The theory of relativity changed everything, but it took a corresponding amount of time.
The detection of gravitational waves by the Laser Interferometric Gravitational Wave Laboratory LIGO occurred exactly one hundred years after Einstein formulated his general theory of relativity in an article where the possibility of the existence of gravitational waves was mathematically described. Or at least that is the story that was presented to the public (including yours truly). And in some respects it even corresponds to reality.
However, the reality of how relativity progressed to the point where people recognized that gravitational waves did seem to exist and that they could be detected turned out to be significantly more complex than the narrative described above. In this week's Nature Astronomy, a group of science historians provide all the details of how we traveled from the dawn of relativity to the LIGO Laser Interferometric Gravitational Wave Laboratory. And in the process, historians show that ideas about scientific revolutions leading to unexpected and radical shifts can sometimes turn out to be untenable.
Has your paradigm changed?
The popular concept of scientific revolution (insofar as it exists) was expounded by Thomas Kuhn. Kuhn described the process by which data gradually moves an existing theory towards crisis, allowing almost everyone to see that it no longer works. After a period of crisis, a revolution occurs and a new theory appears. The theory's ability to solve all the problems that precipitated the onset of the crisis quickly gains support, and a new period of science begins, based on theory or "based on a paradigm," as Kuhn puts it.
On a certain level, this all fits perfectly with the history of relativity. Einstein's proposals did indeed create a new paradigm of curved spacetime, and they solved the many problems of Newton's gravity, and also quickly received experimental confirmation, and were accepted. But less than a year later, Einstein published a paper that used a new paradigm for the generation of gravitational waves. The article turned out to be wrong, but after a few years he published a revised version. This revolution, which marked the beginning of the period of discovery, was completed a century later.
However, the historians mentioned - Alexander Blum, Roberto Lalli and Jürgen Renn - wanted to thoroughly tackle this paradigm shift parade. And they do this by focusing on the implications of Einstein's formulation of general relativity.
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(It should be noted that this approach does not support Kuhn's model of revolution either. People worked well within the framework of Newton's concept even after its problems became obvious, and there was also no obvious crisis period even after Einstein formulated his theory of general relativity In some respects, general relativity only solved the problem that Einstein himself created when he proposed special relativity).
Make waves
For starters, it should be said that gravitational waves did not arise directly from the fact that Einstein was working on them. Apparently, Einstein didn't really think about their existence very seriously until Karl Schwarzschild and his radius fame pushed him to do so. There was an error in his first article on the topic, and the corrected version only worked if the waves propagated inside the cylinder. Although this article provides the basis for the claims that it was Einstein who predicted the existence of gravitational waves, this was undoubtedly an approximate solution in a simplified environment.
And it was here that Einstein left this problem behind. His focus shifts, and he tries to combine his version of gravity with electromagnetism. Not many people were ready to deal with this issue at the time when quantum mechanics was gaining ground, and the First World War disrupted the work of the scientific community and turned the attention of its members to applied physics. According to these historians of science, most of the work in the field of the theory of relativity that was carried out during this period focused on translating existing and well-described physical systems from the language of Newtonian mechanics into the language of the theory of relativity. Much less attention has been paid to attempts to determine what unique possibilities of understanding the universe are provided by the theory of relativity.
The lack of a deep memory of what relativity means was compounded by problems such as Einstein's mathematical errors. When such absurd concepts as singularity appeared in mathematics, it was not clear what they were trying to tell us in this way. Do such abstractions have any basis in reality? Could another mathematical approach offer a smarter solution? Or is the theory of relativity limited in what it can successfully explain? In the absence of a deep understanding of this theory, it will probably be difficult to say which of the following options is most likely.
Since gravitational waves can emerge from the correct equation, there was little interest in determining whether their existence was necessary, and even less interest was in the question of how we can capture them.
Breakthrough
But how did this area manage to break out of stagnation? In the 1950s, physics received a lot of support from the state because of its successes during the war, and as a result, the research community grew. In addition, it was becoming clear that gravitational effects would be needed to understand our expanding corpus of data describing the universe and its evolution.
The relativity community has received support from the growing internationalization of science, and annual conferences have been organized on the full range of topics in this area. This broader community has come to a consensus that the remaining physical questions about the theory of relativity must be addressed if each individual group of researchers wants to have confidence in the work they are doing. Solving the problems associated with the theory of relativity was also considered a prerequisite for integrating it with quantum mechanics, and many were interested in working on this problem.
The existence of gravitational waves was one of these problems, and therefore they began to attract attention. The key breakthrough came at a conference where researchers (including Richard Feynman) were able to understand how the energy contained in gravitational waves could be exchanged with better understood forms of energy in the rest of the universe. Another researcher was able to make a mathematical description of electromagnetic waves and then modify it to describe gravitational waves. The resulting mathematical structures became the basis for understanding that gravitational waves are oscillations in space-time, and this point of view persists to the present time.
Insurrection
All this, as well as progress in other areas of the theory of relativity, has created a solid theoretical foundation. Bloom, Lally, and Rennes believe that at the time general relativity was first presented, humans were thinking in terms of the consequences of relativity for other theories they used to understand the universe. According to historians, by the early 1960s, the theory of relativity should have been given credit for being directly related to the behavior of the universe, and no other theory was needed anymore. This created the basis for the belief that gravitational waves, being a natural consequence of this theory, must have some kind of physical manifestation.
This understanding was also necessary to create a model that would allow us to talk about what gravitational waves should look like, based on the events that generated them. And we were able to separate real events from noise as soon as we had a detector such as LIGO with sufficient sensitivity to detect them.
This 40-year process doesn't fit well with the revolutions Kuhn is talking about. There was no crisis, and there was no period of frantic research at the moment when people tried to develop a new theory that could resolve the obvious contradictions characteristic of its untenable predecessor. However, these historians believe that there is one thing that Kuhn was right about: those people who are deeply immersed in the relativistic world have a fundamentally opposite view of the universe, and it will be difficult for them to share their views with those who live in the Newtonian world.
Kuhn saw this problem as essentially a language problem; old terms acquire new meanings in a new paradigm. However, the above historians seem to believe that such changes in perspective are necessary for any kind of scientific progress. Until people can enter the reality of a new theory and appreciate all its implications, it will be difficult for them to sufficiently grasp its meaning and make predictions - and changes in language are just a by-product.
John Timmer
