Dark Energy Considered Harmful

Simon White has written a treatise published on astro-ph (arXiv:0704.2291v1) where he argues that Dark Energy, or, more specifically, the current bandwagon of interest in Dark Energy, is potentially harmful for astronomy.

Despite the fact that I'm deeply interested in cosmology and Dark Energy, despite the fact that those subjects are my favorite topics for public-outreach lectures, and despite the fact that I was there as one of the major contributors tot he 1998 discovery of the acceleration of the Universe's expansion and hence Dark Energy, I agree with almost everything Simon White has to say. There's one point I vehemently disagree with, and one meta-point I think is worth discussing, but I will save both of those for different posts.

The main point of Simon White's argument is that while Dark Energy was discovered by astronomers (although my group sometimes prided themselves on being particle physicists, and were simultaneously derided by competitors as being particle physicists), and while Dark Energy can for the forseeable future only be experimentally addressed via astronomical observations, the scientific questions associated with it are much more native to fundamental particle physics to astronomy, and the culture of experiment surrounding it is currently, and is likely to remain, the culture of particle physics. Dark Energy is the big sexy topic attracting a lot of attention. If we focus too much of our attention and efforts on it, we risk losing the culture of astronomy in the culture of particle physics. Meanwhile, there remain a huge array of other equally interesting scientific problems which, along with the future viability of any astrophysics at all, could wither and die if we allow the culture of astronomy to be altered and subsumed into the culture of particle physics.

If there is one thing that all physicists can agree upon, it is that "anybody working in a subfield other than my own is ultimately wasting their time on less interesting or less useful questions." As a corollary, this also means that each physicist would agree that "subfields other than my own are currently receiving a too large fraction of the research resources, and my own should be receiving more." It would be easy to read Simon White's essay as a long "Waaaaah! All those Dark Energy people are taking all the money! I want some!" However, I think that would be an unfair characterization. His arguments are thoughtful, and indeed reactions to exactly the "my field is more important" rumblings coming from others. I for a long time a member of the Supernova Cosmology Project— the supernova team which is sometimes characterized in popularizations as "the physicists," in contrast to "the astronomers" of the Schmidt, Kirshner, Riess, et al. team. I have seen this culture class. I have been a part of it. And, indeed, I have suffered somewhat from being caught on the crack between cultures, and that is part (maybe even the major part) of why I no longer really work in cosmology, but now work on interacting and active galaxies.

In one of my first two years at Vanderbilt, I was approached by one of the particle physics experimentalists. At the time, we as a department were discussing the future of the department, including hiring plans in astronomy. Also at the time, my research was completely focused on cosmology, as I was deeply in the process of working on this paper (which probably remains one of the most-cited papers produced by the Vanderbilt physics department— but which is also, much to my detriment, the only first-author paper I've produced in the last five years). This particle physicist expressed concern that the discussions about the future of astronomy were not emphasizing my own work enough, and focusing too much on the stuff that the other people were doing. After all, he said, what I was working on was the only thing that the astronomers were doing that was truly "fundamental."

My response was: David Weintraub is working on the formation of planetary systems. Understanding how the disk of material around young stars eventually evolves into planetary systems is deeply convolved (obviously) with understanding how our own Solar System came to be, and how life may arise in the Universe elsewhere. This is one of the sexiest and most basic questions in astronomy right now, something of interest to a large segment of the astronomical community. This came as a something of a revelation to this particle physicist. He nodded thoughtfully, and said, yeah, he could see where different people might have different ideas about what was fundamental.

The problem is, very few of us really understand what is interesting and important about other fields. We have blinders on. We can see what's so interesting about our own field. But also, as physicists, we're convinced that we know everything. As such, if we don't see what's interesting about other fields, we conclude that there must be nothing interesting about it.

