That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face," Sutter wrote. And neither should you. Light in a vacuum is generally held to travel at an absolute speed, but light traveling through any material can be slowed down.
The amount that a material slows down light is called its refractive index. Light bends when coming into contact with particles, which results in a decrease in speed, according to an explainer article from the Khan Academy.
Related: Here's what the speed of light looks like in slow motion. For example, light traveling through Earth's atmosphere moves almost as fast as light in a vacuum, slowing down by just three ten-thousandths of the speed of light. Light can be trapped — and even stopped — inside ultra-cold clouds of atoms, according to a study published in the journal Nature.
More recently, a study published in the journal Physical Review Letters proposed a new way to stop light in its tracks at "exceptional points," or places where two separate light emissions intersect and merge into one. Researchers have also tried to slow down light even when it's traveling through a vacuum. A team of Scottish scientists successfully slowed down a single photon, or particle of light, even as it moved through a vacuum, as described in their study published in the journal Science.
In their measurements, the difference between the slowed photon and a "regular" photon was just a few millionths of a meter, but it demonstrated that light in a vacuum can be slower than the official speed of light. Science fiction loves the idea of "warp speed. But while faster-than-light travel isn't guaranteed impossible, we'd need to harness some pretty exotic physics to make it work.
Luckily for sci-fi enthusiasts and theoretical physicists alike, there are lots of avenues to explore. All we have to do is figure out how to not move ourselves — since special relativity would ensure we'd be long destroyed before we reached high enough speed — but instead, move the space around us. Easy, right? One proposed idea involves a spaceship that could fold a space-time bubble around itself. Sounds great, both in theory and in fiction. Related: Spaceship could fly faster than light.
Without faster-than-light travel, any "Star Trek" or "Star War," for that matter would be impossible. If humanity is ever to reach the farthest — and constantly expanding — corners of our universe, it will be up to future physicists to boldly go where no one has gone before.
Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community space. Jump to: What is a light-year? By studying Jupiter's moon Io and its frequent eclipses, Roemer was able to predict the periodicity of an eclipse period for the moon Figure 3. However, after several months, he noticed that his predictions were slowly becoming less accurate by progressively longer time intervals, reaching a maximum error of about 22 minutes a rather large discrepancy, considering how far light travels in that time span.
Then, just as oddly, his predictions again became more accurate over several months, with the cycle repeating itself. Working at the Paris Observatory, Roemer soon realized that the observed differences were caused by variations in the distance between the Earth and Jupiter, due to orbital pathways of the planets.
As Jupiter moved away from the Earth, light had a longer distance to travel, taking additional time to reach the Earth. Applying the relatively inaccurate calculations for the distances between Earth and Jupiter available during the period, Roemer was able to estimate the speed of light at about , miles or , kilometers per second. Figure 3 illustrates a reproduction of the original drawings by Roemer delineating his methodology utilized to determine the speed of light.
Roemer's work stirred the scientific community, and many investigators began to reconsider their speculations about the infinite speed of light. Sir Isaac Newton, for example, wrote in his landmark treatise Philosophiae Naturalis Prinicipia Mathematica Mathematical Principles of Natural Philosophy , "For it is now certain from the phenomena of Jupiter's satellites, confirmed by the observations of different astronomers, that light is propagated in succession and requires about seven or eight minutes to travel from the sun to the earth", which is actually a remarkably close estimate for the correct speed of light.
Newton's respected opinion and widespread reputation was instrumental in jump-starting the Scientific Revolution, and helped launch new research by scientists who now endorsed light's speed as finite. The next in line to provide a useful estimate of the speed of light was the British physicist James Bradley.
In , a year after Newton's death, Bradley estimated the speed of light in a vacuum to be approximately , kilometers per second, using stellar aberrations. These phenomena are manifested by an apparent variation in the position of stars due to the motion of the Earth around the sun. The degree of stellar aberration can be determined from the ratio of the Earth's orbital speed to the speed of light. By measuring the stellar aberration angle and applying that data to the orbital speed of the Earth, Bradley was able to arrive at a remarkably accurate estimate.
In , Sir Charles Wheatstone, inventor of the kaleidoscope and a pioneer in the science of sound, attempted to measure the speed of electricity. Wheatstone invented a device that utilized rotating mirrors and capacitative discharge through a Leyden jar to generate and clock the movement of sparks through almost eight miles of wire.
