What Really Happens to the Human Body at Near-Lightspeed?

In the realm of science fiction, spacecraft capable of reaching or surpassing the speed of light allow for vast interstellar expeditions. However, within our earthly confines, hurtling through space at the velocity of light—equivalent to 299,792,458 meters per second or approximately 670,616,629 miles per hour in a vacuum—is physically unattainable with current technology. "Light-speed is exclusively where objects without mass can move," explains Gerd...

In science fiction narratives, spacecraft capable of reaching or surpassing the speed of light open up possibilities for exploring every corner of the universe. However, within our earthly confines, propelling even a cumbersome rocket to travel at such velocity—299,792,458 meters per second or approximately 670,616,629 miles per hour—in the vacuity of space remains an unattainable dream. physical impossibility “It’s how fast massless objects move,” he explains. Gerd Kortemeyer , an associate professor emeritus of physics at Michigan State University. Therefore, any object with mass cannot achieve that velocity. Even particles without mass are constrained by the speed of light. "This is frequently referred to as the cosmic speed limit since nothing can surpass this speed," explains Kortemeyer.

Twice as unlucky for those of us who are keen to explore distant galaxies—even traveling at near Traveling close to the speed of light compared to our home planet is not an option. "It's both unachievable and too dangerous to voyage near the speed of light relative to our dear Earth," explains the physicist.

Aside from wonky theoretical explanations, it would require an enormous amount of fuel and energy to accelerate any crewed spacecraft to such speeds. According to Kortemeyer’s calculations, a vehicle weighing 10 metric tons (considerably light and compact) would need an immense quantity of resources just to reach 99% of the speed of light. than most spacecraft ), while accelerating at a manageable g-force would require over 200 times the annual energy consumption on Earth. This calculation assumes an ideal fuel with perfect efficiency, converting mass directly into propulsion without any heat loss—an impossible scenario under our current understanding of physics. second law of thermodynamics .

The nearest we've gotten to achieving light speed is propelling minuscule individual atoms to incredibly high velocities. approximately 99.99999896 percent the speed of light at the Large Hadron Collider.

But let’s ignore all of that and imagine, for a moment, that we could get close to lightspeed. If we had the perfect, efficient fuel source, a ton of it, a vessel crafted to withstand it, and the gumption–what would near-lightspeed travel be like?

Well, perhaps unsurprisingly, things would get weird.

What’s so special about lightspeed?

First, it’s important to understand a few of the quirks of lightspeed. It isn’t just At this velocity, it is also "one of the basic constants of nature," as Kortemeyer elucidates. Since the 17th century, astronomical observations of planetary motions have been conducted. suggested the velocity of light And in 1865, James Clerk Maxwell determined that light is an electromagnetic wave and computed its velocity, closely matching today’s accepted figure for this value. landmark physics paper , “ A dynamic theory of the electromagnetic field .”

Next, Einstein revolutionized our grasp of physics. In 1905, his theory of special relativity introduced the idea of spacetime as an integrated cosmic sheet, linked through the constant "c," which delineates the connection between energy and mass. Upon calculating this figure, he discovered that it coincidentally aligned with certain expectations. equivalent to the velocity of light This is the renowned E=mc^2 equation.

In the most basic terms, special relativity states that lightspeed doesn’t change, but rather time– the fourth dimension–bends relative to objects’ movements. Therefore, objects in motion experience time differently from objects at rest. At most conceivable speeds on Earth, this isn’t noticeable. But at near light speeds, it would be, in a phenomenon known as time dilation (we’ll come back to this in the next section).

Moreover, due to the distinctive connection between lightspeed and spacetime, it stays consistent regardless of the observer's velocity. Consider this: imagine being inside a vehicle on a freeway. Should you travel at a steady pace of 30 mph and another car ahead zips past you at 60 mph, then that quicker car recedes from you at a rate of 30 mph compared to your own speed. Yet, if you attempted to chase down a photon while accelerating to half the speed of light, that photon would continue to move away from you at precisely the speed of light itself. "The speed of light is always constant, irrespective of movement, which sets it apart from everything else," explains Kortemeyer.

