Dark theories - opinions needed

[athon]

As a freelance science writer, I'm always on the look-out for some interesting ideas I can write about or sell, or do interviews on. I haven't done magazine articles for a while and figured once I've finished my current radio project I'd stitch together something on an idea I had recently.

I'm just needing to make sure the basic premise isn't too much of a stretch.

I've always had a deep interest in the history of science, especially regarding ideas and theories that died along the way. One of my favourite topics concerns the notion of 'vitalism'. Typically, variations of this hypothesis revolve around the belief that life depends on a yet-to-be-discovered, almost supernatural force in order for it to function. Of course, as science progressed, this mysterious force found itself responsible for fewer of biology's actions. Today, psychological dualism seems to be the only place vitalistic-type theories continue to hide (and even then, not with any real seriousness).

Now, that said, from my research vitalism also referred to more materialistic theories, such as the belief that many biological functions such as movement or sensation arose out of vital fluids.

Occasionally, it was used to refer plainly to the unknown, acting as a placeholder for information we're yet to have. 'Vital forces' was used in a context that suggested we don't know what causes it, so we'll refer to it using the term 'vital forces'.

Thus 'vitalism' was always used in reference to attempts to describe mysterious observations in biology (such as sensation, movement, growth and reproduction), with the differences being in the belief of whether this unknown force was unknown interactions of known chemistry/physics, unknown chemistry/physics or completely supernatural.

I can't help but make comparisons between vitalism and our modern theories of dark energy. However, I'm not sure if I'm overthinking this. Dark energy seems to me to be a placeholder for 'we don't know what is causing this observation'. For the most part, from what I understand, dark energy (like historical theories of vitalism) could either be unknown interactions of known physics, or a completely new form of energy.

Do I have this right?

Athon

 

[Vorpal]

There may be some surface similarity, but there are very important differences. The most important is, of course, that we can measure and model it.

Consider the identification of dark energy with vacuum energy/cosmological constant. In the general theory of relativity, it fits perfectly in place. At least qualitatively, it's also suggested by quantum field theory. When two powerful theories independently predict something, the comparison it to an ad hoc placeholder is no longer apt.

 

[arthwollipot]

Well, that's true with our current understanding of science but it's important to remember the scientific culture of the time. Vitalism was just as plausible to the scientific establishment at that time as dark matter is to ours. It's just that the definition of "plausible" has changed since then.

 

[Perpetual Student]

Your comments reminded me of another obsolete biological term, protoplasm, which has an interesting history:
PROTOPLASM

 

[Vorpal]

Well, that's true with our current understanding of science but it's important to remember the scientific culture of the time.

You point out a very good possible angle for the OP. Yes, in many contexts that is very important (e.g., it's healthy to be reminded of this in order to get a bit of humility when one gets the urge to giggle at the understanding of our ancestors). But it's also even more important emphasize that dark energy really is held to a higher standard than vitalism was, in case one gets the urge to dismiss it based on a crude similarity.

 

[arthwollipot]

You point out a very good possible angle for the OP. Yes, in many contexts that is very important (e.g., it's healthy to be reminded of this in order to get a bit of humility when one gets the urge to giggle at the understanding of our ancestors). But it's also even more important emphasize that dark energy really is held to a higher standard than vitalism was, in case one gets the urge to dismiss it based on a crude similarity.

Well, of course. Standards have risen since then.

Oh, and Perpetual Student? Phlogiston.

 

[athon]

Great feedback so far. Cheers.

There may be some surface similarity, but there are very important differences. The most important is, of course, that we can measure and model it.

True, however I think this is more of an important distinction in the progress of science as a practice rather than just a difference in the models themselves. As Art points out, at the time most vitalistic models were in line with current science philosophy. While they weren't quantitative in nature, they did typically account for observations given the limits of the knowledge of the day. Even if it's difficult comparing the nature of the scientific methodologies between now and then, I'm curious to know if the same influences are at work, where an unknown quality is given a name before its precise nature is better understood.

