Multiverse: Encyclopedia II - Multiverse - Arguments against multiverse theories

Multiverse - Arguments against multiverse theories

It's not science. Critics claim that there is a lack of empirical correlation and testability in these theories and thus they are without hard physical evidence and must therefore be considered unfalsifiable, currently outside the methodology of scientific investigation to confirm or disprove, and therefore more mathematically theoretical and metaphysical than scientific in nature.

But Tegmark points out, improved measurements of the microwave background radiation and of the large-scale distribution of matter may fortify or knock down two pillars of the multiverse: the infinitude of space and the theory of chaotic inflation.

It’s bad science. Some have argued that the job of the scientist is to provide fundamental explanations for observed phenomena, without making reference to observers. Resorting to anthropic principles constitutes a “lazy way out” of accounting for features such as the apparent fine-tuning of parameters in relation to the existence of life.

Leonard Susskind claims however that some form of multiverse is unavoidable, given the current state of physics, and that observer effects are inevitable and have to be taken into account in other sciences

Alternative universes violate Occam's Razor. To postulate an infinity of unseen and unseeable universes just to explain the one we do see seems like a case of excess baggage carried to the extreme.

Tegmark answers:"A common feature of all four multiverse levels is that the simplest and arguably most elegant theory involves parallel universes by default. To deny the existence of those universes, one needs to complicate the theory by adding experimentally unsupported processes and ad hoc postulates: finite space, wave function collapse and ontological asymmetry. Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words." [1] Thus paradoxically the multiverse scenario is more parsimonious than that of a single universe.

There is only one possible universe. It is occasionally argued that the observed universe is the unique possible universe, so that talk of “other” universes is ipso facto meaningless. Einstein raised this possibility when he wondered whether the universe could have been otherwise, or non-existent altogether. The hope is sometimes expressed that once a fully unified theory of physics is achieved, it will turn out to have a unique “solution” corresponding to the observed universe.

Measures of fine-tuning are meaningless. The principal observational support for the multiverse hypothesis comes from the Anthropic Principle: the universe we observe is bio-friendly, or we would not be observing it. While this is a tautology, when the sensitivity of biology to the form of the laws of physics and the cosmological initial conditions is considered, it has some apparent credence; but on the other hand, many key parameters of physics do not seem to be very strongly constrained by biology.

Another criticism of the fine-tuning argument is that, as far as we know, there could be a more fundamental law under which the parameters of physics must have the values they do. Thus, given such a law, it is not improbable that the known parameters of physics fall within the life-permitting range.

Multiverses merely shift the problem up one level. Multiverse proponents are often vague about how the parameter values are selected across the defined ensemble. If there is a “law of laws” or meta-law describing how parameter values are assigned from one universe to the next, then we have only shifted the central problems of cosmology up one level, because we need to explain where the meta-law comes from. Moreover, the set of such meta-laws is infinite, so we have merely replaced the question “why this universe?” with “why this meta-law?”. There would seem to be little point in invoking an infinity of universes when it would be simpler to postulate a single universe with a single principle.

In Tegmark’s extreme multiverse theory this problem is circumvented, because in that case all possible meta-laws (or all possible unified theories) are in force and describe really-existing multiverses

The fake universe problem. Most scientists are prepared to entertain the possibility of conscious machines, and some artificial intelligence advocates even claim we are not far from producing conscious computers. It is then but a small step to the point where the engineered conscious beings inhabit a simulated world. For such beings, their “fake” universe will appear indistinguishable from reality. So should we include these simulated universes in the ensemble that constitutes the multiverse? Is it meaningful to assign equal ontological status to our own, observed, universe and universes that are virtual? If it is not then is it meaningful to assign equal ontological status to our own, observed, universe and universes that can never be observed by any sentient being?

Why stop there? The last objection to the existing multiverse theories is a challenge to the criteria for defining universes. In most multiverse theories, universes are labeled by laws of physics and initial conditions. It might be objected that these terms are narrow and chauvinistic; there may be criteria for categorization that lie completely beyond the scope of human comprehension.

Adapted from the Wikipedia article "Arguments against multiverse theories", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki