New Clues About the Nature of Dark Energy 166
Jim Mansfield writes "With the Hubble space telescope no longer being serviced by NASA, it's good to see one of their hardest working and most famous satellites in the news again. According to their press release on the nature of dark energy, Einstein may have been right after all - and even if he turns out to have been wrong, it seems that dark energy is not going 'to cause an end to the universe any time soon' ... whew, that's a relief." See also a space.com story.
I wouldn't worry (Score:5, Funny)
Ok, so maybe there is reason to worry....
Re:I wouldn't worry (Score:2, Funny)
Ok, so maybe there is reason to worry....
Naah... because by then there will be a crew of people who a few years previously will have saved the world once a week for 26 weeks out of the year. We'll be in good hands.
-Rob
Re:I wouldn't worry (Score:2, Funny)
What if they've already used up all 26 of their "Rescue the Earth"s?
Trapped in paranoia-
Re:I wouldn't worry (Score:4, Funny)
Re:I wouldn't worry (Score:1)
Actually, NASA would likely send up a robotic mission to safely take it down over an ocean.
Also, Hubble isn't written off yet -- there's still a chance [hubblesite.org] that a shuttle might service it.
May I just be the first (Score:1, Funny)
The Sith Lord awaits.
Re:May I just be the first (Score:2, Funny)
The restaurant at the end of the universe (Score:4, Funny)
The restaurant at the end of the universe must be really far...
Re:The restaurant at the end of the universe (Score:1, Funny)
Re:The restaurant at the end of the universe (Score:1, Insightful)
14 billion already passed, there are 28 billion remaining, and that's close to the 30 billion figure they said.
Re:The restaurant at the end of the universe (Score:2, Informative)
Re:The restaurant at the end of the universe (Score:2, Insightful)
Re:The restaurant at the end of the universe (Score:3, Funny)
You should have said "it's all relative... generally."
Actually right here: Re:The restaurant (Score:2)
Racists! (Score:2, Funny)
...End of time? (Score:5, Interesting)
This is quite a shift from the implosion theory that results in pre-'Big Bang' conditions causing a loop in time.
Re:...End of time? (Score:5, Interesting)
Re:...End of time? (Score:3, Interesting)
Re:...End of time? (Score:5, Informative)
Well, if you've done any General Relativity you'll know that for a standard cosmology (FLRW cosmology), the final state is one of recollapse, asymptotic expansion, or accelerating expansion. This end state depends on the total mass-energy content of the universe and the nature of the dark energy (cosmological constant). It really isn't a lack of understanding of "basic calculus", but rather a deeper understanding of the physics involved. So, basically, we don't need to know all the derivatives -- we just need to have an understanding of the potential in which our universe evolves.
Re:...End of time? (Score:5, Informative)
Of course they understand basic calculus. They just also understand the currently prevailing model for the constitution of the universe and its evolution. To have the accelerating expansion stop accelerating, decelerate, or turn over would require some additional, extremely bizarre physics that's not indicated by any observation or experiment we presently have. This may seem like an odd constraint for me to place when we're talking about something as bizarre as "dark energy", but it isn't. There were a lot of theoretical reasons from both cosmology and elementary particle physics (and even a few vague extragalactic observational reasons) to at least consider that the cosmological constant may be nonzero; that's why the two high-z supernova teams did their work. And now there's still harder data suggesting same. In contrast, there's just no reason whatsoever to presume unbelievably bizarre physics of the form necessary to produce the behavior to which you appeal. The scale-factor dependence of the currently-known components of the Universe don't have the higher-order derivative behavior you appeal to; while coming up with a hypothetical field that does is pretty damned hard. That doesn't mean you're wrong, of course; it just means the odds are very highly against you. The claims they're making are almost certainly true.
Re:...End of time? (Score:2, Interesting)
This is why the observation of an accelerating rate of expansion (first convincingly made in 1998) indicates that there is something other than mass... and that something, whatever it is, in fact dominates the evolution of the universe at the moment.
