Today, it is unknown how to attain a speed faster than the speed of light. Many say that it is impossible, but people in the past also said that space travel all together was impossible. Scientists believe that one day, we will achieve faster-than-light speed.

At this moment, our surrounding galaxies are getting farther and farther away from us. This is due to our expanding universe, and even if we had the power to live forever, of we left Earth now at the fastest speed we can obtain, we still might not be able to reach another galaxy. That is why traveling at the speed of light would come in handy. We could explore places we can't even imagine. Many scientists and physicists have been dreaming about traveling at this speed for years on end. They say that one day we will get there.

Under the special theory of relativity, a particle with subluminal velocity needs infinite energy to accelerate to the speed of light. Today, it is considered impossible to travel at the speed of light, so it is assumed that a human between the ages of 20 and 60 could never travel farther than 40 light years at the speed we travel now.

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A light signal that left the Earth at the same time as the traveller would always get to the destination before the traveller.
Light travels at a speed of 186,000 miles a second. When we deal with the immense distances of space, though, even light seems slow. When astronauts were on the Moon it took over a second for the radio waves, which travel at the speed of light, to reach us. The distance that light travels in a year is called a light year. To travel the whole length of the Milky Way galaxy, it would take light about 100,000 years. That means that even if we could obtain light speed, it would still be impossible for a single human being to travel that entire distance.

There is also another strange effect from light speed. It is called "time dilation". It means that as a traveler accelerates at light speed, time slows down for them. This in turn affects his measurements. For example, Twin brothers live on Earth. One brother takes a trip to a distant star traveling at a high percentage of the speed of light. When the twin returns he will be younger than his brother because for him time slowed down during the trip.

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