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Galaxy Clusters' Stunted Growth Confirms Dark Energy
A new study of 86 galaxy clusters in the early universe has provided independent confirmation of the existence of dark energy. In its absence, gravity's pull should have caused the number of clusters to increase by a factor of 50 over the last 5.5 billion years. What is observed is a factor of 10 increase. "Together with earlier observations... the new data strengthen the suspicion — but do not prove — that dark energy is a weird antigravity called the cosmological constant that was hypothesized and then abandoned by Albert Einstein as a 'blunder' almost a century ago. If that is true, the universe is fated to empty itself out eventually, and all but the Milky Way's closest neighbors will eventually be out of sight. ... Adam Riess of Johns Hopkins and the Space Telescope Science Institute, said: 'If this was a fox hunt and dark energy was the fox, I think they have closed off another escape route. But there is still a lot of terrain left for the fox, and we've seen little more than a glimmer of fur.'"
I love how one part of logic can necessitate the existence of this dark energy, but the other questions how most of our universe can be made up by something we cannot see. Oh science, why are you such a cruel mistress.
Galaxy Clusters' Stunted Growth Confirms Dark Energy
"Together with earlier observations... the new data strengthen the suspicion â" but do not prove â" that dark energy is a weird antigravity called the cosmological constant that was hypothesized and then abandoned by Albert Einstein as a 'blunder' almost a century ago.
Wait, what?
Hmmm, not sure if I follow, someone please correct me if I'm wrong, but it sounds like what he's saying is that if this were a highway chase and dark energy were a criminal's car, then they have placed a police car as a barracade in the way... but there's still a lot of exits around, and we've only seen a glimmer of chrome?
It's not dark energy, it's your mom!
If that is true, the universe is fated to empty itself out eventually, and all but the Milky Way's closest neighbors will eventually be out of sight.
Not only that, but depending upon the key value of state w, the ratio between dark energy pressure and its energy density, if the value of w is less than -1 then the universe will eventually be pulled apart as the rate of expansion begins to accelerate towards infinity. First the nearest galactic clusters will fade from view, then the nearest galaxies in our cluster, then the stars in our galaxy. Finally, approximately three months before the end, the solar system itself will become gravitationaly unbound, in the last minutes stars and planets will be torn apart, and finally, an instant before the end of everything individual atoms and their subatomic pieces will be ripped into ever smaller pieces until there is nothing left (i.e. the last bits just wink out of existence). The end, if it were to occur in this way, is around 50 billion years, or approximately 3.8 times the current known age of the universe, into the future. This hypothesis is known colloquially as the Big Rip.
(Sigh). Everytime I see a story about the cosmological constant I have to see the obligatory "that dark energy is a weird antigravity called the cosmological constant that was hypothesized and then abandoned by Albert Einstein as a 'blunder' almost a century ago." as if Einstein was so smart he predicted dark energy 100 years ago. No. He put a term in the equation to stabilize the universe, which was then thought to be static, against gravity. Then it turned out the universe wasn't static, it was expanding. That was the blunder. If there's an outward force, as there now seems to be, you'd put a term in the same place. But it's based on new data. I'm sick and tired of the "Aha! Einstein was right all along and he didn't even know it!" comment that has to be stuffed in every cosmological constant story these days.
And I who thought that theories cannot be confirmed by real-world observations, only supported. ...as the blurb also mentions, actually.
I am convinced that I can always be convinced otherwise.
...reportedly spinning and expanding by a factor of 50 as he realizes he shouldn't have called it a blunder. :-)
-- http://ninthagenda.com/
I believe that our knowledge about the universe is quite limited. I can imagine the scientists of the future will laugh about how we could seriously consider dark matter and dark energy. I think it is quite possible that gravity behaves differently over great distances (and I know about the latest "evidence" of dark matter where the dark matter was "imaged" but it is an indirect evidence, there may be other things up in the universe's sleeve which causes this).
I believe there will be another Einstein who will shed light upon this "mistery" and everything will be simple again.
