The Degree of Fine-Tuning in our Universe – and Others
This paper reviews the current constraints on these quantities. The discussion starts with an assessment of the parameters that are allowed to vary.
If the parameters are allowed to vary, there is no physical necessity.
“There is not a shred of evidence that the Universe is logically necessary. Indeed, as a theoretical physicist I find it rather easy to imagine alternative universes that are logically consistent, and therefore equal contenders of reality” (“The Appearance of Design in Physics and Cosmology,” in God and Design: The Teleological Argument and Modern Science, ed. Neil A. Manson [London: Routledge, 2003], 148–49).
First, let’s talk about physical necessity. As I just explained, according to this alternative the universe has to be life-permitting. The constants and the quantities had to have the values that they do. It is literally physically impossible for the universe to be life-prohibiting. It is physically necessary that the universe be a life-permitting universe. 1
String theory, the current best candidate for a "theory of everything," predicts an enormous ensemble, numbering 10 to the power 500 by one accounting, of parallel universes. Thus in such a large or even infinite ensemble, we should not be surprised to find ourselves in an exceedingly fine-tuned universe. [url= https://phys.org/news/2014-04-science-philosophy-collide-fine-tuned-universe.html#jCp]3[/url]
On the very face of it, this is an extraordinarily implausible explanation of the fine tuning. It would require us to say that a life-prohibiting universe is physically impossible – such a thing could not exist. And that is an extremely radical view. Why take such a radical position? The constants, as we have seen, are not determined by the laws of nature. Nature’s laws could hold, and the constants could take any of a wide range of values, so there is nothing about the laws of nature that require the constants to have the values that they do.
As for the arbitrary quantities, remember those are completely independent of the laws of nature – they are just put in as initial conditions on which the laws of nature then operate. Nothing seems to make these quantities necessary in the values they have. The opponent of design is taking a very radical line which would require some sort of evidence, some sort of proof. But there isn’t any proof that these constants and quantities are physically necessary. This alternative is just put forth as a bare possibility; and possibilities come cheap. What we are looking for is probabilities or plausibilities, and there just isn’t any evidence that the constants and quantities are physically necessary in the way that this alternative imagines. 4
Steven Weinberg Department of Physics, University of Texas
In several cosmological theories the observed big bang is just one member of an ensemble. The ensemble may consist of different expanding regions at different times and locations in the same spacetime,7 or of different terms in the wave function of the universe.8 If the vacuum energy density ρV varies among the different members of this ensemble, then the value observed by any species of astronomers will be conditioned by the necessity that this value of ρV should be suitable for the evolution of intelligent life. 5
The first option, physical necessity, is the easiest to dismiss. The idea that it was physically impossible for the universe to have been created in any way other than in a manner that would support life is neither logically necessary nor scientifically plausible. As Barr notes, “In the final analysis one cannot escape from two very basic facts: the laws of nature did not have to be as they are; and the laws of nature had to be very special in form if life were to be possible.” Our options, therefore, are between chance (the anthropic coincidences truly are coincidences) or design (the parameters needed for life were purposely arranged). While it cannot be established with absolute certainty, we can, I believe, determine that design is the most probable explanation.
Paul Davies, Information, and the Nature of reality , page 86:
Given that the universe could be otherwise, in vastly many different ways, what is it that determines the way the universe actually is? Expressed differently, given the apparently limitless number of entities that can exist, who or what gets to decide what actually exists? The universe contains certain things: stars, planets, atoms, living organisms … Why do those things exist rather than others? Why not pulsating green jelly, or interwoven chains, or fractal hyperspheres? The same issue arises for the laws of physics. Why does gravity obey an inverse square law rather than an inverse cubed law? Why are there two varieties of electric charge rather than four, and three “flavors” of neutrino rather than seven? Even if we had a unified theory that connected all these facts, we would still be left with the puzzle of why that theory is “the chosen one.”
"Each new universe is likely to have laws of physics that are completely different from our own." If there are vast numbers of other universes, all with different properties, by pure odds at least one of them ought to have the right combination of conditions to bring forth stars, planets, and living things. “In some other universe, people there will see different laws of physics,” Linde says. “They will not see our universe. They will see only theirs. In 2000, new theoretical work threatened to unravel string theory. Joe Polchinski at the University of California at Santa Barbara and Raphael Bousso at the University of California at Berkeley calculated that the basic equations of string theory have an astronomical number of different possible solutions, perhaps as many as 10^1,000*. Each solution represents a unique way to describe the universe. This meant that almost any experimental result would be consistent with string theory.
When I ask Linde whether physicists will ever be able to prove that the multiverse is real, he has a simple answer. “Nothing else fits the data,” he tells me. “We don’t have any alternative explanation for the dark energy; we don’t have any alternative explanation for the smallness of the mass of the electron; we don’t have any alternative explanation for many properties of particles.
What About God?
For many physicists, the multiverse remains a desperate measure, ruled out by the impossibility of confirmation. Critics see the anthropic principle as a step backward, a return to a human-centered way of looking at the universe that Copernicus discredited five centuries ago. They complain that using the anthropic principle to explain the properties of the universe is like saying that ships were created so that barnacles could stick to them.
“If you allow yourself to hypothesize an almost unlimited portfolio of different worlds, you can explain anything,” says John Polkinghorne, formerly a theoretical particle physicist at Cambridge University and, for the past 26 years, an ordained Anglican priest. If a theory allows anything to be possible, it explains nothing; a theory of anything is not the same as a theory of everything, he adds.
If the life-friendly fine-tuning of our universe is just a chance occurrence, something that inevitably arises in an endless array of universes, is there any need for a fine-tuner—for a god?
“I don’t think that the multiverse idea destroys the possibility of an intelligent, benevolent creator,” Weinberg says. “What it does is remove one of the arguments for it, just as Darwin’s theory of evolution made it unnecessary to appeal to a benevolent designer to understand how life developed with such remarkable abilities to survive and breed.”
” Carr says, “you might have to have a fine-tuner. If you don’t want God, you’d better have a multiverse.”
If these cosmic traits were just slightly altered, life as we know it would be impossible. A few examples:
• Stars like the sun produce energy by fusing two hydrogen atoms into a single helium atom. During that reaction, 0.007 percent of the mass of the hydrogen atoms is converted into energy, via Einstein’s famous e = mc2 equation. But if that percentage were, say, 0.006 or 0.008, the universe would be far more hostile to life. The lower number would result in a universe filled only with hydrogen; the higher number would leave a universe with no hydrogen (and therefore no water) and no stars like the sun.
• The early universe was delicately poised between runaway expansion and terminal collapse. Had the universe contained much more matter, additional gravity would have made it implode. If it contained less, the universe would have expanded too quickly for galaxies to form.
• Had matter in the universe been more evenly distributed, it would not have clumped together to form galaxies. Had matter been clumpier, it would have condensed into black holes.
• Atomic nuclei are bound together by the so-called strong force. If that force were slightly more powerful, all the protons in the early universe would have paired off and there would be no hydrogen, which fuels long-lived stars. Water would not exist, nor would any known form of life. 2
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