P HIL 192 D - Space and Time Miles Andrews

1. PHIL 192D - Space and Time Miles Andrews

2. What is fine-tuning? Over the past century, scientists have discovered that if certain properties of the universe were changed very slightly from what they are, we would not be here. They have to be within a very narrow range for our universe to be life-permitting (habitable). So, we can define fine-tuning as: • the sensitivity of the habitability of the universe to small changes in its properties Or, more precisely: • the claim that the laws and values of the constants of physics, and the initial conditions of any universe with the same laws as our universe, must be set in a seemingly very precise way for the universe to support life

3. Three types of (global) fine-tuning • Laws of nature Existence and forms of physical laws (forces, types of particles, quantum principles, dimensionality of space-time). 2. Constants of physics Masses of fundamental particles, force strengths, cosmological constant value. 3. Initial conditions of the universe Initial entropy, initial expansion rate, initial density fluctuations, inflation, matter/antimatter ratio.

4. Universe creating machine Helpful way to imagine the initial conditions and force strengths:

5. Quotes from notables (read: a shameless appeal to authority) "Thus life appears to depend upon delicate coincidences that we have not been able to explain. The broad outlines of that situation have been apparent for many decades. When less was known, it seemed reasonable to hope that better understanding of symmetry and dynamics would clear things up. Now that hope seems much less reasonable. The happy coincidences between life’s requirements and nature’s choices of parameter values might be just a series of flukes, but one could be forgiven for beginning to suspect that something deeper is at work." -Frank Wilczek "Most of the fundamental constants in our theories appear fine-tuned in the sense that if they were altered by only modest amounts, the universe would be qualitatively different, and in many cases unsuitable for the development of life. … The emergence of the complex structures capable of supporting intelligent observers seems to be very fragile. The laws of nature form a system that is extremely fine-tuned, and very little in physical law can be altered without destroying the possibility of the development of life as we know it." -Stephen Hawking "Any universe hospitable to life – what we might call a biophilic universe – has to be ‘adjusted’ in a particular way. The prerequisites for any life of the kind we know about — long-lived stable stars, stable atoms such as carbon, oxygen and silicon, able to combine into complex molecules, etc — are sensitive to the physical laws and to the size, expansion rate and contents of the universe. Indeed, even for the most open-minded science fiction writer, ‘life’ or ‘intelligence’ requires the emergence of some generic complex structures: it can’t exist in a homogeneous universe, not in a universe containing only a few dozen particles. Many recipes would lead to stillborn universes with no atoms, no chemistry, and no planets; or to universes too short-lived or too empty to allow anything to evolve beyond sterile uniformity." -Sir Martin Rees

6. Quotes (cont.) "the existence of an amazingly strong correlation between our own properties and the values of many parameters of our world, such as the masses and charges of electron and proton, the value of the gravitational constant, the amplitude of spontaneous symmetry breaking in the electroweak theory, the value of the vacuum energy, and the dimensionality of our world, is an experimental fact requiring an explanation." -Andrei Linde "The Laws of Physics … are almost always deadly. In a sense the laws of nature are like East Coast weather: tremendously variable, almost always awful, but on rare occasions, perfectly lovely. … [O]ur own universe is an extraordinary place that appears to be fantastically well designed for our own existence. This specialness is not something that we can attribute to lucky accidents, which is far too unlikely. The apparent coincidences cry out for an explanation." -Leonard Susskind "in the multiverse, life will evolve only in very rare regions where the local laws of physics just happen to have the properties needed for life, giving a simple explanation for why the observed universe appears to have just the right properties for the evolution of life. The incredibly small value of the cosmological constant is a telling example of a feature that seems to be needed for life, but for which an explanation from fundamental physics is painfully lacking." -Alan Guth

7. More "Our universe is much more complex than most universes with the same laws but different values of the parameters of those laws. In particular, it has a complex astrophysics, including galaxies and long lived stars, and a complex chemistry, including carbon chemistry. These necessary conditions for life are present in our universe as a consequence of the complexity which is made possible by the special values of the parameters." -Lee Smolin "There are many ... lucky accidents in physics. Without such accidents, water could not exist as liquid, chains of carbon atoms could not form complex organic molecules, and hydrogen atoms could not form breakable bridges between molecules." - Freeman Dyson "I do not believe that any scientists who examined the evidence would fail to draw the inference that the laws of nuclear physics have been deliberately designed with regard to the consequences they produce inside stars. If this is so, then my apparently random quirks have become a part of a deep-laid scheme. If not then we are back again at a monstrous sequence of accidents." - Sir Fred Hoyle Others: Paul Davies, Bernard Carr, John Barrow, and Frank Tipler (the latter two authored The Anthropic Cosmological Principle, 1988).