As for whether the universe drifts apart in the end... you are right that this is a strong prediction. But it is at least a feature of a fair
Re:...End of time? (Score:5, Insightful)
You always wonder whether astrophysicists understand basic calculus?
I'm doing my best to come up with something witty or intelligent to say to that, but I'm having trouble coming up with anything more than "What...? Huh?"
Considering that modern physics is largely just a whole hell of a lot of math, yes, I think it's safe to say that astrophysicists understand the principles of calculus. Have you even seen a modern physics paper?
Big Rip a Big improbability (Score:5, Informative)
Not with a whimper, but a "Big Rip"? (Score:3, Funny)
That's one depressed satelite! (Score:2, Funny)
Well, it's his own fault now, giving us back such negative waves [the-ocean.com].
Reinout
Never underestimate the power of the schwartz! (Score:3, Funny)
"Now you see that evil will always triumph, because good is dumb!"
- Dark Helmet
Re:Never underestimate the power of the schwartz! (Score:1, Funny)
That's not funny!
</Monty Python Nazi voice>
The future of the Unvierse (Score:4, Interesting)
As dark matter destabalizes, essentially matter is pulled apart at the atomic level. Some thing tells me The Big Rip, is what we are in for.
The universal constant is a nice theory and would be the better, happily-ever-after option, but in reality it seems a little far fetched if the expansion of the Universe is accelerating. It means that eventually speed will over come matter and every thing disintegrate and get ripped apart.
Big Rip != Acceleration (Score:5, Informative)
Relief? (Score:5, Interesting)
Before it gets to that stage, stars will become a rare occurance. The chain of star birth and death results in smaller stars, and once stars get small enough they become like our Sun -- too small to undergo the explosive death that would provide enough mass for future stars. Eventually there won't be enough clouds of hydrogen massive enough to start nuclear fusion.
Given enough time, current theories suggest that the universe seems to be screwed either way.
Re:Relief? (Score:1)
current theories suggest that the universe seems to be screwed either way.
Reminds me of a Futurama episode.. the universe has just been destroyed by a time paradox, but oddly enough the main characters find themselves alive, floating around in white nothingness.
Re:Relief? (Score:2, Interesting)
Re:Relief? (Score:2, Interesting)
Hrm. That's intresting...
Re:Relief? (Score:2, Insightful)
1) I seem to recall there's no such thing as maximum entropy. There's just the law that for any closed system, entropy never decreases. (Third law of Thermo? It's been waay too long ago...;)
2) The eventual cold death/ever expanding argument. I think they're still trying to figure out which way the universe is going to go.
If only the universe were as simple as E=mc2Re:Relief? (Score:3, Interesting)
Re:Relief? (Score:2)
It's sort of as though the "time" dimension itself will be curling up to insignificance the same way we currently understand higher spatial dimensions to be curled up...
Re:Relief? (Score:5, Interesting)
Another person downthread alludes to the idea of surviving through increasing entropy by presumably using decreasing amounts of energy. In other words, as the universe gets older and colder, there will be, say, 1/100th the free energy available utilizable by a heat pump. So a form of alife could simply run itself 100 times more slowly and thereby experience time subjectively at a linear rate. Right? Wrong. Two problems pop up. One is proton decay, which means the building blocks of any sentient computer will eventually decay on their own. And second is the cosmic background radiation. Machines work on the principle of taking in energy and outputting it in the form of waste heat. But once the universe has cooled down to the same temperature as the CBR, it will be impossible for any machine to output waste heat. It will cease to function. There is some work being done on reversible computing [mit.edu] which might, in the long run, be able to tackle the second problem, but not the first.
Re:Relief? (Score:3, Interesting)
Machines work on the principle of energy conversion; waste heat is just an unwanted side effect of imperfect energy conversion.
But once the universe has cooled down to the same temperature as the CBR, it will be impossible for any machine to output waste heat.
