What Would Happen If You Traveled At The Speed Of Light?

If a person were to travel at the speed of light, they would experience a phenomenon known as “time dilation.” This means that time would move slower for them than for someone who is not moving. Additionally, their field of vision would be significantly altered, as they could only see the world through a narrow, tunnel-like window in front of the aircraft they were traveling in.

Many of us might have considered what it would be like to travel at the speed of light. Just imagine the thrill of soaring through the boundaries of time and space and experiencing the universe’s ultimate speed!

Einstein’s Theory Of Relativity: How It Changed Our Perception Of Time

Before the 1900s, the world firmly believed in Isaac Newton’s view of mass, motion, and gravity. However, at the dawn of the 20th century, Albert Einstein came into the picture and changed this world forever.

Einstein’s Theory of Relativity resolved many uncertainties regarding mass and energy. His mass-energy equivalence equation demonstrated that both mass and energy are interchangeable, which means that mass can be converted into energy and vice versa. He also proposed that no standard frame of reference exists, and everything is relative, including time.

Based on this theory, it was concluded that the speed of light is constant and remains independent of the observer. Therefore, if a person travels at half the speed of light in the same direction as light, the light beam will appear the same as it does to a stationary individual. In other words, the speed of light remains constant, regardless of whether the observer is stationary or in motion.

What Does Mass-Energy Equivalence Mean?

It means that if an object moves at a velocity that is 10% of the speed of light, it will experience an increase in its relativistic mass by about 0.5% of its rest mass. On the other hand, if an object travels at 90% of the speed of light, its relativistic mass would be approximately 2.3 times its rest mass (the precise Lorentz factor is 2.294).

Can We Travel At The Speed Of Light?

No, humans cannot survive traveling at the speed of light.

When an object moves at the speed of light, its mass increases exponentially. For instance, the speed of light is 299,792 kilometers per second (186,282 miles per second), and when an object travels at this speed, it behaves as if it has infinite mass.

An infinite amount of energy would be required to propel an object with infinite mass, which is impractical. This is why no object can move at or faster than the speed of light. Attempting to travel faster than light is like going slower when you are at a complete stop. It simply doesn’t make sense!

What If You Moved Almost As Fast As The Speed Of Light?

If we are discussing traveling at speeds close to the speed of light, such as 90% of the speed of light, there would be some fascinating observations. 

The person traveling at such a speed would experience time dilation, which means that time would appear to move slower for them than for someone who is not moving at that speed. In other words, time would seem to slow down for the person traveling at high speed.

At 90% Speed Of Light

Imagine traveling to Mars and back at 90% of the speed of light. Using the average Earth–Mars distance, the round trip covers about 450 million kilometers, and assuming instant acceleration with no stoppage, the trip would take approximately 27 minutes and 48 seconds as observed by humans on Earth.

However, as a space traveler, you would experience only about 12 minutes and 7 seconds during the entire trip! This is due to time dilation, which occurs at high speeds. The faster you travel, the slower you move through time; hence, the slower you age. (At 90% of c the Lorentz factor is 2.294, so Earth time is roughly 2.3 times your onboard clock.) Check out this animated video to visualize and understand the concept of time dilation better.

When you traveled to Mars and back at 90% light speed, observers on Earth aged by about 27.8 minutes, while you aged by just 12.1 minutes! This difference in aging would become far more pronounced at higher speeds, say at 99.99% the speed of light.

At 99.99% Speed Of Light

Now, suppose you could travel at 99.99% of the speed of light. This time, let’s be more ambitious and travel from our solar system to Alpha Centauri, roughly 4.35 light years away from Earth. If you travel at 99.99% the speed of light from Earth to Alpha Centauri and back, with instant acceleration and no stopping, this trip would have taken roughly eight years and eight months for people on Earth observing your trip. During this trip, you would experience only around 1.5 months. In other words, your fellow mates on Earth would have aged 8.7 years after this trip, while you would have aged only one and a half months in comparison!

