Ripples in the Physics World
The Search
The 100-year search for gravitational waves finally came to an end on September 14, 2015 when the two Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Louisiana and Washington, measured gravitational waves. Gravitational waves are ripples in spacetime caused by the movement of massive objects through space. These ripples were predicted by Einstein in his general theory of relativity almost a century ago.
Einstein’s theory
In 1916, Einstein predicted the existence of gravitational waves as part of his theory of general relativity. In his theory, he introduced the concept of a fourth dimension known as spacetime. To understand what this fourth dimension is imagine a large fabric pinned down on a circular loop. Now, if a massive object was to be placed on this fabric it would cause the fabric to bulge in. If another relatively smaller mass was to be placed on that same fabric it would experience a visible pull towards the more massive object and that object would travel towards the object with more mass. Spacetime can be analogous to this fabric and the force between the two masses to gravity. Now looking at the same example, if a massive object was to accelerate on this fabric it would cause visible ripples in the fabric, Einstein described these ripples as gravitational waves.
Technology Used
The detection of gravitational waves was something that was considered impossible, given how small of an impact it creates, so much so that Einstein himself doubted if we would ever be able to detect them. The task that once seemed impossible has now been achieved thanks the technologies used by LIGO. To put it in simple terms, LIGO used a mirror to perpendicularly split a laser down two identical tunnels, the lasers were then reflected back by a mirror at the end of each tunnel. Ideally, the lasers would take the same amount of time to get back and cancel each other out. If there was anything, such as gravitational waves, that was to interfere with either lasers it would cause one to arrive before the other and this discrepancy would be captured by a photodetector. The gravitational waves that were measure by LIGO were predicted to happen and were caused by the collision of two black hole that had been circling around each other and slowly getting closer.
What Does This Mean?
The discovery of gravitational waves has proved the existence of spacetime and has also opened new doors for advances in the field of astrophysics. This new discovery will change the way physicists look at and study the details of our universe.
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