Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe

by Lisa Randall

Dark matter is the elusive stuff in the Universe that interacts through gravity like ordinary matter, but that doesn’t emit or absorb light.

Dark matter is very badly named -- it's not dark at all. It doesn't emit light, and it doesn't reflect light, but light passes right through, affected only by the gravity of the matter.

I’ll tell you right up front that I don’t yet know if this idea is correct.

I like this. A ridiculously fluffy pop science book where the author knows she is treading far from provable.

To be clear, mine is not a religious viewpoint. I don’t feel the need to assign a purpose or meaning.

I don't believe her. We see patterns (real or not) and we assign meanings to those patterns -- that's part of what it means to be human. We can try to not assign a meaning, but we do so struggling against our very nature, and that ends up assigning its own meaning to the pattern.

This newer research

🐙 just curious if the octopus shows up

the molten magma that drives these movements is the result of radioactive material buried near the core of the Earth.

Really? Was I asleep that day in my 9th Grade Earth Science class, or is this new? I was taught that the magma was hot from pressure and friction and was slowly cooling -- that only the crust had cooled enough to harden. Of course, I used to know someone who grew up in North Carolina and was taught that there weren't really many slaves there. We are taught all sorts of wrong shit in school. Fun story about her...

The big lesson at the most fundamental level is that the physics of elementary particles, the physics of the cosmos, and the biology of life itself all connect—not in some New-Age sense, but in remarkable ways that are well worth understanding.

SNAP! Take that New Age crap, you ain't even worth understanding!

The amount of dark matter and dark energy in the Universe too was pinned down only in the last decades of the twentieth century.

At what point did we decide it wasn't just a measurement error? I eagerly await this tidbit of information.

Pluto is not orbiting alone.

This sounds ominous...

The introduction of written language, and later of the printing press, influenced the ways people acquired knowledge and how they thought in ways at least as significant as those that the Internet precipitated.

Please don't be that book. Please?

The perhaps not-so-hidden agenda of this book is to help us better understand the amazing story of how we got here and to encourage us to use that knowledge wisely.

Yeah... Good luck with that. Knowledge increases, but wisdom does not. I remain convinced that the world will be destroyed by a grad student doing something remarkably mundane like trying to genetically manipulate a chicken to have rosemary flavor, or doing something remarkably stupid like trying to create a new letter pair in DNA. But maybe the next species to evolve after us will discover this and be wise enough to heed the warnings. And people say I'm not an optimist.

This section also explains what dark matter is, how we ascertained its existence, and why it is relevant to the Universe’s structure.

I am unnaturally excited by this. How does one make the leap from "I can't figure out what is wrong with my measurements" to "the universe contains secret matter that doesn't show up anywhere but in the errors of my calculations"? I mean, there was an episode of ST:TNG where Doctor Beverly Crusher concludes "Well, if there's nothing wrong with me, there must be something wrong with the universe!" But that's crazy talk. Ok, I guess that is a pretty easy jump. But how do you get other people to buy into that? Because that sounds impossible. It's not like forming a cult or something, is it?

Yet people are mainly preoccupied with the existence and relevance of ordinary matter—which, to be fair, interacts far more strongly.

Also, we are ordinary matter. We're pretty much ordinary matter bigots. To be fair, though, we know a lot more about ordinary matter, so it is a lot easier to be preoccupied with it.

But what if some of the dark matter experiences influential non-gravitational interactions too?

And what if there are forces that only affect dark matter, and which ordinary matter is entirely oblivious to?

If most dark matter is usually relegated to the relatively uninfluential 85 percent, we could then think of the newly proposed type of dark matter as an upwardly mobile middle class—with interactions mimicking those of familiar matter. The additional interactions would affect the makeup of the galaxy and allow this portion of dark matter to affect the motion of stars and other objects in the domain of ordinary matter.

Matter might have a spectrum of darkness -- oh, crap, we're going to end up discussing extra dimensions, aren't we?

unfamiliar animals shadow us when we hike through the woods,

Creepy and ominous. First we learn that Pluto isn't orbiting alone, and now that unfamiliar animals shadow us when we hike through the woods.

Our very bodies host colonies of bacteria. Ten times more bacterial cells than human cells live inside us and help with our survival.

I'm actually kind of surprised that antibiotics don't just kill us.

Participants tend to friend like-minded people, follow others with similar interests, and turn to news sources that represent their own particular worldview. With such restricted interactions, the many people engaged on-line fragment into distinct, non-interacting populations within which they rarely encounter an objectionable point of view.

When presented with many very similar options and positions, people are remarkably quick to learn to discern them and place moral judgements on them. Even as we sort ourselves into increasingly homogenous groups, we still have deep divisions without our group, just over increasingly trivial issues.

Dark matter just isn’t part of ordinary matter’s social network. It lives in an Internet chat room that we don’t yet know how to enter.

This is an absolutely terrible analogy. It makes the dark matter take the role of pedophiles, trading child pornography in the dark corners of the Internet, entirely out of site from us normal people.

Dark matter is not made out of the same material as ordinary matter—it’s not composed of atoms or the familiar elementary particles that do interact with light, which is essential to everything we can see.

That's a pretty big claim right there: "dark" isn't an adjective that describes the matter, the dark matter has an entirely different structure than regular matter -- there are no dark quarks, electrons, protons, neutrons, atoms or molecules. There is no dark Gus reading a book. We cannot take regular matter, "darken" it, pass through some object undetected (a nice wall, perhaps), and the "undarken" the matter. There will be no burglars using this to steal the Crown Jewels of England. Clearly, she would know more than I do, but it's a very bold claim to make with such certainty for something that we can only detect from gravitational effects at a large scale.

Dark energy exists even if no actual particle or other form of stuff is around. It permeates the Universe, but doesn’t clump like ordinary matter. The density of dark energy is the same everywhere—it can be no denser in one region than another.

Does regular energy have density? Gah, I am confused. I cannot remember whether light is an energy or not. Kinetic energy is definitely a property of certain objects, so it is not evenly distributed. I really may be mixing different definitions of energy though.

The dark energy distribution, on the other hand, is always smooth. Dark energy also remains constant over time. Unlike matter or radiation, dark energy does not become more dilute when the Universe expands.

So very weird.

Early in the Universe’s evolution, most of the energy was carried by radiation. But radiation dilutes more quickly than matter so matter took over eventually as the largest energy contribution. Much later in the Universe’s evolution, dark energy—which never diluted whereas both radiation and matter did—came to dominate and now constitutes about 70 percent of the Universe’s energy density.

This would all be way, way clearer with a definition of energy. And how was this dark energy able to keep the same density as the universe expanded?

But although dark energy makes up most of the Universe’s energy today, it is only recently—after matter and radiation were diluted enormously by the Universe’s expansion—that the influence of dark energy began to compete with that of the other types of energy.

Again I am perplexed. If the energy density of dark energy is the same throughout the universe, and unchanging, does that mean that as the universe expands, there is more of it, and that the dark energy is somehow being created from the expansion of the universe? Or, is the universe expanding across a pre-existing field of dark energy, larger than the universe itself -- as if the universe were water spilling onto the floor, expanding across the surface of the floor. I don't think Dr. Randall is doing a great job of explaining dark energy, or even plain old ordinary energy here.

However, given the dominance of dark energy and dark matter, and even the mystery of why so much ordinary matter has survived to today, physicists also joke that we live in the dark ages.

What do you mean, "why so much ordinary matter has survived to today"? Is ordinary matter being destroyed? Is it being destroyed by the thing that orbits with Pluto, or the unknown animal that shadows us as we hike? Is this some kind of monster, destroying ordinary matter? Does it look like this? 🐥

Exploring the geographically varying and challenging territory of the Earth wasn’t always easy. But as demanding as the Earth was to fully understand, it was more accessible and easier to study than its more distant counterparts—the

This probably has the wrong tense -- we haven't really understood the Earth yet.

The study of dark matter is very promising today in that it should be explained by conventional particle physics principles and furthermore should be amenable to a wide variety of currently active experimental probes.

Ok, we are back to dark matter again. Does this mean that dark energy is just some thing that is not dark matter, is not particularly related to dark matter, and can be forgotten for the rest of the book?

Based on his measurements of the velocity of the stars, Zwicky calculated that the amount of mass required for the cluster to have sufficient gravitational pull was 400 times greater than the contribution of the measured luminous mass—the matter that emits light.

