What Happens To All the Universe's Hydrogen?

StartsWithABang (3485481) writes "Just a second after the Big Bang, the Universe was a hot bath of radiation, with a small fraction of protons and neutrons in about equal numbers left over. By time it was four minutes old, it was 92% hydrogen (by number of atoms) and 8% helium. Yet the Universe has aged nearly 14 billion years since then, and have formed many generations of stars, all of which burn hydrogen into heavier elements. So how much hydrogen is left, and how much will be left far into the future? A lot more than you might think."

Comments

Re:So, um, only protons and neutrons?

[rossdee]

So the universe was positively charged? I think theres a mistake somewhere.

Survivalist

[theshowmecanuck]

I'm keeping a two year supply in my basement.

Re:Survivalist

[Tablizer]

I'm keeping a two year supply in my basement.

Right next to your two-year supply of matches and lighters.

Re:Survivalist

[Thanshin]

Well yeah. You know, in case he needs water, RIGHT NOW.

Re:Survivalist

[fermion]

Just accept out fate. Eventually everything will be lead.

Re:Survivalist

[Hillgiant]

What is your basement made of? H2 will diffuse through solid metal. This fact (among others) is what keeps fuel cell vehicles in the realm of science fiction (or very expensive demonstrations anyway).

Re:Survivalist

[theshowmecanuck]

Solider metal.

Re:Survivalist

[Rob Riggs]

Just accept out fate. Eventually everything will be lead.

Red dwarf stars cannot synthesize anything beyond He. They will never create Pb.

Re:Survivalist

[ImprovOmega]

Not lead, iron, actually. It's the element with the maximum nuclear binding energy. Below that you perform fusion for a net gain, and above that fission produces a gain. Iron is kind of the "ground state" from a nuclear perspective.

Thought experiment

[Ukab the Great]

Given an infinite number of chemistry classes with an infinite number of science teachers holding an infinite number of matches to an infinite number of balloons filled with the universe's finite supply of hydrogen, I'd say we'd have 10 years left before the stuff's all gone and the universe is a giant swimming pool

Re:Thought experiment

[flyingfsck]

Bugger all is gonna happen to your infinite number of balloons, unless you have an infinite amount of oxygen too.

Re:Thought experiment

[MouseTheLuckyDog]

The hydrogen is still there, it's just coupled to oxygen. You can use electrolysis to extract the hydrogen.

Re:Thought experiment

[K. S. Kyosuke]

I think all those chemistry classes would probably collapse under their combined weight.

Re:Ahhhhhh

[Tablizer]

No, that's methane. Wrong gas.

Re:Ahhhhhh

[Cryacin]

Well, at least we know that a significant amount of CO2 gas has been successfully sequestered in that article.

And what about dark matter?

[1 a bee]

I'm a bit skeptical of such cosmological estimates. If there is more dark matter in the universe than ordinary matter (by a factor of 4:1 they say), wouldn't you expect it to somehow figure in the "calculations" going back to the big bang? I saw no mention of it in the article. In fact, come to think of it, you seldom hear much about that big elephant dark matter in the room in the first minutes after the bing bag.

Love reading about cosmology, but I think readers should be warned this is a very speculative field of study. Ideas and models in vogue today will likely not be in a few decades. I'm reminded of my physics professor of many years ago who claimed "Cosmology is as mature as botany was before Darwin."

Re:And what about dark matter?

[Anonymous Coward]

I stopped watching the new cosmos after they stated the moon collision theory as if it was fact. They don't understand the ramifications of misleading people like that.

Re:And what about dark matter?

[blue trane]

Doesn't physics have to come to terms with big issues like time and the fact that the laws of thermodynamics are statistical and show violations (fluctuation theorem, conservation of energy violated by dark energy and photons losing energy as they redshift)?

Re:And what about dark matter?

[boristhespider]

Eh?

"If there is more dark matter in the universe than ordinary matter (by a factor of 4:1 they say), wouldn't you expect it to somehow figure in the "calculations" going back to the big bang?"

Yes. And yes, it does, it "figures" right from the start.

"I saw no mention of it in the article."

Who died and made this article God?

"In fact, come to think of it, you seldom hear much about that big elephant dark matter in the room in the first minutes after the bing bag."

That's chiefly becase in the first few minutes after the big bang the universe was radiation dominated, meaning that the density of photons (and neutrinos) was vastly greater than that of dark and normal matter. The transition between radiation and matter domination is governed by the density of dark matter just as much as baryons. Where on Earth are you getting this idea that dark matter is an "elephant in the room"? Here's an interesting fact for you - you know there are waves imprinted both on the CMB and on the large-scale structure of galaxies, right? If you "love reading about cosmology" you must, right? Those waves are the result of oscillations while the universe was radiation-dominated, caused by baryons tending to cluster together under gravity, and a restoring force introduced by radiation pressure, which set up ringing oscillations across the universe. Without dark matter to provide extra clustering under gravity those waves are at totally the wrong wavelength. From the CMB *alone* you can find how much dark matter there has to be relative to normal matter. How's that for an "elephant in the room"?

"I think readers should be warned this is a very speculative field of study."