Government cannot make man richer, but it can make him poorer. - Ludwig von Mises
but I thought we had a glimpse of it's fur
Yeah, he came over here from Digg! /buh-dum-ching
I KUT J00 M4NG!!!
einstein was a goddam genius. the world needs another einstein. Maybe we could clone him ;P
For those interested the full paper is here. Apart from a couple of cosmological parameters they don't really improve previous estimates. It's still nice though that all the parameters agree very well with the previous (CMB + Supernova 1a) data with a completely independent method, hence the confirmation talk. I think though if there had been disagreement our understanding of clusters would have been blamed first. So in some senses this confirmed the current cluster models more than the cosmological constant, but that's not as 'sexy'!
So let me get this straight...we have Dark Matter because there's not enough gravity within a galaxy to explain the observations, and Dark Energy because there's too much gravity between galaxies to explain the observations.
Surely Occam's Razor comes into play here? Surely it's obviously simpler to say 'we've got the maths wrong for gravity beyond solar system scale' and start again at the chalkboard?
Business/App ideas are like arseholes: everyone's got one, they're mostly shit, but very rarely they contain a diamond
The summary makes it sound like they actually proved that dark matter exist, not simply added to the inference of it's existence :(
Science is not in the business of making provable claims. It's impossible to prove anything using the scientific method. Science makes falsifiable claims, and any experiment that fails to falsify them confirms the theory, but most certainly does not prove it. An experiment that "confirms" a theory is one that produces a result compatible with that theory under circumstances where a different result would have falsified it. Confirmation merely strengthens a theory, it cannot ever prove it.
"Convictions are more dangerous enemies of truth than lies."
From someone whose only astronomy education is from popular science:
- is there an assumption that spacetime is smooth? Clearly, areas with concentrations of matter will weigh down on spacetime, like objects on a blanket. What if the blanket isn't smooth, or less so than in the areas where matter exists regularly?
- could there exist anything on the underside of spacetime, which effectively causes the antigravity effect? Could black holes link the overside to the underside, effectively causing acceleration through the transfer of matter or energy from our side of spacetime to the other side?
> It's not dark energy, it's your mom!
That's what she said!
Instead of proving the existence of Dark Energy, perhaps what this finding really does is prove that our models are wrong.
I often wonder if we're looking in the wrong place for an explanation...flaws in our cosmology sound more plausible to me than weird forms of matter and energy.
Dark energy = all the photons that are on their way from whatever source to whatever destination. The universe is full of them. You don't see them unless they hit your retina. Doesn't mean they're not there. Can you "see" photons moving away from you? :)
Let's not forget this man either:
http://nobelprize.org/nobel_prizes/physics/laureates/1970/alfven-bio.html
In that sort of model, the Hubble redshift is only proportional to the expansion ratio as a first approximation (whose range is roughly analogous to the range within the elastic limit of a spring).
There then becomes an upper limit to the possible size of the universe, that corresponds to the total (finite) massenergy contained within it. As we approach that limit, things unravel. The resulting increase in atomic instability can then be expressed as an effect of decreased nominal inertial mass due to the reduced background field strength (nuclear stability is a function of inertia).
But a decrease in local inertia also corresponds to an increase in the local rate of timeflow. The absolute end of the universe then represents a point in time where the nominal rate of timeflow is infinite (although, by then, there's nothing left to measure it with), so the period at which the universe nominally ends, measured in "insider-time", is in the infinitely far future. Okay, so its not quite infinitely far away, because the last proton evaporates at a finite time, but the timescale is effectively infinite to most intents and purposes, as far as we're concerned.
