Dark Energy

I   
couldn't help but say something about this "convergence" ;o). Sooner or later they'll have to come this way. They're not going to get around me on this one. This just describes what I've been writing about.

The first piece is a description of the rational for an accelerating universe (and in part, a slightly flawed justification). The second is amusing to me. They're going to use the dark energy concept to explain apparent absence of dark matter. What lengths they will go to, to squeeze things into a familiar mold !

My comments follow each piece.



From Berkely Labs - Science Beat  (1-30-01)

Light from the most distant galaxies has traveled billions of years, giving a snapshot of the universe at a fraction of its present age. If expansion were slowing under the influence of gravity, supernovae in distant galaxies should appear brighter and closer than their high redshifts suggest.

The distant supernovae found so far tell a different story.

At high redshifts, the most distant are dimmer than they would be if expansion were slowing; they must be located farther away than would be expected for a given redshift -- powerful evidence that the expansion rate of the universe is accelerating.

In the very dense early universe, when matter was close together, gravitational attraction was strong and expansion was slowing. Today, because of continued expansion, matter is farther apart and the density of the universe is low -- so low that it has apparently dropped below the density of some unidentified dark energy now causing it to expand ever faster.



They are using type 1a supernovae as standard candles to determine extra-galactic distances (a formidable task). After 10 years work they have come to the momentous decision that the universe is "accelerating".

Well ........ hmmmm .....

You see the underlined passage. They presume without justification that it was slowing early on. No direct evidence here for the slowing (note the telltale "apparently" in the next sentence). Therefore ... the universe must now be accelerating to "make up the difference" between what's expected and what is.

The better answer is ... let go of the slowing and then ... "it's just cruising along as ever". Nice & smooth ... no bumps, no dips, no slowing and speeding up again. They just can't give up the need to have gravity act independently. In fact, gravity acts "concomitantly" with the dark energy, i.e. the logically necessary repulsion of empty space.

Next ...



From "Spacedaily"  (1-30-01)

They selected five nearby spiral galaxies with well-known "rotation curves" measurements of how the orbital speed of stars varies with distance from the centre of the galaxy. They subtracted the rotation curve that would have been expected if the gravity of the visible material was the only force keeping the whirling stars in check.

What Whitehouse and Kraniotis were left with was a rotation curve in which the velocity increased linearly, in direct proportion to radial distance. "It was exactly the effect you would expect from dark energy," says Kraniotis. Two years ago, a team led by Saul Perlmutter of Lawrence Berkeley Laboratory in California discovered that empty space appeared to contain energy--dark energy--which was pushing galaxies apart and speeding up the expansion of the Universe (New Scientist, 3 April, p 28).

This energy, identified with the "cosmological constant" in big bang models of the Universe, is tiny and its effect is only apparent over very large scales. "Oddly enough, nobody considered whether it might have an effect on the scale of individual galaxies," says Kraniotis.

Whitehouse and Kraniotis claim that the linear contribution to the rotation curves of their five galaxies can only be explained by Perlmutter's dark energy. Since the dark energy in galaxies has an equivalent mass to dark matter, it exerts a gravitational pull on the stars. "It is this that prevents them from flying off," says Kraniotis. "You don't need to postulate large amounts of dark matter."

While other researchers are cautious about the claim, they nevertheless believe it is worth taking seriously. "I think it is very important to seek alternatives to the dark matter hypothesis in explanations of galactic rotation curves," says Miloslav Svec of McGill University in Montreal. "Unobservable dark matter in a completely transparent Universe is a very unsatisfying idea."



Come on guys ! If the dark energy is supposed to push the universe apart. Wouldn't it be more consistent to propose that it pushed matter instead of "pulling" it ? They just can't give up the idea that some dark something is pulling the galaxy together. And these are probably young guys too. Let's see some rebellion.

What do we have here ?



A   failure  to   ... Communicate



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