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Did an apple really fall on Isaac Newton's head? Is there gravity on the ISS? Did Schrödinger, uhh... murder a cat?

Physics is all around us, and yet, most of us hardly understand it. Today, we're going to answer some burning questions, all the way from electrons to atomic bombs.

Host Justin Dodd (@juddtoday) breaks down some common myths and misconceptions about the world of physics.

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When you see those cool images of astronauts  floating on the International Space Station, you might think they’re enjoying the benefits of  gravity disappearing in outer space.

But there is gravity in space. It’s the force holding the  moon in its orbit around Earth, for one thing.

But even if you knew that gravity is exerting  some force on astronauts, you might not have realized that scientists orbiting earth  are actually free-falling through space. Hi, I’m Justin Dodd. Today, we’re breaking down  misconceptions about physics, from how electrons move to whether or not Isaac Newton ever actually got  bonked in the head by an apple like some kind of big old doofus-genius.

Let’s get started. If there’s gravity in space, how come astronauts  fly around inside the International Space Station like it’s a game of Pong? And is it still true  that you can’t eat sandwiches in space because the crumbs would float into the machinery?

The amount of gravity keeping the universe together is actually pretty small. It’s enough to harness  massive celestial bodies in their orbits, but it’s much less than what we recognize on our  own planet. In the ISS, which is not so far from our planet, relatively speaking, the force of  gravity is about 90 percent of what it is on Earth’s surface.

So if you’re looking to lose 10  or 20 pounds, have I got a destination for you! It's right here. In my arms.

You're perfect just the way you are. Astronauts there appear to float not because  there’s less gravity; it’s because they’re actually free-falling, meaning that their motion  is caused only by gravity and no other force. As Galileo figured out (more on him later), in the  vacuum of space, all objects fall at the same rate of acceleration, regardless of their mass.

But the  ISS doesn’t come crashing to the ground because, while it’s falling towards Earth, it’s moving  horizontally nearly five miles every second. The Earth is curving away from the orbiting  space station, meaning it can’t hit the ground. And since both the ISS and the people in it  are falling at the same speed, they float!

Even crumbs from a hypothetical sandwich would be  falling at the same rate as a computer weighing hundreds of pounds, and each would appear  weightless. Special shoutout to YouTube commenter Mark McCombs for mentioning that fact about the  ISS on our misconceptions video about dogs. We have an upcoming episode discussing misconceptions  about prison.

If you know any interesting myths about that topic, you know what to do. You know the famous tale: the physicist Isaac Newton was sitting under a tree minding  his own business when an apple fell on his head. Newton immediately realized there must be  some cosmic force that makes an apple fall straight down to the earth, and possibly a more  metaphysical entity that had damned him to a life of fruit misfortune.

Right then and  there, he devised the theory of gravity. However, like George Washington chopping down  a cherry tree and being unable to lie about it, Newton’s story is something of a  myth. So what really happened?

After his university closed in 1665 due to a  plague outbreak, Newton returned to his rural hometown of Woolsthorpe, England. Moving home  after a deadly pandemic? Who could relate.

After a long day of doing math problems, he liked  to stretch out under the family’s apple tree. According to his biographer William Stukeley,  that is where the eureka moment occurred—but it didn’t involve getting bonked on the head. Newton himself told Stukeley what had gone down when they had dinner together on April 15, 1726.

Newton was then the world’s leading physicist and the president of the Royal Society. After the  meal, Stukeley wrote in his notes, “the weather being warm, we went into the garden and drank  [tea], under the shade of some apple trees … he told me he was just in the same situation, as  when formerly, the notion of gravitation came into his mind. It was occasion’d by the fall of  an apple, as he sat in a contemplative mood.” Newton had wondered to himself why the apple would  always fall perpendicularly to the ground, and not drift sideways or upward, or float on the breeze.

He thought there must be an invisible force or forces that not only put the apple in motion,  but also governed its trajectory and speed. The apple tree episode was just the start of his  experiments and calculations toward solving this puzzle. In the following two decades, he worked on  the problem while also serving as a professor of mathematics at Trinity College, Cambridge.

In that  time, he improved the reflecting telescope, which concentrates light to allow greater visibility of  far-away objects, and then presented his research in optics to the Royal Society. He also sent a  preliminary paper on motion to the astronomer Edmond Halley (of comet fame), who had proposed  that comets do not travel in straight lines but in elliptical orbits around a focal point. I would’ve  told Newton to stop making everyone else look lazy, but Halley encouraged Newton to consolidate  his theories of force and motion into a book.

