New Clues About the Nature of Dark Energy

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.

Comments

I wouldn't worry

[jeffkjo1]

I wouldn't worry about the Hubble, it will just end up drifting off into space only to return 300 years later as H'ble, the super intelligent sentient telescope of the future, bent on destroying the human race.

Ok, so maybe there is reason to worry....

Re:I wouldn't worry

[rknop]

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

[DangerSteel]

Is that why we will have to go back in time to get a whale to talk to the evil telescope... no.. wait.... we will have to explain to it why we decided not to repair the telescope and give it an extended life.....dammit, I'm all confused now...

Re:I wouldn't worry

[turnstyle]

"I wouldn't worry about the Hubble, it will just end up drifting off into space"

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 that a shuttle might service it.

Re:I wouldn't worry

[ThereIsNoSporkNeo]

But... but... what if it falls in an off week?

What if they've already used up all 26 of their "Rescue the Earth"s?

Trapped in paranoia-

Re:I wouldn't worry

[Anonymous Coward]

Is that why we will have to go back in time to get a whale to talk to the evil telescope...

Yes, and the entire situation will seem strangely familiar, but no one will comment on this.

Re:I wouldn't worry

[Anonymous Coward]

>> Also, Hubble isn't written off yet -- there's still a chance that a shuttle might service it.
Unfortunately, Hubble has about the same chance of getting serviced as I do.

Bye bye, Hubble. We hardly knew ye ;>

Re:I wouldn't worry

[Walrus99]

I wouldn't worry about the Hubble, it will just end up drifting off into space only to return 300 years later as H'ble, the super intelligent sentient telescope of the future, bent on destroying the human race.

Then it will use its giant lens to focus the sun's rays on humans and burn us up like ants.

That is unless we find some bald Indian chick to have a super space make-out with a white guy ...Then the female Klingon science officer will go to work in a Boston bar ...

Re:I wouldn't worry

[Anonymous Coward]

...and it when it starts losing it becaue of the clever logical conundrum we have tricked it with, it will start ranting "Gah tah nu ee kah tahn ru!"

Re:I wouldn't worry

[Anonymous Coward]

Then a grassroots fan campaign complete with website and paypal fund will be mounted to give them 26 more.

May I just be the first

[MikeDX]

To say the dark side of the force is much much more powerful than the light.

The Sith Lord awaits.

Re:May I just be the first

[Anonymous Coward]

Pointing out someone is redundant on slashdot is a tadge redundant in itself, no?

Re:May I just be the first

[Patrik_AKA_RedX]

No it's not. It's faster, more seductive. But it'll cost you your soul. Hmm, just like a Ferrari.

What a bitch..

[Anonymous Coward]

So it seems all theorists agree the universe will end one day, they're just not sure how..Thats a bummer..

The restaurant at the end of the universe

[dapyx]

..dark energy probably won't destroy the universe any sooner than about 30 billion years from now, say Hubble researchers.

The restaurant at the end of the universe must be really far...

Re:The restaurant at the end of the universe

[Egekrusher2K]

As always, you are wrong. The TRUE answer is 42.

Re:The restaurant at the end of the universe

[dapyx]

Yes. the total lifespan of the universe must be 42 billion.

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

[mog007]

I assume you're using "far" to discuss lengths of time, and not distance. Everyone who's anyone knows that the Restaurant at the End of the Universe is located on Magrathera, just 30 billion years in the future.

Re:The restaurant at the end of the universe

[j0n4th4nb34r]

Time, distance, it's all space-time...

Re:The restaurant at the end of the universe

[hesiod]

> Time, distance, it's all space-time

You should have said "it's all relative... generally."

Re:The restaurant at the end of the universe

[ChickenAintDone]

I've seen it. It's rubbish, nothing but a gnab gib.

Re:The restaurant at the end of the universe

[etLux]

One hopes for that sake of the distant restaurant that they are not subjected to the same sorts of junk food law suits that earthly fast food restaurants are... and remember, now, everyone, for the sake of your health -- lay off the relativistic doughnuts .

Racists!

[dapyx]

the dark energy probably won't destroy the universe any sooner than about 30 billion years These damned white scientists are racists: yesterday they said that a black hole destroyed a star, now this: the dark energy will destroy our universe!

Re:Racists!

[warrax_666]

What would you rather they called it? A minority hole?

...End of time?

[nharmon]

If the repulsion from dark energy is or becomes stronger than Einstein's prediction, the universe may be torn apart by a future "Big Rip," during which the universe expands so violenty that first the galaxies, then the stars, then planets, and finally atoms come unglued in a catastrophic end of time.

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?

[sbma44]

Yeah, but that theory's been out of vogue for a while. It's theoretically tidy (and therefore attractive), but I believe the last few years' astronomical data has shown the universe's rate of expansion is accelerating. Something new woulkd have to turn up for the Big Crunch to come into vogue again.

Re:...End of time?

[SashaM]

I always wonder whether the "It's accelerating so it'll drift apart in the end" folks understand basic calculus. The rate of expansion accelerating doesn't mean it will continue accelerating - the third derivative of x(t) could be negative, or the fourth, and then the fifth could be positive again. You need to know all of the derivatives to know the function itself (and even that isn't true for some functions - e^(-1/x^2) IIRC).

Re:...End of time?

[srleffler]

They understand the physics behind the overall rate of expansion of the universe, or at least they think they do. Knowing the current rate of expansion and its derivative is probably sufficient to predict the future outcome, assuming the theoretical model is correct. Of course, there are some questions about the basic model and it is not clear how they will be resolved in the end.

Re:...End of time?

[V_M_Smith]

I always wonder whether the "It's accelerating so it'll drift apart in the end" folks understand basic calculus. The rate of expansion accelerating doesn't mean it will continue accelerating

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?

[Bootsy Collins]

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?

[Anonymous Coward]

In a Friedmann-Lemaitre cosmology, if the universe is dominated by mass, then the rate of expansion cannot accelerate.

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 fairly general class of models for dark energy. I'm pretty sure that, at this point, most astrophysicists think it is quite likely that the universe will expand forever.

Re:...End of time?

[egomaniac]

I always wonder whether the "It's accelerating so it'll drift apart in the end" folks understand basic calculus.

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?

Re:...End of time?

