Exposing PseudoAstronomy

November 20, 2008

A Post on Physics and Astronomical Terminology

Filed under: terminology — Stuart Robbins @ 2:28 pm
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There is a lot of terminology that is in popular culture and the media that are often used incorrectly, or they are implied to mean the incorrect thing. The purpose of this post is to address three of them, in order from used most often correctly to used least often correctly: Light-year, parsec, and quantum.


The Bad: People often mistake this for a unit of time or advancement. For example, “Buy our products! We’re light years ahead of the competition!” Unless they’re around another star, this phrase has no meaning.

The Good: A “light-year” is a unit of length, NOT a unit of time. It is defined as the distance that light will travel in 1 year in a vacuum (such as space). Light travels at 299,792,458 meters per second (186,282 miles per second).

It takes light about 1.5 seconds to reach the moon from Earth, and so for very close astronomical objects, we sometimes talk about “light-seconds” (the distance light travels in 1 second).

Light from the sun takes about 8.3 minutes to reach Earth, and so distances within the solar system are sometimes referred to as “light-minutes,” the distance light travels in 1 minute. This is important for communications with spacecraft, even those that are at Mars. At its closest, the round-trip light time for for a signal to be sent from Mars to Earth and then for Earth to send a signal back is about 8 minutes. At its farthest, the round-trip light time is about 40 minutes. Because of this, craft have to at least have some autonomy in their decision making ability.

Light from the closest star system – the Proxima, Alpha, and Beta Centauri stars – takes about 4.3 years to reach us, and hence we have a distance of 4.3 light-years. Distances within our galaxy are generally measured in light-years, with our galaxy being about 100,000 light-years in diameter.


The Bad: People often mistake this for a unit of time. The most famous example is from Star Wars, where Han Solo states that his ship is so good, it “made the Kessel Run in less than 12 parsecs.”

The Good: A parsec, like a light-year, is a unit of distance and NOT time. The definition of a parsec is a mathematical one that I am simply providing a link to rather than explain. It is approximately equal to 3.26 light-years, making the distance to the nearest star system about 1.3 parsecs away. Astronomers will often use parsec and light-year interchangeably for the near-by universe, out to about the closest galaxies. Beyond that, they generally use parsecs instead of light-years.


The Bad: After I took a 2-semester class in quantum mechanics in college, this became one of my biggest pet-peeves in advertising: “This product represents a quantum leap over the competition!” Or even news to describe something in (gasp!) science: “This is a quantum leap in our understanding of this phenomena!”

It sounds cool, and “quantum” is the catch-word of the day because it sounds sciency and technical and cool. And everybody’s doing it. It makes whatever it is being used to describe to be huge, major, and fantastic. But it’s not.

The Good: The “quantum” in quantum mechanics is really the basis of the whole theory: That there is no continuum of energy levels or states, but rather things come in discrete levels. A good analogy is to think of a trombone versus a flute (not an open-holed flute for you flautists). A trombone has a slide, and by moving the slide, you can create a seamless variation in pitch, going from low to high and back without hitting discrete notes. With a flute, however, you have keys, and though you can hit every pitch on the scale, the instrument is not designed to allow you to make notes that are in-between “real” notes.

The trombone represents the classical way of thinking about energy levels. The flute represents the quantum way. To extend the analogy, each note on the flute represents a different “quanta,” and making a jump – or leap – from one quanta to another (so from a C# to B, for example) is a “quantum leap.”

When you’re talking about energy levels of atoms, though, this leap in energy is very small. The largest single step is when an electron goes from the ground state (lowest energy level) in a hydrogen atom to the 1st energy level. This has an energy transition of 13.6 eV (a number that’s ground into any physicist’s mind over and over and over and over and …). An “eV” is an “electron-volt” It is a very small amount of energy, with 1 eV = 1.6ยท10-19 Joules. 1 Watt is 1 Joule/second. So, to power a 60 Watt bulb for 1 second, you would need around 1018 electrons around hydrogen atoms to go from the 1st state to the ground (to release the energy). This is about 0.01 milligrams of hydrogen, which isn’t much.

However, my point in spewing out all these numbers is to drive the idea that a “quantum” is an extremely small amount, and to state that something represents a “quantum leap” over what has been done before is, when using the true definition of the word, saying that the new thing has not changed any perceivable amount.

Final Thoughts

You may read this diatribe and think that it’s a rant about nothing. That may be, but my impression of blogs in general is that they are rants about nothing.

This post is really more about trying to bridge the gap between the popular usage of scientific-sounding words and what they really mean. Without clearly defined language, ideas cannot be successfully communicated, and even though I know that an advertiser’s “quantum leap” in their product that makes it “light-years ahead” of the competition is supposed to mean it’s fantastic, it’s really just reflecting ignorance on the part of the marketing firm.

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