*The multiverse is not progressive science. Falsifiable alternatives may be disastrous for quantum computing.*

I’m not a mathematician, physicist or even a cosmologist, but I do know logic. I spend a good deal of time thinking about complex problems and something doesn’t quite add up. What doesn’t add up is the fashionable notion that there is a multiverse. As well as being unscientific, a scientific alternative to the multiverse may end up having drastic consequences on the viability of quantum computing.

**So what is the multiverse?**

Let’s go with cosmologist Max Tegmark’s definition. According to Tegmark, there are four levels of the multiverse:

- level 1: our universe beyond that which is observable
- level 2: other universes with different physical constants
- level 3: many-worlds interpretation of quantum mechanics
- level 4: the collection of all universes

I can understand the level 1 multiverse because due to the speed of light and the ongoing expansion of the universe we can only observe a “Hubble volume” of our universe. Think of this as being akin to being lost in a fog. You can see, say five metres in all directions, and as you move that sphere of visibility moves with you. It’s the same for observing the universe from a point in space, but the effect is born from expansion versus the speed of light.

It’s the level 2, level 3 and level 4 multiverses that I struggle with for a number of reasons. To understand why I struggle with this we need to go back to some basics, namely what constitutes good science.

The folly of relying upon mathematics solely is that we can end up in a dilemma where the theory works mathematically, but there is no way to make an observation to either prove or disprove the hypothesis.

**Good and bad science**

For science to progress, we need to have a testable hypothesis, one where science is based on observation. Mathematics is an excellent tool for encoding observation and making predictions; however, mathematics in itself does not equal observation. The folly of relying upon mathematics solely is that we can end up in a dilemma where the theory works mathematically, but there is no way to make an observation to either prove or disprove the hypothesis. The case for the multiverse is one based on an untestable hypothesis.

So what are the arguments for the multiverse? Broadly they fall into two categories:

- The anthropic principle
- The existence of a universal wave function in quantum mechanics

The anthropic principle endeavours to explain why the universe is fine-tuned to support life. The principle comes in two forms; strong and weak. The strong anthropic principle states that the universe is compelled to create conscious and sapient life. The weak anthropic principle states that our universe has created life as a result of “fine-tuning”. This “fine-tuning” is one of many possible combinations of conditions that exist in the entirety of all level 2 multiverses. Therefore, it is the weak anthropic principle that is used to support the level 2 multiverse. Within an infinite collection of universes, one will exist with the exact fine-tuning that we have in our universe.

Quantum mechanics is then used to explain the level 3 multiverse. Observations in quantum mechanics cannot be predicted absolutely; instead, the outcome exists as a probability (or probability wave). Measurement doesn’t cause the wave function to collapse. Instead, each of the probabilities split off (i.e. the existence of a universal wave function) to create their own level 3 universe with their own history.

The level 4 multiverse then takes it to the extreme. As well as being the collection of all universes from level 1 to level 3, the level 4 multiverse in Tegmark’s theory is the ultimate ensemble that is not defined by mathematics but is mathematics. Mathematical existence is physical existence.

**Proving the multiverse**

So how do we prove the existence of the multiverse? Well, that’s the difficulty, we can’t. It’s an investigative dead end. The other universes from level 2 onward have no causal effect on our universe, so we will never know. Although the multiverse is viewed by many as science, in reality, it is no more than a myth based on a philosophical viewpoint. So how can we explain the observed facts that the multiverse “mythimaticians” are attempting to explain and what would constitute good philosophy?

The multiversers are attempting to progress to a unified theory of everything (ToE) by explaining the measurement problem in quantum mechanics and by promoting their belief that the universe is mathematical. As a philosophical backup, they use the weak anthropic principle along with Occam’s razor. I’ve already discussed the science, or rather lack of science to explain the multiverse. On the philosophical side, the weak anthropic principle, like the multiverses, is an untestable theory providing no falsifiable predictions, therefore, while it poses the fundamental questions of “why us and why this universe?” it should form no part of science and should be thought of as a consideration rather than a principle. Occam’s razor is the principle that the simplest solution is usually the correct one. Although the multiverse does not sound like a simple solution, its supporters claim that it is simpler than trying to explain the anthropic principle any other way. This is debatable both ways; however, Occam’s razor should only be used as a guide, not an arbitrator and as we have seen, the anthropic principle is not a principle but a consideration.

**An alternative**

…whether it is right or wrong, it is falsifiable and can be used as an agenda to drive science forward rather than taking us down dead ends.

To unpick this, we need to go back to some basic principles. The landscape in which the multiversers operate is one of immutable laws, created by mathematics that have existed since the birth of our universe, i.e. the mathematical structure. The opposing view would be that the laws of our universe have evolved over time and that mathematics can codify these laws, but mathematics does not create them. This alternative view promoted by philosophers such as Roberto Unger and physicists such as Lee Smolin, jar with the mainstream for suggesting that there is only one singular universe and it is not mathematical.

The advantage of this alternative view, whether it is right or wrong, it is falsifiable and can be used as an agenda to drive science forward rather than taking us down dead ends. This singular universe may be one of many in a sequence (or bounces), born from collapse then re-birth, but to progress scientifically, we should look to prove/disprove all we can absolutely in this universe.

To elaborate on this singular universe, instead of the laws of physics being driven by mathematics, the laws can be thought of as evolving. When enough scenarios of similar complexity have taken place over time, a law has evolved. The law is not absolute but an approximation to the granularity of the observation. This lawmaking breaks down at the quantum level because a law is not an absolute rule for all individual components, rather a statistical approximation for a repeatable outcome.

**Implications for quantum computing**

This novel problem that quantum mechanics poses has potentially disastrous consequences for the future of quantum computing. Many quantum theories have been proposed to explain the breakdown of laws at the quantum level. The multiversers claim that all probabilities exist, albeit in different level 3 universes. However, as part of the singular universe theory, we have the real ensemble interpretation. This interpretation supposes that quantum dynamics only holds for systems which have copies and this is why we only observe quantum dynamics in the very small with lots of copies. When scaled up, macroscopic bodies are not described by quantum mechanics as they are not part of an ensemble of copies.

…it’s time we put science back on the agenda and work with what we have in our universe.

The dilemma for quantum computing is that we are assuming the validity of theories that cannot be tested. If the multiverse theory is wrong and the singular universe theory is correct along with the real ensemble interpretation, this may mean that we will never be able to exceed a point of complexity with quantum computers. This is because as a quantum computer’s complexity increases the chances of there being exact copies of the configuration elsewhere in the universe diminishes. With the singular universe being a falsifiable theory, surely this should be a focus for research.

I think it’s time we put science back on the agenda and work with what we have in our universe to progress as far as we can scientifically before we start worrying about other universes.

*For more information on quantum computing, Adrian Fern has written an excellent article here.*