My telescope is designed for astrophotography in my light gum San Diego backyard, pointing to a galaxy far from the earth. My wife, Cristina, walked onto the first space photo and then flowed to my tablet. It sparkled on the screen in front of us.

“That’s the windmill galaxy,” I said. The name comes from its shape - although the windmill contains about a trillion stars.

The lights of the windmills traveled 25 million years across the universe (about 15 billion miles) toward my telescope.

My wife wondered: “Will the light be tired during such a long journey?”

Her curiosity sparked thought-provoking conversations about the light. Ultimately, why does light lose energy without wear over time?

Let's talk about light

I'm an astrophysicist and the first thing I've learned in my research is that light often behaves in a way that ignores intuition.

Light is electromagnetic radiation: basically radio waves and magnetic waves are connected together and travel through space and time. It has no quality. This is crucial because the mass of an object, whether it is a spot of dust or a spacecraft, limits the maximum speed it can travel through space.

But since light is massless, it is able to reach its maximum speed limit in vacuum - about 186,000 miles (300,000 kilometers) per second, or nearly 6 trillion miles (9.6 trillion kilometers) per year. Nothing can travel through space faster. Put it on perspective: When you need to blink, light particles spread more than twice around the earth's circle.

So fast, the spread of space is incredible. The 93 million miles (about 150 million kilometers) of sunlight from Earth takes only more than eight minutes to reach us. In other words, the sun you see has been 8 minutes.

The Sun is 26 trillion miles away from our nearest star, Alpha Centauri. So when you see it in the night sky, it's light for over four years. Or, as the astronomers say, there are already four lights.

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Considering these huge distances, consider Christina’s question: How to travel throughout the universe instead of slowly losing energy?

In fact, some light does lose energy. This happens when it bounces something like interstellar dust and spreads it in scatter.

But most light just goes without anything. Almost always, because space is mostly empty - nothingness. So there is no way.

When light travels unhindered, it does not lose energy. It can maintain a speed of 186,000 miles forever.

It's time

Here is another concept: portraying yourself as an astronaut on the International Space Station. You travel at 17,000 miles (about 27,000 kilometers) per hour. Your watch will be 0.01 seconds slower in a year compared to someone on Earth.

This is an example of time expansion - time moves at different speeds under different conditions. If you move very fast, or are close to a large gravitational field, your clock will move slower than you, or be more powerful from your gravity. To put it simply, time is relative.

Now, considering that light is inseparable from time. The picture sits on a photon, which is the elementary particle of light; here, you will experience the maximum time expansion. Everyone on Earth will be your time at the speed of light, but from your frame of reference, time will stop completely.

This is because the "clock" measures the speed of time at two different places: photons move at the speed of light, while the speed of the earth is relatively slow.

What's more, when you travel at or approach the speed of light, the distance between where you are and where you want to be short. That is, the space itself becomes more compact in the direction of movement - so the faster you can go, the shorter your journey must be. In other words, for photons, space is squeezed.

This brings us back to photos of my windmill galaxy. From a photon's perspective, a star in the galaxy emits it, and then exactly at the same time, a pixel in my backyard camera absorbs it. Because space is compressed, the journey on photons is infinitely fast and short, a small part of a second.

But from our perspective on Earth, Photons left the Milky Way 25 million years ago and traveled 25 million light-years in space until it landed on my tablet in my backyard.

There, on a cool spring night, its stunning image inspired a pleasant conversation between a nerd scientist and his curious wife.