Consider the identification of dark energy with vacuum energy/cosmological constant. In the general theory of relativity, it fits perfectly in place. At least qualitatively, it's also suggested by quantum field theory. When two powerful theories independently predict something, the comparison it to an ad hoc placeholder is no longer apt.

Ah, now this is where I was hoping to get.

Breaking it down for a lay physicist like myself, do these theories predict a novel form of energy, or simply predict the observations we see? I apologise if this seems like a naive or stupid question, but let me outline the comparison I'm testing here: vitalistic fluids of 'elans vitale' were commonly cited as the cause for a number of living factors. We now understand that rather than a completely new form of energy/fluid/matter, such factors could be accounted for by voltage potentials, the chemical arrangements of certain tissues or the structure of polymers. In other words, rather than a simple fluid or new form of energy explaining the observations, it was a complicated interaction of known physics and chemistries.

I'm wondering whether these theories you allude lead directly to the assumption that there is a novel form of energy in the universe (similar in concept to how some vitalists assumed there was a novel form of energy explaining life), or whether they simply predict the observations we've made, indirectly suggesting there is an element to the universe we don't yet quite understand.

Let me know if this makes sense, or I'll see if I can clarify.

Athon

 

[athon]

You point out a very good possible angle for the OP. Yes, in many contexts that is very important (e.g., it's healthy to be reminded of this in order to get a bit of humility when one gets the urge to giggle at the understanding of our ancestors). But it's also even more important emphasize that dark energy really is held to a higher standard than vitalism was, in case one gets the urge to dismiss it based on a crude similarity.

It would be wrong to dismiss it on the basis that vitalism was eventually explained using a range of more detailed theories. In the case of a single vital essence explaining how life was different to non-life, vitalism was overly simplistic. Yet as I suggested, in some cases it was a place-holder which was used with the admission of not having enough information to understand the complex details.

For instance, there was no way that anybody could understand how DNA accounted for cellular differentiation in the 18th century. Yet it is also premature, in hindsight, to state it must be a novel type of energy or simple essence.

Could dark energy prove to be a complex interaction of understood laws, or do we actually require in this case the invention of a novel form of energy?

Athon

 

[Vorpal]

Breaking it down for a lay physicist like myself, do these theories predict a novel form of energy, or simply predict the observations we see?

I'm not sure that I understand your question, but if I do, than it depends.

For the first of these, general relativity, you probably know that spacetime curvature is identified with energy (and momentum, pressure, etc.). If one asks what is the most general relationship between them that reduces to Newtonian mechanics and still conserves energy (+&c.), one gets something like
Curvature + (constant) = energy (+&c),
and that "cosmological constant" Λ should be small in order to predict the correct orbits in the solar system. But over over large distances, even a tiny constant can have very dramatic effects--which is what we observe as large-scale expansion. In modern terminology, that equation is slightly rearranged and the constant is identified with energy of completely empty space.

It's true that GTR doesn't say where it "ultimately comes from", if that's your question. Λ is a parameter that must be measured. But I don't think that this alone makes the comparison valid. Newton's gravitational constant G is a also a parameter that must be measured and once measured, it models the planetary orbits, the tendency of apples to fall, and much else. All GTR does is introduce one more number, Λ.

It seems to me that places some strict limits: an analogy between GTR and vitalism are approximately as valid an analogy between Newtonian gravitation and vitalism (vital force<-->gravitational potential energy, perhaps?). That doesn't mean there can't be a valid or pertinent analogy, however.

I'm wondering whether these theories you allude lead directly to the assumption that there is a novel form of energy in the universe (similar in concept to how some vitalists assumed there was a novel form of energy explaining life), ...

It's probably important to note that Λ was around before we knew that the universe was expanding. It has a very natural place in GTR.

... or whether they simply predict the observations we've made, indirectly suggesting there is an element to the universe we don't yet quite understand.

There's plenty about the universe we don't understand,

In this specific instance, the situation in QFT is a kind of reversed. Dark energy can have an origin--the vacuum fluctuations of empty space that QFT directly predicts. However, the difficulty is that it just plain predicts too much of it, and the puzzle is mainly to discover what cancels it out. (That's why I said "qualitatively" above.)

