#4 The Speed of Light

Most people usually think of the speed of light as being really fast. It's 671 million miles per hour. That seems tantalizingly zippy if you're caught in traffic.

However, once you think about the speed of light within the context of our solar system, it starts to seem unimpressive.

It takes about 1.3 seconds for light or radio waves to reach us from the Moon, which really isn't all that far away (it's only 20 times farther away than Australia is to the United States). This was an issue during the Apollo space program, because due to the round trip time of the radio signals, NASA had to wait about three seconds to hear the answer to every question they asked the astronauts.

When Mars is closest to the Earth, it takes light three minutes to travel between the two planets. If you asked a question to an astronaut on Mars, you'd have to wait at least six minutes for an answer, and Mars is usually a lot farther away than that. At its greatest distance, you'd have to wait 42 minutes, or even longer if the astronaut is watching Gilmore Girls. In the future, there will be no such thing as sending an "instant message" to your friends on the Mars base. There also won't be any day trading or free pizza delivery.

The Voyager 1 spacecraft was launched only 29 years ago. It's currently the farthest away from the Earth of any man-made object. In just a short amount of time, this spacecraft, designed by primitive 1970's-era engineers, many of whom were wearing corduroy bell bottoms, has managed to travel so far away from the Earth that it takes radio signals travelling at the speed of light 14 hours to reach it.

I am not making this up. An object that was recently built by people is now far enough away that if you could travel to it at the speed of light, for the in-flight movie you could watch the original director's cut of Water World four times, break for a dinner, and then watch Ishtar before having to put your tray in its upright position.

Light takes four and half years to travel to the nearest star (other than the Sun), 100,000 years to travel across the width of the galaxy, and 100 billion years to travel across the observable Universe.

The speed of light isn't all that fast. Get over it.

Update: In my description of the trip to Voyager 1, I forgot to take into account time dilation. Thankfully, you actually wouldn't have to wait through all those boring movies. In the crazy world of Einstein's theory of relativity, if you travelled close to the speed of light, very little time would appear to pass from your point of view, even though time would pass normally for everyone else, and they would have to do all the waiting around. The upshot of this is that if you travelled at near-light speeds to the nearest star and back, only a few seconds would seem to pass, but when you returned to the spaceport on Earth, you would still be responsible for nine years of parking fees.

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