Whether we are talking about travelling in between the cities or traveling to space, we are actually talking about speed relative to time. According to Einstein, laws of physics will be same in all frames of reference moving at constant velocity and the light speed is always constant. Now the question is, can we travel at light speed?
Imagine you are traveling in a train and you have a ball in your hand. Now you and the ball are moving at a constant velocity. So for you the ball is a stationary object. For an outside person who is not in the train, for him the ball looks like a moving object. So here in both the cases the ball is stationary but the reference is different. This is called special theory of relativity proposed by Albert Einstein.
Can We Reach Speed of Light?
At light speed, time slows down. For example the time taken to travel between A to B via car is 12 hours and by Air it takes 2 hours. So here the distance is same but the speed at which you travel is different. Because airplane is faster than car you reach B in less time when traveled by air. Similarly go out for a space trip travelling at the speed of light. When you comeback home from space your family and friends would have already become old. As we watched in the movie Interstellar by the time hero returns home from a 5 dimensional space, his daughter becomes old and is on death bed. Also when you travel at light speed the world looks like a time-lapse for you and at some point everything becomes dark because you are out of visible light spectrum.Paragraph
Light is composed of photons which are mass-less. That’s why light can travel at a speed of 299,792 km/s. Think about a space craft, in order to get the space craft out of earth’s atmosphere we need rocket propellant to lift the craft and move against gravity. To achieve more speed we need more propellants but the mass of the craft gets increased. Eventually it needs infinite energy to push craft at the speed of light. So technically speaking it’s not possible and thus we can’t travel at the speed of light. How ever scientists are trying to find ways to surpass light speed. It is expected that neutrons are faster than light. Also a research organisation backed by Stephen Hawking are planning to use laser energy to build a laser array that can beam a strong laser which can send small objects at 25% of the light speed. At this speed the object can reach Mars in 30 mins. So I hope in coming decades we can travel at light speed so that interstellar travel becomes possible. What do you think, can we travel at the speed of light?