See Inside June 2006

Hard Landscape

Finding our universe in string theory appears impossible

Cosmology was always going to be trouble for particle physics. Traditional quantum theory predicts that the vacuum of space should bubble over with short-lived "virtual" particles, whose combined energy, represented by the so-called cosmological constant, would have long ago blown galaxies far and wide like grease on water at the touch of detergent. Lately, trying to make sense of why the cosmological constant is tiny, physicists have toyed with a concept based on string theory. Called the landscape model, it supposes that many universes with different cosmological constants are realized in a larger multiverse. Despite long-standing hopes to the contrary, landscapers now have found that singling out a universe from this array is mathematically nigh impossible.

In 1998 astronomers discovered that the universe's expansion is accelerating at a rate consistent with a cosmological constant 10-120 times the value predicted by quantum theory. String theory, which unites gravity with quantum mechanics, offered the hope of explaining the attenuated cosmological constant. It recasts particles as one-dimensional strings, or filaments of energy, which play around in tiny tangles of extra spatial dimensions. The shape of the tangles influences the properties of strings and therefore the vacuum's energy. But no mathematical principle forces the extra dimensions to fold in a unique way.

This is only a preview. Get the rest of this article now!

Select an option below:

Customer Sign In

*You must have purchased this issue or have a qualifying subscription to access this content

It has been identified that the institution you are trying to access this article from has institutional site license access to Scientific American on
Click here to access this article in its entirety through site license access.

Rights & Permissions
Share this Article:


You must sign in or register as a member to submit a comment.
Scientific American Holiday Sale

Scientific American Mind Digital

Get 6 bi-monthly digital issues
+ 1yr of archive access for just $9.99

Hurry this offer ends soon! >


Email this Article


Next Article