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Galaxy Clusters' Stunted Growth Confirms Dark Energy
Posted by
kdawson
on Wed Dec 17, 2008 01:26 AM
from the glimmer-of-fur dept.
from the glimmer-of-fur dept.
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.'"
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Logic (Score:2)
Re: (Score:2, Informative)
Yeah, I often wonder about how I manage to breathe. There's all this stuff I can't see, and I'm not really sure it's really there.
(Hint: Just because something doesn't interact with photons doesn't make it pseudo-scientific.)
Re:Logic (Score:5, Funny)
You think that's air you're breathing now?
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Re: (Score:3, Funny)
That whooshing sound was GP's Matrix themed joke flying right over your head. Turn in your geek card at the desk on your way out please.
Re: (Score:2, Funny)
I think missing a reference to a the Matrix should only burnish ones geek credentials--it's like the star wars prequels. I've tried so hard to forget.
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(Hint: Just because something doesn't interact with photons doesn't make it pseudo-scientific.)
*cough*
Air does interact with photons. Just not ones we've evolved to see. Because, you know, what would be the point otherwise?
Re: (Score:3, Interesting)
It also interacts with the photons we can see. Otherwise, the refractive index of air would be exactly 1, instead of 1.00029
Re: (Score:2, Insightful)
Yes, what an impossible thing. To think, that humans, the pathetic little barely-smarter-than-a-chimp creatures on a rock in the middle of nowhere might have... *gasp* limits ;)
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In either case dark matter may not be necessary at all. This is because in logic necessary has a hugely different meaning than the way you used it
Re: (Score:3, Interesting)
I agree dark matter may not be the correct answer, but more like, the current best fit answer, given current available evidence. One concept that could explain what is going on, without the need for dark matter, is the idea of Dark Flow.
If Dark Flow can be proven, (big if?!
Article Confirms kdawson Doesn't Read Articles (Score:5, Informative)
"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?
Re:Article Confirms kdawson Doesn't Read Articles (Score:5, Informative)
Dictionary: confirm
1. To support or establish the certainty or validity of; verify.
2. To make firmer; strengthen
See definition 2. Incidentally, in science, "confirm" always means 2. Certainty is impossible to establish using the scientific method. An experiment that produces the expected result confirms the theory, but certainly does not prove it.
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Re: (Score:2)
I hope you don't try to evaluate regexps in your head.
1) ((To support) || (establish) ) ( (the certainty) || (validity of) ); verify.
Number one works--to support the validity of.
Re: (Score:2, Insightful)
Isn't dark energy a general name for whatever it is that causes our universe do things that aren't explained by our equations?
So I guess this confirms Dark Energy even more because it invalidates even more equations than before. So it isn't the old equations that are wrong; it is only because part of the equation does not include variable D.
Fox Hunt? (Score:5, Funny)
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?
Re:Fox Hunt? (Score:5, Funny)
You got it wrong, he wasn't talking about fox, the animal, but about Fox Mulder.
Dark energy is what took his sister to a distant galaxy and that distance is growing every day. The FBI are closing escape routes, but the dark energetic abductor has still much galaxy to run.
The glimer of fur thing must be a reference to the sister.
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Re:Fox Hunt? (Score:5, Funny)
NASA confirms it! [nasa.gov].
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Re: (Score:3, Informative)
Seeing as fox hunting involves a bunch of extremely rich (inherited rich, never worked a minute in their life rich) people with a taste for animal blood riding horses around, sending a small army of dogs after a fox and ripping it to shreds just for the sake of it, I think your analogy is actually better.
I'm not sure there are many rich physicists out there that ride horses round their labs wearing red jackets and joppers, nor am I sure how dogs would help track down dark matter but I am at least sure it's
Re: (Score:3, Funny)
...nor am I sure how dogs would help track down dark matter...
Duh! You take one of dark matter's old socks give the tracking dogs a whiff. It doesn't take an astro-physicist to figure that out.
Not exactly (Score:2)
Obligatory xkcd (Score:5, Funny)
The Ultimate Fate of the Universe (Score:5, Informative)
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 [wikipedia.org].
Re:The Ultimate Fate of the Universe (Score:5, Insightful)
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"And AC said: "LET THERE BE LIGHT!" And there was light--"
Timescales (Re:The Ultimate Fate of the Universe) (Score:4, Informative)
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
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Re:Timescales (Re:The Ultimate Fate of the Univers (Score:3, Funny)
blunder (Score:5, Interesting)
Re:blunder (Score:5, Funny)
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Re: (Score:2)
Re: (Score:3, Insightful)
With the technology available in his time, not only was it impossible for him to verify atomism, but in fact if he had tried to do so experimentally, then the only reasonable conclusion would have been that atomism is highly unlikely, since matter can easily be subdivided indefinitely to the limit of visual perception. As such, steadfastly maintaining the truth of atomism would mark him out as a crackpot nowadays, a
Re:blunder (Score:5, Informative)
Einstein invented his "repulsive" effect to explain why the universe was static, and neither expanding or contracting. Unfortunately for Einstein, Hubble's redshift observations a few years later indicated that the "static" property of the universe that Einstein's CC had been invented to reproduce within GR, wasn't correct.