Once the universe cools to CBR levels, there will be no differences in energy levels, and thus no energy flow is possible (thus, no motion, no conversi
Re:Relief? (Score:3, Interesting)
You do realize that no one has seen one proton decay. Not one, right? Proton decay assumes supersymmetry is valid, and as many physicists have noted, supersymmetry is an excellent theory, which predicts a whole host of particles - half of which have been discovered.
Proton decay isn't real - not yet. And there is no a priori reason to assume that it is. Its current lower bound is 10^33 or so ye
Re:Relief? (Score:2)
The heat death argument relies on the 2nd law of thermodynamics -i.e. there can't be an entropy loss. But this is not exactly true. It is unbelievable improbable that an entropy loss occurs. If one supposes that time goes one after a heat death, there can and will be a restructuring(*) of the universe. The probability that a restructuring happens is unbelievable small. But as time approaches infinity, the probability that this happens will approach one.
Such an argument would only hold if that unbelieva
Re:Relief? (Score:5, Informative)
non-physical physics (Score:5, Interesting)
Of course, 2x (near-as-dammit-zero-certainty) is pretty much the same as (near-as-dammit-zero-certainty)...
A lot of new physics does seem to be increasingly theoretical and "out there" on the proverbial limb. It would be good for the practical lot to catch up with the theoretical lot... unfortunately, trying to verify these out-there hypotheses seems to involve larger and larger atom-smashing accelerators. Lets just hope they don't need to find the 'Higgs Boson' (hint: ohhh WAAAY ohhh, ummm barrray
Simon
Re:non-physical physics (Score:4, Insightful)
All new physics is out on the proverbial limb. Galileo's ideas were so outrageous at the time that the church had him outcast from society (IIRC).
It doesn't take that much of an open mind to consider these new (or old) theories based on new facts. But, I'm glad the majority don't follow such theories, because most people tend not to leave things in the grey ("THIS theory is RIGHT") otherwise, actual scientific progress would be severely hindered, as people would become quite disheartened, and possibly ANGRY at science.
The border between "Practical" and "Theoretical" isn't very black-and-white either. Often theoretical sceince leads to very practical applications (as in the case of forward error correction, originally just mathematics) and practical turns out quite sour (as in the Wankel(?) engine).
Just my 2c
Re:non-physical physics (Score:4, Informative)
Great man.
Re:non-physical physics (Score:2, Informative)
Re:non-physical physics (Score:2)
Galileo's ideas were so outrageous at the time that the church had him outcast from society (IIRC).
Well, that and he called the Pope an idiot for advocating the copernican model. He did it in print, too.
Re:non-physical physics (Score:2, Interesting)
I'd say this is a bit flimsier limb to stand on. For a bit of perspective, let's consider the sheer mountains of daily empirical data that a meteorologist has to work with, and yet the "ultimate fate" of weather can rarely be predicted more than a few days in advance.
Of course the size of the system does come into play, and the scope of the effects being observed. It may be far easier to understan
Re:non-physical physics (Score:2)
Re:non-physical physics (Score:2)
Glad to see one person got it, anyway
ATB,
Simon.
Re:non-physical physics (Score:2, Interesting)
Re:non-physical physics (Score:2)
Actually, according to Kuhn [amazon.com] (and I tend to agree), Planck actually didn't realize he was making that break from classical physics.
Planck had worked on the black-body problem for a long time, and only after that time did he cave in to follow Boltzmann's ideas, thinking at the time that the quantization condition was simply a mathematic
Re:non-physical physics (Score:2)
Physicists are particularly prone to assuming that the mathematical derivation parallels the historical
Dark Matter and Ether (Score:3, Insightful)
I think dark matter doesn't exist. It can be useful in the models, like ether could, but nothing more than that.
