Is the speed of light slowing down?

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

Credit: Melmak, Pixababy.

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.


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Photos: Courtesy of Let Grow
Sponsored by Charles Koch Foundation
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New research establishes an unexpected connection.

Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

Image source: Vaccaro et al, 2020/Harvard Medical School
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We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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