Cosmology and our View of the World
Anthropic Principle Lead: Michael Dunn
Summary by Marcy Elliott
On March 6, 2007 Mike Dunn led the class discussion on the Anthropic Principle. He began by discussing six numbers of great significance to the mathematical laws of the universe. The six numbers he noted were Epsilon (.007), Omega (1), D ( 3), N (10^36) Lambda (.7), and Q (1/100,000). Epsilon is the ratio of the weak nuclear force constant relative to the strong force. How firmly atomic nuclei bind together and how all atoms are made. This value controls the power from the sun and how the sun is able to transmute hydrogen into all the elements on the periodic table via nuclear fusion. It is measured as the proportion of the mass of a hydrogen nucleus which is converted to energy when hydrogen fuses to become helium. If it were .006, the universe would consist of only hydrogen, if it were .008, hydrogen would have immediately fused to make heavier elements.
Omega is the ratio of the actual density of the universe to critical density. It is a measure of the amount of material in the universe (galaxies, diffuse gas, dark matter). Omega is the relative importance of gravity expansion energy as it is actually found in our universe. Inflationary theory says that this value must be 1. “If Omega were small compared to 1, matter would have expanded so rapidly that no galaxies or stars could have even formed, and vice versa, if Omega were large compared to 1, the universe would have collapsed back into a big crunch after only a very short time, thus leaving no time for the formation of stars and planets. This was a long standing conundrum. Then came inflation theory, which actually predicted on basic grounds that Omega should be 1. Most recently, cosmic background radiation observations with WMAP have shown that Omega is indeed very close to 1, giving supporting evidence to the inflation model.” (Moebius).
D is the number of spatial dimensions. The statement was made that we live in a 3D universe, and life cannot exist if there were 2 or 4 dimensions. One discussion participant asked the question why can’t there be life in more than 3 dimensions. Dunn clarified himself by saying life as we know it, cannot be.
The discussion was not halted at this, debate moved on to going over N, the strength of the electrical forces that hold atoms together divided by the force of gravity between them. If it were smaller only a tiny universe would exist, with no creatures larger than insects.
Lambda is Einstein’s cosmological constant. It was measured in 1998, although the precise value is still uncertain. Lambda is a sort of cosmic antigravity that controls the expansion of the universe. If it were larger it would have stopped galaxies from forming. Q is the ratio of gravitational binding energy to mass energy, two fundamental numbers. If it were smaller the universe would be inert and structureless. If it were larger the universe would be violent and dominated by black holes.
These numbers speak to the importance and delicacy of the physical laws that underpin our universe and the precise value of the physical constants. Physical constants describe things quantitatively and they need to be measured. Are these numbers a coincidence or the proof of a higher being? The Anthropic Principle attempts to make sense of our universe from a mathematical, and what some may call philosophical perspective.
The Anthropic Principle was first coined by Brandon Carter in 1974. It is hard with only our one perspective as humans in our own universe, to guess as to how other universes form and the possibilities of life arising. Dunn offered this as an analogy: “This is the equivalent to drawing the king of hearts from a magician’s deck of cards. You have no idea of the contents of the rest of the deck.” This analogy was briefly discussed among the participants because there was skepticism around the analogy. It is obviously not meant to be taken literally and there were a few different interpretations of the analogy.
The Anthropic Principle attempts to constrain facts about the universe by taking into account our presence. We are able to more accurately calculate the odds of certain events happening, reducing the possibilities from an infinite amount, to a much smaller range that allows life to develop.
The Weak Anthropic Principle (WAP) states that the observed values of all physical and cosmological quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirements that the universe be old enough for it to have already done so. The WAP says that our existence allows us to infer values of certain fundamental constants for a universe with life as we know it. Our existence is an indicator of what values these constants have.
The Strong Anthropic Principle (SAP) states that the universe must have those properties which allow life to develop within it at some stage in its history. Different interpretations of this are “There exists one possible Universe designed with the goal of generating and sustaining observers”, “Observers are necessary to bring the Universe into being”, “An ensemble of other difference universes is necessary for the existence of our Universe.” The SAP claims not just that our existence allows us to infer the values of the constants, but that it is moreover the explanation of why they have just the values that we find.
The Final Anthropic Principle states that intelligent information-processing must come into existence in the Universe, and, once it comes into existence, it will never die out.
For the rest of the class we discussed interpretations of the Anthropic Principle. Some of these interpretations are God, the Emergence Theory, Chance (Drake Equation), Multiverse, Universal Inflation, Universe Evolution, and the possibilities of other universes.
