Self-referencing doomsday argument rebuttal
Encyclopedia
Self-referencing doomsday argument rebuttals attempt to refute the Doomsday argument
(that there is a credible link between the brevity of the human race
's existence and its expected extinction
) by applying the same reasoning to the lifetime of the Doomsday argument
(DA) itself.
The first researchers to write about this were P. T. Landsberg and J. N. Dewynne in 1997; they applied belief in the DA to itself, and claimed that a paradox results.
and the Copernican principle
then based on the length of its current existence, and assuming that it is randomly drawn from a reference class of probabilistic speculations it is 95% certain that it will be refuted before the year 2500.
If the DA is not itself subject to these principles then its assumption that the human race's survival-time can be modeled using them appears to be a paradox
(to Lansberg & Dewynne).
Alternatively, if the DA is subject to these presumptions, then as it is expected to expire (be refuted) earlier that its own prediction for the likely survival time of humanity there is a second paradox: The predictions of a theory concerning events to occur after it has been refuted (such as human extinction) are not logically meaningful. Conversely, if the DA survives until the end of human civilization (in the year 5000, say) then it will have dramatically beaten the odds against the expectations of the Copernican principle. This can create a paradox for an argument based on probability, as shown if future scenario
s are broken into three groups:
The "quick extinction" in possibility 1 is considered fairly likely in those Doomsday arguments using the number of births as a reference class, but comparing like-for-like we should compare the length of time the DA survives before refutation with the length of time the human race survives before extinction. Therefore, J. Richard Gott
's (temporal) DA is used to calculate the probabilities of the three scenarios above:
) and probably wrong (as a prediction).
Therefore, Landsberg and Dewynne argue that it is more likely that the Doomsday argument is wrong (even if its logic is correct) than that the human race will become extinct in 9,000 years (which the DA calculates at around 95% likely). The interesting paradox is that the Doomsday argument is probably wrong even assuming it to be completely right (in its 95% estimate).
extended this by arguing that Gott's DA inevitably refutes itself.
Doomsday argument
The Doomsday argument is a probabilistic argument that claims to predict the number of future members of the human species given only an estimate of the total number of humans born so far...
(that there is a credible link between the brevity of the human race
Human Race
Human Race refers to the Human species.Human race may also refer to:*The Human Race, 79th episode of YuYu Hakusho* Human Race Theatre Company of Dayton Ohio* Human Race Machine, a computer graphics device...
's existence and its expected extinction
Human extinction
Human extinction is the end of the human species. Various scenarios have been discussed in science, popular culture, and religion . The scope of this article is existential risks. Humans are very widespread on the Earth, and live in communities which are capable of some kind of basic survival in...
) by applying the same reasoning to the lifetime of the Doomsday argument
Argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...
(DA) itself.
The first researchers to write about this were P. T. Landsberg and J. N. Dewynne in 1997; they applied belief in the DA to itself, and claimed that a paradox results.
The paradox
If the DA's lifetime is governed by the principle of indifferencePrinciple of indifference
The principle of indifference is a rule for assigning epistemic probabilities.Suppose that there are n > 1 mutually exclusive and collectively exhaustive possibilities....
and the Copernican principle
Copernican principle
In physical cosmology, the Copernican principle, named after Nicolaus Copernicus, states that the Earth is not in a central, specially favored position. More recently, the principle has been generalized to the relativistic concept that humans are not privileged observers of the universe...
then based on the length of its current existence, and assuming that it is randomly drawn from a reference class of probabilistic speculations it is 95% certain that it will be refuted before the year 2500.
If the DA is not itself subject to these principles then its assumption that the human race's survival-time can be modeled using them appears to be a paradox
Paradox
Similar to Circular reasoning, A paradox is a seemingly true statement or group of statements that lead to a contradiction or a situation which seems to defy logic or intuition...
(to Lansberg & Dewynne).
