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I answered a question here with a quote with the following quote from Cosmologist George Ellis.

“Similar claims [about a multiverse] have been made since antiquity by many cultures. What is new is the assertion that the multiverse is a scientific theory, with all that implies about being mathematically rigorous and experimentally testable. I am skeptical about this claim. I do not believe the existence of those other universes has been proved—or ever could be. Proponents of the multiverse, as well as greatly enlarging our conception of physical reality, are implicitly redefining what is meant by ‘science.’”—pg 39

“For a cosmologist, the basic problem with all multiverse proposals is the presence of a cosmic visual horizon. The horizon is the limit to how far away we can see, because signals traveling toward us at the speed of light (which is finite) have not had time since the beginning of the universe to reach us from farther out. All the parallel universes lie outside our horizon and remain beyond our capacity to see, now or ever, no matter how technology evolves. In fact, they are to far away to have had any influence on our universe whatsoever. That is why none of the claims made by multiverse enthusiasts can be directly substantiated.”—pg 40-41

“A remarkable fact about our universe is that physical constants have just the right values needed to allow for complex structures, including living things. Steven Weinberg, Martin Rees, Leonard Susskind and others contend that an exotic multiverse provides a tidy explanation for this apparent coincidence: if all possible values occur in a large enough collection of universes, then viable ones for life will surely be found somewhere. This reasoning has been applied, in particular, to explanation the density of the dark energy that is speeding up the expansion of the universe today. I agree that the multiverse is a possible valid explanation for the value of this density; arguably, it is the only scientifically based option we have right now. But we have no hope of testing it observationally.”—pg 42

“All in all, the case for the multiverse is inconclusive. The basic reason is the extreme flexibility of the proposal: it is more a concept than well-defined theory. Most proposals involve a patchwork of different ideas rather than a coherent whole. The basic mechanism for eternal inflation does not itself cause physics to be different in each domain in a multiverse; for that, it needs to be coupled to another speculative theory. Although they can be fitted together, there is nothing inevitable about it. … Nothing is wrong with scientifically based philosophical speculation, which is what multiverse proposals are. But we should name it for what it is.”—pg 43

Now with this in mind if these theories cannot be independently verified should their truth not lie in method outside physics or what is also known as meta physics?

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    Can someone please help with the quotes. I'm really bad with these things. (-; – Neil Meyer Oct 13 '13 at 12:00
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    Metaphysics in philosophy does not always refer to concepts that are 'meta' in relation to standard physics... The term covers a very broad range of concepts, and because of the highly technical nature of multiverse theories (it seems one would require an extensive background in physics to seriously discuss such theories) I reckon they're still a better fit under physics. This is because I tend to value the sentiment that one can be a great philosopher without specialized technical knowledge in any field, and I don't think philosophy can help much there without having that knowledge prior. – stoicfury Oct 13 '13 at 22:30
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    Considering that in my first undergraduate metaphysics class, the bulk of the material was David Lewis's possible worlds theory, I have to ask: what do you mean re-brand? – Ryder Oct 31 '13 at 21:34
  • Just for the record, I happen to have unknowingly posted something close to a duplicate to this question here: philosophy.stackexchange.com/q/10389/5473 – Urs Schreiber Mar 26 '14 at 11:56
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    There are several varieties of 'multiverse' theories. Which do you mean? The 'many worlds' interpretation of quantum physics is not a theory, it is a simplifying framework for elaborating thought experiments -- 'as a theory' all interpretations are identical. The notions of 'branes' and the related mechanisms are a theory, and they have real physics behind them, if not enough to become testable yet. The idea of 'parallel universes' that do not intersect is a non-falsifiable fantasy, and this seems to be most of what Ellis is trashing -- but nobody ever really considered this science. – jobermark Nov 29 '18 at 20:47
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I haven't come across the term meta physics, perhaps you should provide a link? Unless, you of course you mean metaphysics? I'd differentiate between the two because multi-verse theories or string theories or the like are highly speculative, but also very mathematically and physically based. This is very different from the tradition of metaphysics proper.

Speculative physics, is not a standard term either, but from what your quote this is I think what you mean by meta physics. It has a grand tradition going back to the early cosmological speculations of the pre-Socratics at least in the Western tradition - a school that is sometimes called the Milesian materialists. Philosophers such as Thales, Parmenides, Zeno & Democritus amongst others tackled problems that originated in the physical world; (and there is a direct link between the physics of antiquity & the origins of modern physics - for example, Newton had a copy of Lucretious De Rerum Natura, a polemical poem by a Roman poet on atomism. One suspects this directly influenced Newton championing of a corpuscular theory of light, and his use of point particles in modelling motion & gravity).

This should be distinguished from Physics proper, from Galileo onwards when the notion of an experimentally based physics began to gain ground. This innovation was partly driven by technological progress - that is instruments began to be precise & regular enough to make an experimentally based physics possible.

This experimental approach resulted in an explosive advance in physical knowledge until say the mid to late 20 Century, when the energies and distances probed were too high & too small for a direct experimental approach to be feasible. For example the Higgs Boson was predicted over 50 years ago, it is only now that probing at the energy level required is feasible.

This means that research at a fundamental level is driven by a combination of physical intuition and (mathematical) aesthetic considerations. For example, the move from a point particle to a particle with some extension (string theory); the move from a homgenous and continuous background space to a space that is also atomic (Spin networks, Spin foam, causal sets, entropic gravity).

