Space science contains big void - Astronomers admit they don't understand dark energy and matter

Mercury News ^ | 6/30/03 | Robert S. Boyd - Knight Ridder

[NormsRevenge]

WASHINGTON - In ``Star Wars,'' Darth Vader rules the ``dark side'' of a fantasy universe. In real life, astronomers are exploring the ``dark side'' of our own universe. They find it a mystifying place.

According to a batch of new reports published in a special ``Welcome to the Dark Side'' issue of the journal Science, most of the cosmos cannot be seen, even with the most powerful telescopes. All but a tiny fraction of creation consists of two exotic, invisible ingredients called ``dark energy'' and ``dark matter.''

[Physicist]

Suppose that the gravitational warping is cause by the presence of "structures" that exist in those other dimensions?

Well, that's rather an exotic idea, so in the absence of evidence it's hard to see why it should be preferred to what is, after all, a very prosaic explanation that fits the bill at least as well. Occam's razor, and all that.

But more to the point, what you've presented doesn't strike me so much as an alternative to dark matter, as it is a form of dark matter.

[Gary Boldwater]

If the light rays entering a telescope are indeed parallel for images of distant objects, then that implies the light path is simply a cylinder equal to the width of the telescope aperture (neglect sidelobes). Is it really realistic to use the ensemble gravitational field of a cluster "causing" the bending of the lights path? Wouldn't it be more accurate to use the highest gravitational potentials the path crosses? Doesn't the gravitational field in a bend causing cluster vary widely across the cluster? I could shine a light through our solar system and come up with many different values for the bending depending where the light path was - near Jupiter, near the sun, near Pluto, etc. There is no uniform gravitational potential in our solar system and I don't think it is uniform across a cluster that bends light.
So couldn't the dark matter be really making up for the assumption that a bending cluster acts as a point gravitational source rather than a non uniform distributed one, which it really is?

[Physicist]

So couldn't the dark matter be really making up for the assumption that a bending cluster acts as a point gravitational source rather than a non uniform distributed one, which it really is?

But they explicitly don't make any such assumption. The path that light takes through the universe can be quite complicated. But fortunately, there are enough distant sources that scientists can deconvolve the distortions to make detailed maps of the distribution of dark matter. A professor here at Penn, Gary Bernstein, is one of the world experts on doing that.

The following plot is from one of his papers.

[esopman]

Great picture! Alas, I fear that the predominance of dark matter is between the ears of some posters...

[Gary Boldwater]

Interesting, this sounds more like an Inverse Problem, rather than a deconvolution. Is the solution as a result of the "deconvolving" unique? In trying to determine sources from mapping potentials over a surface surrounding the source the solution is not unique. How can one get a unique solution from a single observation point (the earth)and a few lightpaths, especially considering the light is not coherent (has no phase information)?
Secondly, is what you are saying is that the ensemble mass of the bending galaxy is not a factor, but rather the gravitational potential along the light's path? If so, then wouldn't a few errors in the distance from the bending body, or its mass account for dark matter?

[AFPhys]

My reading of that comment was also that dark_lord was describing what I would consider a "form" or "explanation" of what "dark matter" is. I agree with your comment here.

As far as the "light changing speed" comments: I agree that the "evidence" is not very convincing as the experiments have typically emphasized an upper limit, and the precision of this is getting better. However, it is VERY easy to imagine an effect of light slowing but that a measurement of that decrease being hugely difficult because the mechanism responsible for the decrease is also changes the march of time, the "clock" (or "clocks") which was used for determining the speed for that experiment. Very different types of measurements would be needed for comparison to determine that, and I'm not certain such measurements are available.

Thanks for the pictures you added to the discussion, Physicist.

[Jeff Gordon]

Proving God destroys that particular version of God, making it finite rather than infinite.

Well said. Very well said indeed.

[Dimensio]

Actually, the "theory" as they present it has lightspeed leveling off to a fixed rate in 1965, when subsequent measurements stopped varying. Very convenient.

As for lightspeed's inital speed: "almost infinity". Very precise measurements these creationists use.

[Dimensio]

When you want to know about nuts & bolts I hope I can be as informative.

You know, I have been having some problems with my lawn mower...

[SouthParkRepublican]

Thanks for the pic. Ping for later reading.

[Clinging Bitterly]

Usually I deal with bigger stuff than lawnmowers.

If you need more power I have this thing called a hot saw. About 250 HP, 5,000 RPM, 54" diameter carbide toothed blade. It's the closest thng to a mower that I have, but if it's too much, a fresh spark plug might get you going.

As for me, I relish every day my mower is broken down, because that's a day I don't have to mow. I found a good repair shop - their turnaround time for a repair is about six weeks.

Dave in Eugene

[AndrewC]

For decades, theorists speculated that much of the universe was beyond their ken. Only in the last few years have observations on extremely sensitive telescopes confirmed that speculation and clarified a few of its details. Various experiments are under way, or proposed, to unravel the many remaining mysteries.

Masterful quote.

[JSteff]

Not a black hole but where a black hole took you. Did you see the movie?

[Silverdrake]

Yeah, late post, but I just found this thread.

Going with Occam's Razor, why postulate something as bizarre as "dark energy" as the reason for continued and accelerated expansion? It seems to me that the distance between galaxies has simply grown enough that gravity no longer has much, if any, effect, and the remaining impetus from the Big Bang is flinging them on. The initial deceleration was gravity *trying* to overcome the Big Bang-imparted velocity, but it wasn't enough, and now the great void beyond is sucking it all out. To use the popular "balloon" analogy, you have a balloon in a vacuum. For a while, the balloon wall's inherent cohesiveness slowed down the expansion, but now it's been overcome and the balloon has exploded. Occam's Razor. I see no need to postulate that something is continuing to "inflate" the balloon.

Background: Took Astronomy circa '96. Heard about dark matter; this is the first I've heard of dark energy. (To be honest, I really see no need to postulate exotic, undiscovered particles as the source for dark matter, either.)

BTW, why would experiments on gravity reactions at 0.1mm test models of dark energy when DE is supposed to operate over vast distances?
http://www.space.com/scienceastronomy/astronomy/cosmic_darknrg_020115-2.html