MPI for Gravitational Physics/W.Benger-ZIB
This computer simulation shows the production of gravitational waves during a black hole collision.
Exactly 100 years ago on Nov. 25, 2015, physicist Albert Einstein, then 36, presented a fourth and final lecture to the Prussian Academy of Sciences about his new general theory of relativity. The idea not only redefined the concept of gravity, but also ended up reshaping humanity’s perspective on reality. Here’s a look at the theory in thought and action.ANALYSIS: Event Horizon Telescope Will Probe Spacetime's Mysteries
Max Planck Institute for Gravitational Physics
Einstein was famous for his thought experiments, which often played out for years in his imagination. From the gedankenexperiment, as it is known in German, Einstein grasped fundamental concepts about the physical world that could be verified by observation and experiments. One of his most famous ones began in 1907 when Einstein pondered if a person inside a windowless elevator could tell if he was in a gravitational free-fall, or if the elevator was being hauled up by a constant acceleration. Einstein decided the laws of physics must be the same in both cases. The mathematical equation he derived to explain this so-called principle of equivalence, which equated the effects of gravitation with acceleration in zero-gravity, became the basis for general relativity.NEWS: Einstein's Theory Passes Extreme Gravity Test
A total solar eclipse on May 29, 1919, gave astronomers an opportunity to verify Einstein’s general theory of relativity by proving that the sun’s gravitational field was bending the light of background stars. The effect was only observable during time when the sun’s light was dim enough for stars to become visible. British astronomer Arthur Eddington led an expedition to the island of Principe, off the West Coast of Africa, to photograph the eclipse, which lasted nearly seven minutes. The images of stars in the region around the sun proved that Einstein’s interpretation of gravity trumped the 200-year old Newtonian model, which interpreted gravity as a force between two bodies. Einstein saw gravity as warps and curves in space and time.Time Probe: Crowdsourcing Einstein's Relativity
In 1917, Einstein amended his general relativity theory to introduce what he called the “cosmological constant,” a mathematical way to counter the force of gravity on a cosmological scale and stave off the collapse of the universe, which the general relativity theory posited. At the time, astronomers believed that the Milky Way was surrounded by an infinite and static void. In 1923, Edwin Hubble and other astronomers find the first stars beyond the galaxy and by 1929 Hubble provides evidence that space is expanding. Einstein realized the cosmological constant was a blunder. Or perhaps not. In 1998, scientists made the startling discovery that the expansion of the universe is speeding up, driven by an anti-gravity force called dark energy, which in many ways acts like Einstein’s cosmological constant. Pictured here is the Hubble Space Telescope’s extreme deep field view, which contains about 5,500 galaxies. The telescope is named after Edwin Hubble.ANALYSIS: Hawking Tries to Find Black Hole's Emergency Exit
One of the first implications of the general relativity theory was the realization that if an object is compressed enough, the dimple it generates in the fabric of space and time will be too strong for even photons of light to escape. Thus, the idea of black holes was born. Though they can’t be directly observed, astronomers have found black holes of all sizes by measuring how they affect nearby stars and gas. Pictured here is an artist’s rendering of a black hole named Cygnus X-1, siphoning matter from a nearby star.ANALYSIS: Is the Wormhole in 'Interstellar' Possible?
NASA/Swinburne Astronomy Productions
Like ripples in a pond, scientists believe that gravity transmits in waves, deforming space and time across the universe. It is similar to the movement of electromagnetic radiation, which propagates in waves, except that gravitational waves are moving the fabric of space and time itself. So far, attempts to find gravitational waves, such as those caused by two black holes colliding for example, have been unsuccessful. Next week, the European Space Agency plans to launch a prototype space-based observatory called the evolved Laser Interferometer Space Antenna (eLISA) to test a technology to find gravitational waves. Pictured above is an artist's rendering of two merging galaxies rippling space and time.NEWS: Advanced LIGO Resumes Quest for Gravitational Waves
A century after being proposed by physicist Albert Einstein, scientists have made the first detection of gravitational waves -- massive celestial objects on the move causing spacetime itself to ripple -- a historic discovery that opens up an entirely new way of studying the cosmos.
