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If the universe sprung into existence and then expanded exponentially, you get gravitational waves traveling through space-time. These would fill the universe, a pattern of echoes of the inflation itself.

When gravitational waves reach the earth, the waves stretch and squeeze space. This is a tiny stretch and squeeze. Far too small to detect with ordinary human senses.

Gravitational waves will bring us exquisitely accurate maps of black holes - maps of their space-time. Those maps will make it crystal clear whether or not what we're dealing with are black holes as described by general relativity.

We're going to need a definitive quantum theory of gravity, which is part of a grand unified theory - it's the main missing piece.

We know there is gravity because apples fall from trees. We can observe gravity in daily life. If we could throw an apple to the edge of the universe, we would observe it accelerating.

There was a long history of speculation that in quantum gravity, unlike Einstein's classical theory, it might be possible for the topology of spacetime to change.

I've been noticing gravity since I was very young.

Gravitation is, so far, not understandable in terms of other phenomena.

The Universe is the periodical manifestation of this unknown Absolute Essence.