So, scientists have discovered gravitational waves - ripples of space-time. Albert Einstein assumed their existence 100 years ago, and direct observation provided the final proof of the great scientist's masterpiece: general relativity. Scientists at Caltech and MIT have discovered a gravitational wave generated by two colliding black holes.
Einstein was not always considered a genius. When he first voiced his questionable thoughts about relativity, some scientists organized protests. Others simply vilified Einstein in the press, blaming him for both dangerous ideas and Jewish origins.
But the scientist's work turned physics upside down from its very foundations. Einstein's universe quickly and naturally plays with the concepts of position and speed - except for light, which is always sweeping through the vacuum at 300 million meters per second. Space and time are mixed into a four-dimensional molasses called space-time, which can be stretched and distorted by matter, matter, mass. And moving matter follows the curves of space-time - a hidden geometry that we perceive as gravity.
Sounds like sheer nonsense.
But over the past 100 years, experiments have shown over and over again: Einstein is right. His theory has been proven too many times to list all of these times here, but even the most striking cases are impressive.
Light is both a wave and a particle
Promotional video:
Einstein's name is most often associated with relativity, but he won the Nobel Prize for his work on light. Classical physics postulated that light is a wave, but this theory could not explain how and why metals emit electrons when illuminated - this phenomenon is called the photoelectric effect.
Einstein explained this strange behavior by suggesting that light is actually made up of discrete wave packets (photons) with energies associated with their frequency. This discovery led to the emergence of quantum physics, in which all atoms behave in a strange wave-like manner, and Einstein helped make this discovery happen.
Spacetime can bend
Einstein's first major victory in general relativity came when he explained the mysterious wobble of Mercury's orbit. In 1859, the brilliant French astronomer Urbain Le Verrier attributed this effect to a never-before-seen planet called Vulcan, they say, it attracts Mercury. But years of searching did not lead to anything, no one found any Vulcan.
To Einstein's great delight, his new theory of relativity brought Vulcan to his feet, showing that the mass of the Sun bends near spacetime, much like a bowling ball would bend an elastic but soft surface. Since Mercury is so close to the Sun, its wobbling orbit is the closest path through spacetime curved by the Sun's mass. There is not and there was no other planet: it's all about the geometry of the universe, which Newton did not suspect.
Spacetime can be a "lens"
Einstein was right again in May 1919 during a total solar eclipse. According to the theory of relativity, spacetime, curved by the mass of the sun, will bend the incoming starlight like a lens.
British astronomer Arthur Eddington took large pictures of the eclipse and found that the Sun had stretched out the Hyades star cluster, bending the light of individual stars by about one-two-thousandth of a degree, as predicted by Einstein, who doubled the curvature predicted by Newtonian physics.
Even Einstein did not expect how useful this phenomenon would be for astronomers: using the galaxies themselves as giant lenses, astronomers can look into the past, in the earliest years of the universe. And when astronomers see that the lensing is caused by some invisible masses, it allows them to map vast areas of dark matter.
Rotation of masses twists space-time
Not only does matter warp space-time, like the bowling ball, but rotating masses like the Earth easily pull space around them, like a spoon in molasses. This affects the orbits of nearby satellites - the bizarre effect of dragging inertial reference frames, the Lense-Thirring effect.
Predicted in 1918 by general relativity, the Lense-Thirring effect was confirmed in 2004 when scientists discovered that the Earth's rotation easily displaced the orbits of two satellites. In 2011, NASA's Gravity Probe B probe confirmed the find and refined the numbers.
Gravity slows down time
Einstein's equations also endow matter with the ability to speed up or slow down time - and change the color of light.
We can see this strange prediction correct even from Earth: light from distant stars takes on higher frequencies - or looks bluer - than an observer would see in deep space. And the further you move away from the gravitational well of the Earth, the lower and lower the frequency the light emitted from the Earth receives, obeying the effect of the gravitational redshift.
After all, even your smartphone cannot ignore the theory of relativity: without relativistic corrections, clocks on GPS satellites would tick 38 microseconds faster every day than on the Earth's surface, destroying the accuracy of the system after two minutes and adding 10 kilometers of errors daily.
