Speed is thrilling to human beings – there’s no denying it. This has been the case ever since the wheel was invented and speed was no longer determined by the strength of our legs. The faster one goes, the more thrilled one feels, although, for some, speed can be intimidating. In today’s modern age, we’ve developed some really fast objects. We have incredibly fast planes, ultra-fast fighter jets, super-fast bullet trains, and so on. Still, there is one thing in the universe that is faster than anything we can conceive: Light. Perhaps some of you haven’t thought about this, but many surely have.
At that speed, you could circle Earth more than seven times in one second, and humans would finally be able to explore outside our solar system. In 1947, humans first surpassed the much slower speed of sound, paving the way for the commercial Concorde jet and other supersonic aircraft. So will it ever be possible for us to travel at light speed? Based on our current understanding of physics and the limits of the natural world, the answer would probably disappoint you.
The Theory of Relativity put forth by Einstein cleared up many doubts about mass and energy. The equation of mass-energy equivalence proved that mass and energy are interconvertible, meaning that mass can be converted into energy and vice-versa. He proposed that there is no standard frame of reference. Everything is relative – even time. From this, it was inferred that the speed of light is constant and independent of the observer. Therefore, if a person is moving at half the speed of light in the same direction as light itself, then the light beam will appear the same as it does to a stationary individual. But What Does this Mass-Energy Equivalence Mean?
It means that if an object moves at a velocity that is 10% of the speed of light, then it would experience an increase in its mass by 0.5% of its original mass. On the other hand, if an object travels at 90% of the speed of light, then its mass would be 2 times its original mass. So, what would happen if humans could travel at a speed equivalent to light? Let’s imagine a technology arose that made it possible for humanity to reach 99.99 percent of light’s speed.
A secondary effect of such a velocity is that space-time becomes highly shortened from the perspective of the traveler, specifically, shortened in the vector of travel, which is simply another way of looking at time dilation. Thus, a light-year of distance, as seen from the perspective of those back on earth, becomes, for the traveler, instead less than 0.5 percent of a light-year in distance. For such a reason, from the traveler’s perspective, this distance will be traversed in only some 1.63 days. To be clear, it will still take almost exactly one year from the perspective of those back on earth.
To extend this, from the traveler’s perspective, a destination that folks on earth see as 100 light-years away could be traveled to, so far as the traveler’s clock is concerned, in only some 163 days — less than half a year. Suppose our traveler reaches the said destination, spends a year of exploration there, and embarks on a return journey to earth, likewise making the journey at 99.99 percent of light’s speed. Our traveler thus spends another 163 days in transit as reckoned by his or her clock, but another 100 years as reckoned by clocks on earth. Thus, our traveler returns to earth after a very reasonable two-year mission, as measured by the traveler’s clock. In the meantime, the earth’s calendar has advanced some 201 years. Of course, one aspect which cannot be overlooked in the above scenario is the time that would be required to accelerate to 99.99 percent of light’s speed, and time to slow again upon nearing one’s destination.
Supposing maintenance of 1G acceleration/deceleration, about one year would be required for gaining speed, and about one year for reducing speed. Another thing is that your field of vision would change drastically. The world would appear to you through a tunnel-shaped window in front of the aircraft in which you are traveling. Also, the stars in front would appear blue and the stars behind you would appear red. This is because light waves from stars in front of you will crowd together, making the objects appear blue, while the light waves from stars behind you will spread apart and appear red, causing an extreme Doppler Effect.
After a certain speed, you would only see blackness because the wavelength of the light entering your eyes would be outside of the visible spectrum. Even with all the obstacles to traveling at the speed of light, it would certainly be the experience of a lifetime. Surprisingly, speed – defined as a rate of motion – in itself is not at all a problem for us physically, so long as it’s relatively constant and in one direction. Therefore, humans should – in theory – be able to travel at rates just short of the “Universe’s speed limit”: the speed of light.
But assuming we can overcome the considerable technological obstacles in building faster spacecraft, our fragile, mostly-water bodies will have to contend with significant new hazards that come with such high-speed travel. Speculative dangers could arise, too, if humans achieve faster-than-light travel, either by exploiting loopholes in known physics or through paradigm-shattering discoveries. However, if we attain speeds over 40,000 kph, we will have to ramp them up patiently.
Rapid acceleration and deceleration can be lethal to the human organism: witness the bodily trauma in car crashes as we go from a mere tens-of-kilometers-per-hour clip to zero in seconds. The reason? A property of the Universe is known as inertia, whereby any object with mass resists change to its state of motion. The concept is famously expressed in Newton’s first law of motion as “an object at rest stays at rest and an object in motion stays in motion at the same speed and in the same direction unless acted upon by an outside force”.
Jim Bray of the aerospace firm Lockheed Martin says that “For the human body, the constant is good. It's the acceleration we have to worry about.” About a century ago, the invention of sturdy aircraft that could maneuver at speed led to pilots reporting strange symptoms related to speed and directional changes. These included temporary vision loss and the sensation of either leadenness or weightlessness. The cause is G-forces, otherwise called gravitational forces. These are units of accelerative force upon a mass, such as a human body. An average person can withstand a sustained force of about five Gs from head to toe before slipping into unconsciousness.
Pilots wearing special high-G suits and trained to flex their torso muscles to keep blood from whooshing out of their heads can still operate their aircraft at about nine Gs. But to sustain that for a long period, not too many humans can do it. If G forces aren’t a problem for Light speed travel missions, small space rocks – “micrometeoroids” – might be. These grain-sized bits can reach impressively devastating speeds of nearly 300,000 km/h.
To protect the traveler, the spacecraft must have a protective outer layer varying in places from 18 to 30 cm thick, plus other shielding and clever equipment placement. However, as breathtaking light-speed travel may sound, it’s almost impossible for us to travel at such great speed and come out of it alive. According to Albert Einstein’s theory of special relativity, summarized by the famous equation E=mc2, the speed of light is something like a cosmic speed limit that cannot be surpassed. So, light-speed travel and faster-than-light travel are physical impossibilities, especially for anything with mass, such as spacecraft and humans. Even for very tiny things, like subatomic particles, the amount of energy needed to equal the speed of light poses a significant challenge to the feasibility of almost light-speed space travel.
The Large Hadron Collider, the largest and highest-energy particle accelerator on Earth, has boosted protons as close to the speed of light as we can get. However, even a minuscule proton would require near-infinite energy to reach the speed of light, and humans haven’t figured out near-infinite energy quite yet. And even if we do, it’s highly unlikely that humans would be able to survive light-speed travel.
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