Editing 1642: Gravitational Waves

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Now, let's consider spacetime fabric as a thin rubber sheet. If you mark any two points on this sheet and stretch or compress it along the axis joining those two points, the relative positions of these points with respect to their neighboring points do not change, but the distance between them changes.
 
Now, let's consider spacetime fabric as a thin rubber sheet. If you mark any two points on this sheet and stretch or compress it along the axis joining those two points, the relative positions of these points with respect to their neighboring points do not change, but the distance between them changes.
  
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{{w|LIGO}} (Laser Interferometer Gravitational-Wave Observatory) is a large-scale physics experiment designed to detect this compression/expansion, and it was LIGO who discovered the signal that caused this comic. (For a very detailed description of what the team at LIGO did and the history behind see this 90 minutes feature [https://www.youtube.com/watch?v=xj6vV3T4ok8 Gravitational Waves: A New Era of Astronomy Begins] from the 2016 World Science Festival).
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{{w|LIGO}} (Laser Interferometer Gravitational-Wave Observatory) is a large-scale physics experiment designed to detect this compression/expansion, and it was LIGO who discovered the signal that caused this comic.
  
 
Two facts need to be remembered to easily understand the experiment. First, the {{w|speed of light}} (c) is constant and the speed of an object is the distance moved divided by the time taken to travel that far. Second, gravitational waves cause opposite effects (compression and expansion) in directions perpendicular to each other. At LIGO, an experiment is set up where two perpendicular long tunnels are constructed with apparatus to emit and detect laser beams. The beam from a laser is split into these two tunnels. After going through the tunnel and back again a few times the beams are brought back together. The lengths of the tunnels are set up in such a way that, in the absence of gravity waves, destructive interference between the two combined beams causes them to cancel one another out, resulting in the detector observing zero light intensity. When the gravitational wave passes through earth, one of the tunnel is expected to expand while the other is expected to compress. Due to the difference in lengths, the destructive interference is incomplete and the detectors will be able to detect the presence of light. This observation can be concluded as "detection of the gravitational wave passing through".
 
Two facts need to be remembered to easily understand the experiment. First, the {{w|speed of light}} (c) is constant and the speed of an object is the distance moved divided by the time taken to travel that far. Second, gravitational waves cause opposite effects (compression and expansion) in directions perpendicular to each other. At LIGO, an experiment is set up where two perpendicular long tunnels are constructed with apparatus to emit and detect laser beams. The beam from a laser is split into these two tunnels. After going through the tunnel and back again a few times the beams are brought back together. The lengths of the tunnels are set up in such a way that, in the absence of gravity waves, destructive interference between the two combined beams causes them to cancel one another out, resulting in the detector observing zero light intensity. When the gravitational wave passes through earth, one of the tunnel is expected to expand while the other is expected to compress. Due to the difference in lengths, the destructive interference is incomplete and the detectors will be able to detect the presence of light. This observation can be concluded as "detection of the gravitational wave passing through".

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