Last week I spent an enjoyable few days in Tenerife, one of the Canary Islands, for a conference on the Philosophy of Cosmology. The slides for all the talks are now online; videos aren’t up yet, but I understand they are forthcoming.
It was a thought-provoking meeting, but one of my thoughts was:Β “We don’t really have a well-defined field called Philosophy of Cosmology.” At least, not yet. Talks were given by philosophers and by cosmologists; the philosophers generally gave good talks on the philosophy of physics, while some of the cosmologists gave solid-but-standard talks on cosmology. Some of the other cosmologists tried their hand at philosophy, and I thought those were generally less successful. Which is to be expectedΒ — it’s a sign that we need to do more work to set the foundations for this new subdiscipline.
A big part of defining an area of study is deciding on a set of questions that we all agree are worth thinking about. As a tiny step in that direction, here is my attempt to highlight ten questions — and various sub-questions — that naturally fall under the rubric of Philosophy of Cosmology. They fall under other rubrics as well, of course, as well as featuring significant overlap with each other. So there’s a certain amount of arbitrariness here — suggestions for improvements are welcome.
Here we go:
- In what sense, if any, is the universe fine-tuned? When can we say that physical parameters (cosmological constant, scale of electroweak symmetry breaking) or initial conditions are “unnatural”? What sets the appropriate measure with respect to which we judge naturalness of physical and cosmological parameters? Is there an explanation for cosmological coincidences such as the approximate equality between the density of matter and vacuum energy? Does inflation solve these problems, or exacerbate them? What conclusions should we draw from the existence of fine-tuning?
- How is the arrow of time related to the special state of the early universe? What is the best way to formulate the past hypothesis (the early universe was in a low entropy state) and the statistical postulate (uniform distribution within macrostates)? Can the early state be explained as a generic feature of dynamical processes, or is it associated with a specific quantum state of the universe, or should it be understood as a separate law of nature? In what way, if any, does the special early state help explain the temporal asymmetries of memory, causality, and quantum measurement?
- What is the proper role of the anthropic principle? Can anthropic reasoning be used to make reliable predictions? How do we define the appropriate reference class of observers? Given such a class, is there any reason to think of ourselves asΒ “typical” within it? Does the prediction of freak observers (Boltzmann Brains) count as evidence against a cosmological scenario?
- What part should unobservable realms play in cosmological models? Does cosmic evolution naturally generate pocket universes, baby universes, or many branches of the wave function? Are otherΒ “universes” part of science if they can never be observed? How do we evaluate such models, and does the traditional process of scientific theory choice need to be adapted to account for non-falsifiable predictions? How confident can we ever be in early-universe scenarios such as inflation?
- What is the quantum state of the universe, and how does it evolve? Is there a unique prescription for calculating the wave function of the universe? Under what conditions are different parts of the quantum state “real,” in the sense that observers within them should be counted? What aspects of cosmology depend on competing formulations of quantum mechanics (Everett, dynamical collapse, hidden variables, etc.)? Do quantum fluctuations happen in equilibrium? What role does decoherence play in cosmic evolution? How does do quantum and classical probabilities arise in cosmological predictions? What defines classical histories within the quantum state?
- Are space and time emergent or fundamental? Is quantum gravity a theory of quantized spacetime, or is spacetime only an approximation valid in a certain regime? What are the fundamental degrees of freedom? Is there a well-defined Hilbert space for the universe, and what is its dimensionality? Is time evolution fundamental, or does time emerge from correlations within a static state?
- What is the role of infinity in cosmology? Can the universe be infinitely big? Are the fundamental laws ultimate discrete? Can there be an essential difference between “infinite” and “really big”? Can the arrow of time be explained if the universe has an infinite amount of room in which to evolve? Are there preferred ways to compare infinitely big subsets of an infinite space of states?
- Can the universe have a beginning, or can it be eternal? Does a universe with a first moment require a cause or deeper explanation? Are there reasons why there is something rather than nothing? Can the universe be cyclic, with a consistent arrow of time? Could it be eternal and statistically symmetric around some moment of lowest entropy?
- How do physical laws and causality apply to the universe as a whole? Can laws be said to change or evolve? Does the universe as a whole maximize some interesting quantity such as simplicity, goodness, interestingness, or fecundity? Should laws be understood as governing/generative entities, or are they just a convenient way to compactly represent a large number of facts? Is the universe complete in itself, or does it require external factors to sustain it? Do the laws of physics require ultimate explanations, or can they simply be?