 

[Vorpal]

Alright, I think I now understand your viewpoint. I agree with only half of it, however.

Could dark energy prove to be a complex interaction of understood laws, ...

Absolutely. It's very much hoped that it will be so. In fact, there is a well-understood mechanism to produce something like dark energy already--again, what's not understood is how to get it to get it low.

... or do we actually require in this case the invention of a novel form of energy?

But it isn't a novel form of energy in the sense that it's postulated to exist after we made those observations. QFT was even made completely independently of astronomical observations of any kind, and as above, GTR's Λ was there before expansion was known (although not its value).

 

[athon]

It's true that GTR doesn't say where it "ultimately comes from", if that's your question.

Essentially that's the crux of it. In one early form of vitalism, nobody knew (for example) why muscles moved. A succession of discoveries led us to eventually marry together voltage potentials with electrochemistry and cytology. Prior to all of that it was proposed to simply be a form of fluid that had all of the same properties.

If I read it all correctly, dark energy is simply a term we use to describe the unknown cause behind the observation that when we have that particular value for the cosmological constant, our universe is an expanding one, right? Please let me know if I've oversimplified that - part of the joys of being a science communicator is finding the balance between saying something simply without losing essential meaning.

It seems to me that places some strict limits: an analogy between GTR and vitalism are approximately as valid an analogy between Newtonian gravitation and vitalism (vital force<-->gravitational potential energy, perhaps?). That doesn't mean there can't be a valid or pertinent analogy, however.

Interesting. Good idea.

There's plenty about the universe we don't understand,

In this specific instance, the situation in QFT is a kind of reversed. Dark energy can have an origin--the vacuum fluctuations of empty space that QFT directly predicts. However, the difficulty is that it just plain predicts too much of it, and the puzzle is mainly to discover what cancels it out. (That's why I said "qualitatively" above.)

Hm, ok. How certain are we that dark energy arises due to vacuum fluctuations?

Thanks again for the help.

Athon

 

[athon]

Alright, I think I now understand your viewpoint. I agree with only half of it, however.

That's ok, so long as you can put me back on track. The reason I started this thread was because I was aware my view was based on naive assumptions that needed clarifying.

Absolutely. It's very much hoped that it will be so. In fact, there is a well-understood mechanism to produce something like dark energy already--again, what's not understood is how to get it to get it low.

Makes sense to me.

But it isn't a novel form of energy in the sense that it's postulated to exist after we made those observations. QFT was even made completely independently of astronomical observations of any kind, and as above, GTR's Λ was there before expansion was known (although not its value).

Ok, all that makes sense as well. I think I'm getting a better grasp on the limits of the analogy, which is what I was after.

Vitalistic theories took three essential forms - they proposed the mechanics behind known observations (living functions) through invoking a discrete new force or material; they suggested unknown mechanisms involving understood physical and chemical principles were responsible for known observations; they invoked supernatural causes, thereby dismissing the need to ever test or explore the potential underlying mechanics.

Just to confirm I have this right: does the notion of dark energy resemble any of these?

Athon

 

[Vorpal]

If I read it all correctly, dark energy is simply a term we use to describe the unknown cause behind the observation that when we have that particular value for the cosmological constant, our universe is an expanding one, right?

Well, yes, but keep in mind that it's in the same kind sense that Newton used the term 'gravity' to describe the unknown cause behind the various observations.

If you're interested in continuing a comparison with Newton, there's actually a kind of chain going down:
-- Newton was puzzled how things could affect each other at a distance, but rather than worrying about explaining it, he simply quantified it. He provided no cause, but a formula ('hypotheses non fingo').
-- Einstein made gravity an entirely local theory, thus explaining its cause (as curvature of spacetime), but GTR also introduced Λ, without explaining what brings it about.

(Although it's worth noting that science has generally been most successful precisely when it stopped worrying too much about ultimate causes and focused its attention on quantifiable effects instead.)

