Fine-Tuning of the Force Strengths to Permit Life

“As we look out into the Universe and identify the many accidents of physics and astronomy that have worked together to our benefit, it almost seems as if the Universe must in some sense have known that we were coming.[1]” Physicist Freeman Dyson

In my previous blog, I discussed how numerous changes to the laws of physics would have resulted in a lifeless universe. I admitted that this was relatively modest evidence for my fine-tuning claim:

“In the set of possible physical laws, parameters and initial conditions, the subset that permits rational conscious life is very small.”

I say relatively modest because the evidence I cite in my blog about the fine-tuning of initial conditions is so powerful and the same I argue applies to the evidence I present in this blog. This blog examines how the constants governing the four fundamental forces of physics must be finely-tuned to support life. Refer to my previous blog for the qualitative aspects of these forces and how they have to be just right to permit life. I now focus on the quantitative constraints on the strengths of these forces if intelligent life is to plausibly exist anywhere the universe. First some background – physicists typically refer to coupling constants for those dimensionless constants[2] which represent the strength of each force. The strength of these forces ranges over about 40 orders of magnitude – that is to say that the strongest force is 1040 times stronger than the weakest force. Thus, it would be surprising if the strengths of these forces must lie in narrow ranges to permit life – at least if the values were set at random such as would be the case in a universe without God. Let’s look at how sensitive these parameters are with respect to permitting life:

1)      Strong nuclear force

This force is important for the existence of stable atoms beyond hydrogen. If the strong force were 50% weaker, no elements used by life would exist because protons couldn’t be held together in the nucleus. The strong nuclear force must exceed the strength of the electromagnetic force sufficiently to overcome the electromagnetic repulsion of positively charged protons. While learning chemistry would be much easier if only the first few elements existed in the periodic table, there would be no physical creatures around to learn it! If the strong force were about 50% stronger no hydrogen would be left over from nuclear fusion processes occurring in the early universe. Hydrogen plays a critical life-supporting role not only as a constituent of water but hydrogen-burning stars last 30 times longer than alternatives. This particular constraint may not make intelligent life impossible but life would certainly be much harder to originate if the available time were so limited and if neither water nor hydrocarbons existed.

Also, hydrogen-bonding is very important in biology for many reasons: information storage in DNA, antibody-antigen interaction, and for the secondary structure of proteins. Remember that parameters that seem beneficial for life but are more fine-tuned than is strictly necessary counts against a multiverse explanation of the fine-tuning because multiverse scenarios predict only what is minimally necessary for life.[3] An even tighter constraint is that if the strong force were more than about 2% stronger protons wouldn’t form from quarks – in which case no chemical elements would exist![4] If the strong force were 9% weaker, stars would be unable to synthesize any elements heavier than deuterium (which is heavy hydrogen).

2)      Electromagnetic force

This force is responsible for chemistry and plays a critical role in stellar fusion which powers life. The electromagnetic force needs to be much weaker than the strong nuclear force for atoms to be stable – so that the radius of the electron orbit is much larger than the radius of the nucleus.[5] Unless the electromagnetic coupling constant (which represents its strength) is less than about 0.2, there would be no stable atoms because electrons orbiting the nucleus would have enough kinetic energetic to create electron-positron pairs which would then annihilate each other and produce photons. Additional examples of fine-tuning for this force strength will be described later in this blog.

3)      Weak nuclear force

The weak force controls proton-proton fusion, a reaction 1,000,000,000,000,000,000 times slower than the nuclear reaction based on the strong nuclear force. Without this, “essentially all the matter in the universe would have been burned to helium before the first galaxies” were formed. Because the weak nuclear force is so much weaker than the strong nuclear force, a star can “burn its hydrogen gently for billions of years instead of blowing up like a bomb.[6]” I’ve previously described the negative ramifications for life if there were no hydrogen in the universe.

John Leslie points out several other ways in which the weak nuclear force is finely-tuned. “Had the weak force been appreciably stronger then the Big Bang’s nuclear burning would have proceeded past helium and all the way to iron. Fusion-powered stars would then be impossible.[7]”

Neutrinos interact only via the weak force and are just powerful enough to blast off outer layers of exploding stars but and just weak enough to pass through parts of the star to get there. The weak force also plays a role in fusing electrons and protons into neutrons during the core collapse of stars to keep the collapse proceeding until it becomes an exploding star (supernova). UK Astronomer Royal Sir Martin Rees estimated that a change in the strength of the weak nuclear force by about 1 part in at least 10,000 relative to the strength of the strong force would have prevented supernova explosions which allow heavier elements to find their way to planets.[8] Without these supernova explosions key heavy elements would be unavailable for life.

