The Fine-Tuned Universe
Our universe requires fine-tuning. Of what? The precise values of nature’s fundamental constants. But why? For stars, galaxies, planets and life to exist. The fundamental nature and interactions of matter and energy are theoretically explained by the Standard Model (SM) of Physics. There are many components to this model but essential are about 25 constants (parameters) describing the masses of the elementary particles, values to compute the interactions or forces between them and some others. Plus, we need to include a few constants not part of the SM such as the Gravitational Constant and some constants in cosmology related to how the universe is expanding (Refs 1, 2). In total there are about 30 constants, and each of these is set within a very narrow range for our universe to exist.
Physicists are not dogmatic about the total number of constants. In fact, there are about 300 constants in nature like Avogadro’s Number and Faraday’s Constant, but these are not considered truly fundamental compared to those defined by the Standard Model of Physics and cosmology (Ref 3 and NIST list).
Each fundamental constant must be precisely tuned such that a life sustaining universe exists. Why these constants have their specific values is a mystery to physicists. The most fundamental parameters are like orphans with no connecting relationships between them. They are what they are.
The Parameter Landscape
Fig 1 illustrates the special nature of the physical constants. It shows a “magnitude line” with just six constants (not explained here) and their values (units not shown). The range of values span, just for these six, almost 54 zeros of magnitude. A trillion dollars is only 12 zeros of magnitude. Other fundamental parameters, not shown here, span up to 120 zeros of range.
Each of the constants could have values much different from what they are. For example, consider the gravitational constant, G (related to the force of gravity). Its actual magnitude is 6.673×10^-11. The theoretical value of G could have been much weaker (~10^-30, 30 zeros of smallness) or much stronger (~10^30, 30 zeros of bigness). So, the actual value is “fine-tuned” from an enormous range of possible values. This logic applies to all the fundamental parameters. More information about each of these constants is provided on the main tuning page.
Imagine a radio that can tune in a trillion stations. However, there is only one channel in your language and that suits your tastes. Every other station is unintelligible to you. In a way, this is similar to how Nature's constants are fine tuned. They are exactly at the value/setting that we need for life. By far, other values/settings are not favorable.
Now imagine 30 radios (each representing a constant of Nature) each with trillions of possible tunable settings. Each must be tuned to its "sweet spot", the one or a few channels that are favorable for life. The probability of this occurrence tuned-in by chance on all 30 radios is beyond rare. Note what Nobel Prize winner Steven Weinberg says:
“How surprising it is that the laws of nature and the initial conditions of the universe should allow for the existence of beings who could observe it. Life as we know it would be impossible if any one of several physical quantities had slightly different values.”
True, some constants allow for a wider range of settings, but not by much. A few can swing a factor of two or more and still enable a livable universe. See Extreme Accuracy page to appreciate the need for accuracy for the values of Nature's constants.
Figure 2 demonstrates another view of fine-tuning for two parameters selected from the fundamental constants list.
Figure 2 (Source: Ref 1)
The figure shows what can go wrong as the strength of the Strong Nuclear force (which holds atoms together) and the value of the Fine-Structure constant (characterizes the strength of the electromagnetic force between charged particles) are varied from their ideal values. The small, white sliver represents the area where life is possible. Within that region, “x” marks the spot where the two parameters are set for our universe. Not much room for error with just two parameters, imagine 30 combined. See Endnote 2.
As with any mystery of science, there are differing viewpoints. By far, most respected physicists agree that fine-tuning is a miracle of sorts and we don’t really understand why the constants are set for life. Some claim that we live in one of many parallel universes (multiverse hypothesis) and we just happen to be in one where humans can ponder its physics. Others believe there is only a singular universe. Some believe that another permutation of the constants could produce a different universe with the possibility of life (see Endnote 3). The bottom line is we live in a universe that exists because of many critical parameters perfectly aligning for our benefit. As author Agatha Christie penned;
“Any coincidence”, said Miss Marple to herself, “is always worth noting. You can throw it away later if it is only a coincidence.”
So, why build this Universe Fine-Tuning Machine? To explore, to learn, and to wonder -- why us?
The machine enables users to simulate tuning-in up to six fundamental parameters and to appreciate their importance in our life. Users control a “parameter dial” to discover the precise value of the selected parameter. For amusement the tuning is dual purpose. Give it a try!
One more thing, the fundamental constants can be defined as dimensionless (no units) or with dimensions (mass of electron). The reasons for this are beyond our scope here. On the tuning page for this site, constants with dimensions are given. Using one style or the other does not change the fact that they must be accurately set.
1: The Fine-Tuning of Nature’s Laws, Luke A. Barnes, The New Atlantis Journal of Technology and Society, Number 47, Fall 2015
3: Our Mathematical Universe, Max Tegmark, Vintage Books, 2014 (page 252)
Note 1: There are other parameters not usually included in the official list of fundamental constants that are also vitally important for life. One of these is the “Mass density [1 ns after] the Big Bang”. It is a cosmological parameter that requires extreme precision for our universe to form as it did. Another is related to the mysterious and diminutive neutrino, a roaming elementary particle estimated about one millionth (.0001%) the mass of an electron. Max Tegmark (MIT) and colleagues theorize that by increasing the neutrino’s mass by a factor of only two would prevent life. Galaxies would not form, and the universe would be filled with shapeless matter.
Note 2: Figure 2 shows the range of the X axis and Y axis going from 0 to nearly infinity – this is the theoretical value range for each parameter. The true value of a parameter can vary by some small amount and still produce a universe close to the one we live in.
Some parameters can vary by a factor of 2x without adverse effects while if others wobble by 1% the change causes a catastrophe. Note the “sliver” in Figure 2 where carbon-based life is possible. Both the Fine Structure Constant and Strong Nuclear Force are both permitted to wiggle a tiny amount and still stay within the white sliver area.
Note 3: If the current list of 30 constants (with variations as permissible) is defined as “Ensemble_A” then some suggest there may be an “Ensemble_B” (or C, D...) where possibly some or all the 30 have completely different values compared to the A settings. In the B case, a completely different universe with life of some kind may be possible. This is a hypothetical conjecture and not proven.