Hm, ok. How certain are we that dark energy arises due to vacuum fluctuations?

In as much as it connects to the observed Λ? It's an open problem. What I'm only sure of (and you can look easily look those up yourself) is that:
-- many QFTs predict a vacuum energy due to those vacuum fluctuations,
-- the leading cosmological model, ΛCDM^WP, models dark energy as a cosmological constant Λ
-- Λ is completely equivalent to having a vacuum energy in all ways.
It is an open problem because (1) it's not the only model of dark energy, although it is the simplest, and (2) those QFTs don't predict the right amount.

---

Vitalistic theories took three essential forms - they proposed the mechanics behind known observations (living functions) through invoking a discrete new force or material; ...

That's only half fair. Vacuum energy, both in terms of Λ and QFTs, has been expected before the observation of cosmic expansion, and so were not proposed to explain those observations (again, in the latter case, it doesn't even have anything to do with astrophysics!). I say 'half' because there is an alternative model of dark energy that's like this: quintessence^WP, but it is alternative precisely because it proposes a new mechanism that isn't necessitated by observations, so identifying dark energy with quintessence is invalid.

If you want a more in-depth response about this issue, then what we really need here is an actual physicist, rather than just some math guy that only happens to have GTR as hobby. Hopefully Sol will chance upon this thread and see if any bludgeoning needs to be done on either of us.

... they suggested unknown mechanisms involving understood physical and chemical principles were responsible for known observations; ...

That seems fair.

... they invoked supernatural causes, thereby dismissing the need to ever test or explore the potential underlying mechanics.

That's definitely not the case with dark energy.

Just to confirm I have this right: does the notion of dark energy resemble any of these?

Half of three.

 

[athon]

Excellent. Thanks for taking the time to explain that. As I suspected, I was in the right ball park but needed clarification on the details. The comparison with gravity is a good one which I'll consider as well.

I'll play with the angle and see if I can get a fair approach, once I get a chance. I'm current doing a half hour radio doco on the technological singularity (getting to interview a favourite author of mine, Richard Morgan!), but once that's out of the way I'll look into nutting this one out.

Athon

 

[Soapy Sam]

athon- how would you explain "conventional" energy?

 

[athon]

athon- how would you explain "conventional" energy?

Not sure of your question, Soapy. If you're asking what I mean by a 'new form of energy', I guess there are a few ways I could view the term.

One is using the same convenient shorthand many people casually use the term as, such as when people refer to life energy. In other words, it's vague and essentially meaningless.

Or, I could view it as referring to anew manifestation of energy, as per a more physical meaning. In other words, like heat or light, only in this form it contributes to the expansion of the universe.

In other words, while I myself might be able to come up with an understanding of what dark energy is, I'm curious to know how the term is understood by others and how it might compare to previous theories which also referred to a discrete, simple term to describe a potentially non-discrete and complicated mechanism.

Athon

 

[sol invictus]

Occasionally, it was used to refer plainly to the unknown, acting as a placeholder for information we're yet to have.

You might check out the discussion of "g" in the "Girl of two has IQ of 156" thread.

Essentially that's the crux of it. In one early form of vitalism, nobody knew (for example) why muscles moved. A succession of discoveries led us to eventually marry together voltage potentials with electrochemistry and cytology. Prior to all of that it was proposed to simply be a form of fluid that had all of the same properties.

If I read it all correctly, dark energy is simply a term we use to describe the unknown cause behind the observation that when we have that particular value for the cosmological constant, our universe is an expanding one, right?

To me, one of the trickiest aspects of understanding and communicating science is the epistemology - when you know you know, or when you decide you understand something. We understand how muscles move in general, but I'm sure there are many aspects we do not understand, particularly once you get down to a greater level of detail. How do you really quantify our level of understanding - or is that impossible?

It certainly seems to me qualitatively that we do not understand dark energy very well. For example we only know its current density to within a few percent, and its behavior in the past is very poorly constrained (that would be one of the crucial tests of whether it's really a cosmological constant). And there's a huge mystery associated with it - if it's a cosmological constant why is it so small compared to everything we know that contributes to the vacuum energy, and if it's not a cosmological constant, why is the CC even smaller?