As is all theory. However, I think readers should be warned that the fundamentals of cosmology are very far from speculative - even if the results might in principle be phenomenological, they will not change. Cosmology, particularly in the early universe but after the first microsecond, say, is based on well-understood science and is anything *but* speculative, and questions about whether dark matter or dark energy are physical quantities or are emergent in one way or another are not unique to cosmology but also arise on astrophysical scales. (And in some ways are irrelevant, since whatever dark matter and dark energy actually are, they have to work as cosmology describes them anyway. Small changes to the Lambda CDM model cause large disagreements with the data.)

"I'm reminded of my physics professor of many years ago who claimed "Cosmology is as mature as botany was before Darwin." "

Err, yeah. How many years ago? If he held the same opinion now I'd be surprised. If he held that opinion after the late 90s then he was ignorant of the field. That's OK, my Masters supervisor, in the early 2000s, is a brilliant physicist and held a similar opinion (although not stated quite so... badly, with a lousy analogy that could never work), and he was wrong too, increasingly so as the datasets grow ever huger and the tools with which to analyse them evermore sophisticated. This kind of view is untenable, and I say that as a man who has gone on record repeatedly with statements such as "cosmology is wrong. It is demonstrably wrong, it is wrong in its fundamentals and it is wrong in its principles" - because that's a statement I also surround with caveats. Cosmology is "wrong" in the same way that thermodynamics is "wrong", or that much of chemistry is "wrong", or much of biology is "wrong", in that it's at heart a descriptive, phenomenological theory. (Before chemists or biologists come to me to scream, those fields are typically phenomenological, although both contain subfields that are avowedly not so; but ultimately if you're not mapping up from the behaviour of the individual atoms you're dealing with phenomenology, and I'm well aware of how brutally difficult it is to do chemistry directly from the Schroedinger equation, which is what that implies. 'Phenomenology' is not a criticism, unless it's taken as so by people who mistakenly think they're dealing with the underlying science directly.)

Re:And what about dark matter?

[boristhespider]

Time, yes. Not sure what you're referring to with thermodynamics - it's just a statistical theory that emerges when you deal with vast numbers of particles. (And if I did want to treat thermodynamics as inviolate, which it basically is for large enough systems of particles, there is no issue with conservation of energy with the loss of energy due to cosmological expansion. I'm not totally sure why you'd think there is: energy conservation is inherent in the system. There's nothing controversial about the idea that if you work in an expanding spacetime then photons that are not being pumped by an external source of energy will be stretched. Similarly if you work in a collapsing spacetime then photons not being drained with be blue-shifted. The Friedmann equation can ultimately be interpreted as an energy conservation equation if one is so minded, it just comes from the Hamiltonian constraint.)

Re:And what about dark matter?

[1 a bee]

Who died and made this article God?

Nobody. We're discussing the article here.

As for the relatively recent evidence of dark matter showing its imprint in the CMB, well, again, doesn't this support my thesis that this is a rapidly evolving field? Cosmology textbooks have a short shelf life. Thirty years ago, for example, one of the big questions was whether the universe was open or closed. Now that we know it's open, and in fact expanding at an accelerating rate, we find that wasn't quite the right question. My physics textbooks, by contrast, are still readable. If a science gets dated quickly, then isn't that reason to think it's speculative?

Re:And what about dark matter?

[Anonymous Coward]

There is no dark side of matter really. As a matter of fact it's all dark.

Re:And what about dark matter?

[mythosaz]

I'm pretty sure all sorts of people are self-selecting to not watch Cosmos because it goes counter to their personal sacred cows.

Re:And what about dark matter?

[bberens]

The beauty of science is that any of the "facts" we know today could be proven completely wrong tomorrow. I don't think there's anything special about the moon collision theory that should require extra qualifiers compared to anything else in that show as it's generally considered the prevailing theory of moon formation.

Re:And what about dark matter?

[meta-monkey]

The problem with the new Cosmos is not all the "facts" they present are scientific. They also deal with history, and some of their "facts" are misleading or downright wrong, and we don't apply the scientific method to history.

I get that Seth MacFarlane is an atheist and wants to push his creed (or lack thereof) on people. But in the first episode of Cosmos, the whole story about Bruno and his persecution was just wrong. Yes, Bruno did have an idea that the universe was infinite and that the sun was just another star. But he was not a scientist, did not apply the scientific method and did not back up his ideas with experiment or observation. He was "right" in the same way a broken clock is right twice a day. He was a mystic who wrote books about magic and thought the stars and planets had souls. While no one should be burned at the stake for any reason, he was not killed because of his scientific views, he was burned because of his religious heresies like denying the divinity of Christ. The bit went on for about 8 minutes of airtime, in a 40 minute show. They spent 20% of a science show talking about the persecution of a religious man for his religious views but making it out as if he were persecuted for his scientific practice, when he wasn't. It was purely a shot at religion in general and the Catholic Church in particular in order to push MacFarlane's world view. I thought they sacrificed their credibility by intentionally misleading people about historical facts.

When my kid is old enough to understand Cosmos, I'll be showing him Sagan's version. Little has changed with regards to the history of science since the original Cosmos and now, and Carl wasn't pushing an agenda. He was just giving you facts. Also, CGI not withstanding, I thought the production values of the original were better. I like the way they hired actors to portray famous moments in science rather than Neil's version with cartoons to depict past events.

