Why does gravity distort time

P H Y S I K : Does gravity have a future? Per gravity:


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It is the basic physical force that is most familiar to us. Gravity ensures that we stand with both feet firmly on the ground, that a football does not disappear in the stadium sky and that the earth reliably moves its orbit around the sun. There is no life without mutual attraction. Man was not made for the detached weightlessness of the universe. Astronauts become space sick there, and bones and muscles recede. No sooner does the dream of weightlessness come true than a person first realizes what he has in his familiar weight.

Without gravity, even modern physics wouldn't exist. The fall of an apple triggered the idea in Isaac Newton's head that led to the establishment of the law of gravitation in 1687 and thus to the birth of mechanics. Since then, gravity has held scholars under its spell like no other of the four basic physical forces. Although the mass attraction was discovered much earlier than the electromagnetic interaction, the "weak" and the "strong" nuclear force, science knows least about it to this day. The lack of understanding of gravity is not only the decisive obstacle on the way to the "world formula", but also the deeper reason why we can at best speculate about the fate of the universe. At the moment, not even the exact value of the gravitational constant G is known - the measure of the force with which two masses of one kilogram each attract each other at a distance of one meter. Although every physics book gives a value for this, it is by no means clear whether this oldest known natural constant really deserves its name. But more on that later.

Gravity's greatest mystery: why is it so weak? The force between the aforementioned lumps of uniform matter corresponds to only about one percent of the weight of an E. coli bacterium. This means that gravity is 30 to 40 powers of ten weaker than electrical or nuclear forces and is almost insignificant for elementary particles. The fact that we feel anything of it at all is thanks to a special property of matter: There are positive and negative electrical charges, but only positive masses. Positively and negatively charged particles neutralize each other. In contrast, masses - and the associated effects of gravity - can only add up.



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Albert Einstein was also haunted by the mysterious force. While in Newton's conception of gravity every mass directly influenced every other mass in space, Einstein's gravity has a rather indirect effect in comparison: Every mass warps and warps the four-dimensional space-time that surrounds it - black holes are probably the most exotic example of this strange circumstance. Conversely, curved spacetime dictates how bodies should move.

Einstein's equations, drawn up at the beginning of the 20th century, led to other strange predictions, which even to the master himself sometimes struck absurd. But almost all of them turned out to be correct. "We don't understand why the world can be described with a handful of formulas that fit on a piece of paper," says the astonishment of the physicist Bernard Schutz from the Max Planck Institute for Gravitational Physics in Golm near Potsdam. With a little luck, Einstein's last still open prediction could be verified later this year: the existence of gravitational waves.

A powerful cosmic event like a supernova generates not only electromagnetic waves, but also wave-like distortions of space itself, which run out into space at the speed of light. Space-time itself vibrates and trembles. The existence of these waves has already been proven indirectly. The later Nobel Prize winners Russell Hulse and Joseph Taylor discovered a system of two compact stars circling faster and faster. The measurements exactly confirmed the theory that energy is radiated in the form of gravitational waves.

But now the waves should be detected directly. In Ruthe near Hanover there is such a gravitational wave detector with the name Geo 600. There, a laser beam whizzes back and forth in two corrugated iron vacuum tunnels, each about one meter in diameter, arranged at right angles to one another. The phases of the rays are adjusted so that they cancel each other out when they meet at the end of their travel path. However, if a gravitational wave hit the earth, the space would begin to distort - rhythmically one tunnel would be longer, sometimes the other. The result: the laser beams no longer extinguish each other exactly, there would be light pulses - and they could be measured.