Antimatter powers the warp engine on the USS Enterprise. Prof. Robert Langdon wrestles with it in Dan Brown’s novel “Angels & Demons.” Even if you’re not a Star Trek or a Dan Brown fan, you’ve probably heard of antimatter. Let’s wonder a bit about this curious part of physics.
“The engines are overloading, Captain!” Scotty, the ship’s engineer in the original Star Trek series, is gravely concerned. And no wonder – his ship is powered by antimatter, and an out-of-control antimatter reaction in the warp core of the starship Enterprise would result in a catastrophic explosion.
Star Trek . . . a staple of science fiction. Surely antimatter is as fictional as Star Trek.
Actually, not so.
As it happens, Scotty – and the writers of Star Trek – had it right. Antimatter is real, and an uncontrolled interaction between matter and antimatter would surely blast the Enterprise into bits. We know how to make antimatter, and it also occurs naturally in small quantities.
To be sure, most of the stuff in our world is composed of what physicists call “matter.” The Earth, buildings, your hand – these are all clumps of atoms. Atoms, in turn, are clumps of electrons, protons, and neutrons. And although the individual properties of these particles differentiate them from one another, they all have one property in common. This property results in them behaving a certain way and interacting in a certain way; it is this property that results in physicists classifying all of these as “matter.”
What’s a Positron?
A curious relative of the electron was proposed in the 1920s and discovered experimentally not long after. This particle – dubbed the positron – is identical to the electron in every way except one. While the charge of an electron is negative, the charge of a positron is positive.
Positrons have a remarkable relationship with electrons: when a positron and an electron meet up, the two particles wink out of existence, leaving nothing but a small bit of energy. No pairs of matter particles do this; positrons and electrons annihilate each other.
In a real sense, positrons are the opposite of electrons. For this reason we classify them as “antimatter.” Every matter particle has an antimatter partner.
Antimatter Is in You Right Now!
One way that positrons are created naturally is through the decay of a radioactive form of the element potassium. There are very small amounts of radioactive potassium in foods we eat – such as bananas, yogurt, and baked potatoes, as well as table salt – which means there is a small amount in you. This radioactive potassium produces about two positrons a minute. They don’t stick around for very long, however – as soon as one of those positrons encounters an electron, it (and the electron) disappear, replaced by an equivalent amount of energy.
Am I Going to Explode?
No need to worry about these tiny bits of energy! They result in no discernible effects. About two of these tiny annihilations occur in your body in a minute; it would take about ten trillion every second just to power a small flashlight.
Remember: E = mc2
When a matter and an antimatter particle annihilate, the “stuff” of the two particles disappears and is replaced by energy. The laws of physics allow for matter and energy to be interchanged: they are equivalent to one another. So said Albert Einstein in his famous equation E = mc2. The equivalence of energy E and mass m is a fundamental property of the universe. In this equation c is the speed of light in a vacuum.
Is mass really equivalent to energy, or is this just some mathematical physics trickery? Consider a proton and a neutron, which are about the same size and have about the same weight (or mass, to be precise.) If you get a proton and a neutron close enough they’ll stay together, prevented from drifting apart by a small amount of energy shared between them. From where does this energy come?
The Weight of Two Is Less Than One? Please Explain
It’s almost too incredible to be true: the weight of the proton and neutron when stuck together is slightly less than the sum of the weights of the proton and neutron separately. Less! Some of the mass of the proton and neutron has changed into energy, and it is that energy which holds the two particles together. Energy and matter are interchangeable.
An antimatter particle has an energy equivalent, as does a particle of matter. Bring them together and they disappear, releasing all of that energy. To be sure, there’s not much energy released in any one such annihilation. But get enough of antimatter “fuel” together, and the available energy adds up quickly. Were we able to assemble just one kilogram of the fuel Scotty uses in his warp drive engine, it would provide the energy needs of the entire city of San Francisco for two or three years!
Questions to ponder:
If you could create an antimatter copper atom and annihilate it with a matter copper atom, you’d need to do that every second for sixty thousand years just to charge your smartphone. But there are billions upon billions of copper atoms in a quarter; if you could create an antimatter quarter, the amount of energy released in annihilation with a regular quarter would cover the energy needs for all of the households in the city of Santa Clara for an entire year. Why don’t we do this?