(1) What NEW IDEAS about science and humanity emerged in the early 20th century? (2) How did they DIFFER from previously accepted ideas? (3) Did they effect the established SOCIAL AND RELIGIOUS STRUCTURES?
I would agree that Freud's emphasis on the unconscious had a dramatic effect on the way Europeans thought about humanity. I would also argue that a unique form of nationalism, influenced by social Darwinism, took root during this period as well. This way of thinking encouraged colonial acquisitions, cast foreign relations as an eternal (and noble) struggle, and had the dangerous effect of motivating smaller nations, like Serbia, to struggle for regional dominance, and bigger nations, like Austria-Hungary, Germany, and Russia, to involve themselves in their struggles. It also encouraged a new spirit of militarism that emphasized martial prowess as an indicator of masculinity. We all know how it turned out in the second decade of the 20th century.
I'm surprised that no one brought up the topics about gender equality and racial equality. These were very important developments in the 20th century. In the past, too many people had false views of superiority in terms of race and gender. The 20th century helped tremendously to dispel these very harmful ideologies. To be sure, more work need to be done, but there has been some important developments.
I think we need to look at the way the arrival of the internet has completely transformed society and changed traditional notions of life and the world. This of course can be linked to globalisation and the way that the world is becoming a much smaller place. How we relate to people all over the world is changing as a result, and in particular our relationship with knowledge, as we are able to find any piece of information at the click of a button.
In 1905 Einstein delivered his famous paper on the Photoelectric Effect, which started other scientists on the road to developing new theories of how matter and energy work, and culminated in the scientific revolution of Quantum Mechanics. Splitting the atom indeed came out of that research, with all its attendant problems.
This was also the time that Marconi improved upon Tesla's design and developed a functional radio, one that could be mass-produced and sold cheaply. The first instrument of mass-media was born.
Freud's theories obviously had an enormous impact. The theories of Einstein helped lead, ultimately, to the atom bomb, which may be (in unfortunate ways) the most scientific development of the 20th century, at least in its potential to devastate life on earth. Never before had it been thought possible to release so much energy from such a tiny bit of matter. It doesn't seem an exaggeration to say that life on earth was altered forever by the discovery of atomic energy.
One new idea was that ailments should be cured, and people should not suffer from any sickness. Medicine made huge gains with technology, and some of those gains came from basic sanitation and healing. Diseases that used to kill could not be cured.
I would have to agree with pohnpei. I believe that Freud's concept of the unconscious had a great impact on many different avenues during the 20th century. Based upon Freud's thought, the idea and use of the stream of consciousness was incorporated in literature. His gift to psychology reached far beyond the boundaries of the sciences.
I'd say that the biggest idea that became widely accepted in the early 20th century was Freud's theory of the unconscious. What Freud's theory did was to undermine the idea that people had had that we human beings are rational and that our rationality would allow us to progress consistently over time.
There were also ideas, like those of Nietzsche, that tended to undermine traditional religious beliefs.