It was two millenia before the early physical theories could be tested directly; one could suppose with the energies required to probe the Plank length a similar time-scale may be required. In which case it would make good sense to have a term distinguishing between experimental & philosophical/speculative/metaphysical physics.

  • You might want to zoom in on the whether the distinction between practical feasibility and theoretical feasibility is essential. – user3164 Oct 13 '13 at 20:20
  • You have invoked Muphry's Law. You may be pedantically attacking a space and imagining a definition, but 'multi-verse' implies a text of multiple verses. – Magus Aug 11 '14 at 20:28
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Word are words, so we can define them as we like. The definition of "metaphysics" which I have found most meaningful in my research is "things beyond the explanation of physics."

The key to that definition is that it is not just things beyond the explanation of known physics, it's beyond physics in general. In this context, physics is usually classified as the study of repeatable testable things with rules.

As an example, there is a metaphysical belief that ghosts generate EMF readings. This is metaphysical because they do not seek to explain it, they just use it as "definitive proof" that a ghost is there.

There is also a physics based belief that ghosts generate EMF readings. Those who follow this belief aim to create repeatable tests which demonstrate, quantify, and model the EMF effects of ghosts. In doing so, they also make their theory falsifiable. I consider this just as much physics as the hunt for the next subatomic particle. That being said, I also hold it to the same standards: so far the proof of this belief is very lacking. While I would call it physics, I would also call it weak physics.

If I were to use this edge to dissect the original arguments, I would say the argument "there is a multiverse, and everything occurs every which way in some universe." to be metaphysics. However, if you begin to discuss the topology of these universes, and start suggesting models of what would be required to interact with one of these other universes in a repeatable fashion, I would call it weak physics.

Similar arguments are made for why string theory is still "physics." String theory admits testable repeatable behaviors; the lack of such behaviors would falsify the theory. The fact that such a test requires energy levels focused on microscopic regions far beyond our current capacity does not push it into metaphysics, it just means String theory continues to be "weak" until we can actually test it and strengthen it.

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The multiverse theories can be science insofar as they are mere predictors of physical outcomes. All science can do is predict experience. The multiverse theories might hint at actual multiverses, but whether or not they exist is not science. What I am doing is applying Ayer's criteria towards science (not philosophy!). I think we always have to be careful about using the qualitative nature of current scientific theories to try to prove the qualitative nature of reality. Scientific theories are ultimately upturned, and qualitatively disparate theories might take its place.

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I agree with Mozibur Ullah. I am no expert in the field, but I thought I would add my own opinion. I think that we cannot say just yet whether it is metaphysics or not. As our knowledge of a theory grows through mathematical reasoning, and our experimental techniques improve, we may realise that we can in fact test the multiverse theory (although I think that the real problem is thinking that a result that agrees with the predictions made by multiverse theory but not with those made by any other currently existing theory is evidence for the multiverse theory being correct, rather than just evidence about how the universe works which could be explained by the multiverse theory).

You may find the following article interesting https://www.quantamagazine.org/20141110-multiverse-collisions-may-dot-the-sky/

So if our experimental aparatus becomes sensitive enough to be able to see the tiny differences in the CMB fluctuations that would distinguish the multiverse theory from some other theory that predicts similar CMB fluctuations, then you could say we have evidence for the multiverse theory (assuming that different theories do make different predictions, although now in modern physics one of the most used techniques is changing the values of parameters as a result of experimental data and then seeing whether these parameters give rise to further distinctive predictions, and if not whether we can tweak the parameters some more when new experimental data arises so that it does not end up being inconsistent with the previous data).

So I suppose what I'm trying to say is that we are in a bit of an unknown. The line between physics and metaphysics seems to be becoming increasingly blurry. To be honest, it seems to me that there is no reason at all why the universe should work in a way that our minds can comprehend e.g. Ther being a soup of universes or particles being everywhere at the same time. Although we don't really understand this and it seems counterintuitive, the fact that we are even able to put these theories into words shows that it is something that we can conceptually comprehend. Although I suppose that is the only way to be making progress in science, because having some understanding of the theory allows us to make guesses about what could happen and then see if the maths, and then the experiment, works out. So with regards to multiverses, I don't know if we may, some day, be able to make a prediction using this theory that is validated by experiment and that we can be certain in saying that no other theory, whether comprehendable or not, could produce such a result. But I sure hope so.

I feel like what I have said doesn't really answer your question :/ but I hope that the article gives some food for thought...

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The "Many Worlds" type of multiverse is hardly metaphysics. It is rather the consequence of rigorous mathematical application of Shrodinger's famous (and magnificent and indispensable) wave function equation, and the simplest solution to the paradox of quantum superposition. Many Worlds seems to be the necessary outcome of the wave function equation if the wave function does not undergo (the persistently problematic) collapse. Anyway, the mathematical predictions of theoretical physics come true far too often to consider them as metaphysical thought experiments.

Read, if you haven't, Hugh Everett's 1957 dissertation, "The Theory of the Universal Wave Function." He's the one that started it all. Sadly, he was scorned for it.

http://www-tc.pbs.org/wgbh/nova/manyworlds/pdf/dissertation.pdf

  • What does metaphysics mean in your answer here? – virmaior Jul 11 '16 at 2:41
  • Downvoting because the answer doesn't address weaker "riders" on these multiverses or attempt to restrict its approval of "Many Worlds" to things demanded by rigorous application of mathematics to experimental results. – elliot svensson Nov 29 '18 at 17:27

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