Within the context of a life-permitting universe, fine-tuning involves “the claim that the laws of nature, the fundamental parameters of physics, and the initial conditions of the universe are set just right for life to occur.” Robin Collins, The Fine-Tuning of the Cosmos: A Fresh Look at Its Implications,” in The Blackwell Companion to Science and Christianity, 207.
This does not mean, necessarily, that the universe was designed but, rather, as physicist Luke Barnes states: “In the set of fundamental parameters (constants and initial conditions) of nature… an extraordinarily small subset would have resulted in a universe able to support the complexity required by life.” But the implication is that it is more likley to have occured via design than by chance.
Examples of fine Tuning
While some believe that the many observed constants and quantities seem finely tuned for developing intelligent life, others have suggested that there is no way to scientifically test the effect of fine-tuning since there is no way to adjust the values to observe the consequences. As physicist Sabine Hossenfelder stated, a fine-tuned universe represents “an observational constraint on our parameters.” In other words, our knowledge of fine-tuning is interesting but is of limited scientific value since the parameters cannot be changed.
Virtually no scientists dispute the science behind fine-tuning. What they dispute is what it all means. Three popular explanations for the existence of a fine-tuned universe are:
The Multiverse
The multiverse explanation of fine-tuning proposes the existence of a vast, if not infinite, number of universes with different initial conditions or fundamental boundaries of physics and perhaps even different laws of nature. If there were an endless system of universes, we could expect that at least one universe would be structured to support intelligent “observers.” Thus, we shouldn’t be surprised to find human-like life forms or other embodied conscious agents somewhere in a multiverse. In this scenario, we were randomly selected to live in a universe that supports life.
Evaluation: One problem with the multiverse hypothesis is that NO scientific evidence supports it. None. If multiple universes exist, they are unobservable—without observation and testing, there is no way to generate scientific evidence to support a multiverse hypothesis. One cannot test a hypothesis when no data is forthcoming.
According to physicist Sabine Hossenfelder, any universes outside our own would be “causally disconnected from us.” and “The vast majority of multiverse ideas are presently untestable, and will remain so eternally.” Lost in Math: How Beauty Leads Physics Astray, p 101-107
Advocates of the multiverse often posit a "universe-generating" mechanism to explain the origin of other universes. By postulating a universe generator, proponents think that it may increase the probability of getting a life-friendly universe somewhere in the multiverse. However, the speculative cosmologies that are purportedly responsible for generating multiple universes (i.e., string theory, inflationary cosmology) invoke mechanisms that themselves require fine-tuning. Thus, the multiverse hypothesis cannot explain fine-tuning without appealing to some prior fine-tuning mechanism (either the universe generator or whatever generated the generator).
For example, suppose one tries to explain the design of a car by referring to the assembly plant that produces many similar cars. Such a description doesn’t alleviate the need for an explanation for the design of the car. Indeed, it simply points to the need for an explanation of the design of the assembly line that produces the cars. In other words, it shifts the need for explanation to the next level. The shortcoming of this approach is that it leaves one in doubt about the source of all prior fine-tuning processes and mechanisms and still leaves open the question of why these should be random rather than designed.
Thus, even if a multiverse exists, theism may provide a better explanation than naturalism. An infinite set of universes is better explained by an unbounded cause than a random cause. Since there is no good reason to believe that the multiverse must be randomly caused, and since the universe generator must also be finely tuned, a simpler explanation [via Occam's Razor] seems more likely: If a multiverse exists at all, then a single transcendent intelligence designed it to support life.
Single-universe naturalism
Philosophical naturalism [PN] is a worldview that asserts that the existence of intelligent life in our universe is the result of chance processes governed by natural laws. There are no design influences, only blind material causes. However, naturalism is unproven scientifically and therefore requires a substantial defense to warrant belief. And PN is also self-refuting.
Fine-tuning is a brute fact
If one assumes in advance that the fine-tuning found in the universe is the result of chance, then any arrangement of matter is equally improbable (or probable), and there is no reason for one to ask why or how we exist. Naturalists who see fine-tuning as a brute fact say we don’t need to search for a deeper explanation: The universe “just is.”
Evaluation: First, to say that fine-tuning “requires no further explanation” is a matter of opinion. Undoubtedly, many people seek deeper explanations than are readily available. And to say that human existence is “unremarkable” is, at best, arguable.
