Paul Dirac, who predicted the existence of antiparticles (Image: Nobel Foundation)
In 1928, British physicist Paul Dirac wrote down an equation that combined quantum theory and special relativity to describe the behaviour of an electron moving at a relativistic speed. The equation – which won Dirac the Nobel Prize in 1933 – posed a problem: just as the equation x2 = 4 can have two possible solutions (x = 2 or x = −2), so Dirac's equation could have two solutions, one for an electron with positive energy, and one for an electron with negative energy. But classical physics (and common sense) dictated that the energy of a particle must always be a positive number.
Dirac interpreted the equation to mean that for every particle there exists a corresponding antiparticle, exactly matching the particle but with opposite charge. For example, for the electron there should be an “antielectron”, or “positron”, identical in every way but with a positive electric charge. The insight opened the possibility of entire galaxies and universes made of antimatter.
But when matter and antimatter come into contact, they annihilate – disappearing in a flash of energy. The Big Bang should have created equal amounts of matter and antimatter. So why is there far more matter than antimatter in the universe?
At CERN, physicists make antimatter to study in experiments. The starting point is the Antiproton Decelerator, which slows down antiprotons so that physicists can investigate their properties.
Amazon.com: What Einstein Told His Barber: More Scientific Answers to Everyday Questions eBook: Wolke, Robert: Kindle Store
Praise for Robert L. Wolke's What Einstein Didn't Know:”Wolke is a glib and entertaining writer….This is the book for anyone who claims to be overwhelmed by the science of everyday things….It's a fun read.”
- —The San Diego Tribune
- —Baton Rouge Advocate
- From the Trade Paperback edition.
“Fascinating….Will provide hours of fun and knowledge for kids of any age (and we mean up to 90) and offer helpful tips and satisfy the curiosity of the average householder.” ce cubes cloudy? How do shark attacks make airplanes safer? Can a person traveling in a car at the speed of sound still hear the radio? Moreover, would they want to…
Do you often find yourself pondering life's little conundrums? Have you ever wondered why the ocean is blue? Or why birds don't get electrocuted when perching on high-voltage power lines? Robert L.
Wolke, professor emeritus of chemistry at the University of Pittsburgh and acclaimed author of What Einstein Didn't Know, understands the need to…well, understand.
Now he provides more amusing explanations of such everyday phenomena as gravity (If you're in a falling elevator, will jumping at the last instant save your life?) and acoustics (Why does a whip make such a loud cracking noise?), along with amazing facts, belly-up-to-the-bar bets, and mind-blowing reality bites all with his trademark wit and wisdom.
If you shoot a bullet into the air, can it kill somebody when it comes down?
Do you often find yourself pondering life's little conundrums? Have you ever wondered why the ocean is blue? Or why birds don't get electrocuted when perching on high-voltage power lines? Robert L. Wolke, professor emeritus of chemistry at the University of Pittsburgh and acclaimed author of What Einstein Didn't Know, understands the need to … well, understand. Now he provides more amusing explanations of such everyday phenomena as gravity (If you're in a falling elevator, will jumping at the last instant save your life?) and acoustics (Why does a whip make such a loud cracking noise?), along with amazing facts, belly-up-to-the-bar bets, and mind-blowing reality bites all with his trademark wit and wisdom.
If you shoot a bullet into the air, can it kill somebody when it comes down?
You can find out about all this and more in an astonishing compendium of the proverbial mind-boggling mysteries of the physical world we inhabit.
Movin' and Shakin'Everything is moving.You may be sitting quietly in your armchair, but you are far from motionless. I don't mean merely that your heart is beating, your blood is coursing through your veins and you are panting at the prospect of learning so many fascinating things from this book. In short, I don't mean simply that you are physically and mentally alive.I mean that while you are sitting there so peacefully, Earth beneath your feet is spinning you around at about 1,000 miles per hour (1,600 kilometers per hour). (The exact speed depends on where you live; see p. 119). Mother Earth is simultaneously hauling you around the sun at 66,600 miles per hour (107,000 kilometers per hour). Not to mention the fact that the solar system and all the stars and galaxies in the universe are racing madly away from one another in all directions at incredible speeds.Okay, you knew all that. Except maybe for the exact speeds. But we're still not done.You are made of molecules. (Yes, even you.) And all your molecules are vibrating and jiggling around to beat the band, assuming that your body temperature is somewhere above absolute zero (see p. 82). In motion also are many of the atoms of which your molecules are made, and the electrons of which the atoms are made, and the electrons, atoms and molecules of everything else in the universe. They were all set into motion about 12 billion years ago (see p. 175) and have been quivering ever since.So what is motion? In this chapter we'll see how everything from horses to speeding automobiles, sound waves, bullets, airplanes and orbiting satellites move from one place to another.