Redshift And Blueshift

Besides time dilation, the phenomenon of blueshift and redshift would also come into effect if you were to travel at near-light speed. When you leave Earth, the light waves that bounce off you are stretched, which makes the wavelength longer and makes them look red to people on Earth. This effect is called redshift. On the other hand, while returning from your journey at near light speed, the light waves bouncing off you would get squished and compacted together by the time they reach into the eyes of observers on Earth, making you appear blue to observers on Earth. This is called blueshift.

For you, as you travel at that speed, everything in front appears to be squished together into a blurry tunnel. In fact, after a certain speed, you would only see blackness because the wavelength of the light entering your eyes would be out of the visible spectrum.

Although traveling at the speed of light is not practically possible, traveling at near-light speed can also have interesting consequences, such as time dilation, where time appears to slow down for the traveler relative to someone stationary. Time flies at near-light speed, but it also slows down!

If You Travel Near Light Speed For A Year, How Much Time Passes On Earth?

This is the question most people really want answered, so let us put a number on it. The trick is a single quantity called the Lorentz factor (written as the Greek letter gamma, γ). It is defined as γ = 1/√(1 − v²/c²), where v is your speed and c is the speed of light. The rule is beautifully simple: for every unit of time you experience on board (your proper time), the people you left behind on Earth experience γ units of time.

So if you cruise for one year of your own time, Earth time elapsed is just γ multiplied by that year. The faster you go, the bigger γ gets, and the more lopsided the gap becomes.

Here is what one year, one hour, and five years of your time work out to back on Earth at three different speeds:

• 90% of light speed (γ ≈ 2.29): 1 of your years = about 2.3 Earth years; 1 of your hours = about 2.3 Earth hours; 5 of your years = about 11.5 Earth years.
• 99% of light speed (γ ≈ 7.09): 1 of your years = about 7.1 Earth years; 1 of your hours = about 7.1 Earth hours; 5 of your years = about 35.4 Earth years.
• 99.99% of light speed (γ ≈ 70.7): 1 of your years = about 70.7 Earth years; 1 of your hours = roughly 71 Earth hours (just under 3 days); 5 of your years = about 354 Earth years.

Notice how nothing dramatic happens at, say, half the speed of light (γ is only 1.15, so a year for you is barely 14 months for Earth). The effect explodes only as you sneak right up against c, which is exactly why those last few decimal places matter so much.

Would You Age If You Traveled At The Speed Of Light?

Yes, you would still age, but far more slowly than everyone you left behind. Your heartbeat, your watch, and your cells all run on the same clock, and time dilation slows that whole clock down together. From inside your spaceship you would notice nothing odd: an hour would feel like an hour, and you would not feel yourself aging in slow motion. The strangeness only appears when you compare notes with the people back home.

This is the famous twin paradox. Send one twin off at 99% of light speed for what feels to her like one year, and she returns having aged a single year, while her stay-at-home sibling has aged about 7 years. Crank the speed to 99.99% and a one-year round trip for the traveler matches roughly 71 years on Earth, so she could come back younger than her own great-grandchildren. As NASA puts it, the faster you travel, the slower you experience time. You are not cheating biology; you are genuinely living through less time than everyone else.

Would Traveling At The Speed Of Light Kill You?

We have already seen that hitting the speed of light itself is impossible. But suppose you could get close to it. Could a human body survive the trip? The honest answer is that two very different things would try to kill you, and neither of them is the speed itself.

The first danger is acceleration, not velocity. Coasting at a steady near-light speed would feel like sitting still; you cannot even feel constant velocity (think of how smooth a cruising airliner feels). The problem is getting up to that speed. Your body can only tolerate a few g of acceleration for any length of time, and no more than about 9 g for a handful of seconds before blood drains from your brain and you black out, as detailed in Scientific American. Any “jump to light speed” quick enough to be useful would crush a passenger long before the ship ever got close to c.

The second danger is the universe itself. Space is not truly empty; even the thin gas between the stars holds a sprinkling of hydrogen atoms. At a leisurely pace they are harmless, but slam into them at 99% of light speed and those gentle atoms arrive as a withering stream of high-energy radiation. A 2006 study of relativistic interstellar flight concluded that this oncoming interstellar gas would become an intense radiation hazard requiring serious shielding, frying both unshielded travelers and electronics. So even if you somehow built an engine to do it, the cosmos has stacked the deck against any human ever surfing along at the edge of light speed.