Do We Live in a Special Part of the Universe?

Article written: 1 Apr , 2016
Updated: 23 Feb , 2017
by

We’ve already talked about how you’re living at the center of the Universe. Now, I’m not going to say that the whole Universe revolves around you… but we both know it does. So does this mean that there’s something special about where we live? This is a reasonable line of thinking, and it was how modern science got its start. The first astronomers assumed that the Sun, Moon, planets and stars orbited around the Earth. That the Earth was a very special and unique place, distinct from the rest of the Universe. But as astronomers started puzzling out the nature of the laws of physics, they realized that the Earth wasn’t as special as they thought. In fact, the laws of nature that govern the forces on Earth are the same everywhere in the Universe. As Isaac Newton untangled the laws of gravity here on Earth, he realized it must be the same forces that caused the Moon to go around the Earth, and the planets to go around the Sun. That the light from the Sun is the same phenomenon as the light from other stars.

 ESO’s La Silla Observatory in northern Chile. Credit: Iztok Bon?ina / ESO

ESO’s La Silla Observatory in northern Chile. Credit: Iztok Bon?ina / ESO

When astronomers consider the Universe at the largest scales, they assume that it’s homogeneous, and isotropic. Technical words, I know, so here’s what they mean. When astronomers say the Universe is homogeneous, this means that observers in any part of the Universe will see roughly the same view as observers in any other part. There might be local differences, like our mostly harmless planet Earth, orbiting the future course of an interstellar bypass. Or a desert planet with two suns, or a swampy world in the Dagobah system. At the smallest scales, they’ll be different. But as you move to larger and larger scales, it’s all just planets, stars, galaxies, galaxy clusters and black holes. And if you unfocus your eyes, it all looks pretty much the same. Isotropic means that the Universe looks the same in every direction. If you were floating alone in the cosmic void, you could look left, right, up, down out to the edge of the observable Universe and see galaxies, galaxy clusters and eventually the cosmic microwave background radiation in all directions. Every direction looks the same. This is know as the cosmological principle, and it’s one of the foundations of astronomy, because it means that we have a chance at understanding the physical laws of the Universe. If the Universe wasn’t homogeneous and isotropic, then it would mean that the physical laws as we understand them are impossible to comprehend. Just over the cosmological horizon, the force of gravity might act in reverse, the speed of light might be slower than walking speed, and unicorns could be real. That could be true, but we have to assume it’s not. And our current observations, at least to a sphere 13.8 billion light years around us in all directions, confirm this.

The Hubble Telescope's view of Omega Centauri. Credit: NASA / ESA / The Hubble SM4 ERO Team

The Hubble Telescope’s view of Omega Centauri. Credit: NASA / ESA / The Hubble SM4 ERO Team

While we don’t live in a special place in the Universe, we do live in a special time in the Universe. In the distant future, billions or even trillions of years from now, galaxies will be flying away from us so quickly that their light will never reach us. The cosmic background microwave radiation will be redshifted so far that it’s completely undetectable. Future astronomers will have no idea that there was ever a greater cosmology beyond the Milky Way itself. The evidence of the Big Bang and the ongoing expansion of the Universe will be lost forever. If we didn’t happen to live when we do now, within billions of years of the beginning of the Universe, we’d never know the truth. We can’t feel special about our place in the Universe, it’s probably the same wherever you go. But we can feel special about our time in the Universe. Future astronomers will never understand the cosmology and history of the cosmos the way we do now.

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10 Responses

  1. ronfurg says

    Mr. Cain – What would things look like to someone (hypothetical or otherwise) on the outermost edge of the expansion sphere 13.8 Billion light years from us. Perhaps if you can explain it to me I’ll be able to get a better grip on the big cosmological picture. I really do appreciate and comprehend your explanation of our uniqueness due to our position vis-a-vie time. Thanks.

    • Harmonograms says

      @Ronfurg: No matter when or where you are within the universe, you will share a common frame of reference with every other point within the universe and view yourself to be the oldest, the most central and the most distant point from the Big Bang event as each and every other point within the singularity.

      From our unique reference frame, the origin point of the singularity (the big bang event when new spacetime began unfolding within the singularity) is observed to be about 47.5 billion light years away in every direction within our 13.8 billion year-old universe.

      No matter where you are within the singularity, the universe appears the same in every direction.

