This Week's Amazing Sky: What Is the Universe Expanding Into?

Jan 29, 2016


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What Is the Universe Expanding Into?” A reader recently asked that question. So here's the inside scoop.

But first, what exactly is expanding?

  • Not our solar system with its planets orbiting the sun
  • Not our Milky Way galaxy of 400 billion stars. It never gets any bigger.
  • Not the galaxies right around us. Indeed, the nearest spiral, Andromeda, is approaching us at 70 miles per second and will someday harmlessly collide with us!

In fact, nothing the naked eye can see, even on the clearest night in the country, is expanding. In our own galaxy, stars do have small random motions, but just as many approach us as are flying away.

So what's expanding?

It's the empty space between galaxy clusters. That's the only thing that grows larger. That's the whole story.

Therefore, no matter where in the cosmos you lived, you'd see other galaxy clusters increasing their distance from your own. This is the simple truth and we can all picture it.

The problem arises when we try to visualize the entire universe as if it were an inflating balloon that we're observing as if we are outside it. There is no “outside” to the universe. So that perspective is non-existent. Our headline question may seem meaningful, but it isn't, and therefore no answer can make sense.

You can be outside a galaxy such as this one, but you can never be outside the universe to look back at it.

Do you still find this limitation frustrating? You're not alone. That's because the cosmos taken as-a-whole does not play by the same logical rules we've devised to help us understand its parts.

About This Blog

Welcome to “This Week’s Amazing Sky,” the Almanac’s blog on stargazing and astronomy. Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, he covers everything under the Sun (and Moon)! Bob, the world’s mostly widely read astronomer, also has a new weekly podcast, Astounding Universe

Reader Comments

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Lee, the idea of space

Bob Berman's picture

Lee, the idea of space expanding is indeed weird. It seems caused by "dark energy" but that's a term attached to a total mystery. As for telescopes, glad you have a 10-incher. What's in the photo is my old C-5 that I sometimes use when I need portability. My main observatory instruments, pier-mounted, are a research grade f/6 refractor, with a Takahashi 5-inch refractor mounted piggyback. About 130 pounds to drive, with another 130 pounds of counterweights! Love talking shop!

I don't know how much of this

I don't know how much of this is exactly true. The possibility of a point of perspective outside of the universe is there, it just requires the existence of at least one more universe and a perceptual bridge between them. Just because we view space from the inside doesn't mean an outside view doesn't exist, at least in theory. There are certainly higher orders of spacial dimensions. There's no reason to think that the totality of the bubble of space-time that we float around in, couldn't also be floating around in a fourth(or fifth, or higher)-dimensional hyper-space ether.

We don't have to throw out the baby with the bath water on the concept of an ether in order to accept Einstein's relativity.

I prefer Nikola Tesla's

I prefer Nikola Tesla's explanation better than Einstein's on the curvature of space anyway.

It depends on definitions. If

Bob Berman's picture

It depends on definitions. If the universe is defined as "everything" then you can never go outside of it, can you? So any imagined view from out there becomes an imaginary question....

Is the galaxy expanding- is

Is the galaxy expanding- is our galaxy and another we are comparing this thought to moving away from each other? Or is our galaxy moving through space away from others or are they moving away from us? :) fun as it is to speculate and generate "thinking outside the box", I sure wish there was more of a foundation of truth shown to us. Rather than to just take someone's word for it, whether or not they believe they are telling the truth because someone else informed them of thinking this certain way, it'd just be comforting to believe everyone had our best interests lined up within the truth. :)

What's happening is that

Bob Berman's picture

What's happening is that within each galaxy cluster, there's no expansion. In our own (called the "local group") the biggest galaxy is actually approaching our own Milky Way. But the space between clusters is growing larger. You can count on this much to be totally true.

I am an amateur astronomer

I am an amateur astronomer and wonder about the expansion of space as a quality of space itself. If it was simply emptiness, it obviously could not have this property of elasticity. However, one of Einstein's great proofs was the non-existance of the ether, an assumption that space had to be filled by something. Whatever the space is between all the really big stuff, isnt an elastic space a throwback to the discarded concept of the ether?

The other question I have is the photo of you on this website.
What kind of telescope is that, and what is piggybacked on the right side. I own a 10 " SCT and it looks about the same size.


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