Dark energy was invented to explain why, when we take an expanding universe model decribed with general relativity, and try to compare it with reality, the numbers still don't appear to match up with the theory.
----
Einstein's Cosmological Constant was an attempt to force GR to produce a wrong answer that Einstein (at that time) happened to think was a mathematically elegant one. The system seemed to describe a universe that would have to be expanding or contracting, and Einstein said ... "Well we know that THAT has to be wrong, so to make things nice and static, I'll write in an additional term for a necessary effect that I've just made up, that would exactly cancel the large-scale effect of gravity ... "
The motivation, function, and results for the two hypothesised effects are different. Both effects are repulsive, and both of them are essentially "made up" as accounting fudges without any deeper physical or philosophical justification, to force a theory that generates one result to generate a different result that we like better, but that's about all they have in common.
They're really different animals. Dark energy isn't an effect designed to explain why the universe is static. However, if you're inventing an arbitrary effect to bring your theory into line with experiment, the awkwardness of admitting that you're basically making stuff up to force the answer you want is reduced if you can claim some "provenance" for the idea, and present your "new" effect as if it's a logical historical development of an earlier idea by a Famous Physicist. That adds an air of legitimacy.
But if we think that the DE idea is any good, then the idea that DE is a historical extension of Einstein's CC is phoney. Einstein's CC is dead and buried. The only way that DE might turn out to be able to claim descent would be if DE turns out to be a rotten idea too, in which case we could say that there's a common theme running through both bad ideas. :)
But if the Dark Energy idea is good, then it's really not "bringing back Einstein's cosmological constant in revised form".
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Huh, confirming theories... that's a new one (Score:2, Interesting)
In other news, Einstein's grave is... (Score:2, Funny)
We have much to learn (Score:3, Insightful)
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.
Re: (Score:2)
I believe there will be another Einstein who will shed light upon this "mistery" and everything will be simple again.
Simple again?
Whan was the last time everything was simple?
I'm thinking caveman's "If you don't know how something works, it must be a spirit".
Link to full paper (Score:5, Informative)
Matter and Energy...or not? (Score:5, Insightful)
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?
Re:Matter and Energy...or not? (Score:5, Insightful)
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?
Well, from what I've understood adjusting the constant of gravity would explain some things but would make other predictions incorrect again. All in all, dark matter / dark energy is causing less headaches than the opposite, so unless you can pair it off with some other theory to make the world right again it won't get accepted.
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Re:Matter and Energy...or not? (Score:4, Interesting)
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?
Which is, in effect what we are saying. However, it makes little sense to simply scratch the whole, current understanding of the world and start over; introducing an assumption that gravity behaves differently outside a certain distance begs the question why it should be so, and we don't have any compelling answer to that.
My own favourite, which admittedly comes out of thin air, is that negative gravity corresponds to negative mass. If you look at the classical equation as a rough approximation, you'll see that a negative mass should repel a positive mass, but attract another negative mass. Intuitively this seems to potientially explain the "dark energy" phenomenon, and it might explain how, at the beginning, mass seems to have been created from nothing - perhaps an equal amount of positive and negative mass was created, so that mass was preserved, in total, and then it exploded apart. How about that for an explanation?
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"Really new trails are rarely blazed in the great academies. The confining walls of conformist dogma are too dominating. To think original
Re:Matter and Energy...or not? (Score:5, Insightful)
I have to agree with ghostdoc. IANAP
Obviously. If you were even passingly familiar with the area, you'd realize that a) people *have* been re-examining the orthodoxy (see MOND, among other things), because, you know, some scientists are as smart as you (or perhaps even smarter) and realize that it's an interesting area of research, and b) no one has found an alternate theory that explains the current set of observations (see the Bullet Cluster, and some even more recent results).
Honestly, what is it with laymen who somehow believe that *they* have some insight into an area that those who've been studying it their entire lives do not?
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Re: (Score:3, Insightful)
Yeah, if the history of physics has shown us anything, it's that laymen have never had any special insight into areas that professional physicists do not.
You really need to educate yourself if you honestly believe Einstein, a man who graduated in 1900 with a physics degree from ETH Zurich with a physics degree, was a layman.
Re: (Score:3, Insightful)
Are you saying he was secretly a professional physicist
Do you even know what a "layman" is? Here, let me explain: It's someone who is uneducated in the subject manner about which he is speaking.
Einstein was *not* a physics layman. The man was formally educated in the topic!
He wasn't a layman like you and I are, but he was hardly a member of the physics establishment.
Fair enough, but my comment wasn't directed at people who are both educated and outside the establishment. It was directed at *laymen*. Pe
Alternative explanation (Score:4, Insightful)
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.
Re: (Score:3, Interesting)
Well, if we are able to go about it in a totally different way, that the dark matter/energy estimates weren't ad hoc-adjusted to fit, and we still see that those estimates fit, it means something. It might be something else, including a weirdness in gravity, but overall the data fits well with something that is quite similar to matter.
Just a Question (Score:2)
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.
"we've seen little more than a glimmer of fur." (Score:2)
!Confirmed (Score:2)
"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 affect
Re: (Score:2)
but I thought we had a glimpse of it's fur
Re:Needs a better headline & summary (Score:5, Informative)
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.
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