[Anonymous Coward]

Assuming that I remember the two-body gravitation equation correctly (F = Gm1m2/d^2 ?), past the second, all derivatives will be 0. (I think... I'm not gonna sit down and do the math.)

Of course that's a vast simplification, but my point is that if you know the general form of the equation, you will often know how many nonzero derivatives there will be without knowing for certain what the behavior approaching infinity is.

Re:...End of time?

[Anonymous Coward]

Are you sure you are not confusing astronomers with astrologers?

That's one depressed satelite!

[Reinout]

Poor, poor huble. Getting scrapped by Nasa. You can just see he's getting really depressed. He already has a black outlook on life, all that dark energy...

Well, it's his own fault now, giving us back such negative waves.

Reinout

Never underestimate the power of the schwartz!

[mikeophile]

Oh sorry, I thought the headline was New Clues About the Nature of Dark Helmet.

"Now you see that evil will always triumph, because good is dumb!"

- Dark Helmet

Re:Never underestimate the power of the schwartz!

[DarkHelmet]

You already know that my schwartz is big.

What else do you want to know, maybe Slashdot will interview me.

Re:Never underestimate the power of the schwartz!

[Anonymous Coward]

<Monty Python Nazi voice>
That's not funny!
</Monty Python Nazi voice>

The future of the Unvierse

[Neuropol]

After we have all (I assume that doesn't include any creationsists) adhered to the scientific theory of The Big Bang and the beginning of the Universe as we know it, I can only think that we can begin to accept the fate of the Universe.

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.

Relief?

[philbert26]

If a big crunch doesn't end the universe, then heat death will. Eventually the universe will reach a state of maximum entropy, and nothing interesting will happen.

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?

[plams]

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.

Some guy: Where are we?!
Al Gore (playing as himself): Well, I can tell you where we are not; THE UNIVERSE!!

Re:Relief?

[Anonymous Coward]

Maybe you'r right, but the thing people don't give a damn. Remember we only live a short life, so therefore we think only for the short term. Hence this screwed up world that we live in.

It only takes a nearby star to go supernova to end this planet. And we now how predicitable they are.

Have a nice life, whats left of it.

Re:Relief?

[thelasttemptation]

Tho what's to say that we won't have the tech to scoop up the matter and make our own stars? Maybe the universe counts on intelligent life to keep it going?

Re:Relief?

[Gr8Apes]

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=mc2

Re:Relief?

[sploxx]

Being a physics student, I really don't understand the heat death argument. 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. Of course, for us, that doesn't really matter much because we'll all dead before. (*) - restructuring here: Formation of stars a solar-system and something like an earth.

Re:Relief?

[Psiren]

Stephen Baxter (I think?) wrote a very good book (Time) based around the idea of heat death. Some of the ideas that civilzations come up with to make the most out the last remaining energy in the universe is very neat. Well worth a read.

Re:Relief?

[jafuser]

I'm not a physicist either, but just looking at this from a simple perspective, if heat death occurs, and everything is slowly approaching 0 degrees kelvin, isn't the concept of time fading as well? Once everything comes to a halt and nothing is happening, then time becomes a frivolous dimension anyway.

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?

[xigxag]

It's true that entropy can decrease when matter/energy enters a spontaneously ordered state, e.g. all the gas collects in the corner of the room. In itself that's infinitesimally unlikely, yet still possible. But in the case of the universe we live in, there's an additional wrinke. The edges of the "room" are expanding faster than the speed of light. Which means, eventually, every particle will disappear over every other particle's event horizon, and it will be impossible to put them back together again.

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 which might, in the long run, be able to tackle the second problem, but not the first.

Re:Relief?

[Bootsy Collins]

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 unbelievably small probability is also constant (or at least, decreases sufficiently slowly). In fact, in the cosmological context, it's continually decreasing, because of the expansion and the consequential redshifting away of free particle energies. Then, on top of that, there's the expectation of what are essentially one-way processes associated with baryon number violation. A bath of photons, neutrinos, and electrons, their energies well below constantly decreasing from the expansion, isn't going to form a new solar system.

Re:Relief?

[naasking]

Machines work on the principle of taking in energy and outputting it in the form of waste heat.

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 conversions, etc).

Re:Relief?

[Darby]

Stephen Baxter (I think?) wrote a very good book (Time) based around the idea of heat death.

Manifold Time.
Thanks for not spoiling it. I'm halfway through ;-)

Re:Relief?

[barawn]

One is proton decay, which means the building blocks of any sentient computer will eventually decay on their own.

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 years. At this point you can't simply claim that proton decay happens - in fact, you'd rather claim that it doesn't.

Re:Relief?

[thelasttemptation]

So the Second Law of Thermo says we can't scoop up matter and shove it together?

Hrm. That's intresting...

non-physical physics

[Space cowboy]

Right now we're about twice as confident than before that Einstein's cosmological constant is real,

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

[Anonymous Coward]

Well, it's a way to employ a glut of physicists with little hope of finding academic positions who didn't switch gears to go work in finance or the stock market.

Re:non-physical physics

[poindextrose]

A lot of new physics does seem to be increasingly theoretical and "out there" on the proverbial limb

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.

It would be good for the practical lot to catch up with the theoretical lot...

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

[grogzilla]

Understanding dark energy and determining the universe's ultimate fate will require further observations.

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 understand the largest of systems (universa level) than the smallest (sub-quantum level), and the mid-point (human-size events) may be the most difficult. Just thinking out loud here, IANAAP (i am not an astro-physicist)

But does anyone else find at least mildy amusing, the apparent ease with which such a whimsical statement is made?

Re:non-physical physics

[DdJ]

(hint: ohhh WAAAY ohhh, ummm barrray :-)

I think you mean: vayo a-o, a home va ya ray, vayo a-rah, jerhum brunnen g.

Re:non-physical physics

[EnVisiCrypt]

Actually, Galileo was excommunicated, which at the time was almost as bad as being driven out entirely. In addition, he was placed on house arrest and was confined there until he died, refusing to recant his observations.

Great man.

Re:non-physical physics

[Space cowboy]

Indeed I do, but (blush) had neglected to look it up, just did it from memory :-)

Glad to see one person got it, anyway :-)

ATB,
Simon.

Re:non-physical physics

[beanyk]

The thing is, he did recant. That doesn't mean he changed his mind, but he did change his official line. There's a writeup here, for instance.