I suppose I cannot really complain when reading a pop science book, but this is a really preposterously brief description of the measurements. I want a little more of the how than just "measurements based on the velocity of stars"? How do we determine the velocity of stars in a distant galaxy? Do we mean velocity in the physics sense, with mass attached, or in a more colloquial sense of just speed? Are these measured together or separately?

Yet despite these early observations, dark matter for a long time was essentially ignored.

Did Lundmark and Oort even really believe their figures? With so little known about cosmology at the time, it would seem more probable that the measurements were in error, or that the standard model was wrong.

She changed the direction of her research after her thesis—which measured galaxy velocities and confirmed the existence of galaxy clusters—was initially rejected by most of the scientific community, in part for the ungallant reason that it trod on others’ scientific domain.

This also needs more explanation. Studies and papers confirming or refuting the work of others are allegedly valued in the scientific community, and this big of a breach requires a bit more substance to back it up. But, whatever, she switched from galaxies to stars.

Rubin’s decision led to what is perhaps the most exciting discovery of her time.

I do find it pretty awesome that a woman is credited with huge discoveries in dark matter -- women are frequently overlooked in science and technology, and having one of these invisible people discovering invisible matter is perfect.

That is, stars rotated with constant velocity, even well beyond the region containing luminous matter.

Rotate as in spin on their own axis, or rotate as in revolve around the center of the galaxy? Wouldn't the latter be better called orbital velocity? Do planets around the sun have the same rotational velocity? I know their orbits for N days cuts the same area of a pie slice around the sun, and the orbits would be dependent on the velocity of the planets. I'm not aware of any similar relationship between the length of their days and the mass, speed or velocity of the planet itself.

Without this additional contribution, the stars with the velocities that Rubin and Ford measured would fly off out of the galaxy.

Ok, this is definitely the velocity of the stars rotating around the center of the galaxy. No idea why that is rotational velocity rather than orbital velocity.

These researchers’ remarkable deduction was that ordinary matter accounted for only about a sixth of the mass that was required to keep them in orbit. Rubin and Ford’s observations yielded the strongest evidence at the time for dark matter, and galaxy rotation curves have continued to be an important clue.

I remember, possibly from Carl Sagan's "Cosmos", that galaxies had supermassive black holes in the center. Is this 1970s science gone awry, using black holes to explain the missing mass? Since we only have measurements on the rotational velocity of the stars at this point, how would we distinguish the two scenarios?

In elliptical galaxies, as with Zwicky’s measurement of galaxy clusters, one can measure velocity dispersions—how much velocities vary among the stars in the galaxies.

Can we not measure this in spiral galaxies? If not, why not?

The idea behind the gravitational lensing proposal, which the versatile Fritz Zwicky was the first to suggest, was that the gravitational influence of dark matter would also change the path of light emitted by a luminous object elsewhere.

I'm kind of loving Fritz Zwicky -- he's not afraid to announce his ideas to the world, regardless of how outlandish they might be. He makes some measurements, they don't add up, and he decides there must be another form of matter. How many of his ideas are wildly wrong? Zwicky don't care.

Gravitational lensing is exciting because it is (in a sense) a way to view the dark matter directly. The dark matter between an emitting object and the viewer bends light.

Have we completely given up on black holes? Again, 1970s "Cosmos" talking here... You know, it would probably be terrifying to discover that black holes are responsible for 85% of the mass of the universe. Dark matter is way more reassuring -- we aren't living in a dying universe where everything is being devoured and it is 85% gone.

Gas experiences electromagnetic interactions and this is enough to effectively keep the gas of the two clusters from continuing to move past each other, with the result that the gas that was initially moving along with the clusters gets gridlocked in the middle. The dark matter, on the other hand, interacts very little—both with the gas and, as the Bullet Cluster demonstrates, with itself.

Ok, that is very cool. If I understand this correctly, the ordinary matter acts like two people walking into each other -- they collide, as expected. The dark matter colliding with ordinary matter passes right through -- weird, but expected with what we know so far. Dark matter colliding with dark matter -- I would have expected it to act like people walking into each other, but it passes through. Weird as fuck. It makes me wonder if there are multiple forms of dark matter, each of them non-interactive with the others. If the two galaxies formed around different types of dark matter, their ordinary matter would collide, but their dark matter would pass through each other. Which seems more absurd? Dark matter doesn't even interact with itself, or there are multiple types of matter we cannot directly observe rather than just one? Dunno.

time. In an even more subtle effect, dark matter also influenced how much time elapsed between when matter began to collapse (which happens when the energy density in matter exceeds that in radiation) and the time of recombination—when stuff began to oscillate.

