We're all made of star stuff
October 27, 2011 4:04 PM   Subscribe

Carl Sagan famously said that we are all made of star stuff. In his vision the basic building blocks of life were jettisoned into interstellar space by the massive explosions of stars going supernova. Now scientists from Hong Kong University have claimed that the results of their latest study(paywall), published in Nature, indicate that stars can create complex organic compounds on the very short timescale of weeks.

Not only are stars producing this complex organic matter, they are also ejecting it into the general interstellar space, the region between stars. The work supports an earlier idea proposed by Kwok that old stars are molecular factories capable of manufacturing organic compounds. "Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions," says Kwok. "Theoretically, this is impossible, but observationally we can see it happening."

Here is a link to a previous paper on the subject: Synthesis of Organic Matter by Stars and its Effect on the Origin of Life on Earth
posted by AElfwine Evenstar (48 comments total) 26 users marked this as a favorite
stars can create complex organic compounds apple pies on the very short timescale of weeks from scratch.
posted by nathancaswell at 4:09 PM on October 27, 2011 [15 favorites]

but a mixture of aromatic (ring-like) and aliphatic (chain-like) components. The compounds are so complex that their chemical structures resemble those of coal and petroleum.

IANAOC (I am not an organic chemist), but I don't consider benzine rings and hydrocarbons particularly complex. Now if they were making amino acids ...
posted by ZenMasterThis at 4:12 PM on October 27, 2011

IIRC Hydrocarbons have been spotted in circumstellar disks since the 70s.
posted by Artw at 4:16 PM on October 27, 2011 [2 favorites]

Obligatory link to Sagan, Feynman, deGrasse Tyson and Nye in "We are all Connected".

I love Symphony of Science.
posted by inturnaround at 4:24 PM on October 27, 2011

stars can create apple pies on the timescale of from scratch.

Are you sure that apple pie is made with real apples? Science is tricky like that.
posted by filthy light thief at 4:26 PM on October 27, 2011 [1 favorite]

Two words: genesis torpedo.
posted by justsomebodythatyouusedtoknow at 4:29 PM on October 27, 2011 [6 favorites]

I GIS'd "stars apple pie scratch" and got results that alternated between Carl Sagan, astronomic photos, and apple pies.
posted by Renoroc at 4:31 PM on October 27, 2011


I can eject complex organic matter too.
posted by Brandon Blatcher at 4:35 PM on October 27, 2011 [12 favorites]

I can eject complex organic matter too.

Into interstellar space?
posted by AElfwine Evenstar at 4:43 PM on October 27, 2011 [6 favorites]

But you are no star.
posted by Ayn Rand and God at 4:43 PM on October 27, 2011 [1 favorite]

Into interstellar space?

Put me up there.
posted by Brandon Blatcher at 4:44 PM on October 27, 2011 [3 favorites]

But seriously, the implications are just mind boggling. If stars are ejecting organic matter then all those planets we discovered just got a lot more interesting.

It also makes our solar system more interesting, especially Titan and Enceladus. There's so much we don't know about the our own planet and bodies and minds and environment, let along the universe, it's like there's a endless box of Christmas surprises hidden in a cosmic Christmas tree.
posted by Brandon Blatcher at 4:57 PM on October 27, 2011 [13 favorites]

I'm with you, Brandon Blatcher. It really makes the universe sound like a more lively place. Although the question still stands: Where is everybody?

Maybe there's plenty of life, just not much intelligent life that sends radio signals.
posted by mccarty.tim at 5:07 PM on October 27, 2011

Two words: genesis torpedo.

It's funny that the first instantaneous reaction to this post was a vision comprised of a cacophony of Dr. McCoy's various alarmist, knee-jerk, cantankerous, and sarcastic remarks. Only after a brief chuckle at that thought came the wonder of this intriguing and damn peculiar discovery.

But seriously, if all the stars since the beginning of the universe have slowly created all known matter, just after the big bang, and before stars formed, what is the stuff/particles/whatever that didn't aggregate and become stars?

