Thoughts on our small and young universe



When I was age 7 someone gave me a pop-up book about the Apollo astronauts, including a little paper space capsule that swung over a fold via a wire when I opened to page 10, and I fell in love with astronomy. Sadly, astrophysics didn’t stick, but today I often read books on the universe … which usually start off with its immense scale. What bothers me is the universe is actually very young, and small, if you think about it.

First, consider our sun — it’s only 4.6 billion years old, about age 40 in human terms on its way to 13 billion years of burning before death. We’re lucky as humans that our sun is in its stable middle period, for in about 1 billion years it will grow 10% hotter as the helium accumulates in its core causing hydrogen to burn faster, and we’ll then be fried off planet Earth unless we try something radical like pushing asteroids past us in near collision for gravitational boosts to shift the Earth’s orbit outward or, led by Elon Musk, abandon mothership for a terraformed Mars.

Still, our sun is only 4.6 billion years old — and our entire universe is only 13 billion years old. Which means our sun is just one-third as old as the universe.

This simple fact, once discovered, bends the mind. We are circling around a star that was created only two-thirds of the way into the entire age of the universe. About one preceding entire star’s lifetime in. This is akin to being 32 years old and learning your father was Adam, the first human being who ever lived. And because our carbon-based life-forms are based on the explosive degeneration of a preceding star (because complex elements are only created when a star spits them forth from its own dying lifespan), we are the first generation of life species who ever could have existed in the universe. Complex carbon molecules which hook other atoms were created when a preceding star blew up, and there was only one star generation before us.

We, as life, are so young.

And what about the universe’s scale?

Putting timelines aside, the universe itself isn’t that big, when viewed in perspective. First, let’s pick up a yardstick. The speed of light is 670,616,629 miles per hour, or in human terms, just over 1 million times the top speed of a Boeing 747 jet. Light does have a speed limit, so the size of the universe is usually measured in “light years,” or the distance a photon of light can fly through space in 365.24 days. It takes 8 minutes and 19 seconds for light beamed from our sun to reach Earth. Alpha Centauri, the nearest star to our system, is 4.3 light years away. This is hard to fathom, but if one year has 525,949 minutes, Alpha Centauri is about 272,000 times further away than the distance of the Earth to the sun. If we look at Alpha Centauri compared to the width of our local solar system, about the loop of Pluto, it’s only 6,800 times that width away.

The nearest star is closer than you think — in simple terms, if Pluto-to-sun were an inch, the closest star is only 1/10 mile away.

If we pan out, the greater universe is small, too, if we imagine ourselves a giant striding amongst the stars. Our galaxy is no more than 120,000 light years across, or 28,000 times the distance from our system to Alpha Centauri. If the road from Earth to the closest star were 1 inch, the width of our galaxy would be less than half a mile.

And how far apart are galaxies? The distance between galaxies is only about 20 galaxy-widths apart. If you drove across our Milky Way in a Star Trek car that measured a half mile, it would be only another 10 miles to get to the nearest other galaxy.

Yes, the entire universe is huge. The entire “observable” universe, the parts in which light can reach us, is about 93 billion light years wide, which sounds enormous until you consider if you lined up 10 galaxies in a row, each 20 galaxy-widths apart from its neighbor, the universe is about … 3,900 10-galaxy clusters wide. That 3,900 times a local star-cluster group is a big number, but not one impossible to fathom.

If a local cluster of galaxies were an inch, the entire observable universe is 325 feet across — about the length of a football field.

And that’s all the universe we can see.

Of course, there are parts of our universe that are accelerating so far, so fast away from us, due to the flying shrapnel of the Big Bang and the apparent acceleration of this expansion due to “dark energy,” that the universe may be wider than we’ll ever measure. On the distant outskirts of the real universe, stretching way from us rapidly as space itself expands, a beam of light sent to us will never reach us, because the space stretching in-between that galaxy and ours is “moving” faster than the light can overcome. (Einstein allowed for this in his theories, oh yes he did.) Let’s hazard a guess and assume the entire universe is 10 times as big as what we can see from the light reaching our telescopes. So all of reality is 39,000 times as wide as a nearby lineup of 10 galaxies with some space between, in which one, the Milky Way, we reside on a happy blue planet orbiting a mid-life star the son of another star formed in the birth of the entire universe.

It’s all so young, and so small. When put into perspective, our universe isn’t even a teenager yet.

Posted by Ben Kunz

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