Phlogiston, Dark Energy and Modified Levity

What happens when something burns?

Had you aslked a seventeenth-century scientist that question and the chances are the answer would  have involved the word phlogiston, a name derived from the Greek  φλογιστόν, meaning “burning up”. This “fiery principle” or “element” was supposed to be present in all combustible materials and the idea was that it was released into air whenever any such stuff was ignited. The act of burning was thought to separate the phlogiston from the dephlogisticated “true” form of the material, also known as calx.

The phlogiston theory held sway until  the late 18th Century, when Antoine Lavoisier demonstrated that combustion results in an increase in weight of the material being burned. This poses a serious problem if burning also involves the loss of phlogiston unless phlogiston has negative weight. However, many serious scientists of the 18th Century, such as Georg Ernst Stahl, had already suggested that phlogiston might have negative weight or, as he put it, “levity”. Nowadays we would probably say “anti-gravity”.

Eventually, Joseph Priestley discovered what actually combines with materials during combustion:  oxygen. Instead of becoming dephlogisticated, things become oxidised by fixing oxygen from air, which is why their weight increases. It’s worth mentioning, though, the name that Priestley used for oxygen was in fact “dephlogisticated air” (because it was capable of combining more extensively with phlogiston than ordinary air). He  remained a phlogistonian longer after making the discovery that should have killed the theory.

So why am I rambling on about a scientific theory that has been defunct for more than two centuries?

Well,   there just might be a lesson from history about the state of modern cosmology. Not long ago I gave a talk in the fine city of Bath on the topic of Dark Energy and its Discontents. For the cosmologically uninitiated, the standard cosmological model involves the hypothesis that about 75% of the energy budget of the Universe is in the form of this “dark energy”.

Dark energy is needed to reconcile three basic measurements: (i) the brightness distant supernovae that seem to indicate the Universe is accelerating (which is where the anti-gravity comes in); (ii) the cosmic microwave background that suggests the Universe has flat spatial sections; and (iii) the direct estimates of the mass associated with galaxy clusters that accounts for about 25% of the mass needed to close the Universe. A universe without dark energy appears not to be able to account for these three observations simultaneously within our current understanding of gravity as obtained from Einstein’s theory of general relativity.

We don’t know much about what this dark energy is, except that in order to make our current understanding work out it has to produce an effect something like anti-gravity, vaguely reminiscent of the “negative weight” hypothesis mentioned above. In most theories, the dark energy component does this by violating the strong energy condition of general relativity. Alternatively, it might also be accounted for by modifying our theory of gravity in such a way that accounts for anti-gravity in some other way. In the light of the discussion above maybe what we need is a new theory of levity? In other words, maybe we’re taking gravity too seriously?

Anyway, I don’t mind admitting how uncomfortable this dark energy makes me feel. It makes me even more uncomfortable that such an enormous  industry has grown up around it and that its existence is accepted unquestioningly by so many modern cosmologists. Isn’t there a chance that, with the benefit of hindsight, future generations will look back on dark energy in the same way that we now see the phlogiston theory?

Or maybe the dark energy really is phlogiston. That’s got to be worth a paper!

11 Responses to “Phlogiston, Dark Energy and Modified Levity”

  1. Phillip Helbig Says:

    “In other words, maybe we’re taking gravity too seriously?”

    It’s hard not to, since it’s such a heavy subject.

  2. Phillip Helbig Says:

    Google brings up 36,800 hits for “dark energy is phlogiston”. 🙂

  3. Phillip Helbig Says:

    “Anyway, I don’t mind admitting how uncomfortable this dark energy makes me feel. It makes me even more uncomfortable that such an enormous industry has grown up around it and that its existence is accepted unquestioningly by so many modern cosmologists.”

    Is it really accepted unquestioningly? Bob Kirshner tells an interesting story where he ran into Richard Ellis, who knew what Bob was working on. Richard: It’s not the cosmological constant, is it? Bob: Yes, I’m afraid so.

    I think that one needs to be a bit more precise. What does it mean to say that the existence of dark energy is unquestioningly accepted? If you mean “there is evidence that a matter-dominated universe doesn’t fit the data” then, yes, I think that this is now mainstream (though it wasn’t just 20 years ago). Because that is what the data say. There are still several people trying to explain it with something else (e.g. back-reaction or even Lemaitre-Tolman-Bondi models). If you mean dark energy instead of the traditional cosmological constant, then there are also several people working on this, since many people are uncomfortable with the traditional cosmological constant. These people accept the fact that something else is needed, but because they don’t like the traditional explanation, they work on “quintessence” and other such stuff.

