can begin to grow. The second
stage of plants might consists of grasses, herbs, and small shrubs. A characteristic
of these plants is that they devote a great deal of energy producing
huge numbers of seeds. They may live only one year, and spend
the greatest part of their energy to ensuring that offspring will arise the
following year. Species of this kind are known as opportunist species.
Grasses are a common example of opportunist species.
Plants that make up the early stages of succession also die, decompose,
and contribute to the growing layer of soil. This process takes place
over hundreds or thousands of years, however. Eventually, the soil is able
to support more complex plants, such as larger shrubs and small trees including
aspen, black spruce, and jack pine. These plants gradually take
over from earlier communities since they are taller, have more leaves, and
can capture more sunlight that was originally captured by simpler plants.
In the final stages of succession, taller trees begin to grow. They, in
turn, block out the sunlight needed by smaller trees and replace them. The
final stage of ecological succession is known as a climax community. A
climax community in the scenario outlined here might consist of birch,
white spruce, and balsam fir.

The formation of a supernova

Astronomers did not know what causes a star to explode in a
super nova until the 1939, when Indian-born American astrophysicist
Subrahmanyan Chandrasekhar (1910–1995) pieced together the sequence
of events leading up to a supernova. He also calculated a figure for the
mass of a star (known as Chandrasekhar’s limit) that would determine if
it would end up as a neutron star or a black hole.
Various theories have been proposed to explain the reasons a star
explodes outward while collapsing inward. One theory is that the explosion
is caused by a final burst of uncontrolled nuclear fusion. A more
recent theory is that the explosion is due to the ejection of a wave of
high-energy subatomic particles called neutrinos (electrically neutral
particles in the lepton family). The neutrino theory gained greater acceptance
following the 1987 supernova in the Large Magellanic Cloud, our
galaxy’s closest companion. Just before the supernova came into view, a
surge of neutrinos was detected in laboratories around the world. This supernova,
called Supernova 1987A, was the first visible to the naked eye
since 1604.