<ul>
<li>The radius of the observable Universe is 41.5billion light years (<a href="https://en.wikipedia.org/wiki/Observable_universe" rel="nofollow noreferrer">ref</a>).</li>
<li>A light year is <span class="math-container">$9.5\cdot10^{12}$</span> km.</li>
<li>The radius of the Earth is 6371 km.</li>
</ul>

<p>So the answer is <span class="math-container">$6371 km \cdot \frac{6371 km}{41.5\cdot10^9\cdot9.5\cdot10^{12}km} = 1.03\cdot10^{-16}km = \underline{\underline{1.03\cdot10^{-13}m}}$</span>.</p>

<p>The size of the atoms are <span class="math-container">$\approx 10^{-10}m$</span>.</p>

CC BY-SA 4.0
2019-01-27T08:49:55.600Z
@PM2Ring Your link states 28.5e+9 ly diameter, which is 14.25e+9 ly radius. I calculated here with radius of 13.7bln ly, the difference is imho not significant in this context, but I fixed it.
peterh
CC BY-SA 4.0
2019-01-27T08:54:39.970Z
It says 28.5 gigaparsecs, or 93 billion light years, for the diameter. Also see https://physics.stackexchange.com/questions/57402/size-of-the-observable-universe although that does get a bit technical.
PM 2Ring
CC BY-SA 4.0
2019-01-27T09:14:41.810Z
@PM2Ring Uhm, it seems it is not my day :-) I fixed it again.
peterh
CC BY-SA 4.0
2019-01-27T09:16:28.057Z
It's always a good day to learn new stuff. ;)
PM 2Ring
CC BY-SA 4.0
2019-01-27T09:47:01.940Z
Don't understand these symbols. Could you also provide a simple answer in layman's terms?
larry909
CC BY-SA 4.0
2019-01-27T10:15:43.867Z
@larry909 $10^-{10}$ is 0.0000000001 .  $10^{-13}$ is 0.0000000000001. The answer is around a tousandth of an atom.
peterh
CC BY-SA 4.0
2019-01-27T08:38:07.840Z
2019-01-27T09:14:23.753Z
2019-01-27T09:14:23.753Z
peterh
<p>If the whole observable Universe is as big as planet Earth, how big would Earth be?</p>

CC BY-SA 4.0
2019-01-27T08:39:11.067Z
Take a look at the other question that you asked about the relative size of earth and the milky way.  Then look up the size of the observable universe.  You will be able to show your understanding of that answer by doing the same calculations for the observable universe, and then you can write your own answer for this question.
James K
CC BY-SA 4.0
2019-01-27T09:46:19.043Z
@JamesK I don't understand this math
larry909
CC BY-SA 4.0
2019-01-27T10:35:32.920Z
It is multiplication and division. Please read the answer there again, carefully. You can understand the maths if you think about it.
James K
<observable-universe><size>
If the whole observable Universe is as big as planet Earth, how big would Earth be?
larry909
# If the whole observable Universe is as big as planet Earth, how big would Earth be?

(Asked by: username_0 on 2019-01-27)

If the whole observable Universe is as big as planet Earth, how big would Earth be?

**Tags:** observable-universe, size
> **Comments:**
> **username_1**: Take a look at the other question that you asked about the relative size of earth and the milky way.  Then look up the size of the observable universe.  You will be able to show your understanding of that answer by doing the same calculations for the observable universe, and then you can write your own answer for this question.  
> **username_0**: @JamesK I don't understand this math  
> **username_1**: It is multiplication and division. Please read the answer there again, carefully. You can understand the maths if you think about it.  

---

## 1 answers

### Answer by username_2 on 2019-01-27. Score: 4 | Accepted answer

* The radius of the observable Universe is 41.5billion light years ([ref](https://en.wikipedia.org/wiki/Observable_universe)).
* A light year is $9.5\cdot10^{12}$ km.
* The radius of the Earth is 6371 km.

So the answer is $6371 km \cdot \frac{6371 km}{41.5\cdot10^9\cdot9.5\cdot10^{12}km} = 1.03\cdot10^{-16}km = \underline{\underline{1.03\cdot10^{-13}m}}$.

The size of the atoms are $\approx 10^{-10}m$.

> **Comments:**
> **username_2**: @PM2Ring Your link states 28.5e+9 ly diameter, which is 14.25e+9 ly radius. I calculated here with radius of 13.7bln ly, the difference is imho not significant in this context, but I fixed it.  
> **username_3**: It says 28.5 gigaparsecs, or 93 billion light years, for the diameter. Also see https://physics.stackexchange.com/questions/57402/size-of-the-observable-universe although that does get a bit technical.  
> **username_2**: @PM2Ring Uhm, it seems it is not my day :-) I fixed it again.  
> **username_3**: It's always a good day to learn new stuff. ;)  
> **username_0**: Don't understand these symbols. Could you also provide a simple answer in layman's terms?  
> **username_2**: @larry909 $10^-{10}$ is 0.0000000001 .  $10^{-13}$ is 0.0000000000001. The answer is around a tousandth of an atom.  

---

