Moorad Alexanian wrote:
> Thursday, May 10, 2001
>
> Einstein was right! (for the wrong reason)
>
> Astronomers struggle with basic theories about the universe, following the
> discovery of "dark energy."
There are a number of important mistakes in this report. Details follow
but they fall in three general (though connected) categories:
1) The suggestion that the cosmological constant was considered a nutty
idea by all relativists & cosmologists from the discovery of cosmic expansion
until the last couple of years,
2) the notion that the cosmological constant was a pure fudge factor,
and
3) the idea that the cosmological term is known definitively to be due
to quantum vacuum energy.
(& there is also the minor error that "Edwin Hubble published his
evidence in 1925 that
the universe was expanding". It was in 1929.)
1) Even after Hubble's discovery there were experts - Eddington,
McVittie, LeMaitre, & Schroedinger are the most notable - who retained or were
willing to retain the cosmological constant. There seems, however, to have been
the odd idea among some physicists - Pauli, e.g. - that the cosmological term
could be dropped just because Einstein thought that it should be. One could
"refute" quantum theory in the same way!
2) In the period between 1929 and 1995 there were a number of proposed
arguments for a non-zero cosmological constant besides the anachronistic one of
getting a static universe. Briefly -
a. The cosmological term is simply a mathematical possibility in the
field equations - as a note in Einstein's original general relativity paper
implied even before he considered cosmology. If Einstein hadn't introduced it
to get a static universe, somebody else would soon have seen the possibility.
b. Einstein didn't just introduce this term as a pure fudge factor but
tried to relate it to the "Poincare stresses" which were supposed to hold the
classical electron together.
c. The cosmological constant (which has dimensions of an inverse length
squared) can be understood as defining a basic length scale for the universe.
d. In the type of unified field theory developed by Schroedinger in
which affine connection rather than metric is fundamental, a non-zero
cosmological term is needed in order for space-time to be given a metric
structure.
e. The steady state cosmology has the basic structure of a relativistic
universe with a positive cosmological constant. McCrea explained Hoyle's
"creation field" in terms of a medium with negative energy - an idea which has
some connections with quantum vacuum energy.
f. A logical generalization of the Lorentz invariance of special
relativity is invariance under the de Sitter group - i.e., the group of motions
in an empty universe with a cosmological constant.
These are all in addition to the many attempts to use the cosmological
term to solve various observational problems - the latest of which has finally
gotten the cosmological community as a whole to take this term seriously.
3) The cosmological term in the field equations has the _form_ of the
density & pressure contributions due to quantum vacuum energy, as Zeldovich
realized over thirty years ago. But the _numerical value_ resulting term is too
large by many orders of magnitude - unless one postulates particles of extremely
low rest mass for which there is no independent evidence.
Shalom,
George
George L. Murphy
http://web.raex.com/~gmurphy/
"The Science-Theology Interface"
> By Peter N. Spotts Staff writer of The Christian Science Monitor
>
> Michael Levi is finding a golden opportunity in Albert Einstein's "greatest
> blunder."
>
> In 1917, Einstein pulled a fudge factor out of thin air to coax his
> equations on general relativity into describing a universe astronomers
> actually saw.
>
> Three years ago, two teams of astronomers startled the scientific world with
> evidence that this figment of Einstein's chalk board - which the legendary
> physicist later repudiated - has a measurable impact on the universe.
>
> Now, what Einstein called a cosmological constant appears to be "the largest
> form of energy in the universe," Dr. Levi, a physicist, says. And, he
> laments, "we know nothing about it."
>
> That is about to change.
>
> On June 30, the National Aeronautics and Space Administration is slated to
> launch a spacecraft that will map the afterglow of the Big Bang in
> unprecedented detail. Data from the craft are expected to carry further
> clues about the "dark energy" Einstein's fudge factor describes.
>
> Meanwhile, at the Lawrence Berkeley National Laboratory in Berkeley, Calif.,
> Levi and
>
> colleague Saul Perlmutter are designing a space-based telescope that will
> use light from exploding stars in distant galaxies to trace the history of
> this energy's influence on the cosmos.
>
> These projects are two among several aimed at unraveling the mysteries of
> dark energy, which has earned that moniker less for its lack of luminosity
> than for the ignorance surrounding it, some researchers say.
>
> Fundamentally bizarre phenomenon
>
> Indeed, the very idea of dark energy in the cosmos "is so bizarre from a
> fundamental-physics point of view that in their heart of hearts, people are
> still extremely skeptical," says Scott Dodelson, an astrophysicist and
> theoretician at the Fermi National Accelerator Laboratory in Batavia, Ill.
> "They say: 'You've got to prove it to me again and again - and you've got to
> prove it in different ways - or I won't believe it.' "
>
> For his part, Einstein invoked dark energy out of expedience.
>
> As he watched his equations on general relativity unfold, they led to the
> conclusion that the fabric of space-time is not holding steady, but could
> either expand or contract, depending on the universe's shape and on how
> densely it is packed with matter. Above a certain threshold, a densely
> packed universe would collapse under the pull of its combined gravity. Below
> that threshold, gravity grip loosens and the universe expands.
