Fine-tuning in a Multiverse

Hi,In regards to the multiverse theory, I understand that it could be stated that a near infinite number of universes could exist each with minutely varying physical laws. I also understand that for the universe to exist at all much less function, the laws of physics must be exactly what they are, any deviation would cause the universe to stop working or never begin/exist in the first place. My question is this: if our current universe only exists because the laws of physics are exactly what they are, then how could any variant universe exist without having identically duplicate laws and, ergo, being an identically duplicate universe? There wouldn't be a multiverse then right? Because there could only ever be one universe that could begin/exist in the first place. I'm not trying to disprove the multiverse theory, I'm just wondering what someone would say to that. Thanks.
- Jonathan (age 16)
Tucson, AZ, USA

There are a couple of adjustments to make in what you've understood from other discussions.

The usual multiverse story makes no claim that universes have to be just like this one in order to exist. The claim is that any universe with basic laws a bit different from this wouldn't persist long enough with enough interesting chemistry going on to allow the formation of intelligent life. So the claim is not that different types of universes aren't "there", it's that nobody is in them asking why the laws are just the way they are. 

Secondly, although some of the parameters (notably the cosmological constant) require amazingly precise tuning to allow for life, so far as we know none require absolutely exact tuning. So the philosophical problem of asking whether identical copies are really copies or just the same thing doesn't have to come up.

Please follow-up if those adjustments don't suffice to take care of your questions.

Mike W.

(published on 07/07/2015)