I don’t think I ever said it demands. One thing that I actually said amounts to this: low probability of the constants is something of a feature of the multiverse,
Put that way, fair enough!
Probability may feature in the multiverse idea to the extent that the constants in the bubbles are ultimately a result of randomness, rather than an underlying mechanism of physical necessity.
But my point was that this doesn’t make it indicative of there being a multiverse, just because a constant is deemed in the eyes of some to have a low statistical probability.
On its own, cosmic inflation might result in bubble universes if it is “eternal” (rather than chaotic, which is the other viable model and doesn’t lead to a multiverse) but those universes, by themselves in the eternal inflation model, would all have the same constants without the existence of a string landscape.
The multiverse needs cosmic inflation that is eternal and a string landscape, and the string landscape in turn needs supersymmetry or SUSY as I like to call it (in most articulations of string theory).
No SUSY = no string theory = eternal inflation that produces bubble universes all with the same constants… and that’s not even getting to the contested evidence for inflation, since there are a number of prominent theoretical physicists who don’t even believe inflation exists either (whether eternally or chaotically). Get my drift?
What I’m saying to you is that this inflationary-string landscape model is being dealt lethal blows at the moment and appears to be on its last legs. It’s a house of cards. Nobody knows yet what to replace it with but its not producing any testable predictions, after some thirty years of the biggest colliders known to human history smashing particles together at the highest energies our civilization can produce short of a collider the size of the entire solar system and billions upon billions of taxpayer funded dollars/pounds/euros to boot.
The prognosis is not good, therefore, for the “multiverse” even being scientifically possible - so, to look at someone saying, “I believe the value of this constant is improbably small for xyz reasons" and arguing that this logic lends itself to the multiverse, just doesn’t register with me because I doubt whether its even possible anymore to conceive of a multiverse in the first place.
If the multiverse lacks any substantive, testable foundations from the offing, courtesy of lack of evidence for the models that have the multiverse as a consequence and make it possible, or indeed made people start thinking about the idea (namely eternal inflation and the string landscape), then one wouldn’t have any grounds to think that low probability of a constant naturally infers it, would we?
That’s what I’m saying.
As an addendum, a question for you: The value of the cosmological constant can’t be calculated working from first principles. This indicates there may not be a “natural” mechanism to account for why it takes the value that it does. Likewise, quantum physics provides formulas for calculating what the Higgs mass should be, and the Higgs should be very, very heavy. Only its value is actually very, very light with cancellations down to a very fine degree of precision.
This situation undermines and mitigates against the physical necessity “high probability” argument you referred to earlier and which you favour theologically if I read you right (i.e. that the constants are what physics says they must be). “Naturalness” is out as a solution.
An “unnatural” (and to many physicists unsettling) explanation for the Higgs mass or cosmological constant may then be sought, invoking “anthropic” reasoning. Perhaps the Higgs mass isn’t fixed precisely by any underlying theory, but can assume a wide range of values in different regions of the universe - that is, in different bubble universes in a multiverse. It takes the heavy materials-complexity-life permitting value in our universe, simply by chance.
So one might next consider this random throw of the dice to explain the fine-tuning anomaly. For that, you need the multiverse, for the probability distribution. But for the multiverse, you need string theory and eternal inflation and SUSY…
And if the probability-multiverse argument is also out, hypothetically, for the reasons I’ve outlined regarding string theory and SUSY…where do we go next?
No natural “physical necessity” explanation; no “anthropic” explanation relying on a probabilistic multiverse.
God is not and can never be a scientific explanation. No supernatural invocation can be, because that ain’t testable. So where do we go from here to solve the fine-tuning problem?
I’m afraid this increasingly looks to be where we are at. A serious impasse.
I must be remembering incorrectly, for I thought it was invented precisely for that reason; to deal with the fine-tuning required to avoid the horizon and flatness problems.
Inflationary theory (one of the two foundations needed for the multiverse concept) was indeed conceived to account for those two fine-tuning problems but not the multiverse itself, which actually emerged from the confluence between eternal inflation and string theory.
You could, I suppose, argue for an indirect genesis leading back to fine-tuning as the original problem, in that respect, but my point still stands: the multiverse itself is independent of fine-tuning or probabilistic speculation, arising as it does as a consequence of inflation and the string landscape. If either of those two theories aren’t true, then you can kiss bye-bye to the multiverse irrespective of how many people think finely-tuned parameters are improbable, because in that eventuality it wouldn’t even be an option to account for a claim of low probability of a constant.
That inflation in turn arose to explain away a fine-tuning is, however, a rather neat irony though isn’t it? Talk about circular!