- Are the Laws of Physics Really Universal?
- Chapter 4: The Laws of Scientific Change – Introduction to History and Philosophy of Science
- The Theory of Scientific Change
Sometimes laws are found to be true under certain conditions, but not others. For example, Newton's Law of Gravity holds true for most situations, but it breaks down at the sub-atomic level. Scientific laws do not try to explain 'why' the observed event happens, but only that the event actually occurs the same way over and over. The explanation of how a phenomenon works is a scientific theory. A scientific law and a scientific theory are not the same thing—a theory does not turn into a law or vice versa.
Both laws and theories are based on empirical data and are accepted by many or most scientists within the appropriate discipline. For example, Newton's Law of Gravity 17th century is a mathematical relation that describes how two bodies interact with each other.
Are the Laws of Physics Really Universal?
The law does not explain how gravity works or even what gravity is. The Law of Gravity can be used to make predictions about events and perform calculations. Einstein's Theory of Relativity 20th century finally started to explain what gravity is and how it works.
Share Flipboard Email. In science, a theory is a well-substantiated and comprehensive set of ideas that explains a phenomenon in nature.
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A scientific theory is based on large amounts of data and observations that have been collected over time. Scientific theories can be tested and refined by additional research , and they allow scientists to make predictions. Though you may be correct in your hunch, your cookie jar conjecture doesn't fit this more rigorous definition. All scientific disciplines have well-established, fundamental theories.
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For example, atomic theory describes the nature of matter and is supported by multiple lines of evidence from the way substances behave and react in the world around us see our series on Atomic Theory. Plate tectonic theory describes the large scale movement of the outer layer of the Earth and is supported by evidence from studies about earthquakes , magnetic properties of the rocks that make up the seafloor , and the distribution of volcanoes on Earth see our series on Plate Tectonic Theory.
The theory of evolution by natural selection, which describes the mechanism by which inherited traits that affect survivability or reproductive success can cause changes in living organisms over generations , is supported by extensive studies of DNA , fossils , and other types of scientific evidence see our Charles Darwin series for more information. Each of these major theories guides and informs modern research in those fields, integrating a broad, comprehensive set of ideas. So how are these fundamental theories developed, and why are they considered so well supported?
Let's take a closer look at some of the data and research supporting the theory of natural selection to better see how a theory develops. The theory of evolution by natural selection is sometimes maligned as Charles Darwin 's speculation on the origin of modern life forms. However, evolutionary theory is not speculation. While Darwin is rightly credited with first articulating the theory of natural selection, his ideas built on more than a century of scientific research that came before him, and are supported by over a century and a half of research since.
Research about the origins and diversity of life proliferated in the 18th and 19th centuries. Carolus Linnaeus , a Swedish botanist and the father of modern taxonomy see our module Taxonomy I for more information , was a devout Christian who believed in the concept of Fixity of Species , an idea based on the biblical story of creation. The Fixity of Species concept said that each species is based on an ideal form that has not changed over time.
In the early stages of his career, Linnaeus traveled extensively and collected data on the structural similarities and differences between different species of plants. Noting that some very different plants had similar structures, he began to piece together his landmark work, Systema Naturae, in Figure 1.
In Systema , Linnaeus classified organisms into related groups based on similarities in their physical features. He developed a hierarchical classification system , even drawing relationships between seemingly disparate species for example, humans, orangutans, and chimpanzees based on the physical similarities that he observed between these organisms. Linnaeus did not explicitly discuss change in organisms or propose a reason for his hierarchy, but by grouping organisms based on physical characteristics, he suggested that species are related, unintentionally challenging the Fixity notion that each species is created in a unique, ideal form.
Also in the early s, Georges-Louis Leclerc, a French naturalist, and James Hutton , a Scottish geologist, began to develop new ideas about the age of the Earth. At the time, many people thought of the Earth as 6, years old, based on a strict interpretation of the events detailed in the Christian Old Testament by the influential Scottish Archbishop Ussher. By observing other planets and comets in the solar system , Leclerc hypothesized that Earth began as a hot, fiery ball of molten rock, mostly consisting of iron.
Using the cooling rate of iron, Leclerc calculated that Earth must therefore be at least 70, years old in order to have reached its present temperature. Hutton approached the same topic from a different perspective, gathering observations of the relationships between different rock formations and the rates of modern geological processes near his home in Scotland. He recognized that the relatively slow processes of erosion and sedimentation could not create all of the exposed rock layers in only a few thousand years see our module The Rock Cycle.
Based on his extensive collection of data just one of his many publications ran to 2, pages , Hutton suggested that the Earth was far older than human history — hundreds of millions of years old. While we now know that both Leclerc and Hutton significantly underestimated the age of the Earth by about 4 billion years , their work shattered long-held beliefs and opened a window into research on how life can change over these very long timescales.
With the age of Earth now extended by Leclerc and Hutton, more researchers began to turn their attention to studying past life. Fossils are the main way to study past life forms, and several key studies on fossils helped in the development of a theory of evolution. Through his work, Cuvier became interested in fossils found near Paris, which some claimed were the remains of the elephants that Hannibal rode over the Alps when he invaded Rome in BCE.
In studying both the fossils and living species , Cuvier documented different patterns in the dental structure and number of teeth between the fossils and modern elephants Figure 2 Horner, Based on these data , Cuvier hypothesized that the fossil remains were not left by Hannibal, but were from a distinct species of animal that once roamed through Europe and had gone extinct thousands of years earlier: the mammoth.
The concept of species extinction had been discussed by a few individuals before Cuvier, but it was in direct opposition to the Fixity of Species concept — if every organism were based on a perfectly adapted, ideal form, how could any cease to exist? That would suggest it was no longer ideal. While his work provided critical evidence of extinction , a key component of evolution , Cuvier was highly critical of the idea that species could change over time.