I mean, as the early universe was expanding, one could assume there had to be leftover stuff that didn't become stars, as no system is 100% efficient. So if I understand this right, one could categorize everything into two types of matter in the universe: ones that come from stars, and stuff (using the term liberally, even if just charged particles without mass or whatever) that were direct leftovers from the big bang. Could 'original' particles be identified, or would it be safe to assume that all the leftovers are just be outside the light cone/particle horizon of the observable universe?
posted by chambers at 5:11 PM on October 27, 2011 [1 favorite]

IIRC, isn't all the mater from the big bang that hasn't been through a star mostly hydrogen and helium, as supernovas are needed to produce heavier elements?
posted by mccarty.tim at 5:15 PM on October 27, 2011 [2 favorites]

artw is correct: the existence of organic molecule synthesis in space has been known for some time now. Even simple amino acids such as glycine have been noted in space. Evidently, in some regions of space, the concentration of organic building blocks is just sufficient and for these molecules to form under ambient conditions. I was talking with an astronomer colleague of mine about this a few years ago and the implications are, indeed, staggering.
posted by darkstar at 5:24 PM on October 27, 2011

(Buh, that was inartfully said, but you get the idea.)
posted by darkstar at 5:37 PM on October 27, 2011

It's like the universe is alive. Amazing.
posted by saulgoodman at 5:39 PM on October 27, 2011 [6 favorites]

So if I understand this right, one could categorize everything into two types of matter in the universe: ones that come from stars, and stuff (using the term liberally, even if just charged particles without mass or whatever) that were direct leftovers from the big bang.

If you believe the standard cosmology, you can divide the mass in the universe into Baryonic matter (the "stuff" we know of, overwhelmingly in stars) and dark matter (the stuff that needs to be there for the universe to make sense, but which we can't see). There's something like 5 times more dark matter than baryonic matter.

Could 'original' particles be identified, or would it be safe to assume that all the leftovers are just be outside the light cone/particle horizon of the observable universe?

I think the closest thing to what you're looking for is the Cosmic Microwave Background. Photons that where created shortly after the big bang that we can still measure directly with telescopes. Whether other particles can be considered direct leftovers of the big bang depends on how you define "particle", "leftover" and "big bang" I think.
posted by auto-correct at 6:20 PM on October 27, 2011

Maybe there's plenty of life, just not much intelligent life that sends radio signals wants to talk to us.
posted by Chairboy at 6:26 PM on October 27, 2011 [1 favorite]

It's like the universe is spraying organic matter and screaming "Goddamn it, grow! I'm going to be hear a while and need some company."
posted by Brandon Blatcher at 6:27 PM on October 27, 2011 [1 favorite]

I can eject complex organic matter too.

Into interstellar space?

It's actually quite easy. I just go to my cd rack, get to the John Coltrane section...
posted by LionIndex at 6:46 PM on October 27, 2011 [1 favorite]

The lovely thing about chemistry is that if you put the right bits in the right energetic configuration, you get all sorts of fabulousness. It doesn't matter where you do it, so if you have a rich enough set of possible conditions, some of them will produce just the right fabulousness. Stars are enormous and complex and make the space around them enormously complex too. There will be something happening, for a very wide range of somethings.

Going back to the where is everyone question... I'm increasingly of the persuasion that looking for radio signals isn't going to be much cop. We've already been through peak radio - the days when you built a big-arsed transmitter just to get enough coverage to be useful to crude receivers have gone. Broadcast is moving very rapidly from megawatt transmitters spewing out in all directions to much lower power, more cleverly modulated systems. I listened to a radio programme coming home tonight which was sent to my phone from a set of transmitters that would be hard to pick up in the next borough, let alone the next star, but thirty years ago I'd have been relying on a huge-masted thunder god which would reach to Jupiter when the wind was in the right direction. They still exist, but they're getting turned off.

Same's true for radar, where doing more with less is a way of life.

We're moving - rapidly - to radio comms being a very wide band, low power, high entropy system that won't be that distinguishable from the noise floor, and we're only about a hundred years on from the first radio transmitters. That's a very, very narrow window of opportunity for anyone looking for us through strong, coherent, classic radio signals.

I think this boils down to a simple rule, which I shall call 'the five Es' because I can: effective entities evolve energy efficiency. Looking for wholesale waste - and spewing your wattage into space certainly counts - won't get very far.

