What did Einstein think of consciousness?

general theory of relativity "The most valuable find of my life"

Einstein was one of the founders of quantum theory and created the most famous formula in the world with the special theory of relativity - E = mc². His greatest stroke of genius, however, was another: 100 years ago he presented the general theory of relativity in Berlin. A brief set of mathematical equations that is still considered the perfect description of the most familiar of all natural forces - gravity. But the road to the revolutionary set of rules was rocky: Einstein struggled for eight years to find the right concepts, studied highly abstract mathematics and in the end had to fear that others would overtake him.

Ultimately, however, the theory was to make him a legend: When British astronomers confirmed the formulas for a solar eclipse in 1919, Einstein rose to become a pop star in the world's public consciousness - a nimbus that still exists today. The program focus on space and time begins with the story of discovery. Until November, research is currently honoring the general theory of relativity with short articles, reports and features.

"At the end of the 19th century it was thought that physics as a building was essentially fixed and that there was still a little renovation to be done here and there, but that the foundations would remain."

Jürgen Renn, Max Planck Institute for the History of Science, Berlin.

"That turned out to be wrong."

The turn of the century. Unexpected phenomena shake the foundations of physics. Wilhelm Conrad Röntgen discovers an invisible, penetrating radiation. Marie and Pierre Curie describe the radioactivity. Max Planck lays the foundations for quantum theory. And then, in 1905, a young employee of the Swiss Patent Office amazes with an epoch-making piece of work.

"On the electrodynamics of moving bodies; by A. Einstein."

Stroke of genius with flaws

The special theory of relativity. According to Einstein's point of departure, light rushes through space at a constant speed. At almost 300,000 kilometers per second, and nothing in the world can be faster. A simple assumption. Einstein draws from it - solely through logical conclusion - a revolutionary insight: space and time are not separate, but united to form a space-time. They are not absolute, but depend on the viewer - the space sometimes appears compressed, time stretched. And: energy and mass are of the same nature - E = mc2, the most famous formula in the world. In the professional world, the special theory of relativity will soon be considered a milestone. But it quickly becomes clear: the stroke of genius has flaws.

"The special theory of relativity only works for movements with constant speed."

Dennis Lehmkuhl, Einstein Papers Project, California Institute of Technology, USA.

"And Einstein thought that this is not yet a consistent theory of relativity. Really all movement should be relative. A really generalized theory of relativity that makes movement something completely relative."

The special theory of relativity only relates to uniform movements, for example when particles race through space at a constant speed. But far more processes are not uniform. When a planet circles around a star, it experiences a circular acceleration - similar to the fair visitor in the chain carousel. For such processes, the theory of relativity has to be generalized to accelerated movements. And there is another shortcoming.

"The problem was that special relativity had established that there is no interaction that propagates faster than the speed of light."

Tilmann Sauer, science historian, University of Bern.

"While Newton's theory of gravity said that the force of gravity is a force acting at a distance that propagates infinitely fast. These two properties did not match."

To describe gravity, Isaac Newton's law of gravity was the measure of all things. But it contradicts the special theory of relativity, and fundamentally. Albert Einstein set to work to resolve the contradiction. It should last almost ten years. A path full of obstacles and dead ends.

"To belong to those people who are allowed and able to devote their best energies to contemplating and researching objective things is a special grace."

"Einstein explained the effect of gravity by the fact that the geometry of space and time itself takes part in the action."

"The revolutionary thing was: Einstein replaced the idea that gravity is a force with the idea that gravity is a result of the curvature of space and time."

"I was sitting in an armchair in the Bern patent office when the thought suddenly occurred to me: If a person is in free fall, he will not be able to feel his own weight. A light dawned on me. This simple thought made a lasting impression on me. The enthusiasm that I felt drove me to the theory of gravity. "

Application of the theory to the force of nature

1907. Einstein picks up the trail.

Einstein is 28 years old, married and has a young son. He is still working in the patent office in Bern, as an expert second class. He thinks about how he can apply his special theory of relativity to a fundamental force of nature, gravity. In doing so, he encounters a problem: How does the observation fit into the picture that all bodies fall at the same speed, at least in a vacuum?

