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A Skeptical Look At The Multiverse
sjanich writes "The NY Times has a short, interesting article on multiverse theory. The author, Paul Davies, writes: 'This idea of multiple universes, or multiple realities, has been around in philosophical circles for centuries. The scientific justification for it, however, is new.' It is quite an interesting read. The author is a Physicist and pretty good science writer." Davies is not kind to the multiverse theory.
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The May issue of Scientific American contains a much more in-depth article on parallel universes, which has enough points in common that it might have inspired the op-ed piece.
Teaser for the article is here. To get the whole thing, you either have to have a subscription or wait until next month.
The gist of it is as follows:
In principle, these other "universes" can interact with our own, but in practice they're far enough away that it doesn't matter. Physical laws are likely similar.
Re. an infinite universe, the article states that a finite universe would leave artifacts in the cosmic microwave background that weren't seen.
These parallel universes are utterly unreachable, as the space between them a) exists in a different coordinate system that puts it in our past from our point of view, and b) is expanding exponentially quickly, dragging other universes away from ours at mind-boggling speed.
As far as I understand it, interaction between these universes wouldn't be possible without violating some of the ground rules involved (the history tree could be thought of as a state transition diagram for all possible states of a closed system; if it's closed, it can't interact with anything else).
If you call this a "real" universe, then Everquest and the reality hosting the United Federation of Planets are also real universes. It depends on your point of view (and what you mean by "real" in this context).
The existance of "universes" of the first type is certain if the universe is infinite, from information theory arguments. The infinite or non-infinite nature of the universe is something that can be empirically tested (though the final test - waiting for every part of it to come within our observation horizon - is impractical).
The existance of the second type of universe hinges on the nature of the scalar fields proposed in the various inflationary models. In principle, this is testable, either by recreating the energies required or by observing distant parts of the universe that are undergoing inflation.
The existance of the third type of universe is not testable, due to the requirement for closed systems. So it's pretty much a moot point.
The existance of the fourth type of universe is a metaphysical question, whose answer depends on what you mean by "exist".
The full article has a lot of additional discussion, and pretty pictures. By all means pick up a copy, if the topic interests you.
> Paul Davies is a religious person.
Some may find it useful to google for "paul davies" creationism.
> But whenever you drop something like God into your explanation, you've only made your job harder. Now instead of explaining life or the universe, you have to explain the existence of this vastly powerful and mysterious creature that made it all take place.
Moreover, the existence of an all-powerful agent that acts on its whim of the day is compatible with any observation, and thus is absolutely useless as an explanation for anything. One universe exists? God wanted it that way! An infinite number of universes exist? God wanted it that way!
The only things incompatible with the "theory" of creation by a willful omnipotent agent are the things the believers in that agent don't choose to believe (such as biological evolution, in much of the USA).
Sheesh, evil *and* a jerk. -- Jade
This should not be in the "Science" heading it's just creationist political opinion.
It's the opinion of a well-known scientist, who isn't particularly kind to the Creationist argument either (he calls it unsatisfying and unscientific in the article, if you would notice).
Man do you know anything about this guy? Check out his home page: http://aca.mq.edu.au/pdavies.html. He is a professor of Natural Philosophy. You don't seem to be familiar with this term, however it's the simply the old name for what we now call Science. It does not in any way make him a "philosophy professor". This guy has done much work (and written books about) cosmology, gravitation, and quantum field theory. He's published 25 books and over 150 papers to places like Nature and The Journal of Physics. Pretty hard core. Don't be so quick to dismiss someone because you don't understand their title.
Also, as a previous post pointed out, he hinted at a basic problem with multiverse theories: many are unfalsifiable. Unfalsifiable theorys cannot be tested, and are thus scientific. So yes, maybe some fantastic equations someone gets imply there may be other universes out there, however if they are completely separate from ours, then we cannot test whether or not they exist. It's like asking if God exists or not, no experiment can disprove his existence (or indeed prove it), and thus it's not science!
This article was his scientific opinions of a theory which deals with cosmology, which is one of his primary areas of study. Maybe you don't agree with what he has to say, but it is clear cosmology is something he knows at least a little about!