# Distance analogy - am I being accurate?

## Main Question or Discussion Point

Hi guys,

I am giving a schools talk and would like your opinion on whether or not you think the following reasoning is accurate and roughly scientific.

Lets we assume that on average there is only one hydrogen atom per cubic metre on average in the universe. The diameter of a hydrogen atom is 1.7e-15m.

Scaling up to the size of a human, can I say that the distance between hydrogen atoms in the universe is equivalent to:

0.3 (diameter of a small human) / 1.7e-15 = 1.76e14 m = 1100 AU

So the distance between hydrogen atoms in the universe is roughly equivalent to one of the kids standing the classroom and another kid standing 1000 times further away than we are to the sun (or if you can think of a better landmark to use I'd appreciate it! Mine is quite clumsy)

Does that logic hold, or is it outright wrong?

Thanks,

Leo

Related Astronomy and Astrophysics News on Phys.org
Staff Emeritus
2019 Award
The diameter of a hydrogen atom is 1.7e-15m.
That's not right. More like an angstrom.

That's not right. More like an angstrom.
Wikipedia says 2.4 A, so I'm wrong either way. But aside from that - can I use this as a useful analogy?

Nabeshin
I think what you used for diameter of the hydrogen atom is more like diameter of a proton.

The analogy makes sense, but I'm not sure how useful it is. These kind of analogies can be helpful because they put astronomically small or large numbers in some type of context humans have experience with. Even after your scaling, your factor is still 1100AU, which no child (or person, for that matter) has an intuitive grasp of.

Try using something smaller, like a pea or a grain of salt. Maybe then you'll get a distance comparable to that between cities or something. That would greatly increase the usefulness, in my opinion.

Even after your scaling, your factor is still 1100AU, which no child (or person, for that matter) has an intuitive grasp of.

Try using something smaller, like a pea or a grain of salt. Maybe then you'll get a distance comparable to that between cities or something. That would greatly increase the usefulness, in my opinion.
I think you have a very good point - there's no point taking an ungraspable analogy and replacing it with another one! I'll see what numbers come out of smaller things like a pea.