top of page

Astrophysics for People in a Hurry by Neil DeGrasse Tyson

Really good book by Neil DeGrasse Tyson on astrophysics. Sums up a lot of the really interesting and big ideas about the universe in a very simple and easy to read book. I learned a lot and rehashed a lot about the basics of Einstein's theory of relativity, atoms, energy, the speed of light, the expanding universe, Newton's discoveries, the forces of the universe and a lot more. I highly recommend this book to anyone curious about the universe.


In the beginning, nearly 14 billion years ago, all the space and all the matter and all the energy of the known universe was contained in a volume less than 1 trillion the size of the period that ends the sentence.

By now, one second of time has passed. The universe has grown to a few light-years across, about the distance from the sun to its closest neighboring stars.

The one we call Earth formed in a kind of goldilocks zone around the sun, where oceans remain largely in liquid form. Had Earth been much closer to the sun, the oceans would have evaporated. Had Earth been much further away, the oceans would have frozen. And either case, life as we know it would not have you evolved.

People who believe they are ignorant of nothing have neither looked for, nor stumbled upon, the boundary between what is known and unknown in the universe. What we do know, and we can assert without further hesitation, is that the Universe had to beginning. The universe continues to evolve. And yes, every one of our bodies atoms is traceable to the big bang into the thermonuclear furnaces with in high mass stars that exploded more than 5 billion years ago. We are Stardust brought to life, then empowered by the universe to figure itself out - and we have only just begun.

Newton had figured out that the force of gravity pulling ripe apples from their Orchards also guides that tossed objects along their curve tragic toys and directs the moon in its orbit around Earth. Newton's law of gravity also guides planets, asteroids, and come it's in their orbits around the Sun keeps hundreds of billions of stars in orbit with in our Milky Way galaxy.

The universality of physical laws tells us that if we land on another planet with a thriving alien civilization, it will be running on the same laws that we have discovered and tested here on Earth - even if the aliens harbor different social and political beliefs.

Among all constants, the speed of light is the most famous. No matter how fast you go, you will never overtake on a beam of light. Why not? No experiment ever conducted has ever revealed an object of any form reaching the speed of light.

After the laws of physics, everything else is opinion.

Because light takes time to reach us from distant places in the universe, if we look out in deep space we actually see eons back in time.

Ordinary matter is what we are all made of. It is gravity and interacts with light. Dark matter is a mysterious substance that has gravity but does not interact with light in any known way. Dark energy is a mysterious pressure in the vacuum of space that acts in the opposite direction of gravity, force in the universe to expand faster than it otherwise would. What our phrenological exam says is that we understand how the universe behaved, but that most of the universe is made of stuff about which we are clueless.

The latest estimate shows that the observable universe may contain a hundred billion galaxies. Bright and beautiful and packed with stars, galaxies decorate the dark voice of space like cities across a country at night.

Our own spiral-shaped galaxy, The Milky Way, is named for its spilled milk appearance to the unaided eye across Earth's nighttime sky.

The nearest galaxy larger than our own is 2 million light years away, beyond the stars that trace the constellation Andromeda.

Hated by modern detectors, and modern theories, we have problems are cosmic Countryside and revealed all manner of: dwarf galaxies, runaway Stars, runaway stars explode, million degree x-ray emitting gas, Dark Matter, faint blue galaxies, ubiquitous gas clouds, super duper high-energy charged particles, and the Mysterious Quantum vacuum energy.

[The galaxies like the Milky Way that we live in can eat small galaxies. They also collide and leave behind the titanic mess.]

Galaxies are so vast, the travel time for light to reach us can be millions or even billions of years.

Quesars are superluminous galaxy chords whose laid has typically been traveling for billions of years across space before reaching our telescopes.

Where there is mass there is gravity. And where there is gravity there is curved space, according to Einstein's general theory of relativity.

The precisely measured temperature of these microwaves is 2.725 degrees, sometimes written as simply 2.7 degrees, and if you are numerically lazy, nobody will fail you for rounding the temperature of the universe to 3 degrees.

