Everyone has heard of Albert Einstein’s special theory of relativity. Just imagine the universal explosion of praise that happened when he published this momentous work of science! Then stop imagining. Whatever you’re thinking, it probably went nothing like that.
Fig: Einstein in his office at the university of Berlin, 1920 IMG credit: Wikimedia Commons
When Einstein published his paper on special relativity in 1905, the reception wasn’t exactly warm. His paper talks about “ether,” a theoretical substance that was then accepted as the stuff space is made of, mostly because its existence helped the equations work out. As JSTOR Daily reports, “Einstein argued that space and time were bound up together (something he would elaborate on in his theory of general relativity of 1915, adding gravity to the mix of space/time), a complicated idea that contradicted the long-held belief in something called ether. Einstein’s theory noted there was no experimental confirmation for the substance. There was no proof it existed, other than that the scientific establishment had accepted the concept.”
Change is hard. For years after Einstein put his contradiction of ether out into the world, Germany remained the only place it was really taken seriously. In Britain, the idea fell on deaf ears. (Britain was, after all, where the idea of ether originated.) In France, Einstein’s work wasn’t really even considered until after he visited the country in 1910. A few understood it in the U.S. but generally considered it impractical and absurd. What made Germany different? According to scholar Stanley Goldberg, “Many German physicists opposed Einstein’s theory, but it is only in Germany that its opponents understood it. It was the seriousness of the German response, in my view, which ultimately led to the acceptance of relativity, for it insured that the theory would be examined, criticized, and elaborated upon.”
WHAT DOES HIS THEORY ACTUALLY SAY?
Besides denying the existence of ether, Einstein’s special and general theories of relativity helped modern science take a grand leap in its understanding of the universe. Nola Taylor Redd does a wonderful job of summing up both theories: In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time. Einstein then spent 10 years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he he worked out the equations for his general theory of relativity, and determined that massive objects causes a distortion in space-time, which is felt as gravity. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.
So, have we got any experimental evidence?? Well friends, although instruments can neither see nor measure space-time, several of the phenomena predicted by its warping have been confirmed.
1) Gravitational lensing: Friends, in this light around a very massive object, such as a black hole, is bent, causing it to act as a lens for the things that lie behind it. Astronomers routinely use this method to study stars and galaxies behind massive objects. Einstein’s Cross, a quasar in the Pegasus constellation, is an excellent example of gravitational lensing. Four images of the quasar appear around the galaxy because the intense gravity of the galaxy bends the light coming from the quasar.
Gravitational lensing can allow scientists to see some pretty cool things, but until recently, what they spotted around the lens has remained fairly static. However, since the light traveling around the lens takes a different path, each traveling over a different amount of time, scientists were able to observe a supernova occur four different times as it was magnified by a massive galaxy. In another interesting observation, NASA’s Kepler telescope spotted a dead star, known as a white dwarf, orbiting a red dwarf in a binary system. Although the white dwarf is more massive, it has a far smaller radius than its companion.
2) Changes in the orbit of Mercury: The orbit of Mercury is shifting very gradually over time, due to the curvature of space-time around the massive sun. In a few billion years, it could even collide with Earth.
3) Frame-dragging of space-time around rotating bodies: The spin of a heavy object, such as Earth, should twist and distort the space-time around it. In 2004, NASA launched the Gravity Probe B GP-B). The precisely calibrated satellite caused the axes of gyroscopes inside to drift very slightly over time, a result that coincided with Einstein’s theory.
4) Gravitational redshift: The electromagnetic radiation of an object is stretched out slightly inside a gravitational field. Think of the sound waves that emanate from a siren on an emergency vehicle; as the vehicle moves toward an observer, sound waves are compressed, but as it moves away, they are stretched out, or redshifted. Known as the Doppler Effect, the same phenomena occurs with waves of light at all frequencies. In 1959, two physicists, Robert Pound and Glen Rebka, shot gamma-rays of radioactive iron up the side of a tower at Harvard University and found them to be minutely less than their natural frequency due to distortions caused by gravity.
5) Gravitational waves: Violent events, such as the collision of two black holes, are thought to be able to create ripples in space-time known as gravitational waves. In 2016, the Laser Interferometer Gravitational Wave Observatory (LIGO) announced that it found evidence of these tell-tale indicators.
In 2014, scientists announced that they had detected gravitational waves left over from the Big Bang using the Background Imaging of Cosmic Extragalactic Polarization (BICEP2) telescope in Antarctica. It is thought that such waves are embedded in the cosmic microwave background. However, further research revealed that their data was contaminated by dust in the line of sight.
LIGO spotted the first confirmed gravitational wave on September 14, 2015. The pair of instruments, based out of Louisiana and Washington, had recently been upgraded, and were in the process of being calibrated before they went online. The first detection was so large that, according to LIGO spokesperson Gabriela Gonzalez, it took the team several months of analyzation to convince themselves that it was a real signal and not a glitch.
A second signal was spotted on December 26 of the same year, and a third candidate was mentioned along with it. While the first two signals are almost definitively astrophysical—Gonzalez said there was less than one part in a million of them being something else—the third candidate has only an 85 percent probability of being a gravitational wave.
Together, the two firm detections provide evidence for pairs of black holes spiraling inward and colliding. As time passes, Gonzalez anticipates that more gravitational waves will be detected by LIGO and other upcoming instruments, such as the one planned by India.
Einstein’s theories about space and time have proven to be the most accurate we have so far.