Is the speed of light slowing down?

Several things in nature go faster than the speed of light, without challenging general relativity.

Modern physics rests on the foundational notion that the speed of light is a constant, which in a vacuum is 186,000 miles per second (299,792 km/s). Einstein established this within his theory of general relativity, first developed in 1906 when he was just 26 years-old. But what if it doesn’t? A few albeit controversial incidents in recent years challenge the idea that light always travels at a constant speed. And in fact, we've known for a long time that there are several phenomena that travel faster than light, without violating the theory of relativity.


For instance, whereas traveling faster than sound creates a sonic boom, traveling faster than light creates a "luminal boom." Russian scientist Pavel Alekseyevich Cherenkov discovered this in 1934, which won him the Nobel Prize in Physics in 1958. Cherenkov radiation can be observed in the core of a nuclear reactor. When the core is submerged in water to cool it, electrons move through the water faster than the speed of light, causing a luminal boom.

On another front, while no particle with mass can travel faster than light, the fabric of space can and does. According to Inflation Theory, immediately after the Big Bang, the universe doubled in size and then doubled again, in less than a trillionth of a trillionth of a second, much faster than the speed of light. More recently, astronomers have discovered that some galaxies, the distant ones anyway, move away from us faster than light speed, supposedly, pushed along by dark energy. The best estimate for the rate of acceleration for the universe is 68 kilometers per second per megaparsec.

Quantum entanglement is another example of a faster-than-light interaction that doesn’t violate Einstein’s theory. When two particles are entangled, one can travel to its partner instantaneously, even if its mate is on the other side of the universe. Einstein called this, "Spooky action at a distance." The last example is a theoretical one (at least for now). If we were somehow able to warp or fold space-time, such as with a wormhole, it would allow a spacecraft to pass instantaneously from one side of space to another. 

Credit: NASA/WMAP Science Team.

Einstein says that light acts pretty much the same throughout the universe. There’s a problem though. Today, scientists marvel at just how homogenous the universe is. One way we can tell, is by investigating the cosmic microwave background (CMB). This is essentially the light left over from the Big Bang, located in every corner of the universe.

No matter where you examine it, it’s always the same temperature, -454 Fº (-270 Cº). If that’s the case and light travels at a constant speed, how could it have made it from one edge of the universe to the other? To date, scientists have no idea, other than to say, some peculiar conditions must have existed in that early “inflation field.”

The idea of light slowing down over time was first proposed by Professor João Magueijo, from Imperial College London and his colleague, Dr. Niayesh Afshordi, of the Perimeter Institute in Canada. Their paper was submitted to Astrophysics in late 1998 and published shortly thereafter. Unfortunately, the proper instrumentation necessary to investigate the CMB to search for clues supporting it, wasn’t available at the time.

Magueijo and Afshordi eliminated the inflation field altogether. Instead, they argue that the intense heat that existed when the universe was young, ten thousand trillion trillion Cº, allowed particles—including photons (light particles), to move at an infinite speed. Light therefore traveled to every point in the universe, causing a uniformity in the CMB that we can observe today. “We can say what the fluctuations in the early universe would have looked like,” Afshordi told The Guardian, “and these are the fluctuations that grow to form planets, stars, and galaxies.” An experiment the following year lent credence to Magueijo and Afshordi’s theory. 

The cosmic microwave background. Credit: NASA/WMAP Science Team.

In 1999, Lene Vestergaard Hau at Harvard stunned the world, after she conducted an experiment where she slowed light down to just under 40 mph (64 kph). Hau studies materials at a few degrees above absolute zero. In such an environment, atoms move very slowly. They begin to overlap, turning into what’s known as the Bose-Einstein condensate. Here, the atoms become one big cloud, and behave like one giant atom.

Hau shot two lasers through such a cloud, comprised of sodium atoms 0.008 inches (0.2 mm) wide. The first blast changed the quantum nature of the cloud. This increased the cloud’s refractive index, which slowed the second beam to 38 mph (61 kph). Refraction is when light or radio waves are bent or distorted when passing from one medium into another.

A discovery in 2001 also lent credence to the variable light theory. The eminent astronomer John Webb made an observation while studying quasars in deep space. Quasars are luminescent bodies billions of times as massive as our sun, which are powered by black holes. Its luminosity comes from an accretion disk, made up of gas, enveloping it.

Webb found that one particular quasar when nearing interstellar clouds, absorbed a different type of photon than would’ve been predicted. Only two things could explain this. Either its charge had changed or the speed of light had. In 2002 an Australian team, led by theoretical physicist Paul Davies, found that it couldn’t have changed polarity, as this would’ve violated the Second Law of Thermodynamics.

Artist’s impression of the quasar 3C 279. Credit: NASA Blueshift, Flickr.

