From: Blunderov (squooker@mweb.co.za)
Date: Mon Mar 29 2004 - 03:33:18 MST
[Blunderov] For those who, like me, find their minds glazing over at the
prospect of any more than four dimensions, the following article from
'Popular Mechanics' may prove helpful.
Best Regards
<q>
The Universe Book of Records
Part 4: The Limits of Size
By Christopher Backeberg
In Part 3 we looked at the most and least massive objects in the
Universe. Now let's contemplate the objects or structures that occupy
the most or least space.
A structure is two or more bodies interacting with each other in some
way and bound together in a cohesive manner. On the cosmic scale, the
force of cohesion is gravity. If we think of our Solar System as a
structure, then its components interact by orbiting the Sun and
constantly tugging at each other gravitationally.
Less than a century ago, the largest known structure in the Universe was
the Milky Way. Astronomers thought the Milky Way was the Universe, with
nothing existing outside it. Our galaxy is indeed an imposing structure,
100 000 light years in diameter, with a population of anything up to 300
billion stars.
As astronomers looked deeper into space with better instruments, they
realised that the Milky Way was but one of billions of galaxies. They
identified much bigger structures - groups or "clusters" of galaxies.
Our Local Cluster, which includes the Milky Way, contains some 50
galaxies. Gigantic voids of space separate the individual galactic
clusters.
There are still bigger structures. Gravity appears to have arranged the
distribution of matter throughout the Universe like a cosmic froth of
soap bubbles. The surfaces of these interconnected bubbles are made up
of walls and sheets of galaxies. Our awesome local cluster is merely a
small part of a much larger supercluster.
Astronomers have mapped the shape of the Universe in some detail out to
a
distance of 400 million light-years from the Sun. Our supercluster of
galaxies is continuous across this entire span and it may well extend
much farther. In the observed Universe, this supercluster is by far the
largest known structure.
There may be objects that would dwarf any structure spanning a measly
few hundred million light-years. Some cosmologists have speculated that
lines of stress may have formed in the miniscule proto-Universe at the
time of the Big Bang, 13,7 billion years ago. As the Universe expanded,
these lines of tension, named cosmic strings, would have expanded in
pace with it. Today, a cosmic string might span the entire Universe, or
at least a significant part of it.
A cosmic string would be an almost dimensionless line twisted through
the fabric of spacetime. Inside it might be appreciable percentage of
the total mass-energy of the Universe. Its gravitational field would be
colossal.
No cosmic strings have been detected in our region of space. If on did
arrive on the scene, its gravitational impact on nearby galaxies would
be devastating. If one passed between the Earth and the Moon, its tidal
force would rip both worlds to molecular shreds. And it might arrive at
nearly the speed of light, so we'd never see it coming.
At the opposite extreme of the Universe, the smallest known structure
the atomic nucleus, consisting of protons and neutrons. For just about
any atom from hydrogen to uranium and beyond, the diameter of the
nucleus is approximately a ten-million-billionth of a centimetre (10-13
CM).
The smallest known particle is the electron. Its diameter has not been
measured with precision, but the current estimate is 10-16 CM - about 1
000 times smaller than a proton or neutron.
Particle physicists have indirect experimental evidence that the proton
or neutron may be not just a particle, but the tiniest of all
structures. These two particles may each be made up of three quarks. A
quark (properly pronounced "kwark," although Americans say "cork") could
have the same diameter as an electron.
And there is mathematical justification - although no physical evidence
- to suggest that there are objects much, much smaller than electrons.
String theory and super string theory (not to be confused with the
cosmic string hypothesis) hold that all particles of matter and force
are no more than vibrations or harmonic resonances of infinitesimally
small loops, or "strings", which - with a diameter of 10-33 are smaller
than an atomic nucleus by a factor of 1 followed by 20 zeroes.
String theory also maintains that the Universe has not just four
dimensions of space and time, but either 10 or 11 dimensions, depending
on which fl of string theory you prefer. If string theory should ever
prove to be true, then you and everything around you are no more than
harmonic frequencies of a tension in an unknowable higher dimension of
the Universe.
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