Travelling Faster Than The Speed Of Light and Time Travel. Part 4
One of the recurring questions throughout the series has been "can the light barrier be broken?" Unless humankind can build a spacecraft with zero mass, we will never truly reach the stars above. Only massless particles can travel at the speed of light. This expectation is unrealistic. The closest a craft can get to light is the StarShot microcraft which has a mass of 1g, can travel at 20% the speed of light and requires a collection of Earth based lazers to fire at it to power it's little light sails.
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A brilliant question from last week was, "is darkness faster than light?" To answer that, darkness as we know it is the absence of light but in the case of Dark Energy, which doesnt interact with the visible light spectrum, has been observed to be accelerating the expansion of the universe faster than the speed of light at a certain distance. So darkness can be observed as being faster than light.
Although reality currently tells us that travelling faster than light will violate causality and is merely impossible, it can be very perplexing to think about. According to Einstein, to travel faster than the speed of light is to travel backwards in time.
Imagine there actually is a faster than light spacecraft. It can travel at twice the speed of light and has a 20 year mission to a distant Star. An observer here on Earth will view the craft only at the speed of light as that is how fast the light emitted from the craft reaches the telescope. If the ship has actually travelled at twice the speed of light for 5 years in space, the observer would see how the craft looked at 5 years although the craft would be 10 light years away. Again, lightspeed is the only speed at which the light from the craft can reach our eyes. We can't view the ship travelling faster than the light it is emitting.
So lets go to the return journey! If you are an astronaut on board this ship, the light emitted by the ship can only go at the speed of light and the ship can go at twice that speed. So in theory, I can land the ship and look up from the ground and see the ship I have just landed, coming in to land!
There are other ways that could be faster than the cosmic speed limit; a warp drive could curve the fabric of space in front of us to bring objects closer and expand it behind us. Again, very hypothetical but the mathematics of it is possible if the immense amount of energy required is achieved.
The second way leaves relativity and cosmology behind. The infinitely tiny realm of the quantum world has shown us particles that appear to be moving faster than the speed of light, and indeed travelling back in time. This opens the door for my Quantum Mechanics series which begins next week.