- How do complex structures and order come into existence and evolve? Is complexity a transient phenomenon that depends on entropy generation? Are there general principles governing physical, biological, and psychological complexity? Is the appearance of life likely or inevitable? Does consciousness play a central role in accounting for the universe?
Chances are very small that anyone else interested in the field, forced at gunpoint to pick the ten biggest questions, would choose exactly these ten. Such are the wild and wooly early days of any field, when the frontier is unexplored and the conventional wisdom has yet to be settled.Β Feel free to make suggestions.
Interesting list of questions, though I was distracted when I got to the comments section and half of the comments are missing due to being voted down. I also noticed quite a few comments voted negatively that didn’t seem to warrant the effort of a thumbs down and potential removal. A discussion like this would be much more interesting with all sides of the conversation visible. How unfortunate.
“Does consciousness play a central role in accounting for the universe?”
Apparently in this part of the universe ego does. π
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The 10 questions together form an excellent vantage point… We can ask ourselves a few simple questions. How many stars/galaxies/universes are there now? How many stars/galaxies/universes will be born? Let quantum sensibilities answer these simple questions… The results will be transformative…
The question ” Are there reasons why there is something rather than nothing. ” interests me. Linguistically it would seem odd to suggest that non-existence can in any sense be said to exist and I wonder if this is more than a linguistic oddity. It might instead reveal a fundamental truth which could be crudely stated as – shit happens.
If science is based on observation rather than pure reason then the most fundamental observation of all is that something is happening. It is logically impossible to account for all observations by tracing cause and effect back since this leads to infinity which explains nothing. Might it not be better to except existence itself as the ultimate observation upon which all else can rely?
Is emergency emergent, or fundamental?
RE: Laurie McGinness:
“The question ‘Are there reasons why there is something rather than nothing.’ interests me.”
Ms. McGinness, I would bring to your attention Jim Holt’s book “Why Does the World Exist?: An Existential Detective Story,” published July 16, 2012 by Liveright.
Gottfried Wilhelm von Leibniz, among others, asked: “Why is there something rather than nothing?” Jim Holt thoroughly explores this question; see, also, “Into the Nothing, After Something,” Dwight Garner’s review of “Why Does the World Exist”: New York Times book review, August 2, 2012.
T.E. Oakley
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Thanks T.E. But it is Mr, Laurie being short for Laurence in this part of the world. I will have a look for the books although my point is really that the question does not make sense since non-existence cannot, in any sense, be said to possibly exist.
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https://itunes.apple.com/us/book/freaky-truths-about-god-evolution/id899016923?mt=11
There are thermal fluctuations even in equilibrium as for quantum fluctuations I don’t know.
I don’t think real equilibrium is even possbile because of the 3rd law of conservation.
If a physical system will really be at absolute zero then entrope=0 and you get a singularity
Re: “Thanks T.E. But it is Mr, Laurie being short for Laurence in this part of the world. I will have a look for the books although my point is really that the question [‘Are there reasons why there is something rather than nothing?’ above posted in “10 questions…” under question no. 8] does not make sense since non-existence cannot, in any sense, be said to possibly exist.”
Perhaps you’re a resident of the United Kingdom? Sorry for my gender error. But to your point:
Mr. McGinness, yes, this assertion of the “existence” of “non-existence,” appears, on the surface at least, to be a contradiction; a paradox. Is this merely a linguistic problem? Or, perhaps, a logical problem? I think those cosmologists, they are referred to as the “nothing theorists” in Jim Holt’s book (Jim Holt: “Why Does The World Exist? An Existential Detective Story,” Liveright, 2013, p.27), believe that this “nonexistence,” which is equivalently defined as the “Null World” (Jim Holt), “…no space, no time, no anything!” (Dr. Lawrence M. Krauss), “a closed spacetime of zero radius” (Dr. Alex Vilenkin)—this “absolute nothingness” shall we say, conceived, to use Dr. Sean Carroll’s description, as a quantum state of the universe “just as good as every other [quantum] state” of the universe, and as “some peculiar non-geometric phase” that the universe “can pass through…” (Dr. Sean Carroll: “A Universe from Nothing?” / Cosmic Variance, April 28, 2012, computer print out, page 3, under the heading “Possibility one: time is fundamental”): this non-geometric nonexistence is surely conceived by these “nothing theorists” as a “synthetic” concept, a scientifically MEANINGFUL conjecture.
