Why faster than light travel is impossible?
If an object ever did reach the speed of light, its mass would become infinite. And as a result, the energy required to move the object would also become infinite: an impossibility.
Only massless particles, including photons, which make up light, can travel at that speed. It's impossible to accelerate any material object up to the speed of light because it would take an infinite amount of energy to do so.
Albert Einstein's special theory of relativity famously dictates that no known object can travel faster than the speed of light in vacuum, which is 299,792 km/s. This speed limit makes it unlikely that humans will ever be able to send spacecraft to explore beyond our local area of the Milky Way.
The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity. There are also technical challenges: it might be possible but would involve vast amounts of energy.
Special relativity states that nothing can go faster than the speed of light. If something were to exceed this limit, it would move backward in time, according to the theory.
That something, the universal conversion factor, is the speed of light. The reason that it is limited is simply the fact that a finite amount of space is equivalent to a finite amount of time.
So one oft-discussed issue regarding space travel is the fact that nothing can travel faster than the speed of light, and nothing made of mass can even reach the speed of light because it reaches infinite mass which would thus require infinite energy to move it.
Indeed, to our knowledge so far, nothing on or off our planet can travel faster than the speed of light. This has been proven time and time again through the laws of special relativity, put on paper by Albert Einstein a century ago.
In short, it means that, the moment that light leaves, darkness returns. In this respect,darkness has the same speed as light.
At any rate, the beam of light emitted by your flashlight would appear to reach the far wall instantly, as the speed of light is independent of your speed and would always be constant at about 300,000 kilometres per second in a vacuum.
Has anyone ever gone back in time?
Although many people are fascinated by the idea of changing the past or seeing the future before it's due, no person has ever demonstrated the kind of back-and-forth time travel seen in science fiction or proposed a method of sending a person through significant periods of time that wouldn't destroy them on the way.
There are known to be solutions to the equations of general relativity that describe spacetimes which contain closed timelike curves, such as Gödel spacetime, but the physical plausibility of these solutions is uncertain. Many in the scientific community believe that backward time travel is highly unlikely.
In fact, according to Albert Einstein's famous equation, E = mc² , time travel is possible, at least in one direction. Going the other way — back to the past — presents a trickier challenge.
The person traveling at the speed of light would experience a slowing of time. For that person, time would move slower than for someone who is not moving. Also, their field of vision would change drastically. The world would appear through a tunnel-shaped window in front of the aircraft in which they are traveling.
So light is the fastest thing. Nothing can go faster than that. It's kind of like the speed limit of the universe.
The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel at the speed of light, and that nothing may travel faster.
Einstein hypothesized that, if something could travel faster than the speed of light, it would break fundamental physical laws by being able to observe, relatively speaking, a stationary electromagnetic wave. Thus, for his theory of relativity to work, he hypothesized that the speed of light must remain constant.
Light is actually energy made of small particles called photons.
Suppose two galaxies in opposite directions on the sky are 20 billion lightyears apart. At the current growth rate of the Universe, their distance will increase by 0.007% (corresponding to 1.4 million lightyears) in one million years, which is clearly faster than light.
We are always observing the past since the speed of light is finite. You cannot reverse causality so going faster than light would not take you into the past. You would see all the photons from the past in rapid succession so that remote objects would approach the present of the traveller heading toward them.
Why do you need infinite energy to travel at the speed of light?
But as an object approaches the speed of light, its observed mass becomes infinitely large. As a result, an infinite amount of energy is required to make an object move at the speed of light. For this reason, it is impossible for any matter to travel faster than light speed.