The Dark Side of the Cosmos

Thursday, October 6, 2016 -- 5:00 PM
Laura Maguire

What a weird and wonderful cosmos we live in! Here’s an astounding fact. If you take all of the ordinary objects you can see, from tables and chairs to all the stars and planets in the universe, you will have accounted for less than 5% of the universe’s total mass-energy. The other 95%? That’s invisible stuff like dark matter and dark energy.

Dark matter and dark energy are so called because they neither absorb nor reflect light, which is why they’ve never been directly observed. Scientists estimate that dark matter makes up more than 25% of the entire universe. The rest—almost 70%—is dark energy. Apart from that, scientists know very little about these mysterious, invisible forces that dominate the cosmos.

A natural question to ask is why scientists are so confident that dark matter and dark energy really exist when no one has ever observed either one. Is the existence of dark matter and energy just a hypothesis or has the theory been confirmed by empirical data?

The science of dark matter and energy is still in its infancy, so there are many unanswered questions and many hypotheses about their exact nature, even if scientists are mostly confident that they really exist.

Take dark matter. All matter, whether dark or visible, has gravitational effects. The reason galaxies form and maintain their structure and steady motion is because of the gravitational pull of matter. However, the matter that has been observed is not nearly enough to explain the measured gravity of galaxies. So, there must be more matter than can be seen. Hence: dark matter exists. Scientists can estimate how much of it there is based on the gravitational effects they measure.

Much of science works in this way. A phenomenon is observed, some effects are measured, a cause of the observed effects is posited, then some experiments are done to confirm the hypothesis. As far as dark matter is concerned, there are various independent ways that the amount of it in the cosmos can be calculated and they all agree. Surely, this should give us confidence that it really exists, even if, for now, we don’t know much more about it than that.

Of course, throughout the history of science many mysterious entities that were posited to explain observed phenomena turned out not to exist. Take the now defunct theory of phlogiston, which was popular amongst scientists in the 18th century. They posited the existence of phlogiston to explain why combustible objects—those containing phlogiston— burned. Phlogiston was thought of as a fire-like element that was released during combustion.

Thanks to the steady progress of science and the discovery of oxygen, by the end of the 18th century, the theory of phlogiston had already been replaced. Looking back, we can see that phlogiston was just something scientists made up to explain a phenomenon that they didn’t yet understand.

The question then is, how do we know that dark matter is not just another phlogiston-like idea? Will some future discovery reveal that dark matter was just something scientists made up to explain a phenomenon they didn’t yet understand?

I will let our guest on this week’s show, astrophysicist Priya Natarajan, be the one to convince you that the evidence for dark matter and dark energy is solid. But I will leave you with what I take to be a more apt comparison than phlogiston— the theory of black holes.

It’s no accident that the names for these cosmic entities are similar. Although both invisible, dark matter and black holes were posited because of the odd gravitational effects they exerted on the visible matter around them. When the theory of black holes was first suggested, many wondered if there really were such elusive entities in the cosmos, or if it was just a crazy idea scientists came up with to make their equations work. Now, everybody accepts their existence as uncontroversial, even if there’s still much to learn.

What an exciting time it must be to working in this area of cosmology that deals with all this mysterious dark stuff, especially knowing that it makes up the bulk of our universe. It will be interesting to see how quickly the science progresses and how much our understanding of this weird and wonderful cosmos will deepen in our lifetime.

Comments (9)


Gary M Washburn's picture

Gary M Washburn

Friday, October 7, 2016 -- 5:00 PM

That's a lot of nutrinos! But

That's a lot of nutrinos! But it's hard to count something you can't see detect or even, properly speaking, calculate. If familiar with the actual conduct of physics you have to recognize that these rough guesses are, however well reasoned, wildly imprecise. Factors of two are often considered adequate for making predictions, and sometimes factors of ten are the best we can do. It's been a long time since I could do the calculus, but even when I was somewhat able to follow the math I wondered that the fact that matter spends most of its time "interfered" with by itself is not looked at as an issue to raise. Quantum positioning is a matter of formulating a curve of the probable location of a particle, because it effaces itself as it moves. But the assumption that it has no physical properties where/when it is not calculably there/then is not justified by the formal assumption, nor excluded by the physical evidence. Dark matter may be nothing more than residual properties of matter out of phase with itself. 

MJA's picture

MJA

Friday, October 7, 2016 -- 5:00 PM

The measure and division of

The measure and division of the Universe be it sub-atomically in super colliders in the search of god particles or astrophysically separating dark from light only leads to greater questions, more uncertainty or doubt. The solution to this manmade doubt can be found by removing the flaws that created it. Removing measure from the equation unites or makes the Universe whole again. This wholeness is the truth they seek. Try it and see, clearly. =  

Gerald Fnord's picture

Gerald Fnord

Saturday, October 8, 2016 -- 5:00 PM

If by 'they' you mean

If by 'they' you mean physicists, I think you don't understand what we generally seek or why. Generally speaking,  we wish to understand measurements well enough to predict other measurements adequately,  and there is also æsthetic appreciation of the explanations and how they fit together, or at least appreciation that they don't. 
 
I think you're speaking of a different type of knowing, which some of us seek when we're 'off the clock', and in which others of us have little or no interest?I am one of the latter, as I think that sort of knowledge is in the end mire about the structure of our own brains than about the Universe outside ourselves, and if I were interested in that I would have become instead a neuroscientist. 