"Then Einstein faced the alternative: Either I insert gravity into the framework of the special theory of relativity in such a way that I have to give up this principle that all bodies fall at the same speed. Or I rephrase the whole thing in such a way that I can from the outset make sure all bodies fall at the same rate. And he chose the latter because he was a person who took such fundamental principles seriously and didn't just think of them as any factor that could be easily changed. "

"As is very often the case with Einstein, the starting point was a thought experiment - the so-called elevator thought experiment. Imagine you're in an elevator. You can't look out the window, you can't see anything outside . But you feel: Okay, me, I'm in an elevator here. "

If the lift is on the ground, the passenger feels the gravitational pull and is pressed down with his or her body weight. But what if the elevator is in space, with absolute weightlessness? What if a drive accelerates it with a force that corresponds exactly to the body weight of the occupant?

"Einstein's idea was that such an observer cannot decide whether one is the case or the other. Is the observer under the influence of a gravitational field? Or is he under the influence of an acceleration?"

In both cases, Einstein concludes, the elevator driver feels nothing more than a force in the direction of the floor.

"That gave him the idea that acceleration forces and gravity are of the same nature, are of the same nature."

This assumption is called the equivalence principle. It is just as simple and fundamental as the basic assumption that led Einstein to the special theory of relativity - the speed of light is constant everywhere. Will the equivalence principle also lead to a new, revolutionary insight? In any case, one thing soon became clear to Einstein: Some rather superficial calculations indicate the potential that lies dormant behind the new approach.

"He was already able to make predictions. For example, he imagined: Now I am sending a light beam through my accelerated box. Then you can see that the light beam does not come out at the opposite end of the box, but slightly downwards because the box is yes has moved in the meantime. The light beam seems to be curved. From this Einstein concluded: So light beams have to bend in the gravitational field. "

Massive celestial bodies should deflect light rays that fly past them. And the light emitted by the sun should lose energy in its enormous gravitational field and change its color. Knowledge that Einstein derives solely by applying his special theory of relativity to the principle of equivalence. But the most important thing is still missing, the core of his theory - the field equations.

The Einstein Tower on Telegrafenberg in Potsdam (Frank Grotelüschen) The Einstein Tower

The Telegrafenberg in Potsdam. An area full of historical laboratory buildings and observatories. Carsten Denker from the Leibniz Institute for Astrophysics stands in front of the most striking building: a tower, whitewashed, 15 meters high. The Einstein Tower.

"There are few buildings in the world that have such a character as the Einstein Tower. If you take a closer look at it, you can see many curved shapes. You can see how the staircases are curved, how the roofs are curved."

The tower was built with one purpose - it was supposed to help prove general relativity. Einstein himself had helped design it, together with the astronomer Erwin Freundlich, employed at the Berlin observatory.

"His job at the Berlin observatory was rather boring. That prompted him to write letters to Einstein. In these letters he tried to discuss with Einstein: How can the general theory of relativity be proven experimentally?"

As early as 1911, when Einstein published the first ideas for his theory, Freundlich was fascinated. Because even the first version made a remarkable prediction: The light of the sun should be influenced by its enormous mass.

"The basic idea goes back to the world-famous formula E = mc2."

According to Einstein, mass can be assigned to light. So that light that leaves the sun would have to fight against its gravitational field - and should lose energy. This can only work with light by changing its color. Therefore, Einstein and Freundlich speculated, the light would have to become a little redder in the gravitational field of the sun. If this redshift could be measured, the new theory would be proven. But for that you needed a new telescope - the Einstein Tower.