You can find no shortage of atomic and condensed matter physicists who can tell you about the arrogance of particle physicists, who think that their fundamental science is the only thing that's really important in Physics. If he were less diplomatic, I suspect that Chad could go on at length about this. A friend of mine who is a condensed matter physicist at a highly regarded small teaching college sometimes complains about his colleagues deciding which students should be nominated for the APS Apker award; they only seem to think that anybody cares about the "black hole geek" stuff, he says.

Meanwhile, given that I'm closer to the particle physicists, I can easily see the expansionary and exclusionary tendencies of the condensed matter physicists. Particle physics is the physics of the 20th century, they seem to think, not the 21st. It's huge, huge groups of people, very long author lists, very few of whom actually do anything. Condensed matter physics is the future; nanoscale physics is what is really going to do something useful for society. That's the attitude. It can get very contentions and noisy at times. Except when they're all agreeing the "classical" (i.e. non-Dark Energy Cosmology) astronomy is generally a waste of time for a physics department.

Simon White makes a big deal about the siren song of the "fundamental" question represented by Dark Energy. It came out of astronomy, and it will take astronomical methods to continue to address it. But we should not let it subsume all of astronomy; the culture of particle physics, where more and more they focus on larger and larger single experiments, could easily push it in that direction if we let it. But there is so much more in astronomy that is of great interest, that it is essential that we maintain the culture of astronomy to recognize that insofar as any "non-practical" scientific investigation is important, all of those other questions must continue to be addressed.

I'll close with a long but pithy quote from Simon White's article. His point is not that particle physics is at all lesser than astronomy, but that they are different, and while the two fields are more and more finding a large degree fo synergy, we should not let that destroy our broader view of what each is.

Astrophysics aims to understand the structure and behaviour of inherently complex systems and as a result is interdisciplinary and synthetic in character. An intuitive feeling for the interplay between phenomena from many areas of physics is needed, for example, to model the formation of a galaxy. High-energy physics, in contrast, is reductionist, aiming to break phenomena down into ever more fundamental and more abstract entities, discarding along the way complexities which may mask the underlying Truth. Thus astrophysicists tend to be generalists, prizing breadth of knowledge, while high-energy physicists tend to be specialists, prizing the depth to which they probe the underlying structure of matter. In experimental work astrophysicists seek many truths associated with many phenomena, and the best forefront research is characterised by diversity and opportunism. In particle physics the quest for the fundamental Truth has led to a focus on a much smaller number of `important' questions (the origin of mass, the unification of quantum mechanics and general relativity...) and to the organisation of industrial-strength teams to address them. New insights in astrophysical research appeal on many levels, intellectual, emotional and aesthetic, but they rarely display the quasi-mathematical rigour of major advances in particle physics such as the understanding of asymptotic freedom or of the Higgs mechanism. Astrophysicists are universalists, democratic in perceiving interest in all aspects of the cosmos, while high-energy physicists are fundamentalists, cleaving to the pursuit of the single Truth.

Update: Sean Carroll at Cosmic Variance has his own take on this.

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Nice post. I was at the KITP when Simon White gave the talk on which this paper is based, though sadly I was out the day it happened. The arguments that ensued are still somewhat legendary.

Rob, note that your final quote from the paper is somewhat garbled --- some words got mangled making it a bit hard to read.

Interesting essay (though you really need to proofread your ending excerpt from White's paper; parts of it are rather chopped up!).

I've actually tended to think of astronomy as something slightly separate from physics, rather than a subdivision thereof. I suspect this is partly because both my undergraduate (Wesleyan University) and graduate (U. Wisconsin) programs were in separate Astronomy departments.

It's probably also due to my historical interests, and to a tendency to see astronomy as somewhat akin to biology, my other main scientific interest.

Agreed. Although the nuances of the difference of the culture of particle physics and culture of astronomy eludes me. As you said, different fields have different priorities; but as a stellar astronomer I do not see how too much focus on finding Dark Energy could be harmful to astronomy. The numbers of astronomers have been increasing by a lot; so we should have enough (wo)manpower. As our colloquium speaker said earlier today, this is one of the best times to be working on Star Formation - in terms of resources, laundry list of things that need to be done. I'll have to read the paper by Simon White, I guess.