Horsing Around on the Highway
Why do they drive on the left in some countries and on the right in others?It goes back to the fact that most humans are right-handed.Long before we had modern weapons such as guns and automobiles, people had to do battle using swords and horses. Now if you are right-handed, you wear your sword on the left, so that you can draw it out rapidly with your right hand. But with that long, dangling scabbard encumbering your left side, the only way you can mount a horse is by throwing your free right leg over him. And unless you are in a Mel Brooks movie and want to wind up sitting backward on your steed, that means that the horse's head has to be pointing to your left. To this day we still train horses to be saddled and mounted from their left sides.Now that you are mounted, you will want to stay on the left side as you start down the road, because anyone coming toward you will be on your right, and if that someone turns out to be an enemy, you can whip out your sword with your right hand and be in position to run the scoundrel through. Thus, prudent horsemen have always ridden on the left side of the road.This left-side convention was also honored by horse-drawn carriages in order to avoid annoying collisions with horsemen. When horseless carriages made their appearance, some countries continued the habit, especially during the overlap period when both kinds of carriages were competing for road space.So why do people drive on the right in the U.S. and many other countries?When swords went the way of bows and arrows, the need for defending one's right flank disappeared and traffic rules were suddenly up for grabs. Younger or less tradition-bound countries migrated to the right, apparently because the right-handed majority feels more comfortable hugging the right side of the road. It quickly occurred to left-handed people that it was unhealthy to argue with them.Some countries that I've been in must have large populations of ambidextrous people, because they seem to prefer the middle of the road.
Why do highway and freeway intersections have to be so complicated, with all those loops and ramps?They enhance the traffic flow–from construction companies to politicians' campaign chests.Sorry.They allow us to make left turns without getting killed by oncoming traffic. It's a matter of simple geometry.When freeways and superhighways began to be built, engineers had to figure out how to allow traffic to make turns from one highway to an intersecting one without stopping for red lights. Because we drive on the right-hand side of the road in the U.S., right turns are no problem; you just veer off onto an exit ramp. But a left turn involves crossing over the lanes of opposing traffic, and that can cause conflicts that are better imagined than expressed.Enter the cloverleaf. It allows you to turn 90 degrees to the left by turning 270 degrees to the right.Think about it. A full circle is 360 degrees; a 360-degree turn would take you right back to your original direction. If two highways intersect at right angles, a left turn means turning 90 degrees to the left. But you'd get the same result by making three right turns of 90 degrees each. It's the same as when you want to turn left in the city and encounter a “No Left Turn” sign. What do you do? You make three right turns around the next block. That's what the loop of a cloverleaf does; it takes you 270 degrees around three-quarters of a circle, guiding you either over or under the opposing lanes of traffic as necessary.The highway interchange is a four-leaf clover, rather than a two- or three-, because there are four different directions of traffic–going, for example, north, east, south and west–and each of them needs a way to make a left turn.
For readers in Britain, Japan and other countries where they drive on the left, just interchange the words “left” and “right” in the preceding paragraphs, and everything will come out all right. That is, all left. You know what I mean.
Robert L. Wolke is a professor emeritus of chemistry at the University of Pittsburgh and an award-winning food columnist for the Washington Post. He is the author of Chemistry Explained and coauthor of What Einstein Kept Under His Hat.
Actor Stephen Hoye is a graduate of London's Guildhall and a veteran of London's West End. An award-winning audiobook narrator, he has won thirteen AudioFile Earphones Awards and two prestigious APA Audie Awards.
4 Everyday Items Einstein Helped Create
Albert Einstein is justly famous for devising his theory of relativity, which revolutionized our understanding of space, time, gravity, and the universe. Relativity also showed us that matter and energy are just two different forms of the same thing—a fact that Einstein expressed as E=mc2, the most widely recognized equation in history.
But relativity is only one part of Einstein’s prodigious legacy. He was equally inventive when it came to the physics of atoms, molecules, and light. Today, we can see technological reminders of his genius almost everywhere we look. (Also read “10 Things You (Probably) Didn’t Know About Einstein.”)