Combined, these ideas result in an exhilarating journey when nearing the speed of light.

How might traveling at speeds close to light feel?

Hues and luminosity would appear altered and significantly distinct, as demonstrated in this 2012 simulation Developed by Kortemeyer and colleagues at MIT, this straightforward game aims to demonstrate the relativistic impacts of traveling close to the speed of light. It takes place in a universe where light moves significantly slower and continually decelerates as you move through it. In such an environment, even though you couldn't attain or surpass the speed of light, you could walk quite quickly toward it.

Just like when an ambulance zooms past you with its sirens wailing, changing pitch as it approaches and then recedes, you'd witness a similar phenomenon visually. If you move toward something, it will look more blue because the light waves compress and shorten. Conversely, moving away from something causes the light waves to stretch out, making everything seem redder.

Approaching something rapidly enhances how brightly you perceive it due to what’s known as the spotlight effect. According to Kortemeyer, this can be likened to moving swiftly through rainfall. When rushing through heavy rain, most of the droplets will strike your body from the front, causing your clothing to become drenched faster. Similarly, within the virtual environment of the simulation game, these 'water droplets' symbolize photons. Traveling along a ray of light nearly at the speed of light implies that many light particles would reach your eyes simultaneously.

If that isn’t bizarre enough, think about how this might affect our perception of time. Recall the theory of time dilation? Due to the curvature of spacetime needed to maintain the consistent velocity of light, an individual hurtling through space close to the speed of light would experience slower aging compared to everyone else who remains stationary on Earth. The illustration of this phenomenon can be seen in various examples. twin paradox thought experiment. The concept of time dilation, along with the difference between time at rest versus time experienced when moving at a specific speed, illustrates be precisely calculated .

If you reached 299,792,458 meters per second (just below light speed), traveling for two minutes at that velocity would equate to approximately six Earth days ticking away back home.

Frequently, this idea of distorted time is employed to elucidate the mechanics of traveling faster than light. "I'm quite a devoted admirer of Star Trek "I prefer not to criticize," states Kortemeyer. Nonetheless, the program’s science fiction concept of "warp speed" presents escape faster than light travels It's purely fictional with no scientific basis, he states. "Distorting space is indeed physically plausible," however, there isn't currently a method to induce or regulate the distortion of space for altering velocity. "The concept of a warp drive has no place in our understanding of physics. I can't fathom which law of physics could facilitate something like that," he explains.

And to bring things back to reality even further, reaching 299,782,450 meters per second represents an enormous challenge by itself. The most significant hurdle when dealing with such high velocities isn't maintaining a steady pace, but rather accelerating to those speeds. We're already traveling much quicker than one might imagine; everyone on Earth moves around the Sun at approximately 67,000 miles per hour. However, since this speed remains consistent, we do not perceive it. Achieving light speed relative to Earth, though, presents a completely different scenario. "It’s impossible to simply accelerate up to the speed of light. Doing so would flatten you," explains Kortemeyer.

The acceleration required to reach near-light speed would result in enormous g-forces, unless done with extreme care. Human bodies are designed to endure 1 g, which is the gravitational pull experienced on Earth’s surface. Typically, individuals can cope with 4-6 g over brief intervals lasting several seconds to minutes. However, enduring greater intensities or prolonged exposure could become problematic. becomes fatal As our body’s internal fluid movements become obstructed.

Based on Kortemeyer’s computations, it would require approximately one year to reach light speed with an acceleration force kept below 3g. However, as highlighted by Kortemeyer, the effects of prolonged exposure to such forces remain uncertain. It is unclear whether enduring this continuous acceleration—far exceeding human physiological design limits—would challenge both the boundaries of physics and our bodily endurance.

This tale is part of Popular Science’s Ask Us Anything series , where we tackle your wildest, thought-provoking questions ranging from mundane to bizarre. Got a question you've always been curious about? Ask us .