Would be interesting to hear about your thoughts about the chances of finding life elsewhere. Yeah, I love finding new planets; it would be nice to know why we exist and to see if similar conditions are replicated somewhere else (I believe they have to be as we cannnot be that special). But I think that chances of seeing a convincing evidence of life elsewhere are pretty remote. We, as astronomers, also like to attract public attention of finding a nearby habitable planet in case the Earth becomes a greenhouse. Isn't this field overblown as well? Are we trying to appease and wheedle the money out of the general public too much?

Rob, as long as we are getting meaningful results, I do not see why it can be bad for astronomy. Yeah, it'll take a lot of resources; but isn't it a problem that really needs to be solved? Should we shelve it because we need to work in groups of 200 and need to devote 30% or 80% of our total budget? If we do not understand dark energy, can we truly understand how galaxies formed?

Besides the interdisciplinary squabbles, Dark Energy risks becoming a major distraction. Consider: With dark matter, astronomers can look at certain galaxies, sort out the vectors, and say "hey, there's dark matter there". Now, obviously, I'm no physicist, but everything I've heard about dark energy indicates that it's supposed to be a single, universe-wide parameter -- not only constant, but apparently remaining constant, throughout the development of the universe as a whole.

As I've said previously, that smells like fudge to me! Specifically, "we" had a situation where observation didn't match up to original theory -- but hey, adding this constant expansion factor makes everything line up. "All it needs is a name...". Well, actually, it would help if there were connections to known material! (Note that much the same challenge applies against MOND, but AFAIK they didn't try to create a new entity, just to see if they could find a fudge-factor that would work.)

By David Harmon (not verified) on 20 Apr 2007 #permalink

All -- sorry about the garbled posted quote. I didn't proofread it, because I trusted my cut-and-paste out of a PDF. Oops. I was in Chile with the departure time for the carryall breathing down my neck.... I'll fix it shortly.

Saurav -- I think Martin White's point is that too often se seem to be selling our next-generation facilities on the basis of "finding out more about Dark Energy." However, you design things very differently if that is all you want to do than if you want to build the sort of general-purpose observatory that has served Astronomy so well for so many years.

When Caty Pilachowski visited, she said that she thought the two most important things done by the 10m Keck telescopes are (a) redshifts of the supernovae that led to the discovery of Dark Energy, and (b) radial velocity curves of nearby stars that led to the discovery of extrasolar planets.

Not to disparage either of these discoveries-- and, indeed, I was sitting in the Keck control room obtaining some of the spectra for (a) myself!-- but I think this really sells Keck monstrously short. The true accomplishment of Keck is the huge contributions it has made to a wide variety of fields. Redshits of the Hubble Deep Field; IR imaging of the orbits of stars in the Galactic Center, confirming and measuring the mass of the black hole there; Black Hole / bulge velocity dispersion relationship ; Quasar absorption lines and DLA-type things ; and lots, lots, lots more.

Simon White makes the argument that we already know everything we need to know about Dark Energy to use it as a prerequisite for other fields of study -- galaxy formation, etc. And I think he's right. It's possible that Dark Energy will turn out to be more perverse than that, but it's likely that DE is close enough to vacuum energy that assuming VE will not alter any other results. Understanding Dark Energy is important because it's a fascinating and fundamental question itself; however, I don't think it's a prerequisite for much of anything else any more.

It's definitely worth doing. And, indeed, a marriage of particle physics and astrophysics is necessary to pursue it. we just need to make sure that we don't all jump so thoroughly on the bandwagon that we don't sacrifice the sorts of design objectives that lead to good astronomical facilities.


As I've said previously, that smells like fudge to me! Specifically, "we" had a situation where observation didn't match up to original theory -- but hey, adding this constant expansion factor makes everything line up.