It may be worth looking, just in case they want us to find them, and they may be looking for us and our tiny window of profligacy, but I'd put money on there being a much better way of beaconing 'here we are' to the universe. (My favourite mad interstellar comms idea involves modulating the emission spectra of your local star by poking it with lasers, but I'm not sure anyone's sorted out the practicalities yet.)
posted by Devonian at 7:02 PM on October 27, 2011 [7 favorites]

dark matter
I was hesitant to use this term, as I have heard of several challenges about the nature/existence of 'darl matter' as it is now known/projected to exist/unknown, and not having kept up on the latest theories and models. On one hand, it seems to make sense, and solves a lot of unknown variables, but I've always picked up an odd, something-off feel about it when I have read and hear scientists speak about it, simply because we're still in heavy theoretical territory as to the a more complete understanding of what it is and how all these multidimensional and string theory models develop and change. It's not as extreme as Lodge's Luminiferous aether as way to make the universe match the model, but I can't help thinking the initial idea of dark matter, which has been refined over time, had a whiff of Lodge's idea to it. At least with dark matter we can detect something, rather than just say it's undetectable like aether. I was a little kid when I learned of this strange stuff. Watching how the understanding of dark matter has been challenged, amended, and evolved over the course of my life fascinates me. I'm actually watching it happen in real time, not on some long timeline with abstract points in time in a textbook.

Cosmic Microwave Background
I meant to add that part to the end of my post, right before the light cone/particle horizon, but got clipped out. I guess the background is all that is left, I just wasn't sure if there was anything additional that had been theorized, or had it all been reduced to microwaves after almost 14 billion years.
posted by chambers at 7:04 PM on October 27, 2011 [1 favorite]

chambers, stars are actually only a small amount of the baryonic matter in the Universe. As auto-correct said, dark matter out-masses baryons by a factor of 5:1 (really, 5.86:1, give or take). But, let's concentrate on the baryons for the moment (protons and neutrons. Electrons are in the mix too, but they'll sort themselves out). First, the stuff that didn't collapse into stars isn't going to suddenly decide to move outside our visible Universe, its around, it's just hard to see. So what's the break-down?

History of the Universe time:

What happened is that the Universe started very smooth; if you looked around, you'd see everything looking pretty much identical: a hot mixture of elementary particles and photons. The perturbations that did were due to quantum fluctuations (basically, random noise in where particles were created after the Big Bang). As the Universe cooled, the first thing we really know is that the QCD phase transition occurred. QCD (quantum chromodynamics) is the strong nuclear force that binds quarks into nuclei and then (residually) nuclei into atoms. When the transition occurred, QCD got "strong" and the free quarks had to hurry to find themselves a nuclei to be in, quickly followed by the nuclei binding themselves together (free neutrons decay in 11 minutes, so every neutron either had to find protons to hang with in the first 11 minutes, or fall apart). This is Big Bang Nucleosynthesis (BBN); and it's where every primordial element comes from. The only things formed were isotopes of hydrogen, helium, and bit of a lithium, and unstable beryllium. I'll come back to these guys in a minute.

During this time, the photons are zipping around, completely dominating the Universe (more energy there than anywhere else, it's REALLY hot at this point). Nuclei "see" photons (they're charged), so they couldn't collapse into the tiny gravitational wells that the initial density fluctuations (remember those?) had created. If they tried to, they'd heat the photons a bit in that region, which would then push them back out. Dark matter though, doesn't interact with photons, so it started collapsing into those perturbations, beginning to build structure (this is how we know that dark matter is "cold" rather than "hot." Cold means it was non-relativistic at this point in the Universe, and the way that slow moving matter builds structure is different than the way that fast moving structure does).

At some point, the Universe got cold enough for the electrons to get bound into nuclei. Suddenly, the Universe went from a soup of charged particles to basically neutral. This meant that the photons stopped scattering as much, and rather than hitting a particle, being scattered, hitting another, etc, they just went sailing off in whatever direction they were pointed at this time (about 300,000 years after the Big Bang). These photons just continued forever, getting redshifted (stretched) as the Universe expands. We see them today as the Cosmic Microwave Background (CMB), at a temperature of 2.74 K. It's the tiny perturbations in the spectrum of the CMB that tells us about structure at the time that the photons decoupled, and cannot be explained in our understanding of cosmology if there wasn't something around before that could start building structure before the photons stopped being important.

