How big is the universe?

The universe as we know it in space and time began about 13.7 billion years ago.  That’s a very very long time, but at least it’s a compact number that, with a little effort, most of us can at least remember.

How big is the universe is a much more challenging concept to get our human minds around.  The numbers are mind-boggling.  And to make matters even trickier, the universe is still getting bigger.

Space in the universe is measured in light years because scientists are pretty sure that nothing can travel faster than light can.  To us that is very very fast.  Here are some examples, all of which are so far beyond human experience that some people are reduced to laughter when they try to grasp the concept.

In a second, light travels:

  • almost 300 million meters (a meter is 40 inches, so just a little more than a yard),
  • which is equal to 186,282 miles
  • which is equal to  299,792 kilometers

Light travels from

  • the moon in 1.3 seconds
  • the sun in 8.3 minutes
  • across the Milky Way in 100,000 years
  • from the Andromeda Galaxy to Earth in 2.5 million years.

Light that first appeared after the Big Bang 13.7 billion years ago has not yet reached us.

It’s a very big place we live in.

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About Terry Sissons

Terry Sissons is the author of The Big Bang to Now: All of Time in Six Chunks, and this blog is a dialogue about the universe and what’s happened in the last 13 billions years.
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6 Responses to How big is the universe?

  1. I absolutely love your blog and find nearly all of your post’s to be just what I’m looking for. Does one offer guest writers to write content in your case? I wouldn’t mind composing a post or elaborating on a number of the subjects you write concerning here. Again, awesome weblog!

  2. What I don’t understand is why we are so far away from that light that hasn’t yet reached us. If everything started out as a speck and then exploded into a universe, why wouldn’t light have kept up with the expanding stuff of that universe–especially if nothing can travel faster than light.

    -Perplexed in Brooklyn

    • The answer that I have always more or less assumed is that what has arrived up to now as far as our patch in the universe did not develop at the instant of the Big Bang. Light, itself, did not emerge for 300,000 years.

      But when you put the question the way you have, it’s obvious that there’s something pretty basic I don’t understand either.

      Hmmm: I wonder if I need a Ph.D. in physics to understand this, or is it one of those things that bright 13-year-olds understand these days. I will have to do some more reading.

      Perplexed in Cambridge.

      • Ray voith says:

        How do we know that ( light emerged only after 300,000 yrs)? If light only emerged 300,000 yrs after the Big Bang, we could never see anything that happened in those first 300,000 yrs. There would have been nothing to see.

      • Although many people might not appreciate it, this is an extremely important question. A complete answer involves what would probably amount to an entire book on the nature of science, but here is a short preview. First of all, we live every day knowing about things that happen that we can’t see. We can’t see the wind, for instance, but we know the effect that the wind has, and when we look out the window and see things moving, although we can’t see anything pushing them and our experience tells us they can’t push themselves, we reach the conclusion that those bending trees and scattering leaves are due to the wind.

        That’s basically how science works too. We can’t see all sorts of things, but we reach the conclusion that they are there because when we apply our theory about how they work, we reach a conclusion about what is there. We can’t see the sun when it’s night, but our theory tells us the earth goes around the sun and so almost everybody on earth today believes the sun is still there, even if we can’t see it. We can’t see atoms because they are too small for the human eye ever to see, but our theories about atoms and how they work explains so many things that we do see that again, almost everybody believes that the existence of atoms has been proved scientifically.

        And that’s how it is with what scientists think happened after the Big Bang. You are right – we can’t see what happened. But scientists do know a lot of the laws of physics, and they can see the world as it exists today. What they do is apply the laws of physics to explain how a huge explosion of energy can possibly have evolved into what we have today.

        Having said that, the questions we still have a huge, and we aren’t 100% positive that our theories are right. It’s possible, actually, the our universe didn’t even begin with a Big Bang. But right now, it’s the theory that most scientists think explains the best how we got to be where we are today.

        I hope this helps answer your question. But please write again if you think I haven’t answered your question. As I say, it’s a very important question and worth thinking hard about.

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