Re:And what about dark matter?

[Will.Woodhull]

Doesn't physics have to come to terms with big issues like time and the fact that the laws of thermodynamics are statistical and show violations (fluctuation theorem, conservation of energy violated by dark energy and photons losing energy as they redshift)?

I don't see why. Sure, any theory of everything would have to account for that, and also answer the question of whether sacred cows fart in a sacred manner.

But we can do perfectly fine with multiple branches of physics that stay away from that problem, where each branch deals with only some aspects of reality. So long as we are mindful of the limitations of each mindset, and respect the ambiguous nature of the borders where one kind of physics butts up against some other kind, we have more than enough to play with to satisfy any theoretician. Within one problem space, we've got Newtonian physics which works peachy-keen. In another problem space we've got quantum mechanics. For the most part we only have to switch between one and the other without having to try to fit them together.

That sometimes means having to learn to dance really fast between different realities when trying to work close to that ambiguous border between two different physics. But with some training, the human mind is capable of some really fast footwork. For the most part, we can razzle-dazzle the problems well enough for the engineers to work with the results, being as how engineers go about doing their thing in relatively crude ways. ("At this scale, Pi is approximately 3", "Whether the glass is half full or half empty is beside the point: what is important is that the glass is twice as big as it needs to be.") And it is the engineering that we live with. That is what flushes the toilets and puts things in orbit. So long as the branches of physics we play with in our minds support the engineers who make modern life liveable, it is all good.

Re:And what about dark matter?

[countach]

"Cosmology, particularly in the early universe but after the first microsecond, say, is based on well-understood science and is anything *but* speculative"

Come now. Applying what might be regarded as well understood math and physics to the first seconds of the universe isn't entirely speculative, it certainly requires some speculation to assume that this is what happened. Nobody knows for sure what conditions existed at that time.

Re:And what about dark matter?

[rgbatduke]

Well said, sir. Repeatedly, even. Although (as a physicist also) I do have to say that DM/DE are a) one of several possible explanations or models that we have -- so far -- and while it has emerged as one of the most consistent that doesn't make it either unique or right. We may not have even hypothesized the right model yet (given the indirect nature of the data, that would hardly even be surprising, if true). b) One of the problems with having a huge amount of mass-energy out there, effectively decoupled to electromagnetic forces, in addition to making said mass-energy literally invisible is that one can imagine entire "universes" of field theories underneath the very loose constraint of the observational data. Does DM couple to e.g. the nuclear force? Are the quanta of DM stable? Is DM not really "dark", but merely very, very weakly interacting, e.g. massive neutrinos? IIRC it is possible to explain the cosmological data by giving three flavors of neutrinos a mass-energy order of an eV. And then we have to ask -- what if there are more than three flavors, and DM is a "leftover" neutrino from a super-heavy lepton that hasn't existed since the big bang so that the neutrinos have nowhere to go? DE is even more difficult to cope with -- are we talking about the massless quantum of a fifth force altogether, or is it somehow tied to the four fields we already know about?

Given that we have yet to fully reconcile gravitation and relativity in a consistent quantum theory and that we lack a TOE (meaning there is still room enough to drive -- err, "elephants" through the gaps:-) we are, as you say, working with descriptive phenomenology -- classical theories of gravitation, or relativistic theories of curved spacetime, quantum models of nuclear (strong and weak) and electromagnetic interactions that works (so far) pretty well in specific contexts. But we don't even know if DM interacts strongly enough with sufficiently dense "known" matter -- matter e.g. in the heart of suns -- to be able to slow down in transit and accumulate. We don't know if DM remains stable and decoupled at energy densities like those accessible inside the cores of stars, or for that matter inside e.g. neutron stars. We don't know if DM interacts with other DM to be able to provide the "friction" needed to cause gravitational collapse of DM. All we know is that when we examine galaxies, the profile of orbital velocities observed is consistent with their being more matter in the galaxy than we can see, distributed in a very unusual way.

Personally, I think it is all very interesting (although definitely not my field), but don't take any of the many assertions about DM or DE too seriously yet. Both are the ultimate "invisible fairy theory" -- literally invisible -- where the fairy is known only indirectly by means of the "the fairy must have done it" argument. This is right up there at the edge of religious thinking, because as long as the fairies remain invisible, it remains almost impossible to falsify any assertion about what the fairies do or do not cause in the observational data. I'd mumble about Ptolomeic epicycles vs gravitation, or the many gods of the many gaps over human history, but in the end, until somebody puts salt on the tail of a darkon or manages to build a TOE that includes DM/DE consistently, explains all observations, and has a prayer of being verified/falsified by more than crude phenomenological agreement it is all in the same category as supersymmetry, string theory, etc -- pretty stories, but which one (if any) of the myriad of possible models within the general approach is true?

rgb

Re:And what about dark matter?

[Anonymous Coward]

It is a "rapidly" evolving field, although maybe not as fast as you suggest. The idea that the universe is dark matter dominated was around in the 80s due to galaxy formation modelling, and the observation of the CMB in the early 90s confirmed that, narrowing down the proportions. Within a couple years dark energy was thrown into the mix, although not really contradicting the previous measurements that dark matter dominated normal matter, and for about 15-20 years now it has been shrinking error bars instead of changes.

