On February 11th, 2016 the world was exposed to a shocking discovery that scientist’s have been questioning since the 1910’s. The idea of Gravitational Waves had been tossed around but never confirmed. This was mostly due to the fact that the detection of a GW seemed impossible because the technology simply did not exist. However, nothing is impossible in the scientific community. The first encounter with GW was with the Hulse-Taylor Pulsar, in which they observed the pulsar’s orbital decay which matched Einstein’s predictions of energy loss by gravitational radiation. This discovery would win them the Nobel Prize in 1993.
Not too many people are familiar with gravitational waves, so I will take this opportunity to clear things up. By the way, the name of the GW detected in the title of this post is the date that it was found! Fun fact for the day.
What is a GW? A gravitational wave is formed by a mass in motion. Think of a stone tossed into a lake. The stone creates ripples, or waves that propagate throughout the lake. The same idea can be applied in space. However, not all masses in space are strong enough to send ripples through spacetime. Only the large, energetic ones like a rotating binary system, supernova’s, black holes, etc. These massive objects are so strong that the space around them will “ripple” as they spin or explode while they are losing energy in the form of gravitational waves. This is why the detection of GW is huge. Only massive violent events in space cause them, therefore, we can study GW to learn more about the events that produced them, like mysterious black holes and possibly the big bang itself.
How do we detect gravitational waves? As previously stated, GW are nearly impossible to detect. As they pass through, they cause distances to change and periodic deformations. Their effect, however, is so small which makes it difficult to detect them. This is because gravity is a weak force and the period of the wave is extremely small. For example, a mass with a diameter of 1 meter would only be deformed by 10^-21 meters. This is why it is very difficult to detect GW. Nevertheless, physicist Albert Michelson came along to show us how we could measure such a small motion. Using the wavelength of light as a measuring device we are able to detect precise movements for exquisitely small distances, or periods.
How is light used as a measuring device? If you’ve ever taken a physics class then you’ve probably learned about Young’s two slit experiment that allowed us to “see” the wavelengths of light. A single light beam that is shined through two slits can be seen on a blank screen some distance away as a pattern of light and dark “fringes.” This is known as interference. The distance between fringes is directly related to wavelength.
LIGO (Laser Interferometer Gravitational-Wave Observatory) is a collaboration between multiple physics institutes and research groups dedicated to the search for GW’s, which began in August 2002. Because the wavelength of a GW is directly related to the size of the cosmic event, detectors must be about the size of the cosmic event. Thus, we have two types of man-made devices: Ground Interferometer’s, designed for small cosmic sites w/ GW of a few thousand kilometers, and Space Interferometer’s, designed for large cosmic sites with wavelengths tens of millions of kilometers. The ground interferometers are located in Hanford, Washington and Livingston, Louisana.
Basically, an interferometer sends out a laser beam that hits a beam splitter, splits the light in two where the light is directed toward mirrors that finally send the light back to the beam splitter to form an interference pattern. The arms of the interferometer are the trajectory of the beams, so the pattern depends on the distance between the arms.
If a GW goes through, the distance between the arms changes, leaving the interference pattern changing periodically!
In theory, LIGO could also detect hypothetical phenomena of GW caused by oscillating cosmic strings, and domain walls
Lisa is the first space interferometer that was successfully launched on December 3, 2015. The mission is to map out the technical difficulties that may be experienced by eLisa, which will be launched with three satellites positioned 5 million km away from each other with laser beams connecting the three satellites. Any change in the distance of laser light will suggest a GW passing through.
To watch and learn more about this fascinating historic event, see the video below!
Are we really able to learn about the creation of the universe by studying a GW?
Because gravity is such a weak force, gravitational waves interact weakly with their environment. In fact, the effect is so small that they don’t change much because of their weak interactions. This makes them the perfect little “messengers” of distant cosmic events, providing us more information on gravity and how the universe works as gravity is turned into waves.
Side note- an interesting comment was made in the discussion post on GW so I thought I would share:
“gravitational waves, to me, would better explain some kind of déjà vù, because space time is being curved, it would be a variation on the time that maybe allows someone to look into the past or future for a few milliseconds (or the time it takes to the wave to pass)” -M.A
Something to think about!
That about sums up the discussion on gravitational waves, next time I will talk about black holes- their mysterious nature, escaping them and how GW will provide us with information we would never be able to gather otherwise!
This post is part of a series, for links to other posts, click here!