Re:non-physical physics

[fermion]

There are two types of out there physics. The type that can be proven to not be true by observation, and those that can't be proven to not be true by observation. Which is a little different from being shown to be close enough to reality. The former go away and the later continue to provide us many hours of speculative enjoyment. The common feature of all of these is that they solve some theoretical problem. Fortunately solving some theoretical problem is not enough and the theories tend to languish until some pratical means of verification can be developed.

It was only a hundred years ago that Planck looked the black body radiation problem and the ultraviolet catastrophe and sent of a postcard claiming that fatal flaw was the assumption that energy was continuous. He threw out that faulty assumption, did up the math, and heralded in a world of devine dice, half dead cats, and apparently solid objects moving through apparently solid walls. In essence, rubbish.

The process of identifying assumption (the hard part) and challenging those assumption is what has brought the western world out of morass partially created by a boorish devotion to greek philosophy and political control by the Church.

Re:non-physical physics

[Anonymous Coward]

Of course, 2x (near-as-dammit-zero-certainty) is pretty much the same as (near-as-dammit-zero-certainty)...

Umm, we have a number of independent experiments, observing independent phenomena (e.g., CMBR anisotropies, supernova luminosity-redshift relations, etc.) that all support the existence of a cosmological constant (or a more general "dark energy") -- and not only that, but they all suggest a cosmological constant of the same order. It's not airtight evidence, but it's far better than "damn near zero certainty".

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'

The Higgs isn't exactly an "out-there" hypothesis either... and if it does indeed exist, the LHC (already funded and well under construction) will see it in a few years.

Re:non-physical physics

[Fulcrum of Evil]

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

[dingbatdr]

He did recant once he was threatened with torture. I doubt many would stand on scientific principle under those conditions. What is rotating around what becomes fairly esoteric when faced with mean people with sharp knives. dtg

Re:non-physical physics

[Darby]

Indeed I do, but (blush) had neglected to look it up, just did it from memory :-)

Glad to see one person got it, anyway :-)

Dude, I thought you were doing the Wicked Witch's theme from The Wizard of Oz ;-)

Re:non-physical physics

[jaoswald]

Planck looked the black body radiation problem and the ultraviolet catastrophe and sent of a postcard claiming that fatal flaw was the assumption that energy was continuous.

Actually, according to Kuhn (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 mathematical tool. It took Einstein and Poincare to point out that the use of Boltzmann's technique implied small quantum occupation numbers in the high-frequency portion of the spectrum; i.e. that the Boltzmann approach was actually radically new physics.

Now, Planck did realize at them time that his introduction of "h" and its failure to be cancelled in the final formula was dramatically new: he was quite proud (justifiably, of course) to have discovered a new fundamental constant. But it took years for the new mechanical implications to become clear, even to him.

Re:non-physical physics

[Anonymous Coward]

Which is the point. We make these claims, like quantization, multiple dimensions, or a speed limited universe, because they make the equation 'work out better'. We don't know if the claims are valid, or where they will ultimately lead. The point is to understand the universe. The number of people who lead us to this absurd physics are many including Einstein who never liked it, DeBroglie, Schodinger, and of course Feynman who did the critical work, again without knowing it, of showing the two interpretations of QM were equivalent.

And, if I may quote Quantum Mechanics, Gaswami, 1992,
Planks genius lay in the observation that if we change the integrals ... to summations, that is, if we assume that an oscillator can take on only discrete values of energy, the average energy per degree of freedom an be made to decrease at high energy
So it was mathematical connivence, but a definite break from what was standard physics.

Re:non-physical physics

[jaoswald]

A 1992 textbook is not the way to understand what Planck was thinking in 1880--1910. Textbooks almost never give a true historical picture of the complicated ways in which ideas get formulated. The point of a textbook is to simplify; it took 30 years for QM to bubble up from the cauldron of statistical mechanics, and a textbook doesn't have time for a play-by-play, so it settles for a crude approximation.

Physicists are particularly prone to assuming that the mathematical derivation parallels the historical development. Planck absolutely did not have a flash of inspiration that oscillators take on discrete values; Einstein and Poincare get the credit for recognizing that oscillators get quantized. Read Planck's papers and you see he talks about continuous values for the oscillator energies. A truer picture of what happened is that Planck couldn't figure out any way ahead, so he finally took a look at Boltzmann's mathematical techniques although he philosophically disagreed with Boltzmann's approach.

Now we can see that the fact Boltzmann's approach WORKS means that the degrees of freedom of the EM field act according to quantum mechanics. That also explains the photoelectric effect (Einstein) and applying that same knowledge to atoms in solids explains the departure from the Dulong-Petit law at low temperature (Einstein again!). Planck had to catch up to Einstein in this thinking.

Einstein gets a bum rap for his position in the Bohr-Einstein debate. In fact, Einstein was the *dominant* figure in the emergence of QM. Take the specific heat of solids: Einstein had ONE experimental curve (diamond, I believe) that showed a disagreement with Dulong-Petit. BOOM, in something like the THIRD paper EVER written on quantum mechanics, Einstein explains it. Now that is totally ground-breaking.

Bohr was a hand-wavy kind of guy, and Einstein felt rightly that there was no justification at the time for believing quantum mechanics apart from statistical mechanics: Einstein knew that atomic spectra were measured with large numbers of atoms in a vapor, not individual atoms. So all you could say for certain is that the quantum rules explained what happens ON AVERAGE for atoms in a gas. Bohr jumped ahead to assuming that QM explained the individual atoms, not just an ensemble, and I think that is what set Einstein off.

Nowadays, we can do experiments on single atoms and single photons and see that quantum mechanics does work in that case, and Bohr turned out to be right. But that doesn't mean that Einstein was wrong, just that he wasn't convinced by Bohr's reasoning.

Dark Matter and Ether

[GerritHoll]

I find it strange that scientists 'believe' in dark matter. The main reason for the hypothesis that dark matter exists, is that otherwise those huge systems of galaxies don't obey Newton's laws. However, throughout the 20th century, there have been numerous occasions where Newton either was proven wrong or where fields of science were found where his laws weren't applicable: ether didn't exist, at nanoscale Newton's laws don't apply (quantum mechanics), at very high velocities they don't either (relativity), and in very complex systems Newton can't be used (chaos). Why would it be so strange if systems with enormous scales and very small accelarations would not obey Newton's laws? It does feel a bit like Ether to me to introduce a form of matter/energy which has never been measured at all...

