Question Video: Understanding the Expansion of the Universe | Nagwa Question Video: Understanding the Expansion of the Universe | Nagwa

Question Video: Understanding the Expansion of the Universe Science • Third Year of Preparatory School

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Which of the following statements is true? [A] The early universe underwent expansion, but the universe is no longer expanding and now stays the same size. [B] The early universe underwent expansion, but now the universe is contracting. [C] The early universe underwent expansion, and the universe continues expanding to this day.

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Video Transcript

Which of the following statements is true? (A) The early universe underwent expansion, but the universe is no longer expanding and now stays the same size. (B) The early universe underwent expansion, but now the universe is contracting. Or (C) the early universe underwent expansion, and the universe continues expanding to this day.

To begin, notice that all of the answer choices say that the early universe underwent expansion. This is true. The rapid expansion of the universe from an infinitely small point to a vast volume is known as the big bang. This initial expansion was the very beginning of our universe. In the first moments after the big bang, all of the energy in the universe was packed into a very small region, resulting in an ultrahigh energy and high pressure environment. And as the universe continued to expand, things cooled down and the rate of expansion gradually decreased.

But the expansion never stopped. It just slowed down significantly compared to the rapid expansion of the early universe. In fact, we can see evidence of the expansion of the universe even today when we observe outer space, since all distant galaxies appear to be moving away from our galaxy, the Milky Way.

But our vantage point isn’t special because of this. If we were to look into deep space from any point in the universe, we would still see galaxies in all directions moving away from us. This is because the very space between all galaxies is itself expanding. By observing how quickly certain galaxies are moving away from us, scientists can even measure the rate of this expansion. Thus, we know that the size of the universe is not constant, so we should eliminate option (A).

We also know that space isn’t contracting, because if that were the case, we’d see distant galaxies moving closer together and closer to us. This isn’t what’s actually observed, so let’s eliminate option (B).

That leaves us with option (C), which is the correct answer. The early universe underwent expansion, and the universe continues expanding to this day.

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