No one looking at this problem (well, ok, ID'ers excepting but I mean no objective person) is suggesting that fine-tuning "logically means God's existence".
For physicists 'fine-tuning’ is indicative that there is a certain sensitivity of an outcome to some input parameters or assumptions, as well as a contrast between the wide range of possibilities and the narrow range of the particular outcome in question. The incredible delicacy of the cancellation is particularly disturbing, perplexing, demanding of a solution. On account of this amazing sensitivity, it means that the properties of our universe have to be, very precisely, just as they are.
No God implied. God is a philosophical/theological concept, not a scientific one.
But we are talking about the universe, the only universe we can observe and know to exist, and whether our universe really is all their is or if spacetime is infinitely larger, with an infinite number of "bubbles" spawned from an eternal cosmic inflation, each with their own distinct vacuum energies in the different regions.
You assume the existence of this infinity of unseen regions beyond our universe, the reach of our telescopes, the particle horizon and the speed of light, where the vacuum energy is much larger and conditions are inhospitable to the existence of life, such that our "fortunate" vacuum energy is therefore a selection effect.
This only works if both eternal inflation and String Theory is true: whereby the mechanism of inflation leads to a diverse multiverse filled with what Alan Guth calls pocket universes. Without the String Landscape, the pocket universes would all have the exact same physical laws. If you combine this idea with String theory, it leads to an infinetly large "Landscape" of possibilities for the local laws of nature in a given pocket, caused by hidden curled up higher dimensions that is in turn dependent on a concept called supersymmetry.
That's perfectly fine and plausible philosophically. But it rests on an untested assumption, an untested belief.
Because whereas we know their are other rocks and other planets, we do not know that their are other universes and have no evidence at the moment to even infer the existence of these other universes, anymore than we do God.
If there are other universes, that is amazing. But we have no way of potentially falsifying the statement, which makes it scientifically meaningless.
Therefore, if you want to put the multiverse probability argument forward as a viable explanation of the problem (which you certainly can), you are nonetheless appealing to an unseen infinity beyond what we can observe and test (indeed beyond conventional science) to explain the features of our own single universe, which is currently unfalsifiable.
As such, it is little different from an argument appealing to the immaterial agency of an infinite God, also being as He is an untestable and unfalsifiable philosophical explanation. Both explanations - infinite God or infinite multiverse - reach for explanations beyond the universe to explain the unique properties of the universe, either as intentional purpose or a selection effect, because they are essentially admissions of failure in trying to find an answer from first principles within the universe itself.
That's all I'm saying.
The multiverse is an extrapolation from other frameworks (namely eternal inflation and the string landscape) that have produced no unassailable, testable predictions despite being studiously analysed by the greatest minds working at the cutting-edge of theoretical physics for 40 years and accounting for about 90% of papers in that time.
Many folks don't want to abandon the inflationary multiverse because (a) even though its not strictly speaking science, its at least philosophically plausible (b) it would solve otherwise intractable fine-tuning problems and (c) they don't want to close the book on 40 years worthy of costly, fruitless endeavour and start again from scratch.
Most physicists, it should be said, would much rather be able to accurately calculate the observed value of the CC from first principles, thereby satisfying "naturalness", rather than being compelled to invoke an infinity of undetectable and accidental universes immune to testability, which relegates the value of this parameter (and the other fine-tunings) to probable luck rather than physical necessity. Steven Weinberg has said this many times.
They just don't see an alternative working from first principles but the problem is that the multiverse also requires the string landscape in M-Theory, which requires string theory which also requires SUSY and there is no evidence for SUSY/string theory. No extra hidden particles, superstrings or hidden dimensions have or are likely going to be discovered. I would be flabbergasted if we saw a Nobel Prize for String Theory by 2020, as Michio Kaku once predicted. I think that prediction at least is going to be falsified. At least it was "wrong".