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

[Aardpig]

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

[quinkin]

Oh man... where to begin.

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 measured at all." - Now that I can agree with.

In my usual agnostic way, I am certain that dark matter might exist.

Q.

Re:Dark Matter and Ether

[snake_dad]

The article is about dark energy, not dark matter. Those are two distinctly different things. Dark matter is simply matter that has not been found, but that astronomers assume must exist to explain certain gravitational behaviour as observed in galaxies. AFAIK there is not much controversy over wether dark matter is real or not. Dark energy however is theorized to be a force that acts opposite to gravity, and that could explain why the rate of expansion of the universe seems to be increasing.

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

[Anonymous Coward]

It is not that easy, relativistic an quantummechanical principles are accounted for in the theories. One can predict when to use which theory to use and what simplifications can be done in order to achieve accurate calculations. Rotation of galaxies lies well in the realm of classical and relativistic mechanics.

Another point of clarification, chaos theory is not in contradiction to Newton/classical mechanics, it is a matter of analytical integrability, so chaos theory is actually a theory that uses Newtons laws and shows it accuracy in its realm very well.

b.t.w. IAAP (Physicist)

Re:Dark Matter and Ether

[mmusson]

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 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.

Re:Dark Matter and Ether

[barawn]

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.

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

[ysachlandil]

>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.

And dark matter (or energy for that matter) is not an empirical modification of the known universe to suit the known physical laws?

At least MOND doesn't require huge amounts of matter and energy that nobody can detect to 'fix' the universe...

--Blerik

Re:Dark Matter and Ether

[Aardpig]

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

[Anonymous Coward]

I find it strange that scientists 'believe' in dark matter. The main reason for the hypothesis that dark matter exists, is that otherwise those huge systems of galaxies don't obey Newton's laws. However, throughout the 20th century, there have been numerous occasions where Newton either was proven wrong or where fields of science were found where his laws weren't applicable:

Well, you have two choices: either introduce some unknown modification into our theories of matter (dark matter), or introduce some unknown modification into our laws of gravity (e.g., MOND or something). Why do you think the former is any more implausible than the latter?

There are many reasons why dark matter is preferred. First, in particle physics it's actually pretty easy to have theories with weakly-interacting particles that can only be detected gravitationally; in fact, one might wonder why such particles don't exist; they're a pretty generic prediction of most unified theories, for instance.

Then, dark matter successfully accounts for a lot of observational evidence, including galactic rotation curves, the measured energy density and near-closure of the universe, and early-universe structure formation. On the other hand, Newton's law of gravity are extremely well-tested, but people have tried to account for these things by modifying Newton's law, such as MOND. The problem is, while such modifications can usually be used to account for one or two of the phenomena that dark matter can explain, they usually can't explain everything dark matter can (e.g. they can explain galaxies but not cosmology or structure formation, or vice versa), so you still have to do more work. Dark matter can take care of it all in one fell swoop.

For instance, there are various difficulties with MOND (I keep bringing it up because people seem to like to cite it here a lot), e.g. this or this; for other reasons why astrophysicists tend not to prefer MOND, see also this. MOND proponents have tried to patch up the theory, but in the opinion of most astrophysicists, it's even uglier than dark matter.

Re:Dark Matter and Ether

[Anonymous Coward]

That's true. On the other hand, not enough of this kind of dark matter (MACHOs) has been found, so you still need to postulate some exotic dark matter (WIMPs).

Re:Dark Matter and Ether

[Fulcrum of Evil]

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

[ceoyoyo]

If I remember correctly, Einstein "believed" in the cosmological constant because it was necessary to balance gravity and allow a static universe (which Einstein believed in for religious reasons). The cosmological constant was regarded as Einstein's greatest mistake... a fudge factor he introduced which was NOT based on any observational evidence, but rather to reconcile his theory with his religion. Now, with the observation that the universe's expansion is accelerating instead of decelerating, we do have observational evidence for the cosmological constant.

Re:Dark Matter and Ether

[kisak]

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 and h=0, which means that for most situations Newton's laws are "exact". Even to simulate molecules and galaxies Newton's equations are "exact enough".

Second, chaos is a general property of any differential equation which is complex enough. So, chaos can appear in classical mechanical systems and are not related to quantum effects or relativity (even though chaos phenomen also appear in these).

Ether was discharged as a hyphotesis by Einstein and others since something that could not be experimentally observed or was not needed theoretically to explain the observations, is per definition an empty concept. If dark matter can explain experimental observation or makes a nice theoretical framework for what is observed, then one should not discharge it even though it is still a bit an empty concept (which is why it is called "dark matter" I guess, can't be seen, don't know what it is). The judge is still out if dark matter will help us in understanding the universe, but it is better to start by building on the fundament of previous physics, instead of throughing out Newton's laws that have passed the test of three hundred years of observations.

Re:Dark Matter and Ether

[barawn]

I was under the impression that dark matter needs fine tuning to explain Tully-Fisher

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

[Darby]

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.

Well, Duh ;-)

Re:Dark Matter and Ether

[tgrigsby]

I completely agree. I find it easier to believe in MOND, in a quanta of gravity that is usually lost in the rounding error except when the distances involved are great enough. In fact, I'd even believe that virtual particles, zipping in and out of existence, are exerting hit-and-run gravitation. The idea of particles that float around without interacting with anything except through gravitational force just smacks of "ether". MOND and dark matter are, at least for now, calculation crutches, but MOND makes more sense to me than dark matter.

Correct me if I'm wrong

[TheRealMindChild]

But the "Cosmological Constant" Einstein was credited for theorizing on was Ether, and eventually disproved the existance of Ether himself by somehow using the earths revolution around the sun.

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

[ooby]

Prior to Kepler, scientists believed their was a planet Vulcan that shared Earth's orbit but the two were 180 degrees apart. Vulcan had the same mass as Earth and without the planet, scientists couldn't fit Earth's orbit into the Law of Universal Gravity.

Re:Correct me if I'm wrong

[GammaRay Rob]

You're wrong. Aether was thought to be a physical fluid whose ripples were the basis of the wave-like nature of light. This was proven not to be so by Michelson and Morely, who showed that the speed of light was the same no matter if it were going with or against the aether (which was presumably flowing past the moving Earth). Dark energy is a field, like light or gravity, which presumably has no preferred frame of reference (like light or gravity).

