Alexis Rondeau

Pale Blue Dot: A Vision of the Human Future in Space

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Cover of Pale Blue Dot: A Vision of the Human Future in Space
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Carl Sagan and Ann Druyan

145 highlights · 39 notes · last read March 2025

Highlights I wrote a note on are shown in full. The other 106 are scrambled: the words are the author's, so here you only see where in the book I underlined something.

In general relativity, gravity is due to the dimensionality and curvature of space. When we talk about gravity we are talking about local dimples in space-time.

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My note eli5: Dimples in spac-time

In the froth of quantum bubbles, the vast majority remain submicroscopic. But a tiny fraction inflate, grow, and achieve respectable universehood.

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My note eli5: frothy bubbles. Some grow to respectable universes

But if our objective is deep knowledge rather than shallow reassurance, the gains from this new perspective far outweigh the losses. Once we overcome our fear of being tiny, we find ourselves on the threshold of a vast and awesome Universe that utterly dwarfs—in time, in space, and in potential—the tidy anthropocentric proscenium of our ancestors.

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My note Overcoming the fear of being tiny

These debates have bread-and-butter consequences.

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My note Bread-and-butter consequence

In everyday life, we often sense—in the bedrooms of teenagers, or in national politics—that chaos is natural, and order imposed from above.

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My note The bedrooms of teenagers

The significance of our lives and our fragile planet is then determined only by our own wisdom and courage. We are the custodians of life’s meaning. We long for a Parent to care for us, to forgive us our errors, to save us from our childish mistakes. But knowledge is preferable to ignorance. Better by far to embrace the hard truth than a reassuring fable. If we crave some cosmic purpose, then let us find ourselves a worthy goal.

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My note It is WE who can create meaning and purpose

Missions to the planets are one of those things—and I mean this not just for the United States, but for the human species—that we do best.

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My note We are great at discovery

She or he must have lived tens, perhaps even hundreds of thousands of years ago. But eventually people all over the world understood that five, no more, of the bright points of light that grace the night sky break lockstep with the others over a period of months, moving strangely—almost as if they had minds of their own.

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My note Only five "stars" are actually planets

In English, Saturday is Saturn’s day. Sunday and Mo[o]nday are clear enough. Tuesday through Friday are named after the gods of the Saxon and kindred Teutonic invaders of Celtic/Roman Britain: Wednesday, for example, is Odin’s (or Wodin’s) day, which would be more apparent if we pronounced it as it’s spelled, “Wedn’s Day”; Thursday is Thor’s day; Friday is the day of Freya, goddess of love. The last day of the week stayed Roman, the rest of it became German.

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My note Intentionally left out Tuesday as an exercise for the reader (?)

A dozen humans, all Americans, have made those odd bounding motions they called “moonwalks” on the crunchy, cratered, ancient gray lava—beginning

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My note Walking on the moon is crunchy

FLOOD: I am for giving it to them as of this minute, Mr. Chairman, with our supplemental, without waiting for somebody downtown to make up his mind to ask for it. If this man means what he says and if he knows what he is talking about—and I think he does—then this committee should not wait five minutes more today. We should give him all the money and all the hardware and all the people he wants, regardless of what anybody else says or wants, and tell him to go up on top of some hill and do it without any question.

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My note I believe in this man

But more important than any of this, Apollo provided an aegis, an umbrella under which brilliantly engineered robot spacecraft were dispatched throughout the Solar System, making that preliminary reconnaissance of dozens of worlds.

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My note An aegis a space for big moves and questions

The Apollo astronauts on their way to and from the Moon photographed their home planet. It was a natural thing to do, but it had consequences that few foresaw. For the first time, the inhabitants of Earth could see their world from above—the whole Earth, the Earth in color, the Earth as an exquisite spinning white and blue ball set against the vast darkness of space. Those images helped awaken our slumbering planetary consciousness.

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My note Whole earth perspective is planetary consciousness

When you view the Earth from farther away, as the Apollo astronauts did, it shrinks in apparent size, until nothing but a little geography remains. You’re struck by how self-contained it is. An occasional hydrogen atom leaves; a pitter-patter of cometary dust arrives. Sunlight, generated in the immense, silent thermonuclear engine deep in the solar interior, pours out of the Sun in all directions, and the Earth intercepts enough of it to provide a little illumination and enough heat for our modest purposes. Apart from that, this small world is on its own.

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My note Earth is pretty much on its own

You can understand why there is no longer such a thing as a local environmental problem. Molecules are stupid. Industrial poisons, greenhouse gases, and substances that attack the protective ozone layer, because of their abysmal ignorance, do not respect borders. They are oblivious of the notion of national sovereignty.

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My note Molecules are stupid. There are no borders on earth

You spend even a little time contemplating the Earth from orbit and the most deeply engrained nationalisms begin to erode. They seem the squabbles of mites on a plum.

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My note Mites on a plum

a physicist whose knowledge of gravity is restricted to falling bodies on Earth—our perspective is foreshortened, our insights narrow, our predictive abilities circumscribed.

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My note Focus narrows insight

By contrast, when we explore other worlds, what once seemed the only way a planet could be turns out to be somewhere in the middle range of a vast spectrum of possibilities.

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My note Exploration broadens imagination

When we look at those other worlds, we begin to understand what happens when we have too much of one thing or too little of another. We learn how a planet can go wrong. We gain a new understanding, foreseen by the spaceflight pioneer Robert Goddard, called comparative planetology.

