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Electromagnetic vs gravitational waves

Pierre Binétruy compares the role of gravitational waves for the Universe, to the one of electromagnetic waves.
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Until now, we’ve encountered many manifestations of gravity. Expansion of the universe, dark matter, dark energy, inflation. We could even say that the very texture of space and time is probably related in a deep sense to the gravitational force. Now, we missed so far one concept, which will be the topic of this week, the concept of gravitational waves.
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Let me first review a few facts about electromagnetic waves, the more familiar type of wave. We all know what is an electromagnetic field. For example, the needle of a compass will orient according to the North Pole– the magnetic north pole of the earth– or two charges of opposite charge will attract each other because of the electric field. So that’s either the electric part or the magnetic part of the electromagnetic field. Now, a moving electromagnetic field is what we call an electromagnetic wave, and you all know a familiar example of an electromagnetic wave, which is the visible light. The light is just a travelling electromagnetic field.
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We’ve already discussed the gravitational field of a star. This attraction– gravitational attraction– develops a field around a star. Now, exactly like in the electromagnetic case, a moving gravitational field is what we call a gravitational wave. Because we have seen the importance of the role of gravitation in the universe, we even said that it is the engine of the universe. You can imagine that detecting these gravitational fields is going to give us very precious information about the way that the universe is functioning.
Just as light has taught us so much about electromagnetic phenomena, one expects that, once they are identified, gravitational waves will be a wonderful tool to grasp our Universe. (2.38)
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Gravity! The Big Bang, Black Holes and Gravitational Waves

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