Re:Correct me if I'm wrong

[CaptainAvatar]

Sorry but the parent post is NOT Insightful; it's utterly confused. Firstly, Vulcan was a hypothetical planet in between the Sun and Mercury, proposed in the 19th century order to explain the advance of Mercury's perihelion (which was later accomplished by general relativity). Some observations were claimed in the 19th century but never verified and we know now that it was bogus.

The thing you seem to be thinking of is the unseen antichthon or counter-Earth; this dates from classical Greece where it was an element of Pythagorean cosmology. It was however not on the other side of the Sun but permanently hidden by the "central fire" which the Pythagoreans also believed in. To my knowledge it has never been taken seriously by scientists since that time - certainly not by a majority of them, anyway.

And finally, there was no universal law of gravitation to fit the Earth's orbit into prior to Kepler, or even for a few decades after his death. That had to await Isaac Newton. Sounds like you are thinking of Kepler's famous attempt to fit the planetary orbits into a nested series of perfect solids (pyramid, cube, etc).

Re:Correct me if I'm wrong

[APL bigot]

Sorry, lack of evidence is not evidence of lack. Michelson and Morely were unable to detect an aether. They did NOT prove aether does not exist. There was some conjecture of frame dragging by the earth, preventing detection.

Re:Correct me if I'm wrong

[Anonymous Coward]

Aether drag can explain the Michelson-Morley experiment, but it cannot simultaneously account for stellar aberration.

Not with a whimper, but a "Big Rip"?

[Anonymous Coward]

"And in the end of days, God shall eat Mexican food and several beers and ye verily shall His mighty thunder rend the Heavens."

The article you must read

[pikkumyy]

It seems this "dark energy" is quicker, easier and more seductive.

I'd buy that for a dollar!

Everything's nonsense

[Anonymous Coward]

The end of the unverse makes me depressive. Nothing that is eternal. No sense in building up things, inventing, scientific discoveries and everything. Just nonsense. Well, if you do not believe in god or are at least agnostic.

Well, back to my OSS/FS projects to gain fame in this dark world :)

Dark Matter? My god...

[Channard]

.. it's full of Goths! I hereby dub the matter 'Mopotronium

Dark Matter conclusively identified...

[Channard]

It's like regular matter, only it has a goatee. I thank yew.

Einstein was wrong anyway

[KjetilK]

It wasn't the introduction of the cosmological constant per se that Einstein thought of as his greatest blunder, it was the failure to realize and predict that the Universe is expanding. The cosmological constant he had there to get a static universe, and that's bad. Also, the cosmological constant isn't Evil, it comes rather naturally from solving the equations. I never got as far as actually doing that, but I followed a back-of-envelope solution once, and it comes out sort of like an integration constant. I think of it as a natural parameter that should be constrained by observations just like any other parameter, and I see no particular reason why it should be 0.

Re:Einstein was wrong anyway

[khallow]

Actually, the cosmological constant can result in an expanding universe.

Re:Einstein was wrong anyway

[GMFTatsujin]

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. Turns out he was wrong, is wrong, and will always have been wrong. Einstein's motivation for putting in the cosmological constant was ideological, not observational -- and that's a recipe for Dumb Science.

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

[tgibbs]

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. Turns out he was wrong, is wrong, and will always have been wrong. Einstein's motivation for putting in the cosmological constant was ideological, not observational -- and that's a recipe for Dumb Science.

Not exactly. Einstein didn't "put in" the cosmological constant; it emerged naturally from the derivation of the equations of General Relativity. But the theory did not provide its value; it was a free variable. It needed to be given some value, and there was at the time no firm observational data to do that. The mathematically simplest course would have been to arbitrarily assume that it had a value of zero, effectively "getting rid of it." That would have implied an expanding universe, and Einstein would have scored quite a coup by predicting the expansion well before the data came in to confirm it. Instead, Einstein chose to assume a value that brought his theory into line with the then-current astrophysical view of the universe--i.e. that it was static. So Einstein didn't "put it in;" he merely chose not to arbitrarily take it out. Yet another possible value of the cosmological constant yields an accelerating expansion. But that is different from the value that Einstein assumed. So the only sense in which the "Einstein was right after all" statement applies is that the correct value may not be zero, after all.

Re: Einstein was wrong anyway

[Black Parrot]

> 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

[KjetilK]

Yep. Actually, the cosmological constant can result in many funny forms of universes, including my favorite "bouncing universe", which, sadly, is now pretty solidly rejected by observations. :-)

Re:Einstein was wrong anyway

[TwistedGreen]

Why is this even relevant? After all, Einstein was just this guy, you know?

Re:Einstein was wrong anyway

[khallow]

Actually, the cosmological constant can result in an expanding universe.

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 respectively) unrelated to the mass in the system, but due to positive or negative energy (respectively) of the vacuum. Thus, with a slight amount of negative curvature of your vacuum, you can have an expanding universe.

Duh!

[UncleBiggims]

I doesn't take an Einstein... oh wait. Nevermind.

Are you Corn Fed?

No info...

[eclectic4]

...in that article. I was hoping for a hint as to what dark energy is, but this article simply states possible changes in theory.

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...

[Silburn_Luke]

If you want more detail you should check out the February issue of Scientific American, which has four or five feature articles discussing the cosmological theories these experiments are addressing.

Regards Luke

Re:Dark Matter or Dark Energy?

[ImWithBrilliant]

we're well out of the Big Bang, there's quite a difference.

No, really?

[TheGreatGraySkwid]

From the article:
"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!

Dark energy

[rotciv86]

Could this possibly be the counter force to grvity?

Re:Dark energy

[jpflip]

Dark energy certainly acts a bit like antigravity, but it's generally not believed to be quite that. We really have no clue of its exact nature, however - we just know vaguely what it does. The usual suggestion (which dates in some ways back to Einstein, though he never guessed at dark energy) is that it's a cosmological constant - an additional term in the equations of general relativity. Others suggest it's a new kind of particle field. Either way, it has negative pressure. The details of negative pressure are a little confusing, but the gist is that if dark energy is the dominant form of energy/matter in the universe, the universe will expand nearly exponentially rapidly. It's not really an antigravity force, but it is really strange.