The advantage of this form of time-scaling is that it tidies up the Hartle-Hawking model - it allows the "equator" of the H-H bubble to represent the apparent end of the universe for insiders, and to be totally smooth. This removes the messiness that we'd otherwise tend to get when the bubble reaches its maximum size and parts of it start to contract. Contraction implies reversed entropic timeflow, so the HH bubble has a problem in that an observer living through the expansion-contraction region might see some mightily strange things going on. Some regions might be seen to be ageing in opposite directions to others. But if the interior rate of timeflow goes to infinity at the equator (as the angle of "proper" time approaches the angle of axial time, and its angle with the radial time-parameter 'a' tends to 90 degrees), then interior detail is totally erased at the equator, and the apparent inconsistencies with observerspace physics disappear ... you can never survive a transition past the equator, and the event-meshes of each hemisphere are isolated from each other by the equatorial evaporation zone.
The expansion and contraction phases of the bubble then both effectively belong to two separate universes, both of which think they're expanding, and both with opposite senses of proper time. The equatorial evaporation zone keeps both sets of causalities isolated, and prevents nasty messy phase transitions where the two "worlds" collide.
If we look at the geometry of one hemisphere of the extended H-H bubble model, and we use axial time as our reference, or we take a tangent to a given zone and extend that zone's local sense of proper time as as a straight line to give us our time-reference for the rest of the bubble, then what we end up with is a description that seems to describe a "Big Rip" at a definite, finite time. Our projection tells us that the universe contents speed up and start to "fizz and whizz" at an increasing rate before finally disappearing altogether. But to physics performed inside that universe, things aren't hotting up, they're cooling down -- instead of matter mysteriously evaporating after few billion years, it's decaying more conventionally over rather vaster timescales.
Cosmological timescales and reference systems
The thing one has to be careful o
Eric Baird
He was saying that they need someone named John Peel on the project to make any progress, along with his assistants Ruby, Ranter, Royal,Bellman and True. (Those who are thinking of the public school educated DJ rather than the Cumberland farmer should refer to this page though I disagree slightly with the version of the song there.
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
The good one? You mean the animated series? 'cause everything later, and certainly those three live action movies, sucked rocks.
maybe just maybe the need for dark energy is simply the evidence of our model of physics being incorrect and relativity isn't where its at after all. Maybe our scientists are just so in love with it that they won't let it go despite observations that are inconsistent and so they invent dark matter/energy instead.
Wouldn't that only happen if they were receding at greater than the speed of light? Otherwise the light would still get to us, just being dimmer because of the increased distance.
"It's the height of ridiculousness to say for those 9 lines you get hundreds of millions."
that a galaxy that was far, far away in the 70s is now far, far, far away?
Probably because you spend all your nights in an observatory staring at the sky. I'd get out to the bars more and feed shots to some sorority chicks on rush week.
I swear to God...I swear to God! That is NOT how you treat your human!
"But there is still a lot of terrain left for the fox, and we've seen little more than a glimmer of fur."
That's a damn stretch from "confirms", especially coming from a primary in the research.
All the study confirmed was that early galaxies appear to have behaved in a manner as though gravity were different or affected by another force. It doesn't mean they did, it means their observations can be taken that way. It doesn't mean there was dark energy, it means they don't seem to act as though they not affected by gravity then as they would be now. The data support the delta-g (gravity changing over time) theory as much as dark energy. Other data makes it less likely (clumpiness in these an similar observations), but my argument is with the difference between the headline and the substance in TFA. If NYT is going to report everything as though it were common news, with the emphasis on spectacularism for the sake of sales, they should respect what science is supposed to be like (ie. accurate and objective to the extent possible) and not touch it.
"I may be synthetic, but I'm not stupid." -- Bishop 341-B
Dark energy
Dark matter
The Higgs boson
My work unifying gravity with the three other forces of Nature suggests that if done right, we get new math to describe how gravity works. All three problems will politely disappear in a few calculations on paper.
Here are 4 things that work great for real and complex numbers: a robust derivative, commuting, visualization, and many connections to group theory. If we can these 4 in 4D, then the major problems in physics will be resolved.
Tensors are not enough. They have addition and its inverse subtraction, but not multiplication and its inverse division. Only 4D tensors could come with division by being isomorphic with quaternions. This would eliminate ALL work on strings.
