Written by Kat Kelly
Kat is a Science Facilitator at Science World and currently working towards a degree in Physics and Astronomy. When Kat isn’t gazing at the stars or sharing her love of science with our visitors, she enjoys reading, singing, playing guitar and attending public lectures and debates.

gravity waves

Created date

Sunday, February 14, 2016 - 9:00am

Gravitational waves have been detected!

On February 11, 2016,  Scientists at the Laser Interferometry Gravitational Observatory (LIGO) announced that they have detected gravitational waves from two merging black holes more than a billion light years away from earth. Merging black holes are detected roughly once every million years in our Galaxy and this collision produced more than 3 times the mass of the Sun in pure gravitational energy. Gravitational waves travel at the speed of light—there is no cosmic speed limit on space itself. That means that these waves that were produced in a fraction of a second have been travelling towards us for over a billion years.

A hundred years ago, Albert Einstein published his theory of General Relativity. In it, he proposed that ripples in the fabric of space-time, or gravitation waves could exist! Gravitational waves, he figured, would be caused by large masses, such as black holes or neutron stars, and could cause space to stretch and squeeze as the masses travel. Scientists have been searching for these gravitational waves for decades in the hopes that they might offer a broader understanding of space and time. There have been some false alarms with gravitational wave detection in the past but scientists are 99.99% sure that this is the real deal. This consensus among scientists makes the discovery the final confirmation that Einstein was right about General Relativity and it is also the first direct detection of black holes!

Gravity is the weakest of the fundamental forces, despite its obvious role in our everyday lives. It is extremely hard to detect something this faint. As is explained in Emanuele Berti's article, the "Advanced" LIGO experiment consisted of two detectors 3,002 km apart, one in Louisiana and one in Washington State, "Each detector is a Michelson interferometer, consisting of two 4km-long optical cavities, or “arms,” that are arranged in an L shape. The interferometer is designed so that, in the absence of gravitational waves, laser beams traveling in the two arms arrive at a photodetector exactly 180° out of phase, yielding no signal. A gravitational wave propagating perpendicular to the detector plane disrupts this perfect destructive interference. During its first half-cycle, the wave will lengthen one arm and shorten the other; during its second half-cycle, these changes are reversed. These length variations alter the phase difference between the laser beams, allowing optical power—a signal—to reach the photodetector."

Where previously we have only been able to observe objects that give off light, scientists say this will open a new window to the universe, through which, we can observe gravity too. 

Other gravitational wave experiments include BICEP2, MiniGRAIL, NanoGrav and LISA.

Want to get involved? Check out a project called Einstien@home to find out how you can help scientists process their data at a much faster pace.



How will observing gravity

How will observing gravity help us better understand how the universe works? Sorry for the broad question, but curious.

Hi Arnold, That's a great

Hi Arnold, That's a great question! There are a few reasons why this discovery will help us to better understand the Universe.

1) Black holes: Gravitational

1) Black holes: Gravitational waves from black holes are created near the event horizon - The point of no return. Weird things happen there, time slows down, light cannot escape etc. Therefore it is very hard to learn about what happens there. Black hole collisions like the one that caused the waves LIGO detected are very rare and mainly happened very soon after the big bang, this gives us a glimpse back in time to the early universe. By using the data from gravitational waves we can learn more about black holes which in turn can tell us more about gravity and galaxy evolution.

2) The big bang: Currently we

2) The big bang: Currently we can only 'see' up to a certain point after the big bang because we are working with light. Light can be redshifted (Stretched into longer wavelengths) due to the expansion of the universe which makes the objects fainter to observe. Alternatively we can look at the universe in other wavelengths like x-ray and microwaves etc but eventually it becomes opaque, one example of this is the Cosmic Microwave Background. With gravity, we don't have that problem. Yes it travels at the speed of light and it does dissipate energy as a it travels as a wave through space, but there is no limit to how far back in time we can detect it from, we just have to be ready to see it at the right time and place, just like LIGO were.

3) Einstein’s theory of

3) Einstein’s theory of relativity (TOR): You may have heard of this theory before and may have thought it was already proven, but we scientists require a lot of evidence the accept something as the truth and move on and base new physics upon those theories. One prediction on Einstein’s theory of relativity was that gravity itself is the curvature of space. One predictable effect of this being true is the presence of gravitational waves. Now that we have directly detected them, we can be pretty much certain that Einstein’s TOR is right. The next big step in physics is to combine the laws of gravity with quantum mechanics for a grand unified theory of everything.

If you are looking for a good

If you are looking for a good explanation of what Gravitational waves actually are, check out this video by Professor Brian Greene: https://www.youtube.com/watch?v=ajZojAwfEbs Thanks for the comments, keep them coming!

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