The result, titled The Mathematical Principles  of Natural Philosophy, broke science when it was published in 1687. Newton laid out his three  laws of motion, which describe inertia, momentum, and actions and reactions, as well as his theory  of universal gravitation. Newton posited that inertia would make the moon fly out of its  orbit around Earth in a straight line unless Earth exerted a force on it, keeping it  in its elliptical path.

Long story short, Newton concluded that Earth’s force on the moon is  the same force that pulls apples off a tree—which we now know as gravity. But the whole bonking thing… that's probably just a modern addition to make kids giggle in science class. You probably remember a diagram from your high school physics or chemistry class.

It shows  electrons traveling around the nucleus of an atom, kind of like a planet travels around  the sun. The little ellipses make it look like a train track that the electron rides. But that’s not really an accurate representation of how electrons move.

There might not even be a  way to accurately represent how electrons move. In 1913, the Danish physicist Niels Bohr  published his model of an atom’s structure. It had positively charged protons and non-charged  neutrons held together in the atom’s nucleus, plus negatively charged electrons circling the  nucleus in concentric orbits, called shells.

When an electron hopped from an interior, lower  energy shell to an outer, higher energy shell, it absorbed a finite amount of energy; when  the move was reversed, the electron gave off a specific amount of energy. This is the  model you probably remember from high school. It’s also called the planetary model, because it  mimics the movements of planets around the sun.

The problem is, the developers of quantum physics  eventually realized that electrons don’t exist in this straightforward way. Remember:  when you get to a small enough scale, things start to behave a lot differently than  the way we’re used to thinking about objects in the human-sized physical world. Electrons are quantum objects, meaning they have a dual nature and can act like  either a particle or a wave.

They’re not solid, discrete objects. Instead of moving in neat  circles, electrons linger around the nucleus as waves, called orbitals, that vibrate at different  frequencies. They don’t have defined trajectories or positions at all.

Heisenberg’s Uncertainty  Principle tells us that we can’t simultaneously define their position and speed—just forget about  trying to make a date for coffee with an electron.   ....speaking from personal experience. Rather than putting an electron at a specific  place in a diagram, like a city on a map, it’s more accurate to think of a range of probabilities  where an electron could theoretically be. To make matters even more complicated, believe it or not, there’s an  exception to this indeterminate behavior.

These probabilistic, cloud-like orbitals can glom  together into things called “wave packets.” And according to a study from 2004, the packets  can orbit the nucleus in a way that is actually not dissimilar to the high school textbook  diagram. Now, at this point, we’re getting into physics that are honestly way above my pay grade. Let’s just leave it at this: If your conception of individual electrons has them zooming around  in a nice little ellipse, you should know that’s not quite right.

The actual representation… my  brain hurts, just trust me on this one okay? It’s like a scene out of a movie—a movie about  experimental physics, which are disappointingly lacking in modern Hollywood. Galileo climbs  to the top of the Leaning Tower of Pisa and drops two spheres of different weights to test the  belief the heavier one will hit the ground first.

Shockingly, the spheres land at the same time. The reason? The heavier ball has a greater mass, and because of that, gravity acts on it more  forcefully.

But thanks to inertia the heavier ball needs more force to get it to accelerate. And  weirdly those two effects cancel each other out. Therefore, two objects of different masses  will fall at the same speed in a vacuum.

But thankfully for us and annoyingly for  physics we don’t live in a vacuum, so we need to look at a third force—air resistance. Let’s say Galileo drops a big piece of plywood and a brick out the window. Rude.

But, ya know,  I guess in the name of science. The plywood has more mass and therefore more gravitational  force than the brick, but as both fall, the wood’s shape experiences more air resistance,  so the brick should hit the ground first. But getting back to the spheres …  Galileo heaving them off the tower probably didn’t happen.

The legend can be traced  to a biography of the scientist written by his secretary and disciple Vincenzo Viviani, who,  uh, embellished a few things. In addition to the tower story, Viviani attributes Galileo’s  discovery of the principles of pendulum motion to his observation of a swinging lamp in Pisa  Cathedral, which also likely didn’t happen. Those poetic origin stories proved popular; the fanciful  details were repeated by Galileo’s followers.

These falling-body experiments didn’t end with  Galileo, though. They became popular public scientific displays where non-scientists could  see marvelous demonstrations of physical laws, none more memorable than astronaut David Scott  reenacting Galileo’s theory on the moon. During the Apollo 15 mission in 1971, Scott set himself  up in front of a TV camera on the lunar terrain.

He held a hammer in his right hand and a falcon  feather in his left. As the camera zoomed out, Scott dropped both objects at the same time, and  both fell to the moon’s surface at the same time in the near-vacuum of space—despite  their different masses and shapes. The moon is no leaning tower  of Pisa but ,you know it’ll do.