Any field can be due for a sudden upset. A colleague of mine was told in grad school not to study optics, because it was done and the decades old books haven't changed, then the laser and nonlinear optics popped up.

Re:And what about dark matter?

[Mr. Slippery]

but ultimately if you're not mapping up from the behaviour of the individual atoms you're dealing with phenomenology...'Phenomenology' is not a criticism, unless it's taken as so by people who mistakenly think they're dealing with the underlying science directly.)

Working with the theoretical (i.e., mental) constructs we call "particles" and "atoms" is no less and no more "phenomenology" than is any other branch of science. Our observations about electrons and atoms are phenomena, not noumena.

Re:And what about dark matter?

[VortexCortex]

The bit went on for about 8 minutes of airtime, in a 40 minute show. They spent 20% of a science show talking about the persecution of a religious man for his religious views but making it out as if he were persecuted for his scientific practice, when he wasn't. It was purely a shot at religion in general and the Catholic Church in particular in order to push MacFarlane's world view. I thought they sacrificed their credibility by intentionally misleading people about historical facts.

Well, they did say that Bruno's guess was a guess. The whole point of that segment was that religion was so opposed to views that challenged their world views. Whether his hypothesis or guess was that the sun was just another star, or that the "prophets" were just ordinary people (not divine), or that the Earth is older than 6000 years, really doesn't fucking matter. The issue is they burnt a guy at the stake for challenging their beliefs.

Apparently, they should have devoted more than 8 minutes because you still managed to miss the point.

Re:And what about dark matter?

[Anonymous Coward]

energy conservation is inherent in the system.

Come and see the conservation inherent in the system! Help! Help! I'm being conserved!

Re:And what about dark matter?

[Bengie]

we don't apply the scientific method to history

Politicians apply scientific theory to history all the time, that's why it's so repeatable.

Re:And what about dark matter?

[meta-monkey]

Why didn't they say that, then? They could have said "The Church was intolerant of dissenting views, and Bruno was burned at the stake because he challenged the Church's belief that Christ was the son of God." But they didn't. They presented that he was persecuted for stating that the universe was infinite and the sun was just another star. But the truth is, he wasn't. Nobody gave a crap about his views on astronomy.

So why lie? That's the problem. They straight-up lied about about the persecution of Bruno.

Re:And what about dark matter?

[boristhespider]

I absolutely agree with your first paragraph. (Actually with pretty much your entire post.)

For the record, my feeling on dark energy is that it's a mirage caused by analysing recent (highly inhomogeneous) cosmology through a model that at its base assumes homogeneity and isotropy, which a hunch would suggest is liable to cause odd effects, and which closer study through inhomogeneous models imply that at the least the effects of dark energy can be generated in pure dust (ie baryon + CDM) universes. My own research focusses on another, related issue -- cosmology is a theory built on averages, but that average *is never defined anywhere*. An average over a tensor field is ill-defined, and any average that we've been able to write that more or less makes sense relies on a globally-hyperbolic spacetime, meaning no geodesic crossings. Alas, the universe is full of gravitational lenses which are nothing but massive regions where null geodesics cross, so we have an inbuilt issue with the idea of mapping up from small-scale (well, galaxy scale) objects to an entire cosmology -- it's currently quite impossible.

Dark matter is a slightly different topic. You can argue that the effects of dark matter might also arise from averaging effects (ie constructing a model which is after all nothing more than a homogeneous and isotropic solution fitted to the inhomogeneous reality), and some have attempted to do so, with a bit more success than with dark energy. (Practically every attempt to find a dark component from averaging has found dust, except the most refined and plausible which have found curvature.) I suspect that's a part. You can also argue that GR simply does not operate on such large scales, and that even GR should be modified on large scales before we apply an average, and I suspect that's a part, too. Then we have particles that can act as a dark matter -- neutrinos are massive, and as you point out definitely contribute, but they certainly can't be the whole answer because they imply a washed-out structure because they're relativistic for too much of the universe's evolution, meaning that they tend to propagate out of gravity wells rather than falling into them. There are other, speculative, particles that could contribute; if SUSY has any basis in fact (and I hope not but even now it may still do) then there's a lightest supersymmetric particle, which would be stable and massive and act as a dark matter. We *also* have that gravity may not be described by GR, and may not map up to cosmological scales with a simple average, but also that since it's geometric, attempting to describe smaller scales on which evidence much of the basis for dark matter rests is a bit suspect: we have to check what the dynamics of stars are in the geometry produced by a galaxy. That's basically impossible (and is linked to the averaging issue, since we'd be wanting a mean-field, along with the backreaction of the star itself on the mean-field) but it's also got to be done before we believe particle physicists when they blithely declare that they've found "the" dark matter.

My suspicion is that dark energy doesn't exist and is a mirage, while dark matter is a combination of all the above: modifications to GR, effects of averaging GR, the related effects of stellar motion in realistic geometries, massive neutrinos, perhaps even sterile neutrinos, some currently unknown particle or particles that arise in high energy particle physics... and given the number of parameters that are introduced from all of that, also probably impossible to constrain. Hey ho.

Re:And what about dark matter?