OK, so now you have dark matter forming large structure (which is a beautiful process, see the movies here), and light elements that can finally follow gravity and free-fall into the dark matter halos that are forming. Now, finally, we can start building more interesting things. So most of the gas in the Universe, all those light elements, will fall into the halos. Some small fraction of it will end up dense enough to ignite the first round of star formation, and the remnants from that end up the 2nd generation of stars and so on. This is where everything heavier than lithium comes from, though the details of the process are a bit unclear (though it isn't my area of expertise).

However, the vast majority of gas doesn't end up in a star. If I remember right, about 90% of all baryons are not identified with stellar populations, it's just gas floating out there in space. Some of it is "backlit" by stars and other energy sources, and we can use these to figure out the primordial abundances by looking at absorption lines of spectra. We actually use this to calibrate our early Universe BBN models, since deuterium is destroyed in stars and not easily created, we look for deuterium (and lithium, if I remember right) and then can be pretty sure that a cloud with deuterium in it never went through a star. Without dark matter, incidentally, the deuterium abundances would be incorrect between theory and observation.

So there you have it: of the stuff you see in the sky, that's only 0.4% of the energy density of the Universe. 3.6% is stuff like us that never got processed through a star, and is just sitting out there, mostly in intergalactic space, but some in the galaxies as well. About 26% is stuff that clumps but doesn't participate in BBN or talk to photons (dark matter), and the rest is the totally insane stuff that pushes rather than pulls (dark energy). So yeah, we're even less important than we thought.

As for string theory, that has nothing to do necessarily with dark matter. It might be right, it might be wrong, it's likely right and not testable at the moment. My first post on metafilter is here, which might answer some questions that you're having here. It's absolutely untrue that dark matter is a kludge to fit one or two oddities in observation. Multiple lines of reasoning lead to remarkably similar conclusions, and I'm reasonable confident that we're getting close to nailing down what this stuff is experimentally. Regardless, for dark matter not to be the solution to these observations (large scale structure, BBN, rotation curves, energy budget of the Universe, etc), we'd have to be very wrong on many fronts. Which would be interesting in it's own way.
posted by physicsmatt at 7:27 PM on October 27, 2011 [19 favorites]

There's plenty of hydrogen and helium nuclei (and even a little lithium) that formed in the first few minutes after the Big Bang and are still around - stars work by fusing hydrogen etc. into heavier elements, but the Universe is still 90% hydrogen today. There are a few processes that could produce hydrogen from heavier elements, but they're rare -- most of that hydrogen is primordial. (I specified nuclei rather than atoms as most hydrogen was ionized early in the history of the universe, but much of it isn't today). Any proton is entirely identical to any other proton in the Universe, any helium 4 nucleus is identical to any other helium 4 nucleus, etc.; so it is completely impossible to pick out a particular atom as being primordial or not.

As was pointed out, any dark matter around likely formed within the first second after the Big Bang, and there's a lot more mass in that than hydrogen or helium or anything else.

Finally, there's a cosmic background of neutrinos (not just light) that formed in the first few seconds of the history of the Universe. There are about 100 background neutrinos per cubic centimeter. Thus, even if you ignore that our bodies are full of primordial hydrogen, there are plenty of relics of the Big Bang all around us today.
posted by janewman at 7:36 PM on October 27, 2011 [2 favorites]

"stars can create complex organic compounds apple pies on the very short timescale of weeks from scratch."

Sagan on apple pies
posted by Blasdelb at 7:38 PM on October 27, 2011 [1 favorite]

Maybe there's plenty of life, just not much intelligent life that sends radio signals wants to talk to us.

That reminds me of They're Made Out of Meat.
posted by Silly Ashles at 7:39 PM on October 27, 2011 [5 favorites]

Oh, and correction time: While I gave some very specific times there (11 minutes, 300K years), of course these processes are somewhat gradual. There's some "depth" to the surface of last scattering that makes up the CMB, for example, and the collapse of baryons into dark matter gravitational potential wells doesn't turn on in an instant. However, each of these processes has a characteristic time, and these numbers should give you a sense of scale. When you plot the history of the Universe, time scales are a crazy thing: BBN lasts a few tens of minutes, but the QCD phase transition occurs at 10^-6 seconds (also, there's a bit of a breather between the two times, which I neglected above. You have to wait for a minute or so for temperatures to drop down to a point where helium doesn't get torn apart by the photon bath). Most theories of dark matter have it forming well before a picosecond (if I'm converting from temperature to time correctly).

janewman, you know the galactic/stellar history way better than me, as my sudden handwaviness in the previous explanation shows. I get to the CMB and then go "meh, then stuff happened and the Galaxy formed, blah blah blah, history of the Earth."
posted by physicsmatt at 7:43 PM on October 27, 2011

physicsmatt, I think we balance out pretty well... I tend to handwave my way through nucleosynthesis instead.