As a result of his extensive studies of animal anatomy, Cuvier had developed a holistic view of organisms , stating that the. In other words, Cuvier viewed each part of an organism as a unique, essential component of the whole organism. If one part were to change, he believed, the organism could not survive. His skepticism about the ability of organisms to change led him to criticize the whole idea of evolution , and his prominence in France as a scientist played a large role in discouraging the acceptance of the idea in the scientific community.
Jean Baptiste Lamarck, a contemporary of Cuvier's at the National Museum in Paris, studied invertebrates like insects and worms. As Lamarck worked through the museum's large collection of invertebrates, he was impressed by the number and variety of organisms. He became convinced that organisms could, in fact, change through time, stating that. We know that for her time has no limit, and that consequently she always has it at her disposal.
This was a radical departure from both the fixity concept and Cuvier's ideas, and it built on the long timescale that geologists had recently established. Lamarck proposed that changes that occurred during an organism 's lifetime could be passed on to their offspring, suggesting, for example, that a body builder's muscles would be inherited by their children.
As it turned out, the mechanism by which Lamarck proposed that organisms change over time was wrong, and he is now often referred to disparagingly for his "inheritance of acquired characteristics" idea. Yet despite the fact that some of his ideas were discredited, Lamarck established a support for evolutionary theory that others would build on and improve.
In the early s, a British geologist and canal surveyor named William Smith added another component to the accumulating evidence for evolution. Smith observed that rock layers exposed in different parts of England bore similarities to one another: These layers or strata were arranged in a predictable order, and each layer contained distinct groups of fossils.
From this series of observations , he developed a hypothesis that specific groups of animals followed one another in a definite sequence through Earth's history, and this sequence could be seen in the rock layers. Smith's hypothesis was based on his knowledge of geological principles , including the Law of Superposition. The Law of Superposition states that sediments are deposited in a time sequence, with the oldest sediments deposited first, or at the bottom, and newer layers deposited on top.
The concept was first expressed by the Persian scientist Avicenna in the 11th century, but was popularized by the Danish scientist Nicolas Steno in the 17th century. Note that the law does not state how sediments are deposited; it simply describes the relationship between the ages of deposited sediments.
Smith backed up his hypothesis with extensive drawings of fossils uncovered during his research Figure 3 , thus allowing other scientists to confirm or dispute his findings. His hypothesis has, in fact, been confirmed by many other scientists and has come to be referred to as the Law of Faunal Succession.
His work was critical to the formation of evolutionary theory as it not only confirmed Cuvier's work that organisms have gone extinct , but it also showed that the appearance of life does not date to the birth of the planet. Instead, the fossil record preserves a timeline of the appearance and disappearance of different organisms in the past, and in doing so offers evidence for change in organisms over time. It was into this world that Charles Darwin entered: Linnaeus had developed a taxonomy of organisms based on their physical relationships, Leclerc and Hutton demonstrated that there was sufficient time in Earth's history for organisms to change, Cuvier showed that species of organisms have gone extinct , Lamarck proposed that organisms change over time, and Smith established a timeline of the appearance and disappearance of different organisms in the geological record.
He took extensive notes on the geology of the places he visited; he made a major find of fossils of extinct animals in Patagonia and identified an extinct giant ground sloth named Megatherium. He experienced an earthquake in Chile that stranded beds of living mussels above water, where they would be preserved for years to come.hukusyuu.com/profile/2019-12-15/spion-apper-til-iphone.php
Chapter 4: The Laws of Scientific Change – Introduction to History and Philosophy of Science
These subtle differences made the animals highly adapted to their environments. This broad spectrum of data led Darwin to propose an idea about how organisms change "by means of natural selection" Figure 4. But this idea was not based only on his work, it was also based on the accumulation of evidence and ideas of many others before him.
Because his proposal encompassed and explained many different lines of evidence and previous work, they formed the basis of a new and robust scientific theory regarding change in organisms — the theory of evolution by natural selection.
The Theory of Scientific Change
Darwin's ideas were grounded in evidence and data so compelling that if he had not conceived them, someone else would have. In fact, someone else did. Between and , Alfred Russel Wallace , a British naturalist, wrote a series of letters to Darwin that independently proposed natural selection as the means for evolutionary change. The letters were presented to the Linnean Society of London, a prominent scientific society at the time see our module on Scientific Institutions and Societies.
This long chain of research highlights that theories are not just the work of one individual. At the same time, however, it often takes the insight and creativity of individuals to put together all of the pieces and propose a new theory. Both Darwin and Wallace were experienced naturalists who were familiar with the work of others. While all of the work leading up to contributed to the theory of evolution , Darwin's and Wallace's theory changed the way that future research was focused by presenting a comprehensive, well-substantiated set of ideas, thus becoming a fundamental theory of biological research.
Since Darwin and Wallace first published their ideas, extensive research has tested and expanded the theory of evolution by natural selection. Darwin had no concept of genes or DNA or the mechanism by which characteristics were inherited within a species.
A contemporary of Darwin's, the Austrian monk Gregor Mendel , first presented his own landmark study, Experiments in Plant Hybridization, in in which he provided the basic patterns of genetic inheritance , describing which characteristics and evolutionary changes can be passed on in organisms see our Genetics I module for more information.
Still, it wasn't until much later that a "gene" was defined as the heritable unit. In , the Ukrainian born geneticist Theodosius Dobzhansky published Genetics and the Origin of Species , a seminal work in which he described genes themselves and demonstrated that it is through mutations in genes that change occurs.