Gerald Fnord's picture

Gerald Fnord

Saturday, October 8, 2016 -- 5:00 PM

An interesting thought, but

An interesting thought, but when a galaxy is observed, by definition any superposition of possible quantum states collapses, and the uncertainties remaining in this exceedingly macroscopic measurement are negligible.   One of the boundary conditions of quantum theory is that on a large scale it matches classical physics as modified by General Relativity, which at the speeds and distances involved isn't much.

MJA's picture

MJA

Saturday, October 8, 2016 -- 5:00 PM

Gerald, If by measure you

Hi Gerald, If by measure you mean the measure of nature or the universe then what is the measurement of nature or the universe? Is nature truly measurable or is it merely a dice game that Einstein found so objectionable? =

mirugai's picture

mirugai

Saturday, October 8, 2016 -- 5:00 PM

DARK EXPLAINING

DARK EXPLAINING
 I have ranted on too much in this forum against science as explainer. But I can?t resist it! John pretty much summed it up when he said that whoever defines the terms gets to provide the explanation because they have presented the only ?valid? (self-defined) framework for the question. And I argue that the greater the ?wonder-content? of the ?solution? the more it is accepted, happily. But not ?everything? needs to be ?explained?; as a quantum mechanics philosopher once asked John and Ken, ? Why do you think everything needs to be explained?? This is not a rhetorical question. Why, indeed?
 Now don?t get me wrong, it is great fun to chart the vectors on everything, and finding that they don?t predict exactly the motion (and energy!?!) of everything is a blast.
 But Gerald this ?different kind of knowing? (better: ?exploring?) is what philosophy is all about. And neuroscience (plugging people into brain scanners and looking at places where red, green and blue lights light) has nothing to help a philosopher explore. The brain is not the mind. Gerald, as one committed to the explainings by science, I urge you to stay far away from philosophy, which will never satisfy your hunger ?to know? in the (very limited) way you think of knowing something. Hey, wouldn?t there be multiple ways of ?knowing? in these myriad parallel quantum frames? But as MJA implies, examine your urges to measure things, and to state with certainty that measurement is the measure of everything. See the tautology? If you think that ?another way of knowing? is nutty, just how nutty is the whole dark matter thing, entirely made up on the stuff we can?t know. The inferences are almost entirely conjectural extensions?lot?s of fun, but ?knowing?? Don?t think so.
 What I really want to know is how much grant money, and publication fees, and tenure salaries are the result of dark matter study applications? Spend the money trying to find ways to clean up water, scientist.  At least no philosopher gets a grant to sit in a chair and think about things. 

Gary M Washburn's picture

Gary M Washburn

Sunday, October 9, 2016 -- 5:00 PM

The measurable fact of an

The measurable fact of an expanding universe doesn't make sense in terms of the current paradigms. That cannot be overlooked. I just suggest we need to look closer to home rather than invent outlandish notions or exaggerated extrapolations of highly underdeveloped and incomplete surmises. I think, knowing what we know about space/time, there is a case to be made for a negative gravity, not a repulsion, but an attraction that operates most at a distance. If matter out of phase with itself pulls on the universe as the inverse of the inverse square law, most intense at the most distant and inversely diminished is proportion to the square of that distance, the issue of the expanding universe might have a candidate explanation. If space/time really is enfolded upon itself as Relativity suggests, then matter out of phase with itself might be effectively exerted its properties at the outermost extremity of the universe. And maybe this could be described mathematically to see if its would fit the model, but I don't currently have the skills for the calculation.
In any case, while it is true that science must take as given everything outside its immediate issue, a philosopher is not free to do so. If you cannot define defend and explain every term, what it is means and how it is derived, you are not doing philosophy at all. As I've said elsewhere, the most lethal critique of a philosopher is that he has not justified his terms. Nothing can be taken as given or on faith. "It just is" is not saying anything at all, it's just noise. And this is the problem Wittgenstein passes over. Because the ladder he says we must kick aside, in silence, is just noise. We haven't explained anything. We haven't yet even begun to do philosophy.

MJA's picture

MJA

Sunday, October 9, 2016 -- 5:00 PM

Marugai, Yes!!!

Marugai, Yes!!!
Call it ego but sometimes I think I am the only One.
Thanks, =
 

Harold G. Neuman's picture

Harold G. Neuman

Monday, October 10, 2016 -- 5:00 PM

I've been reading a bit about

I've been reading a bit about cosmology lately; and quite a bit over time. Just made way through Roger Penrose' CYCLES OF TIME. Therein I discovered he and I have shared a thought for some number of years. Penrose talks about things like dark matter and something he terms Conformal Cyclic Cosmology. He also raises and reinforces the notion of what might have been extant prior to the ubiquitous Big Bang and whether or not that big noise truly was the beginning of time, the Universe, and the unfolding of things leading up to life as we know it. I have, myself, asked questions about whether the great thud WAS the beginning of all things timeless and universal, or whether it was only an important event in a grander (and even more timeless) timelessness (i.e., the universe was, long(?) before any sort of big bang; had no beginning in any sense we can truly fathom; and, therefore, the concept of time is mostly meaningless on any universal scale. Physics is a fascinating subject and Penrose' views are striking, whether one can grasp and/or agree with them or no. Dark matter and dark energy may or may not be finally revealed. And just so with quantum gravity. I am thinking, though, that there are things our knowledge will never permit us to know...without a lot more direct experience. Scientific thinkers (and some others) almost always raise more questions than they can answer.
Neuman

 

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