What is Gravity, Anyway?

Welcome to my second “Science Answers” post! About a month ago, I sent out a post requesting science questions from all of you; you can find it here. This post addresses the second of the questions I was asked. If you have a question, you can ask it in the comments here or on that post, or ask it in an email. Or find me on Facebook!

Q: What is gravity? (asked by Simon)

Wow…great question. This is a question the greatest scientific minds have asked and tried to answer for centuries. It’s a question not even Stephen Hawking, the scientific genius of the century, has fully answered.

There are a few parts to the gravity question, and they have each been addressed one by one over time:

  • How does gravity work?
  • What is gravity?
  • Why does gravity work?

Isaac Newton stood on the shoulders of the giants before him—Aristotle, Ptolemy, Copernicus, and Kepler—and figured out how gravity works. But he was at a loss to explain what exactly this mysterious force was.

Einstein built on Newton’s work and came up with a theory for what gravity is—that is, distortions in space-time.

spacetime

We have yet to understand why gravity works. Why is space-time warped? Why do objects distort it as if it were the material of a trampoline? What exactly is the nature of space?

But, lucky for me, the question above specifically asks what gravity is. And that, I can explain.

The best way to do that is to turn one of gravity’s oldest tricks, one that has perplexed scientists and philosophers for thousands of years: What makes the planets move? Continue reading

Einstein: Space-Time Curvature

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When you hear about “space-time,” it’s just a way to say that space is related to time. And the curvature of space-time, as Albert Einstein predicted, is the way space and time alike literally bend around a mass such as the Earth or the sun.

That’s what’s diagramed above. This is a three-dimensional concept diagram of the way space sort of “clings” to an object. Notice the way it sort of tightens up when you get close to Earth? And because time is part of this whole equation…time sort of tightens up, too.

I assume that explains the “twin paradox,” as it’s called. That’s where the space-traveling twin returns home to Earth younger than their Earth bound twin.

Why? Seems to me it’s because time was tighter and passed faster on Earth, while it spread out and passed a bit slower for the traveler. (Don’t quote me on that, I just guessed that from this diagram.)

Einstein figured all this out. But scientists need evidence. Trusting Einstein’s genius wasn’t enough for them. How did they accept relativity as fact? Continue reading

How Orbits Work

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Since Aristotle’s time over 2000 years ago, we have accepted that the moon orbits the Earth. We didn’t always know why, and we didn’t always accept this for the right reasons.

We used to assume that it happened just because we saw the moon move across the sky, and we believed the Earth to be the center of all motion in the solar system. But even when we realized—in the 1540s CE—that the sun was in fact the center of the solar system, the moon kept its place around the Earth.

And rightfully so. Astronomers now know that the moon orbits the Earth based on scientific observation, rather than the “logical” guesses of Aristotle’s time. And we even know why it orbits—gravity, the one force in all the universe we can’t escape.

But I can tell you, the moon’s orbit isn’t a perfect circle, and if gravity were the only reason it orbited, it would crash straight into the Earth. After all, people stay grounded on Earth’s surface because of gravity, and we don’t orbit our planet, do we?

So how does the moon orbit the Earth? For that matter, how does any satellite? Continue reading

Johannes Kepler and Planetary Motion

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Thales and Pythagoras suggested that the natural world could be understood. Aristotle dared to imagine what was beyond the Earth. Plato encouraged thought about the universe, even if he did take astronomy one step forward and two steps backward.

Copernicus followed in Ptolemy’s wake, devising the revolutionary heliocentric (sun-centric) model of the universe. Tycho Brahe may have (incorrectly) rejected that model, but he did make some of the most detailed night sky observations yet.

What’s more, by Johannes Kepler’s time, Tycho had cast doubt on the idea of uniform circular motion that had plagued astronomy for centuries.

At last, the world was ready for a more mathematical take on a question that had confounded philosophers, mathematicians, and classical astronomers alike: how do the planets truly move through space?

By standing on the shoulders of giants, Johannes Kepler was finally able to devise his three laws of planetary motion, which are still the leading mathematical theory today. Continue reading

The Solar Eclipse

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A solar eclipse is the most amazing astronomical sight you’ll ever see.

Not only is it the only time you’ll ever be able to clearly see the “new moon” phase of the moon, it’s the only time you’ll ever see the sun’s corona. And it’s the only time that, under very specific circumstances, you can actually look directly at the sun for a few moments.

But before you get too excited about that, let me tell you what’s happening in the sky—and give you a few important safety warnings!

(This is just the first of a few posts that will talk about solar eclipses; they’re all worthy of a read. Even if you don’t read all of mine, make absolutely certain you’re caught up on safety warnings before you view a solar eclipse!) Continue reading

Lunar Phases and Motion

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The lunar phases…who really understands ’em?

We see them all the time. When we look up at the moon in the sky, we’re bound to notice that it looks just a little bit different from the last time we saw it. It changes from a slivery crescent to a full circle, and then wanes back to the crescent phase again.

The moon has behaved the same way in the sky for billions of years, ever since a Mars-sized space rock collided with the newborn Earth and the debris collected into our own personal satellite.

For that long, the moon has watched over us and captivated scientists and amateur skywatchers alike.

But what are the secrets behind its monthly changes? Continue reading

Orbit and Climate

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You have probably all heard of ice ages.

v1.bjsxMTYxNDc0O2o7MTc0NzM7MTIwMDsyNTAwOzE1MDA.jpgAnd no, I don’t mean the Ice Age movies…

Although, Ice Age is actually a pretty good example of what happens during a real-life ice age. I haven’t seen enough of the movies to really talk about how accurate they are, but I know there’s a lot of ice.

And a lot of breaking of ice.

These movies take place during a time when much of the northern and southern regions of the Earth were covered in glaciers. The world looked a lot like the satellite image up above. Whether mammoths and smilodons (sabre-toothed cats) actually lived then is another question entirely.

For the record, dinosaurs were definitely not still alive back then. Even deep under the ice. The quote from the third movie basically sums it up:

“I thought those guys were extinct!”

“Then that is one angry fossil…”

Yeah, they were extinct. But fiction can do whatever it wants.

But why do ice ages happen…and why isn’t the world covered in glaciers now? Continue reading