"At the time, Einstein had very good contacts in the German economy, was able to call for an Einstein donation there relatively quickly and collect around 500,000 Reichsmarks."

"The elementary concepts are all spatiotemporal. Such concepts only occur in the laws of nature; in this sense all scientific thinking is geometric. It was always assumed that space and time are flat. But Einstein said: No, spacetime is curved, by the presence of a mass. And the larger this mass, the more curved the space and the stronger the gravity. "

"Grossmann, you have to help me, otherwise I'll go crazy."

Competitive pressure from other scientists

1911. Einstein gets to work.

"Between 1907 and 1911 he hardly worked on it at all, but rather only struggled with quantum theory. And when it somehow didn't work out as he wanted, he turned back to the problem."

Einstein first dedicates himself to his career. In 1909 he quit the Bern patent office, went to Zurich as a professor, then to Prague, then back to Zurich. During this time, he more or less lets work on the general theory of relativity rest.

"But there were other people like the physicist Max Abraham who took up these ideas from 1907. Einstein then came into competition with these others and hurried to work out his insights. That must have played a role."

"And the first step he took: After a while, he realized that he was saying: The best way to describe these unified forces is to imagine that this four-dimensional space-time - three space dimensions, one time dimension - is curved in this way he found the first reference to the mathematical formulation of the theory, namely the theory of curved surfaces. "

The problem: As a physicist, Einstein doesn't know how to calculate with curved surfaces, whether there is mathematics for it.

"And so it suited him, it was really lucky that in 1911 he got a call to the University of Zurich, where his old student friend Marcel Grossmann was professor of mathematics."

"That was always important to him. When he skipped lectures at ETH Zurich, he had already lent him his notebooks so that he could copy them."

"Einstein told Grossmann about his project, but wasn't sure how he could implement it. And Grossmann told him about a mathematical tool kit that is tailor-made for this project."

"Einstein first had to teach himself everything. He continued to develop this theory, although nobody but himself really believed in it, you have to say."

Einstein is looking for the field equations - for that set of mathematical formulas that brings the theory to the point in a nutshell. But: the possibilities are almost unlimited. How can you recognize the right formulas in this variety?

"It was a tortuous path. In particular, the collaboration between Einstein and Grossmann got off to a very promising start in 1912 and 1913, when they had already identified the correct mathematics. But at the time they had not yet succeeded in finding the final equations as such to identify even though they were very close. "

"There is an interesting Einstein notebook from this phase. And we have indeed found that Einstein wrote equations in this notebook that are equivalent to the field equations that he published three years later and that have become his greatest success."

The crucial field equations. Einstein noted it as early as 1912, but simply did not recognize it as a solution. Maybe a miscalculation. But maybe Einstein is just not ready yet.

"He had certain expectations of what a theory of gravity should look like. But those expectations were still rooted in the ideas of the previous century. And he first had to free himself from certain prejudices, which did not allow him to see these equations until three years later actually represented the solution to the problem he was trying to solve. "

Professor Carsten Denker, Leibniz Institute for Astrophysics, Potsdam (Frank Grotelüschen) In the Einstein Tower, Carsten Denker trudges up the steps to the top.

"We are now standing directly from the two mirrors. There is a wooden dome above us. It looks exactly as you imagine a dome for a telescope. You have to open it with muscle power so that you can look outside."

Thinker grabs a rope and pulls it with some force.

"Now I've just opened the gap in the dome. The dome is now in the wrong direction. Now we need a little more electricity, just a second."

At an old-fashioned desk, thinker flips the switch.

"Now the dome is moving east. And now we have to turn the dome until we actually find the sun."

An electric motor turns the dome as if in slow motion. Then it stops.

"Now we have arrived there. The sun is now west, would then fall on the first mirror. From the first mirror it falls on the second mirror. Then it goes straight down."

Carsten Denker goes down the stairs and follows the path of the sunlight down into the cellar. It's dark there and the temperature is stable. Ideal conditions for Einstein and Freundlich to be able to measure the light precisely.

