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.
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
Does this image look familiar?
It should—these are soap bubbles.
Okay, now you’re probably going to ask me how soap bubbles have anything to do with the battery of the sun.
Well…you might be surprised to know that soap bubbles actually work as models of stars.
How? Continue reading
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
Albert Einstein may have been the genius among physicists, but like all others before his time, he stood on the shoulders of giants.
Einstein did not propose that the sun was the center of the solar system; that idea was already widely accepted when he came around. He didn’t discover elliptical orbits; that distinction belongs with Johannes Kepler.
But Kepler never could figure out why planets orbit the sun in ellipses instead of circles. Even Isaac Newton, who at last identified gravity as the reason we stick to Earth’s surface, couldn’t explain what gravity was—only how it worked.
Einstein provided that explanation with his general theory of relativity. Continue reading
Have you ever been to the beach?
If you’re from California like me, then I’m betting you have. If you’re from a place that’s not near an ocean and you’ve never been near the water all your life, then I’ll tell you a little bit about the tides.
They happen every day, twice a day. If you find yourself a nice comfortable spot overlooking the beach, you can see the waves come into the shore and then gently roll out again. If you stay for hours on end, you’ll see the water level eventually rise a bit.
And if you stay even longer, you’ll see the water level lower back down. When it’s high, it’s called high tide, and when it’s low, it’s called low tide.
The tides are partially responsible for the myth that the moon’s gravity affects you in some kind of metaphysical way. But this isn’t true at all.
So why do the tides happen? Continue reading
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
So, the moon stays in orbit around the Earth, right?
Yeah, I thought so. But why? The moon’s orbit is not a straight line, which means it’s accelerated motion (using the physics definition, which is absolutely any change in speed or direction).
And in order for acceleration to happen, according to Newton’s first law of motion, a force has to happen—meaning, something has to reach out, touch the moon, and drag it into orbit around Earth.
Well, that doesn’t happen, last I checked. I mean, it’s not like we have some kind of giant cord connecting us to the moon. How crazy would that be?
So why does the moon orbit the Earth? Continue reading
It’s said that Sir Isaac Newton was sitting under an apple tree when an apple fell on his head, and that’s when all his discoveries began.
Personally, I doubt that story—just as I doubt that Galileo Galilei ever dropped iron and wooden balls off the Leaning Tower of Pisa. His goal would have been to show that both objects hit the ground at the same time. Unfortunately, wind resistance would have gotten in the way.
Regardless of how Newton discovered gravity, his scientific achievements are monumental. In fact, we recognize him today as one of the greatest scientists to ever live, second only to the famous Albert Einstein.
Newton’s revelation that gravity draws objects toward Earth changed the course of modern science. But what exactly did he find out? Continue reading
Before Galileo’s time, Aristotle was the god of gravity.
Seriously. Before Galileo came along, the question of how gravity worked was answered with another question: “What would Aristotle say?” Obviously, this method was faulty, since Aristotle was actually wrong about most scientific things he wrote about.
But Galileo began a tradition that would persist into the modern day. He’s credited for having performed the first true science experiments when he observed falling objects.
You could, of course, call Tycho Brahe’s night sky observations and Kepler’s correct application of mathematics to the heavens true science, but neither of them really performed experimental science. That distinction lies with Galileo.
Wait a second…so I thought Isaac Newton was the guy who discovered gravity? Continue reading
We have a bit of a shorter post today—I thought precession warranted its own post, before I go on to talking about the ecliptic.
Precession is refers to the way Earth wobbles around on its axis, a bit like a top. This motion is caused by the sun and moon’s gravity tugging on the planet, and is key to understanding how many ancient cultures viewed the sky.
So what is precession, exactly? Continue reading