"De rerum natura (Latin: [deː ˈreːrʊn naːˈtuːraː]; On the Nature of Things) is a first-century BC didactic poem by the Roman poet and philosopher Lucretius (c. 99 BC – c. 55 BC) with the goal of explaining Epicurean philosophy to a Roman audience. The poem, written in some 7,400 dactylic hexameters, is divided into six untitled books, and explores Epicurean physics through poetic language and metaphors. Namely, Lucretius explores the principles of atomism; the nature of the mind and soul; explanations of sensation and thought; the development of the world and its phenomena; and explains a variety of celestial and terrestrial phenomena. The universe described in the poem operates according to these physical principles, guided by fortuna ("chance"), and not the divine intervention of the traditional Roman deities.
To the Greek philosopher Epicurus, the unhappiness and degradation of humans arose largely from the dread which they entertained of the power of the deities, from terror of their wrath. This wrath was supposed to be displayed by the misfortunes inflicted in this life and by the everlasting tortures that were the lot of the guilty in a future state (or, where these feelings were not strongly developed, from a vague dread of gloom and misery after death). Epicurus thus made it his mission to remove these fears, and thus to establish tranquility in the minds of his readers. To do this, Epicurus invoked the atomism of Democritus to demonstrate that the material universe was formed not by a Supreme Being, but by the mixing of elemental particles that had existed from all eternity governed by certain simple laws. He argued that the deities (whose existence he did not deny) lived forevermore in the enjoyment of absolute peace—strangers to all the passions, desires, and fears, which affect humans—and totally indifferent to the world and its inhabitants, unmoved alike by their virtues and their crimes. This meant that humans had nothing to fear from them.
Lucretius's task was to clearly state and fully develop these views in an attractive form; his work was an attempt to show through poetry that everything in nature can be explained by natural laws, without the need for the intervention of divine beings. Lucretius identifies the supernatural with the notion that the deities created our world or interfere with its operations in some way. He argues against fear of such deities by demonstrating, through observations and arguments, that the operations of the world can be accounted for in terms of natural phenomena. These phenomena are the result of regular, but purposeless motions and interactions of tiny atoms in empty space."
"The state of the poem as it currently exists suggests that it was released in an unfinished state. For instance, the poem concludes rather abruptly while detailing the Plague of Athens, there are redundant passages throughout (e.g., 1.820–821 and 2.1015–1016) alongside other aesthetic "loose ends", and at 5.155 Lucretius mentions that he will spend a great deal of time discussing the nature of the gods, which never comes to pass. Some have suggested that Lucretius died before being able to edit, finalize, and publish his work."
"Main ideas
Metaphysics
Lack of divine intervention
After the poem was rediscovered and made its rounds across Europe and beyond, numerous thinkers began to see Lucretius's Epicureanism as a "threat synonymous with atheism." Some Christian apologists viewed De rerum natura as an atheist manifesto and a dangerous foil to be thwarted. However, at that time the label was extremely broad and did not necessarily mean a denial of divine entities (for example, some large Christian sects labelled dissenting groups as atheists). What is more, Lucretius does not deny the existence of deities; he simply argues that they did not create the universe, that they do not care about human affairs, and that they do not intervene in the world. Regardless, due to the ideas espoused in the poem, much of Lucretius's work was seen by many as direct a challenge to theistic, Christian belief. The historian Ada Palmer has labelled six ideas in Lucretius's thought (viz. his assertion that the world was created from chaos, and his denials of Providence, divine participation, miracles, the efficacy of prayer, and an afterlife) as "proto-atheistic". She qualifies her use of this term, cautioning that it is not to be used to say that Lucretius was himself an atheist in the modern sense of the word, nor that atheism is a teleological necessity, but rather that many of his ideas were taken up by 19th-, 20th-, and 21st-century atheists.
