# We can see things moving faster than light | Summary and Q&A

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October 15, 2021
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Physics Girl
We can see things moving faster than light

## TL;DR

Galaxies can be billions of light years away, and the expansion of space causes galaxies to move away from us faster than the speed of light.

## Key Insights

• πΎ The expansion of space causes the distance between galaxies to increase over time.
• π Some galaxies are moving away from us faster than the speed of light, but we can still see them as they were when the light was emitted.
• π€ The observable universe is larger than initially thought due to the expansion of space.
• π The Hubble sphere represents the limit where galaxies are moving away from us slower than the speed of light.
• πΎ The expansion of space does not affect local clusters of galaxies significantly.
• πΎ Gravity can overcome the movement caused by the expansion of space.
• πΎ Space itself can expand, but objects within space do not get bigger.

## Transcript

imagine a galaxy and its light took 25 000 years to get to us how far away is that galaxy uh 25 000 light years away beautiful now imagine a galaxy that it took the light 13.4 billion years for the light to get to us how far away do you think that galaxy is i would imagine it's 13.4 billion light years away the answer is actually 32 billion light y... Read More

## Questions & Answers

### Q: How is it possible for a galaxy to be 32 billion light years away if its light took only 13.4 billion years to reach us?

The expansion of space causes the distance between galaxies to increase over time, even though it only took 13.4 billion years for the light to reach us. The galaxy itself may have moved further away due to the expansion.

### Q: Can we see galaxies that are moving away from us faster than the speed of light?

We can see some galaxies that are moving away from us faster than the speed of light because the light emitted from those galaxies can eventually reach us. However, we will only see them as they were when the light was emitted, not as they are currently.

### Q: Does everything in the universe expand with space?

No, objects like local clusters of galaxies are not significantly affected by the expansion of space. Gravity can overcome the expansion, causing objects to stay relatively close despite the movement of space.

### Q: What is the difference between the event horizon and the Hubble sphere?

The event horizon represents the boundary of what we can observe, while the Hubble sphere marks the edge of the region where galaxies are moving away from us slower than the speed of light. The Hubble sphere is found inside the event horizon.

## Summary & Key Takeaways

• Galaxies can be billions of light years away, with some taking 13.4 billion years for their light to reach us.

• The distance between galaxies is not fixed; space itself is expanding, causing the distance to increase over time.

• The observable universe is much larger than initially thought because the expansion of space allows us to see galaxies that are now further away.