EvC Forum: Cosmology 101

If the universe came with any old rag-bag of laws, life would almost certainly be ruled out. Indeed, changing the existing laws by even a scintilla could have lethal consequences. For example, if protons were 0.1 per cent heavier than neutrons, rather than the other way about, all the protons coughed out of

Another new scientist article shows how this may be true but wrong.

Not so fast

A Universe Without Weak Interactions is an excellent paper, with some fascinating insights into screwing around with the Stanadrd Model (not mention it is great as a teaching tool for graduates into how certain features of the SM arise)

BUT, it certainly does not demonstrate that random tinkering with fundamental physics preserves the ability to create life-friendly structure. This is one (relatively small) change that is finely tuned by hand to match many of the features of our Universe. It is a potential life-supporting point in the global parameter space, slightly separated from our own Universe. We expect these, and I made reference in my earlier post.

What we don't know is:
How many combinations are possible.
How many of those are life supporting and how many are not.

In other words the whole argument is spurious since it pretends to suggest an answer for which we have none of the inputs.

Well, in *theoretical* physics, we do have inputs. We have been looking at such scenarios for over thirty years with SuperGravity and its successor, String Theory/M-Theory. There have long been attempts to come up with THE specific string theory arrangement (compactification) that would reduce to something resembling our Universe and the Standard Model. It was remarkably difficult, and made us realise that coming up with our Universe is not as easy as we originally thought. Some of us (those of us fond of anthropic reasoning) believed that this would not be necessary, that there would be a vast array of different compactifications spanning the 10d (now 11d) space-time, and our 4d-Universe would simply arise in some small corner where the merging compactifications would be just right. This has now become mainstream (within the String fraternity) with the concept of the String Landscape. It is the biggest get-out clause ever devised - whatever fine tuning is or is not required for life, it is provided by the Landscape.

Edited by cavediver, : No reason given.

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