 

[athon]

Hey, I was hoping you'd comment.

You might check out the discussion of "g" in the "Girl of two has IQ of 156" thread.

Will do - that might be a better comparison, actually.

To me, one of the trickiest aspects of understanding and communicating science is the epistemology - when you know you know, or when you decide you understand something.

Definitely. The difficulty there is that epistemology is not easily communicated in a single piece, but relies on the audience's background and philosophical position.

We understand how muscles move in general, but I'm sure there are many aspects we do not understand, particularly once you get down to a greater level of detail.

Oh, I agree. However we know enough to realise an entirely unique field of physics is not required to explain how living things move.

I guess what I'm curious about is if we find that dark energy is due to a combination of vacuum fluctuations and the interactions of several other understood factors, would we still call the entire mechanism 'dark energy'? Would we still see it as a moderately discrete concept, as we see electromagnetic radiation as a discrete field? The field of genetics essentially progressed from vitalism, yet even though vital essences more or less described (simplistically) a material or physical property that performed the same function.

I do realise physics is rather different to biology, which I'm starting to think could make it difficult to faithfully draw an real parallels between each paradigm.

It certainly seems to me qualitatively that we do not understand dark energy very well. For example we only know its current density to within a few percent, and its behavior in the past is very poorly constrained (that would be one of the crucial tests of whether it's really a cosmological constant). And there's a huge mystery associated with it - if it's a cosmological constant why is it so small compared to everything we know that contributes to the vacuum energy, and if it's not a cosmological constant, why is the CC even smaller?

Yeah, starting to understand that side. I think I might put this idea on the backburner, though. At least for a bit.

Ta.

Athon

 

[Cuddles]

Dark energy seems to me to be a placeholder for 'we don't know what is causing this observation'.

Vorpal has given gravity as an analogy, but that suffers from the same narrow focus as your question. The thing to remember is that that is true for pretty much everything in science, especially physics. Science describes how things work, but it doesn't say why. Or, more accurately, the only way it can answer a "Why?" is by creating at least one more.

Gravity works, and we can describe how it works, but we can never say why gravity actually exists or why it is described in that particular way and not another. Electromagnetism works, and we can describe how it works, but we can't say why it exists in the first place. Electrons exist and we can describe what they're like, but we can't say why electrons and not something else. Dark energy exists, although we can't describe how it works as well as we'd like to yet. Either way, we'll never be able to say why it exists or why it is the way it is.

The anthropic principle says that things are the way they are because otherwise we wouldn't be able to be here wondering about them, and that's about the closest science can ever get to answering "Why?" questions. Things are the way they are because otherwise they'd be different.

I guess what I'm curious about is if we find that dark energy is due to a combination of vacuum fluctuations and the interactions of several other understood factors, would we still call the entire mechanism 'dark energy'? Would we still see it as a moderately discrete concept, as we see electromagnetic radiation as a discrete field?

Yes. We still have the concept of gravitational potential energy even though it's a result of gravity and not a separate thing that pops up all by itself. Even if dark energy turns out to be a consequence of something else, it will still exist in its own right.

The field of genetics essentially progressed from vitalism, yet even though vital essences more or less described (simplistically) a material or physical property that performed the same function.

As you say, I'm convinced this is a particularly good comparison. Modern genetics may have some roots in parts of vitailsm, but vitalism also contained nonsense that never led anywhere, while genetics also has many parts that came from other places or were thought up independently. Vitalism was a general idea that tried to explain many different things in an overly simplisitic, and wrong, way. Dark energy, on the other hand, describes a single specific observed phenomenon.

 

[Soapy Sam]

I'm simply curious about how a teacher explains the notion of "energy", athon.

Once we get to a certain level of basic concept we can no longer understand that concept in terms of something simpler. One curse of science orientated TV and pop sci books is that they tend to go straight for these deep issues, bypassing the less sexy stuff on the way.