4)      Gravitational force

Many physicists think that we’ll eventually discover a Grand Unified Theory, uniting gravity with the other 3 fundamental forces. For this reason Stanford physicist Leonard Susskind remarks that “the properties of gravity, especially its strength, could easily have been different. In fact, it is an unexplained miracle that gravity is as weak as it is.[9]” This probable underlying relationship leads to a natural expectation that gravity could be as strong as the strongest force. The strength of gravity is about 40 orders of magnitude weaker than the strong nuclear force. Based on this expectation that gravity can vary up to strong nuclear force strength, the level of fine-tuning required for life is pretty remarkable:

If gravity is weaker by 1 in 1036, stars are unstable to degeneracy pressure (for small stars) or unstable to radiative pressure just expelling huge chunks of the star (for larger stars).

If gravity is stronger by 1 in 1040, the universe is dominated by black holes not stars.

If gravity is weaker by 1 in 1030, the largest planet that would avoid crushing effects of gravity on any large-brained creatures would have a radius of about 50 meters – which is not a good candidate for an ecosystem and the development/sustenance of intelligent life.

These are huge numbers that may be hard for most readers to visualize.  Thus, consider the following analogy to help understand the improbability of 1 part in 1036. Suppose one could make a sand pile encompassing all of Europe and Asia and up to 5 times the height of the moon.[10] Suppose one grain of sand is painted red and randomly placed somewhere within this pile. A blind-folded person then randomly selects one grain of sand from the pile. The odds that she would select that one red grain of sand are slightly better than the 1 in 1036 odds of a life-permitting strength of the gravitational force based on just one of the above criteria.

Let’s explore a few more fine-tuning cases constraining multiple constants concurrently.

Long-Lived Stars

As I’ve discussed previously, stars play at least two key roles in making the universe life-permitting:

1) As a long-lived power source that helps life overcome the effects of the Second Law of Thermodynamics that would otherwise lead to an eventual state of disarray and equilibrium.

2) For synthesizing elements not created by the Big Bang (which is basically everything past beryllium).

We take the sun for granted as a long-lived stable source of power but note the lack of any comparable long-lived power source on earth as an indication that is not always the case. A star is basically a controlled nuclear explosion held together by gravity – that it can last so long requires a delicate balance of various physical parameters. Consider that the Sun outputs less energy per kilogram of its mass than a person does – without fine-tuning, stars would die out much sooner. Obviously the sun is still able to output enormous quantities of energy because it’s so huge! Another surprising aspect of the sun is that photons generally take at least several thousand years to travel from the sun‘s core to its surface through the ionized plasma.[11] There are significant constraints on the strength of gravity and electromagnetism if there are to be long-lived stars. Luke Barnes summarizes some of the key physics research in this arena:

“There is a window of opportunity for stars – too small and they won’t be able to ignite and sustain nuclear fusion at their cores, being supported against gravity by degeneracy rather than thermal pressure; too large and radiation pressure will dominate over thermal pressure, allowing unstable pulsations.[12]”

Barnes does some calculations based on the possibility that gravity could vary in strength up to the strength of the strong nuclear force and uses a uniform prior distribution of possible values for the gravitational coupling constant and the electromagnetic coupling constant. Using this approach, he computes that “the stable-star-permitting region occupies 10–38 of parameter space.” This is even less probable than my previous sand analogy!

Production of Both Carbon and Oxygen in Stars

One of the earliest examples of fine-tuning was discovered by astronomer Fred Hoyle with regard to the fine-tuning required to make both carbon and oxygen in stars. Three distinct coincidences are required to abundantly make both types of elements in stars. These restrictions impose a constraint of about 1 part in 250 on the relative strength of the strong force and the electromagnetic force in both directions. Actually a more recent study by Ekström[13] in 2010 indicated that a change of just 1 part in 10,000 in the electromagnetic coupling constant would have resulted in the inability of stars to synthesize both carbon and oxygen. Despite being an atheist Hoyle conceded:

“Some super-calculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule. A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question.[14]”

Other Constraints among Force Strengths

For a more comprehensive examination of fine-tuning constraints, refer to Luke Barnes excellent review article that I’ve previously referenced. This review article is an excellent summary of a hundred or so physics articles, and in many cases references multiple articles per fine-tuning constraint. Barnes lists several additional constraints I haven’t mentioned and provides additional details. Just among constraints involving powers of these coupling constants, Barnes lists a half dozen or more cases. Usually the power involves just a squared term but it’s important to note that there are linear, quadratic and inverse relationships among the coupling constants. For example, the electromagnetic force strength is constrained in one way based on a linear constraint and in another way based on a quadratic constraint and in another way based on the inverse of the force strength relative to some other constant. It is remarkable that there is a life-permitting region that simultaneously satisfied these multifaceted constraints.

Also, since each coupling constant can be expressed in terms of more fundamental parameters such as Planck’s constant and the speed of light there are very tight constraints on those parameters as well – especially because of the constraints across different powers of the coupling constant. Thus, Planck’s constant is constrained in one way and the square of this constant is constrained based on a different life-permitting criterion – and likewise for the speed of light.

