Light travels how fast

This principle allows astronomers to see the universe as it looked after the Big Bang , which took place about Objects that are 10 billion light-years away appear to astronomers as they looked 10 billion years ago — relatively soon after the beginning of the universe — rather than how they appear today.

As early as the 5th century, Greek philosophers like Empedocles and Aristotle disagreed on the nature of light speed. Empedocles thought that light, whatever it was made of, must travel and therefore, must have a rate of travel.

Aristotle wrote a rebuttal of Empedocles' view in his own treatise, On Sense and the Sensible , arguing that light, unlike sound and smell, is instantaneous. Aristotle was wrong, of course, but it would take hundreds of years for anyone to prove it.

Each person held a shielded lantern. One uncovered his lantern; when the other person saw the flash, he uncovered his too.

But Galileo's experimental distance wasn't far enough for his participants to record the speed of light. He could only conclude that light traveled at least 10 times faster than sound.

To create an astronomical clock, he recorded the precise timing of the eclipses of Jupiter's moon , Io, from Earth. He noticed that the eclipses appeared to lag the most when Jupiter and Earth were moving away from one another, showed up ahead of time when the planets were approaching and occurred on schedule when the planets were at their closest or farthest points — a rough version of the Doppler effect or redshift.

In a leap of intuition, he determined that light was taking measurable time to travel from Io to Earth. Since the size of the solar system and Earth's orbit wasn't yet accurately known, argued a paper in the American Journal of Physics , he was a bit off. But at last, scientists had a number to work with. In , English physicist James Bradley based a new set of calculations on the change in the apparent position of the stars due Earth's travels around the sun. Two new attempts in the mids brought the problem back to Earth.

French physicist Hippolyte Fizeau set a beam of light on a rapidly rotating toothed wheel, with a mirror set up 5 miles 8 km away to reflect it back to its source. Varying the speed of the wheel allowed Fizeau to calculate how long it took for the light to travel out of the hole, to the adjacent mirror, and back through the gap. Another French physicist, Leon Foucault, used a rotating mirror rather than a wheel to perform essentially the same experiment. Another scientist who tackled the speed of light mystery was Poland-born Albert A.

Michelson, who grew up in California during the state's gold rush period, and honed his interest in physics while attending the U. Naval Academy, according to the University of Virginia. In , he attempted to replicate Foucault's method of determining the speed of light, but Michelson increased the distance between mirrors and used extremely high-quality mirrors and lenses.

In his second round of experiments, Michelson flashed lights between two mountain tops with carefully measured distances to get a more precise estimate. And in his third attempt just before his death in , according to the Smithsonian's Air and Space magazine, he built a mile-long depressurized tube of corrugated steel pipe. The pipe simulated a near-vacuum that would remove any effect of air on light speed for an even finer measurement, just slightly lower than the accepted value of the speed of light today.

Michelson also studied the nature of light itself, wrote astrophysicist Ethan Siegal in the Forbes science blog, Starts With a Bang. The best minds in physics at the time of Michelson's experiments were divided: Was light a wave or a particle? Michelson, along with his colleague Edward Morley, worked under the assumption that light moved as a wave, just like sound.

And just as sound needs particles to move, Michelson and Morley and other physicists of the time reasoned, light must have some kind of medium to move through. This invisible, undetectable stuff was called the "luminiferous aether" also known as "ether".

Though Michelson and Morley built a sophisticated interferometer a very basic version of the instrument used today in LIGO facilities , Michelson could not find evidence of any kind of luminiferous aether whatsoever. According to the laws of physics, as we approach light speed, we have to provide more and more energy to make an object move. In order to reach the speed of light, you'd need an infinite amount of energy, and that's impossible!

You may have heard that an object traveling at the speed of light gains infinite mass. But that's not exactly true. So, if mass can't travel at the speed of light, how come light can? Light is made up of photons, which are massless particles and therefore they don't require energy to move. Time dilation.

Time slows down as you approach the speed of light and when you reach it, time stops. For a photon, there is no time, everything happens instantaneously. Trying to make a photon go faster than the speed of light is like bringing your car to a stop and trying to go slower.

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. However, the fastest any spacecraft has ever gone is NASA's Parker Solar Probe at about , mph ; at that speed, it'd take 13, years to reach Proxima b.

A Russian-American billionaire's Breakthrough Starshot project envisions a way to address this speed problem. Yet the entire concept is still theoretical, may end up not working, and would operate at a fraction of light-speed. Space is impossibly vast. Although the universe is about That's far too big to illustrate in a simple animation. One illustration comes close, though: this image created by musician Pablo Carlos Budassi , which combines logarithmic maps of the universe from Princeton and images from NASA to capture it all in one picture.

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