# The Scale (and Limits) of the Universe!

“The chess-board is the world, the pieces are the phenomena of the universe, the rules of the game are what we call the laws of Nature. The player on the other side is hidden from us.” –T. H. Huxley

There’s an amazing interactive application on the Scale of the Universe that was just pointed out to me (thanks, Brian L.), and I had to share! So go play with it (again, link here), and let’s talk about it.

You are here, of course. A human being is somewhere between 1 and 10 meters, to be rough. Being able to zoom from scales as small as the Planck Scale (~10-35 meters) all the way up to the size of the observable Universe (1027 meters) is kind of mind boggling, so let’s put it into some perspective for you. With pictures, of course.

So here’s a human, and a (perhaps more typical) example of a giant earthworm. These are scales we’re comfortable with — around a meter or so — and we consider something quite small if it’s maybe a few centimeters (or inches), and something quite large if it’s maybe 30 to 100 meters (or yards) big.

But we don’t have time to step up or down by just one or two factors of ten, or we’ll be here all day. Let’s go all the way up by around a factor of a million in length, from a human to an entire planet!

The continental United States, the Moon, the Earth, Mars, and Venus, to name a few, are all about a factor of a million larger in length than a human is, with a size (or radius, where appropriate) measured in thousands of kilometers rather than in meters.

Think, for a moment, about how small you are compared to the planet.

Now, that’s the rough size of the steps we’re going to be taking. So the size of you compared to the Earth is about the same as the Earth compared to…

the largest stars ever discovered! These are stars the size of the entire Solar System (out past Pluto!), a million times the radius of Earth and more than a thousand times as large as the Sun!

And yet, they’re still just one single star. But we can step up by about another factor of a million from these incredible, massive, gigantic Suns. Another factor of a million, larger than these hypergiant stars is…

a large globular cluster! These collections of hundreds of thousands to millions of stars span about a hundred light years across! These are the smallest “isolated” objects found in the Universe, and — like M62 below — they normally cluster around galaxies.

Remember how large this is! You compared to the Earth is the same size difference as the Earth compared to either the largest star in the Universe or the entire Solar System, is the same difference as that hypergiant star compared to this globular cluster. And to scale up again, this globular cluster — zooming out by a factor close to a million — is to…

A huge supercluster of galaxies! That’s right, bypassing dwarf galaxies, regular galaxies, giant galaxies, the largest galaxy in the Universe, and normal clusters of galaxies, we have gigantic superclusters — containing tens of thousands of galaxies — that span tens of millions of light years from end-to-end.

And I’d love to scale up by another factor of a million or so, but I can’t. Why not?

Because I run out of Universe.

Contrary to what the website tells you, when the observable Universe ends, so does our definitive knowledge. If the laws of physics are, indeed, the same outside of our observable Universe as they are inside, then we can conclude that the “actual” Universe is at least 150 times as large as the observable part, much bigger than that site claims. In fact, if inflation — as we understand it — is true, it’s quite likely that the Universe is many trillions of times larger than our paltry observable part.

But at the very least, we can place a lower limit on the size of the Universe based on what we see. And, suffice to say, it’s huge.

But what, now, if we went the other way? From humans, instead of larger scales, what if we put away our telescope and broke out our microscopes? What would we see?

Well, going down to the scale of maybe ten microns, we bypass things like pollen spores, dust mites, and the paramecium, and come all the way down to individual blood cells. Tiny, tiny things. A single blood cell compared to you is slightly larger than you compared to the Earth.

And remember, your lone body contains somewhere around 40 billion blood cells at any given time. And if I went down by another factor of a million from here, I’ll pass by everything interesting. All the most primitive cells, the tiniest virus, a single strand of DNA, a single molecule, everything. A blood cell to a human is the same scale as…

the smallest single atom in the Universe, hydrogen, is to a single cell. Hydrogen, the simplest atom out there, with just one proton and one electron.

And yet, I can go smaller still. Another factor of a million takes me inside the atom’s nucleus, inside a single proton, down to the smallest subatomic constituents I know of.

Kind of. These fundamental constituents of matter — as far as we can tell — aren’t 10-18 meters in size. They’re constrained, by our strongest particle accelerators, to be less than 10-18 meters in size!

In other words, all the sizes less than or equal to 10-18 meters are upper limits! While the interactive demonstration will take you smaller and smaller, and will show you (possibly fictional) particles like preons and strings, this brings us to the particle physicist’s nightmare. What if all of these subatomic particles: quarks, gluons, electrons, neutrinos, etc., are really, really tiny?

What if they go all the way down to the Planck scale, for example?

It would mean that — other than the Higgs — there are no new particles to find by building accelerators. (Not, at least, until we build an accelerator larger than the Solar System.)

And that’s the Universe we know, from the largest to the smallest, as we run up against the limits! What lies beyond? Well, like Huxley said, the other side — at least for the time being — is hidden from us.

Hope this takes you into a great weekend!