In my backyard in bright, polluted San Diego, my telescope was aimed at the unforgettable galaxy, far from Earth. My wife, Christina, stood by as the first image from space appeared on my tablet, sparkling brilliantly on the screen.
“That’s it,” I exclaimed, “Pinwheel Galaxy.” The name comes from its shape, which contains about a trillion stars.
The light from the Pinwheel traveled 25 million years (around 150 Kintirion) across the universe to reach my telescope.
Her curiosity sparked a dialogue that led us to ponder the behavior of light. Ultimately, why does light lose energy over time?
Let’s talk about light
I’m an Astrophysicist, and one of the key insights I discovered early in my research is that light often behaves in counterintuitive ways.
Light is electromagnetic radiation: a combination of radio and magnetic waves that propagate through space-time. Importantly, it has no mass. This is significant because the mass of an object determines the maximum speed it can travel through space.
Since light is massless, it can reach the ultimate speed limit in a vacuum—around 186,000 miles per second (300,000 km/s), or approximately 6 trillion miles per year (9.6 trillion kilometers). Nothing can move faster through space. Just to provide perspective, particles of light travel around the Earth’s circumference multiple times within the blink of an eye.
The speed of light is astonishing, and space is vast. Light from the Sun, which is 93 million miles (around 150 million kilometers) away from Earth, takes 8 minutes to reach us. In simpler terms, the sunlight you observe is from 8 minutes ago.
Alpha Centauri, the nearest star to us beyond the Sun, is 26 trillion miles (about 41 trillion kilometers) away. Therefore, the light we observe from it has traveled for over four years or, as astronomers say, 4 light-years.
Related: Light shape: Scientists reveal images of individual photons
Thinking of these immense distances, let’s revisit Christina’s question. How does light traverse space and gradually lose energy?
In fact, some light does lose energy, occasionally bouncing off interstellar dust and other matter scattered throughout space.
However, most light travels unhindered. This is usually true because space is nearly empty—there’s rarely anything to obstruct its path.
When light encounters no obstacles, it retains its energy and can maintain its speed of 186,000 miles per second indefinitely.
It’s about time
Now, let’s consider another concept: Imagine being an astronaut on the International Space Station, orbiting at 17,000 miles per hour. In comparison to someone on Earth, your watch will run 0.01 seconds slower over a year.
This is known as time dilation—time behaves differently under varying velocities and gravitational fields. If you move really fast or are close to a significant gravitational field, your clock runs slower than that of someone either moving slower or farther from the gravity source. In simple terms, time is relative.
Consider that light is intricately tied to time in significant ways. Imagine me sitting on a photon, the fundamental particles of light. At that point, time dilation is at its extreme. From the perspective of everyone on Earth, you are traveling at the speed of light, while from your vantage point, time completely stops.
This discrepancy arises because the time measurements are occurring in two different frames; photons move at the speed of light, whereas the relatively slower pace of Earth revolves around the sun.
Additionally, when you approach the speed of light, or travel near it, the distance between your position and your destination compresses. Essentially, space becomes more condensed in the direction you are moving. Hence, the faster you go, the shorter your journey will be. For photons, space is compressed.
This brings us back to the light from the Pinwheel Galaxy. From the perspective of a photon, the stars within it emitted light, and that light reached a single pixel of my tablet instantaneously. To the photon, the journey was infinitely fast and infinitely short.
However, from our viewpoint on Earth, those photons left the galaxy 25 million years ago and traveled across 25 million light years until they reached my tablet in the backyard.
On a cool spring evening, that breathtaking image inspired a delightful conversation between a curious wife and her scientific husband.
This edited article has been republished from the conversation under a Creative Commons license. For further information, please read the original article.
Source: www.livescience.com