Explain the concept behind the multiverse. 2. what did astronomer edwin hubble discover in 1929? 3. explain what the two teams of astronomers found in the 1990s. what question did their discovery create? 4. what is the mystery greene discusses and why does he say it is something we should all care about? 5. describe string theory. what is the central idea behind it? 6. greene explains that though the big bang theory explains how the universe evolved, it fails to explain what actually powered the bang. how does greene say the big bang was powered and based on this theory, discuss what this means regarding the possible existence of other universes? what does an expanding universe really mean? < - second lab link 1. discuss why the article says the fact that we're in our universe complicates our understanding of the expansion of the universe. 2. explain the significance behind the universe having a flat geometry. 3. discuss how gravity impacts how galaxies behave when they get close to one another.

PART A)
1) The Multiverse is a system of multiple parallel Universes, in which our Universe is only one of the possible configurations.

2) Hubble in 1929 discovered, looking at distant galaxies, that they are moving away from us with a speed greater than expected as if they are on a moving pavement. This led to the idea of expanding Universe.

3) In the 1990s it was discovered that the Universe is expanding not at a decelerating rate, but, on the contrary, at an accelerating rate. The question that arose is: what is accelerating the expansion of the Universe?

4) The amount of dark energy that is making the Universe expansion to accelerate, also know as repulsive gravity, that is needed to explain what we see, is very small, therefore it must come out from laws of physics, but no one has yet found how. Although this amount is so small to be called a detail, Greene thinks it is important because it could prove the existence of other Universes.

5) The idea behind the string theory is that every sub-atomic particle is made of tiny vibrating strings and the way they vibrate determines what kind of particle is created. In order to make this theory to work, we need to allow the possibility of dimensions other than the four (3 of space + 1 of time) we experience every day.

6) Greene says that the Big Bang was fueled by an explosion, called inflation. Since this fuel is very efficient, it could have powered not only our Universe but also other parallel Universes, with different characteristics from ours. A forever expanding Universe will lead to galaxies so far away from each other not to be visible anymore because the light departing from them could not reach us anymore. Therefore in the future, the sky could be totally black, and future astronomers could believe that the Universe is nothing else than the planet they live in.

PART B)
1) The problem of living in our Universe is that we can only see it from inside and we cannot have the big picture of how things work, we can only see things that are inside our observational limits.

2) A flat geometry means that if you draw a triangle the sum of the angles is always 180°, exactly like in the Euclidean plane. Also, that two parallel lines remain parallel forever, therefore light travels in a straight line.

3) Gravity is an attractive force, therefore a galaxy can be redirected from its original direction when passing close to another galaxy. In some cases, the two galaxies start rotating around each other and at the end they merge, forming a new galaxy.

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2. they have negligible mass.