This desperately needs a definition of energy and energy density. Sure, sure, e = mc^2, but what is all this free energy?

The percentage of energy in dark matter is about 26 percent, in ordinary matter about 5 percent, and in dark energy about 69 percent.

Where does plain, ordinary energy come in? This would say it doesn't exist, which makes me really confused about what the dark energy is.

In other words, dark matter carries five times the energy of ordinary matter, meaning it carries 85 percent of the energy of matter in the Universe.

But, energy of dark energy is still the vast majority... So confusing.

Their observations led to the remarkable conclusion that some unanticipated energy source was accelerating the rate of the Universe’s expansion. Dark energy fits the bill, since its gravitational influence makes the Universe expand at an increasingly rapid rate over time.

I think I might be more interested in the dark energy than the dinosaurs.

A couple of times when I’ve told people that I work on cosmology, they have mistaken me for a cosmetologist, which I find very funny given how poorly suited I would be for this vocation.

Perhaps they didn't mistake her for a good cosmetologist.

the German scientist and explorer Alexander von Humboldt gave a series of lectures, which he wrote up in a treatise titled Kosmos. This treatise influenced many readers, including the writers Emerson, Thoreau, Poe, and Whitman. You might joke that Carl Sagan did the original rebooting of the popular Kosmos series.

I was literally about to make that very same joke. I am figuratively stunned.

I just think something is more likely. After all, nothing is very special. If you have a number line, “zero” is just one infinitesimal point among the infinity of possible numbers you can choose. “Nothing” is so special that without an underlying reason, you wouldn’t expect it to characterize the state of the Universe. But even an underlying reason is something. You at least need physical laws to explain a very nonrandom occurrence.

Meh. There are far more describable concepts that have no objects that match that description than there are objects. For instance: 80 foot tall pink bunnies -- none, nada, zilch.

Scientists and the popular press frequently refer to the Big Bang explosion that happened back when the Universe was less than 10−43 seconds old and the Universe was 10−33 cm big,

Fun fact, if the universe started as a single point and expended outwards, at one point it was the size and the age of a newborn kitten. An incredibly dense and exploding newborn kitten.

Someday soon we might know the answer, and such a discovery would be worth the wait.

I kind of think this entire chapter was a waste of my time. It might be necessary for some readers, I guess, but it provided me with no information, and didn't present the bigger questions in an interesting light.

A rather funny and outspoken Russian theoretical physicist startled everyone over coffee recently when he was describing the colloquium he was planning for the following week.

A priest, a rabbi and a nymphomaniac duck walk into a bar...

But it is space itself that is expanding, meaning that the distances between objects like galaxies increases with time.

So it's not that everything is moving away from each other, but that more space is appearing in between? If the void of space was filled with ping pong balls, would new ping pong balls be being created, or would the existing ping pong balls be stretched and expanded? And, if an object was n light years from us, the light would take n years, plus a bit longer to adjust for the expansion of the universe? And, is this only empty space that expands? Do atoms get slowly bigger, or do the electrons' orbits adjust and slowly everything solid rejiggers itself into keeping their relative positions because of gravity and other attractive forces? Is this smooth, or are there spacequakes?

I am frequently asked, “If the Universe is expanding, what is it expanding into?” The answer is that it is not expanding into anything. Space itself grows.

With my spotty knowledge based on a 12 year watching cosmos 30 years ago, and then not paying enough attention in modern physics in college, I had assumed that the universe was the area with matter and energy, and what lied outside was just empty void and otherwise unknowable since we cannot see that far and there is nothing out there to reflect or emit light anyway.

If you imagine the universe as the surface of a balloon, the balloon itself stretches. (See Figure 4.) If you had marked two points on the balloon’s surface, those two points would grow farther apart, just as galaxies recede from each other in an expanding universe.

Assuming the points are dots drawn with a marker, the dots themselves would grow. Does Dr. Randall mean points in the scientific mathematic sense, or the colloquial sense?