Re:Dark Matter and Ether (Score:5, Interesting)
and in very complex systems Newton can't be used (chaos)
Hang on a moment; I thought the Lorenz attractor (which is the canonical example of chaos) was based on a system obeying Newtonian mechanics.
Why would it be so strange if systems with enormous scales and very small accelarations would not obey Newton's laws?
This is the line of thinking which led Mordechai Milgrom to propose Modified Newtonian Dynamics (MOND) in the 1980s. MOND posits that Newtons second law (F=ma) is modified when the acceleration is very small. It is able to "explain" the unusual rotation curves of galaxies, without the need to invoke dark matter. It can also explain phenomena which the dark matter hypothesis can't, such as the Tully-Fisher relationship observed in the surface brightness of galaxies.
However, its important to remember that MOND cannot be considered a physical theory; it is more of an empirical modification of known physical laws (like the Lorentz transformation was), which still awaits a physical explaination.
Re:Dark Matter and Ether (Score:4, Informative)
The Tully-Fisher relation has been explained by dark matter for some time. You can find a brief derivation in Carroll & Ostlie p. 1002, for instance. There's no need to invoke MOND at all - it just comes from the fact that the luminosity is proportional to the maximum velocity to the 4th power, which you can get by using the expression for total mass contained within the galaxy derived from rotational velocity curves.
Re:Dark Matter and Ether (Score:2)
There's no need to invoke MOND at all - it just comes from the fact that the luminosity is proportional to the maximum velocity to the 4th power, which you can get by using the expression for total mass contained within the galaxy derived from rotational velocity curves.
I was under the impression that dark matter needs fine tuning to explain Tully-Fisher, while MOND needs no further parametric adjustment beyond that used to fit rotation curves. That is the point I was (poorly) trying to make.
Re:Dark Matter and Ether (Score:5, Informative)
Yes and no: The typical Tully-Fisher coefficients for Sa, Sb, and Sc type galaxies are 9.95, 10.2, and 11.0 or so. These are all within 10%, and for Sa and Sb types, within 5%, of 10. Simple assumptions get you a coefficient of 10, if you assume that the mass-to-light ratio is the same for all spirals, and that the surface brightness is the same for all spirals.
The first assumption (mass-to-light ratio) is a clearly idiotic assumption. It assumes that galaxies form with same proportions of light and dark matter, which we *know* is not true for other types of galaxies (dwarf ellipticals, in particular). Aside: This is also the "nail in MOND's coffin", more or less - MOND was hoping to replace the dark matter hypothesis by saying physics works differently at large distances. The problem is that galaxies which contain the same amount of light-emitting matter and have the same spatial extent should therefore have the same rotation curves. This isn't true. You then have to add a new parameter with MOND to fit it, which is OK, sure, but now you've started to lose the elegance originally intended, and now MOND becomes a more complicated theory than the dark matter hypothesis, which just says "well, that galaxy formed around less dark matter."
Anyway, back to the subject: the point is that those two assumptions clearly are not completely true, and therefore there's plenty of room for a 10% correction due to forming biases in spiral galaxy types. If the mass-to-light ratio is a very weak function of mass (which is believable - perhaps smaller galaxies formed when the dark matter density was slightly lower, due to their late formation times), you can easily get those corrections.
MOND allows you to get that 10% correction due to the parametric fit of the rotation curve, which is essentially identical to the way that it's done in the dark matter case - the corrections are due to the variation in the rotation curve, which MOND says is due to a modified Newtonian field, and dark matter says is due to a dark matter density. It's the same reasoning - one isn't more natural than the other.
(It should also be noted that the Tully-Fisher data has a crapload of spread to it, just like all astronomical data. Each galaxy varies a fair amount.)
Re:Dark Matter and Ether (Score:2)
Hang on a moment; I thought the Lorenz attractor (which is the canonical example of chaos) was based on a system obeying Newtonian mechanics.
Perhaps it would be better so say that Newton's laws make no meaningful predictions in such a situation, or at least, they don't converge nicely.
