“The slow philosophy is not about doing everything in tortoise mode. It’s less about the speed and more about investing the right amount of time and attention in the problem so you solve it.” -Carl Honore

Most likely, as you’re reading this right now, you’re sitting down, perceiving yourself as stationary. Yet we know — at a cosmic level — we’re not so stationary after all. For one, the Earth rotates on its axis, hurtling us through space at nearly 1700 km/hr for someone on the equator.

That’s not really all that fast, if we switch to thinking about it in terms of kilometers per second instead. The Earth spinning on its axis gives us a speed of just 0.5 km/s, hardly a blip on our radar when you compare it to all our other motions.

The Earth, you see, much like all the planets in our Solar System, orbits the Sun at a much speedier clip. In order to keep us in our stable orbit where we are, we need to move at right around 30 km/s. The inner planets — Mercury and Venus — move faster, while the outer worlds like Mars (and beyond) move slower than this.

Image credit: NASA / JPL, retrieved fromhttp://www.dailymail.co.uk/sciencetech/article-2454094/Could-life-Earth-end-March-16-2880-Scientists-predict-giant-asteroid-collide-planet-38-000-miles-hour.html.

But even the Sun itself isn’t stationary. Our Milky Way galaxy is huge, massive, and most importantly, is in motion. All the stars, planets, gas clouds, dust grains, black holes, dark matter and more move around inside of it, contributing to and affected by its net gravity.

From our vantage point, some 25,000 light years from the galactic center, the Sun speeds around in an ellipse, making a complete revolution once every 220–250 million years or so. It’s estimated that our Sun’s speed is around 200–220 km/s along this journey, which is quite a large number compared to not only our rotational speed of Earth but of our planet’s revolution around the Sun.

Nevertheless, we can put all these motions together, and find out what our motion through the galaxy is.

Image credit: Rhys Taylor of http://www.rhysy.net/, via his blog at http://astrorhysy.blogspot.co.uk/2013/12/and-yet-it-moves-but-not-like-that.html.

But is the galaxy itself stationary? Most certainly not! In space, you see, there’s the gravitation of every other massive (and energetic) object to contend with, and gravitation causes any masses around to accelerate.

Give our Universe enough time — and we’ve had some 13.8 billion years of that — and everything will move, drift and flow in the direction of the greatest gravitational attraction. That’s how we go from a mostly uniform Universe to a clumpy, clustered, galaxy-rich Universe in relatively short order.

So what does that mean out near us?

It means our Milky Way is being pulled by all the other galaxies, groups and clusters in our vicinity. It means that the closest, most massive objects around are going to be the ones that dominate our motion. And it means that not only our galaxy, but all the nearby galaxies are going to experience a “bulk flow” due to this gravitational force. Recently, this has been mapped to the greatest precision ever, and we’re continually coming closer to understanding our cosmic motion through space.

But until we fully understand everything in the Universe that affects us, including:

the full suite of initial conditions under which the Universe was born,

how each individual mass moved and evolved over time,

how the Milky Way and all the associated galaxies, groups and clusters formed, and

how that happened at every point in cosmic history up through the present,

we won’t be able to truly understand our cosmic motion.

At least, not without this one trick.

Image credit: NASA / WMAP science team.

You see, everywhere we look in space, we see this: the 2.725 K radiation background that’s left over from the Big Bang. There are tiny, tiny imperfections in various regions — on the order of just a hundred microkelvin or so — but everywhere we look (except in the polluted plane of the galaxy), we see that same temperature: 2.725 K.

This comes about because the Big Bang happened everywhere at once in space, 13.8 billion years ago, and the Universe has been expanding and cooling ever since.

Image credit: NASA, ESA, and A. Feild (STScI), via http://www.spacetelescope.org/images/heic0805c/.

This means that in all directions that we look in space, we should see that same “leftover radiation” where neutral atoms formed for the first time. Prior to that time, some 380,000 years after the Big Bang, it was too hot to form them, as photon collisions would immediately blast them apart, ionizing their components. But as the Universe expanded and the light redshifted (and lost energy), it eventually became cool enough to form these atoms after all.