My personal opinion is that I don't have much of an opinion either way. If it is finite, it is destined to recollapse in 20-50 billion years or so, and all life in the universe is doomed to being fricasseed like just so much beef on a bar-b-q grill. If it is infinite, matter as we know it will cease to exist in another trillion trillion trillion years as its quarks may decay away into lighter particles, and again life is doomed.
Technically, the question is whether the universe contains more of less that a critical mass density of gravitation material. If it has more, then the gravity of everything pulling on everything else will slow the expansion of the universe so that re-collapse can occur.
Just by counting-up how much luminous matter there is in stars and galaxies, we can only find about half of 1 percent of this critical matter. If we use the predictions of Big Bang cosmology as a guide, the abundance of cosmological hydrogen, helium and deuterium indicates that the universe can not contain more than 10 to 15 percent of the critical density. So, in terms of normal matter ( in protons and neutrons) the universe looks like it is destined to expand forever. But there is now a catch to this.
Physicists have begun to show evidence that neutrinos may have just the slightest amount of mass. Since there are about as many neutrinos in the universe as the photons of light left over from the Big Bang, adding a little bit of mass to each one adds up, cosmologically to a total mass in matter and neutrinos of about 30 percent of the critical density. But there may be more!
For decades astronomers have been weighing clusters of galaxies in space and often find that the luminous matter is only a few percent of the total gravitating mass of some clusters. The amount of 'dark matter' if present in all clusters, would bring the total gravitating mass to about the critical amount and perhaps a tad more, so that the universe would be finite. The jury is still out on all of this, but it is very troubling to know that the universe might be filled by 'dark matter' of which the luminous kind in stars is only 1 percent.
So, we still don't know if the universe is infinite or finite, but we seem to be moving closer to answering this question, possibly in the next 20 or 30 years or so.
Since 1998, the consensus has moved towards a critical universe with 'Omega = 1" and with 30% in dark matter and 70% in a cosmological constant which is causing accelerated expansion. NASA's MAP mission will settle, once and for all, this debate of open versus closed by measuring all of the necessary cosmological parameters to a precision of better than 5% by 2003.The figure above shows the results of several independent studies that confirm a large cosmological constant ( Omega-Lambda) and a large dark matter component, (Omega-m).
Copyright 1997 Dr. Sten Odenwald
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