[boristhespider]

Sure but you know what I'm meaning. In physics we have a very distinct hierarchy of descriptions. At the base are the "fundamental" theories, which are assumed to hold for point particles and fundamental forces (ie forces that don't reduce to different ways of viewing another force). These are the likes of the electroweak theory, the strong theory, and any random speculation about quantum gravity that you choose to believe (or not - I don't believe any of the theories of quantum gravity at the minute, though the approaches of loop quantum gravity, dynamical triangulations, or non-commutative geometries are to my mind a lot more promising than the approach of superstring theories; less ambitious and following more closely the ethos that lead to QED in the first place). Above that is the emergent theory of quantum mechanics, which in principle should arise out of QED but which in practice is a staggeringly successful and ultimately phenomenological theory. The two are related, however, and both involve similar quantisations of classical concepts - a Lagrangian density in the case of the "fundamental" theories which are therefore quantum field theories describing the fundamental forces; and a Hamiltonian or Hamiltonian density in the case of quantum mechanics which is therefore a direct quantum theory of particles.

Then above that, quite a long way, sit the likes of thermodynamics and fluid mechanics. Thermodynamics arises by describing a system of interacting particles -- atoms, molecules, what have you -- through a Hamiltonian and then applying a statistical average of this. What emerges is a simple description of the behaviour of vast numbers of particles which is coincidentally the phenomenological theory developed in the 19th century, except that entropy is now a determined quantity rather than defined only to within an additive constant. Fluid mechanics can be recovered by setting up a Boltzmann equation, which is itself a statistical quantity, and then integrating out the lower moments, which become density, momentum, momentum flux etc. Similarly chemistry in principle can be recovered by modelling atoms with Schroedinger equations, and that's certainly done but it's computationally expensive.

Then above *that* (which holds on our scales) lies cosmology. Cosmology is the extrapolation to gigaparsec scales, of all things, of a force known to operate on scales between a millimetre and, with mounting inaccuracy in the measurements, solar system scales. It seems likely to hold on at least parsec scales but the extrapolation to kiloparsec scales is questionable, and the application in galaxies is actually ill-defined (meaning that it is impossible with current knowledge to calculate the mean-field of a galaxy due to the numerous gravitational lenses a galaxy is filled with, and the fact that such lenses break any spatial average we've currently been able to define in metric-based theories; we're also still working on straight statistical averages for gravitating systems). The application up to first mega- and then gigaparsec scales is subject to similar caveats.

So yes, in principle I totally agree wtih you that ultimately all numerical science is phenomenology, but the way the word is typically used in physics is slightly different -- a phenomenology is a theory that is not assumed to be related in any direct way to the theories that are assumed to hold on laboratory or, particularly, atomic scales and below.

Re:And what about dark matter?

[boristhespider]

Well, we can have a very good bash at it by taking the science we have at the minute, extrapolating back, noting every place where the story seems to get shaky and the edge cases that can arise, and see when things die. Surprisingly, the story of the last five billion years is a hell of a lot shakier than the story from, say, the fifth second up to the ten billionth year. Very early cosmology, yes, I totally agree -- it's speculation, and in particular (the slight overreaction to the BICEP2 results aside) I don't think anyone actually working on inflationary theories would pretend that they are dealing with anything that isn't, strictly speaking, phenomenology. I think most theorists believe something that *behaved* like inflation had to occur, and I would agree with that, but I don't think anyone has made any particularly strong claims for any particular inflationary theory, since they're all by their nature nothing but speculation about how higher-energy theories might act viewed with our current techniques.

But by the time of big bang nucleosynthesis in the first seconds to the first minutes, the science is really well understood -- we have direct evidence from accelerators for how matter behaves at such energy scales, and the very fact that the predictions of the theory based on this match so closely to observation at every point up to (and even beyond) the ten billionth year of the galaxy can give us a hell of a lot of faith that the fundamental picture is (at least phenomenologically) correct. I say this as someone who has chopped away at cosmology's fundamentals for over a decade -- the broad idea of inflation is probably accurate; something that closely resembles a universe composed of "baryonic" (ie normal) matter (about 5% of critical density), cold dark matter (about 25% critical density), photons, and three species of slightly massive neutrinos, *had* to hold between the first few seconds and roughly around the 10th or 12th billionth year, at which point that model breaks down unless one additionally adds in something that looks like a cosmological constant or a dark energy. Whether the physical identifications are actually precise or not is a totally different question -- and they're not, with dark energy on particularly shaky grounds but "dark matter" certainly hiding a world of complication beneath its single boring equation (w = 0) -- but the actual model is far too successful to simply be ignored. And I wouldn't consider using a different model for the period from just before BBN up until around a redshift of, say, 2 or 3, because there would be little to be acheived. Precisely how I generate the different components of course is model dependent, but it will look and act a lot like Lambda CDM.

For lower redshifts, meh, many bets are still off.

Re:And what about dark matter?

[rgbatduke]

Yeah, yeah. What you said. If DM/DE is an elephant in the room, it's an elephant that we know only in the sense of the blind men trying to describe the elephant by feel -- one says it is long and pliable, like a snake, another says that it is flat and massive, like a house, a third says that it is floppy and flat, like a large tree-leaf. We cannot yet see the whole elephant, and part of what we CAN see may turn out to be only the shadow of the elephant cast on the walls of Plato's Cave in some projection, nothing like the actual multidimensional elephant. Our knowledge of physics (so far) helps define a few of the projective dimensions or the parts of the elephant we can feel out, but it, too, is incomplete, being part of an even bigger elephant known in various projections by the blind...

rgb

Re:And what about dark matter?

