• Choose a category
• All
• Classic-Fiction

By Root 650 0

could have differed considerably in these undetermined properties from what we currently see. Their physical meaning reveals the quantum theoretical nature of the universe: While classical properties such as the volume or the expansion rate could be determined quite precisely, this is not the case for the quantum mechanical uncertainty of these quantities. In principle, the universe before the big bang could have been much less distinct than it is today, or its volume could have fluctuated much more. Thus we cannot be sure about the exact state whence the universe as we know it came. Within science, this does not appear more constrainable—unless one would allow oneself to make additional, prejudiced assumptions about the state. Although quantum cosmology can clarify questions about the universe in unprecedented ways, it does leave modest freedom for the myths.

LIMITS: NO ULTIMATE ANSWER?

The limits of my language are the limits of my world.

—LUDWIG WITTGENSTEIN, Tractatus Logico-Philosophicus

Loop quantum cosmology has shown mechanisms to prevent the collapse to singularities by counteracting forces. Results available so far are based on models simple enough to be treated precisely by mathematical methods; otherwise the described behavior would not have been revealed. Such a procedure is common in theoretical physics, in which one often starts with the simplest model characterizing a situation, only to make it more realistic by systematic extensions. In quantum cosmology, one might, for instance, consider different matter types or use fewer symmetry assumptions. In such a situation, the unavoidable question arises whether results obtained in the simple model are generally valid, or need to be revised in extended models. This general issue must also be taken into account for statements in quantum cosmology, such as those about repulsive forces or the associated cosmic forgetfulness, both seen in some models but not yet proven in general.

In this context, there is a considerable difference between negative statements about what can be known, such as cosmic forgetfulness, and positive results such as are often found in model systems. An example of the latter would be the specific density in a simple model universe at the time when it bounces. Initially one is often interested in such concrete data. In simple situations many computations can be done, but the question always remains of how reliable the result is under realistic conditions, which are more difficult to incorporate in the model. With cosmic forgetfulness, by contrast, we are dealing with a negative property: a result about limitations of knowledge. Such results may be less concrete, but they are more secure against extensions of models. Any extended version would, after all, only complicate the original model; otherwise one would directly have taken the more complex model as the starting point of one’s analysis. And with a more complex situation, knowledge can be gained only in more difficult ways than in the simpler model. If knowledge was already limited, it surely will be even more so in the more general situation. It is thus safe to consider cosmic forgetfulness as a general property.

For physicists, limits to knowledge are depressing. The success of the deterministic worldview only strengthened the common belief in it; challenges are viewed skeptically. Cosmic forgetfulness is such a challenge, and it has been criticized. But most counterarguments so far deployed constitute acts of Zenoic desperation, abusing infinity, and are therefore invalid. One argument goes as follows: It may well be that the total uncertainty of the universe before the big bang cannot be determined, but there are many more, even infinitely many, properties characterizing a quantum universe. One uncertainty parameter out of infinitely many properties is almost nothing, and so nothing is being forgotten.

That this argument is nonsensical is obvious when it is applied to human forgetfulness: It is like saying that we all have perfect memory! It may well be that once in a while