In the previous article I gave a very quick overview of the fine tuning problem of cosmology. Why do the laws of physics and the fundamental constants of nature, which are believed to be random, just perfect for creating a Universe that permits life to develop and exist.

One particularly interesting potential solution arises from the foundations of quantum mechanics. While it might sound more like philosophy than physics, it is possible that the Universe cannot exist unless there is someone here to observe it.

Even though quantum mechanics was experimentally confirmed over a century ago, we still do not really understand it. We know that on a subatomic scale, particles exist as some sort of wave that propagates through space and time, and then when we make an observation that wave collapses to a single particle. But what do we mean by an observer? What do we mean be 'collapse'? These are questions that are still unanswered, but may hold the answer to the fine-tuning problem.

Suppose that the Universe exists as a cosmic scale wavefunction, in which every possible state of the Universe exists simultaneously. (Don't worry if you cannot imagine that, since no one really understands quantum mechanics, and quantum cosmology is even weirder!). If the same rules of quantum mechanics apply, then this wave continues to exist for billions of years because there is no one around to make an observation. A single particle that formed in the Big Bang would remain in its wavefunction for this span of time, so why couldn't the entire Universe?

Then sometime in the last few billion years, life formed on Earth. However we don't really know what sort of observation or measurement is required to collapse this cosmological wavefunction. Maybe the first life forms looked up at the sky, and collapsed its wavefunction. Maybe it didn't collapse until sentient life forms started studying it. Or perhaps different parts of the cosmological wavefunction collapsed at different time. Perhaps each time scientists measure another fundamental constant, they partially collapse this wavefunction and in a sense are creating those constants with their measurements.

If this interpretation of quantum cosmology is true, then it would mean that the Universe is tuning itself by producing observers who can make measurements. Since a Universe that does not support life would not collapse the wavefunction, it never becomes real. Only a Universe suitable for life can ever become real, and therefore fine tuning happens no matter how improbable.

Another variation on this idea is the consistent histories and similar interpretations of quantum mechanics. In these versions of quantum mechanics, a measurement of a wavefunction sends a signal backwards in time which then alters the previous states of the system to make them consistent with observations in the present. (I will write a full explanation of this interpretation in the future, but for this simple argument this oversimplified explanation should suffice). So far all experimental tests of the consistent histories interpretation have been inconclusive - this could be the correct model of nature, or it might not be. We just don't know yet.

Suppose though that the consistent histories version of quantum mechanics is correct. The if we apply it on cosmic scales, we find that the Universe will always be fine tuned because we are here making observations. A scientist making a measurement of some fundamental constant of nature sends a signal backwards in time that propagates all the way back to the Big Bang. At the moment of the Big Bang, this signal interferes with the wavefunction of the Universe and effectively erases those combinations of constants and physical laws which conflict with the measurement that the scientist just made. It makes the Big Bang consistent with the measurement just made.

Then there is no fine tuning required. The Universe supports life, because a scientist observed that it does in the present, and that observation altered the state of the Universe at the moment of the Big Bang.

So perhaps the issue of fine tuning is not a problem, because quantum mechanics and quantum cosmology require the Universe to always produce an observer. It is an interesting solution, but it is not the only one. Next we will consider the possibility of many Universes...