As Professor Steven Weinberg himself explained in an interview only last month:
Model physicist - CERN Courier
"...Unlike many particle physicists on the day of the Higgs announcement on 4 July 2012, Weinberg doesn’t recall exactly what he was doing when he heard the news. What he is sure of is that we are entering what he described several years ago as the “nightmare scenario” of having found a SM Higgs boson and nothing else.
He says we’ve gotten ourselves into a rather unfortunate situation because the SM describes all the physics that can be addressed experimentally except things outside the SM like gravity and the neutrino masses. “It’s nobody’s fault. It is not an intellectual failure. It’s just a fix we’ve got into.”
He doesn’t hold out too much hope in mainstream theoretical arguments for the existence of physics beyond the SM at the energies currently being probed at the LHC – i.e. that new heavy particles must exist to cancel out quantum contributions to the Higgs mass that would cause it to spiral to infinity. The fact that we now know that an elementary Higgs scalar exists makes this “hierarchy problem” somewhat harder, Weinberg concedes, but he points out that we’ve been living with the problem already for 40 years.
So far the LHC has not found evidence for physics beyond the SM, including the most popular solution to shield the Higgs from getting additional mass: supersymmetry (SUSY). “Worse, there isn’t any one completely satisfactory SUSY model. Every SUSY model has things in it that are troublesome,” says Weinberg.
He thinks we might have to find other explanations for this and other absurdly fine-tuned parameters in the universe, such as the very small value of the vacuum energy or cosmological constant, or even abandon traditional explanations altogether.
“No one has come up with a plausible suggestion there except for the somewhat desperate suggestion that it is anthropic – that you have a multiverse and by accident there are occasional sub-universes where the vacuum energy is small and it’s only those in which galaxies can form – and people have suggested similar anthropic arguments for the smallness of the Higgs mass and the quark-mass hierarchy,” says Weinberg, who himself used anthropic reasoning in the 1980s to estimate, correctly, the approximate value of the cosmological constant a decade before it was inferred observationally from the velocities of distant supernovae. It’s a depressing kind of solution to the problem, he accepts. “But as I’ve said: there are many conditions that we impose on the laws of nature such as logical consistency, but we don’t have the right to impose the condition that the laws should be such that they make us happy!”..."
He says we’ve gotten ourselves into a rather unfortunate situation because the SM describes all the physics that can be addressed experimentally except things outside the SM like gravity and the neutrino masses. “It’s nobody’s fault. It is not an intellectual failure. It’s just a fix we’ve got into.”
He doesn’t hold out too much hope in mainstream theoretical arguments for the existence of physics beyond the SM at the energies currently being probed at the LHC – i.e. that new heavy particles must exist to cancel out quantum contributions to the Higgs mass that would cause it to spiral to infinity. The fact that we now know that an elementary Higgs scalar exists makes this “hierarchy problem” somewhat harder, Weinberg concedes, but he points out that we’ve been living with the problem already for 40 years.
So far the LHC has not found evidence for physics beyond the SM, including the most popular solution to shield the Higgs from getting additional mass: supersymmetry (SUSY). “Worse, there isn’t any one completely satisfactory SUSY model. Every SUSY model has things in it that are troublesome,” says Weinberg.
He thinks we might have to find other explanations for this and other absurdly fine-tuned parameters in the universe, such as the very small value of the vacuum energy or cosmological constant, or even abandon traditional explanations altogether.
“No one has come up with a plausible suggestion there except for the somewhat desperate suggestion that it is anthropic – that you have a multiverse and by accident there are occasional sub-universes where the vacuum energy is small and it’s only those in which galaxies can form – and people have suggested similar anthropic arguments for the smallness of the Higgs mass and the quark-mass hierarchy,” says Weinberg, who himself used anthropic reasoning in the 1980s to estimate, correctly, the approximate value of the cosmological constant a decade before it was inferred observationally from the velocities of distant supernovae. It’s a depressing kind of solution to the problem, he accepts. “But as I’ve said: there are many conditions that we impose on the laws of nature such as logical consistency, but we don’t have the right to impose the condition that the laws should be such that they make us happy!”..."
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