Partly Paradoxes, Part 3

Let’s continue our whirlwind tour of Cracked’s roundup of 20 Paradoxes Most Human Minds Can’t Wrap Themselves Around.  If you haven’t already read them, you might want to check out Part 1 and Part 2.

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Universally Self-Centered

Center of the Universe

Oh, but it is you.  And it’s me.  And it’s everybody else.  We’re all the centers of our own Universes. And I don’t mean that in some sort of philosophical or self-help way; I quite literally mean that you are the unique center of a unique observable Universe.  Go you.

This bears explaining, and the explanation can get a bit lengthy.  But hey, the Universe has been around for 13.8 billion years; surely we can spare a few moments to talk about how it works.

The Universe is expanding, which means that distant galaxies are getting more distant by the second.  Now obviously we don’t have a tape measure zillions of kilometers long, so how do we know this?  We know because the light from distant galaxies looks redder than the light from nearby galaxies.

If you carefully study the light from an object you can tell a lot about what it’s made of, without ever having the visit the object directly.  The process is called spectroscopy.  Spectroscopy tells us that the Sun is made mostly of hydrogen and helium, because sunlight contains the characteristic spectral lines of those two elements.  In fact, this is true of all stars, big or small, near or far.  Stars across the Universe seem to be largely made of the same two elements.  This fact can be a useful tool in determining if those stars are moving toward or away from Earth, and how fast.  Why?

If a star is moving toward or away from Earth, we see the familiar spectral lines of H and He in its starlight, but they seem to be slightly out of place.  This is because of the Doppler effect.  If you’ve ever heard the whistle of a train change pitch as the train rushes past you, you’re already familiar with the Doppler effect.  The Doppler effect works with light as well as with sound.  When a star is moving toward Earth, its spectral lines are shifted toward the blue end of the visible spectrum.  We call this phenomenon blue-shifting.  When a star is moving away from Earth, its spectral lines are red-shifted.  The faster the star moves, the more blue- or red-shifted its spectral lines become.  Scientists can determine not only which direction a star is moving, but how fast, by analyzing the light that reaches Earth.

All starlight shows the same set of spectral lines, but the light from receding stars is redshifted. Source:

All starlight shows the same set of spectral lines, but the light from receding stars is red-shifted. Source:

Distant galaxies are made of stars, just like our galaxy is, and those stars are made of hydrogen and helium.  We see the same spectral lines in the light from distant galaxies that we see in light from relatively nearby stars, but the light from distant galaxies is all red-shifted.  This lets scientists know that all distant galaxies are moving away from Earth.  Also, the further away a galaxy is, the faster it recedes from our location.  For example, a galaxy that is 1 billion light years away from Earth is moving away at about 21,600 kilometers per second, while a galaxy that is 2 billion light years away recedes twice as fast.  Scientists have reached the conclusion that space itself must be expanding.  That’s kind of a weird concept; when we think of space, we may think of empty nothingness.  But space is a thing; it’s the fabric in which all matter and energy is embedded.  And this thing – this space – is constantly expanding, creating new space between us and distant galaxies.  The further away a galaxy is, the more space there is between us and it, and the faster new space is being formed.  That’s why the most distant galaxies are receding faster than those that are closer to us.

The farther away a galaxy is, the more redshifted it is, and the faster it is receding from us. The redness of distant galaxies has been exaggerated in this diagram. Not to scale.

The farther away a galaxy is, the more redshifted it is, and the faster it is receding from us. The redness of distant galaxies has been exaggerated in this diagram. Not to scale.

The expansion of space seems to be uniform in all directions, which has an interesting consequence: no matter where you go in the Universe, you are at the “center” of expansion.  If you teleport to the most distant galaxy ever seen, you won’t find yourself on the outside of a bubble of expanding space; no, it will still seem as if you are in the center of it all.  The Observable Universe – that volume of space whose light has had sufficient time to reach us since the Universe started – is always centered on the observer.  Your Observable Universe is different from mine, and it always will be.

So in a way, you could claim that you are the center of the Universe – the Observable Universe, anyway.  Of course, I am too, and so is everybody else.  Each person has their own Observable Universe that carves out a unique volume of space that is not observable to anybody else.  Granted, compared to the scale of the Universe, we’re very close to every other person on Earth, and in the grand scheme, our multiple Observable Universes are functionally identical.  But if you like to split hairs (and you know I do), you are the center of a unique Observable Universe.  Congratulations!

But wait…there’s more.  No really, there’s probably a lot more Universe beyond what we can see.  The results of the WMAP experiment strongly suggest that there may be infinitely more.  If the Universe at large is infinite in extent, then it has no true center, and it never has.

So either way you look at it, this meme is wrong.  If you consider only the Observable Universe (which you may as well do, since that’s the only part of the Universe we’ll ever know anything about), then you are the center.  You always have been, and you always will be.  It doesn’t matter where you go or what you do; as long as you are an observer of the Universe, then you are its center.  It is worth pointing out, though, that you are only the center of your own Universe.  You are not the center of other peoples’ Universes, which might have been a better way for this meme to state its point.

If you consider the Universe at large, then this meme is also wrong, because there is no center, and scientists will never discover one.  Q.E.D.