The Fabric of the Cosmos: Space, Time, and the Texture of Reality by Brian Greene
Authors: Brian Greene
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move.
But what is absolute space, really? In dealing with this question, Newton responded with a bit of fancy footwork and the force of fiat. He first wrote in the
Principia
"I do not define time, space, place, and motion, as [they] are well known to all," 3 sidestepping any attempt to describe these concepts with rigor or precision. His next words have become famous: "Absolute space, in its own nature, without reference to anything external, remains always similar and unmovable." That is, absolute space just is, and is forever. Period. But there are glimmers that Newton was not completely comfortable with simply declaring the existence and importance of something that you can't directly see, measure, or affect. He wrote,
It is indeed a matter of great difficulty to discover and effectually to distinguish the true motions of particular bodies from the apparent, because the parts of that immovable space in which those motions are performed do by no means come under the observations of our senses. 4
So Newton leaves us in a somewhat awkward position. He puts absolute space front and center in the description of the most basic and essential element of physics—motion—but he leaves its definition vague and acknowledges his own discomfort about placing such an important egg in such an elusive basket. Many others have shared this discomfort.
Space Jam
Einstein once said that if someone uses words like "red," "hard," or "disappointed," we all basically know what is meant. But as for the word "space," "whose relation with psychological experience is less direct, there exists a far-reaching uncertainty of interpretation." 5 This uncertainty reaches far back: the struggle to come to grips with the meaning of space is an ancient one. Democritus, Epicurus, Lucretius, Pythagoras, Plato, Aristotle, and many of their followers through the ages wrestled in one way or another with the meaning of "space." Is there a difference between space and matter? Does space have an existence independent of the presence of material objects? Is there such a thing as empty space? Are space and matter mutually exclusive? Is space finite or infinite?
For millennia, the philosophical parsings of space often arose in tandem with theological inquiries. God, according to some, is omnipresent, an idea that gives space a divine character. This line of reasoning was advanced by Henry More, a seventeenth-century theologian/philosopher who, some think, may have been one of Newton's mentors. 6 He believed that if space were empty it would not exist, but he also argued that this is an irrelevant observation because, even when devoid of material objects, space is filled with spirit, so it is
never
truly empty. Newton himself took on a version of this idea, allowing space to be filled by "spiritual substance" as well as material substance, but he was careful to add that such spiritual stuff "can be no obstacle to the motion of matter; no more than if nothing were in its way." 7 Absolute space, Newton declared, is the sensorium of God.
Such philosophical and religious musings on space can be compelling and provocative, yet, as in Einstein's cautionary remark above, they lack a critical sharpness of description. But there
is
a fundamental and precisely framed question that emerges from such discourse: should we ascribe an independent reality to space, as we do for other, more ordinary material objects like the book you are now holding, or should we think of space as merely a language for describing relationships between ordinary material objects?
The great German philosopher Gottfried Wilhelm von Leibniz, who was Newton's contemporary, firmly believed that space does not exist in any conventional sense. Talk of space, he claimed, is nothing more than an easy and convenient way of encoding where things are relative to one another. Without the objects
in
space, Leibniz declared, space itself has no independent meaning or existence. Think of the English alphabet.
But what is absolute space, really? In dealing with this question, Newton responded with a bit of fancy footwork and the force of fiat. He first wrote in the
Principia
"I do not define time, space, place, and motion, as [they] are well known to all," 3 sidestepping any attempt to describe these concepts with rigor or precision. His next words have become famous: "Absolute space, in its own nature, without reference to anything external, remains always similar and unmovable." That is, absolute space just is, and is forever. Period. But there are glimmers that Newton was not completely comfortable with simply declaring the existence and importance of something that you can't directly see, measure, or affect. He wrote,
It is indeed a matter of great difficulty to discover and effectually to distinguish the true motions of particular bodies from the apparent, because the parts of that immovable space in which those motions are performed do by no means come under the observations of our senses. 4
So Newton leaves us in a somewhat awkward position. He puts absolute space front and center in the description of the most basic and essential element of physics—motion—but he leaves its definition vague and acknowledges his own discomfort about placing such an important egg in such an elusive basket. Many others have shared this discomfort.
Space Jam
Einstein once said that if someone uses words like "red," "hard," or "disappointed," we all basically know what is meant. But as for the word "space," "whose relation with psychological experience is less direct, there exists a far-reaching uncertainty of interpretation." 5 This uncertainty reaches far back: the struggle to come to grips with the meaning of space is an ancient one. Democritus, Epicurus, Lucretius, Pythagoras, Plato, Aristotle, and many of their followers through the ages wrestled in one way or another with the meaning of "space." Is there a difference between space and matter? Does space have an existence independent of the presence of material objects? Is there such a thing as empty space? Are space and matter mutually exclusive? Is space finite or infinite?
For millennia, the philosophical parsings of space often arose in tandem with theological inquiries. God, according to some, is omnipresent, an idea that gives space a divine character. This line of reasoning was advanced by Henry More, a seventeenth-century theologian/philosopher who, some think, may have been one of Newton's mentors. 6 He believed that if space were empty it would not exist, but he also argued that this is an irrelevant observation because, even when devoid of material objects, space is filled with spirit, so it is
never
truly empty. Newton himself took on a version of this idea, allowing space to be filled by "spiritual substance" as well as material substance, but he was careful to add that such spiritual stuff "can be no obstacle to the motion of matter; no more than if nothing were in its way." 7 Absolute space, Newton declared, is the sensorium of God.
Such philosophical and religious musings on space can be compelling and provocative, yet, as in Einstein's cautionary remark above, they lack a critical sharpness of description. But there
is
a fundamental and precisely framed question that emerges from such discourse: should we ascribe an independent reality to space, as we do for other, more ordinary material objects like the book you are now holding, or should we think of space as merely a language for describing relationships between ordinary material objects?
The great German philosopher Gottfried Wilhelm von Leibniz, who was Newton's contemporary, firmly believed that space does not exist in any conventional sense. Talk of space, he claimed, is nothing more than an easy and convenient way of encoding where things are relative to one another. Without the objects
in
space, Leibniz declared, space itself has no independent meaning or existence. Think of the English alphabet.
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