Filling the blank?

[cabazorro]

I get the feeling that we are trying to fill
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 ..explosions and ever
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.

They were wrong ??

[thrill12]

"This would lead to a "big crunch" where the universe ultimately implodes. "This looks like the least likely scenario at present," says Riess."
This can't be, coz' even Red Dwarf had an episode about that!

http://www.ebtx.com/ntx/ntx16.htm

[Anonymous Coward]

Whats more likely? This mysterous dark energy exists and compromises 70% of the mass/enery of the universe even though we can't see it anywhere locally, or our theories are wrong?

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.

Re:http://www.ebtx.com/ntx/ntx16.htm

[Anonymous Coward]

I think you are mixing up dark matter and dark energy.

Re:http://www.ebtx.com/ntx/ntx16.htm

[Anonymous Coward]

Whats more likely? This mysterous dark energy exists and compromises 70% of the mass/enery of the universe even though we can't see it anywhere locally, or our theories are wrong?

Either way, our theories are wrong, because they didn't predict an accelerating expansion. The question is, are our theories about the matter/field/vacuum content of the universe wrong (dark energy/cosmological constant), or are other theories (such as our theories of gravity) wrong? You obviously seem to prefer the latter, but why?

I suggest reading www.ebtx.com on the nature of dark energy. This guy is right, or at least close.

What nonsense. He doesn't even have a theory, let alone a right one. He doesn't have any physical laws (i.e., equations) that can even qualitatively be compared to observational data, let alone quantitatively compared. Where is his calculation of the Tully-Fisher relation? The CMBR anisotropies? His derivation of early universe structure formation? How can you claim that this guy is even close to right, when his ideas can't be scientifically compared to experimental evidence??

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).

Gee, that sounds deep, but can I use it to predict anything meaningful, like a flat rotation curve?

Re:http://www.ebtx.com/ntx/ntx16.htm

[Anonymous Coward]

Is the universe expanding, or are we all shrinking? From a relative point of view there is no difference.

That's an interesting idea, and it would be nice to know, but what difference does it make?

I mean, I want to be careful to not say that usefulness defines truth, but wouldn't all of our theories work exactly the same way if that were true?

Re:http://www.ebtx.com/ntx/ntx16.htm

[Decimal]

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).

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".

Big Rip a Big improbability

[Pi_0's don't shower]

If you fear things involving physics, skip the rest of this post. Alright, for those who are interested, it seems like 70% of the current energy density of the universe is in some form of "dark energy", as was previously stated. The Universe is currently 13.7 billion years old. We say that every component in the universe has an energy density and a pressure. Dark energy is different from things like normal matter and light, because these have positive pressures. (Normal matter has a very small pressure). But dark energy has a negative pressure, which means it works opposite to gravity. Everything that has a pressure that we can physically think of (well, that I can physically think of) has a pressure between (-1)*energy density and (+1)*energy density. A big rip will only occur (and it will only occur in the very distant future) if the dark energy has a pressure that is outside this range, such that pressure is less than (-1)*energy density. This is, of course, possible, but unlikely in my view.

Comment removed

[account_deleted]

Comment removed based on user account deletion

"the repulsive force"

[panurge]

is how it's described in the article. I think that's a bit unfair. It can't help its appearance.

Big Rip != Acceleration

[jpflip]

The fact that the universe is accelerating is not the same as the "big rip". The accelerating universe, as we understand it now, sort of means that the space between everything and everything else is getting bigger all the time. However, in order to discover this (and the expansion of the universe in general), we have to look at very distant galaxies - we don't see our own galaxy flying apart, and some other galaxies bound together in our local galaxy cluster are orbiting or moving toward ours. In general, objects that are in bound states - whether gravitational bound states (like solar systems and galaxies) or other bound states (atoms, etc.) will remain held together even as the distant galaxies which are not tightly bound to us zoom away. Our own situation on earth would be completely unaffected - you'd need a big telescope to even tell the difference. The idea of the "Big Rip" is that this condition that "bound things stay bound" (the dominant energy condition) might be violated, that dark energy might be so extreme that not even bound objects could keep from eventually dissipating. That idea is HIGHLY theoretical - there's no particular evidence for it, and until recently most theorists thought it was ridiculous. But, of course, this is science - we have to think about even the weird possibilities.

There's more to dark matter...

[jpflip]

You're right, the natural step when we learn that the universe doesn't obey Newton's laws should be to try to modify Newton's laws, not to imagine that there is a magic 95% of the universe with funny unobserved properties. The thing is that this isn't the only evidence for dark matter. There are a number of different lines of evidence which lead to the same conclusion - the orbital behaviors of galaxies and their clusters, the adundances of various light elements in the universe, the behavior of the cosmic microwave background, x-ray emission from clusters, etc. It turns out that no matter how hard we try, we can't modify Newton's laws to get the right answer to all of these. Gravitational lensing (the bending of light by the mass of distant galaxies and clusters) is really impressive in this regard - modifying Newton's laws (and general relativity) in the desired ways should have essentially no effect on it, and it definitely looks like there's dark matter (and even allows us to map its distribution). Dark matter really seems like the SIMPLEST answer, from the point of view of someone who knows the data! Dark energy was the subject of the article, however, and that's quite a bit different. As of right now, I'd say that we DON'T have very convincing evidence that this isn't just a modification of general relativity. All of our particle physics-related ideas seem far too complicated. Oh, and chaotic systems still obey the laws of classical physics - the systems are just so complicated that knowing how the individual atoms are behaving is not very helpful for predicting the behavior of the macroscopic system.

Excellent question!

[Pi_0's don't shower]

You're absolutely right. If the third derivative is negative, or higher derivatives affect physics, this would change things again. Or, as you say, if there is some potential that is chosen, you can construct whatever universe you like.

This second idea is actually the basis of quintessence, one of the leading theories of dark energy. But there is no motivation for choosing these potentials, which is why many physicists find them unsatisfactory.

The problem with your reasoning for higher derivative physics is, well, physics just doesn't seem to depend on higher derivatives. Newton's law is F=ma. It could have been F=ma + something*(da/dt), but it appears physics doesn't work that way. There are stability arguments people have used to "disprove" that physics depends on anything higher than second derivatives, actually.