In classical physics, predating  Schrodinger and his contemporaries,   'particles' and 'waves' were thought of as two  distinct categories of atomic existence. Particles could be identified in space and time; they had  qualities like mass and volume. No two particles could be in the same place at the same time.

Waves, on the other hand, could be spread out in space, like sound waves being heard  by different people in different places. The physics that replaced this classical model  recognized that reality is much more complex. In a nutshell, quantum mechanics analyzes  how matter behaves on the atomic and even subatomic levels.

It describes the actions and  qualities of atoms and subatomic particles, such as protons, neutrons, and electrons,  as they interact with things like electromagnetic radiation. This model holds  that any particle can behave as a wave, and vice versa. Schrödinger’s equation recognized  this duality of atomic bits of matter—and in an important breakthrough, it demonstrated  the quantum behavior of wave functions.

That is, in order to describe waves, the most accurate  mathematical model can only show the probability of certain events happening, not the kind of  fixed information we're used to analyzing in the larger physical world. If a quantum system  is not observed or measured, Schrodinger claimed, then it does not have definable properties. You may not be surprised to hear that discoveries about atomic behavior following Schrödinger’s  equation struck scientists as kind of illogical.

The theories might be correct on the atomic level,  but in the normal world, they make no sense. Even Schrödinger himself was annoyed by this  paradox. In 1935, he proposed a hypothetical situation to illustrate its absurdity.

A cat  is locked in a steel box with a “tiny bit of radioactive substance.” Over the course of an  hour, if the substance decays, it will trigger the release of a poison that will kill the cat. If  the substance does not decay, the cat will live. Both scenarios are equally probable.

But,  Schrödinger wrote, one will not know if the cat is alive or dead without opening the box and  looking inside, thereby observing the whole system and defining its properties as either living or  dead. Until the box is opened, the cat is both. The hypothetical experiment showed how the laws of  quantum physics don’t always line up with reality, and physicists still debate the nature of  the quantum world compared to the world experienced at the scale we’re familiar with.

Schrödinger was not advocating that anyone actually try this experiment, and fortunately, no  one has. But why a cat? His reasons for choosing a cat for this exercise, and not a dog or hamster,  are not clear.

But he did grow up with an aunt who owned as many as 20 Angora cats, so there’s that. 1905 was a banner year for Albert Einstein. The German theoretical physicist had earned his doctorate and published four major papers in  a German research journal. Though each one described a revolutionary new approach  to understanding aspects of the universe, the final paper demonstrated the equivalence  of mass and energy and summed up the complex theory in the iconic equation, E=mc2.

Unfortunately, Einstein’s discovery had an unintended effect. It spurred European  research into using the equivalence of energy and mass to develop atomic weapons. In 1939, German chemists Otto Hahn and Fritz Strassman (with Austrian physicist Lise Meitner)  announced they had achieved nuclear fission.

Soon after, Einstein was contacted by the  Hungarian physicists Leo Szilard, Eugene Wigner, and Edward Teller. Szilard expressed their  concern that German forces could potentially seize Belgium’s supply of uranium, which it mined in  its African colonies, for atomic weapons. Knowing that Einstein was friendly with the Belgian Queen,  Sziliard wanted him to sign off on a letter asking Belgium to stop selling uranium to Germany and  give it to the United States.

Einstein suggested sending it to a cabinet minister instead, and  that was that. It was quickly realized that a letter should be sent to Roosevelt about  the threat, which Einstein also signed. An envoy hand-delivered the letter to President  Franklin Roosevelt and even read it out loud to make sure the commander-in-chief understood  the precipice on which humanity stood.

The signature of Einstein, the world’s  most famous scientist, undoubtedly helped convey the importance of the matter. Roosevelt approved the research and the funding to launch what was essentially the  predecessor of the Manhattan Project. Years later, Los Alamos National Laboratory director J.

Robert  Oppenheimer led a team of scientists, including physicist Enrico Fermi and nuclear chemist Glenn  Seaborg, with oversight from the U. S. Army.

Einstein never worked on the Manhattan Project  and was denied a security clearance because of his pacifist stance. The project eventually developed  and tested the world’s first nuclear weapons. The only two atomic bombs ever deployed in warfare  landed on Hiroshima and Nagasaki, Japan, in 1945.

By then, Szilard was writing petitions AGAINST  using America’s nuclear weapons. Ironically, the Axis Powers never got close to mastering  the technology for their own nuclear weapons. Einstein regretted his role, however small or  large, in promoting nuclear development.

As he said, “Had I known that the Germans would  not succeed in developing an atomic bomb, I would have done nothing for the bomb.” Thanks for watching Misconceptions. Physics is a bit confusing for my worm brain, but at least it’s something I can blame whenever I drop my phone and crack the screen for the 11th  time. I’ll see you next time.

Damnit physics.