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• What is a gravitational wave?

• It’s a ripple in the fabric of space and time.

• Imagine that space is a giant sheet of rubber:

• things that have mass cause that rubber sheet to bend, like a bowling ball on a trampoline.

• The more mass, the more that space gets bent and distorted by gravity.

• For example, the reason the earth goes around the sun is that the sun is very massive, causing

• a big distortion of the space around it.

• If you just try to move in a straight line around such a big distortion, you will find

• yourself actually moving in a circle.

• That’s how orbits work: there’s not an actual force pulling the planets around, just

• a bending of the space.

• Gravitational waves are produced whenever masses accelerate, changing the distortion

• of space.

• Everything with mass and/or energy can make gravitational waves.

• If you and I started to dance around each other, we would also cause ripples in the

• fabric of space and time.

• But these would be extremely small. Practically undetectable.

• Now gravity is very weak in the scale of the other forces in the Universe, so you need

• something really, really massive moving very, very fast, to make the big ripples that we

• can detect.

• How would you observe a ripple in space?

• If the space between you and me stretched or compressed, we wouldn’t notice it if

• we had made marks on our metaphorical rubber sheet, for example, using equally spaced rocks.

• Because these marks would also get stretched further apart.

• But there is one ruler that doesn’t get stretched, one made using the speed of light.

• If the space between two points gets stretched, then light will take longer to go from one

• point to the other.

• And if the space gets squeezed, light takes less time to cross the two points.

• This is where the LIGO experiment comes in.

• It has 4 kilometer long tunnels and uses lasers to measure the changes in the distance between

• the ends of the tunnels.

• When a gravitational wave comes through, it stretches space in one direction, and squeezes

• space in the other direction.

• By measuring the interference of the lasers as they bounce between the different points,

• physicists can measure very precisely whether the space in between has stretched or compressed.

• And the precision needed is incredible.

• To detect a gravitational wave, you need to be able to tell when something changes in

• length by a few parts in 10 to the 23.

• It’s like being able to tell that a stick one sextillion meters long has shrunk by 5mm.

• The effect of a Gravitational Wave is so minuscule and easily confused with random noise you

• need a smart data analysis technique.

• Scientists hope to identify the patterns of gravitational waves by comparing the wiggles

• they measure in the experiment to the wiggles they expect from Gravitational Waves.

• That’s like trying to identify a song being hummed at a noisy party. A very, very noisy

• party.

• Imagine that your whole life you had been deaf until one day your hearing was restored.

• You’d be able to explore the Universe in this whole new way.

• That’s why detecting gravitational waves is so significant.

• It’s a completely new way of studying the Universe.

• Anytime there's a new way to observe the Universe we discover things that we didn't expect.

• It's really about looking for new things that we didn't know existed, examining the extreme

• edges of our knowledge of physics and testing our theories about how the Universe works.

What is a gravitational wave?

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Gravitational Waves Explained

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Jack posted on 2016/02/14
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