Give Now

A Moment of Science

Alone In The Dark

If cosmic trends continue, night is going to get a whole lot darker.

doppler effect

Photo: Pbroks13 (Wikimedia Commons)

This computerized depiction of the Doppler effect shows waves radiating outward from a source that is moving from right to left. Notice how the bands are farther apart behind the object compared to in front of it. It is this difference that produces observed pitch-slides and color-shifts.

Back in 1929, astronomer Edwin Hubble discovered a peculiar correlation: The farther a galaxy is from the Milky Way, the faster it seems to be moving away.

This principle, since dubbed ‘Hubble’s Law’, has led to a rather strange consensus among scientists that space is expanding.

More recently, during the 90′s, astrophysicists Saul Perlmutter, Brian Schmidt and Adam Riess amended this law, postulating that the rate of space’s expansion is actually accelerating!

The implications are profound for both present-day cosmologists as well as for earthlings of the distant future.

Doppler Effect

When a truck races past us, horn blaring and glasspacks blasting, we notice the cacophony sliding upwards and then downwards in pitch as the vehicle recedes into the distance.

The technical term for this phenomenon is ‘Doppler Effect’. It’s the result of sound waves being stretched or squashed by the relative motion of what’s making a noise and what’s listening.

Something similar happens with light, only in place of pitch-bends, we have modulations of color. Starlight, for example, appears bluer when a star is moving towards us (‘blueshift‘) and redder when it’s moving away (‘redshift‘).

Hubble’s realization stemmed from the fact that galactic redshifts become more severe with distance, which indicates that farther away galaxies are moving away from us more quickly than ones closer by.

What Perlmutter, Schmit and Riess found much later with the aid of new-and-improved telescopes, however, was that Hubble’s description was incomplete. Not only are galaxies becoming more separated, the rate of their separation is actually increasing.

They were awarded the Nobel Prize in physics for their work last Tuesday.

Dark Energy, Dark Skies

To account for this speeding up, theorists have postulated dark energy, an exotic force that serves as the engine for cosmic expansion. Like its more massive counterpart, dark matter, dark energy’s existence has yet to be directly confirmed.

More palpably, space’s accelerated expansion means that there will come a day when light from our celestial neighbors will no longer be able to reach us. First we will lose sight of remote superclusters, then of galaxies in the Local Group. Finally, eons from now, not even the pale glow of Alpha Centauri will make it, and, each night, earthlings will be plunged into near-complete darkness.

Read More:

  • Expanding Universe Theory Wins Nobel Prize (Al Jazeera)
  • A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae (Edwin Hubble, 1929)
Ben Alford

Ben Alford works in Indiana Public Media's online dimension and holds an M.A. from Indiana University Bloomington's History and Philosophy of Science department. When not vegetating in front of a computer screen or geeking out over a good book, he can be found outside exploring.

View all posts by this author »

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science