Slashdot Mirror
Chandra Provides Support For Dark Energy
starannihilator writes "The Chandra X-Ray Observatory has provided new evidence supporting the existence of dark energy, the force causing the acceleration of universal expansion. The new findings support the theory that the universe will expand forever, provided there is enough dark matter. CNN and Newsday are running the story, originally reported by NASA. Chandra's site has some good images and information on the three galaxies clusters studied (Abell 2029, MS2137.3-2353, and MS1137.5+6625)."
Maybe someone can explain... But when the CNN article states that the universe is "accelerating", does that mean it's really accelerating? I thought it was decided that the universe's expansion was expanding at the speed of light. So, I would assume that by accelerating they mean growing bigger and not actually accelerating faster than the speed of light. Unless, this Dark Matter is something that can bend the known laws of physics and travel faster than the speed of light?
Hmmm.
Gravitation is a shadowing effect. (Yes, all the formulae still work, except when you get out towards the edges of space)
--Mike--
Does anyone else think that the cutting edge of physics is starting to resemble Ptolemy's system of astronomy? With all this 'dark' energy, and 'dark' matter, it's beginning to look like a lot of hand-waving.
Increasingly complex adjustments (e.g. epicycles) were made to Ptolemy's system to explain the observed motions of the heavenly bodies. Then along comes Copernicus and tells us that we've been looking at it inside out all along, things are simple after all, we just have to adjust our viewpoint.
I think physics is overdue another Copernicus.
The original poster has it wrong, more dark matter decreases the expansion of the universe as one would expect, dark energy does the opposite changing the state function of the universe and thus allowing it to expand. IAA astro-physicist
I've seen a few references to a theory of a final "big rip," in which everything (even atoms) are torn apart by the expansionistic force.
Would this apply to black holes, as well? If black holes aren't ripped apart, would they continue to provide areas of gravity strong enough that particles in the vicinity don't undergo the rip?
--When you buy proprietary software, you don't get better software. What you get is the right to complain about it.
There was some PBS special a little while back that talked about "string theory" of reality and the possibility that the "Big Bang" was actually a big "collision" between this and another dimmension. The "collision" or interaction between the two different dimmensions not only created tremendous energy but also left some material from the other dimmesion in this one, dark matter. That is why the stuff is invisible with no known origin but somehow detectable. Kind of like the Old Ones.
Why not? Because observations do not support it. Other than that, it's a fine idea!
HCG 50a = 2MASX J11170638+5455016
11h17m06.4s +54d55m02s
Now blow the balloon up a little more such that P0 and P1 are 1mm further apart, and thus P1 and P2 are also 1mm further apart (P0 and P2 are 2mm further apart). Then (D=distance, dD=change in distance):
dD01/D01 = 1mm/10mm=0.1
dD12/D12 = 1mm/10mm=0.1
dD02/D02 = 2mm/20mm=0.1
i.e., dD/D = constant. Since the dD occured over the same time for the two distances, you can also write this as
(dD/dt)/D = V/D = constant = K
(This is the Hubble equation, where K=H.)
So, in theory, you could blow up a balloon such that two points are moving faster than c relative to each other (V=c=D*K). Let's see how to do this. The distance between any two points on the surface is D = r*Q (r=balloon radius, Q = angle between the points in radians which stays constant as the balloon expands). The change in distance over time is
dD/dt = V = dr/dt*Q.
The furthest two points can get apart is Q=pi (opposite points on the balloon), hence the fastest relative velocity will be between these points. Let V = c and solve:
dr/dt = V/Q = c/pi
In other words, if the radius of the balloon was expanding at a rate of just under 1/3 the speed of light, two points on the balloon would be moving relative to each other at the speed of light. (This would not only take a lot of air, but the rate of air required would go up with the cube of the radius, so you'd want to do this when the radius is very small.)
Applying this 2D analogy to the 3D universe, it doesn't have to be expanding at the speed of light for two distant points to be moving greater than c relative to each other. But it does have to be expanding above a certain rate to achieve this. If it's expanding slower than this critical rate, no two points can be moving faster than light relative to each other. If it's expanding faster, they can. Since the expansion seems to be accelerating, it seems inevitable that it will happen at some point if it hasn't already.
We should also be able to figure out if it has already happened or when it will. We know the constant H (from the Hubble equation H = V/D). (It's easy to calculate anyway, given the distance to any star and it's measured relative velocity.) If we know the history of the expansion rate we know how big the universe is, i.e., this furthest distance Dmax between any two points. We can then solve the Hubble equation V = H*Dmax and see if it is less than or greater than c.
By the way, I don't think this violates relativity, it doesn't say anything about the rate of expansion of the universe. I think this falls into the "warp" concept of traveling faster than the speed of light, i.e., if you can locally expand the universe fast enough, it appears you are moving away faster than the speed of light, and vice-versa if you can contract it fast enough locally it appears that you are approaching faster than the speed of light. I could be wrong about that though.
So does anybody have a good,cheap,quick (pick two) primer on Quantum Physics? Something that can explain what we do know, along with the outstanding issues that we don't know?
Kinetic stupidity has a new brand leader: Allen Zadr.