Surely, you can remember waking up at night at least once to see something horrifying in a dark corner of the room - something scary that gave you goosebumps. Can you think of such an episode? Very quickly, your fear must have dissipated: you analysed the situation and realised that it must have been just a shadow. Congratulations: you are not a solipsist.

Solipsism is a worldview that is based strictly on what you see; in this framework, nothing exists outside of your consciousness. Should we forbid people to pursue this worldview? Of course not, be we could try to suggest to such a person that they try to cross a street full of traffic during the rush hour wearing headphones and blindfolded. After all, if you do not see the traffic, it does not exist. This would be nothing more than self-deception, though.

Our main instrument is the scientific method (which I am going to describe in much more detail in one of my upcoming articles). Observation forms one of its key parts. The only way to achieve a more complete picture of the world is by combining observation, experimentation, and logical conclusions, by forming hypotheses that can be either confirmed or refuted, by figuring out laws and creating mathematical models to describe natural processes. But even among the things we seem to know, there are some controversies; the so-called anthropic principle is one of them.

Physics has a great number of constants: the Planck constant, the speed of light, the gravitational constant, the Boltzmann constant, the masses of an electron, proton, and neutron, the elementary charge... Together they form a foundation for all our laws of physics.

It is mind-boggling to think of how many different factors had to coincide to make life - not only on Earth, but in the whole Universe - even physically possible. Could that happen if the physical constants had different values? Let us try to analyse the matter.

Our Universe has three spatial coordinates; however, it is not difficult to imagine that there could easily be more or fewer of them. Gravity remaining constant, a model of space with more than three coordinates does not hold up. Orbits would become highly unstable in their gravitational fields, a four-dimensional Earth would simply fall onto the Sun, and four-dimensional electrons would collide into four-dimensional nuclei.

The mass of a neutron exceeds that of a proton and an electron combined, which keeps atoms stable. Masses of protons, neutrons, and electrons are all physical constants, and if they were even slightly different, particles would not gather into atoms, atoms would not form molecules, and our whole world would be unrecognisable. The first to voice this idea was Robert Dick. He noticed that all physical constants have a very narrow range of values that allow for the appearance of life in the Universe. Finally, in 1973 the physicist Brenton Carter gave a full definition of the so-called anthropic principle.

Here is an informal definition of the 'weak' anthropic principle: the fact that we are here means that the Universe can support our being here, that its conditions allow living organisms to appear. This principle sounds a bit too obvious.

Far more interesting is the 'strong' anthropic principle: the Universe must function in such a way as to give rise to life. This statement can provoke some resistance: indeed, the Universe seemingly doesn't owe anything to anyone. But let us stress that such an idea has nothing to do with the underlying causes for everything that happens. We should accept the possibility of existence of multiple universes, all with different values of physical constants. This principle has been misinterpreted and mutilated by groups with various agendas, especially the proponents of 'intelligent design': supposedly, they are the only ones to know why everything is the way it is and who made it that way…

Modern physicists are very skeptical about the strong anthropic principle, and for a good reason. In order to judge the validity of this principle, one has to to answer a very difficult question: can the Universe exist without an observer? How can you possibly get a peek inside an observer-less universe when you are yourself an observer? Once you look inside a universe, you observe it. Thus, it seems impossible to prove or disprove the statement within the framework of the scientific method.

However, there exists another, more interesting proposal, which has been formulated very recently by the US physicist Lee Smolin.

Smolin has called his hypothesis cosmological natural selection. According to this idea, our Universe is definitely there, with all its physical constants, but there are other universes, too; they are born out of black holes. A new universe forms on the other side of a collapsing black hole, and just like our genes are subject to mutations, a new universe is subject to variations in physical constants. Of course, you may say that in order for a universe to be 'complete' - that is, in order for life to appear - values of the constants must fall into that narrow range that allows life. It is true, but just how it is with people, who often fall victims of unfortunate mutations and do not pass the natural selection, so it is with universes: conscious observers arise in those universes that have suitable conditions. And those conditions that are good for black holes are also good for life. This hypothesis can be used to explain the so-called fine tuning of the Universe; and taken together with the facts of mathematical statistics, this idea seems far more objective.