Alternatively, if the DA is subject to these presumptions, then as it is expected to expire (be refuted) earlier that its own prediction for the likely survival time of humanity there is a second paradox: The predictions of a theory concerning events to occur after it has been refuted (such as human extinction) are not logically meaningful. Conversely, if the DA survives until the end of human civilization (in the year 5000, say) then it will have dramatically beaten the odds against the expectations of the Copernican principle. This can create a paradox for an argument based on probability, as shown if future scenario
Scenario
A scenario is a synoptical collage of an event or series of actions and events. In the Commedia dell'arte it was an outline of entrances, exits, and action describing the plot of a play that was literally pinned to the back of the scenery...
s are broken into three groups:
- Human extinctionHuman extinctionHuman extinction is the end of the human species. Various scenarios have been discussed in science, popular culture, and religion . The scope of this article is existential risks. Humans are very widespread on the Earth, and live in communities which are capable of some kind of basic survival in...
occurs before the year 2,500 AD. - Human extinction occurs after the year 2,500 AD and the DA is never refuted.
- Human extinction occurs after the year 2,500 AD but not before the DA is refuted.
The "quick extinction" in possibility 1 is considered fairly likely in those Doomsday arguments using the number of births as a reference class, but comparing like-for-like we should compare the length of time the DA survives before refutation with the length of time the human race survives before extinction. Therefore, J. Richard Gott
J. Richard Gott
John Richard Gott III is a professor of astrophysical sciences at Princeton University. He is known for developing and advocating two cosmological theories with the flavor of science fiction: Time travel and the Doomsday argument.- Exotic matter time travel theories :Paul Davies's bestseller How...
's (temporal) DA is used to calculate the probabilities of the three scenarios above:
- According to Gott's DA it is extremely unlikely that the human race will become extinct before the year 2,500 AD, as this would make us extremely special observers; applying the indifference principle to the duration of the human race makes the odds around 400:1 against (0.25% chance).
- If the Copernican principle applies to the lifetime of theories as well as species (depending on the reference class evidence says it does) then the chance of the (relatively young) DA surviving sustained critical analysis for the next 500 years = 22/500 = 4.4%
- By eliminating the other two outcomes we are left with the third, that the human race will survive to see the Doomsday argument refuted. The chance of this = 100 - (4.4 + 0.25) = 95.35%
Paradoxical conclusion
If the Doomsday Argument can apply to itself it can be simultaneously right (as a probabilistic argumentProbabilistic argument
Probabilistic argument can refer to the following:* In some contexts, probabilistic argument means any argument involving probability theory...
) and probably wrong (as a prediction).
Therefore, Landsberg and Dewynne argue that it is more likely that the Doomsday argument is wrong (even if its logic is correct) than that the human race will become extinct in 9,000 years (which the DA calculates at around 95% likely). The interesting paradox is that the Doomsday argument is probably wrong even assuming it to be completely right (in its 95% estimate).
Extensions
In 2001 Bradley Monton and Sherrilyn RoushSherrilyn Roush
Sherrilyn Roush is an Associate Professor of Philosophy at U. C. Berkeley specializing in the Philosophy of Science and Epistemology.Tracking Truth presents a unified treatment of knowledge, evidence, and epistemological realism and anti-realism about science, based on the idea that knowing is...
extended this by arguing that Gott's DA inevitably refutes itself.
Critique of the self-referencing doomsday argument rebuttal
This "meta"-DA application of the concept to the DA itself, requires some assumptions that are not universally accepted:- The hypothesis that the same reasoning can be applied to the lifetime of mathematical theories as can be applied to the survival time of a speciesSpeciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. One difference is that evidence exists for the average "lifetime" of a scientific (falsifiable) prediction; there are libraries full of refuted, unrefuted, and forgotten papers published on mathematics. - The truth-value of the DA and the survival of the human race are un-correlated in the simple calculation above.
- The concept that the DA is susceptible to refutation; if the DA is not falsifiable then there is no mechanism for refuting it, even if it is false. This would make it incomparable to mortal survival. (Landsberg & Dewynne say that the DA is a physical theoryPhysicsPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
rather than a mathematical hypothesis, and that any such theory is inherently falsifiable, as "experience has shown that any theory in physics, however successful, is only an approximation to reality and will eventually be refuted and require modification." )
External links
- Monton & Roush's Summary of Doomsday argument & objections Objection 4: Self-Reference Leads to Refutation argues that a deterministic interpretation of Gott's DA is sufficient to refute it when considering how its truth or falsity applies to its own expected period of (pre-refutation) survival. (A deterministic approach to a probabilistic argument is probablyProbabilityProbability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...
inappropriate though.)