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Astrophysics for People in a Hurry

Updated: May 21, 2018

“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 a beginning. The universe continues to evolve. And yes, every one of our bodies’ atoms is traceable to the big bang into the thermonuclear furnaces within 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.”

-Neil deGrasse Tyson

Neil deGrasse Tyson does another fabulous job of making such a difficult subject easy to understand in his new book Astrophysics for People in a Hurry. He discusses some of the most interesting ideas in physics such as gravity, black holes, atoms, extraterrestrial life, space, the sun, moons, light, the big bang and so much more.

Take the quote that I started this post with. Just in those couple of sentences we learn that we are made of atoms and those atoms that we are made of came from stars that exploded more than 5 billion years ago. And what are atoms? Atoms are tiny particles that make up elements, and elements are matter made up of only one kind of atom.

“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.”

Two of those naturally occurring elements manufactured in the big bang were hydrogen and helium with hydrogen being the lightest element on the periodic table.

“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 lightest element and the second most abundant in the universe.

“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.”

Carbon, which wasn’t created in the big bang, was created later on from exploding stars. Carbon is an important substance because it is the base of the diversity of life. Animals aren’t made of gold (AU), iron (FE), titanium (TI), or aluminum (AL). They are made of carbon.

“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 big bang is one of the most popular theories discussed in astrophysics because it theorizes how the universe began. It is how the universe went from nothing to a complex world of galaxies full of planets, stars, atoms, many different gases and so much more that didn’t exist before.

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

Then as split seconds passed, this incredibly tiny world that we live in today expanded even more until it reached a few light years across.

“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.”

Then as more seconds passed, planets and galaxies were formed - including the planet we are most familiar with of them all: Earth.

“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 evolved.”

And the universe continues to expand even more today. That’s right. The world continues to expand right now as you are reading these lines and it was Edward Hubble who discovered this.

Since the universe is expanding that means all of the other galaxies are receding away from Earth. To understand this, think of a balloon that you just took out of a brand new bag. Draw a bunch of dots on this balloon and then slowly blow the balloon up. As you puff air into the balloon to blow it up, the balloon gets bigger and those dots move further and further away from each other. This is a simple thought experiment to understand the expansion in the universe that occurs today.

“[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.”
“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.”

And this understanding that the universe is expanding through time is what led to the discovery of the beginning of the universe also known as the big bang. If the universe is expanding then it had to have been smaller at some point in time.

There are 3 scenarios of an expanding universe:  1. It continues to expand forever 2. It continues to expand forever but then the expansion rate slows down 3. It continues to expand but then stops and starts to collapse

In all scenarios above, the rate at which the universe is expanding at will slow down because of gravity. Gravity as we all know is a very powerful force. It is one of the four forces of the universe. The other 3 are weak nuclear force, strong nuclear force, and electromagnetism.

It’s a very strong force here on Earth and it is what keeps us humans on the ground instead of floating into outer space. It is also what keeps the Earth from floating out of its orbit around the sun and what keeps our galaxy, the Milky Way, from floating away also.

“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, in 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.”

Gravity is not only strong but it is very attractive also. Every object in the universe attracts every other object. It also gives some needed assistance along with another plant in our system to Earth as you see from the following quote.

“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 harm’s 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.”

Physicists do a lot of hard work observing and studying the universe. They use many complex and powerful instruments such as telescopes and particle accelerators. A particle accelerator is a machine that propels charged particles to almost light speed by using electromagnetic fields and telescopes are used to see far, far away in outer space. Telescopes have become so advanced these days that they can see billions of light years away. The farthest that the Hubble telescope has seen was about 10–15 billion light years away.

And the most interesting part about viewing the universe through a telescope is that whatever object you are looking at during that moment in time, isn’t what that object looks like right at that second. Your’re looking at that object as it appears in the past because it takes time for the light from that object to travel the distance to reach your eyeballs.

Since it takes time for light to travel through space, if you are viewing an object that is a little bit more than 670,000,000 miles away then you are seeing that object through your telescope as it appeared one hour ago. This is because the speed that light travels at is a little bit more than 670,000,000 miles per hour.

“Galaxes are so vast [that] the travel time for light to reach us can be millions or even billions of years.”
“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”

And all of the information delivered through a telescope is delivered to the viewer on a beam of light which nothing in the universe can travel faster than.

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

Another really interesting part about physics — unlike language, politics, culture — is that the same rules apply for physics for all other countries in the world. The laws of physics aren’t any different from where I am located in New York than they are for anyone located in Asia or Europe.

When the Egyptians built the pyramids they may have had an entirely different language, political system, and culture than any civilization alive today, but their laws of physics were the same as they are today. Gravity didn’t work any different back then than it does today.

And this goes for not only civilizations on Earth, but also civilizations on other planets as well. If an alien civilization were to be discovered on another planet tomorrow then they would be operating under the same exact laws of physics that we operate with here on Earth.

It’s a really interesting idea and very hard to imagine at first as you think about how different the rest of the universe is from here on Earth.

“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.”
“After the laws of physics, everything else is opinion.”
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