(I put disprove in quotes not because it isn't right, but because I don't understand the arguments well enough to know whether it's right or not. But it's still an excellent point.)

Physicists generally write down equations for the scale factor, it's first derivative, and it's second derivative. Higher derivatives do exist and can be written down, but the general consensus is that there is no new physical information in there.

Re:Excellent question!

[Tablizer]

Physicists generally write down equations for the scale factor, it's first derivative, and it's second derivative. Higher derivatives do exist and can be written down, but the general consensus is that there is no new physical information in there.

Maybe God doesn't understand calculus, so he instead just tweaks a knob every few billion years to adjust the espansion rate.

The main problem with Dark Energy...

[little1973]

...is that no mainstream theory predicts its existance. It is based solely on observations. Scientists try to bend/modify current theories in order to include Dark Energy.

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.

Re:The main problem with Dark Energy...

[Anonymous Coward]

...is that no mainstream theory predicts its existance.

Eh, you can write down lots of theories that involve fields which act as dark energy. The question is finding out which, if any, are right. Since we can't do that yet, none of these alternative theories are mainstream. If we could, then maybe we could go looking for other predictions of these theories.

Actually right here: Re:The restaurant

[sammyo]

Recent topological cosmological theories suggest there universe is 'connected'. Thus the ends 'wrap' around like an n dimensional torus (doughnut) and if you travel all the way you are actually back where you started.

A "Circular" argument?

[Cragen]

Whatever happened to the idea that something going away from us would eventually "re-appear" on the opposite side of the Universe and start heading towards us? (I have no clue what hypothesis was/is called.) Perhaps everything expanded to the edge, ALREADY, and is now "expanding" towards the center, again, and is therefore being more attracted to everything else cause it's getting CLOSER! (I have to stop now. My brain is going to take a little break.) Whew. Next?

Re:A "Circular" argument?

[DynaSoar]

Cragen (697038) sez: "Whatever happened to the idea that something going away from us would eventually "re-appear" on the opposite side of the Universe and start heading towards us?"

It's still around, as an untestable hypothesis. It would take longer than the total lifetime of the universe to make the trip.

big rip?

[tommeke100]

Take cover! The big rip has already started, it's called SCO! oh, wait...sorry, that's "the big rip off".

Re:big rip?

[Anonymous Coward]

that was the fucking worst SCO joke i've ever read.

I for one...

[Anonymous Coward]

...welcome our new Sith Overlords.

Here we go again...

[jpflip]

I agree, it's very possible that some basic notion of ours about gravity is wrong - dark energy is very possibly a manifestation of that. This doesn't mean the stuff on the webpage you link to is any good. The main page contains such crap as an attempt to use "logic, mathematics, and geometry" to explain why the constitution isn't working, how propulsion systems for UFOs work, and so on. This is yet another example of someone thinking they can provide a "simple" explanation for the scientific phenomenon-of-the-week without bothering to learn any real facts about what he's trying to explain. Such stuff almost invariably makes no physical predictions and gives you no way to calculate anything important - it's just pseudological bluster. Science is hard, and it works a lot better than some armchair philosophers seem to think - if you want to make a contribution, learn something about it.

hypothesis, theory and faith

[GerritHoll]

I think it is very well possible to believe in a hypothesis. There is a thin line between hypothesis and theory. It's possible to believe in a theory. Evolution is a theory. I think evolution is a fact, and that means I believe this theory is true. It can be dangerous to believe in a hypothesis, because it may mean closing they eyes for alternatives. I am not saying this is happening with dark matter, but it happened in the past, happens in the present and will happen in the future - just because scientists are human too, and often conservative.

I too am certain that dark matter might exist, but that doesn't say anything. It merely states that the chance is larger than 0 and smaller than 1 - which is true for every non-mathematical chance, so we don't progress with this in the discussion. I think it's highly unlikely that dark matter truly exists.

I mean with 'believing': thinking the hypothesis is true. I think the dark matter hypothesis is false. I think evolution theory is true. Not sure whether big bang is theory or hypothesis, but I think it's true. Its a language issue, but IMHO, believe==think here.

Re:hypothesis, theory and faith

[quinkin]

Nah, disagree completely. It is semantic hair splitting though... Belief has no place in science - only confidence. Belief in a possibility (ie. theory/hypothesis) is an obvious oxymoron.

Q.

Re:hypothesis, theory and faith

[Anonymous Coward]

Most subscribers to Bayesian probability theory would describe a probability as a degree of belief, and as such, belief is everything in science.

Re:hypothesis, theory and faith

[quinkin]

Pick your favourite religious zealot and try and get them to agree that their belief is equivalent to a high probability. As I said, semantic hair splitting, but hey I brought it on myself. Was in an argumentative mood after dealing with my two year old breaking his leg. :(

Q.

hmmmm....

[Anonymous Coward]

why does kosmology lately
sound sooo pedohile?

from all data sources soo far, everything
indicates that no one has a clue as
to why the univers exists in the state it
is at the moment.
"70%" this really is very troublesome since
honest people base their day-to-day assumptions
on law of physics and now this: "70%" un-known.

sounds serious enough not to go to university.
not to trust anyhing but your most basic
instincts, damn "70%" unknown.

so what's really at roswell?
what are they REALLY doing in geneva with their
energy leech maschine?
is this "radioactivity" really what they claim?
etc.

stay tuned for some serious revolution comeing
to you really soon. "70%" unknown and my
physics teacher is stillt trying to give me marks?
damn!

Hmmmm...

[linoleo]

What if our Big Rip is the next universe's Big Bang? Or, to be more more precise, the next universe's inflationary period?

*phew*

[MoFoQ]

and I thought it was about Enron again.
(or if u live in california, any company that sells power; duke, reliant, etc.)

and in the computing world; SCO at the moment though history shows that it'll return to microsoft as soon as SCO goes under (it's not a matter of if but a matter of when).

Big Rip in 30 billion years

[Anonymous Coward]

Um.... so?

How many of us are going to be around in 30 billion years? Aside from the people who are cyrogenically (sp?) frozen.

Indeed...

[master_p]

C is the root of all evil!!!

This Einstein was right stuff

[xihr]

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 reasonable model, a universe must expand or contract, he introduced a cosmological constant with the intent of negating that expansion or contraction, resulting in a static, unchanging universe. (Specifically, he thought the universe was closed -- this is one of his boundary assumptions in general relativity -- but static.)