Repudiation of immortality
De rerum natura does not argue that the soul does not exist; rather, the poem claims that the soul, like all things in existence, is made up of atoms, and because these atoms will one day drift apart, the human soul is not immortal. Lucretius thus argues that death is simply annihilation, and that there is no afterlife. He likens the physical body to a vessel that holds both the mind (mens) and spirit (anima). To prove that neither the mind nor spirit can survive independent of the body, Lucretius uses a simple analogy: when a vessel shatters, its contents spill everywhere; likewise, when the body dies, the mind and spirit dissipate. And as a simple ceasing-to-be, death can be neither good nor bad for this being, since a dead person—being completely devoid of sensation and thought—cannot miss being alive. To further alleviate the fear of non-existence, Lucretius makes use of the symmetry argument: he argues that the eternal oblivion awaiting all humans after death is exactly the same as the infinite nothingness that preceded our birth. Since that nothingness (which he likens to a deep, peaceful sleep) caused us no pain or discomfort, we should not fear the same nothingness that will follow our own demise:
Look back again—how the endless ages of time comes to pass
Before our birth are nothing to us. This is a looking glass
Nature holds up for us in which we see the time to come
After we finally die. What is there that looks so fearsome?
What's so tragic? Isn't it more peaceful than any sleep?
According to the Stanford Encyclopedia of Philosophy, Lucretius sees those who fear death as embracing the fallacious assumption that they will be present in some sense "to regret and bewail [their] own non-existence."
Physics
Lucretius maintained that he could free humankind from fear of the deities by demonstrating that all things occur by natural causes without any intervention by the deities. Historians of science, however, have been critical of the limitations of his Epicurean approach to science, especially as it pertained to astronomical topics, which he relegated to the class of "unclear" objects.
Thus, he began his discussion by claiming that he would
"explain by what forces nature steers the courses of the Sun and the journeyings of the Moon, so that we shall not suppose that they run their yearly races between heaven and earth of their own free will [i.e., are gods themselves] or that they are rolled round in furtherance of some divine plan...."
However, when he set out to put this plan into practice, he limited himself to showing how one, or several different, naturalistic accounts could explain certain natural phenomena. He was unable to tell his readers how to determine which of these alternatives might be the true one. For instance, when considering the reason for stellar movements, Lucretius provides two possible explanations: that the sky itself rotates, or that the sky as a whole is stationary while constellations move. If the latter is true, Lucretius, notes, this is because: "either swift currents of ether whirl round and round and roll their fires at large across the nocturnal regions of the sky"; "an external current of air from some other quarter may whirl them along in their course"; or "they may swim of their own accord, each responsive to the call of its own food, and feed their fiery bodies in the broad pastures of the sky". Lucretius concludes that "one of these causes must certainly operate in our world... But to lay down which of them it is lies beyond the range of our stumbling progress."
Despite his advocacy of empiricism and his many correct conjectures about atomism and the nature of the physical world, Lucretius concludes his first book stressing the absurdity of the (by then well-established) round earth theory, favoring instead a flat earth cosmology.
Drawing on these, and other passages, William Stahl considered that "The anomalous and derivative character of the scientific portions of Lucretius' poem makes it reasonable to conclude that his significance should be judged as a poet, not as a scientist." His naturalistic explanations were meant to bolster the ethical and philosophical ideas of Epicureanism, not to reveal true explanations of the physical world.
The swerve
Determinism appears to conflict with the concept of free will. Lucretius attempts to allow for free will in his physicalistic universe by postulating an indeterministic tendency for atoms to veer randomly (Latin: clinamen, literally "the turning aside of a thing", but often translated as "the swerve"). According to Lucretius, this unpredictable swerve occurs at no fixed place or time:
"When atoms move straight down through the void by their own weight, they deflect a bit in space at a quite uncertain time and in uncertain places, just enough that you could say that their motion has changed. But if they were not in the habit of swerving, they would all fall straight down through the depths of the void, like drops of rain, and no collision would occur, nor would any blow be produced among the atoms. In that case, nature would never have produced anything."
This swerving provides the indeterminacy that Lucretius argues allows for the "free will which living things throughout the world have" (libera per terras ... haec animantibus exstat ... voluntas)."
(from Wikipedia)