Monthly Archives: February 2011

Scale of the universe

Hubble Ultradeep Field

Hubble Ultra Deep Field

Until 500 years ago the premise of an Earth-centric solar system and universe prevailed. And until 100 years ago it was thought that we lived within the confines of a single galaxy, our Milky Way. But in 1915 Albert Einstein introduced general relativity, the highly successful theory of gravity which couples mass, energy and the geometry of space-time. In the 1920s Alexander Friedmann and Georges Lemaitre introduced solutions to the equations of general relativity for an expanding universe. Lemaitre’s work indicated distant galaxies would have their light shifted to be redder than that of nearby galaxies. And by 1929 this was observed by Edwin Hubble. Now with the Hubble Space Telescope we can observe galaxies at much greater distances than Hubble could over 80 years ago. The image above is a very long exposure from the Hubble Space Telescope revealing close to 10,000 galaxies; many of these are billions of light-years away.

Hubble essentially measured the rate of expansion of the universe at the present epoch. The universe is expanding and galaxies are generally receding from one another except when they are gravitationally bound to their near neighbors. The value for the rate of expansion has been refined over the intervening years but is now accurately measured and indicates an age of just under 14 billion years for our universe.

The size of the universe as a whole we are unable to measure! We are limited by our own horizon, due to the finite speed of light. Only galaxies apparently moving away from us at less than the speed of light are within our horizon (also known as light cone). General relativity allows for space itself to stretch at faster than the speed of light if the separations between two galaxies are large enough; objects do not travel faster than light speed within their own local frame.

Our own observable portion of the universe has a lookback time distance of 14 billion light-years and what is known as the comoving distance of nearly 50 billion light-years. The comoving distance takes into account the expansion of the universe as the light moves through it from the Big Bang until now.

Note from the table below how much larger the universe is than the distance to the center of our galaxy or to the nearest star.

Object                    Distance (light travel time)

Nearest Star                        4.2 years
Center of Milky Way         25,000 years
Andromeda Galaxy           2.5 million years
Oldest Galaxies                  13 billion years
Big Bang                              13.8 billion years


Herschel infrared telescope studies Dark Matter

The space-borne Herschel infrared telescope, launched by the European Space Agency with NASA participation, is studying galaxy formation in the early universe. It allows astronomers to look back to the first 3 billion years of the universe’s approximately 14 billion year history.

The degree of clustering of these early galaxies is a reflection of the amount of dark matter relative to ordinary matter. The researchers also note that to form large galaxies (such as our Milky Way) that are efficient sites for robust star formation that one needs enough dark matter relative to the ordinary matter in stars and interstellar gas, but not so much that one ends up with many smaller galaxies.


Foreword, by Rich Brueckner

“Through our eyes, the universe is perceiving itself. Through our ears, the universe is listening to its harmonies. We are the witnesses through which the universe becomes conscious of its glory, of its magnificence.”

— Alan Watts

We all know of the Big Bang, how our universe came to be in a massive explosion, seemingly starting from nothingness. And for those who study cosmology, further understanding requires us to define the dark energies that somehow endowed our world with order.

Now, we haven’t observed dark energy, dark matter, and the secrets of dark gravity directly, but we do see their effects. As we learn in this book, without them, the universe would not have formed in a way that could have spawned intelligent life.

As a writer, I am intrigued by these dark energies because they imply a backstory–phenomena that happened first that led to this outcome. So in this way, dark energies seem to me to be metaphors of science. Like the stories of Genesis and Adam and Eve, what they really represent is a deeper truth.

In this book, Dr. Perrenod does a wonderful job of explaining the origins of the universe in way that is accessible to the layman. When you want to understand how the universe came to be, you ask an astrophysicist. But when you really want to know why, I think you have to start by asking yourself some questions. Try a thought experiment.

Put yourself in the place of a Universal Mind before the Big Bang. If you really wanted to understand yourself, you would need to have something intelligent outside of yourself that could experience that which is you. Not to get metaphysical here, but if we were at the scene of a crime, what I’d be suggesting here is motive.

Thanks to modern physics and cosmology, we no longer live in a universe where dark forces lurk far beyond our capacity for comprehension. I believe that, through the works of Stephen Perrenod and others, we will come to that knowing. But even as we look out to the stars, I think it begins with understanding that not only are we within the universe, but the universe is within us.

Rich Brueckner is President of

Dark Matter, Dark Energy, Dark Gravity

Enabling a Universe that Supports Intelligent Life

Author: Stephen Perrenod

An e-book now available through:

We are immersed in a sea of light emanating from ordinary matter that is floating, as it were, on an ocean of dark matter. The dark matter itself floats on the dark energy of the particle vacuum that in turn is in embedded within the scaffolding of space-time – which is shaped by the dark gravity effects from all matter and energy.

Table of Contents

  • Dedication
  • Foreword (by Rich Brueckner)
  • Preface and Acknowledgements
  1. Scale of the Universe
  2. The Big Bang Model
  3. Inflation
  4. Dark Matter
  5. Dark Energy
  6. Dark Gravity
  7. Future of the Universe
  • Glossary
  • References, Suggested Reading and Viewing
  • About the Author