"Now we are in the heart of the Einstein Tower. The optical laboratory."

The sunlight penetrates through a hole in the basement ceiling and hits a crack in a wall. Behind the gap is the measuring instrument, the spectrograph.

Like a prism, it splits the sunlight into its rainbow colors.

"It looks like you have a film of oil on a puddle and you can see different color fringes."

A structure that was supposed to prove perhaps Einstein's most important work, the general theory of relativity.

"Although I am a typical single horse in everyday life. But the awareness of belonging to the invisible community of those who strive for truth, beauty and justice has prevented the feeling of loneliness."

"Its formulas are long and complicated. But it is elegant because it starts with a particularly small number of basic assumptions, from which it then deduces all the consequences cleanly."

"I am now exclusively concerned with the gravitational problem. One thing is certain, that I have not bothered nearly as much in my life. Let us smoke a chimney, work like a horse, eat without thought and choice, unfortunately rarely go for a walk, sleep irregularly. "

Einstein is getting closer to his goal

1915. Einstein wrestles - and wins.

"He really seems to have been obsessively working on it these months."

Einstein, meanwhile at the Kaiser Wilhelm Institute for Physics in Berlin, is getting closer to his goal. He continues to narrow the range of equations in question. But others are also involved, especially David Hilbert in Göttingen, one of the most brilliant mathematicians of his time.

"In the summer of 1915, Hilbert invited Einstein to Göttingen. And Einstein gave a series of six lectures."

Einstein does not fail to see the interest with which Hilbert follows the lectures and how knowledgeable and detailed he is.

"Einstein had no illusions that Hilbert was far superior to him in mathematics. And that Hilbert might now pass him on the home straight and publish the final field equations before Einstein."

"They faced a certain amount of competition in those hectic weeks."

"It played a big part in his obsessive work over the past few months."

To this day, it is not entirely clear who was the first to have the equations - Einstein or Hilbert. In any case, the mathematician will prove to be a fair colleague later on.

"As a mathematician, Hilbert interpreted Einstein's theory and developed it further. At no point did he deny that he was referring to Einstein's work."

Einstein's breakthrough

In November 1915, after months of feverish work, the breakthrough. Einstein has penetrated the complex mathematics of curved surfaces and can write down the field equations.

"Then there were four works that he presented to the academy one week after the other in Berlin. And then gradually came closer to the correct solution. He finally had them on November 25, 1915. That was the official hour of birth the theory. "

The triumph is perfect: Einstein's starting point was a simple and plausible assumption - the principle of equivalence. He consistently and unwaveringly combined this principle with his special theory of relativity - and in doing so, he came across a most astonishing, unexpected insight: Gravity arises when space and time are bent by the presence of mass. The new theory can solve one problem immediately - certain deviations in the orbit of the planet Mercury. Newton's classical law cannot explain these fluctuations. Only Einstein is able to do this. The professional world is reacting cautiously.

"This general theory of relativity seemed a strange story to many. Because it solved a problem that others didn't even see as a problem."

"There were some people who saw very clearly: this is a great achievement now. But that was not the majority of physicists and in any case not the general public either."

"Even famous people like Nobel Laureate Max von Laue, a close friend of Einstein, thought: Oh, this is so complicated, it can't be right."

Einstein is disappointed. He will have to wait years for his work to be widely recognized.

"A law of nature is invariably required to be valid. It is rejected when one is convinced that one of its conclusions is incompatible with a single fact of experience. The most fascinating thing about Einstein's theory is how thoroughly it has been tested by experiment. To date we have not found the slightest indication that something might be wrong with her.

"It would be very much to be hoped that astronomers would take up the question raised here, even if the considerations should appear insufficiently well-founded or even seem adventurous."

