A "Weakless" universe would have a hard time synthesizing oxygen, or atoms much larger than iron (e.g. uranium)

Problems in a weakless universe - L. Clavelli, R. E. White III:

. . . on closer examination the proposed "weakless" universe strongly inhibits the development of life in several different ways. One of the most critical barriers is that a weakless universe is unlikely to produce enough oxygen to support life. Since oxygen is an essential element in both water, the universal solvent needed for life, and in each of the four bases forming the DNA code for known living beings, we strongly question the hypothesis that a universe without weak interactions could generate life.

If you'd bother reading my earlier posts on this thread you'll find I mentioned the fine tuning implications of particle mass ratios, along with ratios of electric, nuclear, and gravitational forces. However leading theories of quantum gravity involving the Planck scale implied that the cosmological constant was on the order 1 in Planck units -- which turns out to be

slightly off:

The CC [cosmological constant] is by far the most troubling parameter for effective field theorists since (1) it is the most technically

unnatural parameter, i.e., it must be tuned to one part in 10120, and (2) we have no understanding why it should be numerically small but non-zero. As the CC is increased, holding everything else fixed, the universe eventually becomes CC dominated early enough that density perturbations in the universe do not have enough time to grow and go non-linear to form large scale structure.

A Universe without Weak interactions - Roni Harnik, Graham Kribs, Gilad Perez - Phys. Rev.D74:035006,2006.

Furthermore:

"How can we calculate the energy density of the vacuum? This is one of the major unsolved problems in physics. The simplest calculation involves summing the quantum mechanical zero-point energies of all the fields known in Nature. This gives an answer about 120 orders of magnitude higher than the upper limits on Lambda set by cosmological observations. This is probably the worst theoretical prediction in the history of of physics! Nobody knows how to make sense of this result. Some physical mechanism must exist that makes the cosmological constant very small."

General relativity: an introduction for physicists By Michael Paul Hobson, George Efstathiou, Anthony N. Lasenby Cambridge University Press, 2006 (emphasis mine)

The internets are wonderful aren't they? In my research for the above citations I discovered that Steven Weinberg, no theist, relied on the anthropic cosmological principle just as Hoyle had done in the early '50s with his prediction of the triple alpha process resonance state; he actually pointed out this problem with the cosmological constant as far back as 1986: S. Weinberg, Phys. Rev. Lett. 59, 2607 (1987).

The cc is, as you yourselves have conceded, just one parameter. Martin Rees points points also to several others. For example the strong force (among other factors) ξ the force binding protons and neutrons, basically allowing the efficiency of thermonuclear fusion of hydrogen to helium in stars, ξ = 0.007, if it were 0.008 little hydrogen would survive the big bang, if it were 0.006 a proton could not be bonded with a neutron. Ouch!

Just one more example of many others I could elaborate on but it really shouldn't be my job to spoon feed all this to you, again the internets are a great resource . . . .

Recall your challenge?:

Oldskeptic says:

Pick a different natural constant from their lists, one that would really matter. Say, the strong force, or the weak force, or the electromagnetic force, or gravity. A value that that we actually know.

Then you can try to argue that infinitesimal differences would have drastic effects, but first you would have to show that these differences were possible.

Good luck with that.

You say I would have to show that "differences were possible". It is in fact only the possibility that differences are possible (or at least not disproved by our current knowledge) that allows for multi-verse weak anthropic arguments. Pal, if I could demonstrate differences were

not possible your argument would be destroyed beyond all your imaginings. Just think if we lived in a reality in which

both fine tuning AND invariance of physical constants could be proved; At once all of the colossal improbabilities would be stamped on all possible universes!

Thommo

Now let's consider the scenario you're presenting us with:-

X possible universes are placed in a bag, Y of them have cosmological constant=10-120, one universe is selected randomly. What is the probability the universe selected has cosmological constant=10-120?

There's a major problem - We don't know X or Y. We don't know what proportion of possible universes have cosmological constant in the "required" range, the question cannot be answered and we can assert neither probability nor improbability.

See above.