| Topic: |
Religions > Atheism |
| User: |
"stoney" |
| Date: |
11 Oct 2004 11:53:49 PM |
| Object: |
OT: How to build the Universe |
http://www.nature.com/news/2004/041004/full/041004-17.html
News
Published online: 08 October 2004; | doi:10.1038/news041004-17
How to build the Universe
Philip Ball
Including cause-and-effect in equations produces 4-dimensional
space-time.
Tiling together tiny triangles of space-time gave rise to a universe
that looks just like our own.
Is causality an inherent and necessary characteristic of the Universe,
or just an illusion produced by the way our brains interpret the
world?
It's real, say physicists, who believe they have worked out how the
Universe is constructed from the tiniest building-blocks of
space-time. The finding could also help the development of a theory of
quantum gravity, which would marry the two currently estranged
physical theories of the Universe: quantum theory and relativity.
Quantum theory describes the Universe at the tiniest possible scale -
about 10-35 metres (about 1020 times smaller than the radius of a
proton). It predicts that on this scale the apparently smooth fabric
of space and time must degenerate into a kind of 'foam' in which
connections between different points are constantly appearing and
vanishing.
Physicists have long been trying to figure out how the fuzzy nature of
space-time at this tiny scale can give rise to the large
four-dimensional Universe we see around us, as described by Einstein's
theory of relativity.
Scientists studying the problem assume that each tiny piece of the
foam is a kind of four-dimensional triangle, with three dimensions of
space and one corresponding to time. The smooth fabric of space-time
can be built up by gluing these triangular tiles together, just as a
smoothly curved surface can be made from flat, two-dimensional tiles.
Because the quantum foam fluctuates through all kinds of
configurations, constructing the physical Universe means adding up all
the possible tiling patterns. You might think that this would
inevitably generate a four-dimensional Universe - but it doesn't.
Earlier researchers found that they got a space-time with either an
infinite number of dimensions or just two. Neither of these looks at
all like our Universe.
Construction work
Renate Loll of Utrecht University in the Netherlands and her
co-workers have now found a way to assemble the pieces so that they
inevitably produce a four-dimensional Universe. Instead of assuming
that all tilings are allowed, they impose two constraints.
First, the theory of relativity must apply within each individual tile
(so that nothing can travel through it faster than light) and second,
the assembly must preserve causality. This means that a piece of
space-time cannot be constructed in such a way that an 'event' - some
change in the Universe - precedes its cause.
When they enforced these criteria on their calculations, the
researchers ended up with universes with three spatial dimensions and
one time dimension - just like our own1. It was "like magic", says
Loll.
Even more startling, they found that typical universes generated this
way started off small and got bigger - they expanded, just like the
real Universe has done since the big bang. This was completely
unexpected - there was nothing in the tiling rules that seemed to
demand it. "We're completely stunned," says Loll.
She admits that there's no a priori reason to demand that quantum
space-time has to observe causality: the researchers put it into their
equations by hand. But that, it seems, is the only way to end up with
a realistic Universe.
Top
References
1. Ambjørn J., Jurkiewicz J. & Loll R. Physical Review Letters, 93.
131301 (2004). | Article | ChemPort |
/end
--
Contempt of Congress meter reading-offscale.
Vote for Bush. Why vote for the lesser of two evils?
No matter the candidates the superstition industry wins.
'Jesus' is a sock-puppet Christians utilize to add 'authority' to
whatever action they intend on taking. -Stoney
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