Thursday, September 22, 2005

Multiple Universes

The cover story of the current issue (October 2005) of Astronomy magazine is about the growing consensus among physcists that our little place in the cosmos is simply one universe in a larger multiverse. This cuts right to the heart of one of ID's main arguments: that cosmological “fine-tuning” can only be explained as the direct result of an intelligent designer. If there are an essentially infinite number of universes, each with different fundamental constants, then chance alone is an adequate explanation for why our universe has just the constants it does.

The article, by Steve Nadis, is not freely available online, so here are a few excerpts:

More than 400 years ago, the Dominican monk Giordano Bruno was burned at the stake for making a heretical claim: that our universe was inifnite and contained an infinite number of worlds.

Today, cosmologists arguing a similar point - that our universe is but one of many universes comprising a larger “multiverse” - are hoping for a better fate, maybe even a Nobel Prize. There is growing acknowledgement among physicists and astronomers that this idea, outlandish as it sounds, just might be true.

One picture emerging from cosmology, astronomical observations, and particle physics is that there's a lot more to the universe than we can see: The universe is not only vast, extending far beyond the visible portion, it may be composed of distinct, exponentially large regions with wildly divergent features. For all practical purposes, these realms could be regarded as separate universes within an all-embracing multiverse.

While schemes exist for multiple or parallel universes, one promising approach reflects what Haravrd physcicist Nima Arkani-Hamed calls “the confluence of things now pushing us toward the notion of a multiverse.”

These include: measurements that indicate the universe's expansion is accelerating; empirical tests that bolster the inflationary universe scenario; thoeries of eternal inflation that suggest an endless number of Big Bangs; and recent developments in string theory that show how to design universes with widely different properties. Collectively, these developments support the proposition that on the largest scales, diversity, not uniformity, characterizes our universe.

Later on we find this:

Eternal inflation creates a different kind of universe than the simple sphere we once envisioned. Think of Swiss cheese instead. Each hole represents a bubble universe; the cheese represents the space between the bubbles and is expanding faster than the speed of light. Not only do the bubbles get farther and farther apart, new bubbles keep forming withn the cheese - the result of new Big Bangs popping off in a never-ending chain reaction. Eternal inflation doesn't just produce an oversized hunkof cheese; it produces a multiverse.

How convincing is this scneario?

“Many, no doubt, would call it a house of cards, but from my point of view, it looks very plausible,” says MIT's Alan Guth, generally credited as inflation's inventor. Inflation has been very successful in making predictions - flatness, homogeneity, and scale-invariance - for the part of the universe we can observe, he says, “which means we should also take seriously its predictions for parts of the universe we can't observe.”

Indeed. As I recall, I said something very similar in this blog entry, and took some grief in the comments for it. Nice to have Guth on my side.


As scientists, adds [MIT physicist Max] Tegmark, “We're not testing the general idea of a multiverse. We're testing inflation - a mathematical theory that predicts a multiverse and all kinds of other stuff.” So far, inflation has passed all empirical tests to date, but the idea faces even more rigorous challenges coming later this decade and beyond.

“We still have no idea whether these is one universe or many,” says [Cambridge University astronomer Martin] Rees. Yet at a 2003 Stanford University conference, he was confident enough of the multiverse's existence to stake his dog's life. Stanford's Andrei Linde went further, claiming he would put his own life on the line.

The article has much more to say, including some stuff specifically about the anthropic principle. I recommend picking up a copy (or at least reading it in the bookstore, leaning against the newsstand).

As I read the article I was mostly thinking about just how pathetic the ID folks really are. The fine-tuning of the universe for life is something that needs to be explained. One possibility is to hypothesize that we are part of a multiverse, a conclusion that follows logically from tolerably well-established principles of modern physics. This possibility only requires us to hypothesize that the sorts of forces that led to our Big Bang led to other Big Bangs as well. There is absolutely no argument, beyond personal incredulity, against the idea, and the theorists investigating the possibility are routinley led to other important discoveries for their troubles.

Another possibility is to invent, out of whole cloth, an intelligent agent fundamentally different from any known intelligent agents. This intelligent agent would have unfathomable, supernatural powers. There is absolutely nothing in the way of direct evidence for the existence of such an agent. And if you further hypothesize that this agent is omnipotent and omnibenevolent, there is evidence against his existence (the problem of evil and suffering). Choosing this possibility leads to no insight into any physical process. A physicist choosing this path continues to do research in spite of his belief, not because of it.

I'm with the folks who, by sheer hard work and brain power, are trying to figure out how things really work. Choose the God cop-out if you wish, but stop pretending there's anything scientific about your conclusion.


At 12:18 PM, Anonymous Anonymous said...

A lot of physicists aren't all that excited by the hype surrounding these multi-universe theories. Peter Woit's blog is a bit more critical of the Astronomy article:
See here.

Steven S

At 12:30 PM, Blogger Macht said...

Bruno wasn't burned at the stake for thinking the universe was infinite.

At 2:48 PM, Anonymous Anonymous said...

At one point a few years back, I considered the formation of a singularity inside a blackhole. The temperature and density would at some point approach that which existed during the hyperinflationary period, matter would pass through the three major phase transitions which separated the four fundamental forces, and matter itself would resemble that which existed when our universe was born. As such, one could expect such matter to go through its own hyperinflationary process, giving rise to new universes. Later, I ran across Guth stating essentially the same thing.

It is an interesting possibility...

-Timothy Chase

At 3:08 PM, Blogger Dale Callahan said...

How would you make a distinction between "many" universes [multiverse] with no set standards, and one universe.

Unless we ourselves are infinite how can we claim that our universe is infinite?

How can we justify the standards we have in our universe?
Laws of logic, uniformity of nature, ethics?

At 12:07 AM, Anonymous Anonymous said...

This isn't really any different from the steady-state universe is it? "Think of Swiss cheese instead. Each hole represents a bubble universe; the cheese represents the space between the bubbles and is expanding faster than the speed of light. Not only do the bubbles get farther and farther apart, new bubbles keep forming withn the cheese - the result of new Big Bangs popping off in a never-ending chain reaction"

And besides, inflation theory doesn't necessarily mean eternal inflation. As I understood it (mainly through Brian Greene, admittedly) inflation theory allows for (leads to?) a single-bang interpretation that fits with pretty much all observed data. Is this not the case?

At 8:24 AM, Blogger M.C. said...

Hmmmmm. What is the evidence for this theory?

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At 7:33 PM, Anonymous Anonymous said...

qmMaybe matter,in one form or another,has always existed.Physicists may never find the answer to this.I seriously doubt anything exist,god,id, etc,that isn't controlled or dependent on something else. We have knowledge of this universe.It could be very microscopic,as compaired to what really exist.It is very interesting.Physicists,scienctists, may come up with some very amazing discoveries, of what is going on around us,and of what could possibly exist.

At 1:27 AM, Anonymous Joseph Chklovski said...

I am so excited to read your post.Thanks for giving such an informative post. It has lots of information about Astronomy And Space. We can get more information from your post.


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