Posted on 12/31/2015 6:56:29 PM PST by LibWhacker
Another year passes. Another 365 planetary spins completed (14.6 million kilometers of combined distance traveled if you live at the Earth's equator), and another journey of 940 million kilometers around the Sun. Time is marked off for us by a largely predictable, if not tedious, set of cycles.
Except, this is by no means all the cosmic traveling we've done in the last 31.5 million seconds.
For one thing, the solar system is not at rest with respect to its host galaxy. The Sun and its planetary entourage are moving in an orbital path within the Milky Way. The generally quoted properties of this motion are that we're heading around the galactic center at about 220 kilometers a second, but with an additional 'bobbing', or sinusoidal, motion perpendicular to this. In other words the solar system is meandering up and down 'through' the plane of the galaxy, while making a full circuit roughly every 220 to 250 million years.
The solar system's up and down galactic path has intrigued scientists for a long time because it may have a period of anywhere from about 20 to 60 million years. This period is on a par with various claims for distinctly spaced extinction events on the Earth, or episodes of enhanced comet and asteroid bombardment.
But the truth is that - as is so often the case - the jury is still firmly out on whether there's a connection between our passage through the galactic plane and what has happened here on Earth. In fact we really don't even know what the precise up and down motion of our solar system has been during the past 4 billion years. The Milky Way is not a simple, smooth, distribution of mass. It has lumps, and there are other stellar objects buzzing around, so we don't yet have good enough models to pin down our past galactic trajectory with any real accuracy - despite what anyone says.
Stepping a little further out in scale; the Milky Way and the Andromeda galaxy are falling towards each other at roughly 110 kilometers a second, from about 2.5 million light years away. So in the past year we've got about 3.5 billion kilometers closer to a likely galactic collision in about 4 billion years time. In the meantime, around us, the other 54 or more galaxies of our Local Group have continued to hang together as a gravitationally bound system, resisting the undercurrent of cosmic expansion.
But these are all parochial motions, the kind of to-ing and fro-ing that happens in a little village. None of these spins, orbits, circulations, and infalls really get us anywhere in the long term, we're just stewing in our own gravitational pot. What about our journey across a greater cosmic frame?
The snag to evaluating such displacement is that on the biggest scales of an expanding and centerless gulf of spacetime, the concept of absolute motion is not terribly useful. If we're concerned about measuring progress through the universe, what are we actually moving with respect to?
There is one helpful gauge. The universe is filled with radiation, with photons zinging endlessly across space. These come from stars, supernovae, quasars, hot gas cooling down, and many other sources. In particular, at any instant in time, a cubic centimeter of the universe will contain, on average, about 400 cosmic microwave background photons moving in effectively random directions. This ocean of ancient photons can serve to as a tool for sensing our motion. The blue and red Doppler-shifts of the microwave radiation allow us to build a sky map reflecting our passage through space.
Given that we know the Earth's motion around the Sun very well, and the Sun's motion around our Galactic center quite well, and the Milky Way's motion with respect to the other galaxies of our Local Group with some confidence, we can factor those velocities out and deduce the true drift of our intergalactic neighborhood with respect to the cosmic microwave background.
The answer is that our patch of universe, containing the Milky Way, Andromeda, and all the attendant, gravitationally bound galaxies, is moving at about 627 kilometers a second in a direction close to the constellation of Centaurus from our perspective. So in the course of a terrestrial year we make a journey of some 20 billion kilometers 'through' the universe.
Why is this happening? In a nutshell, it's because the distribution of matter in the universe is not actually uniform - at least not on scales of up to at least several hundred million light years. We're surrounded by a vast assortment of further galaxies, galaxy clusters, and superclusters. The direction that our Local Group is moving in is set by the net gravitational pull of all these matter distributions, and that's somewhat imbalanced - so we're falling in a direction along the vector sum of all those pulls.
The precise details of the matter distribution responsible for this - the large-scale cosmic structures - are still unclear, although regions such as the Shapley Supercluster, containing tens of thousands of galaxies, are involved. Chances are that we've not yet surveyed the full distribution of responsible galaxies (and therefore matter). We may need to go some billion light years out to account for all the 'pull' that is acting on our local patch.