[boristhespider]

That's like a description of high energy physics in general, and it's a very good one for M theory, particularly with the elephant's shadow given the AdS/CFT duality....

Re:And what about dark matter?

[blue trane]

Where is the energy removed to?

In the edx Greatest Unsolved Mysteries of the Universe MOOC, a student asked a question:

First:At the 2nd lesson you said that the energy of photons and particles, at the young universe, is the same (equipartition) and higher of the today energy. But the first law of thermodynamic says that the energy is constant in a closed system. We have any violation of the law?

To which Professor Paul Francis replied:

First question - it turns out that energy is not necessarily conserved in General Relativity on very large scales. So it is possible that the energy just goes away! Some people believe that there is a sort of potential energy built into space-time, and so as space expands, this potential energy increases, compensating for the loss of energy of the photons etc. They sometimes go on to say that this (negative) potential energy is exactly equal and opposite to the energy of everything in the universe, so the whole universe has a net energy of zero (and is hence the ultimate free lunch).

Re:And what about dark matter?

[blue trane]

What happens when you get macroscopic objects displaying quantum effects, as in the experiments of Andrew Cleland and Aaron O'Connell?

Or Yves Couder et al., who reproduce the two-slit experiment on a macroscopic scale - but it seems to require an ether if that's what's happening on the quantum level, which goes against physics dogma?

Re:And what about dark matter?

[blue trane]

What's expanding the space, though? Where is that energy coming from?

Re:And what about dark matter?

[Will.Woodhull]

You handle these by stating the blatantly obvious, that these phenomena are currently outside the realms physics works with, and then you move on.

Hell, physics cannot even handle ancient problems that are cracks in the bedrock of all western science. What is the reason that Pi is irrational (and don't just site one of the many different definitions of Pi as the reason: that is simply crippling your critical thinking ability with a blind belief in one or another tautology).

We live in a universe that we not only do not understand, but which we are innately incapable of ever completely understanding. So sayeth the Copenhagen convention on which much of modern physics is constructed: the best we can do is make simplified models and play with them. So get over it, and praise the engineers for being too concrete in their modes of thinking to be deterred by these impossibilities. For without the ability to occasionally say "in this situation, 3 is a good enough approximation of Pi", nothing would ever get built.

Re:And what about dark matter?

[blue trane]

So, the physics prof who said cosmology was like biology before Darwin (in the post I was originally responding to in this thread), was just projecting?

Re:And what about dark matter?

[blue trane]

It's converted into potential energy, which then becomes kinetic energy again as it falls. But when is the potential energy lost from photons stretching as they travel long distances through space converted back into kinetic energy? Is there any evidence for that, as there is for a ball thrown up, then stopping, then coming back down?

Re:And what about dark matter?

[Neil Boekend]

That's just because $deity wants it to be so.

But seriously, we don't know. To give it a name we call the force "dark energy" but it isn't clear what does it. Just that it happens (with reasonable certainty).
Maybe future research will indicate the research that proved the universe was expanding was just a statistical fluke. Maybe we will find some force hidden in the equations that drives it. Maybe we'll never find out.
Stay tuned to know more!

Re:And what about dark matter?

[Will.Woodhull]

the physics prof who said cosmology was like biology before Darwin (in the post I was originally responding to in this thread), was just projecting?

The original quote:

"Cosmology is as mature as botany was before Darwin."

I have no idea what was meant by that. My suspicion is that the professor provided enough context in his lecture that these nine words conveyed a distinct meaning, but we don't have that context here and I won't speculate on what the intended meaning might have been.

To generalize my earlier statement: there are some things about the way the Universe is put together that are impossible to understand, and that has to be accepted. We can deal with this by recognizing that physics (and all sciences) create simplified mental models of reality that we can then play with to our hearts' content. Some of our models are well enough constructed that some of our playmates-- the engineers-- can build marvelous things. But don't confuse our ability to build castles made of sand with an understanding of what sand is. The best we can do is replace one crude model with another that is maybe a little less crude, but is still just a model; just a bunch of thoughts in the head that have no direct relationship to whatever is Out There.

Re:And what about dark matter?

[boristhespider]

It's just how gravity works - if you fill a universe with not quite enough matter to make it collapse it will expand. Meaning if the universe was a bit denser it would collapse, but since it's not it's expanding. Then, as Neil Boekend says, due to something we're currently calling "dark energy" for want of a better term, with the amount of matter we've got we would expect the universe to be expanding but slowing whereas it's actually accelerating.

Sorry I can't give a better answer but really no-one can -- just that given the theory we've got, and the starting point we assume (an initial expansion coming from the point at which the theory simply breaks down), that's how it goes.

Re:And what about dark matter?

[blue trane]

Right, so my original motive for the first post in this thread, was to challenge the smugness of the guy who said his physics teacher described cosmology as being like biology before Darwin. My point was, physics has problems too. One of those problems being the supposedly sacrosanct law of conservation of energy.