8. Some examples of fine-tuning: • If the initial explosion of the Big Bang had differed in strength by as little as one part in 1060, the universe would have either quickly collapsed back on itself, or expanded too rapidly for stars to form. In either case, life would be impossible. • Calculations indicate that if the strong nuclear force, the force that binds protons and neutrons together in an atom, had been stronger or weaker by as little as five percent, life would be impossible. • Calculations by Brandon Carter show that if gravity had been stronger or weaker by one part in 1040, then life-sustaining stars like the sun could not exist. This would most likely make life impossible. • If the neutron were not about 1.001 times the mass of the proton, all protons would have decayed into neutrons or all neutrons would have decayed into protons, and thus life would not be possible. • If the electromagnetic force were slightly stronger or weaker, life would be impossible, for a variety of different reasons.

9. How is fine-tuning defined? • Robin Collins: “...we can think of the claim that a parameter of physics is 'fine-tuned' as the claim that the range of values, r, of the parameter that is life-permitting is very small compared with some non-arbitrarily chosen theoretically “possible” range of values R. The degree of fine-tuning could then be defined as the ratio of the width of the life-permitting region to the comparison region." • Consider a ruler analogy: A ruler manufacturer can make rulers with an accuracy of 1 cm. This is a dimensional quantity. A more useful quantity is the relative error, a dimensionless quantity. For a 10 cm. ruler, the relative error of 1 cm. is 10%, whereas for a 100 cm. ruler, it is 1%. Similarly, for fine-tuning, we need to define a suitable comparison range. It could be theoretical or empirical. A physical property of the universe is usually considered fine-tuned if the life-permitting range is <10% (most are <1%) of the comparison range.

10. One- vs. Two-sided Fine-Tuning • Some cases of fine-tuning are one-sided, meaning that a parameter falls near the edge of the life-permitting region (either an upper or lower limit). • Some cases of fine-tuning are two-sided (both an upper and lower limit).

11. Example: dimensionless range of force strengths Set the comparison range of force strengths in nature to be 1040G0. This is a lower limit on the actual comparison range.

12. Some numbers • The maximum value of the electromagnetic force that allows for a periodic table of sufficient length (complex chemistry required for life) is 14 x 1037G0 / 1040G0 = 1.3%. • The maximum value of the gravitational force that allows stars to last at least 109 years is 3000G0. Its degree of fine-tuning is 3000G0 / 1040G0 ~ 1/1036. • If the weak force is decreased by a factor of 30, initial neutron/proton ratio ~ 0.90, leading to nearly pure helium universe (i.e. no interesting chemistry). Degree of fine-tuning is ~1/109.

13. The cosmological constant (dark energy) “Our current understanding of gravity and quantum mechanics says that empty space should have about 120 orders of magnitude more energy than the amount we measure it to have. That is 1 with 120 zeroes after it! How to reduce the amount it has by such a huge magnitude, without making it precisely zero, is a complete mystery. Among physicists, this is considered the worst fine-tuning problem in physics.” - Lawrence Krauss, (Scientific American, Aug. 2004, pp. 83-4).

14. The initial entropy of the universe • The initial state of the space-time (and thus gravity fields) of the early universe were very smooth and homogeneous (very low entropy). • Present entropy of universe >> initial entropy. • Initially low entropy is required for a habitable universe, in which high-entropy structures like stars form out of the surrounding low-entropy space-time. • Roger Penrose estimated that the amount of fine-tuning required of the initial entropy to allow for a habitable universe is 1 part in 1010^123!

15. Multidimensional fine-tuning • To be precise, you cannot just change one parameter while holding all others constant. Changing another parameter might compensate for the life-inhibiting effects of a particular parameter change. • Example: reducing the weak force can be compensated by reducing the mass difference between the proton and neutron in the early universe. • However, it is usually the case that changing a parameter has multiple different effects. Reducing the weak force also affects the explosion of massive star supernovae and radioactive decay. “If we modify the value of one of the fundamental constants, something invariably goes wrong, leading to a universe that is inhospitable to life as we know it. When we adjust a second constant in an attempt to fix the problem(s), the result, generally, is to create three new problems for every one that we 'solve.' The conditions in our universe really do seem to be uniquely suitable for life forms like ourselves, and perhaps even for any form of organic chemistry." - John Gribbon and Martin Rees

16. So What? What does fine-tuning have to do with it? • The Likelihood Approach: L = the existence of a life-permitting universe FT = only a narrow range of constants sustain life/fine-tuning. Cx= the fraction of settings on which the constants are capable of supporting life is x. T = theistic hypothesis NSU = naturalistic (or atheistic) single-universe hypothesis • Law of likelihood: E supports H1 over H2 given background beliefs B iff P(E | H1& B) > P(E | H2 & B) P(L | T & Cx) > P(L | NSU & Cx) Read: The probability that there exists a life-permitting universe on the theistic hypothesis and given our background knowledge that the fraction of settings on which the constants are capable of supporting life is x is greater than the probability that there exists a life-permitting universe on the naturalistic single-universe hypothesis and given our background knowledge that the fraction of settings on which the constants are capable of supporting life is x.