It took the mind of the millennium's most brilliant and influential person, Isaac Newton, to realize that gravity's mysterious action-at-a-distance arises from the natural effects of every bit of matter, and that the attractive force between any two objects can be described by a simple algebraic equation. It took the mind of the last century's most brilliant and influential person, Albert Einstein, to show that we can more accurately describe gravity's action-at-a-distance as a warp in the fabric of space-time, produced by any combination of matter and energy.

Intergalactic space is regular pierced by super duper high energy, fast-moving, charge, subatomic particles. We call them cosmic rays. The highest energy particles among them have a hundred million times the energy that can be generated in the world's largest particle accelerators.

If we could boost Earth's orbital speed to more than the square root of 2 (1.4142) times its current value, our planet would achieve "escape velocity", and leave the solar system entirely. We can apply the same reasoning to much larger systems, such as our own Milky Way galaxy, and which stars move in orbits that respond to the gravity from all the other stars; or in clusters of galaxies, where each galaxy likewise feels the gravity from all the other galaxies.

If all mass has gravity, does all gravity have mass? We don't know

As a wave, light was thought to require a medium through which to propagate its energy, much as sound requires air or some other substitute transmits wave so. But light turns out to be quite happy traveling through the vacuum of space, the void of any medium to carry it. Unlike sound waves, which consists of air vibrations, light waves were found to be self-propagating packets of energy requiring no assistance at

It's not about seeing, it's about measuring, preferably with something that is not your own eyes, which inextricably can join with the baggage of your brain. That baggage is more often than not a satchel of preconceived ideas, post conceived notions, and outright biased.

[The four forces of the universe are] gravity, weak nuclear force, strong nuclear force, and electromagnetism.

[Gravitational] waves, predicted by Einstein, are ripples moving at the speed of light across the fabric of space-time, and are generated by severe gravitational disturbances, such as the Collision of two black holes.

General relativity regards gravity as the response of a mass to the local curvature of space and time caused by some other mass or field of energy. In other words, concentrations of mass cause distortions - dimples, really - in the fabric of space and time.

[Edward Hubble] had found and assembled convincing evidence that the more distant a galaxy, the faster the Galaxy recedes from the Milky Way. In other words, the universe is expanding.

He was the first direct evidence that a repulsive Force permeated the universe, opposing gravity, which is how and why the cosmological constant rose from the dead. Lamb the suddenly acquired a physical reality that need a name, and so "dark energy" took center stage in the cosmic drama, suitably capturing with the mystery and are associated ignorant of its cause.

Dark energy. 68%
Dark matter 27%
Regular matter 5%
All if the matter in the universe 100%

Einstein's greatest blunder was having to declare that Lambda was his greatest blunder.

Dark energy is real.

As a consequence, anything not gravitationally bound to the neighborhood of the Milky Way galaxy recede at ever-increasing speed, as part of the accelerating expansion of the fabric of space-time. Distinct galaxies now visible in the night sky will ultimately disappear on an unreachable horizon, receding from us faster than the speed of light. If he's allowed, not because they are moving through space at such speeds, but because the fabric of the universe itself carries them at such speeds. No law of physics prevents this.

Only three of the naturally occurring elements are manufactured in the Big Bang. The rest were forged in the high temperature hearts and explosive remains of dying stars, enabling subsequent generations of star systems to incorporate this enrichment, forming planets and, in our case, people.

With only one proton in its nucleus, hydrogen is the lightest and simplest element, made entirely during the big bang. Out of the 94 naturally occurring elements, hydrogen lays claim to more than two-thirds of all the atoms in the human body, and more than 90% of all atoms in the cosmos, on all scales, right on down to the solar system.

Helium is the second simplest and second most abundant element in the universe. Although a distant second to hydrogen in abundance, there is four times more of it than all other elements in the universe combined.

The element carbon can be found in more kinds of molecules than the sum of all the kinds of molecules combined. Given the abundance of carbon in the cosmos - forged in the cores of stars, churned up to their surfaces, and released copiously into the galaxy - a better element does not exist on which to base the chemistry and diversity of life. Just edging out carbon in abundance rank, oxygen is common, too, forged and released in the remains of exploding stars. Both oxygen and carbon are major ingredients of life as we know it.