Re:And what about dark matter?

[boristhespider]

Well, I wasn't a particular fan of that comment either... :) But your comments about the conservation of energy are basically wrong -- like I say, the expansion of the universe is governed basically by two equations:

1) The Friedman equation, which is the "Hamiltonian constraint" and which can be interpreted as an energy constraint equation
2) The matter continuity equations, which arise directly from conservation of equation of matter

(Technically, and apologies for the ugly LaTeX notation here, matter is described in relativity by "stress-energy" or "energy-momentum" tensors, which bundle together the classical concepts of energy, momentum flux, energy flow, and momentum flux density. The gradient of the more familiar Momentum flux density produces momentum conservation, while the time derivative and gradient of the energy give, well, energy conservation otherwise known as matter continuity. In terms of the stress-energy tensors, if energy is conserved then the covariant gradient of these is conserved -- written T^{\mu \nu}_{; \nu} = 0 where the \mu and \nu describe the four spacetime coordinates, and the repeated \nu means we sum across them. In Euclidean spacetime this immediately reduces to normal energy and momentum conservation. That semi-colon means "covariant derivative", meaning it has contributions coming from interactions with the spacetime geometry; if instead you insist on writing the conservation equation as a partial derivative (as in familiar classical mechanics and fluid dynamics) then you get T^{\mu \nu}_{, \nu} = [gravitational terms]^\mu and if you were unaware of the form of a covariant derivative this would look like a violation of energy and momentum conservation rather than what it is -- an interaction of the stress-energy of matter with the geometry of spacetime.

(The energy density, with respect to some chosen time coordinate which can be described as the vector n^\mu normal to a purely spatial three-dimensional surface, is found by the contraction \rho = n^\mu n^\nu T_{\mu \nu} which basically just means the scalar product of the stress-energy tensor with the time coordinate, or phrased differently, the stress-energy tensor projected along the time coordinate. This energy is conserved. Similarly, if we take the full Einstein equations they can be written as G^\mu_\nu = 8\pi G T^\mu_\nu where the G^\mu_\nu is the "Einstein tensor" that basically characterises the local gravitational field, and the G is newton's constant which infuriatingly has the same god damned symbol. If we project these equations along the time coordinate then we get out an energy on the right-hand side, and something that therefore can be interpreted as embodying the "gravitational energy" on the left-hand side. The result of this is the Hamiltonian constraint, and in the specific case of a cosmological spacetime the result is the Friedmann equation. Both these equations therefore express energy conservation -- one for the gravitational field, and the other for the matter.)

Said a bit less technically, the second equation is simply what you expect -- for normal matter we except the density changes with scale factor as rho = rho_0 / a^3. That is, the density decays as the volume of the universe increases. For photons we would expect instead rho=rho_0 / a^4, where we've got the normal volume dilution (1/a^3) and, since a photon's energy is proportional to length and the expansion of the universe will stretch that length, we should have an extra decay in the energy of 1/a. So rho = rho_0 / a^4. To a good approximation the same can be said for neutrinos (although to be exact we should make these massive, albeit extremely light.) Put these together and you have rho = rho_matter / a^3 + rho_photons / a^4. This is nothing but what happens when space expands.

That's well and good but it doesn't answer your issue with energy conservation, because it seems to violate it. That's where the other equation comes in, because these equations are only *half* the story. In GR (and other

Re:And what about dark matter?

[blue trane]

Given no further context, the default assumption is that physics is in a much better state than cosmology. That was what I was reacting to.

Universal Hydrogen shortages expected soon!

[captainpanic]

Universal Hydrogen shortages expected soon!! -- that better?

It's an interesting read... and although none of it is breaking news, it's definitely stuff for nerds and I am happy that /. link to it.

Re:Universal Hydrogen shortages expected soon!

[boristhespider]

"Reading for nerds - stuff that matters"

Or in this context "Reading for nerds - matter that stuffs"

Re:Ahhhhhh

[donaldm]

No, that's methane. Wrong gas.

I realise the AC was making an off colour joke but the chemical symbol of Methane is CH4 so it does have hydrogen in its chemical formula.

Re:Ejected hydrogen

[davester666]

Great. Now I have to search for the porn video of this.

Lithium and beryllium

[fremsley471]

10E-10 levels of lithium and 10E-14 levels of beryllium are usually overlooked in discussions of Big Bang nucleosynthesis. But even minute proportions of Everything still results in rather large amounts of Something.

Re:Lithium and beryllium

[nbritton]

Wouldn't it actually be lithium hydride? The hydrogen atoms would instantly give up their electrons to form LiH. Free elemental lithium just doesn't happen in nature because it's only one electron away from a stable configuration.

Re:So, um, only protons and neutrons?

[flyingfsck]

That must be why the big bang happened - all charged up and nowhere to go.

Re:I was wondering this myself...

[Blaskowicz]

Hydrogen cars are a scam. H2 has a great energy density by mass, but a very poor energy density by volume. You need very high pressure storage in a tank.. Heavy, expensive and the hydrogen consistently "wants" to leak out, being so thin.
Or you need liquid hydrogen, which needs a non trivial cryogenic apparatus. A non-starter, not even all launch rockets use liquid hydrogen.