I don't know of any studies looking at lithium in intergalactic gas - I think because the resulting absorption lines would be in the infrared, where the atmosphere is much brighter than the quasar you're trying to use as a backlight (even at night), making observations difficult. Studies of lithium abundances have instead used extremely metal-poor stars, and attempt to extrapolate to how much lithium you'd see as (say) the oxygen or iron abundance goes to zero. It's a difficult business.
posted by janewman at 7:58 PM on October 27, 2011

This whole thread has been worth it just to learn the phrase "photon bath."
posted by vibrotronica at 8:07 PM on October 27, 2011

Physicsmatt and janewman, I only regret that I have but one favorite to give for your answers. Over the years, I've been taught so many different models and theories over the years, from books and science programs both old and new about the earliest moments after the big bang, and each with their own set of ideas that are slightly different depending on when they were created, that when it comes to the most current models, I've get muddled about what the current state of affairs about all this really is right now. Your posts were refreshingly clear and straightforward, especially because of the fact that what you're describing are events that appear at the start to be the opposite of clear and straightforward. Thanks to you both for taking the time to address my curiosity.
posted by chambers at 9:48 PM on October 27, 2011

3.6% is stuff like us that never got processed through a star

Wait a second... are you saying we're *not* all made of star stuff? Now, confusion.
posted by amorphatist at 10:03 PM on October 27, 2011

Wait a second... are you saying we're *not* all made of star stuff? Now, confusion.

By 'stuff like us' physicsmatt meant ordinary matter - atoms, ions, molecules, etc. - as opposed to dark matter. I.e., the 'stuff' is made out of the same components we are, but that hasn't been incorporated into stars, cold interstellar gas clouds, or other directly visible forms. All told, the ordinary matter makes up 4% of the mass-energy density of the universe, and something like 90% of that is outside of galaxies. In physicsmatt's accounting, we are part of the 10% out of the 4% of the universe that is reprocessed galactic material, not the comparatively pristine intergalactic gas that makes up 3.6% (=90% of 4%) of the total.

In other words: we are the 0.4%.
posted by janewman at 11:45 PM on October 27, 2011 [4 favorites]

How does this stuff fit in with the Holographic principle where the 3 dimensional universe is actually just information on a 2d surface?
posted by delmoi at 11:52 PM on October 27, 2011

That's probably more of a physicsmatt question; but the holographic principle has to replicate the results of all the same calculations that underly what both he and I are saying (or else it's a bad model of physics and would be rejected). So in other words: even if the universe is really a projection from 2d to higher dimensions, it still has to be true that in 3d you would conclude there are atoms, molecules, stars, a Big Bang, etc. etc. It's actually pretty hard to come up with ways to test the holographic principle because of this (though there are people at Fermilab trying): if all of physics worked out exactly the same with the holographic principle as with conventional formulations, there would be no measurement you could make to tell which is right, and the situation is pretty close to that.
posted by janewman at 12:06 AM on October 28, 2011

In other words: we are the 0.4%

Ah. Confusion defused.
posted by amorphatist at 12:09 AM on October 28, 2011

I like my username even more after this discussion.
posted by dust of the stars at 4:50 AM on October 28, 2011

I have a strong hunch that, one day, today's "understanding" of the universe will be thought of as "quaint".

That day will only come if our interpretations stop getting in the way of our observations. We have a dangerous tendency to want Answers - which lead to dogma - which ... you know.

"Dark matter", "dark energy" are placeholders. Someone may find that by re-shuffling the pieces, the need for them disappears. If dogma keeps that someone from being heard, we're all losers. That's the lesson I take from Sagan's somewhat mumbled apology for how science treated Velikovsky, or from how Arp was tarred and feathered and run out of town on a rail. Beware orthodoxy.
posted by Twang at 6:37 AM on October 28, 2011

Maybe there's plenty of life, just not much intelligent life that sends radio signals.

