# 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][1] that was just pointed out to me (thanks, Brian L.), and I had to share! So go play with it (again, link [here][1]), and let’s talk about it.

[![scale10+1.jpg][2]][3]

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.

[![Microchaetus rappi.jpeg][4]][5]

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**!

[![scale10+6.jpg][6]][7]

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.

[![File:The Earth seen from Apollo 17.jpeg][8]][9]

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…

[![scale10+12.jpg][10]][11]

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!

[![canis.jpeg][12]][13]

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…

[![scale10+18.jpg][14]][15]

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.

[![m62large.jpeg][16]][17]

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…

[![scale10+23.jpg][18]][19]

A huge supercluster of galaxies! That’s right, bypassing dwarf galaxies, regular galaxies, giant galaxies, the [largest galaxy][20] 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.

[![abell_902902_supercluster_dark_matter_map.jpeg][21]][22]

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**.

[![scale10+26.jpg][23]][24]

Contrary to what the [website][1] 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 _micro_scopes? What would we see?

[![scale10-5.jpg][25]][26]

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.

[![white-blood-cell-amungst-red.jpeg][27]][28]

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…

[![scale10-11.jpg][29]][30]

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.

![][31]

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.

[![scale10-18.jpg][32]][33]

_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!

[![lhc-sim.jpeg][34]][35]

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?

[![scale10-35.jpg][36]][37]

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!