Macroscopic scale
The macroscopic scale refers to the range of sizes of objects that can be seen without the aid of magnifying devices, spanning from approximately 0.1 millimeters to the entire observable universe, which is about 93 billion light-years in diameter. This scale is contrasted with the microscopic scale, where objects require lenses or microscopes to be seen. The prefix "macro-" originates from Greek, meaning "large," emphasizing the substantial sizes involved. In scientific measurements, the International System of Units (SI) uses the meter as its base unit, along with various prefixes to indicate different magnitudes, such as millimeters for small objects and kilometers for larger entities like mountains.
The macroscopic properties of materials, such as the expansion of water when it freezes, can differ significantly from the behaviors observed at the microscopic level, where individual molecules rearrange rather than expand. Additionally, patterns observed at the macroscopic scale can sometimes echo those seen at the microscopic level, creating intriguing visual similarities. The study and application of physics also vary between these scales, as classical mechanics governs the macroscopic realm, while quantum mechanics becomes necessary at the microscopic level. Understanding these distinctions is crucial for exploring both the physical world and the universe.
Macroscopic scale
The macroscopic scale includes all the lengths at which objects can be seen with the unaided eye. In contrast, a lens or microscope is required to view an object at the microscopic scale. The prefix macro- comes from a Greek root word meaning "large or excessive," while micro- means "very small." The smallest object visible to the unaided human eye is about 0.1 millimeters across. The macroscopic scale ranges from this length to the length of the entire visible universe.
Measurements on the Macroscopic Scale
In science, the International System of Units’ (SI) unit of measure for length is the meter. A macroscopic object can be a small fraction of a meter long, or many trillions of meters across. Scientists may use SI prefixes or scientific notation to denote lengths of more or less than several meters. The list below includes both, along with examples of objects at that scale.
Prefix, scientific notation, and example:
micro- (µm); 1.0 × 10–6 m; red blood cell (8 µm) (microscopic)
milli- (mm); 1.0 × 10–3 m; grain of salt (0.5 mm)
centi- (cm); 1.0 × 10–2 m; height of average U.S. woman (162 cm)
none (m); 1.0 × 100 m; length of a U.S. football field (110 m)
kilo- (km); 1.0 × 103 m; peak of Mount Everest (8.8 km)
Mega- (Mm); 1.0 × 106 m; Earth’s polar circumference (39.94 Mm)
Peta- (Pm); 1.0 × 1015 m; one light-year (9.5 Pm)
In practice, SI units larger than the kilometer are rarely used. Units commonly used in astronomy, which deals with extremely large distances, include the astronomical unit (1 AU = 1.5 × 1011 m), the light-year (1 light-year = 9.5 × 1015 m), and the parsec (1 pc = ~3.1 × 1016 m).
The Upper and Lower Limits of the Macroscopic Scale
The smallest object the human eye can see, at a close distance, is about 0.1 millimeters (1.0 × 10–4 m) across. This is about the length of an ameba or paramecium, which are both single-celled protists. It is also about the diameter of a human egg. Because the lens of the eye hardens over time, people lose the ability to see objects this tiny as they get older.
The largest object that people can observe is, in fact, the observable universe itself. The diameter of the observable universe (that is, those parts of the universe from which light reaches us) is about 93 billion light-years, or 28 billion parsecs. Because the universe is expanding, in the distant future this number will be even larger. The universe contains numerous galaxies, or clusters of stars. The galaxy we are in, called the Milky Way, is a spiral galaxy about 100,000 light-years or 30 kiloparsecs across. Our solar system lies about 8 kiloparsecs from the Milky Way’s center, in a branch known as the Sagittarius arm. The next closest spiral galaxy is the Andromeda galaxy, which is 2.5 million light-years away. Andromeda appears as a small, faint blur in the night sky and is the most distant object that can be seen with the unaided eye. The invention of more sophisticated telescopes in the twentieth century has allowed scientists to explore the macroscopic scale in more detail than ever.
Macroscopic vs. Microscopic Scales
Properties of matter that can be observed at the macroscopic scale are not necessarily the same as those observable at the microscopic scale. For example, water expands when it freezes. This expansion can be detected without the use of a microscope; it is a macroscopic property. However, the individual molecules that make up a sample of water do not, themselves, expand. Rather, these molecules re-arrange so that there is slightly more space between them. This is an example of a change at the micro scale resulting in a different type of change at the macro scale.
Sometimes, patterns observed at the macro scale can resemble those seen at the micro scale. For example, satellite images of Earth’s surface taken from space can resemble microscopic images of tissues and organs. Patterns in a snake’s scales, visualized through an electron microscope, can resemble those seen in satellite images of landscapes with different types of vegetation.
Classical vs. Quantum Physics
The type of physics a scientist uses depends on whether he is working at the macroscopic or the microscopic scale. Physical theories that describe the macroscopic scale (as well as the larger end of the microscopic scale) were discovered by Isaac Newton (1642–1727). Newton’s work is known as classical mechanics (mechanics is the branch of physics that describes forces and motion). Today, classical mechanics is still used by scientists and engineers working at the macro scale (for example, sending rovers to explore Mars or launching astronauts into orbit around Earth).
However, in the twentieth century, as physicists began to work at the micro scale of light waves and atoms, classical mechanics began to fail. For example, Newton's laws predict that the electrons surrounding the atomic nucleus will soon fall toward the nucleus. This is not what scientists observe. Instead, electrons remain in orbits in a cloud that surrounds the nucleus. To explain this and other observations, scientists devised quantum mechanics. The upper limit of the quantum realm in which this type of physics applies is still microscopic, but macroscopic objects are normally outside of the quantum realm. As a microscopic system becomes larger—as it approaches the macro scale—classical mechanics can be used to describe it.
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