How does gravity bend time and space?

A massive collision occurred in space 1.3 billion years ago. Two black holes, the burned-out, collapsed remains of super-heavy stars, came so close that their own gravity forced them to a deadly waltz. The two celestial bodies, each so massive that not even light waves can escape their attraction, began to orbit each other increasingly quickly and ever closer. In the end, they raced around each other at half the speed of light, only to merge shortly afterwards in a collision unimaginable by human standards.

1.3 billion years later, on September 14, 2015 at 11:50 a.m. German time, a shock wave from this cosmic crash reached Earth. An experiment called "Advanced Ligo", which consists of two detectors in the Northwest and Southeast of the USA, recorded a brief tremor of space and time with high-precision laser beams. For less than half a second, two four-kilometer-long tunnels with the laser beams in each of the two detectors were suddenly no longer of the same length. The vibrations from space briefly caused the entire globe to vibrate, and with it the tubes of the test facility. The death dance of the two black holes had chased waves of gravity across space, which wherever they hit the fabric of space and time.

This effect, first suspected by Albert Einstein 100 years ago, has now been measured for the first time. It is a sensation of the century for physicists. It is the last experimental piece of the mosaic that confirms Einstein's work of formulas. It is also direct evidence that there are black holes, because the holes cannot be seen with optical devices. And it opens up a whole new window for cosmologists to study space. In addition to the classic methods of looking into space by catching light, radio waves or X-rays, the cosmos can now be eavesdropped for gravitational vibrations.

The signal was so clear that the researchers first thought of a joke or sabotage

The discovery even came as a surprise to the approximately 1,000 physicists involved in "Ligo". Shortly before, they had improved their test facility for more than 200 million euros. The demands on the precision of such an experiment are enormous: the collision of the black holes that has now been measured threw enormous energy into space, but the resulting trembling of space-time has stretched and compressed the entire globe by the diameter of an atomic nucleus. Measuring such tiny changes in length is only possible with all sorts of highly technical tricks. The detectors are so sensitive that they can even register ocean surf on the coast of the American continent. When the signal arrived from space in autumn, the test facility was still in test operation. Because it was night in the USA, colleagues from the Max Planck Institute for Gravitational Physics in Hanover first discovered the trembling of the laser beams on a control screen.

"The signal was strong and looked so perfect that we wondered if it was real," recalls Bruce Allen, one of the institute's directors. Did a colleague feed in an artificial test signal? Was it a joke at all? Or sabotage? All of these possibilities have apparently been ruled out in the past few months. In addition, the signal was measured at a distance of 0.007 seconds, which matched the runtime of a gravitational wave, at both locations in the USA.

On Thursday, the physicists therefore officially announced the discovery of gravitational waves and published it as a specialist publication. The measurement is so precise that theory experts like Alessandra Buonanno, director at the headquarters of the Albert Einstein Institute near Berlin, were even able to calculate the masses of the collided black holes: one was 29 times as heavy as the sun, that one another 36 times.

Since Einstein, space and time have been understood as flexible quantities

In their dance of death, which lasted less than half a second, the two dark colossi briefly radiated more power than all the stars in the Milky Way combined. About three times the solar mass was converted furioso into energy in this finale according to Einstein's equation E = mc². But none of this made itself felt as light, radio waves, or X-rays. The energy only shook the cosmic structure of space and time, which has been malleable and malleable since Einstein. While in Isaac Newton's time the universe was still a rigid framework in which planets, stars and galaxies are hung like in a puppet theater, Albert Einstein swapped subject and object, so to speak: space and time are flexible quantities and are spanned by massive celestial bodies in the first place. Each star bends the space-time of its surroundings like a lead ball lying in a rubber mat. And if two such lead balls rotate around each other, they cause the rubber mat to tremble. Physicists call this gravitational waves.

The earth also sends out gravitational waves when it circles the sun. However, the emitted power is only 200 watts - far too little to ever be measured experimentally. If, on the other hand, two stars rotate close together, the energy loss can be measured. In 1993 there was even the Nobel Prize for this. The resulting vibrations of space-time, the gravitational waves, were only discovered on September 14, 2015. The proof of their existence is now as significant as the proof in 1919 that massive celestial bodies bend light rays - precisely because they dent space-time. The latter brought Einstein into the focus of public attention at the time and made him an icon of physics.

For astronomers, it is now as if they no longer only have eyes to explore space, but also ears or a sense of touch. From now on, mankind is able to measure vibrations in space-time - the tremors of the universe, with everything that goes with it, stars, galaxies, black holes as well as humans with all the atoms in their bodies. This is undoubtedly worth a Nobel Prize.