From link in OP.
> There are a whole lot of properties – like say how heavy an electron is – we don’t know why they are that weight. And if you change them, even slightly, the universe becomes too simple to make life. Imagine gravity is on a dial that ranges from one to 100. It needs to be tuned right to make atoms compress into stars. Without stars, there are no planets, and without planets there is no life. The odds of our universe being so perfect are too low
Yep.
> if we exist in a multiverse containing all possible universes
Whoa. Don’t need all.
> scientists like Dr Barnes are trying to find ways of estimating the probability of the existence of a multiverse.
Isn’t that back to front? Assuming the existence of a multiverse, find the probability of the universe?
> Return to the idea of gravity as a dial that can range between one and 100. According to the mathematical model, multiverses with one “setting” will be more likely than those with another setting.
How does he calculate “more likely”? I’m not saying it can’t be done, just saying that I’d like more information about the method. Off the top of my head I can think of at least three and possibly four different methods. One would be string theory compactification. A second would be evolutionary, with a strictly reducing vacuum energy at each step. A third would be satisfying constraints such as long duration metastability. A possible fourth, and I don’t know how to do this, would be a random walk through a quantum multiverse.
> Then you can check the strength of gravity in our universe. If the model deems it likely, it adds weight to the possibility of the existence of a multiverse. If the model deems it unlikely, it suggests something else altogether is going on.
I’m tempted to say no. What he’s really doing is testing the assumpions by which he assigned “more likely” above.
> It was thought you needed a small amount of dark energy in the universe to allow stars to form. The fact we had about the right amount was considered good evidence for the multiverse. … We turned it up to 300 and still did not kill the universe. We tried, but we still did not see that star obliterating universe. The team found nearly every setting from 1 to 300 could support life.
That’s a very interesting result. Dark energy is not nearly as fine tuned as had been thought.
Although it’s a very interesting result, it doesn’t really tell us anything about the existance of a multiverse. It only tells us that the universe isn’t as unique as we thought.
Let me think a little deeper about this. About the nature of dark energy. The cosmological constant has value … what is the value of the cosmological constant? Lambda is Λ = 2.036 × 10^−35 s^−2 . Not a nice value like 1. OK.