I'm not sure about this, but I don't think we should start by defining intelligent life as that which sends radio signals. Unless we're talking about this guy? We make these kind of projections all the time, but mostly they just get in the way.
posted by sneebler at 7:02 AM on October 28, 2011

Twang: There are plenty of people looking for alternatives to dark matter and dark energy - in fact, coming up with tests of 'modified gravity' (i.e. alternatives to general relativity that could explain accelerated expansion) is an extremely fashionable subject in cosmology right now.

The problem is that dark matter and dark energy work much better as explanations of the Universe in matching the observations than anything else people have come up with. I recently went to a talk by Stacy McGaugh in which he was pushing MOND, a non-GR theory that was invented largely to remove the need for dark matter to explain the rotation speeds of galaxies. At this point, to reconcile it with the observations, he has to add dark matter to MOND (and make it a particular, fairly funny type) - largely defeating the point of the exercise. The basic problem is that it's very difficult to come up with a theory of gravity that simultaneously can explain the velocity of stars and gas in galaxies as well as of gas and galaxies within galaxy clusters; whereas dark matter does a stupendous job (as well as providing a beautiful match to CMB observations, predicting the same sort of cosmic web of galaxies we see, etc., etc.). We also have a lot of extremely sensitive tests of GR at this point that few other simple/elegant theories of gravity meet, giving us confidence that our understanding of gravity can't be completely wrong (at least at solar system scales and smaller).

As a result of this, plus the fact that there are way too many possibilities for dark matter coming from particle physics to list, extremely few cosmologists doubt the existence of dark matter (there are even a few possibilities that aren't just a new particle, like black holes that formed randomly during the Big Bang). The nature of dark energy is a much more open question, especially because you could get around it by modifying gravity only at the very largest scales where it is difficult to test. Cosmologists will pretty much all want to debate with you if you assert there's no dark matter - even the skeptics are now convinced by the overwhelming evidence. Any astrophysicist worth their salt will accept the possibility that dark matter might not be the right explanation for what we observe, but in that case it has to be something that has all the observable consequences of dark matter -- i.e., you have to get the same result from any calculation with the right model as you would in a dark matter model -- dark matter is at minimum an excellent 'effective theory' for calculating what's going on, even if it's not the right explanation in detail.

In contrast, astrophysicists would welcome with open arms new alternatives to dark energy that can explain the cosmic acceleration. We're still in the early days of figuring that out.
posted by janewman at 7:40 AM on October 28, 2011 [4 favorites]

delmoi (and getting back to chambers' string theory question), things like the holographic principle and string theory are theories about physics at a scale when gravity becomes important in quantum mechanics. In the early Universe, that scale occurs more or less when the energy density of the matter/photon/dark matter/etc soup is high enough that we'd naively think that everything would just collapse into a black hole. This occurred when the temperature of the soup was around the Planck Mass, which we derive from fundamental constants thusly:
m_PL = sqrt{\hbar c/G} = 1.22 10^19 GeV
(really, GeV/c^2, but I'm working in natural units where c = 1).
G is the gravitation constant, so how strong gravity is, and \hbar is the Planck constant, which tells you the scale at which quantum effects are important.

So, to see stringy effects, you'd need to worry about the Universe when the temperature was 10^19 GeV (see, everything has units of energy!). The first time we really know anything about the Universe (as in, directly measured, rather than extrapolated) is BBN, which occurs when the temperature is around 1 GeV to 1 MeV, so 19-22 orders of magnitude lower energy. Now, you can certainly imagine that futzing around with the state of the Universe at higher temperatures would give you observable quantities today, but most theories turn out not to give you too much to work with on that score (though there are things we are trying to measure that would give us some hints). In fact, all the theories we spend time on don't give us giant deviations from "vanilla" predictions - sort of tautologically, since if they did we wouldn't spend time on them, they'd be clearly wrong. This is as janenewman alluded to, every theory has to explain the data, and in this case the data is so far removed from many of the ideas about string theory that experiment doesn't directly speak to the theory. Which is a real problem.