Nevertheless, the assumption of naturalism receives no help from science because naturalism is not a scientific position; it is a philosophical one. To merely assume the truth of naturalism amounts to nothing more than a “naturalism-in-the-gap” belief. Thus, single-universe naturalism is a belief that requires one to put forth evidence and arguments to demonstrate the rationality of naturalism and that it's the best explanation of the evidence
When scientists (or anyone else) assume the truth of philosophical naturalism, they naturally begin to reject anything and everything that does not fit their predetermined viewpoint. Many people take the side of naturalism simply because of a prior commitment since it's the methods and institutions of science that compel us to accept a material explanation of the phenomenal world. They have an unspoken, a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce only material explanations, no matter how counter-intuitive. But that is not rational. The cure for that, of course, is Reason.
The design hypothesis
For many theists, it is unsurprising that the universe is fine-tuned for intelligent life. After all, if an intelligent being wanted to create a world where intelligent life exists, it seems reasonable that it would set the initial conditions and physical constants of the universe to favor that outcome. A finely tuned universe - one that supports intelligent, self-reflective, rational beings - is perfectly consistent with a theistic explanation. It is a coherent and simple explanation that need not appeal to unnecessary conjectures (e.g., the multiverse) to support its case.
Theists (specifically monotheists) have historically believed that God created the universe and populated it with all forms of life including intelligent life. This has inspired many theists, as well as non-theists, to seek answers to the “how” question through the study of biology, chemistry, and physics. To theists, fine-tuning leads one to look for an ultimate explanation for the universe and its many features. In a theistic world, the Designer could have used any number of methods to ensure the establishment of intelligent life, including a fine-tuned single universe or a multiverse.
Evaluation: Like the multiverse and chance hypotheses, theism cannot be proven scientifically. In other words, the theistic explanation is not a scientific position but a philosophical one. But that's okay since reason is the basis of all knowledge, not science. Nevertheless, many philosophical/theological arguments favor theism, while naturalism has few if any, positive arguments. Therefore, the success of theism depends on demonstrating why it explains fine-tuning better than the other two hypotheses.
Conclusion
Although each of the three explanations offered is consistent with a fine-tuned universe, none of them can explain fine-tuning with absolute certainty. But then we know almost nothing with aboslute certainty.
Objection B - Design is unscientific,
Repy: SETI looks for design [or artificiality - i.e. not generated by natural processes], an arson investigator can tell if a fire came about naturally or was started by a human, the police can determine if a death was natural or at the hands of a human, an archeologist can say whether it’s a just rock or an arrowhead, etc. An appeal to a designer is accepted in every field of inquiry, including biology - we can determine whether a virus, like Covid-19 was designed of was natural.
An a priori non-design stance seems to be an a priori ideological conclusion, rather one that is driven by the facts
Objection C -This is a God of the gaps argument.
Reply: A God of the Gap argument assumes an act of God as the explanation for an unknown phenomenon. But I’m not citing an unknown phenomenon or a gap in our knowledge. I am using the inference to the best explanation and citing what we do know about the universe, in order to choose between design [purposeful, intentional guided process with a goal] over chance [a purposeless, unintentional unguided process without a goal] or an the scientifically unknowable [the multiverse]
Objection D -You can't apply Zeno's paradox to causal chains.
Objection F -Saying that "God" is the TOE is literally meaningless. It provides no knowledge or insight into the universe, it's just wordplay. Pumpkin soup is the explanation for everything. See, we call all assert meaningless things.
Objection G - how can a designer create the universe without time, space, or energy/material?
I'll let Wiliam Lane Craig address this:
Does string theory, or M theory, predict the distinctive features of our universe, like a spatially flat four dimensional expanding universe with small fluctuations, and the standard model of particle physics? Most physicists would rather believe string theory uniquely predicts the universe, than the alternatives. These are that the initial state of the universe, is prescribed by an outside agency, code named God. Or that there are many universes, and our universe is picked out by the anthropic principle.
Notice that the options mentioned by Hawking are precisely the three alternatives which I address. Hawking argues that the first option, physical necessity, though the option most physicists would prefer to be true, is a vain hope: “M theory cannot predict the parameters of the standard model. Obviously, the values of the parameters we measure must be compatible with the development of life. . . .But within the anthropically allowed range, the parameters can have any values. So much for string theory predicting the fine structure constant.” He wrapped up by saying,
"...even when we understand the ultimate theory, it won’t tell us much about how the universe began. It cannot predict the dimensions of spacetime, the gauge group, or other parameters of the low energy effective theory. . . . It won’t determine how this energy is divided between conventional matter, and a cosmological constant, or quintessence. . . . So to come back to the question. . . Does string theory predict the state of the universe? The answer is that it does not. It allows a vast landscape of possible universes, in which we occupy an anthropically permitted location.
In fact, this idea of a “cosmic landscape” predicted by string theory has become something of a phenom in its own right. It turns out that string theory allows around 10^500 different universes governed by the present laws of nature, so that the theory does not at all render the observed values of the constants physically necessary. [source]