Why Can Light Travel Billions of Years Without Running Out of Energy? | Brian Greene Explains

#briangreene #physics #lightspeed #cosmology #universe #einstein Why can light travel for billions of years across the universe without ever running out of energy? In this video, Brian Greene explains the physics behind one of the most fascinating questions in science. Unlike a car or a rocket, light doesn’t carry fuel and doesn’t “burn” energy as it moves. Photons are massless particles that travel at the speed of light, and in the vacuum of space there is no friction or air resistance to slow them down. Light only loses energy when it interacts with matter, or when the universe itself expands and stretches its wavelength, a process known as cosmological redshift. In this video you’ll learn: Why photons never “run out” of energy while traveling through empty space How the speed of light and the nature of massless particles work What cosmological redshift is and why distant starlight looks red How we can see galaxies that are billions of light-years away What Einstein’s relativity says about light, space, and time If you love physics, cosmology, and mind-bending science explained simply, subscribe for more deep dives into the universe, quantum mechanics, and the laws of nature. 👍 Like this video if it expanded your mind 💬 Comment: What science question should we explain next? 🔔 Subscribe and turn on notifications for weekly science content #brian greene is written without spaces, so here they are properly formatted: #briangreene #physics #lightspeed #cosmology #universe #einstein #astrophysics #sciencexplained