Another breakthrough study in 2015 further challenged this staple of science. Scottish physicists from Glasgow and Heriot-Watt universities successfully slowed a photon at room temperature, without refraction. They basically built a racetrack for photons. It was made so that two photons raced side-by-side.

One track was unencumbered. The other held a “mask” which resembled a target with a bullseye. In the center was a passageway so narrow, the photon had to change shape to squeeze through. It slowed that photon down about one micron (micrometer), not a lot, but enough to prove that light doesn’t always travel at a constant speed.

By now, instrumentation had improved to the point where the CMB can be successfully probed. As such, in 2016 João Magueijo and Niayesh Afshordi published another paper, this time in the journal Physical Review D. They are currently measuring different areas of the CMB, and studying the distribution of galaxies, seeking clues to support their claim that light in the universe's earliest moments broke free of it's presumed speed limit.

Again, this is a fringe theory. And yet, the implications are astounding. "The whole of physics is predicated on the constancy of the speed of light," Magueijo told Vice’s Motherboard. "So we had to find ways to change the speed of light without wrecking the whole thing." Their calculations should be complete by 2021.

Want to learn more about the speed of light and whether it’s actually a constant, Click here.


Will China’s green energy tipping point come too late?

Pay attention to the decisions made by the provinces.

Surprising Science
  • China leads the world in numerous green energy categories.
  • CO2 emissions in the country totaling more than all coal emissions in the U.S. have recently emerged.
  • This seems to be an administrative-induced blip on the way towards a green energy tipping point.
Keep reading Show less

Got a question for a real NASA astronomer? Ask it here!

NASA astronomer Michelle Thaller is coming back to Big Think to answer YOUR questions! Here's all you need to know to submit your science-related inquiries.

Surprising Science

Big Think's amazing audience has responded so well to our videos from NASA astronomer and Assistant Director for Science Communication Michelle Thaller that we couldn't wait to bring her back for more!

And this time, she's ready to tackle any questions you're willing to throw at her, like, "How big is the Universe?", "Am I really made of stars?" or, "How long until Elon Musk starts a colony on Mars?"

All you have to do is submit your questions to the form below, and we'll use them for an upcoming Q+A session with Michelle. You know what to do, Big Thinkers!

Keep reading Show less

5 communication pitfalls that are preventing people from really hearing what you're trying to say

If you want to be a better and more passionate communicator, these tips are important.

Photo by CloudVisual on Unsplash
popular

If you identify as being a socially conscious person in today's age of outrage, you've likely experienced the bewildering sensation when a conversation that was once harmless, suddenly doesn't feel that way anymore. Perhaps you're out for a quick bite with family, friends, or coworkers when the conversation takes a turn. Someone's said something that doesn't sit right with you, and you're unsure of how to respond. Navigating social situations like this is inherently stressful.

Below are five expert-approved tips on how to maintain your cool and effectively communicate.

Keep reading Show less

Take the Big Think survey for a chance to win :)

Calling all big thinkers!

  • Tell us a little bit about where you find Big Think's videos, articles, and podcasts.
  • Be entered for a chance to win 1 of 3 Amazon gift cards each worth $100.
  • All survey information is anonymous and will be used only for this survey.
Keep reading Show less
(Photo: ANGELA WEISS/AFP/Getty Images)
Culture & Religion
  • The next Mega Millions drawing is scheduled for Oct. 23 at 11 pm E.T.
  • The odds of any one ticket winning are about 1 in 300 million.
  • This might be a record-setting jackpot, but that doesn't mean you have a better chance of winning.
Keep reading Show less

The value of owning more books than you can read

Or how I learned to stop worrying and love my tsundoku.

(Photo from Wikimedia)
Personal Growth
  • Many readers buy books with every intention of reading them only to let them linger on the shelf.
  • Statistician Nassim Nicholas Taleb believes surrounding ourselves with unread books enriches our lives as they remind us of all we don't know.
  • The Japanese call this practice tsundoku, and it may provide lasting benefits.
Keep reading Show less

How to raise a non-materialistic kid

Money makes the world go 'round. Unfortunately, it can make both children and adults into materialists.

Robert Collins / Unsplash
Personal Growth
  • Keeping a gratitude journal caused children to donate 60 percent more to charitable causes.
  • Other methods suggested by researchers include daily gratitude reflection, gratitude posters, and keeping a "gratitude jar."
  • Materialism has been shown to increase anxiety and depression and promote selfish attitudes and behavior.
Keep reading Show less

Elon Musk's high-speed test tunnel will give free rides on Dec. 11

The Boring Company plans to offer free rides in its prototype tunnel in Hawthorne, California in December.

Image: Getty Images/Claudia Soraya
Technology & Innovation
  • The prototype tunnel is about 2 miles long and contains electric skates that travel at top speeds of around 150 mph.
  • This is the first tunnel from the company that will be open to the public.
  • If successful, the prototype could help the company receive regulatory approval for much bigger projects in L.A. and beyond.
Keep reading Show less