The Gravity Wave ‘Discovery’

You may have heard about the leaked rumour about the discovery of gravitational waves from earlier this week.  It was from Lawrence Krauss, who is an amazing science communicator and author, as well as a darn good astrophysicist.

It’s safe to say that as a guy with an inside scoop on a lot of the latest science news, this is something to get excited about.  The ‘LIGO’ he is referring to stands for the ‘Laser Interferometer Gravitational-Wave Observatory,’ and is one of the major projects on the planet that is searching for the elusive gravity waves.  Before we get too excited, it’s important to remember that no official results have been published, but if the rumour is true, we should see the official results in a few months.

But what are gravitational waves? And why are they so important?  It all goes back to that Einstein guy, who characterized gravity as the physical warping of the four dimensional fabric of our universe, what he called space-time.  The typical analogy for gravity is if you image space-time as a flat two-dimensional sheet.  When you place a weight on it, it produces a warping, and the warping is greater the closer you are to the mass.  It also warps in the third dimension.  So by analogy, for us the gravity we experience is masses like the Sun warping four dimension space-time.  Watch this video to get an idea of general relativity.

So we know about Space-time warping, but that still doesn’t explain a gravitational wave.  Well, when two massive objects orbit one another and then merge, like the merger of two black holes, each will have their own effect on space-time.  But when they collide and merge, Space-time will ripple like the surface of a pond to account for the quick change.  This is predicted by Einstein’s theory and most scientists expect it’s only a matter of time until we find them.  The reason we haven’t found them yet is that they are expected to be very small ripples, way smaller than atoms.

So how is LIGO looking for them?  The ‘LI’ is the key: Laser Interferometry.

Laser Interferometry 101

The way this works is to have a laser shine at a mirror that splits the beam into two separate beams that travel perpendicular to one another.  The beams travel a long distance (4 Km for LIGO) and reflect off a mirror, back to the beam splitting mirror, where they recombine and hit a detector.  If the waves are shifted in any way on the trip to their respective mirrors, they will be slightly out of phase, creating an interference pattern at the detector.  Gravitational waves would cause the beams to move out of phase and produce such a pattern.  This is how LIGO works.

If indeed the gravitational waves have been discovered by LIGO, such an announcement would have required substantial data before being published.  It’s the old ‘Extraordinary claims require extraordinary evidence’ argument.  But if it’s confirmed a few months down the road, we will have a powerful new tool with which to probe the extremes of the Universe.  Using the waves like light waves we will be able to map the entire sky and look for strong gravity wave sources, such as black holes or other gravitational events that we can’t see across the electromagnetic spectrum.

However, the true power of gravitational waves is the ability to see back to the beginning of the universe.  Using light, the farthest we can see is the cosmic microwave background radiation.  But that light didn’t originate until 380,000 years after the big bang.  But gravity waves have likely been around from the start.  So understanding them will allow us to see beyond the veil and look at the universe in it’s infancy, probing physics at a deeper level than ever before.

I’m optimistic that it’s true, though if it is, it will still be a good long time before the detection methods can be perfected and a new generation of detectors can obtain useful information from gravitational waves.  I’m glad I’ll be around to see it all unfold, bringing humanity one step closer to a deeper understanding of the universe.

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