# B Balloon Analogy - 3D universe on a 2D plane

1. Dec 6, 2017

### Souhardya Nandi

This has been a real famous analogy and I understand it, except the fact that the balloon surface is a 2D structure. How is it possible to depict a 3D universe on a 2D plane ? What happens when we work with stars at multiple planes ?

2. Dec 6, 2017

### PeroK

There are two things you have to imagine in order to understand the balloon analogy. These are not necessarily easy to grasp, depending on how well you can think abstractly and mathematically:

1) You have to imagine that the surface of the balloon is all there is. A real 2D balloon surface, of course, has an inside and an outside. But, imagine that the inside and outside simply do not exist and that only the surface exists.

2) You have to imagine an additional physical dimension - in this case the 3D surface of a 4D balloon. In this case, as above, the 3D "surface" is all there is: again the space you may imagine inside and outside the 3D surface simply does not exist.

Note that all the models you have seen that use 2D shapes for the universe do so because this is easier to draw. Not because the universe is really 2D! (Although, recently we had someone on here who would not accept this and insisted that all the 2D models of the universe were that way because the universe really is 2D! That was a puzzle that he never solved.)

3. Dec 6, 2017

### phinds

I recommend the link in my signature

4. Dec 6, 2017

### PeroK

Having just read it, I recommend it too!

5. Dec 6, 2017

### Souhardya Nandi

As a beginner here, I dont really know how to access the signature of someone. Can you plz guide me ?

6. Dec 6, 2017

7. Dec 6, 2017

### phinds

You click on the link in the signature

8. Dec 7, 2017

### Comeback City

I agree, read it @Souhardya Nandi

9. Dec 7, 2017

### Mordred

@ Phinds Evidentally I need to replace the hyperlink to your balloon analogy on my web page lol

10. Dec 7, 2017

### phinds

You mean because I move the body to the Insights article?

11. Dec 7, 2017

### Mordred

lol yeah several of your other links I already have on my page. I always found your balloon analogy coverage well done. I've seen it have good success with numerous posters over the years.

I also usually combine it with Bapowell's article the combo seems to work well