Here are a few of the everyday products that showcase Einstein’s contributions to science beyond relativity.
Credit for inventing paper towels goes to the Scott Paper Company of Pennsylvania, which introduced the disposable product in 1907 as a more hygienic alternative to cloth towels. But in the very first physics article that Einstein ever published, he did analyze wicking: the phenomenon that allows paper towels to soak up liquids even when gravity wants to drag the fluid downward.
This process is what pulls hot wax into a candle wick (thus the nickname). More formally known as capillary action, it is also what helps sap rise in trees and keeps ink flowing into the nib of a fountain pen.
Einstein’s paper, published in 1901, was an attempt to explain how this attraction worked. It wasn’t a very good attempt, as he himself later admitted.
He argued at the time that water molecules were attracted to molecules in the walls of a tube via a force similar to gravity, which isn’t correct.
Nonetheless, that first paper did demonstrate that Einstein was already embracing the notion of atoms and molecules—something that was controversial at the time. Because these tiny, hypothetical lumps of matter were far too small to see or measure, a lot of senior physicists claimed that they could not be part of rigorous science.
Einstein was siding with younger, more radical physicists who believed that capillary action was just one of many phenomena that could be explained by the way atoms and molecules interact. In that sense, he was right, and so helped lay the scientific foundation for modern paper towels.
Wall Street trading firms hire armies of mathematicians to analyze the daily ebb and flow of stock prices using the most sophisticated tools at their command. If these math wizzes can come up with even a slight hint about which way the prices will jump, their employers stand to make billions.
Deep probe of antimatter puts Einstein’s special relativity to the test
After 2 decades of work, Jeffrey Hangst and experimenters with ALPHA-2 can now make and trap antihydrogen atoms by the dozen.
After decades of effort, physicists have probed the inner working of atoms of antihydrogen—the antimatter version of hydrogen—by measuring for the first time a particular wavelength of light that they absorb.
The advance opens the way to precisely comparing hydrogen and antihydrogen and, oddly, testing the special theory of relativity—Albert Einstein’s 111-year-old theory of how space and time appear to observers moving relative to one another, which, among other things, says that nothing can move faster than light.
“It's a stunning result,” says Alan Kostelecky, a theorist at Indiana University in Bloomington who was not involved in the work. For decades, experimenters have dreamed of measuring the spectrum of light absorbed by antihydrogen, Kostelecky says. “Here it is. They're doing it now.”
Just as an atom of hydrogen consists of an electron bound to a proton, antihydrogen is an antielectron (or positron) bound to an antiproton. Of course, antihydrogen doesn't occur in nature.
Because matter and antimatter particles annihilate each other, antihydrogen would vanish as soon as it touched matter. So physicists must make the stuff in the lab.
Still, they expect the properties of antihydrogen to exactly mirror those of hydrogen.
Explaining exactly why special relativity requires antimatter to mirror matter involves a lot of math. But in a nutshell, if that mirror relationship were not exact, then the basic idea behind special relativity couldn’t be exactly right, Kostelecky says.
Special relativity assumes that a single unified thing called spacetime splits differently into space and time for observers moving relative to each other. It posits that neither observer can say who is really moving and who is stationary.
But, that can’t be exactly right if matter and antimatter don't mirror each other.
That's why physicists have been itching to measure the spectrum of antihydrogen. A hydrogen atom cannot absorb or emit light of any old wavelength.
Instead, it can absorb or emit light only of certain distinct wavelengths, as the electron in it jumps from one quantized energy level to another—the fact that a century ago spurred the invention of quantum mechanics.
If relativity is right, those wavelengths must be exactly the same for hydrogen and antihydrogen.
Now, Jeffrey Hangst of Aarhus University in Denmark, and 53 other physicists with an experiment called ALPHA-2 have measured the wavelength of light absorbed by antihydrogen as the positron in it jumps between two particular levels—the so-called 1s and 2s levels.
Working at the European particle physics laboratory, CERN, in Meyrin, Switzerland, they measured that “spectral line” to a precision of a few parts in 10 billion, as they report online today in Nature. In hydrogen, that line has been measured 100,000 times more precisely.
Still, the result marks the beginning of antihydrogen spectroscopy, Hangst says. “I've been working for more than 20 years to get to this point.
To make antihydrogen, physicists trapped about 1.6 million positrons and 90,000 antiprotons in opposite ends of a cylindrical trap using electric fields.