17. An easier way to understand it P1: The existence of life-permitting values for the constants of physics is not epistemically improbable under theism. P2: Because of the fine-tuning, the existence of life-permitting values for the constants is epistemically very improbable under the atheistic single-universe hypothesis. C: Since both theism and the atheistic single-universe hypothesis were clearly not constructed merely to account for the fine-tuning data (not ad hoc), it follows from premises 1 and 2 and the restricted prime principle that the fine-tuning data provide strong evidence in favor of the design hypothesis over the atheistic single-universe hypothesis. Here, the restricted prime principle implies that we reject the consideration of hypotheses constructed merely to account for the particular evidence in question.

18. Support for P1 P1: The existence of life-permitting values for the constants of physics is not epistemically improbable under theism. Here, we need to add some qualifications to what we meant by "life" when we defined fine-tuning earlier. In order for this to have any bearing on the probability of theism, we need to specify this further as referring to embodied conscious agents (ECAs) who can make what they take to be moral choices. Collins: "In contrast to the naturalistic multiverse explanation, theism does render it unsurprising that an ECA-structured universe exists. To begin, we would expect an all-good God to create a reality with at least a positive, if not optimal, balance of good over evil. Thus, arguably, theism should lead us to expect a universe structured toward the realization of moral and aesthetic value. Given that we can glimpse some special value that highly vulnerable embodied conscious agents like us can realize that could plausibly be thought to outweigh the evils - such as suffering - resulting from such embodiment, it follows that it is not surprising that God would create an ECA-structured universe. I propose that one such value is the ability to engage in particular kinds of virtuous actions - such as self-sacrificial love, courage, and the like - that the vulnerability that comes from embodiment allows. ...these actions allow for eternal connections of appreciation, contribution, and intimacy between conscious agents. For example, is someone significantly helps me in times of suffering, it can create a connection of appreciation in me that has the potential of lasting all eternity, and hence growing in value."

19. Support for P1, cont. Agnostic philosopher Paul Draper concludes similarly (in email correspondence to philosopher Greg Ganssle): “To make the fine-tuning argument work, it is not enough to argue that fine-tuning is very unlikely given naturalism. One must argue that fine-tuning is much more probable on theism than on naturalism. And my biggest worry about the fine-tuning argument has always been that neither life nor even intelligent life -- at least of the sort we find in our world -- seems all that probable on theism. A moral world is, however, very probable on theism. Thus, your ideas don’t just strengthen the fine-tuning argument. To use religious terminology, they save it!”

20. Support for P2 P2: Because of the fine-tuning, the existence of life-permitting values for the constants is epistemically very improbable under the atheistic single-universe hypothesis. Collins: "...we must appeal to some principle that allows us to move from the fact that the life-permitting range of the parameters of physics is very small to the claim that it is improbable that the parameters of physics would fall into the life-permitting range under the atheistic single-universe hypothesis. I do this by appealing to a version of the probabilistic principle of indifference, what I will call the restricted principle of indifference. Applied to the case at hand, this principle could be roughly state as follows: When we have no reason to prefer any one value of a parameter over another, we should assign equal probabilities to equal ranges of the parameter, given that the parameter in question directly corresponds to some physical magnitude (or occurs in the simplest way of writing the fundamental theories in the relevant domain)."

21. Other features • Observability/discoverability • The "unreasonable effectiveness of mathematics" • Beauty/Elegance

22. Anthropic Principle Of course the universe is just right for life...otherwise, we wouldn't be here asking questions! Confusion: A. If observers who have evolved within a universe observe its constants and quantities, it is highly probable that they will observe them to be fine-tuned for their existence (true claim)*. A'. It is highly probable that a universe exist which is finely tuned for the evolution of observers within it (false claim). Response: firing squad analogy Fifty sharpshooters all aim their rifles at you and fire. You are still alive. But you wouldn’t accept the explanation, “Of course you are alive…otherwise you wouldn’t be here asking questions!” You would instead conclude that the sharpshooters intentionally missed, were given faulty rifles, or something else (in other words, a causal explanation for the highly improbable fact that fifty expert marksmen could all have missed you). We still need an explanation for FT. * This is sometimes called the observer-selection principle.