Will we ever reach these regions, embracing the cosmic web of irregularity that surrounds us? No, it seems that we will not at our present velocity. The relentless (and accelerating) expansion of the universe will prevent that encounter, eventually isolating our little island.
Indeed, while we can measure that we've traversed 20 billion kilometers of the cosmos in the past year, during that same period any place a hundred million light years away will have further receded from us by some 200 billion kilometers.
This cosmic indifference to any hopes of progress may leave us feeling a little depressed. After another year, another circuit of the Sun, we're back in a place very, very similar to the one we left, and that is how it will continue to be.
Except, the very fact that our minds have figured all of this out, from the spin of the Earth to our modest traversal of an ocean of cosmic photons, is itself remarkable. Whether or not any other sentient beings exist anywhere else in the entire observable universe, here, for a fleeting moment, we can gaze in awe at the cosmos that has allowed our existence. Another 20 billion kilometers through the universe may represent a certain cosmic futility, but at least it is a journey that belongs to us.
Gravitational pot...
Yeah man. I had some of that once
couldn’t move for hours!!!
And then was I Hungry!!!
Fascinating. Thanks for posting. HOORAY Caleb A. Scharf
And what about the local cluster? Well, we’re all being pulled in the direction of what is called the Great Attractor, which I don’t like the sound of.
I’ve traveled a bunch of light years in my 52 years.
Rotation on the surface of the earth, Orbit around the sun, wandering with the solar system, rotation around the galaxy, galactic movement through the universe.
That adds up to a crapload of miles.
We'll have to make the best of things,
It's an uphill climb.
The Earth orbits the Sun at the rate of about 66,000 miles per hour. That’s roughly 18 miles per second.
Are we there yet?
I’m still trying to understand, if we’re ‘physical’,
how can there NOT be an end to the universe
Actually, the idea I liked most about the GA, was that it was a nearby universe dragging us toward it in the multiverse. But this fellow said nothing about that, so that theory must be out of favor nowadays.
Our own galaxy is so big that, even if we could travel at the speed of light (186,000 miles/sec), it would still take us about 100,000 years to go from one end to the other. And there are believed to be galaxies so distant it would take 13 or 14 billion years to get there at that same speed.
Curvature. It’s like an ant living on the surface of a beach ball asking how can there not be an end, or a wall of some kind, marking the end of our “universe?” He can walk forever and never bump into a boundary of any kind. Likewise, we can look out into space and never see an end.
Which as a kid I did and pondered (before the shopping malls obliterated the night skies).
However, the 'ball' as you explain it, still has dimension and dimension has limitations (as do we... supposedly).
What's beyond the ball?
Interesting.
Turtles. It's turtles all the way down.
Sounds like we are on a collision course with Andromeda Galexy and no one is putting on the brakes.
Oh my dear Watson, Then we realize just how powerful our God is. After all, He made this and yet we think that we are Him.
Whenever life gets you down, Mrs.Brown
And things seem hard or tough
And people are stupid, obnoxious or daft
And you feel that you’ve had quite enough
Just remember that you’re standing on a planet that’s evolving
And revolving at nine hundred miles an hour
That’s orbiting at nineteen miles a second, so it’s reckoned
A sun that is the source of all our power
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour
Of the galaxy we call the ‘milky way’
Our galaxy itself contains a hundred billion stars
It’s a hundred thousand light years side to side
It bulges in the middle, sixteen thousand light years thick
But out by us, it’s just three thousand light years wide
We’re thirty thousand light years from galactic central point
We go ‘round every two hundred million years
And our galaxy is only one of millions of billions
In this amazing and expanding universe
The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, the speed of light, you know
Twelve million miles a minute and that’s the fastest speed there is
So remember, when you’re feeling very small and insecure
How amazingly unlikely is your birth
And pray that there’s intelligent life somewhere up in space
‘Cause there’s bugger all down here on Earth
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