They brought the positrons and antiprotons together to form about 25,000 uncharged antihydrogen atoms, which they immediately tried to snare with magnetic fields. They snagged about 14 atoms per trial.
That’s about 10 times more antihydrogen per go than the team produced in 2012, when it first tickled antihydrogen atoms with radio waves.
Were they working with hydrogen, physicists could have excited the atoms with, say, electricity and analyzed the light they radiated. With so few antihydrogen atoms, they had to do something more subtle.
They shined through the trap a laser tuned to excite the antimatter atoms. Once excited, an atom could “relax” back to the original state. Or it could absorb another photon and lose its positron or relax in a way that would flip the positron’s spin.
The last two possibilities would change the atom so that the trap would no longer hold it.
As a result, Hangst and company could determine whether the atoms were absorbing the light by shining the laser on them for 10 minutes and then counting the atoms left in the trap.
They merely turned off the trap and let the remaining anti-atoms float into a surrounding particle detector. “The antihydrogen atoms sort of blow up in your face,” Hangst says, “so you can count every one of them.
” The researchers compared the count between instances when the laser was tuned to the positron transition, versus times when the laser was tuned away from it, or left off.
The rough first measurement already tests special relativity, Kostelecky says. In 1997, he developed a theoretical framework called the standard model extension (SME) that begins with the prevailing theory of particle physics and encompasses every possible violation of the concept behind special relativity.
However, he says, because there are many types of particles, there is no single definitive test of the principle. For example, other physicists have compared the masses and lifetimes of particles called K mesons and their antiparticles. But those comparisons test different parts of the SME, Kostelecky says.
ALPHA-2 physicists can improve the measurement by carefully sweeping the laser’s wavelength through the 1s-2s transition, as they plan to do next year, Hangst says. They plan to measure other spectral lines and even test the pull of gravity on antihydrogen—to see if it is pulled down or pushed up.
Stories by Everyday Einstein Sabrina Stierwalt
The Mariana Trench in the Pacific Ocean is so deep your bones would literally dissolve. What's down there in its black, crushing depths?
Lots of things seem to trigger the involuntary reflex known as the hiccups, but does science understand why that reflex happens in the first place?
Some famous musicians—from Mariah Carey to Jimi Hendrix—have a gift known as perfect pitch. What is it? Could you have it, too?
Most of us have experienced deja vu—that sensation when new events feel eerily familiar. Could this “glitch in the Matrix” be a brain short-circuit?
Every time you turn around someone is suggesting aromatherapy. Essential oils are a $1 billion industry, but are they effective?
There’s a portal to the center of the earth in the wreckage of an abandoned project site in Murmansk, Russia. What’s it for? And why is the Internet Googling “Kola Superdeep Borehole screams?”…
We laugh even before we can speak. But why? Science has some answers to the mystery of human laughter, and some of them might surprise you
Put down that jelly donut and learn the evolutionary science behind why sugar makes us salivate
What Is Antimatter?
Antimatter is the general name given to a category of particles that share the same properties as other forms of matter, only with a reversed charge. For example, the antimatter particle called a positron shares all the properties of an electron, but with a positive charge instead of a negative one.
The idea of an anti-particle was first developed by the physicist Paul Dirac in the late 1920s.
Combining the emerging field of quantum mechanics with Albert Einstein's work on relativity, he revealed how particles behave at different speeds.
Interpreting the consequences of his equations, Dirac suggested particles with the same mass and spin as electrons could theoretically exist, only with an opposite charge.
The following decade, tracks of particles left by cosmic rays inside a cloud chamber were considered to be the first sign that Dirac's anti-electrons existed in reality.
How does anitmatter interact with normal matter?
When antimatter particles meet with their matter equivalents, each particle decays into gamma radiation.
This transformation of energy has made antimatter the perfect fuel for everything from engines to weapons in science fiction.
While it's a natural product of decay in radiating materials such as potassium, and can be generated using particle colliders, collecting enough in one place to serve as a source of power is challenging.
For CERN to amass a gram of the material at its current rate of generation, it would take about 100 billion years.
So far there is nothing in physics that makes matter special. Both types of particle should exist in equal amounts, but why we don't see this remains one of the biggest mysteries in physics.
Since both forms of particles annihilate each other and leave only high energy radiation, it's also a mystery as to why we have particles of a particular variety at all.
All topic-based articles are determined by fact checkers to be correct and relevant at the time of publishing. Text and images may be altered, removed, or added to as an editorial decision to keep information current.