Tag Archives: Lawrence M. Krauss

The Anthropic Principle

the astronomerWhy are we here? This is perhaps the most fundamental philosophical question. One can imagine contemplating this question at any time in human history. Many stories have been inspired by this question, usually taking the form of myths, or religious and spiritual traditions. Today, ‘why are we here’ is also a scientific question. The anthropic principle arose as a response to the question of human existence. The idea was first proposed in 1973 by theoretical astrophysicist Brandon Carter. Since then it has been expanded and stated in several forms.

What is the Anthropic Principle?

The word anthropic is defined by the Merriam-Webster online dictionary as: “Of or relating to human beings or the period of their existence on Earth.” That’s a start. For simplicity I will stick close to Brandon Carter’s original formulation, which he expressed as two variants. I will paraphrase based on the description from a few sources:

  1. The Weak Anthropic Principle refers to our special location in the universe (both in time and space), which is conducive to our existence. The fact that we can observe the universe means that planet Earth must have the conditions necessary for our existence.
  2. The Strong Anthropic Principle refers to the fundamental laws of physics, which are precisely set for our existence. The strong principle takes into account the properties of the universe as a whole.

The Burden of Proof

habitable zoneIn a vast universe it is not surprising that a planet, like the Earth, has a special location (usually called a habitable zone or a Goldilocks zone). The specific laws of the universe needed for human life are more difficult to explain (usually called fine tuning). Using a legal metaphor, the strong anthropic principle has a greater burden of proof than the weak anthropic principle. In this case, burden of proof is a figure of speech, because the anthropic principle is as much a philosophical idea as a scientific one. 

In The Grand Design, Stephen Hawking and Leonard Mlodinow describe the weak anthropic principle as an environmental factor. They write:

“Environmental coincidences are easy to understand because ours is only one cosmic habitat among many that exist in the universe, and we obviously must exist in a habitat that supports life”

The strong anthropic principle is all-encompassing and generally more controversial. Hawkings and Mlodinow go on:

“The strong anthropic principle suggests that the fact that we exist imposes constraints not just on our environment but on the possible form and content of the laws of nature themselves”

Stating the Obvious or a Profound Insight

Is the anthropic principle a satisfying explanation? On the surface, it seems like an obvious statement that explains very little. But as I reflect on the idea, I am not so sure. Maybe it is suggesting something profound. Perhaps the answer to why we are here is simple: it could not be otherwise.

Lawrence KraussFor example, Lawrence Krauss provides an anthropic interpretation to one of the universe’s properties. In the book, A Universe from Nothing, he examines the relationship between the energy density of matter and the energy density of empty space. Yes, space has energy and it can be measured. The density of matter in the universe can also be measured. It turns out that now is the only time in cosmic history that both values are comparable. That’s a curious result.

The universe has been expanding since the big bang, and as it expands the density of matter decreases. Matter gets diluted as galaxies get farther apart from each other. Meanwhile the energy in empty space remains constant (there is nothing to dilute or increase in empty space). Therefore at the time galaxies formed the density of matter was greater than the energy in empty space. That’s a good thing, because the gravitational effect of matter was dominant, which allowed matter to come together.

However, if the values for matter and energy had been comparable at the epoch of galaxy formation, galaxies would not have formed. Empty space exerts a repulsive force, which would have canceled out normal attractive gravity. Matter would not have clumped together. Krauss writes in A Universe from Nothing:

“But if galaxies hadn’t formed, then stars wouldn’t have formed. And if stars hadn’t formed, planets wouldn’t have formed. And if planets hadn’t formed, then astronomers wouldn’t have formed!”

It seems highly coincidental that the energy values for matter and space are roughly equal now, but they could not have equalized too much earlier. Otherwise, no one would be here to observe it. Similarly, if one of a number of physical properties were slightly different, we would also not be here. That’s when anthropic reasoning steps in: An observer must observe the conditions of the universe that allows the observer to exist.

astronomersMaybe a change of perspective is needed: Instead of focusing on our present circumstances and looking back, we can look at the evolution of the universe. Life is a latecomer to the process, of which an incalculable series of events occurred. Our existence is the result of all that came before. Although it does appear that the universe was made for us, it is in fact, the universe that made us. We were formed from the conditions that were set long before conscious beings could observe any of it.

Is Physics an Environmental Science?

The traditional approach of physics is to discover and understand the universe we live in. The fundamental laws and the values for the constants of nature are consistent throughout the observable universe. The physical laws discovered on Earth can be applied to the universe as a whole. But there can only be one exact set of laws and history that allow for our existence. That’s unless our universe is not the only one.