Now it turns out that we seem to live in a universe which is not only, to most cosmologists' surprise, open, but also with a nonzero cosmological constant that is accelerating that expansion. The entity -- the cosmological constant -- which Einstein introduced would appear to have some use (though in fact we already knew that, since inflation theory, a pretty solid part of our Standard Model, involves an effective cosmological constant), but not for the reasons he introduced it (that is, our universe is emphatically not static and the cosmological constant does not help it become so). In theoretical physics, you don't get bonus points for getting the right answer for the wrong reasons.

In fact, in many ways, theoretically the cosmological constant is a bad theoretical feature, because it indicates a tweakable parameter that you need to find observationally -- hence, the desire to find the theoretical basis for the value of the cosmological constant.

Quick summary

[TMB]

w=-1

This comes as a great shock to exactly no one. ;-) Postulating anything else is like introducing epicycles when you've only just figured out that there are orbits.

[TMB]

Questioning dark energy

[forgetful]

Coming from a classical perspective, matter would be "condensing" from the primordial "hot stuff" for a long time after the Big Bang. Classical hypothesis is that E + Matter = E +Matter for the universe in the long haul. I ask as a layman: the condensation of matter for a long time following the big bang would have equated to a gradual increase in gravitational forces, wouldn't it, because matter expresses gravitation more effectively than energy? At some point about five billion years ago, the condensation of matter crossed a threshold where it no longer condensed from the primordial "hot stuff" at a rate sufficient to override the expansion of space and the contained energy from the original expansion. The universe at that point didn't accelerate so much as it continued to expand with less overiding constraints from the diminishing role of condensing matter. Perhaps matter is less infinite than energy in the equilibrium of this universe. Is dark energy only the limiting of exhausted matter in the grand equation? That being said, I hope for tapping the energy of the zero point field and the success of overunity devices based on that premise. I tire of classical explanations--including my own--based on post-classical observation

Re:Questioning dark energy

[dadman]

the condensation of matter for a long time following the big bang would have equated to a gradual increase in gravitational forces, wouldn't it, ...

No, it wouldn't.
Remember E=mc^2? Energy is matter.

Re:Questioning dark energy

[forgetful]

I'm only a lay person and I ask these questions for enlightenment. Yes, matter and energy are inter-convertible, but light expresses pressure which can be expansive. Over the life of a star, for example, a relatively small percentage of matter is converted into energy (say about 4% --I don't know the average value for all star classes, but I seem to recall that is about the binding energy released in the H+H = He Rx). In our rarified region of the galaxy, stars "mine" about 16 cubic light years of space for matter for their formation, i.e., the nearby stars average about 5 light years apart. Now the average curvature of space (gravitation effect) would be the same whether the matter was thinly dispersed across space or concentrated into the "point source" of a star. As the energy is radiated from the star, however, it exerts a small repulsive pressure on any matter with which it interacts. My question is: Is the gravitation force between gamma rays, for example, equivalent to the gravitational force between the small mass of matter which was converted into those gamma rays? I assume it is, but gravitation, to my knowledge, has never been empirically measured even at the atomic level. There is no doubt that kinetic energy is converted into mass in particle accelerators, for example, but does the space curvature effect hold for gamma rays released, say, in matter/anti-matter annihilations? If energy does not curve space, then there should have been a small reduction in the curvature of the universe ever since the Big Bang as matter was converted to energy in stellar crucibles. If energy does curve space, then it seems to me that you would also have to deduct the repulsive force of energy as it has radiated from stars, and this should have led to a speed up in the expansion of the universe as matter was converted to energy. The observations that lead to assumptions about dark energy are based on very small deviations from expected "classical" values over the whole range of the universe. The universe is approximately 25 billion light years "across" as the oldest objects are a bit over 12 billion light years from Earth. That means the average rate of expansion over the "life" of the universe is approximately the speed of light. It is not half "c" for example, or those oldest stars would only be 6 billion light years from us. This is intriguing. Why c, why Planck's constant, why... Energy/matter/time/charge/space distilled out of the "cosmic egg" following the big bang (whatever that event was). And gravitation must not have been sufficient to hold the "egg" together. A small fraction of the original matter formed early in "time" has been converted into energy over the life of the universe. I assume that physicists and astrophysicist believe that the total, inter-convertible quantity of light and dark energy, and light and dark matter, has remained the same over the life of the universe. I only ask this because I've never seen an article that specifically addressed the gravitational effects (or curvature) associated with energy. Personally, I think the observation of dark energy and matter is one of the greatest scientific mysteries reported in my lifetime, and its explanation may rate right up there with the demise of the aether or the solving of the ultraviolet catastrophe about a century ago, which led ultimately to the special theory of relativity; or so I hope.

Asimov

[gd2shoe]

Isaac Asimov is certainly best known for his work as a science fiction writer. What most people don't know is that he also knew and enjoyed science. I don't have the understanding to discuss many of the theories that I have read here being debated, but I think something Isaac said once bears repeating. From his scientific work "The Neutrino", let me paraphrase:

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. You can use a different red ball. Eventually you may adopt the theory that red balls when thrown up must come back down. You may eventually expand that theory to include blue balls, and then green balls, and then any ball. That would lead to further experimentation and the conclusion that "what goes up, must come down."

Later on though, you may let go of the helium balloon that you were holding. Helium balloons do come back down once they've gone flat, but you may need to modify your theory to say "what goes up, must come down, but not necessarily right away." Airplanes do this too. But what if something reaches escape velocity.

"What goes up, must come down, but not necessarily right away, and only if it doesn't reach escape velocity."

As our knowledge and data base grows, our theories expand or get thrown out in favor of something that better fits our observations. But they are just that: our observations. If a model doesn't fit an observation, don't blame the model, or the observation, or the scientist. Such will only be modified again as our understanding grows.

proton decay

[Anonymous Coward]

The worst of all the possibilities, the end of the universe will be by "photon death".

Ask COBE

[Anonymous Coward]

The details I don't fully understand myself but I believe the patterning of the cosmic background radiation shows that this is not the case. It has to do with the standing waves that could exist in a universe of a specific shape and boundary conditions.

w=-1?

[Hoi Polloi]

I thought the answer was 42?