>
> At the time, however, astronomers saw no large-scale motion. So Einstein
> added the cosmological constant, which applied brakes to the universe his
> equations described. When Edwin Hubble published his evidence in 1925 that
> the universe was expanding, and distant objects were receding from us at
> faster rates than close ones, Einstein tossed the cosmological constant out
> the window.
>
> "Einstein was pulling something out of a hat," says Sean Carroll, an
> assistant professor of physics at the University of Chicago. "He thought of
> it as an extra term in his equations changing the response of spacetime to
> ordinary matter."
>
> But, he adds, "We know now that the term he added is precisely equivalent in
> all ways" to a form of energy that has come to be known as vacuum energy.
>
> Take a volume of space, he continues, strip it of every form of matter, and
> general relativity still allows the vacuum to contain energy. Its density
> would be constant: The amount of vacuum energy in a cubic inch of space in
> our solar system would match that of a cubic inch of space billions of
> light-years away. Depending on the value assigned to it, this energy could
> either retard or accelerate the expansion of the cosmos.
>
> Many cosmologists hold that the universe got its kick-start with the sudden
> release of vast amounts of pent-up vacuum energy. During the universe's
> first billion trillion trillionth of a second, it burst from subatomic size
> to nearly its current volume. The result was the Big Bang, the primordial
> explosion that scientists say gave birth to the universe.
>
> Yet only in 1998 were astronomers able to spot what looked to be the action
> of vacuum energy on the universe.
>
> Two teams - one led by Dr. Perlmutter, the other by Brian Schmidt, with the
> Mt. Stromlo Siding Springs Observatories in Australia - reported that light
> from distant supernovae was dimmer than inflation theories said it should
> be. Currently, inflation holds that all the "stuff" in the universe is just
> dense enough to prevent collapse, but that expansion will slow without ever
> reaching a stop.
>
> Yet light measurements taken from the supernovae, roughly 7 billion
> light-years away, indicated that the galaxies hosting the supernovae were
> farther away then they should have been if the universe was decelerating.
>
> Last month, Lawrence Berkeley's Peter Nugent and Adam Riess of the Space
> Telescope Science Institute bolstered the 1998 results with data from a
> supernova more distant yet, which does fit with the expected rate of
> deceleration.
>
> One explanation, researchers say, is that scientists have now bracketed the
> period in the universe's history when matter thinned sufficiently for
> gravity to give way to the universe's residual vacuum energy, which
> counteracts gravity and pushes clusters and superclusters of galaxies away
> from each other.
>
> The most recent observation virtually eliminates objections that the 1998
> data might merely be showing the effect of dust obscuring the supernovae, or
> other measurement errors, says Dr. Nugent, who also is a member of
> Perlmutter's team.
>
> The Hubble Space Telescope result Dr. Riess and Nugent reported also "gives
> us a look at the epoch when gravity was dominant," Nugent says.
>
> This distance scale is likely to be one of the most fruitful for followup
> studies of vacuum energy - if that's what it is - LBL's Levi says, because
> farther out, when the universe was younger and smaller, matter's higher
> density would give gravity the advantage over the much weaker vacuum energy.
> Any closer than about 7 billion light-years, and the vacuum energy's effect
> would be swamped by "local" regions of space where matter is relatively
> dense.
>
> This rough distance is the target region for SNAP, a space telescope
> Perlmutter and Levi have proposed to tease more information out of
> supernovae. Known as type-1A supernovae, these stellar explosions yield
> consistent levels and changes of brightness as they evolve.
>
> But type-1A explosions are rare, so researchers say they must gather repeat
> images of thousands of galaxies in less than two weeks to ensure they can
> spot an explosion soon enough to track it through its entire cycle.
>
> With initial funding from the Department of Energy, the team is designing a
> 1.8-meter orbiting telescope with a million-pixel camera to fill that role.
> If all goes well, Levi estimates that the telescope could be ready for
> launch in 2008.
>
> Next month, NASA is scheduled to launch the Microwave Anisotropy Probe, a
> spacecraft that will map the microwave background radiation from the Big
> Bang with extreme accuracy.
>
> Tiny changes in the density of the radiation are thought to be the seeds
> from which galaxies and larger cosmic structures evolved. Buried in those
> fingerprints of the early universe are signatures that will help
> cosmologists refine their estimates of the universe's density and the share
> of that density that different forms of "stuff" account for, says MAP lead
> scientist Charles Bennett, with the Goddard Space Flight Center in
> Greenbelt, Md.
>
> Density defines future of the cosmos
>
> Each cosmological theory predicts a certain pattern in the radiation, he
> says, turning density measurements into "a powerful tool" for pointing
> toward the correct theory.
>
> Recent microwave background measurements from balloon-borne instruments in
> Antarctica have provided stunning confirmations of the inflation theories,
> researchers say. They yield a "flat" universe in which 5 percent of its
> density consists of matter and forms of energy humans can detect, 25 percent
> dark matter, which is inferred from the movement of galaxies, clusters, and
> super clusters. The remaining 65 percent consists of vacuum energy or its
> equivalent.
>
> For Dodelson, it's an amazing time for astrophysics. "The time scale for
> change in cosmology is typically 500 years," he says.
>
> "Five years ago, if someone told you there's a cosmological constant, you'd
> say he's crazy. Today its just the reverse. It might take 100 years to
> figure out what this stuff is. But it's remarkable we're living at this
> time."
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