Space · For ages 7–11
How Big Is the Universe for kids, explained simply
Nobody knows the full size of the universe. We can only see the part whose light has reached us since the Big Bang — the observable universe — which is about 93 billion light-years across. The whole universe is even bigger, and it might go on forever. Scientists are still honestly studying this.
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The big ideas
We can only see part of it
Light takes time to travel, so we can only see places whose light has had time to reach us since the Big Bang, about 13.8 billion years ago. That visible bubble is called the observable universe. Beyond its edge, there is almost certainly much more we simply cannot see yet.
A light-year measures distance, not time
A light-year is how far light travels in one year — roughly 9.5 trillion kilometres. We use it because space is so huge that ordinary kilometres become silly, enormous numbers. Saying a galaxy is “two million light-years away” is far easier than writing out all those zeros.
Space itself is stretching
Here is the surprising part: the observable universe is about 93 billion light-years wide even though it is only around 13.8 billion years old. That is because space itself has been stretching the whole time, carrying distant galaxies even further apart while their light travelled toward us.
A quick quiz
1. How wide is the observable universe?
Choices: About 93 billion light-years · Exactly 100 kilometres · We have measured the whole universe
Answer: About 93 billion light-years. The observable universe — the part whose light has reached us — is about 93 billion light-years across. The whole universe may be even bigger.
2. What does a light-year measure?
Choices: How long a year lasts · A distance: how far light travels in a year · The age of a star
Answer: A distance: how far light travels in a year. A light-year is a distance, not a time. It is how far light travels in one year, about 9.5 trillion kilometres.
3. Do scientists know the total size of the whole universe?
Choices: Yes, it is exactly 93 billion light-years · No — it may be far bigger, even infinite · Yes, it is the size of our galaxy
Answer: No — it may be far bigger, even infinite. We only know the size of the part we can see. The whole universe might be much larger, possibly infinite, and scientists are still studying it.
For parents: helping your child think about how big is the universe
This topic is wonderful for teaching a powerful thinking habit: the difference between “what we can see” and “what is actually there.” Before sharing any numbers, ask your child a gentle question: “Do you think we can see the whole universe, or just a bit of it?” Let them wonder — the surprise that we can only see part of it is what makes the idea stick. The misconception to correct kindly is that 93 billion light-years is the size of everything. It is not — it is only the observable part, the bubble whose light has had time to reach us. The honest, science-accurate answer to “how big is the whole universe” is that nobody knows, and it might go on forever. Modelling that comfortable “we don’t know yet” is a gift; real scientists say it all the time. A second skill here is handling huge numbers through smart units, which is exactly why a light-year exists. Try this together: if light is the fastest thing there is, and it still takes years to cross these distances, how unimaginably far apart are things? Finish by asking your child to explain, in their own words, why we can only see part of the universe. If they can teach it back to you, they truly understand it.
Frequently asked questions
How big is the universe?
Nobody knows the size of the whole universe. We can only measure the observable universe — the region whose light has reached us — and that is about 93 billion light-years across. The rest may be far larger, and scientists honestly say it could even be infinite.
Why is the observable universe wider than its age in light-years?
The universe is about 13.8 billion years old, yet the observable part is roughly 93 billion light-years across. That happens because space itself has been stretching ever since the Big Bang, pushing distant galaxies further apart while their light was still travelling toward us.
What is a light-year?
A light-year is a distance, not an amount of time. It is how far light travels in one whole year — about 9.5 trillion kilometres. Astronomers use it because the gaps between stars and galaxies are too vast to measure sensibly in kilometres.
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