Re:Dark Matter and Ether (Score:3, Interesting)
You say they 'believe', then call it a hypothesis - one is faith the other is science.
"otherwise those huge systems of galaxies don't obey Newton's laws" - As the story notes, the proposed dark matter is related to Einstein's cosmological constant. Now as to why Einstein 'believed'(sic) in it? Because that is what observation showed. The question here is why and is it truly constant.
"It does feel a bit like Ether to me to introduce a form of matter/energy which has never been
hypothesis, theory and faith (Score:2)
Re:hypothesis, theory and faith (Score:2)
Q.
Re:hypothesis, theory and faith (Score:2)
Q.
Re:Dark Matter or Dark Energy? (Score:1)
Re:Dark Matter and Ether (Score:5, Informative)
IANA astronomer, but that's what I've understood from the stuff that I've read about it. Pop science ofcourse because the math is way over my head.
Re:Dark Matter and Ether (Score:2, Interesting)
I find it strange that scientists 'believe' in dark matter. ... I think dark matter doesn't exist.
Dark matter does not necessarily mean exotic matter. There have already been detections [space.com] of white dwarf stars at the edges of a galaxy. These are just very very dim stars. This discovery means that a significant part of the mass attributed to dark matter could be ordinary matter in dead stars that are no longer radiating at currently detectable levels.
There's more to dark matter... (Score:4, Informative)
Re:Dark Matter and Ether (Score:3, Interesting)
First of all Newton was not proven wrong by quantum mechanics and the general relativity, in a way Newton's law has been put on a more secure footing by being supported by these two breakthroughs of modern physics. Sure, modern physics understands that Newton's laws don't apply for high velocities (close to the speed of light, c) and very small systems (when Planck's constant h becomes a siginificant number). But both quantum mechanics and general relativity gives you Newton's equations when c = infinity an
Correct me if I'm wrong (Score:1, Informative)
While this may be a completely seperate idea, it definitely appears that the author is mixing these two (Dark Energy and Ether) Einstein theories.
Re:Correct me if I'm wrong (Score:2, Insightful)
Re:Correct me if I'm wrong (Score:2)
The thing you seem to be thinking of is the unseen antichthon or counter-Earth [wikipedia.org]; this dates from classical Greece where it was an
Re:Correct me if I'm wrong (Score:5, Informative)
The article you must read (Score:2, Funny)
I'd buy that for a dollar!
Everything's nonsense (Score:1, Funny)
Well, back to my OSS/FS projects to gain fame in this dark world
Dark Matter? My god... (Score:1, Funny)
Dark Matter conclusively identified... (Score:1, Funny)
Einstein was wrong anyway (Score:5, Insightful)
Re:Einstein was wrong anyway (Score:4, Informative)
Re:Einstein was wrong anyway (Score:2)
Re:Einstein was wrong anyway (Score:2)
Ok, while that picked up +4 informative, it wasn't really informative. The cosmological constant actually can be used in general relativity models to regulate the rate at which expansion or contraction occurs.
The idea is that, if the vacuum inherently has a positive or negative curvature, then your cosmological model has a cosmological constant. Hence, it has a nontrivial contraction or expansion (positive or negative curvature re
Re:Einstein was wrong anyway (Score:4, Interesting)
Dumb Science isn't "right after all," no matter how much you respect the guy who came up with it.
Re:Einstein was wrong anyway (Score:3, Informative)
Not exactly. Einstein didn't "put in" the cosmological constant;
Re: Einstein was wrong anyway (Score:5, Insightful)
> This whole "Eistein was right after all" angle is misinformed. He wanted a static universe because that was the historic conception of the universe. His own science didn't allow for it, but he wrangled an equation for one out of it anyway.
Remember that at the time Einstein introduced it (1917, if a Web search didn't lead me astray) scientists still thought "the universe" and "the galaxy" were the same thing. We tend to forget how vastly our understanding of the universe has changed in the past ~80 years.