23. More fundamental law • Grand unified theory (or theory of everything)? The laws of nature couldn't be different than they are. • Response: In practice, the search for a GUT (or TOE) seems difficult. String theory is our best candidate. However, this might give us only one law...or 10^500 of them. Are these/this fundamental law(s) fine-tuned? Do they explain the initial conditions (e.g. early inflation)? Why that/those laws? Why string theory? Even if no other possibilities within string theory, there are other possibilities to string theory. • Carr and Rees: “even if all apparently anthropic coincidences could be explained [in terms of some Grand Unified Theory], it would still be remarkable that the relationships dictated by physical theory happened also to be those propitious for life.”

24. Other forms of life: use your imagination! Response: the most plausible alternative form of life conceived: silicon-based. Problems: inferior to carbon in every measurable way (e.g. not as long or stable chains; when mixed with oxygen you get sand instead of breathable CO2). Less possible universes with silicon-based life because it would require better conditions. Furthermore, carbon is made along the way (prior to) silicon. Thus, the possible universes with silicon-based life overlap those with carbon-based life. Also, our bodies make no use of silicon.

25. THE MULTIVERSE: we win the cosmic lottery There are other regions of space-time with different constants and initial conditions, and perhaps even different laws of nature. Is it science, or science fiction? (or metaphysics??) - Perhaps, if there's a universe-making machine. Is the multiverse fine-tuned? Is the multiverse-generator fine-tuned?

26. Problem for the multiverse: Boltzmann Brains Can we test the idea? - We should be typical of all the life in the multiverse. However, it turns out that this is not the case. Astrophysicist Luke Barnes: “We should be wary of any multiverse which allows for single brains, imprinted with memories, to fluctuate into existence. The worry is that, for every observer who really is a carbon-based life form who evolved on a planet orbiting a star in a galaxy, there are vastly more for whom this is all a passing dream, the few, fleeting fancies of a phantom fluctuation. This could be a problem in our universe -- if the current, accelerating phase of the universe persists arbitrarily into the future, then our universe will become vacuum dominated. Observers like us will die out, and eventually Boltzmann brains, dreaming that they are us, will outnumber us. The most serious problem is that, unlike biologically evolved life like ourselves, Boltzmann brains do not require a fine-tuned universe. If we condition on observers, rather than biological evolved life, then the multiverse may fail to predict a universe like ours. The multiverse would not explain why our universe is fine-tuned for biological life.”

27. Collins: “[the multiverse's] seeming ability to explain the fine-tuning was based on conflating the real fine-tuning for ECAs (and secondarily, technology and discoverability) with a non-existent fine-tuning for observers. This in turn was the result of conflating conscious observers that arise through a normal evolutionary process - which are likely to be interacting agents - with mere observers, which need not arise through such a process. Without this initial motivation, however, it is hard to see why we should take the multiverse explanation more seriously than other naturalistic contenders. Finally, it should be clear that the existence of these fluctuation observers also undercuts the so-called weak anthropic principle objections, which claims that, even if there is only one universe, it is illegitimate to claim that fine-tuning is surprising or "improbable" since a universe that is not fine-tuned could not be observed.” With regards to that last point, what Collins is saying is that if fine-tuning is defined with regards to ECAs, thenit is still “surprising,”or improbable,that the universe is fine-tuned for this form of life, since it is the case that a non finely-tuned universe can actually be observed (i.e. by Boltzmann brains).

29. Bibliography Professor of astronomy and physics at Iowa State University, Guillermo Gonzalez, presents fine-tuning and a basic argument for theism: “Why is the Universe Fine-Tuned for Life?” (lecture, YouTube). Astrophysicist Luke Barnes of the University of Sydney presents fine-tuning and a basic outline of explanations for it: “Life in a Fine-Tuned Universe” (lecture, YouTube) Part 1, Part 2, Part 3, Part 4, and Part 5. Also see his article “The Fine-Tuning of the Universe for Intelligent Life.” Robin Collins: “The Teleological Argument: An Exploration of the Fine-Tuning of the Universe” Ch. 4 in The Blackwell Companion to Natural Theology; “The Fine-Tuning of the Cosmos: A Fresh Look at Its Implications” Ch. 19 in The Blackwell Companion to Science and Christianity. Darren Bradley on the reason why fine-tuning has implications for assessing the probability of theism: “Weisberg on Design: What Fine-Tuning’s Got to Do With it.”