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Expansion of the Universe

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Are We Expanding Too?
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Are We Expanding Too?

Credit: NASA
Source: http://en.wikipedia.org/wiki/File:Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg
License: CC BY-NC 3.0

We know that the universe is expanding. But is everything in the universe also expanding? Is an atom expanding? Is a galaxy expanding? Are you expanding?

Amazing But True!

Credit: NASA/WMAP Science Team
Source: http://en.wikipedia.org/wiki/File:CMB_Timeline300_no_WMAP.jpg
License: CC BY-NC 3.0

Graph representing the expansion of the universe (doesn't represent the physical models of expansion) [Figure2]

It turns out that it’s not exactly right to say that the universe is expanding. Although that’s what people say as shorthand to what’s actually happening. What’s really expanding is the space in the universe. The space between objects is expanding but not the objects themselves. That’s true even if that object is a galaxy. But a galaxy is made up of a lot of empty space. Why doesn’t a galaxy expand? An atom is also made up of a lot of empty space. Why doesn’t an atom expand?

Explore More

With the link below, learn more about why atoms, molecules, solar systems and galaxies are not expanding. Then answer the following questions.

  1. What are the two forces that are too strong for the expansion of space to overcome?
  2. How does a leash keep you and your cat at the same distance apart even if the sidewalk beneath you is moving in opposite directions?
  3. Why doesn’t the expansion of the space between stars pull our solar system apart?
  4. How do galaxies grow more distant from each other over time?

Image Attributions

  1. [1]^ Credit: NASA; Source: http://en.wikipedia.org/wiki/File:Hubble2005-01-barred-spiral-galaxy-NGC1300.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: NASA/WMAP Science Team; Source: http://en.wikipedia.org/wiki/File:CMB_Timeline300_no_WMAP.jpg; License: CC BY-NC 3.0


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