Moreover, there is a finely-tuned cosmological parameter, known as Q, which can be expressed in terms of various other parameters including coupling constants. In an equation derived by Max Tegmark and Martin Rees[15], there are the following powers on various coupling constants: -1, 16/7, 4/7. Also, there is a natural log of the electromagnetic coupling constant to the -2 power that is taken to the -16/9 power. Without the various contributions of coupling constants taken to the various powers, the value for this parameter Q would not have been life-permitting. Q represents the magnitude of variations in energy density in the early universe. If Q was larger than 10-5 the universe would have consisted of too many black holes to be life-permitting. If Q were smaller than 10-6 there would be gravitationally bound structures in the universe – no stars, no planets and therefore no life. See Barnes’s article on page 32 for more details on the fine-tuning of Q and its relationship to coupling constants.

Finely-Tuned Output of Stellar Radiation

Brandon Carter first discovered a remarkable relationship among the gravitational and electromagnetic coupling constants. If the 12th power of the electromagnetic strength were not proportional to the gravitational coupling constant then the photons produced by stars would not be of the right energy level to interact with chemistry and thus to support photosynthesis. Note how sensitive a proportion has to be when it involves the 12th power – a doubling of the electromagnetic force strength would have required an increase in the gravitational strength by a factor of 4096 in order to maintain the right proportion. Harnessing light energy through chemical means seems to be possible only in universes where this condition holds. If this is not strictly necessary for life, it might enter into the evidence against the multiverse in that it points to our universe being more finely-tuned than is strictly necessary.

Closing Thoughts

It’s important to note how the values of these constants must lie within narrow ranges to be life-permitting based on multiple, independent criteria! My next blog will provide additional examples of this “coincidence.” This multiplicity makes my fine-tuning claim more robust because even if most of these peer-reviewed articles were wrong about fine-tuning claims, there would still be enough cases left to show that life-permitting physics is rare among possibilities.

Also, the question arises as to the likelihood there would exist any value for a constant that could satisfy multiple finely-tuned life-permitting criteria? Why would the life-permitting regions necessarily overlap at a single value that could then permit life relative to all of the constraints? UT Austin philosopher Robert C. Koons argues that this points to a higher-order fine-tuning and thus to design:

“When the value of a single constant is constrained in more than one way, it would be very likely that these independent constraints put contradictory demands on the value of the constraint. By way of analogy, if I consider several algebraic equations, each with a single unknown, it would be very surprising if a single value satisfied all of the equations. Thus, it is surprising that a single range of values satisfies the various anthropic constraints simultaneously. Leslie argues that this higher-order coincidence suggests that the basic form of the laws of nature has itself been designed to make anthropic fine-tuning possible. In other words, Leslie argues that there is evidence of a higher-order fine-tuning.[16]”

This coincidence grows even more surprising when one goes beyond the sheer multiplicity of constraints and also analyzes how differing powers on the constants appear in equations expressing independent and unrelated life-permitting constraints. Why is it that a given strength of electromagnetism turns out to be just right for long-lived stars, atomic stability, proton stability, electron stability, the synthesis of carbon and oxygen, the energy of photons output by stars, and the magnitude of density fluctuations in the early universe? Even speculative multiverse theories do not explain this type of coincidence.

[1] John Barrow and Frank Tipler. The Anthropic Cosmological Principle, p. 318

[2] Actually, these are constants at current densities but in the early universe the 3 non-gravitational forces are thought to have been unified in the sense that at those energy levels all of the forces behaved in the same manner. Once we get beyond the first 1/100th of a nanosecond of the universe though we can speak of these as being constants.

[3] For an explanation of this widely accepted principle, refer to my previous blog: http://crossexamined.org/god-or-multiverse.

[4] Walter Bradley. (He happened to be the head of an engineering department when I was at Texas A&M). http://www.leaderu.com/offices/bradley/docs/universe.html

[5] Luke Barnes. The Fine-Tuning of the Universe for Intelligent Life. Publications of the Astronomical Society of Australia, p. 42. (http://arxiv.org/abs/1112.4647)

[6] Freeman Dyson, Scientific American 225 (1971), p. 56.

[7] John Leslie. The Prerequisites of Life in Our Universe. http://www.leaderu.com/truth/3truth12.html

[8] Martin Rees, Phil. Trans. Roy. Soc. London A 310 (1983), p. 317.

[9] Leonard Susskind, Cosmic Landscape, p. 9.

[10] I know that this is physically unrealistic but this hypothetical analogy aids in visualizing the magnitude of the fine-tuning.

[11] NASA web site. http://image.gsfc.nasa.gov/poetry/ask/a11354.html

[12] Barnes, p. 30.

[13] Ekström S., et al., Astronomy and Astrophysics, p. 514.

[14] Fred Hoyle. Engineering and Science, 11/81, p8-12.

[15] Max Tegmark and Martin Rees The Astrophysical Journal (1998), p. 499, 526

[16] Robert C. Koons. Theism vs. the Many-Worlds Hypothesis. http://www.reasons.org/articles/theism-vs.-the-many-worlds-hypothesis