No one can visualize 4 spatial dimensions. We can watch 3D animations. I have written the software to do so (quaternions.sf.net). Move from Descartes static analytic geometry to dynamic analytic animations. Weird and wonderful things happen with math in motion.
Feel free to email me with questions. Lots of YouTube videos available.
Doug Sweetser
sweetser@alum.mit.edu
Working on new views of old physics at http://VisualPhysics.org
I honestly can't tell if you're incredibly insightful or just adding words after one another. My brain hurts either way.
The thing one has to be careful of with cosmological descriptions is that they often use geometrically-convenient projective timescales that doesn't necessarily correspond (even approximately) to actual elapsed time, except over small regions.
You've written quite a long-winded screed, but the problem with it is that astronomers usually do use proper cosmological time — i.e., the actual elapsed time — not coordinate time. Yes, sometimes it's easier to write down the metric in some kind of projective coordinates, but when people talk about "X years ago" or "Y years after the Big Bang", they almost always convert from coordinate to elapsed proper time. In particular, the Big Rip scenario uses a FLRW metric (albeit with an odd equation of state), and in the conventional FLRW coordinates the 't' coordinate is proper time, so no conversion is necessary.
None of this has anything in particular to do with Hartle-Hawking quantum cosmology, by the way. It just has to do with coordinate time vs. proper time in ordinary general relativity.
My own favourite, which admittedly comes out of thin air, is that negative gravity corresponds to negative mass.
Dark energy doesn't have the properties of negative mass. It actually has the properties of negative pressure: that is its defining feature (Sean Carroll has suggested renaming "dark energy" to smooth tension for this reason, since "tension" is negative presure).
In general relativity, both mass and pressure gravitate (they're both components of the stress-energy tensor which is the source of gravity). That is in fact why black holes form: you'd think that if you crush a star enough, its internal pressure will increase to the point that the pressure halts the gravitational collapse. But in GR, a high enough pressure actually ADDS to the the collapse, because the pressure itself gravitates, and this attraction outweighs the pressure's own repulsion.
If pressure attracts gravitationally, then negative pressure repels. This is dark energy.
You've written quite a long-winded screed, ...
Yeah, sorry about that. Much too long. Some personal stuff on my mind today. Will try to be a bit more concise in future.
... but the problem with it is that astronomers usually do use proper cosmological time — i.e., the actual elapsed time — not coordinate time. Yes, sometimes it's easier to write down the metric in some kind of projective coordinates, but when people talk about "X years ago" or "Y years after the Big Bang", they almost always convert from coordinate to elapsed proper time. In particular, the Big Rip scenario uses a FLRW metric (albeit with an odd equation of state), and in the conventional FLRW coordinates the 't' coordinate is proper time, so no conversion is necessary.
Really? Ah. (trundles off and checks arXiv) Ohhh-kay. Hm. This is a bit unfortunate, their starting assumptions aren't what I expected. Damn. I should really have checked before diving in. :(
None of this has anything in particular to do with Hartle-Hawking quantum cosmology, by the way. It just has to do with coordinate time vs. proper time in ordinary general relativity.
Well, I knew that this sort of "evaporating universe" description showed up in one approach to trying to fix the "disorderly time-reversal" problem in Hartle-Hawking, and I knew that (with that approach) we end up fitting an infinite amount of observer-time into each half-bubble, so if one wanted to continue treating the bubble (from the outside) as a tidy hypersphere, one was forced not to use "proper time" coordinates. The resulting description was then just as the earlier poster said, so I presumed (wrongly) that that must have been what Caldwell & co had done. I saw the description, recognised it, thought "Ooo, I know this one!", and jumped in with an attempt to explain some of the wider context.
But if their suppled timescales describe "user-time", then that's obviously NOT what they've done, and my description doesn't relate to their model.
Arghh. My bad. :( :( :(
Thanks for pointing it out so politely.
Eric Baird
The moderation proves it.
If Google really cared they would fix Android Chrome to reflow text, instead of discriminating