Blunderov
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"We think in generalities, we live in details"
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« on: 2004-03-29 05:33:18 » |
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[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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