    I think that what convinced many people is the following: Back when the first-order result was “supernova are fainter than we expected”, it could have been many things—grey dust, evolutionary effects, miscalibration, whatever. However, one thing which fit the observations was the traditional cosmological constant: nothing pulled out of the hat, no epicycles, just a return to an idea almost a hundred years old which, really, had only been neglected because, until recently, cosmology had too little data. And this value just so happens to give a flat universe (observed in the CMB, expected by many from inflation) when one puts in the value for the matter density which observers had always claimed was correct. And it just happens to get the age of the universe right as well. That’s good enough. Now we have many more data, more high-redshift data, and this is still a good explanation. The error ellipses for many tests get smaller and smaller, and continue to overlap. This makes it increasingly difficult to fit the data with anything else without special pleading.

    And the standard model makes really good predictions. For instance, at higher redshift, supernovae will become relatively brighter, in a specific way. And, of course, there is the ESO key project to monitor the change in redshift of objects over several years. The concordance model (and any classical cosmological model) makes a very clear prediction here.

    As always, the ball is in the court of those who prefer another explanation: where is the theory, without too many free parameters, which explains the data at least as well, and makes testable predictions? At the “Beyond LambdaCDM” conference in Oslo, there were many people who work on modified gravity and so on. During one discussion, George Efstathiou, after being criticized somewhat for his praise of the concordance model, said “Come up with something better and I will give you a job”.

    I think the situation is better than it used to be. 25 years ago, it was difficult to get a paper published which even considered a non-zero cosmological constant: not claiming evidence for it, just saying “let’s see what the data can rule out and what is allowed”. Today, yes, it has become standard, but not overnight and if many people seem convinced today, those are the people which had to be convinced during the last 20 years. But there is healthy scepticism, pundits like yourself cautioning us not to be too careful, people trying to explain the data with something other than a cosmological constant, and so on. Interesting times.

    There was a time, not that long ago, when it was almost as radical to claim that the mass density of the universe is low. You even risked your career by writing a book on this. 🙂 Now that is mainstream as well, and has become accepted wisdom. Hopefully you’re not critical of this as well now. 🙂

    My take is: the data are explained very economically with a cosmological constant. That will, and should, be the standard wisdom until someone comes up with something better.

  4. Clearly there are problems with dark energy and dark matter that are not satisfactorily explained in the standard model. May I invite you to consider a more radical solution. In a recent paper
    http://arxiv.org/abs/1307.6589
    I have shown that the type Ia supernovae observations are compatible with a static universe. The crucial point is that the calibration process that is needed to remove the strong wavelength dependence of the light (i.e. equivalent to the K correction) has a problem. It cannot distinguish between a common redshift dependence and the wavelength dependence so that any common redshift dependence is removed from the calibrated light curves. In particular the removal of the (supposed) time dilation effects from the epoch differences has negligible effect on the calibrated light curve widths. It doesn’t matter whether time dilation was present or whether it wasn’t to the first order the calibrated widths are the same.

    The paper also includes a brief summary of my cosmological model “Curvature cosmology” that has excellent agreement with all significant cosmological observations. It can explain the observations that led to dark matter and dark energy.

    • Phillip Helbig Says:

      Times have changed. The standard model rests on much more than just the supernova data. In particular, unless your theory can predict the CMB power spectrum better than the standard model, then it is just not a contender.

      • In Curvature Cosmology the CMB seen through a higher density-lower temperature gas cloud will have a lower temperature. For example the Coma cluster gas cloud will produce a fractional temperature drop of about 0.005 over a scale of about 1 degree.

      • Phillip Helbig Says:

        Yes, but look at the observations of the power spectrum. Look at the positions and heights of the peaks. This was all predicted long before it was observed. This is not first-order-effect cosmology, but a very precise match of theory and observation. Can you calculate a theoretical power spectrum?

    • Phillip Helbig Says:

      Furthermore, even if these particular observations are consistent with your model, there is much additional evidence that the universe is not static.

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