The Dark Side of the Cosmos

06 October 2016

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.

一个自然要问的问题是,为什么科学家如此确信暗物质和暗能量真的存在,而没有人观测到它们。暗物质和能量的存在只是一个假设,还是这个理论已经被经验数据证实了?

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.

很多科学都是这样运作的。观察到一种现象,测量到一些效应,并确定产生这些效应的原因,然后做一些实验来证实这一假设。就暗物质而言,有各种独立的方法可以计算宇宙中暗物质的数量,而且它们都是一致的。当然,这应该给我们信心,它真的存在,即使,目前,我们知道的并不比这更多。

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.

由于科学的不断进步和氧的发现,到18世纪末,燃素理论已经被取代。回顾过去,我们可以看到燃素只是科学家们编造出来用来解释他们还不了解的现象。

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

那可是很多中微子啊!But

那可是很多中微子啊!但你很难去计算你看不见的东西,甚至,准确地说,是无法计算的。如果你熟悉物理学的实际行为,你就会认识到,这些粗略的猜测,无论有多么合理的推论,都是极不精确的。人们通常认为2的因素就足以进行预测,有时10的因素是我们能做的最好的预测。我已经很长时间不会做微积分了,但即使我在一定程度上能够理解数学,我也在想,物质大部分时间都在被自己“干扰”,这一事实不应该被视为一个需要提出的问题。量子定位是描述一个粒子可能位置的曲线,因为它在移动的过程中会消失。但是,当它不在那里/那时可计算时,它没有物理特性的假设是不被形式假设所证明的,也不被物理证据所排除。暗物质可能只是物质与自身相异的残余性质。

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

杰拉德,如果你说的测量是指自然或宇宙的测量,那么自然或宇宙的测量是什么?自然真的是可测量的吗?还是仅仅是一个让爱因斯坦反感的骰子游戏?=

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

我最近读了一些关于宇宙学的书;随着时间的推移。刚刚看过罗杰·彭罗斯的《时间周期》在这篇文章中,我发现我和他多年来一直有一个共同的想法。彭罗斯谈到了暗物质和他称之为共形循环宇宙学的东西。他还提出并强化了这样一种观点:在宇宙大爆炸之前可能存在着什么,以及大爆炸是否真的是时间、宇宙的开始,以及我们所知的生命的起源。我自己也曾问过这样的问题:那一声巨响是否是永恒的、普遍的万物的开始,或者它是否只是一个更大的(甚至更永恒的)永恒的重要事件(即,宇宙在任何一种大爆炸之前很久就存在了;在任何意义上都没有我们可以真正理解的开端;因此,时间的概念在任何宇宙尺度上都是毫无意义的。物理学是一门迷人的学科,彭罗斯的观点引人注目,无论人们是否能够理解和/或同意它们。 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