The laws of the Universe are not set in stone. Impossible does not exist. Everything, absolutely everything, is possible given that enough people believe in it.
Centuries ago magic was as real as electricity today. Dragons, fay, unicorns, and other mythological creatures roamed the world. But as beliefs in magic started to lose popularity with the general population, the magic began to dwindle and a couple of centuries ago ceased to exist completely. Fay, unicorns, kobolds, and many other magical species died out. Their bodies and bones dissolved without magic to support them. Dragons fared better, but they grew smaller and less intelligent. Without magic, they transformed into unremarkable reptiles.
Magic was not the only thing affected by the change in beliefs. The very structure of the universe was completely altered. The flat Earth transformed into a sphere. The stars became glowing balls of fire and later immense nuclear fusion reactors. The cosmological constants changed to fit the most popular cosmological theories.
The world as we know it now is a result of our beliefs. It is a perfect case of the tyranny of the majority: Only the most believed ideas gain the power to change the universe.
It is still little known how beliefs and universal laws are connected. The scientists and philosophers are still working on it. However, the most pressing question of the day is how to prevent populists and demagogues from altering reality in a significant way (for example, changing cosmological constants or reviving magic).
Notes on beliefs' mechanics:
This premise is an exploration of the Sorites paradox applied to society, its values and beliefs. The paradox can be summarised in 'How many grains of sand should be removed from a heap for it to become a non-heap?'
The same as with the grains of sand in the Sorites paradox, it is not possible to say how many people precisely are needed and how strongly they should believe in something to trigger a change. Yet, it is possible to say when the beliefs affect the structure of the universe or not:
- the universe conforms to beliefs that are a part of common sense (people cannot fly like birds);
- the universe changes to accommodate the most accepted cosmological theories (i.e. theories taught in schools, university or the ones considered to be common sense, 'natural', part of general knowledge);
- beliefs of one small group of people (a tribe living in a remote location, a religious sect, etc.) do not affect the laws of the universe, however, they may alter the members of the group in ways consistent with the universe in general (i.e. all females are very good hunters [but within the constraints of human abilities, no magic or super-natural luck is possible if magic is non-existent] because the tribe believes that Gods created women to hunt and gave them better hunting instincts and skills);
- god(s) can and do exist if many people believe that gods exist, and if this is the case, gods have the powers as they are believed to have;
- only sincere beliefs (including all kinds of implicit and explicit biases) affect the universe (i.e. if you go to church but question the existence of god(s) you do not contribute to the existence of gods in the universe).
It is no more possible to say when the critical mass of believers is achieved to alter the universe as it is to say how many grains of sand exactly are needed to make a heap. Moreover, the changes do not happen overnight (as belief systems do not change overnight). They follow the changes in belief systems and accumulate over time.
For those who have difficulties imagining how it works, please think about the exact day you became an adult. Unless there is some kind of an initiation ritual in your society, it is very unlikely that you woke up one day and everybody, including you and your parents, suddenly started to treat you as a grown up. The change was (or still is) gradual and almost unnoticeable at the time. However, if you look back 10 or 20 years ago you see dramatic differences.
Please feel free to ask for additional details in comments.
Good answer criteria
- An answer focuses on society, social and psychological mechanisms of populism and crowd control (this is not a question about physics).
- The current state of the universe (almost identical to our real universe) is preserved.
- The society does not have to resort to totalitarianism and mind control.
- The technological progress is not arrested.
A great answer will have links to scientific evidence and relevant scientific papers.