In the end, hydrogen needs to be bound back to other atoms to be a usable fuel for transportation, some promising uses for H2 could be to manufacture CH4 using CO2 from a cement factory, or NH3 using nitrogen from air. But this consumes further energy, which would need to come from a mix of solar thermal, renewable electricity and nuclear from the grid.

Where does the H2 come? There's water electrolysis, which needs a ton of electricity. High tech schemes for cracking water into H2 and O2, using concentrated sunlight and whatever.. I don't know how's that going. And of course, the cheaper way that has actually been done on a massive scale for decades, extract hydrogen from natural gas (if you want to, that can be done from coal ultimately). That's vastly cheaper, and going through the pain of producing hydrogen that way, liquifying it for mass storage, getting it in some form in cars and burning it would make no sense at all next to just burning natural gas in cars.

Re:I was wondering this myself...

[K. S. Kyosuke]

my understanding is that hydrogen bonds with practically anything, and gets really funny about unbonding...where are we going to get all of the free hydrogen from for powering tomorrow's cars

You've answered your question - you should be able to power tomorrow's cars with sexually frustrated young men, since they appear to be chemically similar to hydrogen.

Re:Ahhhhhh

[Anonymous Coward]

Hydrogen is odorless, as is methane. Hydrogen sulfide and the breakdown of complex proteins (especially sulfur containing ones) provide the stink

Obvious conversion

[Anonymous Coward]

It turned into stupidity.

helium

[StripedCow]

And what happens to the world's helium?
Since it is lighter than air, it moves to the top of the atmosphere, and cannot be mined anymore.

Re:helium

[PlusFiveTroll]

It's even worse than that. Helium will escape the atmosphere in to space.

https://en.wikipedia.org/wiki/...

Re:helium

[oodaloop]

There's plenty on the sun we can mine. A bigger problem, though, is the dwindling vacuum supply. We need to get into space and start mining vacuum.

Re:helium

[nbritton]

Is rain the byproduct of hydrogen and oxygen reacting from solar radiation?

Re:helium

[nbritton]

Is rain the byproduct of hydrogen and oxygen reacting from solar radiation?

In other words, what keeps the hydrogen from floating away into space?

Re:helium

[painandgreed]

In other words, what keeps the hydrogen from floating away into space?

Being bound to much heavier oxygen and carbon atoms mostly.

Re:I was wondering this myself...

[Sockatume]

You don't burn hydrogen in a hydrogen vehicle. You use it to run a fuel cell which, being electrochemical, doesn't have the Carnot limit on its efficiency. So even a relatively inefficient hydrogen cycle can actually be better than making liquid fuels for an internal combustion engine. The challenge, as you say, is engineering a good hydrogen storage material. (The chemistry problems involved in the efficient photolysis of water are related to the ones involved in the efficient photocatalytic production of liquid fuels, so the research on each side tends to assist the other.)

On the gripping hand, fast-fuelling long-range vehicles are an artefact of cheap, readily available gasoline rather than an inherent part of the human condition so I can't see them being competitive with modest-range battery vehicles in the long term.

Re:I was wondering this myself...

[kasperd]

In the end, hydrogen needs to be bound back to other atoms to be a usable fuel for transportation, some promising uses for H2 could be to manufacture CH4 using CO2 from a cement factory

And of course, the cheaper way that has actually been done on a massive scale for decades, extract hydrogen from natural gas

Natural gas primarily consists of CH_4. So combining those two ideas sounds like turning natural gas into hydrogen and then turning that hydrogen into natural gas.

Re:I was wondering this myself...

[countach]

As true as all your statements are, unless you have a better solution its really just whining. In a hypothetical future where we have infinite energy from large fusion reactors, we need some way for cars to run, and batteries just aren't practical enough.

Re:So, um, only protons and neutrons?

[jfdavis668]

There were also lots of electrons.

Re:And I stopped when

[OakDragon]

And here he is, high as fuck.

Re:I was wondering this myself...

[Bengie]

Not practical enough yet, but they do have batteries that have 10x-100x the storage of lead-acid that are nearly ready, They just need to get past the fire hazard and figuring out how to mass produce cheaply. They also charge quickly, fast enough to actually replace capacitors in many cases, while maintaining most of their storage capacity after many cycles.

buttugly

[Crass Spektakel]

Man is that Medium.com Site buttugly. Giant Fonts, most parts of the page empty.

Bleark.

So the universe was acidic?

[nbritton]

So would that imply the universe was highly acidic in the beginning? What influence would that have on the creation of life?

technetium?

[PJ6]

One thing jumped out at me in the article in the third link... technetium's abundance looks way too high. It doesn't even exist on Earth, yet it's shown on the order of Molybdenum and Tin in the graph of relative abundance of elements in the universe.

I'm not a cosmologist and Google's no help... anyone want to chime in?

Re:technetium?

[PJ6]

Look closer at that plot, it looks like there is no dot for technetium, it is skipped over with the next dot being for z=44, ruthenium.

Damn, you're right.

"Let's just ignore that point since it's off the chart."

Boo.

catwalk

[minyard]

the big bang model slipped and fell while walking down the runway. perhaps gravity can't be reverse engineered into this model of the universe because it's not exactly correct?