One of the major questions that was raised when considering the interpretations of the Anthropic Principle was the existence of genes and what the odds are of genes coming into existence because they are regions of DNA that consist of hundreds of thousands of base molecules arranged in a specific sequence. The production of this raw material arises from a random process given the odds of the odds of 1 in ten to the thousandth power, even for the smallest gene (equivalent to landing heads on three thousand consecutive coin flips). For a 15 billion year old universe, there has been 10^17 seconds for nature to accomplish this arrangement. And from quantum theory, we know that each second can be divided into 10^43 moments of Planck time, allotting nature 10^60 chances to arrange a gene, far short of the 10^1000 chances needed. If you then included every one of the 10^80 known particles in the universe under the assumption that this process is occurring simultaneously everywhere, the chances only increase to 10^140. This is not including the time it would take for quarks and leptons (the building blocks of matter) to form atoms, and then the complex amino acid molecules necessary to create something to mix. The chances of life as a result have been likened by some skeptical scientists to proposing that a tornado blowing through a junkyard would result in the assembly of the 747. This seems to point towards divine creation or the panspermia theory. The rebuttal raised to this from the WAP is that we should not be surprised that we do not find features in the universe which are incompatible with our existence. This does not explain the vast improbability of our existence and does not satisfy our desire to know why we exist. We know that a process was involved that is very different from random coin tosses every Planck-interval, namely evolution, which allows for the cumulative exploitation of the possibilities available.
Dunn offered this analogy: "Suppose you are dragged before a firing squad consisting of 100 marksmen. You hear the command to fire and the crashing roar of the rifles. You then realize you are still alive, and that not a single bullet found its mark. How are you to react to this rather unlikely event?" As a response to the analogy Dunn offers, "If we applied a sort of WAP to the firing squad scenario, we could state the following: 'Of course you do not observe that you are dead, because if you were dead, you would not be able to observe that fact!' However, this does not stop you from being amazed and surprised by the fact that you did survive against overwhelming odds. Moreover, you would try to deduce the reason for this unlikely event, which was too improbable to happen by chance. Surely, the best explanation is that there was some plan among the marksmen to miss you on purpose. In other words, you are probably alive for a very definite reason, not because of some random, unlikely, freak accident." "So we should conclude the same with the cosmos. It is natural for us to ask why we escaped the firing squad. Because it is so unlikely that this amazing universe with its precariously balanced constants could have come about by sheer accident, it is likely that there was some purpose in mind, before or during its creation. And the mind in question belongs to God." Another theory that follows this analogy says, this universe being one of so many could just make us the right solution and we observe this because we are here in this universe.
If one takes the Anthropic Principle to confirm the presence of God, the Anthropic Principle has little to offer concerning the character of God. One criticism is the chef analogy, although not allowed into the kitchen of a restaurant, one would quickly conclude that a directive force (read an intelligent person) created a seven-course meal served to them. The empirical circumstantial evidence for a chef may be clear. Nevertheless, unless the chef comes out from the kitchen and reveals himself or herself, the eater can only comment on the quality of the meal.
Another criticism is the lottery analogy, equal probability. A million lottery tickets are sold, and then one number out of that million is selected. The holder of that number wins the prize, so that number seems special. But in a deeper sense it is no more special than any of the other numbers in the lottery. By the nature of the lottery, somebody must win, and each of the numbers has an equal chance of winning. It is only after the event that one number gains a special status. The holder may feel lucky as a result; but somebody had to get lucky.
The inverse gambler’s fallacy is another example, a pair of dice is rolled once, and the result is double sixes. This is a quite improbable result; therefore the dice were probably rolled many times before. Humans do not know exactly how many times the universal “dice” have been rolled, so we inherently assume we are special, when this may not be the case.
Dawkins’ Argument says that God would have to be just as unlikely or even more unlikely than the very objects he is supposed to explain, bringing about the where did god come from paradox.
The Emergence Theory was one of the last topics we discussed. “This theory suggests that from functions on a lower level additional functions on a higher level emerge, but any of these may then develop according to an evolution” (Moebius). “Most emergentists have viewed their theory as an attempt to explain why it is the case that significant novelty and complexity can emerge from processes that are themselves relatively simple” (DeVries). Opponents of this theory characterize this as a circular argument because to self-organize there must first be a self, or for the blueprint for the self to follow, there must have been something to create it.
The Drake Equation is an estimate for the likelihood that there are other civilizations out there. Given the probability for many of them in the universe it would give us also an average distance where to expect a next civilization. However, in order to perform such an estimate we need to have good numbers (based on observation and/or solid modeling) for all of the quantities in that equation. (For more information refer to class lecture summary “Are We Alone: Search for Extraterrestrial Intelligence/Life”).
Many physicists suggest that there are many universes, like bubbles in foam in a multiverse. Some also theorize that our universe may reverse itself resulting in a big crunch, only to bounce back into expansion, and has been doing so every 20 billions years forever. It is possible that the six fundamental constants are reset every time to new values which in turn effect the life span of the resulting universe.
As usual, the discussion surpassed the allotted class time. Understanding the Anthropic Principle gives us some insight as to why life, humans, and human intelligence exist in our universe. The many interpretations and criticisms exemplify the complexity of the principle.