For some, recent scientific evidence is suggesting that there are many universes (a multiverse). Others point out that inferring a multiverse is not science; because by definition other universes cannot be observed directly (they would exist outside our observable universe). If we apply the strong anthropic principle to the multiverse theme, it does partly explain the exact parameters of our universe.

If the cosmos is populated with many universes, possibly infinite universes, then the laws of physics could be purely random. They would simply emerge as an environmental consequence. Some physicists have compared the multiverse to a foam of bubbles (each bubble representing a universe). The laws could be different in every bubble of an endless cosmic foam. Some bubble universes could be similar to ours, others vastly different.

Of course, this is a hypothetical argument. Nevertheless, if we could observe every universe in a multiverse, every single one would be finely tuned for its own existence. Anthropic reasoning would state that there is nothing special about our universe. In all the non-life generating universes there is no one to observe them, in ours there is. It’s that simple. Obviously, the anthropic principle (inferring a multiverse or not) is not a proven argument, but it’s one of many possible answers to the question: Why are we here?


References: Stephen W. Hawking and Leonard Mlodinow, The Grand Design (New York: Bantam Books, 2010), 155.

Lawrence M. Krauss, A Universe from Nothing (New York: Free Press, 2012).



A Special Time

This blog site was inspired by our book, The Landscape of Reality (Nov. 18, 2014). The blog is an offshoot or extension from some of the themes in the book. The blog will focus on creative ideas and concepts from science, nature and philosophy. All with the intent of providing a perspective of life that is in line with the physical and natural world. The content will be tailored for a general audience. I define the three fields in the following manner:

  • Science is about a factual and logical understanding of the world and the universe. The foundation of science is verifiable evidence.
  • Nature is more closely associated to living things and how we experience the world, but not exclusively. One could also view nature as the source, and science as the field of study.
  • Philosophy is about how we think and apply the concepts, what it means for us.

 Why a Special Time?

In all of human history, no time compares to the last century in terms of change and increased knowledge. Aside from advancements in science that have eased many of life’s burdens, new and exciting discoveries are revealing the universe’s true colors. The scientific endeavor has uncovered explanations of our world and beyond, which call to question long-held beliefs. We, as individuals and as a species, have the opportunity to understand the nature of our existence in ways that past generations could not have imagined.

Galaxy Cluster

Galaxy Cluster

Lawrence M. Krauss and Bob Scherrer wrote concerning the picture of the large-scale universe:

“We live at a very special time…the only time when we can observationally verify that we live at a very special time!”

There is an intriguing implication behind this quote. According to Krauss, due to the expansion of the universe, galaxies will get increasingly farther apart. At some point in the far future, galaxies will become so isolated that all evidence of the cosmological picture of the universe will disappear. From any galaxy, potential observers will not detect anything beyond their own galaxy. They will arrive at the conclusion that the universe consists of only a single galaxy (the same view that people had before the last century), and they will be completely wrong.

 A Drastic Change of Perspective

  • Before the last century: The earth was viewed as part of a solar system, within a collection of stars (there were no known planets outside our solar system). All stars were contained within a single galaxy of a static universe.
  • After the last century: The earth is now known to be located on the outer edge of an ordinary galaxy (hundreds of planets outside our solar system have been discovered). The Milky Way is part of a huge conglomerate of billions of galaxies within an expanding universe.

 A Philosophical Angle

Before the development of modern science, natural philosophy was the term used to describe the study of nature and the physical universe. In this sense, science emerged out of philosophy. The critical difference that allowed science to branch out from philosophy was the requirement that science relied on experimentation to acquire knowledge. Still, the two have been closely linked for a long time.

In the early period of science the focus was on uncovering the laws that governed nature. The application of science came later as mankind learned they could manipulate nature for their own benefit. Now the applied sciences seem to have captured the imagination of the general population. Technologies of every kind are dominating our lives. But I caution that an opportunity to fully appreciate and understand the laws of nature is being missed. And that our excesses from modernization are growing faster than our ability to monitor the changes to our planet and ourselves.

Nevertheless, it is clear that science cannot be viewed solely as an applied field. The current scientific picture has philosophical implications as well. Learning about science can be an intellectual pursuit that has the power to enrich our lives at a philosophical and emotional level. The time is ripe for making science accessible and meaningful to the general population. Explanations from different areas of science are now merging well together, and form a view of reality that is utterly fascinating and awe-inspiring. Those are the feelings I hope to convey in the blog posts that will follow.

Ray of Sunlight


References: Lawrence M. Krauss, A Universe from Nothing (New York: Free Press, 2012)