Watch the video above and talk about it with a group or mentor. Learn more.

The universe is constantly expanding at a speed faster than light, which would seemingly make it impossible to see the light of distant galaxies. If this is the case, how do we discover new things everyday in this ever-expanding universe?

There was a time when the universe was expanding faster than the speed of light, and that time is now. In fact, the universe has been expanding at this rate since our universe burst into existence. If you were to choose two points in the universe that are far enough apart you would be able to observe this shift in the universe. It is simply due to the expanding space between those two points.

Doesn’t Cosmic Expansion Violate Einstein’s Theory of Special Relativity?

This theory states that nothing is able to move faster than light. However, this theory is referring to things that are moving through space, not space itself. Space can move however it likes. So it doesn’t violate this theory at all.

Hubble’s Observations of the Night Sky Led Us to The Discovery of Universal Expansion

Hubble noticed that the further he peered into space, the faster objects were moving away from him. Imagine a point in space had a recessional velocity or speed at which it is moving away from earth, equal to the speed of light. It would be the same distance in every direction. This creates a sphere that we refer to as the Hubble Sphere. Everything beyond that sphere is moving away from us faster than the speed of light. Common sense would say that we will never be able to see the light from those objects because of how fast they are moving away from us, but this isn’t actually true.

We Can See Objects Outside of the Hubble Sphere

To understand this imagine a galaxy that is located outside of the Hubble Sphere. It would be moving away from us faster than the speed of light, so any light it emits will actually be moving away from us as time goes on. That would make it seem like we would never be able to see that light. But due to the expansion of space, our Hubble Sphere is also expanding. If our Hubble Sphere expands fast enough, the light emitted by the galaxy will eventually enter into the sphere and become visible to us, even though the galaxy itself will remain outside of the Hubble Sphere. All of the discoveries we have made in the universe have come from light that is potentially billions of years old but just recently entered into our Hubble Sphere.

Due to this ever-expanding universe, we will forever discover new galaxies. As science advances, we will one day have the ability to explore these new galaxies and learn even more about our vast universe. Until then, we will have plenty of things to discover in space.

Read more
Read less

Key Points:

  • Doesn’t cosmic expansion Einstein’s Theory of Special Relativity? This theory is referring to things that are moving through space, not space itself.
  • Hubble’s observations of the night sky led us to the discovery of universal expansion. Hubble noticed that the further he peered into space, the faster objects were moving away from him.
  • We can see objects outside of the Hubble Sphere. 

Quote This:

When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That’s relativity. -Albert Einstein

Talk About It
  1. What is your initial reaction to this topic? What jumped out at you?
  2. What is the most interesting thing you know about the universe?
  3. Would you be willing to travel into space? Why or why not?
  4. Do you think scientific advances will one day allow us to physically explore far-off galaxies? Why or why not?
  5. Write a personal action step based on this conversation.