Superstar Einstein

1919. Eddington provides the proof.

"That was a very exciting story. At that time, 1919, a year after the First World War: an English scientist sided with a German scientist in order to oust Newton from the throne. And then with the help of a safari to Africa to watch an eclipse. It was just a very good story. "

There is a problem with Einstein's new theory: at that time it seemed irrelevant to everyday life on earth. Because on earth the masses are so small that they bend space-time only imperceptibly. Here gravity seems to be perfectly described with Newton's law - you don't need Einstein. The sun is different: it is so massive that it should measurably bend space-time. So Einstein dares to make a spectacular prognosis: In the event of a solar eclipse, it should be possible to measure without a doubt how the sun deflects the light from distant stars. The opportunity arose in May 1919. British astronomer Arthur Eddington travels to West Africa to observe a total solar eclipse. His recordings refute the doubts. Einstein's general theory of relativity is considered confirmed.

"That made Einstein a superstar."

Newspapers all over the world are reporting on the sensation. Albert Einstein becomes a legend - and not just because of his brilliant achievements in science.

"Einstein did not behave like many of his colleagues during the war. He did not go along with this hurray patriotism. He campaigned for a European understanding. That was a symbol of hope for the people. And Einstein stood for it."

"One would have to try out the chairs here and then claim to have sat on a chair that Einstein was also sitting on."

In 1924 the telescope in the Einstein Tower was finished, says Carsten Denker. Astronomer Erwin Freundlich immediately got to work, looking for the telltale redshift in the spectral lines of sunlight - in the hope of providing further evidence for Einstein's theory. But the lines showed no shift.

"That's why the result of what you measured here was: you didn't measure anything."

Einstein and Freundlich were disappointed, they couldn't explain the result at all. Was there a measurement error behind this, or was there something wrong with the theory? But the reason, what came out later, was elsewhere. There is turbulence on the sun and hot gas bubbles rise continuously. And they shift the spectral lines into the blue - of all things in such a way that they equalize the redshift you are looking for. So Einstein and Freundlich had no chance of measuring the effect. That did not happen until 1959 in the USA. Nevertheless: The construction of the Einstein Tower was not in vain, says Carsten Denker.

A solar spectrum in the Einstein Tower in Potsdam (Frank Grotelüschen) "This telescope was very good - one of the best telescopes in the world for doing solar research. You looked at sunspots and what else happened on the sun."

And even today, the researchers still use the unusual tower from time to time - as a test stand for modern solar telescopes.

"It is enough for me to sense these secrets with astonishment and to try to humbly grasp a dull image of the sublime structure of beings."

"It's the most valuable find I've made in my life."

"Nowadays Einstein's theory of relativity explains far more than anything that was previously believed to be explained with gravity - extreme states of matter."

In 1919 the general theory of relativity is considered proven - the final breakthrough for Einstein. Nevertheless, it led to an exotic existence for decades. Other topics seem more important, quantum mechanics or nuclear physics. That only changes from the 1950s. Now astronomers with their ever better telescopes are suddenly observing phenomena that cannot be explained without Einstein. Quasars, neutron stars, black holes, the big bang: cosmic acts of violence in which unimaginable masses bend space-time so strongly that Newton fails miserably.

"One speaks of the renaissance of the 50s and 60s, and then the golden 70s of the relativity theory. Where the relativity theory with terms like Big Bang and Black Hole was on everyone's lips."

Impact on today

Today, the theory even has an impact on our everyday lives: Without Einstein, atomic clocks would be significantly more inaccurate, and so would the navigation systems in cell phones and cars. And that's not the only reason why it is considered a cornerstone of physics - and Einstein's greatest masterpiece.

"What really fascinates me is that this theory arose from such less intuitive clues."

"It is certainly one of Einstein's achievements that influenced physics the most."

"The general theory of relativity goes back entirely to Einstein's ideas. It was so original that it is not at all clear, if Einstein had not done this, whether it would not have taken 100 years longer for someone else to come up with the idea . "