Does this problem go away when one describes a non-geometric “world,” absent the physicality of space, time, and matter through a process of negation, a type of medieval “via negativa”? In what sense can “a closed spacetime of zero radius” be conceived to function in a scientific model? Is this merely a linguistic problem for these theorists, resolvable through a reformulation of your question?…or is the problem deeper? And can this question be subsumed under Dr. Carroll’s above question no.4 “What part should unobservable realms play in cosmological models,” if one can argue that this is not even a “realm” (which would imply that it is “something”) and, furthermore, that this concept is not even theoretically empirical, a “nonfalsifiable prediction” to use Dr. Carroll’s phrase, and, thus, by definition is extrascientific, if “scientific” would require, at least, a THEORETICALLY observable state.
T.E. Oakley
Sent from my iPhone
These are fantastic questions. I would promote, as other commenters have before:
1. Are wave functions real? If so, is there a fundamental type of information that is necessary for physical states? Or do physical states just appear to have illusion of information?
2. Is prediction limited? Can we ever hope to have a computer simulate 50 kg of matter, knowing every state of the system and predicting those states for future times? Is the universe deterministic, but incapable of being accurately modeled? Does this imply that a universe with free will is indistinguishable from a universe without free will?
Kevin
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I like the fact that there is a discussion. In my own examination (and reading of others), I have found that physicists sometimes don’t know what they are talking about, with the creation of theories, because they don’t pay enough attention to the history of their own field. For example, up until the early years of the 20th Century, physics was strictly empirical. We tried to take things apart so as to understand them. These “things” got smaller and smaller, until we had to notice that our instruments for observing had an effect on the object we were studying. This caused a philosophical problem, not a physics problem. The real question was what does it mean that we ran into an observational limit. That’s not a question physicists were good at answering, and philosophers tended to believe physicists’ solution to this dilemma. That solution was to walk off of a cliff, into a territory far removed from taking things apart anymore. What was then done, once this observational limit was reached, was that physicists started inventing possibilities – theory started to run ahead of experiments, and then the experiments started trying to prove the theory. Thinking made up stuff, and did not always do this in a satisfactory logical way. Quantum theories came into existence, and tried to resolve the problem of the observational limit, by imagining the universe was based on potentials or possibilities. So we get the idea that on the other side of the observational limit (which limit we empirically knew), the fundamental particle reality could be defined in terms of probabilities. Take the simplist experiment, the coin flip. What got said was that when we flipped the coin it had a more or less 50/50 “chance” of coming up heads or tails. That’s not philosophically or logically true. There will always be an empirical result – the coin will end up heads or tails, but it never is in a state where there is a probability. Never. This “style” of thinking then invaded more and more complex phenomena, and the idea of probable existences became assumed to be true. They are never true. What will happen will happen. Now physics has had almost a century to stay in this imagined realm, and the whole approach has gotten more and more fanciful, and at the same time coupled to some very interesting mathematics. It is believed that experiments prove quantum mechanics, and they appear to do so. But its only an appearance, because the physicist is no a philosopher, and the philosopher is no physicist. Part of the problem is what happens when the physicist makes a “mathematical” statement. It can be made to work, as long as we forget the work of Kurt Godel, which unless I have failed to understand it, basically proved mathematical systems (which vary) are all closed systems. They are bound by their assumptions, and this is what has happened in the mathemathics of Quantum Mechanics. Its a closed system, and like the classic idea of the Oroborus, the snake eats its own tail. The next logical question has to do with predictability and the practical uses made of the ideas of quantum physics in various fields. A historian of science might say that scientific theory approximates reality. The more sophisticated, the better the approximation. This is what we see with experiments that seem to verify quantum mechanics. In certain fields of complex phenomena, that can be mathematically represented, the math seems to work. The problem comes when the scientist takes his ideas and starts to imagine that they can be extrapolated to other kinds of studies. This is part of what we have then in Cosmology, because the theory runs very far ahead of our empirical knowledge. The math is extrapolated in huge ways, such that the assumptions necessary are forgotten, and the physical astronomer starts to believe he can tell us something true about events that happened 13 billion light years away in space and another 13 billion years away in time. That, frankly, is philosophical hubris. Even among astronomers, the assumptions supporting the big bang, red shift, dark matter, dark energy, are getting way out there, while the empirical provable elements are not even on the table. I could go on endlessly, but I don’t expect many (or even one) to read this. So, yes, I think there are questions, but more important is that we need a realistic statement of the history of physics, one that is philosophical rigorous. There are a lot of assumptions and logical mistakes out there, that physicists don’t recognize because they “believe” their own dogmas.