Well... except that it was already in the theory. I can show you review articles about the status of the Cosmological Constant that were written years before the discovery of the Universe's Expansion (here's one by Carroll, Press, and Turner from 1992), and papers from before the discovery of the accelerating Universe that argued there was already enough evidence to believe in a cosmological constant (here's one by Krauss and Turner from 1995).

There are reasons to believe that vacuum energy could be real. It is a likely consequence of Quantum Field Theory, including QED, which an atomic physicist recently described to me as "our best theory" -- and he's right, it's an extremely precisely tested theory. There's also the Casimir experiment, that shows that there are zeropoint states that can be detected if you set things up right. (Connecting the Casimir experiment to the average free-space vacuum energy density is, however, something I believe nobody knows how to do.)

Vaccum energy plugs very naturally into Einstein's GR.

Is it possible that the deviations from the no-Dark-Energy expansion history are a pointer to flaws in our current theories? Absolutely! But Dark Energy isn't as ad hoc and hand-wavy as it sounds to the uninitiated.


Well... except that it was already in the theory. I can show you review articles...

OK, fair enough. Even so, the renaming seems a bit gratuitious, and iirc, the problem with vacuum energy is exactly that nobody really knows how to pin down the free parameters for that either.

Is it possible that the deviations from the no-Dark-Energy expansion history are a pointer to flaws in our current theories? Absolutely!

Agreed, that's how science is supposed to advance. The issue here is, "that next step's a doozie!" I'll be much happier once somebody manages to connect the cosmological observations with some sort of terrestrial, or even orbital, experiments. (And yeah, I think it'll happen eventually.) In the meantime, it may not be a "crisis", but it's surely frustrating.

This sort of thing makes me wonder if natural law might itself have a fractal-like character, where the more you investigate, the more laws and equations you turn up ad infinitum. At least one SF author has toyed with a similar idea -- I don't remember title or author, but the punchline was that the unlucky "last physics student" wound up getting transferred to the Theology department. ;-)

By David Harmon (not verified) on 20 Apr 2007 #permalink

Dark Energy will not ruin the culture of astronomy. Neither will the culture of particle physicists. The goal of ALL science, be it anything from cosmology to meteorology is one in the same. The search for truths within the universe in which we live. Different fields may have different methodologies, because the types of questions they ask require it. To find a phenomena in one field which requires one to draw on the knowledge and resources of another is actually quite a wonderful thing.

The culture of astronomy is vast and rich with history. Thousands of projects are funded annually. The number of HEP projects can easily be counted on a couple of hands. Astronomy enriches the mind and sparks the imagination of mostly everyone who looks up at a clear night sky. When was the last time you saw a child with a portable particle accelerator staring down at quarks? Ask a man on the street to name an astronomer, he will probably be able to name a dozen. How about a particle physicist? uhh hmmm...

Astronomy is here to stay as long as there are stars. HEP is only here as long as there is funding, which is looking pretty dim after LHC. Funding will not stop for astronomy. Flipping the bill to answer such a problem as dark energy can only improve the culture and scientific value of Astronomy.

P.S. Sometimes I wonder why I became a Particle Physicist (however, I never regretted), but I wonder about everything, I guess thats is why I am first and foremost a scientist.

I'm afraid there's one thing wrong with this post.
The title. You know what I mean. Physical scientists don't get to call anything "X Considered Harmful". It ruins the joke for computer scientists.

By Pseudonym (not verified) on 21 Apr 2007 #permalink

The title. You know what I mean. Physical scientists don't get to call anything "X Considered Harmful". It ruins the joke for computer scientists.

Actually, part of the reason it came to mind is that it has already been shanghaied by astronomers. Amateur astronomers, that is. See, in the good old days, amateur astronomers would find the objects they were interested in by "star hopping." A dim galaxy or planetary nebula was too dim to be found just by pointing at the right general area of the sky; you couldn't see it naked eye. So, instead, you'd start on a bright star, and, using your star charts, offset, matching the patterns of stars in the finder scope with the patterns of stars on a star map, until you knew you were at the right field with your object. Then you'd try to see the object in the main 'scope.

