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Skip to 0 minutes and 34 seconds So where are we in our journey through the gravitational Universe? We have been accumulating over weeks some information. We have seen, for example, that gravity is the engine of the Universe, which means that the gravitational force is the force, the fundamental force, behind the expansion of the Universe. We even had to add a new era, a very early epoch in the evolution of the Universe right after the Big Bang, some 10 to minus 38 seconds after the Big Bang, which is called inflation. Inflation is an era of very rapid expansion of the Universe, exponential expansion, which help to solve some of the problems of the contemporary Universe.

Skip to 1 minute and 24 seconds We had to rely on a new concept, the concept of vacuum energy, in order to understand what causes that period of inflation. And we saw that this vacuum is the place of some fluctuations, some quantum fluctuations, which are being seen today as fluctuations in the cosmic microwave background. And so let us pause a second to realise, or to marvel at the fact that theorists are predicting some events at 10 to minus 38 seconds after the Big Bang and are making predictions of what happened at that time, and that these predictions are observed in the sky today in the cosmic microwave background.

Skip to 2 minutes and 11 seconds This is also why one calls the cosmic microwave background a fossil radiation, because those fluctuations are the equivalent of fossils of very early times, times right after the Big Bang.

Skip to 2 minutes and 28 seconds But we will rely on another prediction of the scenario of inflation– the fact that space is flat. And we will see that, in order for space to be flat, we need to introduce other components than matter and radiations, other forms of energy. We have not detected these forms of energy so far, because they are dark. They do not emit light, and so our eyes cannot see them. And this is why, for millennia, we’ve been observing the sky and have not identified these dark components. So let us start this week the search for the dark components of the Universe.

In the Dark

Where are we in our exploration of the gravitational Universe? Inflation has uncovered for us the secrets of the Universe 10-38 seconds after the Big Bang! But among the predictions of inflation, there are some that require new ingredients in the Universe. Are they to be found among the dark components of the gravitational Universe? (3.17)

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Gravity! The Big Bang, Black Holes and Gravitational Waves

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