The detection was made by the twin LIGO interferometers on Sept. 14, 2015, located in Livingston, La., and Hanford, Wash., just two days after the system was significantly upgraded to boost its sensitivity.
Like radio waves, visible light, X-rays and other forms of electromagnetic radiation, Einstein believed that gravity also travels in waves. But even the most energetic events in the universe, such as two black holes crashing together, would cause only the slightest rippling through space and across time.
After decades of failed attempts, scientists fished out the first confirmed measurement of gravitational waves passing through Earth, a detection that required measuring 2.5-mile long L-shaped laser beams to a precision 10,000 times smaller than a proton.
Since everything from traffic to earthquakes will distort the beams, the Laser Interferometer Gravitational-Wave Observatory, or LIGO, consists of two detectors separated by 1,865 miles. Because gravitational waves are believed to travel at light speed, a detection from a cosmic source picked up at one LIGO site should be followed up by an identical detection in the other 10 milliseconds later.
That’s exactly what scientists saw when they fished out waves set off by a pair of black holes 1.3 billion light-years from Earth spiraling toward each other and then colliding to form an even larger black hole, researchers said at a webcast press conference Thursday.
“My reaction was ‘Wow!’ I couldn’t believe it,” said LIGO executive director David Reitze.
In addition to proving that gravitational waves exist, the discovery confirms that black holes exist in binary pairs.
“This is the first time that this kind of a system has ever been seen,” Reitze said.
Decades of work with supercomputers to generate models of what the gravitational waves would look like set the stage for the detection.
“Our theoretical predictions lie right on top of the experimentalists' measurements -- an exciting confirmation of general relativity,” said Cornell University astrophysicist Saul Teukolsky.
The black holes detected by LIGO were roughly about 29 and 36 times the mass of the sun. Their merger created a new black hole about 62 times the mass of the sun. The missing three solar masses is what went into generating the gravitational waves detected 1.3 billion years later on Earth.
The European Space Agency in December launched a pathfinder satellite to test a technique for fishing out longer wavelength gravity ripples in space.
“The colliding black holes created a violent storm in the fabric of spacetime,” said physicist Kip Thorne, with the California Institute of Technology.
The storm lasted just 20 milliseconds, but during that span it pumped out more power than 50 times all the stars in the universe, Thorne added.
Just as light radiates in waves of different lengths, ripples produced by gravity stretch space and time differently, similar to how a bowling ball rolling across a trampoline will warp the surface more than a baseball.
“You get electromagnetic radiation – basically light – when you move some sort of charged particles. It’s the same idea with a radio tower … charges go up and down the antenna. If you’re moving masses, instead of moving charges, you get gravitational waves,” NASA astrophysicist Ira Thorpe, with the Goddard Space Flight Center in Greenbelt, Maryland, told Discovery News.
The longest gravitational waves were produced in the Big Bang explosion 13.8 billion years ago. Colliding black holes are the most powerful cosmic events since the Big Bang.
Thursday’s discovery, which is detailed in a paper in Physical Review Letters, opens the door to an entirely new branch of astronomy, a way to listen to the universe in addition to seeing it.
“The frequency of these waveforms are in the human hearing range. We can hear gravitational waves, we can hear the universe. That’s one of the beautiful things about this. We are not only going to be seeing the universe, we’re going to be listening,” said LIGO physicist Gabriela Gonzalez, with Louisiana State University.
With two LIGO detectors picking up the distinctive “thump” of the black holes’ merger, scientists were able to calculate an approximate direction of the event. The collision occurred in the southern sky, in the direction of the Magellanic Cloud, Gonzalez said.
With additional interferometers coming online in Italy, Japan and elsewhere, the ability to pinpoint the location of future gravitational waves will vastly improve, she added.