Some telescopes had "setting circles" -- dials on the two axes (if the telescopes were "equatorial" scopes whose axis matched those of the sky, rather than "alt-alz" that matchedt he axes of the ground). You could go to a bright star, calibrate your setting circles, and then just use the setting circles to look at the right field. Many considered this cheating.

Now there are these scopes where you don't have to know much of anything. They have computers, they have encoders on the axes. You calibrate them once, and then thereafter you just type the object name into the telescope, and the telescope automatically slews over so it's pointing at what you want to look at. Some amateur astronomers say that this encourages a disconnection with the sky-- it's no accident that professional astronomers (who've had this for decades) often don't know any of the constellations.

These telescopes are called "goto" scopes, so of course some of the early diatribes against them were entitled "GOTO considered harmful."


The BIG problem in the arguments (such as they are - setting aside the sociological rubbish about 'fundamentalism', and the beauty contest between WMAP and Hubble - whose results look prettier to the unaided eye?) is as follows:

"we already know everything we need to know about Dark Energy to use it as a prerequisite for other fields of study -- galaxy formation, etc. And I think he's right. It's possible that Dark Energy will turn out to be more perverse than that, but it's likely that DE is close enough to vacuum energy that assuming VE will not alter any other results."

How can anyone possibly state that with a straight face? Just a decade ago no-one had a clue about what 'dark energy' was, let alone its equation of state. Now we are supposed to believe that we already have enough data that we can shut up shop and go home happy that there is only one viable possibility, or near as makes no difference? Pretty unscientific I'd say. Like stopping after LEP and saying "well probably there's a Higgs boson, it seems to fit the data we've got, let's just assume it's there and go off to do something else." Theories are meant to be tested, aren't they?

As a particle theorist I find overconfident assumptions about a cosmological constant particularly disappointing, because particle physics on its own can't at present say anything meaningful about the cosmological constant or dark energy. You can talk about quantum field theory until you are blue in the face, but it just gives the wrong answer, by many orders of magnitude, so up till a decade ago we found it more convenient to ignore the question. It took the astronomers and cosmologists to get somewhere, now you and White want to give up just when things are getting interesting?

Maybe dark energy could even tell us something about quantum gravity which we can't probe with experiments here on Earth...

If we want to understand what is going on (as opposed to just assuming that it is the simplest thing that seems to fit current data) it would help enormously if we knew whether or not 'dark energy' was really constant to significantly better accuracy and to higher redshifts - and if we could test GR on very large scales - and if we could test whether 'dark energy' clusters at all - etc. - for example see the recent preprint of Zhang, Liguori, Bean, Dodelson.

Thomas -- you completely missed the point.

we already know everything we need to know about Dark Energy to use it as a prerequisite for other fields of study -- galaxy formation, etc.

If you want to understand Dark Energy, then, yes, obviously there's a lot more work to be done. If you want to predict the future of the Universe, there's more work to be done.

However, if what you need is scale factor as a function of time so that you are using the right background cosmology for distance estimations and density estimations for galaxies in the range z=(0,2), then, yes, we've already got enough precision on the various parameters that additional precision really does not help.

It's tempting to say that "Dark Energy is controlling the expansion of the Universe, therefore if we don't know everything we know about Dark Energy, we are basing absolutely everything else we do on something that's potentially wrong." Simon White and I are arguing that that statement is incorrect.

It's possible that Dark Energy is a pointer to something deeper that will affect everything, galaxy formation and such included. I think that's extremely unlikely, however. It's certain that Dark Energy is a pointer to something deeper in fundamental particle physics, but almost certainly anything we don't know about Dark Energy right now isn't any more important for galactic and non-cosmology extragalactic astrophysics than it is for biology.