Which isn't to say holography isn't a fascinating topic. If it comes up in a FPP sometime, I'll be happy to delve into more detail (though I'm certainly no expert), but I think I'm committing enough of a derail as it is. Just that, for the cosmology that we're talking about here, it doesn't have observable effects. Of course, we'd like to know what was going on at higher temperatures, and then these theories will matter. The problem is we just can't measure very much that will directly tell us what really happened.
posted by physicsmatt at 8:29 AM on October 28, 2011

And continuing with my agreement with janenewman, of course dark matter and dark energy are placeholders. Newtonian gravity is also a placeholder, but I can still get a rocket to Mars using it. Certainly our understanding is at an early stage, but as I've explained in the linked thread, dark matter is an incredibly successful placeholder, and seems pretty likely to me to be a good descriptor of the ultimate "full theory," whatever that turns out to be. That is, when we find the missing mass in the Universe, it will very likely be particulate, formed in the early Universe when it was non-relativistic, and does not carry strong nuclear or electric charge. Now, in the end the theory could be different enough that we'll give it a new name, but I think it will be recognizably "dark matter"ish.

Dark energy is a different story, again as janenewman says. There are so many things we don't know about it that the end result could conceivably be very different from our current understanding. However, what is clear is that the Universe appears to be expanding faster than it used to be, and that is best fit by a component of energy that has an equation of state of w = -1 +/- 0.1 (what this means is that it is very close to a cosmological constant, which has the same energy density regardless of whether you expanded the volume or not, which means w = -1 exactly). I have no idea why this is so, and no one else does either, but we're working on it. When we find it, we might call the causative agent "dark energy," or we might not (I'd guess we will, because that name is awesome). What is extremely unlikely to be true is that we'll discover the Universe isn't accelerating.

Basically, science involves a game of figuring out what you really know and what you're guessing at. It's important to realize that today we in fact know an awful lot about the Universe. Sometimes we screw up and over-reach our experimental knowledge, but right now I think we're doing pretty well, and I've explained why previously. Another problem is that we sometimes confuse the public with what we know experimentally and what we're guessing at, which is a communication problem that we should of course work on.
posted by physicsmatt at 9:06 AM on October 28, 2011

as supernovas are needed to produce heavier elements?

Ordinary stars can generate everything up to nickel. Supernovae are necessary for elements beyond that. Among the post-nickel elements required for human life are zinc, selenium, molybdenum, and iodine. So: lots of starstuff, and a little bit of supernova-stuff.
posted by DevilsAdvocate at 11:19 AM on October 28, 2011 [1 favorite]

Newtonian gravity is also a placeholder
Very true - we see no gravitons or waves - but GR tells us that the source of S-T curvature is the matter we know and love... Earth, Sun, Moon. Not spooky action. Not yet another invisible agent for which we have no/little observational evidence, no particles, no waves. Observation is supposed to be the horse that pulls the cart. Else much time can be lost. The map is not the territory.

but I can still get a rocket to Mars using it. The utility of a model is very nice, but I'd rather avoid inferring correctness from utility. Ptolemaic epicycles also had their utility.
posted by Twang at 2:58 PM on October 28, 2011

(Not to take anything away from Sagan, but, strictly speaking, the idea that "We are made of star-stuff" was first said by astronomer Harlow Shapley back in the 1920s; and Sagan is just riffing on Shapley's idea.)
posted by AsYouKnow Bob at 7:14 PM on October 28, 2011 [1 favorite]

Twang, dark matter doesn't fit the definition of an epicycle because, while the idea was proposed to fit a single unusual observation (the mass required to bind the Coma cluster), it also solves several other observations that it was not designed to: galaxy rotation curves, the location of the gas versus total mass in the Bullet cluster as measured by gravitational lensing, the mismatch between the required baryonic matter density versus the required total matter density in BBN, and the growth of structure before matter-radiation decoupling as evidenced in the CMB. No other theory successfully fits all these observations (modified gravity, for example, fits only the galaxy rotation curves without many epicyclical additions - including one that's basically just dark matter), and again, it's important to remember that dark matter was not designed to fix all these problems, the fact that it does so well is the reason that we like it.

So while the general public seems really wedded to the idea that the solution to the missing mass problem should lie with modifying gravity versus a new particle, there are solid reasons to believe that the dark matter paradigm will turn out to be true (I am always open to being wrong on this, but right now, this is the best game in town). Calling them an epicycle on the theory of GR is a misunderstanding of the state of the experimental evidence.
posted by physicsmatt at 3:39 PM on October 30, 2011 [2 favorites]

Hmm. This is interesting; just about the closest thing to what I was ineptly trying to describe - Pristine Big Bang gas found
posted by chambers at 7:38 AM on November 11, 2011

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