  2. BlackWolfStanding says

    By definition of the Big Bang, we can’t be in the center of the Universe. But we can be in the center of our sight. And because of our unique perspective, I think we are somewhere between the center of the Universe and near the edge of the Universe. Possibly about mid-way. As we advance we get more details as to our location in the Universe.
    Think about being in a pool of water that is completely flat. Drop one drop of water into it. The way the circle expands represents our universe. Nothing really can exist in the center because the energy is all pouring out. But that front edge that moving away is making a sphere as to the limit of our universe. We are seeing the edge of the Universe from behind and within the universe – the Cosmic Microwave Background. Like water in the pool within the circle, it’s effects can be seen all around us.
    Like the drop in the water, eventually the circle will stop because it’s all out of energy. But our Universe is still expanding and accelerating. So, energy must be leaking into our universe from outside. And this energy must be accelerating the leakage faster into this Universe than it’s expansion to continue the acceleration – dark energy. Dark Matter must come from from the same same leakage. It’s simply matter that spent all of it’s usable energy. On a cosmic scale, this matter can still be attracted and get dense enough to once again have gravity. But the particles themselves cannot interact yet on a local scale, maybe over billions of more years, these particles could be a source for more hydrogen (or hydrogen like substance) to create more stars in the Universe.

    Kind of makes you think if our Universe will ever go completely dark. (or just delay the darkness by a few billion years.

    • Harmonograms says

      @Blackwolfstanding: An important tenet of Big Bang theory is that we are located at the very center of the universe and this perspective is shared by every other point within the universe.

      Consider that the entire universe is wholly contained within an infinitesimally small dimensionless point called a singularity. Within this singularity was a point of infinite energy which began dissolving into static mass and continuously unfolding new time and space which we call the Big Bang event. We still exist within a singularity and we can measure that time and space began unfolding our universe about 13.8 billion years ago*.

      * The main pieces of evidence supporting BB theory are:
      1. New time and space within the universe is observed to be continuously unfolding uniformly in every direction, as demonstrated by observations of the Hubble red shift of distant galaxies.
      2. The uniformity of the CMBR (Cosmic Microwave Background Radiation), with which we can measure the temperature drop from a point source of infinite energy at the BB event.
      3. The abundance of different elements within the universe, which take time to produce through stellar evolution which is very well understood, is observed to be comprised of a younger elemental composition in every direction as we view deeper into the universe.

  3. Random Sample says

    You know, we consider most of this common knowledge. However, one day, about 14 years ago, I was talking about a shuttle mission that was underway, and one of the people I was talking to was my secretary. She was a fairly bright young woman, and an excellent secretary. She had a little frown on her face, and I asked her what she was thinking. She asked me “Wouldn’t it bump into the stars?” I couldn’t help laughing, but it quickly became apparent that she was quite serious. I started trying to explain why this was impossible, and then it hit me. I stopped talking, and then just asked “You know that stars are suns, right?” She looked at me with this “Mind – Blown!” look.

    She was embarrassed about the whole thing, so I never followed up to find out more about the reason she did not know this incredibly basic information. She was something of a religious fanatic, so she may have been home-schooled, but she did attend college for several semesters, and it was my understanding that she dropped out for financial reasons, not because she couldn’t do the coursework. This does highlight, however, that our educational system in the U.S. can fail to assure that people have even the most basic of a science education, and that this is something we all need to make sure is improved.

    • Eric Jackson says

      Random Sample, you hit the nail on the head about the state of our public schools and its ability to teach even the most basic of scientific principals to our children. As a father of three boys, I spend time teaching as much as I understand and if I don’t, I bring them to this site or others that continue to breakdown scientific theory from fact.

  4. fred says

    I had a similar experience during a stargazing event. A woman in the crowd was so mesmerized to see the stars through binoculars that she wondered out aloud:
    “What are the stars? Why are they so many different colors? Aren’t they just reflecting the sunlight?”.
    It elicited a round of laughter and once someone explained it to her she was embarrassed. Who knows what her background must have been.

  5. Pasander says

    I have been wondering why exactly everything stays the same over vast distances and time. Is it:

    -some kind of “inertia” in space itself
    -a kind of “dynamic stability”, that is, things being in “lowest energy state”, so they tend to keep that way
    -some kind of superluminal affect
    -a small extra spatial dimension (or several) so that points in space are actually much closer than they seem to us
    -some combination or variation of above
    -something completely different

    So, in short, why doesn’t the space “fall apart”, forming regions where forces and constants begin to drift from region to region? What is keeping things so similar all over the universe?

  6. dackwasseri says

    “In the distant future, billions or even trillions of years from now, galaxies will be flying away from us so quickly that their light will never reach us. The cosmic background microwave radiation will be redshifted so far that it’s completely undetectable. Future astronomers will have no idea that there was ever a greater cosmology beyond the Milky Way itself. The evidence of the Big Bang and the ongoing expansion of the Universe will be lost forever.”

    I wonder… After 13.8 billion years, what information about the universe is already lost to us

  7. chfosmith says

    A small point here.
    If you accept that the future rate of expansion can exceed the speed of light, then this universe will end through “wink out”.
    This is caused because spacetime requires a minimum density of matter to exist.
    Under run away expansion, this limit is reached, spacetime collapses, and this universe just ceases to exist.

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