Unfortunately, his calculations and perhaps his instrumentation were in error to such a degree that Wheatstone estimated the velocity of electricity at , miles per second, a mistake that led him to believe that electricity traveled faster than light.
Although he failed to complete his work before his eyesight failed in , Arago correctly postulated that light traveled slower in water than air.
Meanwhile in France, rival scientists Armand Fizeau and Jean-Bernard-Leon Foucault independently attempted to measure the speed of light, without relying on celestial events, by taking advantage of Arago's discoveries and expanding on Wheatstone's rotating mirror instrument design. In , Fizeau engineered a device that flashed a light beam through a toothed wheel instead of a rotating mirror , and then onto a fixed mirror positioned at a distance of 5.
By rotating the wheel at a rapid rate, he was able to steer the beam through a gap between two of the teeth on the outward journey and catch reflected rays in the neighboring gap on the way back. Armed with the wheel speed and distance traveled by the pulsed light, Fizeau was able to calculate the speed of light. He also discovered that light travels faster in air than in water confirming Arago's hypothesis , a fact that fellow countryman Foucault later confirmed through experimentation.
Foucault employed a rapidly rotating mirror driven by a compressed air turbine to measure the speed of light. In his apparatus see Figure 4 , a narrow beam of light is passed through an aperture and then through a glass window acting also as a beamsplitter with a finely graduated scale before impacting on the rapidly spinning mirror.
Light reflected from the spinning mirror is directed through a battery of stationary mirrors in a zigzag pattern designed to increase the path length of the instrument to about 20 meters without a corresponding increase in size.
In the amount of time it took the light to reflect through the series of mirrors and return to the rotating mirror, a slight shift in the mirror position had occurred. Subsequently, light reflected from the shifted position of the spinning mirror follows a new pathway back to the source and into a microscope mounted on the instrument. The tiny shift in light could be seen through the microscope and recorded.
By analysis of the data collected from his experiment, Foucault was able to calculate the speed of light as , kilometers per second approximately , miles per second. The light path in Foucault's device was short enough to be utilized in the measurement of light speeds through media other than air. He discovered that the speed of light in water or glass was only about two-thirds of the value in air, and he also concluded that the speed of light through a given medium is inversely proportional to the refractive index.
This remarkable result is consistent with the predictions about light behavior developed hundreds of years earlier from the wave theory of light propagation. Michelson attempted to increase the accuracy of the method, and successfully measured the speed of light in with a more sophisticated version of the apparatus along a 2,foot wall lining the banks of England's Severn River. Investing in high quality lenses and mirrors to focus and reflect a beam of light over a much longer pathway than the one utilized by Foucault, Michelson calculated a final result of , miles per second , kilometers per second , allowing for a possible error of about 30 miles per second.
What if an Asteroid Hit the Earth. Using a Jeep to Estimate the Energy in Gasoline. How do Police Radars really work? How "Fast" is the Speed of Light? How Long is a Light Year? How Big is a Trillion? Of Stars and Drops of Water. A Number Trick. This timing is growing every day, however, as the moon is drifting farther from Earth at a rate of about 1.
The moon is constantly sapping Earth's rotational energy via ocean tides , boosting its orbit to a greater and greater distance. O'Donoghue's third speed-of-light animation illustrates the challenge that many planetary scientists deal with on a daily basis. When NASA tries to talk to or download data from a spacecraft, such as the InSight probe on Mars , it can do so only at the speed of light.
This is much too slow to operate a spacecraft in "live mode" as you would a remote-controlled car. So, commands must be carefully thought out, prepackaged, and aimed at the precise location in space at the precise time so that they don't miss their target.
The fastest a conversation could ever happen between Earth and Mars is when the planets are at their nearest point to one another, an event called closest approach that happens once roughly every two years.
On average, that best-case-scenario distance is about As that second clip of O'Donoghue's full movie on YouTube shows, light takes 3 minutes 2 seconds to travel between Earth and Mars at closest approach. That's six minutes and four seconds for a light-speed round-trip. But on average, Mars is about million miles from Earth — so the average round-trip communication takes about 28 minutes and 12 seconds. The hurdle of light's finite speed gets even more challenging for spacecraft such as New Horizons, which is now more than 4 billion miles from Earth , and the Voyager 1 and 2 spacecraft, each of which have reached the space between stars.
The situation gets downright depressing when you start looking outside the solar system. The closest-known exoplanet , called Proxima b, is about 4.
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