Blasars, magic telescopes and quantum foam

Speed of What?

An artist's concept of a "blasar"--a black hole
emitting jets and flares of superhot gas.
Credit: NASA/Chandra X-ray Observatory/M. WeissWe all know what it is: 186,300 miles per second, a.k.a. the Speed of Light, the maximum speed limit in the Universe, and an absolute constant speed that all light must travel at in a vacuum, regardless of its wavelength, origin, destination, or inclination.

This Law, that light cannot exceed, or travel slower than, this speed, established by Einstein and his famous Special Theory of Relativity, has been drilled into most of our heads since our births--and even the most fanatical warp-driven Trekkie or hyperspace-jittery Star Wars fan or wormhole-burrowing Stargate loyalist knows it. Science fiction bends, breaks, and bypasses the law of lightspeed mainly to facilitate storylines in which characters need to travel to other stars in a reasonable amount of time.

But is the sacrosanct invariability of light speed about to change, as if by magic? Some recent articles report a very unusual and unexpected observation made by researchers using MAGIC-- the Major Atmospheric Gamma-ray Imaging Cherenkov telescope. The researchers were observing gamma ray outbursts from a blasar (a black hole that occasionally emits bursts of radiation) half a billion light years away, and found that not all of the high energy photons (light "particles") appeared to arrive at Earth at the same time, even though they are believed to have been emitted at the same time. The higher energy gamma rays arrived up to four minutes later than lower energy photons...

That's really weird, to say the least! Sure, these photons have been traveling toward Earth for half a billion years, and in that time the alleged slow-pokes only fell behind by four minutes. Their speed was only slower by a tiny amount, but the point is--by all scientists have believed about the speed of light over the past century--there should have been no difference at all in the arrival times of the different photons!

This is a little like listening to a live concert, and hearing the lower pitched sounds from the instruments before hearing the higher tones, even when the different notes were struck at the same instant.

One theory is that the higher energy gamma rays are being slowed by interaction with something called "quantum foam," a theoretical subatomic structure, or "texture," in space itself that is predicted by quantum gravity theory. How can something that looks so constant have a "texture?" Imagine how the very smooth surface of a city street is actually quite rough when looked at or felt close-up, and you can envision how appearances can be a bit deceiving.

What's the significance of this observation? While it doesn't show that something has been detected moving faster than 186,300 miles per second, finding high energy gamma rays that may have lost a race to fellow photons may reveal something about the nature of space that we didn't know, or had only theorized about--in this case an otherwise unobservable, theoretical property of space itself.

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.