Re:Einstein was wrong anyway (Score:2)
Duh! (Score:4, Funny)
Are you Corn Fed? [ebay.com]
No info... (Score:3, Funny)
At the end it states, "Understanding dark energy and determining the universe's ultimate fate will require further observations." Well great. Didn't we know this already? *sheesh!* Thanks for "almost" nothing....
Re:No info... (Score:2, Informative)
Regards Luke
No, really? (Score:4, Funny)
"Riess' team uses Hubble to find stars that exploded when the universe was about half its present age. A certain type of these supernovas, as they are called, shine with a known brightness."
Supernovas, you say? Wow, what a fascinating new concept for readers of Space.com!
I mean, come on!
Filling the blank? (Score:3, Funny)
a gap but with what???
Observer: Look at those galaxies..they are moving appart.
Braniac: Yes, that's because the big-bang long long time ago.
Observer: They look very old and they appear to move slower as they drift compared to the young galaxies.
Braniac: Of course, they are loosing momentum. But don't be deceived, at some point all universe is going to loose cohesion and become rippi-bits!
Observer: Howbout that cluster over-there? Those galaxies are quite old and they are driftin faster than the young ones! What gives??
Branica: Er ur..is dark energy pushing them appart, dark energy is spreading the galaxies.
Observer: And the big bang.
Braniac: yes, that too
present dark-energy.
Observer: Far out!
Braniac:(scratching her head and punching madly
at her calculator and giving a big sight of
frustration)yeah, riveting.
http://www.ebtx.com/ntx/ntx16.htm (Score:5, Informative)
I suggest reading www.ebtx.com on the nature of dark energy. This guy is right, or at least close.
Matter attracts matter; this we know. The rest of the theory explains that space attracts space, and matter repels space. Matter and space are polar opposites (as well as logical opposites).
Einstein wasn't relative enough in his theories. He declares C as constant and bases all other observations off it, when in fact you can change all the physical constants continuously and arrive at the same results. If C changed, as long as h, G, and about 18 other 'constants' also changed, we couldn't tell, from our point of view.
Is the universe expanding, or are we all shrinking? From a relative point of view there is no difference.
Indeed... (Score:3, Funny)
Re:http://www.ebtx.com/ntx/ntx16.htm (Score:2)
So is it then hypothesized that Space has similar parallels to matter? As certain kinds of matter can attract or repel other matter (electrons, protons), can one kind of space repel another kind of space? It would be interesting if "dark energy" was thought of as "anti-space".
Comment removed (Score:3, Informative)
"the repulsive force" (Score:2)
The main problem with Dark Energy... (Score:3, Informative)
Many formulas and theories are based on observations, however, a good theory not only describes current observations, but predicts things which are not observed, yet. Like Einstein's theory predicted time-dilation, the curvature of space-time, etc. and gave a solution to the orbit of Mercur (which Newton's theory was unable to explain).
A new theory may be needed to include the Dark Enegy from its foundations or to explain these phenomenas without Dark Energy.
A "Circular" argument? (Score:2, Interesting)
Re:A "Circular" argument? (Score:2)
It's still around, as an untestable hypothesis. It would take longer than the total lifetime of the universe to make the trip.
This Einstein was right stuff (Score:2)
It's true that it's looking more and more like we live in a Universe with a nonzero cosmological constant. But that doesn't mean Einstein was right. Einstein introduced a nonzero cosmological constant for a very specific reason: to make a static universe. He lived at a time when the general metaphysical assumption was that the Universe was static and unchanging and had been around forever and always would be. So when he created his field equations and discovered that they insisted that, with a reasonab
Quick summary (Score:2)
This comes as a great shock to exactly no one.
[TMB]
w=-1? (Score:2)
Asimov (Score:2, Insightful)
If you take a red ball, and throw it up in the air, you will observe it come back down. You can repeat the experiment with the same results. Yo