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My note Comparative Planetology

because all life on Earth is built on a common biochemical master plan. The discovery of a single extraterrestrial organism—even something as humble as a bacterium—would revolutionize our understanding of living things.

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My note Aliens could be bacteria

Who discovered that CFCs posed a threat to the ozone layer? Was it the principal manufacturer, the DuPont Corporation, exercising corporate responsibility? Was it the Environmental Protection Agency protecting us? Was it the Department of Defense defending us?

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My note Who discovered the danger of fckw

No, it was two ivory-tower, white-coated university scientists working on something else—Sherwood Rowland and Mario Molina of the University of California, Irvine. Not even an Ivy League university. No one instructed them to look for dangers to the environment. They were pursuing fundamental research. They were scientists following their own interests. Their names should be known to every schoolchild.

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My note Two white-coat scientists saved the ozone layer

Because they were working on the chlorine and fluorine chemistry of the atmosphere of Venus. Venus helped make and helped confirm the discovery that the Earth’s ozone layer is in danger. An entirely unexpected connection was found between the atmospheric photochemistries of the two planets.

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My note Looking at venus helped discover a fatal flaw on earth

Thus part of the reason the topmost layers of Martian soil are antiseptic is that Mars has an ozone hole of planetary dimensions—by itself a useful cautionary tale for us, who are busily thinning and puncturing our ozone layer.

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My note Mars shows us the worst-case scenario of not having an ozone layer. It kills organic matter

(2) Global warming is predicted to follow from the increasing greenhouse effect caused largely by carbon dioxide generated in the burning of fossil fuels—but also from the buildup of other infrared-absorbing gases (oxides of nitrogen, methane, those same CFCs, and other molecules).

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My note Origins of global warming

One way to test this program is to apply it to the very different climates of other planets. Can it predict the structure of the atmosphere on Mars and the climate there? The weather? What about Venus? If it were to fail these test cases, we would be right in mistrusting it when it makes predictions for our own planet. In fact, climate models now in use do very well in predicting from first principles of physics the climates on Venus and Mars.

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My note Verifying weather models for earth by using mars and venus

Some of the most important recent work on global warming has been done by James Hansen and his colleagues at the Goddard Institute for Space Sciences, a NASA facility in New York City.

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My note James Hansen, Goddard Institute New York

Hansen collected a wide range of weather data from this century and last, to see what actually happened to the global temperature, and then compared it to the computer model’s predictions of what should have happened.

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My note Using real data outcomes and compare it to the prediction of the model. Thats like training a neural network

How did Hansen get interested in the greenhouse effect in the first place? His doctoral thesis (at the University of Iowa in 1967) was about Venus.

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My note Hansens impact on climate change started with looking at venus

greenhouse effect. Radio astronomers, you note, find Venus to be an intense source of radio waves. Other explanations of the radio emission fail. You conclude that the surface must be ridiculously hot. You try to understand where the high temperatures come from and are led inexorably to one or another kind of greenhouse effect. Decades later you find that this training has prepared you to understand and help predict an unexpected threat to our global civilization.

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My note First you notice weird radio noise. Then you check venus temperature and finlly arrive back on earth with a red flag

The other planets are a superb training ground for students of the Earth. They require both breadth and depth of knowledge, and they challenge the imagination.

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My note Other worlds provide training and playground to better understand whats going on on earth

The implications for our planetary civilization—especially through the collapse of agriculture—are very dire. It is a consequence of nuclear war that was somehow overlooked by the civil and military authorities of the United States, the Soviet Union, Britain, France, and China when they decided to accumulate well over 60,000 nuclear weapons.

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My note Nuclear war wasnt considered by the nations when building 60.000 bombs

The earliest intimation of nuclear winter came during that same Mariner 9 mission to Mars, when there was a global dust storm and we were unable to see the surface of the planet;

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My note A mission to mars gave an inkling to what a nuclear winter could be

PLANETARY SCIENCE fosters a broad interdisciplinary point of view that proves enormously helpful in discovering and attempting to defuse these looming environmental catastrophes. When you cut your teeth on other worlds, you gain a perspective about the fragility of planetary environments and about what other, quite different, environments are possible. There may well be potential global catastrophes still to be uncovered. If there are, I bet planetary scientists will play a central role in understanding them.

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My note Planetary science helps us on earth

Of all the fields of mathematics, technology, and science, the one with the greatest international cooperation (as determined by how often the co-authors of research papers hail from two or more countries) is the field called “Earth and space sciences.” Studying this world and others, by its very nature, tends to be non-local, non-nationalist, non-chauvinist. Very rarely do people go into these fields because they are internationalists.

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My note Earth and Space Sciences has the most diverse group of people co-create

And once you experience such cooperation—humans from different parts of the planet working in a mutually intelligible scientific language as partners on matters of common concern—it’s hard not to imagine it happening on other, nonscientific matters.

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My note Experience togetherness

When I look at the evidence, it seems to me that planetary exploration is of the most practical and urgent utility for us here on Earth.

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My note Planetary Exploration is super-duper useful for us

The use of robot construction crews under radio command from Earth is said to reduce the cost tenfold.

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My note Human vs Robot cost

The cost of sending a kilogram of something no farther away than low Earth orbit is today about the same as the cost of a kilogram of gold.

Page 205

My note The cost of 1kg cargo into space equals 1kg gold

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