The largest [mountain] on Mars, Olympus Mons, is 65,000 ft tall and nearly 300 miles wide at its base... the cosmic mountain building recipe is simple: the weaker the gravity on the surface of an object, the higher its mountains can reach.

With a head diameter to thickness ratio of 1000 to 1, our galaxy is flatter than the flattest flapjacks ever made. In fact, it's proportions are better represented by a crepe or tortilla.

The sphere to end all spheres - the largest and most perfect of them all - is the entire observable universe. And every direction we look, galaxies recede from us at speeds proportional to their distance. As we saw in the first two chapters, this is the famous signature of an expanding universe, discovered by Edwin Hubble in 1929. When you combine Einstein's relativity and the velocity of light and the expanding universe in the spatial dilution of mass and energy as a consequence of that expansion, there is a distance in every direction from us where the recession velocity for a galaxy equals the speed of light. At this distance and beyond, light from all luminous objects loses all its energy before reaching us. The universe beyond this spherical "edge" is this rendered invisible and, as far as we know, unknowable.

Invisible light; that is to say, of rays coming from the sun, that at such a mental mess to be unfit for vision.

Filling out the entire electromagnetic spectrum, in order of low energy and low frequency to high energy and high-frequency, we have: radio waves, microwaves, infrared, ROYGBIV, ultraviolet, X-rays, and gamma rays.

But in all cases, every bit of information I telescope, comes to Earth on a beam of light.

Most stellar explosions take place in distant galaxies, but if a star were to blow up within the Milky Way, its death throes would be bright enough for everyone to see, even without a telescope.

By spending a couple of years painstakingly tracking and timing the static hiss that registered on his jury-rigged antenna, [Karl] Jansky discovered that radio waves emanate not just from local thunderstorms in other known terrestrial sources, but also from the center of the Milky Way galaxy.

It's not empty, the space between the planets contains all manner of chunky rocks, pebbles, ice balls, dust, streams of charged particles, and far-flung probes. The space is also permeated by monstrous gravitational and magnetic fields.

IO, Jupiter's closest moon, is tidally locked and structurally stressed but interactions with Jupiter and with other moons, pumping enough heat into the little orb to render mountain its interior rocks; IO is the most volcanically active place in the solar system. Jupiter's moon Europa has enough H2O that it's heating mechanism - the same one at work on IO - has melted in the subsurface ice, leaving a warm ocean below. If ever there was a next best place to look for life, it's here.

Newton's Laws specifically state that, while the gravity of a planet gets weaker and weaker the further from it you travel, there is no distant where the force of gravity reaches zero. The planet Jupiter, with its mighty gravitational field, bats out of harms way many comets that would otherwise wreak havoc on the inner solar system. Jupiter acts as a gravitational shield for earth, a burly big brother, allowing long (hundred-million-year) stretches of relative peace and quiet on Earth.

Water covers more than 2/3 of Earth's surface; the Pacific Ocean alone spans nearly an entire side of the planet. Any beings with enough equipment and expertise to detect our planets color would surely infer the presence of water, the third most abundant molecule in the universe.

More bacteria live and work in one centimeter of my calling the number of people who have existed in the world. That kind of information makes you think twice about who - or what - is actually in charge. From then they own, I began to think of people not as the masters of space and time but it's participants in a great Cosmic chain of being, with a direct genetic link across species both living and extinct, extending back nearly four billion years to the earliest single-celled organisms on Earth.

There are more molecules of water in an 8-ounce cup than there are cups of water in all the world's oceans.

Want to know what we are made of? Again, the cosmic perspective offers a bigger answer then you might expect. The chemical elements of the universe are forged in the fires of high mass stars that live their lives in titanic explosions, and reach their host galaxies with a chemical arsenal of life as we know It. The result? The four most common, chemically active elements in the universe - hydrogen, oxygen, carbon, and nitrogen - with carbon serving as the foundation of biochemistry.

bottom of page